Ruth I. Wood

Mating activates androgen receptor-containing neurons in chemosensory pathways of the male Syrian hamster brain

Fos-immunoreactivity is induced during mating in the male Syrian hamster in limbic areas that relay chemosensory information and contain receptors for gonadal steroid hormones. The induction of Fos is an index of neuronal activation. After mating, c-fos expression is greatest in subnuclei of the medial amygdaloid nucleus (Me), bed nucleus of the stria terminalis (BNST), and medial preoptic area (MPOA). The present study determined if individual neurons in these activated subnuclei contain androgen receptors. We aim to understand how essential chemosensory and hormonal signals are integrated to control copulation. Adult male hamsters (n = 6) were allowed to mate with a sexually receptive female for 30 min. They were perfused 1 h later with 4% paraformaldehyde and 40 microns frozen sections were processed for immunocytochemistry using antisera against Fos (Cambridge Research Biochemicals) and the androgen receptor (G.S. Prins). The brains of three non-mated males were also processed for Fos immunocytochemistry. Mating significantly increased the number of Fos-immunoreactive neurons within subnuclei of Me, BNST, and MPOA relative to non-mated males (P < 0.05). These nuclei contained abundant androgen receptors. In the corticomedial amygdala, 20-40% of Fos-immunoreactive neurons in mated hamsters expressed androgen receptors. Although few androgen receptors are found in the anteromedial and postero-intermediate subdivisions of the BNST, these areas exhibited 26% and 47% co-localization, respectively. In posteromedial BNST, which contains large numbers of steroid receptor-containing neurons, androgen receptors were identified in 48% of Fos-immunoreactive neurons. In the MPOA, 54% of Fos-immunoreactive neurons expressed the androgen receptor throughout the rostrocaudal extent of the medial preoptic nucleus (MPN).(ABSTRACT TRUNCATED AT 250 WORDS)

The Medial Amygdaloid Nucleus and Medial Preoptic Area Mediate Steroidal Control of Sexual Behavior in the Male Syrian Hamster

An important goal of studies on steroid receptors in the brain is to understand the functions of specific populations of steroid receptor-containing neurons, particularly in the control of sexual behavior. The present study compared the ability of testosterone implants directed toward the medial amygdaloid nucleus (Me) or the bed nucleus of the stria terminalis (BNST) and medial preoptic area (MPOA) to stimulate mating in castrated males. Twenty adult male hamsters were selected for vigorous sexual behavior, and baseline measures of copulatory behavior during the first 10 min of a 30-min mating behavior test were recorded on two occasions. Twelve weeks after castration, sexual behavior was recorded as before, and each male received a single intracranial implant constructed of 23-gauge tubing packed with crystalline testosterone placed stereotaxically into Me or BNST/MPOA (n = 10 each). Behavior was assessed on two occasions after surgery to determine if implants in Me or BNST/MPOA could stimulate sexual behavior above that observed after castration. In half of the males from each group, testosterone increased the males interaction with the female, anogenital investigation, mounting, and reduced the latency to the first mount. After completion of behavioral testing, males were perfused and the brains processed for androgen receptor immunocytochemistry to determine the extent of brain regions influenced by the testosterone-filled cannula. In tissues stained rapidly in diaminobenzidine, androgen receptor-containing neurons were visible only in steroid responsive brain regions adjacent to the testosterone implant. This approach revealed that steroid receptors in both the posterior subdivision of Me and in the medial subregions of BNST/MPOA can mediate hormonal control of mating behavior in the male Syrian hamster. Implants placed outside these regions failed to stimulate mating. These results suggest that maintenance of copulatory behavior by gonadal steroids is not transduced by a single brain region, but that steroid effects can be elicited at multiple points along the mating behavior pathway.

Androgen and estrogen receptors coexist within individual neurons in the brain of the Syrian hamster.

Many aspects of reproductive neuroendocrine function and sexual behavior are responsive to both androgens and estrogens, suggesting that receptors for these steroid hormones may reside within single cells in brain regions that control reproductive function. We determined the distribution of estrogen receptor-containing neurons in 40-microns coronal brain sections in gonadectomized, DHT-treated male Syrian hamsters using immunocytochemistry with the H222 antibody (10 micrograms/ml; Abbott Laboratories). Subsequently, we colocalized estrogen receptors with androgen receptors using the PG-21 antibody (0.5 microgram/ml; G.S. Prins). In males, the distribution of estrogen receptor-containing neurons was similar to that reported previously for the female hamster. Colocalization of androgen and estrogen receptor immunoreactivity was observed in brain regions that contain numerous androgen and estrogen receptor-positive neurons, including subdivisions of the medial preoptic area, bed nucleus of the stria terminals, ventromedial nucleus of the hypothalamus, and the amygdalohippocampal area. Single-labelled estrogen receptor-containing neurons were most numerous in the amygdalohippocampal area and the rostral medial preoptic nucleus; androgen receptor-immunoreactive cells were most abundant in the ventral premammillary nucleus and the lateral septum. These data suggest the potential of androgens and estrogens to influence neuronal function within individual steroid receptor-containing neurons of the hamster limbic system.

