Limbic Neuropeptidergic Modulators of Emotion and Their Therapeutic Potential for Anxiety and Post-Traumatic Stress Disorder

Home , Angiotensin II receptor, Neuropeptidergic, Neuropeptide K

The Journal of Neuroscience, February 3, 2021 • 41(5):901–910 • 901

Symposium-Mini-Symposium Limbic Neuropeptidergic Modulators of Emotion and Their Therapeutic Potential for Anxiety and Post-Traumatic Stress Disorder

Paul J. Marvar,1 Raül Andero,2 Rene Hurlemann,3 Tiffany R. Lago,4 Moriel Zelikowsky,5 and Joanna Dabrowska6 1Department of Pharmacology & Physiology, Department of Psychiatry and Behavioral Sciences, George Washington Institute for Neuroscience, George Washington University, Washington, DC, 20037, 2Departament de Psicobiologia i de Metodologia de les Ciències de la Salut, Institut de Neurociències, Universitat Autònoma de Barcelona, Barcelona, Spain, 08193. Instituto de Salud Carlos III, Centro de Investigación Biomédica en Red de Salud Mental, CIBERSAM, Madrid, Spain, 28029. ICREA, Pg. Lluís Companys 23, Barcelona, Spain, 08010, 3Department of Psychiatry, School of Medicine & Health Sciences, and Research Center Neurosensory Science, University of Oldenburg, Oldenburg, 26129, Germany, 4Department of Psychiatry, Veterans Administration Boston Healthcare System, Boston, Massachusetts, 02130, 5Department of Neurobiology and Anatomy, University of Utah, School of Medicine, Salt Lake City, Utah, 84112, and 6Center for the Neurobiology of Stress Resilience and Psychiatric Disorders, Discipline of Cellular and Molecular Pharmacology, Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, 60064

Post-traumatic stress disorder (PTSD) is characterized by hypervigilance, increased reactivity to unpredictable versus predictable threat signals, deficits in fear extinction, and an inability to discriminate between threat and safety. First-line pharmacotherapies for psychiatric disorders have limited therapeutic efficacy in PTSD. However, recent studies have advanced our understanding of the roles of several limbic neuropeptides in the regulation of defensive behaviors and in the neural processes that are disrupted in PTSD. For example, preclinical studies have shown that blockers of tachykinin pathways, such as the Tac2 pathway, attenuate fear memory consolidation in mice and thus might have unique potential as early post-trauma interventions to prevent PTSD development. Targeting this pathway might also be beneficial in regulating other symptoms of PTSD, including trauma-induced aggressive behavior. In addition, preclinical and clinical studies have shown the important role of angiotensin receptors in fear extinction and the promise of using angiotensin II receptor blockade to reduce PTSD symptom severity. Additional preclinical studies have demonstrated that the oxytocin receptors foster accurate fear discrimination by facilitating fear responses to predictable versus unpredictable threats. Complementary human imaging studies demonstrate unique neural targets of intranasal oxytocin and compare its efficacy with well-established anxiolytic treatments. Finally, promising data from human subjects have demonstrated that a selective vasopressin 1A receptor antagonist reduces anxiety induced by unpredictable threats. This review highlights these novel promising targets for the treatment of unique core elements of PTSD pathophysiology. Key words: anxiety; angiotensin II; oxytocin; PTSD; tachykinin; vasopressin

Introduction Received June 30, 2020; revised Nov. 6, 2020; accepted Nov. 11, 2020. Animals respond to impending threats or signals predicting This work was supported by National Institutes of Health Grants 1R01HL137103-01A1 and 3R01HL137103- threats through a combination of behavioral and physiological 02S1 to P.J.M., National Institutes of Health Grants R01MH113007 and R01MH113007-04S1 to J.D., Veterans Administration Advanced Research Fellowship to T.R.L., Intramural Research Program, National Institute of responses related to fear and anxiety. Fear is an adaptive defen- Mental Health Grant ZIAMH002798 to T.R.L. (principal investigator Christian Grillon), National Institutes of sive behavior and is necessary for survival (Paré et al., 2004; Health Grant R00MH108734 to M.Z., Sloan Research Fellowship to M.Z., and Klingenstein-Simons Fellowship Gross and Canteras, 2012; Fanselow, 2018). However, maladap- to M.Z. R.A. was supported by National Alliance for Research on Schizophrenia and Depression Young tive processing of fear memories can contribute to stress-related Investigator Grant 22434, Ramón y Cajal program RYC2014-15784, RETOS-MINECO SAF2016-76565-R FEDER psychiatric disorders, such as post-traumatic stress disorder funds, and ERANET-Neuron JTC 2019 ISCIII AC19/00077. Azevan Pharmaceuticals Inc. provided SRX246 and placebo without charge and funded analysis of plasma samples for drug content. (PTSD). PTSD is characterized by hypervigilance, inability to J.D. reports submission of a provisional patent application entitled: Method and System for Testing for properly discriminate between threat and safety, disproportion- Stress-related Mental Disorders, Susceptibility, Disease Progression, Disease Modulation and Treatment ately higher fear reactivity to unpredictable versus predictable Efficacy (#62/673447). R.A. declares potential conflict of interest with the patent PCT/US2015/037629 about threats, and an inability to extinguish learned fear (Craske et al., Tac2 antagonists for treating psychiatric disorders. The remaining authors declare no competing financial 2008; Grillon et al., 2009; Jovanovic et al., 2010). First-line phar- interests. Correspondence should be addressed to Joanna Dabrowska at [email protected]. macotherapies for psychiatric disorders have limited therapeutic https://doi.org/10.1523/JNEUROSCI.1647-20.2020 efficacy in PTSD, and the need for new pharmacotherapies Copyright © 2021 the authors remains largely unmet, as clinical trials of many potential 902 • J. Neurosci., February 3, 2021 • 41(5):901–910 Marvar et al. · Limbic Neuropeptidergic Modulators of Emotion

Figure 1. Limbic neuropeptides and their receptors are promising targets for PTSD prevention and treatment. Translational potential of the limbic neuropeptides is illustrated by gray arrows from preclinical studies using animals models of fear and anxiety (A), to neuroimaging studies on the effects of the neuropeptides (e.g., oxytocin) on the amygdala activity in humans (B), to behavioral studies (anxiety-potentiated startle) testing the effects of compounds targeting neuropeptidergic receptors (e.g., vasopressin receptor antagonist) on anxiety measured in humans (C). A, Neuropeptidergic GPCRs in the extended amygdala modulate unique phases of fear learning and thereby can moderate core features of PTSD pathophysiology. OTRs in rat BNST facilitate fear discrimination by strengthening fear responses to predictable, signaled threats. Nk3R-expressing cells in the BNST mediate trauma-induced aggression in mice, whereas in mouse CeM, the Nk3R antagonist osanetant prevents fear memory consolidation. In the CeL and CeM, AT1R antagonist accelerates fear memory extinction in mice. LH, Lateral hypothalamus; PAG, periaqueductal gray; RF, reticular formation. Solid lines indicate inhibitory (GABAergic) projections. Dashed arrows indicate excitatory (glutamatergic) projections. B, Using 7T fMRI in healthy human subjects, it was shown that, compared with placebo (PLC), oxytocin (OT, 24 IU) dampened the left centromedial amygdala response to fearful relative to neutral faces in a manner similar to lorazepam (LZP, 1 mg) (red-yellow cluster represents OT vs PLC; blue-green cluster represents LZP vs PLC). C, A novel V1aR antagonist, SRX246, decreases startle amplitude during presentation of an unpredictable threat (mild electrical shock) in a translational paradigm of anxiety in humans. Traces represent processed EMG recordings of eye blink startle after administration of a loud white noise. In the safe condition, participants are not at risk of shock. In the unpredictable threat condition, participants can receive a mild electric shock (red lightning bolt) at any time. Anxiety-potentiated startle is quantified as the change in startle amplitude from safe to threat. agents, including initially promising corticotropin-releasing Dabrowska, 2020). Both the CeA and the BNST receive afferent factor antagonists, have delivered inconclusive results (Spierling glutamatergic information from the BLA among many other and Zorrilla, 2017). In this review article, we first introduce the regions (Jennings et al., 2013; Torrisi et al., 2018)(Fig. 1A). brain regions, particularly the extended amygdala, that are critical During fear conditioning (fear memory acquisition), a sensory cue 1 for the modulation of defensive behaviors and learned fear and (conditioned stimulus [CS ]) coterminates with an aversive soma- describe the basic neurobiology of neuropeptides. We then discuss tosensory stimulus (unconditioned stimulus [US]), usually a foot how basic research on the role of limbic neuropeptides in the reg- shock. When tested for fear recall, animals display fear-like behav- 1 ulation of fear and anxiety in animal models is being directly iors when presented with the CS alone and/or in the condition- translated into potential treatments for PTSD in humans. The ing context. In the neurocircuitry of fear conditioning, the lateral content of the review has an important translational validity with amygdala (LA) is the main point of