MANIPULATIONS OF METABOLIC FUEL AVAILABILITY ALTER ESTROUS BEHAVIOR AND NEURAL ESTROGEN-RECEPTOR IMMUNOREACTIVITY IN SYRIAN-HAMSTERS

Decreases in metabolic fuel utilization caused by food deprivation, di abetes, or treatment with metabolic inhibitors have been shown to supp ress steroid-induced estrous behavior in ovariectomized Syrian hamster s. These same manipulations also caused a decrease in the number of de tectable estrogen-receptor immunoreactive (ERIR) cells in the ventrome dial hypothalamus (VMH) and the adjacent area lateral to it (VLH) in o variectomized hamsters. Forty-eight hours of food deprivation or treat ment with pharmacological blockers of glycolysis (2-deoxy-D-glucose) a nd fatty acid oxidation (methyl palmoxirate) decreased the number of d etectable ERIR cells in the VMH/VLH. However, neither inhibitor given alone was sufficient to affect the number of detectable ERIR cells in the VMH/VLH, even when given in much higher doses. Therefore, the numb er of ERIR cells in the VMH/VLH, like steroid-induced estrous behavior , responds only to a combination of glucoprivation and lipoprivation a nd not to either alone. The effects of metabolic fuel restriction are not due to a general suppression of neural ERIR, because food deprivat ion or treatment with 2-deoxy-D-glucose and methyl palmoxirate actuall y increased the number of detectable ERIR cells in the medial preoptic area (mPOA) and had no effect in the nucleus of the solitary tract. L esions destroying the area postrema (AP) prevented the decrease in ERI R cells in the VMH/VLH and the inhibition of estrous behavior caused b y fuel restriction. However, AP lesions did not alter the effects of m etabolic inhibitors on ERIR in the mPOA. On the other hand, subdiaphra gmatic vagotomy abolished the effects of metabolic inhibitors on mPOA ERIR, but did not affect either lordosis or VMH/VLH ERIR. These result s suggest that the suppression of estrous behavior induced by metaboli c fuel restriction is at least in part due to a decrease in the number of ERIR neurons in the VMH/VLH. In addition, the estrogen-sensitive n eurons in the VMH/VLH and mPOA receive metabolic cues via different ne ural pathways. The AP, but not vagus nerves, is required for ERIR neur ons in the VMH/VLH to detect fuel availability; the vagus nerves, but not the AP, are necessary for estrogen-binding neurons in the mPOA to detect visceral information.