Histamine in the Basolateral Amygdala Promotes Inhibitory Avoidance
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Histamine in the basolateral amygdala promotes PNAS PLUS inhibitory avoidance learning independently of hippocampus Fernando Benettia,1, Cristiane Regina Guerino Furinia, Jociane de Carvalho Myskiwa, Gustavo Provensib, Maria Beatrice Passanib, Elisabetta Baldic, Corrado Bucherellic, Leonardo Munarib,2, Ivan Izquierdoa,3, and Patrizio Blandinab,3 aMemory Center, Brain Institute of Rio Grande do Sul, Pontifical Catholic University of Rio Grande do Sul, 90610-000 Porto Alegre, RS, Brazil; bDipartimento di Neuroscienze, Psicologia, Area del Farmaco e Salute del Bambino, Sezione di Farmacologia e Tossicologia, Universitá di Firenze, 50139 Firenze, Italy; and cDipartimento di Medicina Sperimentale e Clinica, Universitá di Firenze, 50134 Firenze, Italy Contributed by Ivan Izquierdo, March 30, 2015 (sent for review March 4, 2015; reviewed by Federico Bermudez-Rattoni and Daniele Piomelli) Recent discoveries demonstrated that recruitment of alternative hippocampal damage before new learning can be overcome, possibly brain circuits permits compensation of memory impairments follow- through recruitment of an alternative circuit. The identity of the ing damage to brain regions specialized in integrating and/or storing compensatory structures is still unknown, but the BLA could specific memories, including both dorsal hippocampus and baso- potentially be one, because it operates to a certain extent in lateral amygdala (BLA). Here, we first report that the integrity of the parallel with the CA1 region in memory processing (9). brain histaminergic system is necessary for long-term, but not for Extensive evidence indicates that emotionally significant experi- short-term memory of step-down inhibitory avoidance (IA). Second, ences activate many hormones and neurotransmitters, including we found that phosphorylation of cyclic adenosine monophosphate histamine, that regulate the consolidation of newly acquired mem- (cAMP) responsive-element-binding protein, a crucial mediator in ories (10, 11). Histamine is synthesized from histidine by histidine- long-term memory formation, correlated anatomically and tempo- decarboxylase (HDC) (12) and released in the brain from varicos- rally with histamine-induced memory retrieval, showing the active ities of axons that ramify extensively throughout the central nervous NEUROSCIENCE involvement of histamine function in CA1 and BLA in different system. The only source of histaminergic fibers is the hypothalamic phases of memory consolidation. Third, we found that exogenous tuberomamillary nucleus (TMN) (13). The histaminergic system is application of histamine in either hippocampal CA1 or BLA of brain crucial in the sleep–wake cycle and is implicated in various brain histamine-depleted rats, hence amnesic, restored long-term memory; however, the time frame of memory rescue was different for the functions, including the modulation of hippocampal synaptic plas- two brain structures, short lived (immediately posttraining) for BLA, ticity (12, 14). Interestingly, when infused into the CA1 region im- long lasting (up to 6 h) for the CA1. Moreover, long-term memory mediately after training of an IA task, histamine induced a dose- was formed immediately after training restoring of histamine trans- dependent promnesic effect through activation of H2 receptors mission only in the BLA. These findings reveal the essential role of without altering locomotor activity, exploratory behavior, anxiety histaminergic neurotransmission to provide the brain with the plas- ticity necessary to ensure memorization of emotionally salient events, Significance through recruitment of alternative circuits. Hence, our findings indi- cate that the histaminergic system comprises parallel, coordinated Integrity of the brain histaminergic system is necessary for long- pathways that provide compensatory plasticity when one brain term memory (LTM) but not short-term memory of step-down structure is compromised. inhibitory avoidance (IA). Histamine depletion in hippocampus or basolateral amygdala (BLA) impairs LTM of that task. Histamine histamine | hippocampus | amygdala | lateral ventricle | inhibitory infusion into either structure restores LTM in histamine-depleted avoidance rats. The restoring effect in BLA occurs even when hippocampal activity was impaired. Cyclic adenosine monophosphate (cAMP) motionally arousing experiences create long-term memories responsive-element-binding protein phosphorylation correlates Ethat are initially labile, but over time become insensitive to anatomically and temporally with histamine-induced memory disruption through a process known as consolidation (1). One- recall. Thus, histaminergic neurotransmission appears