entry of sensory inputs (about regard to psychiatric disorders in humans because we present data CS, US, and context) from the thalamus; LA conveys this sensory on the effects of the same neuropeptides using clinically relevant information to the lateral nucleus of the CeA (CeL) (but see Paré measures (e.g., fear-potentiated startle [FPS] and fear condition- et al., 2004). The CeL projects to the medial CeA (CeM), which is ing) in both animal and human studies. We also address sex-spe- themajoroutputstructureoftheamygdala(Duvarci and Paré, cific effects in both rodents and humans and the importance of 2014). Neuronal activity of the LA and CeL is required for fear sex-specific pharmacotherapies for PTSD. memory acquisition, whereas activity in the CeM is required for the expression of conditioned fear responses (Pascoe and Kapp, The neurocircuitry of fear and anxiety 1985; Fanselow and LeDoux, 1999; Phelps and LeDoux, 2005; The extended amygdala is composed of the central amygdala Wilensky et al., 2006; Ciocchi et al., 2010). (CeA) and the bed nucleus of the stria terminalis (BNST) (Sun The BNST also receives direct projections from the CeA and and Cassell, 1993; Alheid, 2003). Neurons of the extended amyg- the BLA (Roberts et al., 1982; McDonald et al., 1999). Both the dala are primarily GABAergic and they also produce a vast diver- CeM and the BNST project to many overlapping brainstem sity of neuropeptides, thus forming multiplex neural populations effector structures, including the periaqueductal gray (which with a wide range of functions (for review, see Beyeler and mediates freezing behavior), reticular formation (which Marvar et al. · Limbic Neuropeptidergic Modulators of Emotion J. Neurosci., February 3, 2021 • 41(5):901–910 • 903 produces startle response), lateral hypothalamus (which regu- for developing new pharmacological targets and treatment lates cardiovascular and respiratory tone), and paraventricular strategies. nucleus (PVN) (which secretes various hormones) (Gungor and Paré, 2016; Shackman and Fox, 2016). The CeA and The role of tachykinins in the consolidation of fear memory BNST also heavily innervate each other and can modulate and their therapeutic potential for preventing PTSD each other’sactivity(Gungor et al., 2015; Pomrenze et al., development 2018; Yamauchi et al., 2018)(Fig. 1A). The tachykinins are a group of peptides sharing a carboxy-termi- According to the classic theory formulated by Michael Davis nal sequence; they serve as neuromodulators and neurotrans- and colleagues (Walker and Davis, 2008; Davis et al., 2010), after mitters in the mammal brain (Beaujouan et al., 2004). The a threat stimulus, the CeA is required for fear memory of a short, Tachykinin 1 (Tac1) gene encodes a pro-protein that, on post- discrete stimulus (phasic or cued fear), whereas the BNST is nec- translational cleavage, produces two peptides: substance P (SP) essary for long-duration fear responses (sustained or contextual and neurokinin A. The tachykinin 2 (Tac2) gene encodes neuro- fear) that resemble anxiety-like behavior. Recently, it has become kinin B (NkB) (Floor et al., 1982). SP binds preferentially to the apparent that the BNST also mediates fear responses to unpre- neurokinin 1 receptor (Nk1R), whereas neurokinin A binds pref- dictable, diffuse, or unsignaled threats (Gungor and Paré, 2016; erentially to the neurokinin 2 receptor and NkB preferentially Goode and Maren, 2017; Goode et al., 2019), but it might also in- binds at the neurokinin 3 receptor (Nk3R) (Khawaja and Rogers, hibit cued fear responses (Meloni et al., 2006; Moaddab and 1996). SP and Nk1R appear to regulate emotional stress Dabrowska, 2017). Similarly, although the CeA primarily pro- responses, and SP in the CSF correlates with PTSD severity (for motes cued fear, it also modulates anxiety-like behavior (Asok et review, see Dunlop et al., 2012). In addition, the Nk3R receptor al., 2018; Pomrenze et al., 2018). regulates fear memory in healthy mice and a PTSD-like model (Dias et al., 2014). Drugs targeting the tachykinin receptors are Neuropeptidergic modulators versus classic generally safe and well tolerated in humans (Malherbe et al., neurotransmitters 2011; Yuan et al., 2016), raising hopes that they could be used to Although neuropeptides were once viewed as having mild neuro- treat PTSD. To date, however, investigational drugs targeting modulatory effects, we now know they control a variety of tachykinin receptors (e.g., the Nk1R antagonist GR205171) have behaviors. In contrast to classic neurotransmitters that are syn- failed to show clinical efficacy in PTSD (Mathew et al., 2011). thesized at the nerve terminal, neuropeptides are synthesized at But unlike Nk1R, which is expressed in multiple areas of the the cell body and then transported to release sites. They can be human brain (Beaujouan et al., 2004), Nk3R expression is mainly released not only from the axonal terminal (axonal release), but restricted to the amygdala in mice, rats, rhesus monkeys, and also from boutons along the axons, as well as from the soma and humans (Mileusnic et al., 1999; Duarte et al., 2006; Nagano et al., dendrites (somatodendritic release). At the release sites, neuro- 2006). Thus, pharmacological targeting of the Nk3R may be a peptides are stored in large dense core vesicles, as opposed to more effective candidate for PTSD treatment. This hypothesis is small vesicles, such as those storing classic neurotransmitters supported by the discovery that the Tac2 pathway (Tac2, NkB, (van den Pol, 2012). However, there are some exceptions, as in and Nk3R) plays an important role in fear processing. case of angiotensin II: a network of different brain cells (rather A full gene expression analysis of the amygdala after audi- than one cellular phenotype) may contribute to the synthesis and tory fear conditioning uncovered molecular pathways involved storage of this peptide (for review, see de Kloet et al., 2015). in memory consolidation processes. The top gene candidate Because large dense core vesicles are stored further back in the identified was Tac2, which was upregulated 30 min after fear terminal than synaptic vesicles, they typically require a prolonged acquisition, while its protein product, NkB, was upregulated at stimulus and a large influx of calcium to be released. Hence, a 2 h. Additional experiments revealed that Tac2 is necessary and rapid train of action potentials, rather than a single action poten- sufficient for fear memory consolidation in male mice (Andero tial, is needed to trigger the release of neuropeptides (Bondy et et al., 2014). Systemic or intra-CeA blockade of the Tac2 path- al., 1987). In some cases, however, neuropeptides can be secreted way via administration of an Nk3R antagonist reduced fear via activity-independent mechanisms, for example, in hypothala- expression, suggesting it impaired fear memory consolidation. mic magnocellular neurons (which produce oxytocin and/or va- Concordantly, Designer Receptors Exclusively Activated by sopressin), some neurosecretory responses are directly coupled Designer Drugs (DREADDs)-mediated inhibition of Tac2- to voltage but independent of internal or external calcium con- expressing neurons in the CeA after fear acquisition resulted in centrations (for review, see Tasker et al., 2020). diminished fear memory consolidation. In a follow-up study, In contrast to classic neurotransmitters, neuropeptides do not optogenetic stimulation of channelrhodopsin-expressing CeA- possess a reuptake system and are not taken back up into the pre- Tac2 neurons during fear acquisition resulted in impaired synaptic neuron or metabolized in the synapse. As a result, they memory consolidation (Andero et al., 2016). These data high- can diffuse and act at a distance from the release site on a longer light the potential of compounds targeting the Tac2 pathway time scale than synaptic signaling, in a process called volume for preventing and/or treating fear-related neuropsychiatric transmission (Fuxe et al., 2005). Eventually, neuropeptides are disorders (Fig. 1A). In particular, Nk3R antagonists, such as lysed by catabolic peptidases (van den Pol, 2012). Neuropeptide osanetant, show potential as an early post-trauma intervention effects are linked to G-protein coupled receptors (GPCRs); there- against PTSD development because they impair fear memory fore, they require more time to have a biological effect, compared consolidation in the amygdala. with some neurotransmitters acting directly on ion channels and Future studies on the Tac2 pathway and fear memory should causing an immediate change in neuronal activity. Moreover, the consider the effects of this pathway on sex hormones. Indeed, diversity of signaling pathways associated with GPCRs’ transmis- the oral Nk3R antagonist ESN364 has recently been shown to sion gives neuropeptides a much broader and more diverse spec- decrease gonadal hormone levels (testosterone and estradiol/pro- trum of biological effects and functions (Hazell et al., 2012). This gesterone, respectively) in healthy men and women (Fraser et al., diversity of signaling pathways also provides vast opportunities 2016). This is not surprising, given numerous previous reports 904 • J. Neurosci., February 3, 2021 • 41(5):901–910 Marvar et al. · Limbic Neuropeptidergic Modulators of Emotion

