Increased estrogen receptor binding in amygdala correlates with facilitation of feminine sexual behavior induced by olfactory bulbectomy.

In this experiment we tested the hypothesis that the potentiation of feminine sexual behavior following olfactory bulb removal in female rats would be associated with increased ovarian steroid receptor binding in brain. Ovariectomized adult female rats underwent either bilateral olfactory bulb removal (BOB) or a sham operation and were exposed to 100% estradiol (E2) in silastic capsules for 4 or 6 h. Following behavior testing, either cell nuclear estrogen receptor levels were measured in amygdala, hypothalamus, preoptic area and pituitary, or cytosol progestin receptors levels were determined in cortex, preoptic area and hypothalamus. After 6 h E2 exposure, BOB females showed increasing lordosis responding with increasing progesterone (P) doses, at levels significantly higher than those of sham-operated rats. After 4 h E2 exposure bulbectomized rats showed both a facilitation of lordosis and elevated estrogen receptor levels in amygdala. Sham-operates showed neither response to the 4 h E2 stimulus. For both BOB and sham groups, progestin receptors were induced after 6 h E2 exposure, but were uninduced after 4 h E2 exposure. Additional rats were exposed to 5% E2 for 24 or 48 h, followed by P. Lordosis was potentiated in BOB rats at 24 h; sham-operates showed high levels of lordosis only after 48 h of 5% E2 exposure. Proceptivity was enhanced in BOB rats after both 24 and 48 h of 5% E2 exposure. In contrast, proceptivity was rarely observed in sham-operates, or in either group after 4 or 6 h E2 exposure. We propose that increased estrogen receptor binding in the amygdala may provide a biochemical basis for the increased estrogen sensitivity found in olfactory bulbectomized female rats.