Androgen and estrogen concentrating neurons in chemosensory pathways of the male Syrian hamster brain

The medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST), and medial amygdaloid nucleus (Me) are essential for male sexual behavior in the Syrian hamster. These nuclei received chemosensory stimuli and gonadal steroid signals, both of which are required for mating behavior. The objective of this study was to compare the distribution of androgen- and estrogen-concentrating neurons in MPOA, BNST, and Me in the adult male hamster using steroid autoradiography for estradiol (E2), testosterone (T) and dihydrotestosterone (DHT). Adult males (n = 4 per group) received two i.p. injections of tritiated steroid 4-7 days after castration. Six-microns frozen sections through the brain were mounted onto emulsion-coated slides, and exposed for 11-16 months. In MPOA, BNST, and Me, neurons were more abundant and heavily labelled after [3H]E2 treatment than after either [3H]T or [3H]DHT. Tritiated estradiol- and DHT-labeled cells were found throughout the rostrocaudal extent of Me, with a high concentration in posterodorsal Me. Tritiated testosterone treatment labelled cells largely within posterodorsal Me. In MPOA, the majority of E2-, T-, and DHT-labelled neurons were in the medial preoptic nucleus (MPN) and the preoptic continuation of the posteromedial bed nucleus of the stria terminalis (BNSTpm). Few T-labelled cells were present outside these subdivisions. In the BNST, E2- and DHT-labelled neurons were present in all subdivisions, whereas T labelling was confined to the antero- and posteromedial subdivisions of BNST. These results suggest that the distribution of androgen- and estrogen receptor-containing neurons overlap considerably in nuclei which transmit chemosensory signals in the control of mating behavior.

Androgen receptor immunoreactivity in the male and female Syrian hamster brain

To investigate potential mechanisms for sex differences in the physiologic response to androgens, the present study compared the hormonal regulation of intracellular androgen receptor partitioning and the distribution of androgen receptor immunoreactivity in select brain regions from male and female hamsters. Androgen receptors were visualized on coronal brain sections. Two weeks after castration, androgen receptor immunoreactivity filled the neuronal nuclei and cytoplasm in males and females. In gonad-intact males and females, androgen receptor immunoreactivity was limited to the cell nucleus. Whereas exogenous dihydrotestosterone prevented cytoplasmic immunoreactivity, estrogen at physiologic levels did not. These results suggest that nuclear androgen receptor immunoreactivity in gonad-intact females is maintained by endogenous androgens, and that androgens have the potential to influence neuronal activity in either sex. However, sex differences in the number and staining intensity of androgen-responsive neurons were apparent in select brain regions. In the ventral premammillary nucleus, ventromedial nucleus of the hypothalamus, and medial amygdaloid nucleus, androgen receptor staining was similar in gonadectomized males and females. In the lateral septum, posteromedial bed nucleus of the stria terminalis (BNSTpm), and medial preoptic nucleus, the number of androgen receptor-immunoreactive neurons was significantly lower in females (p < .05). Moreover, the integrated optical density/cell in BNSTpm was significantly less in females (1.28+/-0.3 units) than in males (2.21+/-0.2 units; p < .05). These sex differences in the number and staining intensity of androgen-responsive neurons may contribute to sex differences in the behavioral and neuroendocrine responses to androgens.

Central inhibition of gonadotropin-releasing hormone secretion in the growth-restricted hypogonadotropic female sheep.

Growth retardation induced by dietary restriction results in hypogonadotropism, and thus, puberty is delayed. The present studies determined 1) whether reduced LH secretion in the growth-retarded condition is due to a reduction in the frequency and/or in the amplitude of GnRH secretion, and 2) whether the mechanism regulating LH secretion is being actively inhibited via central mechanisms. To determine whether GnRH pulse frequency and/or amplitude are reduced during growth restriction, blood samples were simultaneously collected from pituitary portal blood for GnRH and from jugular blood for LH determinations over a 4-h period in ovariectomized lambs (52 wk of age) that were either growth restricted (28 kg; n = 8) or growing normally (60 kg; n = 7). As expected, the growth-restricted females were hypogonadotropic and exhibited a long LH interpulse interval compared with the normally growing females. However, although the GnRH interpulse interval was longer in the growth-restricted lambs compared with that...