that the Tac2 pathway modulates sex hormones in both male angiotensin type 1 receptor (AT1R), modulates amygdala activity (Danzer et al., 1999) and female rodents (Sahu and Kalra, 1992). and emotional processing (Pulcu et al., 2019; Zhou et al., 2019)and Notably, a new study shows that, whereas osanetant impairs fear accelerates fear extinction (Zhou et al., 2019). These clinical studies memory in male mice, it enhances the memory in females support many earlier rodent studies demonstrating that brain an- (Florido et al., 2020). giotensin receptors are potent mediators of anxiety-like behavior and stress responsiveness (Okuyama et al., 1999; Shekhar et al., The role of Tac2 in trauma-induced aggression 2006; Saavedra et al., 2011; de Kloet et al., 2016a, 2017). As described above, Tac2 signaling in the CeA has been shown Angiotensin II is the principal effector peptide of the RAS. Its to play a key role in fear memory consolidation (Andero et al., actions are mediated by binding to its primary receptor subtypes, 2014, 2016). In addition, recent work has implicated Tac2 in the AT1R and the angiotensin Type 2 receptor (AT2R). These encoding the brain state produced by social isolation stress. GPCRs are expressed in the periphery and throughout brain cir- More specifically, Zelikowsky et al. (2018b) found that prolonged cuits involved in fear and anxiety, including the hypothalamus, social isolation stress is sufficient to upregulate Tac2 expression amygdala, hippocampus, and medial prefrontal cortex (mPFC) across a number of brain regions, and that this upregulation is (Lind et al., 1985; Gonzalez et al., 2012; deKloetetal.,2016b). conserved across species, occurring in mice and fruit flies alike Angiotensin II and associated peptides act on their receptor sub- (Zelikowsky et al., 2018a). Furthermore, region-specific loss-of- types following synthesis from enzymatic cleavage of the precur- 1 function perturbations of Tac2 cells, NK3Rs, and Tac2 signal- sor angiotensinogen (Yang et al., 1999; Grobe et al., 2008). All of ing (using chemogenetics, local Nk3R antagonism, and shRNAi the enzymatic components for the synthesis of angiotensin II approaches) revealed dissociable roles for the anterior dorsal exist in the brain, including renin, angiotensin converting BNST, dorsomedial hypothalamus, and the CeA in the control of enzyme (Mendelsohn et al., 1990; Grobe et al., 2008; de Kloet et isolation-induced persistent fear, enhanced aggression, and acute al., 2015), and more recently discovered (pro)renin and (pro)re- fear, respectively. Collectively, these data suggest that Tac2 acts nin receptor (Xu et al., 2016). Compared with other classic in parallel across multiple brain regions to mediate the effects of neuropeptides discussed here, brain angiotensin II is therefore social isolation stress on a variety of behaviors. unique in that a network of different brain cells (vs one cellular Of particular interest is the role of tachykinins in isolation- phenotype) may contribute to the synthesis and storage of induced aggression. In addition to the findings that Tac2 signal- brain angiotensin II, and thus to its contributions to various ing in the Dorsomedial hypothalamus (DMH) DMH is required physiological and pathophysiological functions, in a region- for such aggression, Zelikowsky et al. (2018b) demonstrated that and cell-specific manner. For further reading, on cellular local- virally mediated, brainwide overexpression of Tac2 combined ization of brain RAS, function, and interaction with other 1 with chemogenetic activation of Tac2 cells was sufficient to brain cell types, the reader is referred to a recent review (de increase aggressive behavior in otherwise docile group-housed Kloet et al., 2015). mice. This gain-of-function effect has also been observed in fruit Brain AT1Rs are expressed by neurons involved in stress flies (Asahina et al., 2014; Wohl et al., 2020), suggesting a con- responses (e.g., the hypothalamic pituitary axis) (Krause et al., served function for tachykinins in controlling aggressive behav- 2011) and in limbic regions important for the emotional regula- ior across species. tion of fear (Hurt et al., 2015). Notably, inhibition of AT1Rs has In addition to examining the role of Tac2 in social isolation- been shown to facilitate fear extinction, a process necessary for induced aggression, recent studies by Zelikowsky et al. (2018b) recovery from PTSD in both rodents (Marvar et al., 2014; have begun to examine the role of Tac2 in mediating aggression Parrish et al., 2019) and humans (Zhou et al., 2019)(Fig. 1A). produced by an acute stressor. Using a rodent model of PTSD Translating between rodent and human studies, Zhou et al. known as stress-enhanced fear learning, these investigations (2019) recently demonstrated that losartan (an AT1R antagonist) found that a series of inescapable, unsignaled, randomized foot improved early extinction learning through increased ventrome- shocks produce a subsequent enhancement in aggressive behav- dial PFC (vmPFC) activity and functional connectivity between ior. This stress-enhanced aggression was found to be mediated the vmPFC and the BLA in humans. This enhanced vmPFC- by Tac2 signaling. BLA coupling could be an important mechanism by which an- Despite a role for Tac2 in both isolation-induced aggression giotensin II signaling improves fear extinction. Future clinical and stress-enhanced aggression, the nature of these contribu- studies are needed for improving the efficacy of targeting the tions is distinct. Nonetheless, compounds targeting the Tac2 RAS in fear-based disorders, while application of modern neuro- pathway might provide promising therapeutics for trauma- science technologies will be critical for elucidating the circuits as induced aggression (Fig. 1A). This is important because veter- well as cellular and molecular mechanisms involved in the role of ans with PTSD exhibit higher incidence of aggressive behavior the brain RAS in fear- and anxiety-based disorders (Stout and relative to their non-PSTD veteran counterparts (Chemtob et Risbrough, 2019). al., 1994; Jakupcak et al., 2007). Future studies will aim to The role of brain Type 2 receptor (AT2R) in fear learning was understand the role of Tac2 in various forms of aggression and recently investigated by Yu et al. (2019) using AT2R BAC-eGFP 1 its therapeutic potential for attenuating trauma and stress- reporter mice. The authors demonstrated that AT2R-eGFP induced aggression as it relates to PTSD. neurons were predominantly expressed in the medial amygdala and the CeM, with little AT2R-eGFP expression in the BLA or The role of angiotensin II in fear extinction and therapeutic CeL. In addition, AT2R-expressing GABAergic neurons in the opportunities for PTSD CeA were found to project to the PAG, a midbrain region con- Growing evidence suggests that the renin angiotensin system trolling defensive responses to threat, such as freezing (Yu et al., (RAS), a regulator of blood pressure and fluid homeostasis, is 2019). These findings suggest that CeM AT2R-expressing neu- another potential therapeutic target for PTSD (Khoury et al., rons may modulate CeA outputs that play a role in fear expres- 2012; Nylocks et al., 2015; Terock et al., 2019; Zhou et al., 2019). sion, and they provide new evidence for an angiotensinergic Recent clinical studies demonstrate that losartan, a blocker of the circuit and CeM cell type in the defensive threat response. Brain Marvar et al. · Limbic Neuropeptidergic Modulators of Emotion J. Neurosci., February 3, 2021 • 41(5):901–910 • 905

A AT1Rs and AT2Rs may therefore differentially modulate fear 1 ). Conversely, systemic administration of oxytocin was memory and threat responding, possibly via inhibitory and exci- shown to reduce background anxiety (noncued fear) meas- tatory CeA circuits and cortical inputs. Additional studies are ured in male rat FPS (Missig et al., 2010; Ayers et al., 2011). needed to test this hypothesis, as well as to further understand These ostensibly contrasting behavioral effects support angiotensin II signaling pathway interactions with other neuro- growing evidence that oxytocin promotes fear discrimination peptide systems described here. by reducing sustained fear responses (contextual fear and noncued fear) yet strengthening fear responses to signaled, The role of oxytocin in fostering accurate fear discrimination predictable, or imminent threats (Janecek and Dabrowska, and strengthening fear responses to predictable threats 2019;forreview,seeOlivera-Pasilio and Dabrowska, 2020). The nonapeptide oxytocin is a hormone and a neuromodulator Indeed, recent studies investigating the BLA support the role produced in the PVN, supraoptic nucleus, and an accessory nu- of OTRs in facilitating accurate fear discrimination by selec- 1 cleus of the hypothalamus. Oxytocin is released in the extended tively strengthening fear responses to discrete cues (CS ) amygdala, including the CeA and the BNST (Ebner et al., 2005; (Fam et al., 2018). OTR-mediated transmission in the CeA Martinon et al., 2019), among many other brain regions, where it has also been shown to mediate a switch from passive freez- acts on its single GPCR, the oxytocin receptor (OTR). Oxytocin ing to active escape behaviors when an animal is confronted has shown anxiolytic properties in animal models (Bale et al., with an imminent, yet escapable, threat, while reducing reac- 2001; Ring et al., 2006) and human studies (Ellenbogen et al., tivity to distant or diffuse threats (Terburg et al., 2018). 