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

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Abstract
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 enhanced mating behavior, medial preoptic area (MPOA) infusions of luteinizing hormone (LH) caused significant depressions in the lordotic response; LH infusions into the arcuate ventromedial area (ARC-VM) had no significant effect. Follicle-stimulating hormone (FSH) infusions into either area did not alter the behavioral response. In the 2nd experiment, in which OVX rats were primed with higher doses of estrone to maintain high preinfusion receptivity, MPOA or ARC-VM infusions of either LH or TRH depressed lordotic behavior significantly; neither LRH nor FSH inhibited the behavioral response. A 3rd 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; 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.