Sexual Differentiation of the Surge Mode of Gonadotropin Secretion: Prenatal Androgens Abolish the Gonadotropin-Releasing Hormone Surge in the Sheep

In sheep, the surge mode of gonadotropin secretion is sexually differentiated, i.e. the LH surge is present in the female, but not in the male. The present study tested the hypothesis that sexual differentiation of the LH surge mechanism reflects a sex difference in the pattern of GnRH, and that prenatal androgens abolish the surge mode of GnRH secretion. We monitored the pattern of GnRH secretion in pituitary portal blood after acute treatment with estradiol in gonadectomized postpubertal males (n=6), females (n=6), and androgenized females (exposed prenatally to testosterone from day 30–90 in gestation, n=7). Four capsules, each containing a 30‐mm column of estradiol were implanted s.c. into each lamb to produce high physiologic concentrations of the hormone. Beginning 7u2003h later, portal and peripheral blood samples were collected hourly for 48u2003h for measurement of GnRH and LH, respectively. All females exhibited a GnRH surge beginning 13.0±0.4u2003h after estradiol treatment; this was accompanied by an LH surge. By contrast, only one male produced a small surge in GnRH (1.7u2003pg/min) with a latency of 32u2003h; a corresponding increase in LH occurred in this male. Likewise, among the androgenized females, only one exhibited GnRH and LH surges which began at about 22u2003h after estradiol treatment. Some of the androgenized females had sporadic increases in GnRH which were of lower amplitude than in the control females, and were unaccompanied by rises in LH. These findings provide the first direct evidence that the sex difference in the surge mode of LH secretion results from the sexual differentiation of the pattern of GnRH release. The study also suggests that androgens during prenatal development abolish the GnRH surge and subsequently, the generation of the LH surge.

Prenatal androgens time neuroendocrine puberty in the sheep: effect of testosterone dose.

In sheep, prenatal exposure to androgens during a critical period for sexual differentiation of the brain (30–90 days of gestation; 145 days is term) can advance the timing of puberty in females and prevent the preovulatory LH surge. The present study tests the hypothesis that in sheep, the timing of neuroendocrine sexual maturation is related to the amount of prenatal steroid exposure. In addition, we determined if different steroid requirements exist for sexual differentiation of the tonic and surge modes of gonadotropin secretion. Testosterone was administered weekly to three groups of pregnant ewes from days 30–90 of gestation at doses of 200, 80, or 32 mg/week. The resulting androgenized female lambs together with control males and females (n = 5–7/group) were gonadectomized at 3 weeks of age, and gonadal steroids were replaced with a SILASTIC brand estradiol-filled capsule. LH concentrations were measured from biweekly blood samples. Sustained increases in circulating LH were considered to reflect t...

7α-Methyl-19-nortestosterone Facilitates Sexual Behavior in the Male Syrian Hamster

Abstract Steroid hormones from the testes promote attraction to estrous females and facilitate copulation in the male Syrian hamster. We compared the ability of testosterone (T) and MENT, a potent synthetic androgen that does not undergo 5α-reduction, to maintain sexual behavior in castrated males. Steroid treatment was initiated immediately after castration at three levels by means of Alzet osmotic pumps in sexually experienced adult male hamsters. Daily doses were 5, 25, or 100 μg T and 1, 5, or 25 μg MENT (n= 5/group). Additional castrated males (n= 5) remained untreated. Sexual behavior was recorded during two 10-min tests before, and at 2, 4, 6, and 8 weeks after orchidectomy. MENT and T maintained equivalent levels of behavior at each corresponding dose of androgen (high, medium, or low). The low dose of T or MENT failed to sustain mating behavior. Eight weeks after castration, males receiving the high and medium doses of androgens continued to express intromissions and ejaculations at gonadally intact levels. However, only males receiving the high dose showed anogenital investigation at the same level as intact males. From these data, we conclude that MENT sustains mating behavior in the male hamster, and that chemoinvestigatory behavior requires higher levels of androgens than those necessary for copulation.

Toward an Understanding of Interfaces Between Nutrition and Reproduction: The Growth-Restricted Lamb as a Model

For many basic and clinical scientists who focus on mechanisms underlying female puberty, the fundamental question has become, “How does the developing female determine when she has grown sufficiently to begin reproductive cycles?” Other investigators, interested in the reason for cessation of reproductive cycles after puberty in response to weight loss or high level exercise, are seeking an understanding about how the reproductive system senses these altered physiologic states.