2014; for review, see Janecek and Dabrowska, 2019). However, In search of potential mechanisms of these oxytocin effects, the role of oxytocin in the regulation of fear responses appears electrophysiological studies in the CeA and the BNST have dem- more complex (Toth et al., 2012; Guzmán et al., 2013; Lahoud onstrated that there are two groups of oxytocin-responsive neu- and Maroun, 2013; Campbell-Smith et al., 2015;forreview,see rons: one group of interneurons that is directly excited by Olivera-Pasilio and Dabrowska, 2020). Several studies to date oxytocin and another group of output neurons that is inhibited by have shown that oxytocin neurons in the hypothalamus are acti- oxytocin via an indirect pathway (Huber et al., 2005; Viviani et al., vated during cued and contextual fear conditioning and during 2011; Knobloch et al., 2012; Francesconi et al., 2020). In the dorso- fear recall, indicating the recruitment of the endogenous oxyto- lateral BNST, oxytocin selectively increases the excitability and cin system in fear learning in male and female rats (Zhu and spontaneous firing of Type I dorsolateral BNST interneurons, and Onaka, 2002; Hasan et al., 2019; Martinon et al., 2019). Notably, inhibits two classes of projection neurons, including Type II neu- activation of these oxytocin neurons has been shown to influence rons, which project to the CeA (Francesconi et al., 2020). Because the level of contextual fear. For example, as demonstrated using BNST activation was shown to induce sustained fear and the vGATE system (virus-delivered genetic activity-induced tag- reduce cued fear (Meloni et al., 2006), activation of OTRs in ging of cell ensembles), optogenetic stimulation of CeL-projecting the BNST might facilitate cued fear and reduce sustained fear ensembles of oxytocin neurons activated during fear-conditioning responses by inhibiting the BNST output. Thus, reciprocal (tagged via vGATE) accelerates extinction of contextual fear in connectivity between the CeA and the BNST plays a major female rats (Hasan et al., 2019). This is consistent with the major- role in modulating fear discrimination. ity of behavioral studies reporting that activation of OTRs in the Inconclusion,oxytocinappearstoincreasethesalienceofim- CeA reduces contextual fear in male and female rats (Viviani et minent threat-signaling environmental cues and thereby promote al., 2011; Knobloch et al., 2012; Terburg et al., 2018). adaptive defensive behaviors while reducing fear responses to In apparent contrast, in male rat BNST, OTR neurotrans- unsignaled, distant, or diffuse threats. This is important because mission has been shown to facilitate cued fear measured as increased reactivity to unpredictable threats and impaired fear dis- FPS. In the rat FPS paradigm, an acoustic startle reflex crimination are two hallmarks of PTSD. In addition, as patients (a whole-body jump, which occurs ,200 ms after a white suffering from PTSD demonstrate increased BNST activity noise burst) is potentiated by an exposure to a cue (CS, e.g., (Awasthi et al., 2020), by ameliorating BNST hyperactivity and 3.7 s light) that has previously been paired with foot shocks improving fear discrimination, oxytocin is a promising target for (US) during a fear-conditioning session. During the FPS test, PTSD pharmacotherapy in humans. rats are presented with startle-eliciting bursts in the presence or absence of the CS (mixed in a pseudorandom order) Clinical translation of the fear-modulating effects of (Davis et al., 1993; Davis, 2001; Walker and Davis, 2002), oxytocin andbothcuedfearandnoncuedfeararemeasured.Whereas While there is a plethora of pharmacological strategies to modu- startle potentiation during cue presentations represents cued late oxytocin signaling, the most established approach in humans fear, startle potentiation observed in between the cue presentations is through activation of brain OTRs through intranasal adminis- reflects noncued fear. However, the latter startle response does not tration of synthetic oxytocin (IN-OT) (Gulliver et al., 2019). IN- occur until after the cue is presented (Missig et al., 2010; Moaddab OT increases both blood and CSF concentrations of the peptide and Dabrowska, 2017; Janecek and Dabrowska, 2019; Walker and (Striepens et al., 2013), which accumulates in brain tissue along Davis, 2002). Therefore, a ratio between cued and noncued fear can the trajectories of the olfactory and trigeminal nerves (M. R. be used as a proxy for proper fear discrimination (Janecek and Lee et al., 2020). There is also emerging evidence for blood-to- Dabrowska, 2019; Martinon et al., 2019). Notably, studies have also brain transport of oxytocin (M. R. Lee et al., 2018; but see shown that noncued fear (or background anxiety) is independent of Neumann et al., 2013), which is regulated by the receptor for contextual fear (Missig et al., 2010; Ayers et al., 2011). advanced glycation end-products on brain capillary endothelial A selective OTR antagonist administered before fear con- cells (Yamamoto and Higashida, 2020). ditioning (acquisition) significantly reduced cued fear and Current concepts guiding the clinical translation of IN-OT tended to increase noncued fear measured during FPS recall to the treatment of anxiety disorders and PTSD emphasize the the next day, overall reducing fear discrimination (Moaddab following: (1) identification of the neural targets, (2) definition and Dabrowska, 2017; Janecek and Dabrowska, 2019)(Fig. of the most effective dosage needed for target engagement, and 906 • J. Neurosci., February 3, 2021 • 41(5):901–910 Marvar et al. · Limbic Neuropeptidergic Modulators of Emotion

(3) comparison with clinically established traditional anxio- relevant brain regions as well as hormonal and behavioral defen- lytics, such as benzodiazepines (Insel, 2016). Given that fMRI- sive responses. Neurons in the PVN, suprachiasmatic nuclei, based meta-analyses implicate hyperactivity of the amygdala in medial amygdala, and BNST synthesize vasopressin (Lu et al., response to perceived threats as a common pathophysiological 2019), and vasopressinergic projections are found in the lateral denominator of anxiety disorders and PTSD (Etkin and Wager, septum and CeA (Hernández et al., 2016; Bredewold and 2007), inhibition of the amygdala appears to be essential for the Veenema, 2018). Furthermore, vasopressin plays an important therapeutic control of these conditions with IN-OT. In line role in activation of the hypothalamic-pituitary-adrenal axis with this premise are analyses of oxytocin-pathway gene net- (Rotondo et al., 2016; Nishimura et al., 2019). In rodents, aver- works in human postmortem brains, which demonstrate sive stimuli (e.g., foot shocks) increase vasopressin levels in the enriched OTR gene expression in subcortical regions, including PFC and amygdala (Karakilic et al., 2018) and increase vasopres- the amygdala (Quintana et al., 2019). sin 1a receptor (V1a) binding in the anterior hypothalamus While there is meta-analytic evidence that IN-OT modulates (Ross et al., 2019). Moreover, intracerebral administration of amygdala responses to perceived threats (Wang et al., 2017), fMRI vasopressin increases anxiety-like behavior (Hernández et al., – data characterizing the dose response profile of this effect were 2016; Hernández-Pérez et al., 2018), while administration of collected only recently. A study conducted in male human subjects vasopressin receptor antagonists or knocking out vasopressin found that IN-OT-induced inhibition of amygdala responses to receptors decreases anxiety-like behavior (Neumann and threats was most effective after administration of 24 IU, whereas Landgraf, 2012; Hodgson et al., 2014; Bayerl et al., 2016). Finally, 48 IU evoked an increase in amygdala reactivity (Spengler et al., vasopressin in the lateral septum and BNST enhances aggression 2017). The latter was also observed in females after administration (for review, see Carter, 2017; Kompier et al., 2019). of 6, 12, or 24 IU (Lieberz et al., 2020), suggesting that IN-OT Clinical research on vasopressin has been limited by incon- effects likely vary as a function of dose and sex. sistent assay methods and restricted pharmacological tools. Notably, interplay between the mPFC and the amygdala has Nevertheless, researchers have found that early-life stress been identified as a hallmark of fear extinction learning, which is affects the vasopressin system in both humans and rodents thought to mediate the efficacy of exposure therapy for anxiety (Hernández et al., 2016; Kompier et al., 2019). Further, vaso- disorders and PTSD. Recently, 7T ultra-high-field fMRI was pressin modulates human neural and physiological responses to used to test IN-OT (24 IU) against the benzodiazepine compar- negative stimuli across many experimental paradigms (Thompson ator lorazepam (1 mg by mouth). While both lorazepam and et al., 2006; Zink et al., 2010; Brunnlieb et al., 2013; R. J. Lee et al., IN-OT inhibited the centromedial amygdala, only IN-OT 2013; Motoki et al., 2016). For example, intranasal vasopressin effects extended to a functional network, including precuneus increased physiological arousal (measured with frontalis EMG) dur- and dorsomedial mPFC (Kreuder et al., 2020)(Fig. 1B). ing trauma recall in veterans (Pitman et al., 1993). Specific to PTSD, Crosstalk between these regions during fear extinction learning in a longitudinal study of 232 war-exposed children, risk alleles on was increased by IN-OT (24 IU), along with inhibitory effects three genes (AVPR1a, which encodes the vasopressin V1a receptor; on the amygdala per se (Eckstein et al., 2015). OXTR,theOTR;andCD38, the cluster of differentiation 38) pre- One of the clinical core symptoms of PTSD is intrusive reex- dicted PTSD development (Feldman et al., 2014). In contrast, periencing, which can be modeled over days in healthy volun- teers exposed to filmed violence. Based on this paradigm, it was plasma vasopressin levels did not predict postdeployment develop- shown that IN-OT (24 IU) not only enhanced functional connec- ment of PTSD in military subjects (Reijnen et al., 2017). Cross-sec- tivity between the amygdala and mPFC, but also diminished tionally, deKloetetal.