Roles of gonadotropins and releasing hormones in hypothalamic control of lordotic behavior in ovariectomized, estrogen-primed rats.

Intrahypothalamic effects of gonadotropins (luteinizing hormone and follicle-stimulating hormone), thyrotropin-releasing hormone (TRH), and luteinizing-hormone-releasing hormone (LRH) on lordotic behavior were evaluated in ovariectomized (OVX) rats maintained at different receptivity levels. Under conditions of low receptivity in which LRH has been shown to enchance mating behavior, medial preoptic area (MPOA) infusions of luteinizing hormone (LH) caused significant depressions in the lordotic response, whereas LH infusions into the arcuate ventromedial area (ARC-VM) had no sigificant effect. Follicle-stimulating hormone (FSH) infusions into either area did not alter the behavioral response. In the second experiment, in which OVX rats were primed with higher doses of estrone to maintain high ptrinfusion receptivity, MPOA or ARC-VM infusions of either LH or TRH were shown to depress lordotic behavior significantly, whereas neither LRH nor FSH was observed to inhibit the behavioral response. A third experiment evaluated the effects of LH, FSH, and TRH on LRH-facilitated mating behavior. Infusions of LRH into either the MPOA or the ARC-VM significantly enhanced mating behavior, whereas the addition of either TRH or LH to the LRH infusates abolished this response. The addition of FSH to LRH infusates neither enhanced nor depressed the behavioral response to MPOA or ARC-VM infusions of LRH. The antagonistic effects of LH and TRH on LRH-facilitated mating behavior were correlated with previous observations of antagonistic effects on hypothalamic unit activity and monoamine metabolism. The antagonistic interrelation between LRH and LH may represent a mechanism for the activation and coordination of sexual receptivity with ovulation.