Co-localization of androgen receptor and nitric oxide synthase in the ventral premammillary nucleus of the newborn rat: an immunohistochemical study

Testosterone interacts with the feedback mechanisms engaged by Tyr985 of the leptin receptor and diet-induced obesity

Inhibitory signaling through Tyr985 of the leptin receptor contributes to the attenuation of anorectic leptin action in obese animals. Leptin receptor (LEPR-B) Tyr985Leu homozygote mutant mice (termed l/l) were previously generated to study Tyr985's contributions to inhibition of LEPR-B signaling; young female l/l mice display a lean, leptin-sensitive phenotype, while young male l/l are not significantly different from wild-type. We report here that testosterone (but not estrogen) determines the sex-specificity of the l/l phenotype. This provides additional insight into the cellular mechanism by which gonadal hormones determine central sensitivity to leptin, and may help elucidate the long-noted sex differences in leptin sensitivity. Additionally, we observed that Tyr985 signaling protects against a diet-dependent switch that exacerbates obesity with high fat feeding, such that the enhanced leptin sensitivity of l/l mice on a normal diet leads to increased adiposity in the face of chronic high-fat diet.

Leptin action through hypothalamic nitric oxide synthase-1-expressing neurons controls energy balance

Few effective measures exist to combat the worldwide obesity epidemic¹, and the identification of potential therapeutic targets requires a deeper understanding of the mechanisms that control energy balance. Leptin, an adipocyte hormone that signals the status of cellular energy stores, acts via multiple types of leptin receptor (LepR-b)-expressing neurons in the brain to control feeding, energy expenditure and endocrine function^2–4. The modest contributions to energy balance attributable to leptin action via many previously-studied LepR-b populations^5–9 suggest that other, heretofore unidentified, hypothalamic LepR-b neurons play important roles. Here, we examine the role of LepR-b in neuronal nitric oxide synthase (NOS1)-expressing (LepR-b^NOS1) neurons that comprise approximately 20% of hypothalamic LepR-b neurons. Nos1^cre-mediated ablation of LepR-b (Lepr^NOS1KO mice) produces hyperphagic obesity, decreased energy expenditure and hyperglycemia approaching that of LepR-b-null mice. In contrast, endocrine functions in Lepr^NOS1KO mice are relatively spared. Thus, hypothalamic LepR-b^NOS1 neurons are essential for the control of energy balance by leptin.

Histological properties of the glomerular layer in the mouse accessory olfactory bulb

In mammals, the vomeronasal system (VS) originating from the vomeronasal organ (VNO; also called "Jacobson's organ") is considered to be a chemosensory system that recognizes "pheromone" signals. In the accessory olfactory bulb (AOB), the primary center of the VS, the glomerular cell layer (GL) of the AOB is regarded as an important functional area in the transmission of pheromone signals from vomeronasal sensory neurons (VSNs) of the VNO. In mice, the most frequently used animal model for the study of the VS, the GL of the AOB has several unique histological properties when compared with the main olfactory bulb (MOB): (i) each glomerular size is far smaller than in the MOB; (ii) many juxtaglomerular cells (JGCs) are GABA immunopositive, but subpopulations of cells distributed in the AOB are tyrosine hydroxylase- or calcium-binding protein immunopositive; and (iii) the dendritic branching pattern of the JGC in the AOB is heteromeric. The biological significance of the mammalian VS is still debated. The unique histological properties of the mouse AOB summerized in the present review may give some useful information that may help in understanding the function of the mammalian VS.

An androgen-dependent sexual dimorphism visible at puberty in the rat hypothalamus

Morphological studies in rodents have well documented the masculinization of the perinatal brain by estradiol derived from aromatized testosterone, and the resulting irreversible quantitative sex-differences generated in cell numbers or expression of chemical phenotypes. Here, using immunohistochemistry, we explored how this applies to the postnatal development and masculinization of the neurokinin B (NKB)-containing system of the arcuate nucleus/median eminence complex (ARC/ME). In adult rats, NKB-immunoreactive neurons exhibit an unusual, qualitative sexual dimorphism of their ventral axonal projections: to the neuropil in females, to capillary vessels in males. In adults, there was no sex-difference in the numbers of NKB-immunoreactive perikarya or capillary vessels in the ARC/ME, suggesting that this sexual dimorphism cannot be explained by the existence of supernumerary structures. At birth (day 0) the NKB system was immature in both sexes, and while its adult features emerged progressively until puberty in females, they did not develop before puberty (day 40) in males, revealing a sexual dimorphism only late postnatally. When males were orchidectomized at day 30, the masculine distribution of NKB-immunoreactive axons expected at day 40 was not seen, while it was apparent after chronic treatment with testosterone or dihydrotestosterone, suggesting a testicular masculinizing action via androgen receptors at puberty. Moreover in these prepubertal-orchidectomized males, the distribution of NKB-immunoreactive axons was surprisingly feminized by chronic estradiol alone, suggesting that NKB neurons are not irreversibly programmed before puberty. Last, in adult females, the distribution of NKB-immunoreactive axons was feminine 30 days after ovariectomy, and it was masculinized after concurrent chronic dihydrotestosterone, suggesting that NKB neurons remain responsive to androgens late in reproductive life. Thus, the sexual differentiation of the hypothalamus proceeds well beyond the perinatal period and includes the epigenetic action of non-aromatizable androgens upon subsets of neurons that have retained bipotent features.