(2008)found that veterans with PTSD had intrusions, at least in subjects who deliberately talked to their higher plasma vasopressin levels than controls and that levels posi- peers about what had scared them (Scheele et al., 2019). tively correlated with avoidance symptoms. However, police offi- A recent meta-analysis confirmed the principle efficacy and cers with PTSD had similar salivary vasopressin levels to safety of IN-OT treatment for PTSD; however, as reflected by trauma-controls (Frijling et al., 2015); and in another study, ci- preclinical evidence (Lieberz et al., 2020), IN-OT exerts differ- vilian urinary vasopressin levels negatively correlated with ential, sometimes even opposing, effects in male and female PTSD severity (Marshall, 2013). Discrepant results may stem patients with PTSD (Peled-Avron et al., 2020). Modulatory from type of assay used, timing of assessments relative to dis- effects of IN-OT (24 IU) on amygdala reactivity (Labuschagne ease state, and/or population differences. et al., 2010), amygdala-mPFC connectivity (Sripada et al., The development of a novel and specific V1a receptor antago- 2013), and decision-making (Hurlemann et al., 2019) have also nist, SRX246 (Azevan Pharmaceuticals), permits the experimen- ’ been reported for social anxiety disorder; however, the influ- tal validation of vasopressin s role in the regulation of anxiety ence of sex as well as the optimal therapeutic dose range for IN- and fear in humans. In a proof-of-concept study, T.R.L. et al. OT in social anxiety disorder are unclear. As a consequence, (unpublished data) examined the effects of SRX246 in a transla- future clinical trials of IN-OT for anxiety disorders and PTSD tional paradigm of fear (i.e., the phasic response to imminent should take dose–response as well as person-related effects into threat) and anxiety (i.e., a sustained response to potential threat) account (Andari et al., 2018). Defining the biological determi- using startle potentiation as a behavioral measure. Each subject nants of IN-OT treatment will not only inform the clinical (n = 36, 16 males, 20 females) received placebo and 300 mg of translation of oxytocin neuroscience, it will also contribute to SRX246, in a counterbalanced order, over 5-7 d. The study used establishing personalized care by identifying subgroups of a double-blind, crossover, washout design. Researchers adminis- patients with anxiety disorders and PTSD who would benefit tered the NPU (neutral, predictable, unpredictable) threat test to most from this novel therapy. probe physiological responses to threat. During neutral periods, participants are safe from shock (i.e., threat). During predictable Modulation of unpredictable threat processing by periods, any geometric shape on a screen (“cue”) indicates risk vasopressin for shock, and the absence of any shape (“no-cue”)indicates Preclinical research suggests that the neuropeptide vasopressin safety. During unpredictable periods, participants are at risk for may contribute to PTSD, as evidenced by its association with shock at all times. Anxiety-potentiated startle was operationally Marvar et al. · Limbic Neuropeptidergic Modulators of Emotion J. Neurosci., February 3, 2021 • 41(5):901–910 • 907 definedasthechangeinstartlescoresduringno-cuefromneutral the central amygdala to the bed nucleus of the stria terminalis disrupts to unpredictable conditions, and FPS as the change from no-cue sustained fear. Mol Psychiatry 23:914–922. to cue during predictable times. Results indicate that SRX246 Awasthi S, Pan H, LeDoux JE, Cloitre M, Altemus M, McEwen B, Silbersweig decreases anxiety-potentiated startle compared with placebo (Fig. D, Stern E (2020) The bed nucleus of the stria terminalis and functionally C linked neurocircuitry modulate emotion processing and HPA axis dys- 1 ). Participants with the highest subjective anxiety scores had the function in posttraumatic stress disorder. Neuroimage Clin 28:102442. greatest decrease of subjective anxiety with SRX246 compared Ayers LW, Missig G, Schulkin J, Rosen JB (2011) Oxytocin reduces back- with placebo. Given that PTSD patients demonstrate higher startle ground anxiety in a fear-potentiated startle paradigm: peripheral vs cen- reactivity to unpredictable threat compared with control patients tral administration. Neuropsychopharmacology 36:2488–2497. (Grillon et al., 2009),theV1areceptorantagonistmaybeanovel Bale TL, Davis AM, Auger AP, Dorsa DM, McCarthy MM (2001) CNS promising treatment target for PTSD and anxiety. region-specific oxytocin receptor expression: importance in regulation of anxiety and sex behavior. J Neurosci 21:2546–2552. Bayerl DS, Hönig JN, Bosch OJ (2016) Vasopressin V1a, but not V1b, recep- Conclusion tors within the PVN of lactating rats mediate maternal care and anxiety- In conclusion, in this review, we discussed the unique transla- related behaviour. Behav Brain Res 305:18–22. tional potential of limbic neuropeptides and their receptors for Beaujouan JC, Torrens Y, Saffroy M, Kemel ML, Glowinski J (2004) A 25 – the prevention and treatment of PTSD. We described the role of year adventure in the field of tachykinins. Peptides 25:339 357. tachykinins in strengthening fear memory consolidation and the Beyeler A, Dabrowska J (2020) Neuronal diversity of the amygdala and the bed nucleus of the stria terminalis. Handb Behav Neurosci 26:63–100. promising effects of Nk3R antagonists as an early post-trauma Bondy CA, Gainer H, Russell JT (1987) Effects of stimulus frequency and po- intervention against PTSD development. We discussed how tassium channel blockade on the secretion of vasopressin and oxytocin Nk3R antagonists might also act against stress- and social isola- from the neurohypophysis. Neuroendocrinology 46:258–267. tion-induced aggression. We reviewed the unique potential of Bredewold R, Veenema AH (2018) Sex differences in the regulation of social angiotensin II antagonists in accelerating fear extinction in both and anxiety-related behaviors: insights from vasopressin and oxytocin – preclinical and clinical studies. Because one of the hallmarks of brain systems. Curr Opin Neurobiol 49:132 140. PTSD is deficit in threat discrimination, we discussed how oxyto- Brunnlieb C, Münte TF, Tempelmann C, Heldmann M (2013) Vasopressin modulates neural responses related to emotional stimuli in the right cin fosters accurate discrimination by strengthening fear amygdala. Brain Res 1499:29–42. responses to predictable or imminent threats yet attenuating fear Campbell-Smith EJ, Holmes NM, Lingawi NW, Panayi MC, Westbrook RF responses to diffuse or distant threats. We further emphasized (2015) Oxytocin signaling in basolateral and central amygdala nuclei dif- the therapeutic potential of intranasal oxytocin, which strength- ferentially regulates the acquisition, expression, and extinction of con- ens functional connectivity between the amygdala and the mPFC text-conditioned fear in rats. Learn Mem 22:247–257. in humans, and therefore might facilitate proper fear extinction Carter CS (2017) The oxytocin-vasopressin pathway in the context of love similarly to angiotensin II antagonists. Finally, we described and fear. Front Endocrinol (Lausanne) 8:356. Ciocchi S, Herry C, Grenier F, Wolff SB, Letzkus JJ, Vlachos I, Ehrlich I, studies showing that vasopressin V1aR antagonist attenuates Sprengel R, Deisseroth K, Stadler MB, Müller C, Lüthi A (2010) anxiety in the face of unpredictable threats in both male and Encoding of conditioned fear in central amygdala inhibitory circuits. female human subjects and thus might serve as a new treatment Nature 468:277–282. for PTSD (Fig. 1A–C). Collectively, these studies identify multi- Chemtob CM, Hamada RS, Roitblat HL, Muraoka MY (1994) Anger, impul- ple neuropeptides as novel and promising targets for the treat- sivity, and anger control in combat-related posttraumatic stress disorder. – ment of PTSD and anxiety disorders. However, given the J Consult Clin Psychol 62:827 832. heterogeneity of PTSD symptoms and clinical manifestation, it is Craske MG, Kircanski K, Zelikowsky M, Mystkowski J, Chowdhury N, Baker A (2008) Optimizing inhibitory learning during exposure therapy. Behav likely that therapeutic targeting of one neuropeptide system may Res Ther 46:5–27. show promise for subsets of PTSD-related symptoms. This sug- Danzer SC, Price RO, McMullen NT, Rance NE (1999) Sex steroid modula- gests a need to establish personalized care by identifying sub- tion of neurokinin B gene expression in the arcuate nucleus of adult male groups of patients who would benefit most from each treatment. rats. Brain Res Mol Brain Res 66:200–204. A combination of compounds targeting neuropeptidergic recep- Davis M (2001) Fear-potentiated startle in rats. Curr Protoc Neurosci tors might provide a more comprehensive treatment approach Chapter 8:Unit 8.11A. for other patients. For these reasons, further preclinical and clini- Davis M, Falls WA, Campeau S, Kim M (1993) Fear-potentiated startle: a neural and pharmacological analysis. Behav Brain Res 58:175–198. cal studies on interactions among limbic neuromodulators and Davis M, Walker DL, Miles L, Grillon C (2010) Phasic vs sustained fear in circuits described here are essential. rats and humans: role of the extended amygdala in fear vs anxiety. Neuropsychopharmacology 35:105–135. References de Kloet CS, Vermetten E, Geuze E, Wiegant VM, Westenberg HG (2008) Elevated plasma arginine vasopressin levels in veterans with posttrau- Alheid GF (2003) Extended amygdala and basal forebrain. Ann NY Acad Sci matic stress disorder. J Psychiatr Res 42:192–198. 