Paraventricular nucleus lesions exaggerate dietary obesity but block photoperiod-induced weight gains and suspension of estrous cyclicity in Syrian hamsters.

Lesions of the paraventricular nucleus (PVN) of the hypothalamus block short photoperiod-induced testicular regression in Syrian hamsters. We examined the effects of PVN or sham lesions on the short photoperiod-induced increases in body weight and adiposity in female Syrian hamsters. PVN lesions did not affect body weight when hamsters were housed in a long photoperiod (LD, 16:8) and fed Purina laboratory rodent chow (No. 5001). However, when fed a high-fat diet both groups gained weight, and the hamsters with PVN lesions gained approximately twice as much as the sham-operated controls. When the hamsters were exposed to a short photoperiod (LD, 8:16), only the hamsters with sham lesions displayed the typical increase in body weight. No further increase in body weight or parametrial fat pad weight was seen when the hamsters with PVN lesions were exposed to the short photoperiod. The lack of a short photoperiod-induced increase in body weight gain in hamsters with PVN lesions seems unlikely to be due to a "ceiling effect" on body weight gain because we have routinely observed neurally intact, melatonin-treated female Syrian hamsters with body weight in excess of 250 g. Finally, the short photoperiod interrupted estrous cyclicity in sham-lesioned hamsters but not in those with PVN lesions. Thus, PVN lesions exaggerate dietary obesity but prevent short photoperiod-induced weight gains and vaginal acyclicity in female Syrian hamsters.