Abstract
BACKGROUND AND AIM: Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide widely implicated in stress responses, appetite regulation, and emotional behavior. While PACAP has been linked to stress-induced appetite suppression, its role in circadian feeding and stress-related hyperphagia remains poorly defined. This study aimed to clarify the contribution of PACAP to circadian feeding behavior, chronic stress-induced hyperphagia, and emotional regulation in mice. MATERIALS AND METHODS: Experiments were conducted using PACAP knockout (KO) and wild-type (WT) CD-1 mice. Acute and chronic restraint stress paradigms were applied, and food intake, body weight, and behavioral assays were recorded. Viral-mediated PACAP overexpression in the ventromedial hypothalamus (VMH) was performed using adeno-associated vectors. Emotional regulation was assessed through forced swim and tail suspension tests (TSTs). PAC1 receptor expression was quantified by reverse transcription and quantitative polymerase chain reaction. RESULTS: PACAP overexpression in the VMH significantly increased nocturnal feeding, demonstrating a circadian-specific effect on appetite regulation. Chronic restraint stress enhanced food intake in both PACAP KO and WT mice, whereas acute stress showed no effect, indicating that chronic stress-induced hyperphagia occurs independently of PACAP signaling. Behaviorally, PACAP-overexpressing mice exhibited reduced immobility in forced swim and TSTs, consistent with enhanced stress resilience and antidepressant-like effects. Importantly, PAC1 receptor expression remained stable throughout the diurnal cycle, suggesting that PACAP's modulatory effects are driven by neuropeptide availability rather than receptor fluctuations. CONCLUSION: This study identifies PACAP in the VMH as a key modulator of circadian feeding and emotional behavior, while demonstrating its non-essential role in chronic stress-induced hyperphagia. The findings suggest that PACAP selectively integrates circadian and emotional signals to regulate feeding, independent of compensatory neuropeptide systems that mediate stress hyperphagia. These insights advance the understanding of neuropeptide regulation of energy balance and mood, with implications for stress-related eating disorders and anxiety.