985:185–205. de Kloet AD, Liu M, Rodríguez V, Krause EG, Sumners C (2015) Role of Andari E, Hurlemann R, Young LJ (2018) A precision medicine approach to – neurons and glia in the CNS actions of the renin-angiotensin system in oxytocin trials. Curr Top Behav Neurosci 35:559 590. cardiovascular control. Am J Physiol Regul Integr Comp Physiol 309: Andero R, Dias BG, Ressler KJ (2014) A role for Tac2, NkB, and Nk3 recep- R444–R458. tor in normal and dysregulated fear memory consolidation. Neuron de Kloet AD, Pitra S, Wang L, Hiller H, Pioquinto DJ, Smith JA, Sumners C, – 83:444 454. Stern JE, Krause EG (2016a) Angiotensin type-2 receptors influence the Andero R, Daniel S, Guo JD, Bruner RC, Seth S, Marvar PJ, Rainnie D, Ressler activity of vasopressin neurons in the paraventricular nucleus of the KJ (2016) Amygdala-dependent molecular mechanisms of the Tac2 path- hypothalamus in male mice. Endocrinology 157:3167–3180. – way in fear learning. Neuropsychopharmacology 41:2714 2722. de Kloet AD, Wang L, Ludin JA, Smith JA, Pioquinto DJ, Hiller H, Asahina K, Watanabe K, Duistermars BJ, Hoopfer E, González CR, Eyjólfsdóttir Steckelings UM, Scheuer DA, Sumners C, Krause EG (2016b) Reporter EA, Perona P, Anderson DJ (2014) Tachykinin-expressing neurons control mouse strain provides a novel look at angiotensin type-2 receptor distri- male-specific aggressive arousal in Drosophila.Cell156:221–235. bution in the central nervous system. Brain Struct Funct 221:891–912. Asok A, Draper A, Hoffman AF, Schulkin J, Lupica CR, Rosen JB (2018) de Kloet AD, Wang L, Pitra S, Hiller H, Smith JA, Tan Y, Nguyen D, Cahill Optogenetic silencing of a corticotropin-releasing factor pathway from KM, Sumners C, Stern JE, Krause EG (2017) A unique “angiotensin- 908 • J. Neurosci., February 3, 2021 • 41(5):901–910 Marvar et al. · Limbic Neuropeptidergic Modulators of Emotion

sensitive” neuronal population coordinates neuroendocrine, cardiovascu- posttraumatic stress disorder but not in generalized anxiety disorder. Biol lar, and behavioral responses to stress. J Neurosci 37:3478–3490. Psychiatry 66:47–53. Dias BG, Goodman JV, Ahluwalia R, Easton AE, Andero R, Ressler KJ (2014) Grobe JL, Xu D, Sigmund CD (2008) An intracellular renin-angiotensin sys- Amygdala-dependent fear memory consolidation via miR-34a and Notch tem in neurons: fact, hypothesis, or fantasy. Physiology (Bethesda) signaling. Neuron 83:906–918. 23:187–193. Duarte CR, Schütz B, Zimmer A (2006) Incongruent pattern of neurokinin B Gross CT, Canteras NS (2012) The many paths to fear. Nat Rev Neurosci expression in rat and mouse brains. Cell Tissue Res 323:43–51. 13:651–658. Dunlop BW, Mansson E, Gerardi M (2012) Pharmacological innovations for Gulliver D, Werry E, Reekie TA, Katte TA, Jorgensen W, Kassiou M (2019) posttraumatic stress disorder and medication- enhanced psychotherapy. Targeting the oxytocin system: new pharmacotherapeutic approaches. Curr Pharm Des 18:5645–5658. Trends Pharmacol Sci 40:22–37. Duvarci S, Paré D (2014) Amygdala microcircuits controlling learned fear. Gungor NZ, Paré D (2016) Functional heterogeneity in the bed nucleus of Neuron 82:966–980. the stria terminalis. J Neurosci 36:8038–8049. Ebner K, Bosch OJ, Krömer SA, Singewald N, Neumann ID (2005) Release of ox- Gungor NZ, Yamamoto R, Paré D (2015) Optogenetic study of the projec- ytocin in the rat central amygdala modulates stress-coping behavior and the tions from the bed nucleus of the stria terminalis to the central amygdala. release of excitatory amino acids. Neuropsychopharmacology 30:223–230. J Neurophysiol 114:2903–2911. Eckstein M, Becker B, Scheele D, Scholz C, Preckel K, Schlaepfer TE, Grinevich Guzmán YF, Tronson NC, Jovasevic V, Sato K, Guedea AL, Mizukami H, V, Kendrick KM, Maier W, Hurlemann R (2015) Oxytocin facilitates the Nishimori K, Radulovic J (2013) Fear-enhancing effects of septal oxytocin – extinction of conditioned fear in humans. Biol Psychiatry 78:194–202. receptors. Nat Neurosci 16:1185 1187. Ellenbogen MA, Linnen AM, Cardoso C, Joober R (2014) Intranasal oxytocin Hasan MT, Althammer F, Silva da Gouveia M, Goyon S, Eliava M, Lefevre A, attenuates the human acoustic startle response independent of emotional Kerspern D, Schimmer J, Raftogianni A, Wahis J, Knobloch-Bollmann HS, modulation. Psychophysiology 51:1169–1177. TangY,LiuX,JainA,ChavantV,GoumonY,WeislogelJM,Hurlemann Etkin A, Wager TD (2007) Functional neuroimaging of anxiety: a meta-anal- R, Herpertz SC, Pitzer C, et al. (2019) A fear memory engram and its plas- – ysis of emotional processing in PTSD, social anxiety disorder, and specific ticity in the hypothalamic oxytocin system. Neuron 103:133 146.e8. phobia. Am J Psychiatry 164:1476–1488. Hazell GG, Hindmarch CC, Pope GR, Roper JA, Lightman SL, Murphy D, ’ Fam J, Holmes N, Delaney A, Crane J, Westbrook RF (2018) Oxytocin recep- O Carroll AM, Lolait SJ (2012) G protein-coupled receptors in the hypothalamic paraventricular and supraoptic nuclei–serpentine gateways to tor activation in the basolateral complex of the amygdala enhances dis- – crimination between discrete cues and promotes configural processing of neuroendocrine homeostasis. Front Neuroendocrinol 33:45 66. cues. Psychoneuroendocrinology 96:84–92. Hernández VS, Hernández OR, Perez de la Mora M, Gómora MJ, Fuxe K, Eiden LE, Zhang L (2016) Hypothalamic vasopressinergic projections in- Fanselow MS (2018) The role of learning in threat imminence and defensive nervate central amygdala GABAergic neurons: implications for anxiety behaviors. Curr Opin Behav Sci 24:44–49. and stress coping. Front Neural Circuits 10:92. Fanselow MS, LeDoux JE (1999) Why we think plasticity underlying Hernández-Pérez OR, Crespo-Ramírez M, Cuza-Ferrer Y, Anias-Calderón J, Pavlovian fear conditioning occurs in the basolateral amygdala. Neuron Zhang L, Roldan-Roldan G, Aguilar-Roblero R, Borroto-Escuela DO, Fuxe 23:229–232. K, Perez de la Mora M (2018) Differential activation of arginine-vasopres- Feldman R, Vengrober A, Ebstein RP (2014) Affiliation buffers stress: cumu- sin receptor subtypes in the amygdaloid modulation of anxiety in the rat lative genetic risk in oxytocin-vasopressin genes combines with early by arginine-vasopressin. Psychopharmacology (Berl) 235:1015–1027. caregiving to predict PTSD in war-exposed young children. Transl Hodgson RA, Mullins D, Lu SX, Guzzi M, Zhang X, Bleickardt CJ, Scott Psychiatry 4:e370. JD, Miller MW, Stamford AW, Parker EM, Varty GB (2014) Floor E, Grad O, Leeman SE (1982) Synaptic vesicles containing substance P Characterization of a novel vasopressin V1b receptor antagonist, purified by chromatography on controlled pore glass. Neuroscience V1B-30N, in animal models of anxiety-like and depression-like 7:1647–1655. behavior. Eur J Pharmacol 730:157–163. Florido A, Velasco E, Soto C, Gómez A, Nadal R, Pozo O, Saura C, Andero R Huber D, Veinante P, Stoop R (2005) Vasopressin and oxytocin excite dis- (2020) Opposite-sex effects of the Tac2 pathway blockade in fear memory tinct neuronal populations in the central amygdala. Science 308:245–248. consolidation: implications for fear-related disorders. In review. Available Hurlemann R, Scheele D, Kinfe TM, Berger R, Philipsen A, Voncken MJ, at https://www.researchsquare.com/article/rs-38533/v2. Kuypers KP, Schruers K (2019) Increased temporal discounting in social Francesconi W, Berton F, Olivera-Pasilio V, Dabrowska J (2020) Oxytocin anxiety disorder normalizes after oxytocin treatment. Psychother selectively excites interneurons and inhibits output neurons of the bed Psychosom 88:55–57. nucleus of the stria terminalis (BNST). Neuroscience. Available at https:// Hurt RC, Garrett JC, Keifer OP, Linares A, Couling L, Speth RC, Ressler KJ, www.biorxiv.org/content/10.1101/2020.06.24.169466v2. Marvar PJ (2015) Angiotensin type 1a receptors on corticotropin-releas- Fraser GL, Ramael S, Hoveyda HR, Gheyle L, Combalbert J (2016) The NK3 ing factor neurons contribute to the expression of conditioned fear. receptor antagonist ESN364 suppresses sex hormones in men and Genes Brain Behav 14:526–533. – women. J Clin Endocrinol Metab 101:417 426. Insel TR (2016) Translating oxytocin neuroscience to the clinic: a National Frijling JL, van Zuiden M, Nawijn L, Koch SBJ, Neumann ID, Veltman DJ, Institute of Mental Health perspective. Biol Psychiatry 79:153–154. Olff M (2015) Salivary oxytocin and vasopressin levels in police officers Jakupcak M, Conybeare D, Phelps L, Hunt S, Holmes HA, Felker B, Klevens with and without post-traumatic stress disorder. J Neuroendocrinol M, McFall ME (2007) Anger, hostility, and aggression among Iraq and – 27:743 751. Afghanistan War veterans reporting PTSD and subthreshold PTSD. J Fuxe K, Rivera A, Jacobsen KX, Höistad M, Leo G, Horvath TL, Staines W, Trauma Stress 20:945–954. De la Calle A, Agnati LF (2005) Dynamics