Social Approach and Social Vigilance Are Differentially Regulated by Oxytocin Receptors in the Nucleus Accumbens
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www.nature.com/npp ARTICLE OPEN Social approach and social vigilance are differentially regulated by oxytocin receptors in the nucleus accumbens Alexia V. Williams1, Natalia Duque-Wilckens 1, Stephanie Ramos-Maciel1, Katharine L. Campi1, Shanu K. Bhela1, Christine K. Xu1, Kenneth Jackson2, Bice Chini3, Patricia A. Pesavento2 and Brian C. Trainor 1 Oxytocin is currently being considered as a novel therapeutic for anxiety disorders due to its ability to promote affiliative behaviors. In the nucleus accumbens (NAc) activation of oxytocin receptors (OTR) promotes social approach (time spent near an unfamiliar individual). Here, we show that stressful social experiences reduce the expression of NAc OTR mRNA, coinciding with decreases in social approach. Social stressors also increase social vigilance, characterized as orienting to an unfamiliar individual without approaching. Vigilance is a key component of behavioral inhibition, a personality trait that is a risk factor for anxiety disorders. To understand whether NAc OTR can modulate both social approach and vigilance, we use pharmacological approaches to assess the impact of activation or inhibition of NAc OTR downstream pathways on these behaviors. First, we show that in unstressed male and female California mice, inhibition of OTR by an unbiased antagonist (L-368,899) reduces social approach but does not induce social vigilance. Next, we show that infusion of Atosiban, an OTR-Gq antagonist/OTR-Gi agonist, has the same effect in unstressed females. Finally, we show that Carbetocin, a biased OTR-Gq agonist, increases social approach in stressed females while simultaneously inhibiting social vigilance. Taken together these data suggest that OTR in the NAc differentially modulate social approach and social vigilance, primarily through an OTR-Gq mechanism. Importantly, pharmacological inhibition of OTR alone is insufficient to induce 1234567890();,: vigilance in unstressed mice, suggesting that mechanisms modulating social approach may be distinct from mechanisms modulating social vigilance. Neuropsychopharmacology (2020) 45:1423–1430; https://doi.org/10.1038/s41386-020-0657-4 INTRODUCTION stressors reduce oxytocin immunoreactivity and oxytocin Avoidance of social situations is a hallmark symptom of a variety receptor (OTR) binding in the NAc, corresponding with reduc- of psychiatric illnesses, including mood disorders, anxiety dis- tions in social approach [24, 25]. Conversely, in the bed nucleus orders [1], and several neurodevelopmental disorders such as of the stria terminalis (BNST) stress increases the activity of autism [2, 3]. Although existing pharmacotherapeutics can help oxytocin producing cells [26, 27], and inhibition of OTR in the mitigate social avoidance in some individuals, for many these BNST prevents stress-induced decreases in social approach and treatments prove insufficient. The neuropeptide oxytocin is being increases in social vigilance in female California mice [24]. Social considered as a novel therapeutic target due to its ability to vigilance is defined as orienting toward an unfamiliar individual promote affiliative behaviors. When administered intranasally, without approaching [24], and resembles responses by rats oxytocin often increases various aspects of social behaviors [4–8]. confronted with a predator [28] and stress-induced stretch- However, other reports find that intranasal oxytocin treatment can attendresponsesinSyrianhamsters[29]. Social vigilance has have very different effects, especially in situations where an also been observed in female C57Bl6/J mice exposed to social undercurrent of stress or threat exists [9, 10]. For example, in some stress [30]. In humans, a combination of increased social cases, intranasal oxytocin has been shown to increase antagonistic vigilance and reduced social approach is characteristic of social interactions in both humans [11, 12] and female Wistar rats behavioral inhibition, a temperamentthatisastrongpredictor [13–15]. Taken together this supports the idea that the impacts of for the development of social anxiety disorders [31–34]. oxytocin on social behavior are complex and differ based on Previously, we showed that treatment with an OTR antagonist context [16, 17]. Actions of oxytocin appear to be circuit-specific increased social approach and decreased social vigilance [24]in [17], which may be one possible mechanism for its context- stressed female California mice if administered either systemi- dependent actions. cally or site-specifically into the BNST. A key question is what the When acting within the mesolimbic dopamine system, specific contributions of NAc OTR are on stress-induced changes oxytocin can promote several forms of social behavior [18–22]. in social approach and social vigilance. Specifically, does Within the nucleus accumbens core (NAc), oxytocin promotes activation of NAc OTR have distinct effects on these behaviors, the formation of social conditioned place preference in male or are social approach and social vigilance universally inversely C57Bl6/J mice [23]. In California mice and prairie voles, social related? 