Estrogen receptor immunostaining in the preoptic area and medial basal hypothalamus of estradiol benzoate- and prazosin-treated female guinea-pigs

Is calcitonin gene-related peptide a modulator of menopausal vasomotor symptoms?

PURPOSE

Calcitonin gene-related peptide (CGRP) is a neuropeptide widely distributed in the central and peripheral nervous systems, which is known as a potent vasodilator. Postmenopausal women who experience hot flushes have high levels of plasma CGRP, suggesting its involvement in menopausal vasomotor symptoms.

METHODS

In this review, we describe the biochemical aspects of CGRP and its effects associated with deficiencies of sexual hormones on skin temperature, vasodilatation, and sweating as well as the possible peripheral and central mechanisms involved in these events.

RESULTS

Several studies have shown that the effects of CGRP on increasing skin temperature and inducing vasodilatation are potentiated by a deficiency of sex hormones, a common condition of postmenopausal women. Additionally, the medial preoptic area of the hypothalamus, involved in thermoregulation, contains over 25-fold more CGRP-immunoreactive cells in female rodents compared with male rodents, reinforcing the role of female sex hormones on the action of CGRP. Some studies suggest that ovarian hormone deficiency decreases circulating endogenous CGRP, inducing an upregulation of CGRP receptors. Consequently, the high CGRP receptor density, especially in blood vessels, amplifies the stimulatory effects of this neuropeptide to raise skin temperature in postmenopausal women during hot flushes.

CONCLUSIONS

The duration of the perception of each hot flush in a woman is brief, while local reddening after intradermal administration of α-CGRP persists for 1 to 6 h. This contrast remains unclear.

Localization of progesterone receptor in brain and pituitary of the ring dove: influence of breeding cycle and estrogen

An immunocytochemical method was used in male and female ring doves (Streptopelia risoria) to localize progesterone receptor immunoreactivity (PR-ir) in the brain and anterior pituitary gland in nonbreeding, incubating, brooding, and estrogen (E2)-treated nonbreeding birds. Progesterone receptor was found in four regions of the brain in males and females: the preoptic area (POA), nucleus preopticus paraventricularis magnocellularis (PPM), nucleus hypothalami lateralis (PLH), and the tuberal region (TR). Quantitative analysis demonstrated that the density of cell nuclei containing PR-ir in the POA, PPM, and PLH in brooding birds was significantly higher than in E2-treated doves or in birds at other stages of the reproductive cycle. The density of PR-containing cell nuclei in the TR of male ring doves was significantly higher on day 1 of incubation than in nonincubating males. In brooding birds, there was a significant decrease in PR-ir in the TR, particularly in the ventral region where nuclei containing PR-ir disappeared. In the anterior pituitary gland the density of cell nuclei containing PR-ir was higher in females than in males at the onset of incubation. E2 treatment resulted in an increase in the density of PR-containing cell nuclei in both males and females. Brooding females had a lower concentration of PR-containing cell nuclei than did females at other stages of the breeding cycle. It is suggested that progesterone receptor in the POA mediates the expression of incubation behavior while progesterone receptor in the TR is involved in the control of neuroendocrine function. The source of estrogen which increases PR appears to be of central nervous origin in the male and may be predominantly peripheral in the female.

Estrogen receptor immunoreactivity in specific brain areas of the prairie vole (Microtus ochrogaster) is altered by sexual receptivity and genetic sex

The prairie vole is a small rodent with an unusual reproductive strategy. A sexually naive female vole requires male contact to initiate the maturation of her reproductive functions. Contact with an unfamiliar adult male vole increases blood estrogen levels, reproductive tissue weights, and brain nuclear estrogen receptor binding levels of female voles. What is not known is: 1) What is the precise distribution of estrogen receptor containing neurons in the prairie vole brain? 2) Does male induced sexual receptivity alter the distribution or number of estrogen receptors in specific brain areas of the female vole? 3) Do male and female voles differ in the distribution or number of estrogen receptor containing neurons? We compared sexually receptive-male-exposed females, sexually naive females, and sexually naive males, for the presence of estrogen receptor immunoreactive (ER-IR) neurons in specific cell groups of the brain. The number of ER-IR neurons per cell group was counted and the relative amount of immunoreactivity per neuron was measured by densitometry. The neuroanatomical distribution of estrogen receptor containing neurons in the vole was similar to the distribution of estrogen receptors in most rodents. The mean number of ER-IR neurons did not differ between naive and male-exposed females. The induction of sexual receptivity however significantly decreased the concentration of estrogen receptor immunoreactivity per neuron in the medial preoptic nucleus, the medial preoptic area, the encapsulated bed nucleus of the stria terminalis, and the ventromedial nucleus of the hypothalamus. Compared with naive males, the mean number of ER-IR neurons was up to four fold greater in naive females in the medial preoptic nucleus, anteroventral periventricular preoptic nucleus, the encapsulated bed nucleus of the stria terminalis, the medial amygdala, and the ventromedial nucleus of the hypothalamus. Additionally the amount of estrogen receptor immunoreactivity per neuron was considerably greater in the medial preoptic nucleus, the medial preoptic area, the encapsulated bed nucleus of the stria terminalis, and the ventromedial nucleus of the hypothalamus of naive females. If the amount of estrogen receptor per cell is a determinant of a tissue's responsiveness to estrogen, reduced estrogen receptor immunoreactivity in males, and in females exposed to males suggests that they may be less responsive to estrogen than naive females. We propose that this reduced estrogen receptor immunoreactivity in males is a result of reduced estrogen receptor protein levels. Currently, we cannot definitively prove our working hypothesis that decreased estrogen receptor immunoreactivity in females exposed to males is due to reduced receptor levels, and not due to ligand altered epitope availability.(ABSTRACT TRUNCATED AT 400 WORDS)

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.