CAUDAL BRAIN-STEM PLAYS A ROLE IN METABOLIC CONTROL OF ESTROUS CYCLES IN SYRIAN-HAMSTERS

In Syrian hamsters, a critical factor necessary for the occurrence of normal estrous cycles appears to be the cellular availability of oxidizable glucose. For example, estrous cycles are inhibited by food deprivation or treatment with 2-deoxy-D-glucose (2DG), a drug that inhibits cellular glucose utilization. Several lines of evidence suggest that these effects require the participation of neurons in part of the caudal brain stem, the area postrema (AP) and adjacent, reciprocally-innervated nucleus of the solitary tract (NTS). This study was designed to examine the role of the AP in 2DG-induced anestrus. Hamsters received either aspiration lesions directed at the AP or sham operations. Between 12 and 16 days after surgery, both sham-operated and lesioned hamsters showed two consecutive 4-day estrous cycles, as measured by estrous behavior and vaginal discharge. Subsequently, both groups were treated with doses of 2DG known to inhibit the estrous cycle (1750 mg/kg every 6 h on days 1 and 2 of the cycle). Hamsters were tested for measures of estrous cyclicity daily after treatment. Only 9% of the sham-operated hamsters showed estrous cycles within 5 days after the start of 2DG treatment. In contrast, all of the hamsters with confirmed lesions of the AP showed estrous cycles within 5 days of the start of 2DG treatment. Histology showed that most lesions removed the AP plus part of the medial NTS, while two lesions removed part of the AP only. These results are consistent with the idea that the AP, and possibly the NTS, play a role in the effects of decreased glucose availability on estrous cycles in Syrian hamsters.