Effects of gonadal hormones on central nitric oxide producing systems

Nitric oxide-containing neurons are widely distributed within the CNS, including regions involved in the control of reproduction and sexual behavior. The expression of neuronal nitric oxide synthase is influenced by testosterone in male rat, and by estrogens in female. Moreover, nitric oxide synthase may co-localize with gonadal hormones' receptors. Gonadal hormones may influence nitric oxide synthase expression in adulthood as well as during the development. In fact, in mice knockout for estrogen receptor alpha, the nitric oxide synthase-expressing population is deeply reduced in specific regions. In physiological conditions, the female in mammalian species is exposed to short-term changes of gonadal hormones levels (estrous cycle). Our recent studies, performed in the rat vomeronasal system and in mouse hypothalamic and limbic systems reveal that, in rodents, the expression of nitric oxide synthase-producing elements within regions relevant for the control of sexual behavior is under the control of gonadal hormones. The expression of nitric oxide synthase may vary according to the rapid variations of hormonal levels that take place during the estrous cycle. This seems in accordance with the hypothesis that gonadal hormone activation of nitric oxide-cyclic guanosine-monophosphate pathway is important for lordosis behavior, as well as that this system is activated during mating behavior. Finally, comparative data available for other vertebrates suggest that class-specific and species-specific differences occur in the nitric oxide synthase system of hypothalamus and limbic structures. Therefore, particular caution is needed to generalize data obtained from studies in rodents.

Sex steroid communication in the ring dove brain during courtship

This review examines possible role of progesterone receptor (PR) and androgen receptor (AR) "cross-talk" in the expression of courtship behaviour in the ring dove (Streptopelia risoria). In doves, although androgen has been mostly associated with aggressive courtship behaviour and progesterone with the initiation of incubation, progesterone administration to courting birds terminates the aggressive component of courtship whilst having no effect on nesting behaviour. Recent results in doves have identified a high density of androgen receptor and progesterone receptor immunoreactivity (AR-ir and PR-ir) in the hypothalamus of both sexes in regions known to be directly involved in courtship and incubation behaviour. Nuclear AR-ir in courting birds is widespread throughout the brain. Nuclear PR-ir is only localized in discrete regions of the preoptic hypothalamus of both sexes. In the anterior and posterior hypothalamus of courting birds an increase number of AR-ir and PR-ir neurons colocalizes (70-90%) in the nucleus preopticus anterior (POA), nucleus preopticus medialis (POM), nucleus preopticus paraventricularis magnocellularis (PPM), nucleus hypothalami lateralis posterioris (PLH), and tuberal hypothalamus (Tu). A lower percentage of colocalization is seen in birds at other stages of the breeding cycle. The high percentage of AR-ir and PR-ir colocalization in the preoptic hypothalamus of courting doves supports previous reports involving progesterone acting in these brain regions to terminate the androgen-dependent aggressive courtship behaviour in male doves. The increase in PR-ir staining intensity in AR-ir neurons in courting birds suggests that this progesterone-dependent termination of aggressive courtship display in males occurs at the receptor level and may be orchestrated by central oestrogen.

Androgen receptor immunolocalization in brains of courting and brooding male and female ring doves (Streptopelia risoria)

Nuclear androgen receptors (ARs) were localized immunocytochemically in the brains of courting and brooding male and female ring doves (Streptopelia risoria). AR immunoreactivity (AR-ir) in courting birds was localized in cell nuclei in the telencephalon, diencephalon, and mesencephalon. In the anterior hypothalamus, high density of AR-ir was concentrated in several nuclei including the nucleus lateralis hypothalami, nucleus periventricularis magnocellularis, nucleus preopticus anterior, nucleus preopticus medialis, and nucleus preopticus paraventricularis magnocellularis. In the posterior hypothalamus, areas showing high density of AR-ir included the nucleus lateralis hypothalami posterioris, nucleus medialis hypothalami posterior, nucleus ectomamillaris, nucleus mamillaris lateralis, and nucleus tuberis. No sex differences in the density or localization of AR-ir were observed. Compared to brains from courting birds, AR-ir density was either extremely low or absent in most brain regions of brooding birds. It is concluded that in the dove, central ARs are closely associated with the sexual stages of the reproductive cycle.

