Biology of Reproduction, Vol 22, 927-934, Copyright © 1980 by Society for the Study of Reproduction

Effects of Corticomedial Amygdala Lesions or Olfactory Bulbectomy on LH Responses to Ovarian Steroids in the Female Rat

¹ Department of Psychology, University of California, Los Angeles, California 90024
² Department of Anatomy and Brain Research Institute, University of California, Los Angeles, California 90024

Adult female rats received bilateral corticomedial amygdala lesions, olfactory bulbectomy, or sham surgery. Following ovariectomy, luteinizing hormone (LH) responses to estradiol benzoate (EB) and progesterone (P) treatment were assessed. With 4 weeks separating each injection, each rat received at 1200 h each of 3 doses of EB: 0.7, 3.5 and 7.0 µg/100 g BW. Oil or 2 mg of P was administered 72 h after EB treatment. Jugular blood samples (0.5 ml) were taken 5 times for each dose of EB: 43 h prior to, and 5, 29, 53 and 77 h after EB administration. Five hours after the 0.7 µg/100 g BW dose of EB, and at both 5 and 29 h after the 3.5 µg/100 g BW dose of EB, plasma LH levels were depressed in all groups, but subsequently recovered to near pre-EB levels. Plasma LH levels were also depressed 5 and 29 h after the 7 µg EB/100 g BW dose in all groups, but by 53 h LH levels were significantly elevated beyond pre-EB levels when analyzed without regard to surgical treatment. However, the rats with corticomedial amygdala lesions did not respond to this high dose of EB; plasma LH titers 53 h post-EB were only equivalent to pre-EB levels. Regardless of surgical treatment, all rats given P 72 h after EB treatment responded with elevated LH levels relative to LH levels in oil-treated controls. As the dose of EB increased from 0.7 to 7 µg/100 g BW, the magnitude of the P-induced rise in LH increased. Thus, although olfactory bulbectomy was without effect, corticomedial amygdala lesions attenuated LH elevations induced by EB but not those induced by EB plus P treatment. The corticomedial amygdala may play a role specifically in the positive feedback action of EB.