Effects of LHRH on avoidance conditioning in normally cycling and ovariectomized female rats.
Several studies have demonstrated that the peptide LHRH can modify behavior in the male rat. Peripheral and intracerebral infusions of LHRH impair the acquisition of conditioned avoidance responses (CARs) and increase some spontaneous motor behaviors, such as head shaking and grooming. The present study was undertaken to detect the effects of LHRH on the acquisition of CARs and spontaneous motility in normally cycling and ovariectomized (OVX) Sprague-Dawley female rats. Normally cycling females were separated in four groups, according to the stage of the estrous cycle. Ovariectomized female rats were pretreated, 48 h before the experiment, with estradiol benzoate (10 microg/kg) or corn oil. LHRH (6.25, 25, or 50 microg/kg) was subcutaneously injected and the behavioral tests began 1 h after. Low doses of LHRH stimulated the acquisition of CARs during proestrus, estrus, and metestrus, whereas higher doses impaired conditioning in all the four stages of the cycle. High doses of LHRH impaired acquisition in OVX rats treated with oil and potentiated the depressant effects of EB on this behavior. The effects of LHRH on spontaneous motor activity were either stimulatory or inhibitory, according to the hormonal status and the dose administered. High doses of LHRH decreased motor responses in the diestrous rat. All the doses of LHRH increased the number of headshakes during proestrus, estrus, and metestrus, while the other motor responses were scarcely or not affected by LHRH in these stages. In OVX rats LHRH increased rearing, head shaking, and grooming behavior. These results support a role of LHRH in the modulation of conditioned and spontaneous behavior. They could provide an explanation to the behavioral changes observed across the estrous cycle and those observed after EB priming in OVX rats.
Instituto de Ciencias Biomédicas, Programa de Farmacología Molecular y Clínica, Facultad de Medicina, Universidad de Chile, Santiago.
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Díaz-Véliz
D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D003213:Conditioning, Psychological / Q000187:drug effects*; D004958:Estradiol / Q000494:pharmacology; D004971:Estrus / Q000187:drug effects; D005260:Female; D018757:GABA Modulators / Q000494:pharmacology*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D009479:Neuropeptides / Q000494:pharmacology; D010052:Ovariectomy; D051381:Rats; D017207:Rats, Sprague-Dawley; D012737:Sex Factors
D018757:GABA Modulators; D009479:Neuropeptides; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol