A daily rhythm in the behavioural sensitivity of the female rat to oestradiol.
Ovariectomized rats were implanted with oestradiol-filled elastomer capsules which were removed at various times after implantation. Sexual receptivity was tested after implantation of a progesterone-filled elastomer capsule 42 h after the onset of treatment with oestradiol. Exposure to oestradiol for about 32 h was required for induction of receptivity. Intact rats with regular 4 day oestrous cycles, and exposed to oestradiol-filled elastomer capsules for 6 h, showed sexual receptivity 24 h after the onset of oestradiol treatment. The behavioural effects of oestradiol in both ovariectomized and intact rats depended on when during the light-darkness (LD) cycle stimulation with oestradiol occurred; maximum effects were seen only if the oestradiol capsules were implanted at 16.00 h (4 h after lights off in the 12 h L : 12 h D cycle). The behavioural effect of progesterone implants, however, did not depend on the phase of the LD cycle. The LD-dependent rhythm in oestradiol sensitivity was eliminated by lesions in the suprachiasmatic nuclei of the hypothalamus.
D000818:Animals; D002369:Castration; D002940:Circadian Rhythm; D004343:Drug Implants; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D051381:Rats; D012726:Sexual Behavior, Animal / Q000187:drug effects*; D013997:Time Factors
D004343:Drug Implants; D004958:Estradiol