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

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Intrahypothalamic effects of gonadotropins (luteinizing hormone and follicle-stimulating hormone, LH and FSH, respectively), thyrotropin-releasing hormone (TRH), and luteinizing-hormone-releasing hormone (LRH) on lordotic behavior were evaluated in 63 Wistar ovariectomized (OVX) rats maintained at different receptivity levels. Under low receptivity, in which LRH has been shown to enhance mating behavior, medial preoptic area (MPOA) infusions of LH caused significant depressions in the lordotic response, whereas LH infusions into arcuate ventromedial area (ARC-VM) had no significant effect. FSH infusions into either area did not alter the response. In Exp II, in which OVX Ss 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, whereas neither LRH nor FSH inhibited the response. Exp III evaluated the effects of LH, FSH, and TRH on LRH-facilitated mating behavior with 50 Sprague-Dawley male rats. Infusions of LRH into either MPOA or ARC-VM significantly enhanced mating behavior, whereas addition of TRH or LH to the LRH infusates abolished this response. The antagonistic effects of LH and TRH on LRH-facilitated mating 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 activation and coordination of sexual receptivity with ovulation. (55 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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