Action of luteinizing hormone-releasing factor (lrf) in the initiation of lordosis behavior in the estrone-primed ovariectomized female rat
Moss, R.L.; McCann, S.M.
Neuroendocrinology 17(4): 309-318
1975
ISSN/ISBN: 0028-3835 PMID: 806824 DOI: 10.1159/000122369Document Number: 506361
The action of luteinizing hormone-releasing factor (LRF) in the induction of lordosis behavior in ovariectomized rats (OVX) is described. 139 sexually experienced Sprague-Dawley female rats were ovariectomized at 80-100 days of age and behavioral testing was done 2-3 weeks later. At 9-10 months after ovariectomy adrenals were removed from 16 rats. These animals were given free access to isotonic NaCl solution. Female sexual behavior was expressed as the ratio of the number of lordosis responses to the number of mounts by the male rat. Ovarian hormones (estrone, E; theelin in oil 1 mg/ml) and progesterone (P; lipolutin in oil 50 mg/ml) were used. The pituitary hormones luteinizing hormone (LH) and follicle stimulating hormone (FSH) and releasing factors LRF and TRF were dissolved in physiological saline. All hormones were injected sc. In Experiment 1 to determine the specificity of LRF-induced lordosis responses 16 rats were tested under 8 conditions. Each rat was pretreated with either .25 ng E or 500 ng LRF. Tests for sexual receptivity were conducted 50 hours after E injections. After repeating these tests, adrenal removals (ADX) were done. After 5 days, the E-primed OVX-ADX animals were tested for sexual receptivity 50 hours following an injection of LRF (48 hours after E). In Experiment 2, to determine the time course for the initial appearance of lordosis and the total period of receptivity induced, 24 E-primed OVX rats were tested throughout and 8-hour period following the LRF injections. Each animal was primed with E at zero hour and given LRF at 48 hours. 49 hours after E injections tests were begun and continued at hourly intervals. This sequence was repeated at least 4 times. In Experiment 3, to determine the dose of LRF needed, 99 E-primed OVX rats were injected with doses ranging from 50 to 4000 ng LRF at 48 hours after E injections. Sexual receptivity tests were done 2 hours later. Results showed that sexual behavior in the female rat is dependent on the ovarian hormones estrogen and progesterone. Synthetic LRF exerted a facilitatory effect on the lordosis response. The LRF-facilitatory behavior was shown to be specific but LRF alone did not lead to mating behavior in OVX females. E-priming was a necessary condition to obtain a hgih level of copulatory behavior. The LRF-induced lordosis pattern was independent of adrenal progesterone and apparently not mediated by pituitary hormones. The time lag between LFR injection and induction of sexual behavior suggests that this is not a simple monosynaptic mechanism but may involve intermediate steps such as the activation of protein synthesis in the postsynaptic neurons of the mating center.