Autoradiographic localization of 3H-dihydrotestosterone in the preoptic area, hypothalamus, and amygdala of a male rhesus monkey

The association of hypogonadism with depression and its treatments

According to World Health Organization estimates, 5% of the adult population worldwide suffers from depression. In addition to the affective, psychomotor and cognitive symptoms which characterize this mood disorder, sexual dysfunction has been frequently reported among men suffering from depression. The most common sexual manifestations are decreased libido, erectile dysfunction and orgasmic disorder. In addition, epidemiological studies have documented a reduction of testosterone concentrations in men with depression and, for these reasons, depressive disorders appear as one possible cause of male functional hypogonadism. Moreover, some largely used antidepressant medications can cause or worsen sexual complaints, thus depression and its treatments rise several andrological-relevant issues. The other way round, men with hypogonadism can manifest depressed mood, anxiety, insomnia, memory impairment which, if mild, may respond to testosterone replacement therapy (TRT). However, the prevalence of functional hypogonadism in depression, and of depressive symptoms in hypogonadal men, is not known. Severe depressive symptoms do not respond to TRT, while the effect of treating major depression on functional hypogonadism, has not been investigated. Overall, the clinical relevance of each condition to the other, as well as the physiopathological underpinnings of their relationship, are still to be clarified. The present review summarizes current evidence on the influence of testosterone on mood and of depression on the hypothalamic-pituitary-testis axis; the clinical association between male hypogonadism and depression; and the reciprocal effects of respective treatments.

Species differences in androgen receptor expression in the medial preoptic and anterior hypothalamic areas of adult male and female rodents

The medial preoptic and anterior hypothalamic areas (MPO/AH) are important androgen targets regulating homeostasis, neuroendocrinology and circadian rhythm as well as instinctive and sociosexual behaviors. Although species differences between rats and mice have been pointed out in terms of morphology and physiology, detailed distributions of androgen receptor (AR) have never been compared between the two rodents. In the present study, AR distribution was examined immunohistochemically in serial sections of the MPO/AH and compared for adult rats and mice. Western blotting and immunohistochemistry clearly demonstrated that AR expression in the brain was stronger in mice than in rats and was stronger in males than in females. In addition, we found (1) an "obliquely elongated calbindin-ir cell island" in mice medial preoptic nucleus (MPN) expressed AR intensely, as well as the sexually dimorphic nucleus in the MPN (SDN-MPN) in rats, strongly supporting a "putative SDN-MPN" previously proposed in mice; (2) AR expression in the suprachiasmatic nucleus (SCN) was much more prominent in mice than in rats and differed in localization between the two species; (3) a mouse-specific AR-ir cell cluster was newly identified as the "tear drop nucleus (TDN)", with male-dominant sexual dimorphism; and (4) two rat-specific AR-ir cell clusters were also newly identified as the "rostral and caudal nebular islands", with male-dominant sexual dimorphism. The present results may provide basic morphological evidence underlying species differences in androgen-modified psychological, physiological and endocrinergic responses. Above all, the findings of the mouse-specific TDN and differing AR expression in the SCN might explain not only species difference in gonadal modification of circadian rhythm, but also distinct structural bases in the context of transduction of SCN oscillation. The current study could also serve as a caution that data on androgen-sensitive functions obtained from one species should not always be directly applied to others among rodents.

Testosterone in the brain: neuroimaging findings and the potential role for neuropsychopharmacology

Testosterone plays a substantial role in a number of physiological processes in the brain. It is able to modulate the expression of certain genes by binding to androgen receptors. Acting via neurotransmitter receptors, testosterone shows the potential to mediate a non-genomic so-called "neuroactive effect". Various neurotransmitter systems are also influenced by the aromatized form of testosterone, estradiol. The following article summarizes the findings of preclinical and clinical neuroimaging studies including structural and functional magnetic resonance imaging (MRI/fMRI), voxel based morphometry (VBM), as well as pharmacological fMRI (phfMRI) and positron emission tomography (PET) regarding the effects of testosterone on the human brain. The impact of testosterone on the pathogenesis of psychiatric disorders and on sex-related prevalence differences have been supported by a wide range of clinical studies. An antidepressant effect of testosterone can be implicitly explained by its effects on the limbic system--especially amygdala, a major target in the treatment of depression--solidly demonstrated by a large body of neuroimaging findings.

