Seasonal regulation of cocaine- and amphetamine-regulated transcript in the arcuate nucleus of Djungarian hamster (Phodopus sungorus)

The hypothalamic neuropeptidergic system involved in the photoperiodic control of energy metabolism in seasonal mammals, is poorly understood. In the present study we examined whether distribution and number of the hypothalamic neuronal cell populations containing cocaine- and amphetamine-regulated transcript (CART) are influenced by different photoperiod and ambient temperature, or by food status in the Djungarian hamster (Phodopus sungorus). Hamsters bred and raised in long day photoperiod at room temperature (16 h light/8 h dark at 23 °C; LD) were transferred to short day photoperiod and moderate cold (8 h light/16 h dark at 16 °C; SD). After a 4 weeks acclimation period, uterus and body weight were decreased in SD as compared to controls maintained in LD. The number of CART-immunoreactive cells within the arcuate nucleus (ARC) was significantly higher in SD hamsters compared to LD control. This increase was restricted to the rostro to mid portion of the ARC, specifically in the hypothalamic retrochiasmatic area close to the rostral ARC and in the hypothalamic region lateral to the ARC and ventral to the ventromedial hypothalamic nuclei. In similar hypothalamic regions, food deprivation for 48 h significantly decreased the number of CART-immunoreactive cells in SD hamsters. Shortening of photoperiod combined with lowering of ambient temperature and food deprivation had no effect on the number of CART-immunoreactive cells in the lateral hypothalamic area. These findings suggest that photoperiod and ambient temperature influence energy metabolism potentially by alterations of the CART neuronal system in the rostral portion of the ARC in Djungarian hamsters.