Effects of cold exposure on estrous behavior and neural estrogen receptor in Syrian hamsters.

Two experiments examined the effects of 72-h exposure to reduced environmental temperature (5 degrees C) on steroid-induced estrous behavior and neural estrogen-receptor immunoreactivity (ERIR) in ovariectomized Syrian hamsters. Cold exposure significantly inhibited sexual receptivity induced by sequential injections of estradiol benzoate (2.5 microg) and progesterone (500 microg), but only if the animals were not permitted to overeat (limited to 110% of ad lib intake at 22 degrees C). The suppression of sexual receptivity was accompanied by decreases in the number of detectable ERIR cells in the ventromedial hypothalamus (VMH) and by increases in the number of ERIR cells in the medial preoptic area (mPOA). The cold-induced decreases in estrous behavior and in VMH ERIR cells were prevented by lesions of the area postrema (AP), but AP lesions did not prevent the increases in mPOA ERIR cells. Thus, cold exposure mimics the effects of treatment with metabolic inhibitors, experimental diabetes, food deprivation, and insulin-induced fattening on these endpoints. These findings are consistent with the hypothesis that dwelling in the cold affects reproduction indirectly via its actions on metabolic fuel availability, rather than by acting directly on neuroendocrine processes.

Estrogen receptors are essential for female sexual receptivity.

One of the most important, robust and evolutionarily conserved functions for neural estrogen receptor (ER) is as a mediator of female sexual behavior. Using homozygotic ER knockout (ERKO) mice we tested the hypothesis that ER controls female receptivity. Females with either two normal copies of the ER gene (wild-types), or an insertational disruption (knockouts) of the ER were ovariectomized. Each female was treated with 17 beta-estradiol (EB) alone, and with EB in combination with progesterone, prior to tests for behavioral receptivity. Under both hormonal conditions female ERKO mice did not display sexual receptivity whereas wild-type litter-mates were receptive to males. Male behavior indicated that females of both genotypes were equally attractive. Brain tissues were examined with immunocytochemical methods showed that ERKOs had greatly reduced levels of ER immunoreactivity in hypothalamus. In sum, the data show that ER is required for the display of sexual receptivity, but is not essential for female attractivity.