1Department of Psychology, University of California, Davis, CA, USA; 2Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA, USA and 3Isnstitute of Neuroscience of National Research Council and NEUROMI Milan Center for Neuroscience, University of Milano-Bicocca, Milan, Italy Correspondence: Brian C. Trainor ([email protected]) Received: 19 December 2019 Revised: 13 February 2020 Accepted: 6 March 2020 Published online: 20 March 2020 © The Author(s) 2020 Social approach and social vigilance are differentially regulated by. AV Williams et al. 1424 An additional layer of complexity stems from the distinct resident) or control handling for three consecutive days as signaling pathways and cellular processes that can be activated by previously described [42, 43]. See Supplementary methods for OTR coupling with different G-protein subunits: excitatory subunit full details. Gq and inhibitory subunit Gi [35]. Biased agonists that selectively activate distinct signaling pathways by promoting G-protein Social interaction test and social vigilance coupled receptor coupling to selective G-protein subunits [36] Social interaction testing was performed as previously described have been proposed as novel treatment options for various mood [42, 43]. Mice were placed in an open arena for 3 min (open field). and pain disorders [37, 38]. Some evidence exists for the ability of Next, an empty wire cage was placed in the arena and the time OTR to reduce general anxiety-like behavior in male Sprague- spent within 8 cm of the cage (interaction zone) was scored for Dawley rats through Gq specific signaling pathways [39], 3 min (acclimation phase). For the last phase, an unfamiliar same- suggesting that agonists that selectively activate OTR-Gq signaling sex mouse was placed into the wire cage and time spent near the could have potential as novel therapeutics for anxiety disorders. In interaction zone was scored for 3 min (interaction phase). We contrast, recent data showed that Atosiban, a biased agonist that define time spent in the interaction zone with a target mouse as induces OTR-Gi signaling and inhibits OTR-Gq [35], had analgesic social approach. Social vigilance was scored during the interaction effects in the spinal cord in male Wistar rats [40]. Here, we test the phase by recording the amount of time the focal mouse spent extent to which biased agonists with distinct signaling properties with its head oriented toward the target mouse while outside the can act in the NAc core to modulate social approach and social interaction zone [24, 44]. See Supplementary Video S1 for vigilance. First, we examined the cellular distribution of Oxtr mRNA representative examples. and assessed whether social stress impacted Oxtr expression in the NAc. Next, we used L-368,899 (OTA, an unbiased OTR Statistical analyses antagonist [24]) to block OTR signaling through both Gq and Gi All statistical analyses were performed using R statistical software. pathways in unstressed mice. We then used Atosiban to block Normality of data was assessed using Shapiro-test. A Fligner- OTR-Gq signaling while activating OTR-Gi signaling in unstressed Killeen test was used to assess homogeneity of variance. Two-way mice. Last, we used Carbetocin, which induces OTR-Gq signaling ANOVA was used to analyze qPCR data as well as behavior without engaging OTR-Gi [41], in stressed mice in order to test the measures in experiment three and four. Three-way ANOVA was extent to which OTR-Gq signaling can reverse stress-induced used to analyze behavioral data in experiment two. For data that deficits in social approach and increases in social vigilance. Our did not follow a normal distribution (vigilance), data were square results suggest that social approach and social vigilance are root transformed to normalize prior to ANOVA testing. For ANOVA controlled by distinct but overlapping mechanisms. analyses that revealed significant interaction effects, pairwise comparisons were used to detect differences between groups. METHODS AND MATERIALS For full details see Supplementary “Materials and Methods”. RESULTS Experiment 1: Oxtr is expressed in inhibitory neurons and Animals expression is reduced by social stress All studies on California mice (Peromyscus californicus) were in To determine whether Oxtr is expressed locally in inhibitory accordance with the NIH Guide for the Care