critical to trial fear-motivated learning tasks, such as step-down inhibitory provide the brain with the plasticity necessary for IA through re- avoidance (IA), a hippocampal-dependent associative learning cruitment of alternative circuits. Our findings indicate that the (2), have largely contributed to the knowledge of consolidation histaminergic system comprises parallel, coordinated pathways process, and convincing evidence indicates that the CA1 region that provide compensatory plasticity when one brain structure is of the hippocampus, the basolateral amygdala (BLA) and the compromised. medial prefrontal cortex, are crucially involved in this process (3, 4). However, the actual contribution of each region remains Author contributions: F.B., C.R.G.F., J.d.C.M., G.P., M.B.P., I.I., and P.B. designed research; F.B., C.R.G.F., J.d.C.M., G.P., E.B., C.B., and L.M. performed research; F.B., C.R.G.F., J.d.C.M., poorly characterized. For instance, it is suggested that they are G.P., I.I., and P.B. analyzed data; and J.d.C.M., M.B.P., I.I., and P.B. wrote the paper. part of mostly independent circuitries specialized in encoding Reviewers: F.B.-R., National University of Mexico; and D.P., University of California, Irvine. specific aspects of information, e.g., the emotional component in the BLA and the cognitive aspect in the hippocampus (2, 5). If The authors declare no conflict of interest. 1Present address: Departamento de Fisiologia, Instituto de Ciências Básicas da Saúde, this relation between structures holds true for an intact brain, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS 90050-17, Brazil. however, examples of learning recovery of individuals bearing 2Present address: Department of Pharmacology and Systems Therapeutics, Mount Sinai large brain lesions suggest that the brain can adapt dynamically, School of Medicine, New York, NY 10029. and interconnected systems can provide compensation for selec- 3To whom correspondence may be addressed. Email: [email protected] or patrizio. tive damage (2). Indeed, hippocampal damage resulted in retro- [email protected]. grade amnesia for acquired fear memories (6), but did not prevent This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. new learning in rodents (7) as well as in humans (8). Therefore, 1073/pnas.1506109112/-/DCSupplemental. www.pnas.org/cgi/doi/10.1073/pnas.1506109112 PNAS Early Edition | 1of7 Downloaded by guest on October 1, 2021 state, or retrieval of the avoidance response (15). Consistently, post- mediator in the formation of long-term memory (21), and an in- training injections into the dorsal hippocampus of histamine H2 or crease in CREB phosphorylation at Ser-133 in the hippocampus is H3 receptor agonists improved memory consolidation after specifically associated with IA memory formation (22, 23). In par- contextual fear conditioning through a mechanism involving extra- ticular, a significant increase of pCREB in the hippocampus occurs cellular signal-regulated kinase (ERK)2 phosphorylation (16). Several immediately after training, followed by a delayed increase of Ser- neurotransmitters, such as dopamine, glutamate, and norepineph- 133 pCREB 3–6 h later (22). It is conceivable that for a short period rine, activate the ERK cascade in the hippocampus (17), and hista- after training, the hippocampus acts in concert with the amygdala mine may interact with these neurotransmitters to orchestrate ERK2 that contributes emotional values (2). phosphorylation that appears to play a critical role in consolidating To examine the influences of histamine depletion on CREB emotional memories (17). Histamine modulates memory of emo- phosphorylation following IA training, rats were euthanized tionally arousing experiences also in the BLA. Administration of H3 10 min or 5 h after training, and pCREB levels were assessed in the receptor antagonists into the BLA impaired consolidation of fear amygdala and the CA1 of rats given saline or a-FMHis infusions memories (18), whereas H3 receptor agonists ameliorated the ex- in the lateral ventricle (LV) 24 h before training. Controls re- pression of adverse memories (19). This effect involved H2 receptors ceived saline into the LV and no foot shock (untrained). pCREB and was accompanied by a bimodal modulation of the local cholin- levels were measured also in rats that received saline into the LV ergic tone (18, 19). and were placed directly over the electrified grid (saline/foot- Although these findings indicate that administration of hista- shocked) to control for potential changes in CREB phosphory- minergic ligands modulates memory consolidation, studies have lation due to the foot shock itself. Representative immunoblots not yet investigated the role of endogenous histamine in creating and the densitometric analysis are shown in Fig. 2 A (10