PAC1 receptor antagonism in the bed nucleus of the stria terminalis (BNST) attenuates the endocrine and behavioral consequences of chronic stress
Introduction
Severe or repeated stress places undue challenges on physiological and psychological systems, which typically results in the mobilization of adaptive response systems designed to reestablish homeostatic states. Multiple response systems are engaged following stressor exposure, including the hypothalamic–pituitary–adrenal (HPA) axis, the sympathetic nervous system, and central nervous system (CNS) circuits mediating fear and anxiety-like behavior. The bed nucleus of the stria terminalis (BNST), a region of the extended amygdala, has been argued to mediate all three of these responses to sustained threats (Walker et al., 2003, Walker et al., 2009, Herman et al., 2005, Walker and Davis, 2008, Radley and Sawchenko, 2011). For example, hypothalamic paraventricular nucleus (PVN) activity, which mediates both the endocrine and autonomic response to stressor exposure, is tightly regulated by both anterior and posterior BNST subregions (Choi et al., 2007, Choi et al., 2008a, Radley and Sawchenko, 2011). Moreover, Waddell et al. (2006) and Walker et al., 2003, Walker et al., 2009 have argued that the BNST mediates responding to long duration threats, and that the BNST may mediate anxiety-like emotional states (Walker et al., 2003, Waddell et al., 2006, Choi et al., 2007, Choi et al., 2008a, Walker and Davis, 2008, Radley and Sawchenko, 2011). Consistent with these observations, the BNST has been implicated in regulating anxious temperament in nonhuman primates (Kalin et al., 2005, Kalin et al., 2008, Fox et al., 2008, Oler et al., 2009) and humans (Straube et al., 2007, Somerville et al., 2010).
Accordingly, altered BNST functioning is likely critical for the etiology of many anxiety disorders associated with stressor exposure (Schulkin et al., 1998, Vyas et al., 2003, Pego et al., 2008, Hammack et al., 2009, Hammack et al., 2010). In support, repeated exposure to stressors or drugs of abuse has been correlated with enhanced BNST neuroplasticity, including increased neuronal peptide expression (Stout et al., 2000, Choi et al., 2006, Hammack et al., 2009), dendritic length and branching (Vyas et al., 2003, Pego et al., 2008), volume (Pego et al., 2008), and synaptic activity (Dumont et al., 2005). These observations suggest that repeated or chronic stressor exposure may enhance BNST function, which may lead to pathological anxiety.
Increasingly, the neuropeptides that mediate BNST signaling during stressor exposure have generated significant interest. In addition to the roles of extra-hypothalamic corticotropin-releasing hormone (CRH) signaling in fear- and anxiety-like behavior (Lee and Davis, 1997, Koob and Heinrichs, 1999, Hammack et al., 2002), pituitary adenylate cyclase activating polypeptide (PACAP) and its cognate PAC1 receptor have been implicated in mediating responses associated with stress and anxiety. PACAP and PAC1 receptors are selectively upregulated in the BNST following chronic variate stress, and BNST PACAP activation is anxiogenic (Hammack et al., 2009). PACAP and PAC1 receptor null mice also demonstrate reduced anxiety-like behavior (Hashimoto et al., 2001, Otto et al., 2001, Girard et al., 2006, Gaszner et al., 2012, Hattori et al., 2012), and the glucocorticoid response in PACAP null animals is altered after stressor exposure (Morita et al., 2006, Hatanaka et al., 2008, Stroth and Eiden, 2010, Tsukiyama et al., 2011, Lehmann et al., 2013). In humans, PACAP dysregulation has recently been associated with a number of psychopathologies including post-traumatic stress disorder (PTSD). Elevated circulating PACAP levels, and PAC1 receptor gene polymorphism and methylation each predicted PTSD symptoms and diagnosis (Ressler et al., 2011, Jovanovic et al., 2013).
However, while accumulating evidence implicate PACAP in the consequences of stressor exposure, the mechanisms and functions of PACAP activities in the BNST are still unclear. In the current work, we examined the intersection of PACAP and CRH in the BNST, the PACAP/VIP receptor subtypes involved in BNST function, and the roles of endogenous BNST PACAP in mediating the stress-induced HPA and behavioral responses. Notably, we demonstrate that blocking BNST PACAP/PAC1 receptor signaling can attenuate the physiological and behavioral consequences of repeated stress exposure which may offer insights for therapeutics.
Section snippets
Animals
Adult male Sprague-Dawley rats (250–275 g) were obtained from Charles River Laboratories (Wilmington, MA). After delivery, rats were allowed to habituate in their home cages for at least one week before experimentation. Rats were single-housed and maintained on a 12 h light/dark cycle (lights on at 07:00 h). Food and water were available ad libitum. All procedures were approved by the Institutional Animal Care and Use Committee at the University of Vermont.
Surgical procedures
For acute infusion studies, rats were
Chronic variate stress induces BNST oval nucleus PACAP expression
Among limbic structures, we have shown previously that repeated variate stress selectively increases dorsolateral BNST PACAP transcript expression (Hammack et al., 2009). The BNST is a complex structure that can be parceled into more than 30 subdivisions based on neurotransmitter/neuropeptide distribution, cytoarchitecture and afferent/efferent projections (Dong et al., 2001). As our previous transcript analyses by quantitative polymerase chain reaction (QPCR) could not discriminate the BNST
Discussion
We have shown recently that BNST PACAP signaling elicits stress-related responses. Chronic variate stress selectively increased PACAP and PAC1 receptor transcript expression in the dorsolateral BNST, and acute BNST PACAP38 infusions produced anxiogenic and anorexic responses analogous to those described for CRH (Hammack et al., 2009). Like CRH, PACAP is highly expressed in the hypothalamus and associated limbic circuits (Ju et al., 1989, Piggins et al., 1996, Day et al., 1999, Hannibal, 2002),
Role of funding sources
This work was supported by grants NIMH MH-97988 and MH-80935, NCRR P30RR032135 and NIGMS P30GM103498 from the National Institutes of Health and intramural funds from the University of Vermont. These institutions had no further role in the study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.
Conflicts of interest statement
None declared.
Acknowledgments
This work was supported by grants NIMH MH-97988 and MH-80935 from the National Institutes of Health and intramural funds from the University of Vermont. The use of the Neuroscience Core Facility supported by National Institute of Health NCRR P30RR032135 and NIGMS P30GM103498 is also gratefully acknowledged. We thank Kristin C. Schutz, Elijah LaChance, Rachel A. Sugarman and Margaret Koch-Schellenberg for excellent technical assistance.
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Current address: Department of Biochemistry, University of Washington, Health Sciences Ctr, Seattle, WA 98195, USA.