Photoperiod-dependent expression of ‘Cocaine- and amphetamine-regulated transcript peptide’ and ‘Neuropeptide Y’ in the brain of anuran Minervarya syhadrensis

Anurans exhibit diurnal behavioral patterns; however, the expression of neuropeptides that modulate these activities remains unexplored. This study investigates day-night expression patterns of Cocaine- and Amphetamine-Regulated Transcript Peptide (CARTp) and Neuropeptide Y (NPY) in the brain of nocturnal frog, Minervarya syhadrensis. Frogs were sacrificed at different timepoints (1) under normal day-night conditions (2) after exposure to 24 h darkness and (3) 24 h light. Brain tissues, including the olfactory system, were collected for immunohistochemical analysis. Photoperiod-dependent alterations in expression of CART and NPY were observed in various brain regions. According to cosine analysis, the oscillation was seen only in the olfactory epithelium (OE) with maxima at 11:00. In anteroventral tegmentum (AV), CARTp and NPY expression were highest at midnight. In few brain regions, NPY or CARTp oscillations were observed. NPY oscillations were seen in preoptic area (POA), with a peak at noon, and in suprachiasmatic nucleus (SCN), anterior ventral hypothalamus (AvHy), and nucleus isthmus (NI) highest expression was at midnight. In Edinger-Westphal nucleus (EW) and posterior ventral hypothalamus (PvHy) CARTp upregulation was observed at midnight. CARTp fluctuated in OE, PvHy, and EW on light exposure, while changes in NPY expression were seen in OE, POA and SCN. Photoperiod-dependent fluctuations in both peptides were noted in OE and AV. While on exposure to darkness, CARTp expression decreased in AV, PvHy, and EW, and NPY expression was affected in AV, POA, SCN, AvHy, and NI. These results suggest neuropeptides in anurans exhibit photoperiod-dependent differential expression, potentially regulating physiological functions and behavioral patterns.