Distribution of androgen and estrogen receptor mRNA in the brain and reproductive tissues of the leopard gecko, Eublepharis macularius

Incubation temperature during embryonic development determines gonadal sex in the leopard gecko, Eublepharis macularius. In addition, both incubation temperature and gonadal sex influence behavioral responses to androgen and estrogen treatments in adulthood. Although these findings suggest that temperature and sex steroids act upon a common neural substrate to influence behavior, it is unclear where temperature and hormone effects are integrated. To begin to address this question, we identified areas of the leopard gecko brain that express androgen receptor (AR) and estrogen receptor (ER) mRNA. We gonadectomized adult female and male geckos from an incubation temperature that produces a female-biased sex ratio and another temperature that produces a male-biased sex ratio. Females and males from both temperatures were then treated with equivalent levels of various sex steroids. Region-specific patterns of AR mRNA expression and ER mRNA expression were observed upon hybridization of radiolabeled (35S) cRNA probes to thin sections of reproductive tissues (male hemipenes and female oviduct) and brain. Labeling for AR mRNA was very intense in the epithelium, but not within the body, of the male hemipenes. In contrast, expression of ER mRNA was prominent in most of the oviduct but not in the luminal epithelium. Within the brain, labeling for AR mRNA was conspicuous in the anterior olfactory nucleus, the lateral septum, the medial preoptic area, the periventricular preoptic area, the external nucleus of the amygdala, the anterior hypothalamus, the ventromedial hypothalamus, the premammillary nucleus, and the caudal portion of the periventricular nucleus of the hypothalamus. Expression of ER mRNA was sparse in the septum and was prominent in the ventromedial hypothalamus, the caudal portion of the periventricular nucleus of the hypothalamus, and a group of cells near the torus semicircularis. Many of these brain regions have been implicated in the regulation of hormone-dependent, sex-typical reproductive and agonistic behaviors in other vertebrates. Consequently, these nuclei are likely to control such behaviors in the leopard gecko and also are candidate neural substrates for mediating temperature effects on behavior.

Androgen receptor-immunoreactivity in the forebrain of the Eastern Fence lizard (Sceloporus undulatus)

Androgen receptor (AR) distribution in the lizard forebrain and optic tectum was examined using PG21 immunohistochemistry. In the male Eastern Fence lizard, AR-immunoreactive (-ir) nuclei were observed in the medial preoptic area, ventromedial and arcuate hypothalamic nuclei, periventricular hypothalamus, premammillary nucleus, bed nucleus of the stria terminalis, and ventral posterior amygdala. Punctate immunostaining of neuronal processes (axons and/or dendrites) was concentrated in the cortex, hypothalamus, and optic tectum. AR-ir nuclei in the female brain were confined to the ventral posterior amygdala and ventromedial hypothalamic nucleus. The AR distribution in the lizard brain is similar to that reported for other vertebrate classes. Sex differences in AR-immunoreactivity may contribute to sex-specific behaviors in the Eastern Fence lizard.

Castration increases and androgens decrease nitric oxide synthase activity in the brain: physiologic implications

Sex differences in nitric oxide synthase (NOS) activity in different regions of the rat brain and effects of testosterone and dihydrotestosterone (DHT) treatment in orchidectomized animals were investigated. Regional but no sex differences in NOS activity were detected in gonadectomized animals. Orchidectomy significantly increased NOS activity in the hypothalamus, "amygdala," and cerebellum but not in the cortex. In the hypothalamus, the increase in NOS activity after castration and its reversal by androgen treatment was mimicked by changes in neuronal NOS mRNA level. In contrast, androgen receptor (AR) mRNA level in the hypothalamus was slightly reduced by castration and increased by treatment with DHT. Again in the hypothalamus, the increase in NOS activity in castrated rats was accompanied by an increase in the number of neuronal NOS+ cells determined immunohistochemically, whereas androgen treatment prevented this increase. The changes in NOS+ neurons correlated with the changes in the number of AR+ cells to a degree. Overlap of AR in NOS+ cells was not present in the regions of the hypothalamus analyzed. These results indicate that testosterone or, most likely, its metabolite DHT down-regulates NOS activity, mRNA expression or stabilization, and the number of neuronal NOS+ neurons.

