Modulation of sex steroid receptors by neurotransmitters: Relevant techniques

Control of fertility by metabolic cues

In female mammals, reproduction is extremely sensitive to the availability of oxidizable metabolic fuels. When food intake is limited or when an inordinate fraction of the available energy is diverted to other uses such as exercise or fattening, reproductive attempts are suspended in favor of processes necessary for individual survival. Both reproductive physiology and sexual behaviors are influenced by food availability. Nutritional effects on reproductive physiology are mediated by changes in the activity of gonadotropin-releasing hormone (GnRH) neurons in the forebrain, whereas the suppression of sexual behaviors appears to be due, at least in part, to decreases in estrogen receptor in the ventromedial hypothalamus. Work using pharmacological inhibitors of glucose and fatty acid oxidation indicates that reproductive physiology and behavior respond to short-term (minute-to-minute or hour-to-hour) changes in metabolic fuel oxidation, rather than to any aspect of body size or composition (e.g., body fat content or fat-to-lean ratio). These metabolic cues seem to be detected in the viscera (most likely in the liver) and in the caudal hindbrain (probably in the area postrema). This metabolic information is then transmitted to the GnRH-secreting or estradiol-binding effector neurons in the forebrain. There is no evidence to date for direct detection of metabolic cues by these forebrain effector neurons. This metabolic fuels hypothesis is consistent with a large body of evidence and seems to account for the infertility that is seen in a number of situations, including famine, eating disorders, excessive exercise, cold exposure, lactation, some types of obesity, and poorly controlled diabetes mellitus.

Hypothalamic ovarian steroid hormone-sensitive neurons involved in female sexual behavior

Estradiol and progesterone regulate sexual behaviors in guinea pigs and rats, at least in part, through interaction with intracellular steroid hormone receptors. In the present review of work from the laboratory of the authors, we summarize recent work which has focused on one of the sites of hormone action in female guinea pigs--the ventrolateral hypothalamus. We summarize results of earlier experiments in which the regulation of steroid hormone receptors in this area was assessed after hormonal treatments with predictable effects on female sexual behavior. We then review the results of recent tract-tracing experiments in which we have examined the projections from the steroid receptor-immunoreactive neurons in this region, as well as the afferent projections from other neuroanatomical areas, including neurons which themselves contain estrogen receptors. We also present studies on the afferent input into these neurons by noradrenergic neurons and discuss the possibility that noradrenergic input influences steroid hormone sensitivity in these neurons. Finally, we discuss the results of experiments in which Fos-immunocytochemistry was used in rats to identify the neurons responding to a particular tactile stimulus associated with female reproduction, i.e., vaginal-cervical stimulation. These experiments further define a complex neuroanatomical system, in which many of the elements are estradiol or progesterone-responsive, that is involved in the hormonal regulation of sexual behavior in guinea pigs and rats.