Central Amygdala PACAP in the Behavioral Stress Response

Abstract

Anxiety‐related disorders are the most common forms of mental disorders; characterized by feelings of excessive worry in the absence of specific external stimuli, they are accompanied by physical, affective and behavioral symptoms.Pituitary adenylate cyclase‐activating polypeptide (PACAP) is a 38‐amino acid peptide located in the hypothalamus and in various extra‐hypothalamic regions including the central nucleus of the amygdala (CeA). PACAP and PAC1 receptor (PAC1R) have been proposed to play a key role in mediating the behavioral and endocrine responses to stress; however, few studies have examined the involvement of the extrahypothalamic PACAP system in the modulation of stress. Our aim was to elucidate the role of the PACAP/PAC1 system of the CeA in the context of anxiety.We first assessed the effects of PACAP microinfused into the CeA of male rats in the elevated plus maze (EPM) and the acoustic startle response (ASR), behavioral tests sensitive to states of anxiety and fear. PACAP was also given into the basolateral amygdala (BlA) as a control brain region. We then used restraint stress to determine whether the endogenous PACAP‐PAC1 system is recruited by acute stressors.Infusion of PACAP into the CeA significantly reduced percent open arm time in the EPM and increased plasma corticosterone levels, while BlA microinfusion had no effect. Infusion of PACAP into the CeA also increased acoustic startle reactivity. Finally, we observed that an acute, 1h exposure to restraint produced a rapid elevation of PACAP and PAC1R expression in the CeA, but not the BlA.These data prove an anxiogenic role for the PACAP/PAC1 system of the CeA and suggest that hyperactivity of this system may underlie the anxiogenic effects of stress.