Castration increases and androgens decrease nitric oxide synthase activity in the brain: physiologic implications

Sex differences in nitric oxide synthase (NOS) activity in different regions of the rat brain and effects of testosterone and dihydrotestosterone (DHT) treatment in orchidectomized animals were investigated. Regional but no sex differences in NOS activity were detected in gonadectomized animals. Orchidectomy significantly increased NOS activity in the hypothalamus, "amygdala," and cerebellum but not in the cortex. In the hypothalamus, the increase in NOS activity after castration and its reversal by androgen treatment was mimicked by changes in neuronal NOS mRNA level. In contrast, androgen receptor (AR) mRNA level in the hypothalamus was slightly reduced by castration and increased by treatment with DHT. Again in the hypothalamus, the increase in NOS activity in castrated rats was accompanied by an increase in the number of neuronal NOS+ cells determined immunohistochemically, whereas androgen treatment prevented this increase. The changes in NOS+ neurons correlated with the changes in the number of AR+ cells to a degree. Overlap of AR in NOS+ cells was not present in the regions of the hypothalamus analyzed. These results indicate that testosterone or, most likely, its metabolite DHT down-regulates NOS activity, mRNA expression or stabilization, and the number of neuronal NOS+ neurons.

BDNF regulation of androgen receptor expression in axotomized SNB motoneurons of adult male rats

Brain-derived neurotrophic factor (BDNF) prevents the axotomy-induced loss of androgen receptor-like immunoreactivity (AR-LI) in the spinal nucleus of the bulbocavernosus (SNB) motoneurons of adult male rats. In this report, we investigated the dose-response effect of BDNF on androgen receptor expression in axotomized SNB motoneurons, and examined whether delayed application of BDNF to the cut SNB axons can completely reverse the axotomy-induced loss of androgen receptor expression. We also used autoradiography to test whether axotomy decreases the ability of SNB motoneurons to accumulate androgens. SNB motoneurons were axotomized bilaterally and BDNF or PBS was applied to the proximal ends of the axons. The percentage of SNB motoneurons expressing medium or high AR-LI was the major measure of androgen receptor expression. AR-LI was significantly higher on the BDNF-treated side than on the contralateral side treated with phosphate-buffered saline (PBS) for all three doses of BDNF (1.45, 2.9, and 5.8 mg/ml) and was higher than in rats treated bilaterally with PBS. Moreover, AR-LI at the highest dose of BDNF was not different from that in intact SNB motoneurons. Delayed application of BDNF to the axotomized SNB motoneurons restored the AR-LI to the intact level. The AR-LI decreased by axotomy started to increase significantly 4 days after BDNF application and returned to the intact level by 10 days. Furthermore, axotomy significantly decreased the percentage of SNB motoneurons to accumulate tritiated testosterone or its metabolites. In conclusion, our data demonstrate that BDNF completely prevents and reverses the axotomy-induced loss of AR-LI. Moreover, decrease of AR-LI by axotomy reflects the decrease in the ability of SNB motoneurons to accumulate androgens.

Female-soiled bedding induced fos immunoreactivity in the ventral part of the premammillary nucleus (PMv) of the male mouse

Previous studies have indicated that the ventral part of the premammillary nucleus (PMv) of rodents is involved in the regulation of aggressive and male mating behavior, although the precise physiological function of the PMv is still unclear. To analyze the physiological role of the PMv in male mating behavior, the effects of exposure to bedding soiled by female mice on Fos immunoreactivity (Fos-ir), an early marker of neuronal activation, were studied in the PMv and some sex-related nuclei. We observed that exposure to female-soiled bedding induced Fos-ir expression in the PMv of the male mouse. Although Fos-ir positive cells were found in the posterodorsal part of the medial amygdaloid nucleus and in the posteromedial cortical amygdaloid nucleus, which are terminals of the neuronal projections from the main and accessory olfactory bulbs, the numbers of Fos-ir cells in those nuclei were not affected by exposure to female-soiled bedding. Moreover, Fos-ir was not detected in the ventromedial hypothalamic nucleus. It is well established that soiled bedding is useful as a source of chemosensory substances, which include "pheromones." Thus, our findings, in agreement with previous behavioral and anatomical data, suggest that the PMv plays a role in initiating male copulative behavior that is induced by a female mice pheromone(s).

Sex-steroid actions on neurotransmission

Although it is well recognized that sex-steroids exert both developmental and activational influences on the brain, the cellular and molecular mechanisms underlying their actions are less well understood. Progress is rapid, however, and this paper reviews recent insights gained through manipulation of sex-steroid receptor genes, identification of phenotypes expressing these receptors and how these proteins may also be activated to regulate transcription by ligand-independent pathways. Advances in our understanding of more rapid actions of sex-steroids and the molecular targets involved are also reviewed, as are new studies describing effects on synaptic plasticity and the recent excitement regarding the neuroprotective effects of oestrogen replacement therapy in Alzheimer's disease.