of volume transmission in the Janecek M, Dabrowska J (2019) Oxytocin facilitates adaptive fear and attenu- brain: focus on catecholamine and opioid peptide communication and ates anxiety responses in animal models and human studies: potential the role of uncoupling protein 2. J Neural Transm (Vienna) 112:65–76. interaction with the corticotropin-releasing factor (CRF) system in the Gonzalez AD, Wang G, Waters EM, Gonzales KL, Speth RC, Van Kempen bed nucleus of the stria terminalis (BNST). Cell Tissue Res 375:143–172. TA, Marques-Lopes J, Young CN, Butler SD, Davisson RL, Iadecola C, Jennings JH, Sparta DR, Stamatakis AM, Ung RL, Pleil KE, Kash TL, Stuber Pickel VM, Pierce JP, Milner TA (2012) Distribution of angiotensin type GD (2013) Distinct extended amygdala circuits for divergent motiva- 1a receptor-containing cells in the brains of bacterial artificial chromo- tional states. Nature 496:224–228. some transgenic mice. Neuroscience 226:489–509. Jovanovic T, Norrholm SD, Blanding NQ, Davis M, Duncan E, Bradley B, Goode TD, Maren S (2017) Role of the bed nucleus of the stria terminalis in Ressler KJ (2010) Impaired fear inhibition is a biomarker of PTSD but aversive learning and memory. Learn Mem 24:480–491. not depression. Depress Anxiety 27:244–251. Goode TD, Ressler RL, Acca GM, Miles OW, Maren S (2019) Bed nucleus of Karakilic A, Kizildag S, Kandis S, Guvendi G, Koc B, Camsari GB, Camsari the stria terminalis regulates fear to unpredictable threat signals. Elife 8: UM, Ates M, Arda SG, Uysal N (2018) The effects of acute foot shock e46525. stress on empathy levels in rats. Behav Brain Res 349:31–36. Grillon C, Pine DS, Lissek S, Rabin S, Bonne O, Vythilingam M (2009) Khawaja AM, Rogers DF (1996) Tachykinins: receptor to effector. Int J Increased anxiety during anticipation of unpredictable aversive stimuli in Biochem Cell Biol 28:721–738. Marvar et al. · Limbic Neuropeptidergic Modulators of Emotion J. Neurosci., February 3, 2021 • 41(5):901–910 • 909

Khoury NM, Marvar PJ, Gillespie CF, Wingo A, Schwartz A, Bradley B, Mendelsohn FA, Allen AM, Chai SY, McKinley MJ, Oldfield BJ, Paxinos G Kramer M, Ressler KJ (2012) The renin-angiotensin pathway in posttrau- (1990) The brain angiotensin system: insights from mapping its compo- matic stress disorder: angiotensin-converting enzyme inhibitors and an- nents. Trends Endocrinol Metab 1:189–198. giotensin receptor blockers are associated with fewer traumatic stress Mileusnic D, Lee JM, Magnuson DJ, Hejna MJ, Krause JE, Lorens JB, Lorens symptoms. J Clin Psychiatry 73:849–855. SA (1999) Neurokinin-3 receptor distribution in rat and human brain: an Knobloch HS, Charlet A, Hoffmann LC, Eliava M, Khrulev S, Cetin AH, immunohistochemical study. Neuroscience 89:1269–1290. Osten P, Schwarz MK, Seeburg PH, Stoop R, Grinevich V (2012) Evoked Missig G, Ayers LW, Schulkin J, Rosen JB (2010) Oxytocin reduces background axonal oxytocin release in the central amygdala attenuates fear response. anxiety in a fear-potentiated startle paradigm. Neuropsychopharmacology Neuron 73:553–566. 35:2607–2616. Kompier NF, Keysers C, Gazzola V, Lucassen PJ, Krugers HJ (2019) Early life Moaddab M, Dabrowska J (2017) Oxytocin receptor neurotransmission in adversity and adult social behavior: focus on arginine vasopressin and ox- the dorsolateral bed nucleus of the stria terminalis facilitates the acquisi- ytocin as potential mediators. Front Behav Neurosci 13:143. tion of cued fear in the fear-potentiated startle paradigm in rats. Krause EG, de Kloet AD, Scott KA, Flak JN, Jones K, Smeltzer MD, Ulrich- Neuropharmacology 121:130–139. Lai YM, Woods SC, Wilson SP, Reagan LP, Herman JP, Sakai RR (2011) Motoki K, Sugiura M, Takeuchi H, Kotozaki Y, Nakagawa S, Yokoyama R, Blood-borne angiotensin II acts in the brain to influence behavioral and Kawashima R (2016) Are plasma oxytocin and vasopressin levels reflec- endocrine responses to psychogenic stress. J Neurosci 31:15009–15015. tive of amygdala activation during the processing of negative emotions? Kreuder AK, Scheele D, Schultz J, Hennig J, Marsh N, Dellert T, Ettinger U, A preliminary study. Front Psychol 7:480. Philipsen A, Babasiz M, Herscheid A, Remmersmann L, Stirnberg R, Nagano M, Saitow F, Haneda E, Konishi S, Hayashi M, Suzuki H (2006) Stöcker T, Hurlemann R (2020) Common and dissociable effects of oxy- Distribution and pharmacological characterization of primate NK-1 and tocin and lorazepam on the neurocircuitry of fear. Proc Natl Acad Sci NK-3 tachykinin receptors in the central nervous system of the rhesus USA 117:11781–11787. monkey. Br J Pharmacol 147:316–323. Labuschagne I, Phan KL, Wood A, Angstadt M, Chua P, Heinrichs M, Stout Neumann ID, Landgraf R (2012) Balance of brain oxytocin and vasopressin: JC, Nathan PJ (2010) Oxytocin attenuates amygdala reactivity to fear in implications for anxiety, depression, and social behaviors. Trends generalized social anxiety disorder. Neuropsychopharmacology 35:2403– Neurosci 35:649–659. 2413. Neumann ID, Maloumby R, Beiderbeck DI, Lukas M, Landgraf R (2013) Lahoud N, Maroun M (2013) Oxytocinergic manipulations in cortico- Increased brain and plasma oxytocin after nasal and peripheral adminis- limbic circuit differentially affect fear acquisition and extinction. tration in rats and mice. Psychoneuroendocrinology 38:1985–1993. Psychoneuroendocrinology 38:2184–2195. Nishimura K, Yoshino K, Sanada K, Beppu H, Akiyama Y, Nishimura H, Lee MR, Scheidweiler KB, Diao XX, Akhlaghi F, Cummins A, Huestis MA, Tanaka K, Sonoda S, Ueno H, Yoshimura M, Maruyama T, Ozawa H, Leggio L, Averbeck BB (2018) Oxytocin by intranasal and intravenous Ueta Y (2019) Effect of oestrogen-dependent vasopressin on HPA axis in routes reaches the cerebrospinal fluid in rhesus macaques: determination the median eminence of female rats. Sci Rep 9:5153. using a novel oxytocin assay. Mol Psychiatry 23:115–122. Nylocks KM, Michopoulos V, Rothbaum AO, Almli L, Gillespie CF, Wingo Lee MR, Shnitko TA, Blue SW, Kaucher AV, Winchell AJ, Erikson DW, A, Schwartz AC, Habib L, Gamwell KL, Marvar PJ, Bradley B, Ressler KJ Grant KA, Leggio L (2020) Labeled oxytocin administered via the intra- (2015) An angiotensin-converting enzyme (ACE) polymorphism may nasal route reaches the brain in rhesus macaques. Nat Commun 11:2783. mitigate the effects of angiotensin-pathway medications on posttraumatic Lee RJ, Coccaro EF, Cremers H, McCarron R, Lu SF, Brownstein MJ, Simon stress symptoms. Am J Med Genet B Genet 168:307–315. NG (2013) A novel V1a receptor antagonist blocks vasopressin-induced Okuyama S, Sakagawa T, Chaki S, Imagawa Y, Ichiki T, Inagami T (1999) changes in the CNS response to emotional stimuli: an fMRI study. Front Anxiety-like behavior in mice lacking the angiotensin II type-2 receptor. Syst Neurosci 7:100. Brain Res 821:150–159. Lieberz J, Scheele D, Spengler FB, Matheisen T, Schneider L, Stoffel- Olivera-Pasilio V, Dabrowska J (2020) Oxytocin promotes accurate fear dis- Wagner B, Kinfe TM, Hurlemann R (2020) Kinetics of oxytocin effects crimination and adaptive defensive behaviors. Front Neurosci 14:583878. on amygdala and striatal reactivity vary between women and men. Paré D, Quirk GJ, Ledoux JE (2004) New vistas on amygdala networks in Neuropsychopharmacology 45:1134–1140. conditioned fear. J Neurophysiol 92:1–9. Lind RW, Swanson LW, Ganten D (1985) Organization of angiotensin II im- Parrish JN, Bertholomey ML, Pang HW, Speth RC, Torregrossa MM (2019) munoreactive cells and fibers in the rat central nervous system: an immu- Estradiol modulation of the renin-angiotensin system and the regulation nohistochemical study. Neuroendocrinology 40:2–24. of fear extinction. Transl Psychiatry 9:36. Lu Q, Lai J, Du Y, Huang T, Prukpitikul P, Xu Y, Hu S (2019) Sexual dimor- Pascoe JP, Kapp BS (1985) Electrophysiological characteristics of amygdaloid phism of oxytocin and vasopressin in social cognition and behavior. central nucleus neurons during Pavlovian fear conditioning in the rabbit. Psychol Res Behav Manag 12:337–349. Behav Brain Res 16:117–133. Malherbe P, Ballard TM, Ratni H (2011) Tachykinin neurokinin 3 receptor Peled-Avron L, Abu-Akel A, Shamay-Tsoory S (2020) Exogenous effects of antagonists: a patent review (2005-2010). Expert Opin Ther Pat 21:637– oxytocin in five psychiatric disorders: a systematic review, meta-analyses 655. and a personalized approach through the lens of the social salience hy- Marshall AD (2013) Posttraumatic stress disorder and partner-specific social pothesis. Neurosci Biobehav Rev 114:70–95. cognition: a pilot study of sex differences in the impact of arginine vaso- Phelps EA, LeDoux JE (2005) Contributions of the amygdala to emotion pressin. Biol Psychol 93:296–303. processing: from animal models to human behavior. Neuron 48:175–187. Martinon D, Lis P, Roman AN, Tornesi P, Applebey SV, Buechner G, Pitman RK, Orr SP, Lasko NB (1993) Effects of intranasal vasopressin and oxyto- Olivera V, Dabrowska J (2019) Oxytocin receptors in the dorsolateral bed cin on physiologic responding during personal combat imagery in Vietnam nucleus of the stria terminalis (BNST) bias fear learning toward tempo- veterans with posttraumatic stress disorder. Psychiatry Res 48:107–117. rally predictable cued fear. Transl Psychiatry 9:140. Pomrenze MB, Tovar-Diaz J, Blasio A, Maiya R, Giovanetti SM, Lei K, Marvar PJ, Goodman J, Fuchs S, Choi DC, Banerjee S, Ressler KJ (2014) Morikawa H, Hopf FW, Messing RO (2018) A corticotropin releasing Angiotensin type 1 receptor inhibition enhances the extinction of fear factor network in the extended amygdala for anxiety. J Neurosci 39:1030– memory. Biol Psychiatry 75:864–872. 