Intrahypothalamic pituitary adenylate cyclase-activating polypeptide regulates energy balance via site-specific actions on feeding and metabolism

Abstract

Numerous studies have demonstrated that both the hypothalamic paraventricular nuclei (PVN) and ventromedial nuclei (VMN) regulate energy homeostasis through behavioral and metabolic mechanisms. Receptors for pituitary adenylate cyclase-activating polypeptide (PACAP) are abundantly expressed in these nuclei, suggesting PACAP may be critical for the regulation of feeding behavior and body weight. To characterize the unique behavioral and physiological responses attributed to select hypothalamic cell groups, PACAP was site-specifically injected into the PVN or VMN. Overall food intake was significantly reduced by PACAP at both sites; however, meal pattern analysis revealed that only injections into the PVN produced significant reductions in meal size, duration, and total time spent eating. PACAP-mediated hypophagia in both the PVN and VMN was abolished by PAC1R antagonism, whereas pretreatment with a VPACR antagonist had no effect. PACAP injections into the VMN produced unique changes in metabolic parameters, including significant increases in core body temperature and spontaneous locomotor activity that was PAC1R dependent whereas, PVN injections of PACAP had no effect. Finally, PACAP-containing afferents were identified using the neuronal tracer cholera toxin subunit B (CTB) injected unilaterally into the PVN or VMN. CTB signal from PVN injections was colocalized with PACAP mRNA in the medial anterior bed nucleus of the stria terminalis, VMN, and lateral parabrachial nucleus (LPB), whereas CTB signal from VMN injections was highly colocalized with PACAP mRNA in the medial amygdala and LPB. These brain regions are known to influence energy homeostasis perhaps, in part, through PACAP projections to the PVN and VMN.