Online

King, S. Bradley

Psychology

2016

MA

Chronic or repeated exposure to stressful stimuli can result in several maladaptive consequences, including increased anxiety-like behaviors and altered peptide expression in brain structures involved in emotion. Among these structures, the bed nucleus of the stria terminalis (BNST) has been implicated in emotional behaviors as well as regulation of hypothalamic-pituitary-adrenal (HPA) axis activity. In rodents, chronic variate stress (CVS) has been shown to increase BNST pituitary adenylate cyclase activating polypeptide (PACAP) and its cognate PAC1 receptor transcript, and BNST PACAP signaling may mediate the maladaptive changes associated with chronic stress. In order to determine whether chronic stress would potentiate the behavioral and/or endocrine response to subthreshold BNST PACAP infusion, rats were exposed to a 7 day CVS paradigm previously shown to upregulate BNST PAC1 receptor transcripts; control rats were not stressed. Twenty-four hours following the last stressor, stressed and control rats were bilaterally infused into the BNST with 0.5 µg PACAP. Startle response to intra-BNST PACAP infusion was assessed post-infusion in Experiment 1. In Experiments 2 and 3, blood was sampled via a tail nick 30 min following PACAP infusion to assess the corticosterone response to PACAP following CVS. We found an increase in startle amplitude and an increase in plasma corticosterone levels 30 minutes following BNST PACAP infusion only in rats that had been previously exposed to CVS. These results were likely mediated via PAC1 receptors, as equimolar infusion of the VPAC1/2 receptor ligand vasoactive intestinal polypeptide (VIP) had no effect on plasma corticosterone levels. These results suggest that repeated exposure to stressors sensitizes the neural circuits underlying the behavioral and endocrine responses to BNST PACAP infusion and BNST PACAP/PAC1 receptor signaling likely plays a critical role in mediating stress responses.