1043. Mathew SJ, Vythilingam M, Murrough JW, Zarate CA, Feder A, Pulcu E, Shkreli L, Holst CG, Woud ML, Craske MG, Browning M, Reinecke Luckenbaugh DA, Kinkead B, Parides MK, Trist DG, Bani MS, Bettica A (2019) The effects of the angiotensin II receptor antagonist losartan on PU, Ratti EM, Charney DS (2011) A selective neurokinin-1 receptor an- appetitive versus aversive learning: a randomized controlled trial. Biol tagonist in chronic PTSD: a randomized, double-blind, placebo-con- Psychiatry 86:397–404. trolled, proof-of-concept trial. Eur Neuropsychopharmacol 21:221–229. Quintana DS, Rokicki J, van der Meer D, Alnæs D, Kaufmann T, Córdova- McDonald AJ, Shammah-Lagnado SJ, Shi C, Davis M (1999) Cortical affer- Palomera A, Dieset I, Andreassen OA, Westlye LT (2019) Oxytocin path- ents to the extended amygdala. Ann NY Acad Sci 877:309–338. way gene networks in the human brain. Nat Commun 10:668. Meloni EG, Jackson A, Gerety LP, Cohen BM, Carlezon WA (2006) Role of Reijnen A, Geuze E, Vermetten E (2017) Individual variation in plasma oxy- the bed nucleus of the stria terminalis (BST) in the expression of condi- tocin and vasopressin levels in relation to the development of combat- tioned fear. Ann NY Acad Sci 1071:538–541. related PTSD in a large military cohort. J Psychiatr Res 94:88–95. 910 • J. Neurosci., February 3, 2021 • 41(5):901–910 Marvar et al. · Limbic Neuropeptidergic Modulators of Emotion

Ring RH, Malberg JE, Potestio L, Ping J, Boikess S, Luo B, Schechter LE, Toth I, Neumann ID, Slattery DA (2012) Central administration of oxytocin Rizzo S, Rahman Z, Rosenzweig-Lipson S (2006) Anxiolytic-like activity receptor ligands affects cued fear extinction in rats and mice in a time- of oxytocin in male mice: behavioral and autonomic evidence, therapeu- point-dependent manner. Psychopharmacology (Berl) 223:149–158. tic implications. Psychopharmacology (Berl) 185:218–225. van den Pol AN (2012) Neuropeptide transmission in brain circuits. Neuron Roberts GW, Woodhams PL, Polak JM, Crow TJ (1982) Distribution of neu- 76:98–115. ropeptides in the limbic system of the rat: the amygdaloid complex. Viviani D, Charlet A, van den Burg E, Robinet C, Hurni N, Abatis M, – Neuroscience 7:99 131. Magara F, Stoop R (2011) Oxytocin selectively gates fear responses Ross AP, McCann KE, Larkin TE, Song Z, Grieb ZA, Huhman KL, Albers through distinct outputs from the central amygdala. Science 333:104– HE (2019) Sex-dependent effects of social isolation on the regulation of 107. arginine-vasopressin (AVP) V1a, oxytocin (OT) and serotonin (5HT) 1a Walker DL, Davis M (2002) Quantifying fear potentiated startle using abso- receptor binding and aggression. Horm Behav 116:104578. lute versus proportional increase scoring methods: implications for the Rotondo F, Butz H, Syro LV, Yousef GM, Di Ieva A, Restrepo LM, neurocircuitry of fear and anxiety. Psychopharmacology (Berl) 164:318– Quintanar-Stephano A, Berczi I, Kovacs K (2016) Arginine vasopressin 328. (AVP): a review of its historical perspectives, current research and multi- functional role in the hypothalamo-hypophysial system. Pituitary Walker DL, Davis M (2008) Role of the extended amygdala in short-duration 19:345–355. versus sustained fear: a tribute to Dr. Lennart Heimer. Brain Struct Funct – Sahu A, Kalra SP (1992) Effects of tachykinins on luteinizing hormone 213:29 42. release in female rats: potent inhibitory action of neuropeptide K. Wang D, Yan X, Li M, Ma Y (2017) Neural substrates underlying the effects Endocrinology 130:1571–1577. of oxytocin: a quantitative meta-analysis of pharmaco-imaging studies. Saavedra JM, Sánchez-Lemus E, Benicky J (2011) Blockade of brain angioten- Soc Cogn Affect Neurosci 12:1565–1573. sin II AT1 receptors ameliorates stress, anxiety, brain inflammation and Wilensky AE, Schafe GE, Kristensen MP, LeDoux JE (2006) Rethinking the ischemia: therapeutic implications. Psychoneuroendocrinology 36:1–18. fear circuit: the central nucleus of the amygdala is required for the acqui- Scheele D, Lieberz J, Goertzen-Patin A, Engels C, Schneider L, Stoffel- sition, consolidation, and expression of Pavlovian fear conditioning. J Wagner B, Becker B, Hurlemann R (2019) Trauma disclosure moderates Neurosci 26:12387–12396. the effects of oxytocin on intrusions and neural responses to fear. Wohl M, Ishii K, Asahina K (2020) Layered roles of fruitless isoforms in spec- Psychother Psychosom 88:61–63. ification and function of male aggression-promoting neurons in Shackman AJ, Fox AS (2016) Contributions of the central extended amygdala Drosophila. Elife 9:e52702. – to fear and anxiety. J Neurosci 36:8050 8063. Xu Q, Jensen DD, Peng H, Feng Y (2016) The critical role of the central nerv- Shekhar A, Johnson PL, Sajdyk TJ, Fitz SD, Keim SR, Kelley PE, Gehlert DR, ous system (pro)renin receptor in regulating systemic blood pressure. DiMicco JA (2006) Angiotensin-II is a putative neurotransmitter in lac- Pharmacol Ther 164:126–134. tate-induced panic-like responses in rats with disruption of GABAergic Yamamoto Y, Higashida H (2020) RAGE regulates oxytocin transport into inhibition in the dorsomedial hypothalamus. J Neurosci 26:9205–9215. the brain. Commun Biol 3:70. Spengler FB, Schultz J, Scheele D, Essel M, Maier W, Heinrichs M, Yamauchi N, Takahashi D, Sugimura YK, Kato F, Amano T, Minami M Hurlemann R (2017) Kinetics and dose dependency of intranasal oxyto- (2018) Activation of the neural pathway from the dorsolateral bed nu- cin effects on amygdala reactivity. Biol Psychiatry 82:885–894. ’ cleus of the stria terminalis to the central amygdala induces anxiety-like Spierling SR, Zorrilla EP (2017) Don t stress about CRF: assessing the trans- – lational failures of CRF1 antagonists. Psychopharmacology (Berl) behaviors. Eur J Neurosci 48:3052 3061. 234:1467–1481. Yang G, Gray TS, Sigmund CD, Cassell MD (1999) The angiotensinogen Sripada CS, Phan KL, Labuschagne I, Welsh R, Nathan PJ, Wood AG (2013) gene is expressed in both astrocytes and neurons in murine central nerv- – Oxytocin enhances resting-state connectivity between amygdala and ous system. Brain Res 817:123 131. medial frontal cortex. Int J Neuropsychopharmacol 16:255–260. Yu Z, Swiercz AP, Moshfegh CM, Hopkins L, Wiaderkiewicz J, Speth RC, Stout DM, Risbrough VB (2019) Angiotensin II signaling and fear extinction: Park J, Marvar PJ (2019) Angiotensin II type 2 receptor-expressing neu- translational evidence and novel receptor targets. Biol Psychiatry 86:874– rons in the central amygdala influence fear-related behavior. Biol 876. Psychiatry 86:899–909. Striepens N, Kendrick KM, Hanking V, Landgraf R, Wüllner U, Maier W, Yuan DM, Li Q, Zhang Q, Xiao XW, Yao YW, Zhang Y, Lv YL, Liu HB, Lv Hurlemann R (2013) Elevated cerebrospinal fluid and blood concentra- TF, Song Y (2016) Efficacy and safety of neurokinin-1 receptor antago- tions of oxytocin following its intranasal administration in humans. Sci nists for prevention of chemotherapy-induced nausea and vomiting: sys- Rep 3:3440. tematic review and meta-analysis of randomized controlled trials. Asian Sun N, Cassell MD (1993) Intrinsic GABAergic neurons in the rat central Pac J Cancer Prev 17:1661–1675. – extended amygdala. J Comp Neurol 330:381 404. Zelikowsky M, Ding K, Anderson DJ (2018a) Neuropeptidergic control of an Tasker JG, Prager-Khoutorsky M, Teruyama R, Lemos JR, Amstrong WE internal brain state produced by prolonged social isolation stress. Cold (2020) Advances in the neurophysiology of magnocellular neuroendo- Spring Harb Symp Quant Biol 83:97–103. crine cells. J Neuroendocrinol 32:e12826. Zelikowsky M, Hui M, Karigo T, Choe A, Yang B, Blanco MR, Beadle K, Terburg D, Scheggia D, Triana Del Rio R, Klumpers F, Ciobanu AC, Morgan Gradinaru V, Deverman BE, Anderson DJ (2018b) The neuropeptide B, Montoya ER, Bos PA, Giobellina G, van den Burg EH, de Gelder B, Tac2 controls a distributed brain state induced by chronic social isolation Stein DJ, Stoop R, van Honk J (2018) The basolateral amygdala is essen- stress. Cell 173:1265–1279.e19. tial for rapid escape: a human and rodent study. Cell 175:723–735.e16. Zhou F, Geng Y, Xin F, Li J, Feng P, Liu C, Zhao W, Feng T, Guastella AJ, Terock J, Hannemann A, Janowitz D, Freyberger HJ, Felix SB, Dörr M, Nauck M, Völzke H, Grabe HJ (2019) Associations of trauma exposure Ebstein RP, Kendrick KM, Becker B (2019) Human extinction learning is and post-traumatic stress disorder with the activity of the renin-angioten- accelerated by an angiotensin antagonist via ventromedial prefrontal cor- sin-aldosterone-system in the general population. Psychol Med 49:843– tex and its connections with basolateral amygdala. Biol Psychiatry – 851. 86:910 920. Thompson RR, George K, Walton JC, Orr SP, Benson J (2006) Sex-specific Zhu L, Onaka T (2002) Involvement of medullary A2 noradrenergic neurons influences of vasopressin on human social communication. Proc Natl in the activation of oxytocin neurons after conditioned fear stimuli. Eur J Acad Sci USA 103:7889–7894. Neurosci 16:2186–2198. Torrisi S, Gorka AX, Gonzalez-Castillo J, O’Connell K, Balderston N, Grillon Zink CF, Stein JL, Kempf L, Hakimi S, Meyer-Lindenberg A (2010) C, Ernst M (2018) Extended amygdala connectivity changes during sus- Vasopressin modulates medial prefrontal cortex-amygdala circuitry dur- tained shock anticipation. Transl Psychiatry 8:33. ing emotion processing in humans. J Neurosci 30:7017–7022.