Where and what is the paralaminar nucleus? A review on a unique and frequently overlooked area of the primate amygdala

The primate amygdala is composed of multiple subnuclei that play distinct roles in amygdala function. While some nuclei have been areas of focused investigation, others remain virtually unknown. One of the more obscure regions of the amygdala is the paralaminar nucleus (PL). The PL in humans and non-human primates is relatively expanded compared to lower species. Long considered to be part of the basal nucleus, the PL has several interesting features that make it unique. These features include a dense concentration of small cells, high concentrations of receptors for corticotropin releasing hormone and benzodiazepines, and dense innervation of serotonergic fibers. More recently, high concentrations of immature-appearing cells have been noted in the primate PL, suggesting special mechanisms of neural plasticity. Following a brief overview of amygdala structure and function, this review will provide an introduction to the history, embryology, anatomical connectivity, immunohistochemical and cytoarchitectural properties of the PL. Our conclusion is that the PL is a unique subregion of the amygdala that may yield important clues about the normal growth and function of the amygdala, particularly in higher species.

Pubertal maturation and programming of hypothalamic-pituitary-adrenal reactivity

Modifications in neuroendocrine function are a hallmark of pubertal development. These changes have many short- and long-term implications for the physiological and neurobehavioral function of an individual. The purpose of the present review is to discuss our current understanding of how pubertal development and stress interact to affect the hypothalamic-pituitary-adrenal (HPA) axis, the major neuroendocrine axis that controls the hormonal stress response. A growing body of literature indicates that puberty is marked by dramatic transitions in stress reactivity. Moreover, recent studies indicate that exposure to stressors during pubertal maturation may result in enduring changes in HPA responsiveness in adulthood. As puberty is marked by a substantial increase in many stress-related psychological and physiological disorders (e.g., depression, anxiety, drug abuse), it is essential to understand the factors that regulate and modulate HPA function during this crucial period of development.

A developmental neurobiological model of motivated behavior: anatomy, connectivity and ontogeny of the triadic nodes

Adolescence is the transition period that prepares individuals for fulfilling their role as adults. Most conspicuous in this transition period is the peak level of risk-taking behaviors that characterize adolescent motivated behavior. Significant neural remodeling contributes to this change. This review focuses on the functional neuroanatomy underlying motivated behavior, and how ontogenic changes can explain the typical behavioral patterns in adolescence. To help model these changes and provide testable hypotheses, a neural systems-based theory is presented. In short, the Triadic Model proposes that motivated behavior is governed by a carefully orchestrated articulation among three systems, approach, avoidance and regulatory. These three systems map to distinct, but overlapping, neural circuits, whose representatives are the striatum, the amygdala and the medial prefrontal cortex. Each of these system-representatives will be described from a functional anatomy perspective that includes a review of their connectivity and what is known of their ontogenic changes.

The regulation of neuroendocrine function: Timing is everything

Hormone secretion is highly organized temporally, achieving optimal biological functioning and health. The master clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus coordinates the timing of circadian rhythms, including daily control of hormone secretion. In the brain, the SCN drives hormone secretion. In some instances, SCN neurons make direct synaptic connections with neurosecretory neurons. In other instances, SCN signals set the phase of "clock genes" that regulate circadian function at the cellular level within neurosecretory cells. The protein products of these clock genes can also exert direct transcriptional control over neuroendocrine releasing factors. Clock genes and proteins are also expressed in peripheral endocrine organs providing additional modes of temporal control. Finally, the SCN signals endocrine glands via the autonomic nervous system, allowing for rapid regulation via multisynaptic pathways. Thus, the circadian system achieves temporal regulation of endocrine function by a combination of genetic, cellular, and neural regulatory mechanisms to ensure that each response occurs in its correct temporal niche. The availability of tools to assess the phase of molecular/cellular clocks and of powerful tract tracing methods to assess connections between "clock cells" and their targets provides an opportunity to examine circadian-controlled aspects of neurosecretion, in the search for general principles by which the endocrine system is organized.

Distribution of androgen receptor-like immunoreactivity in the brains of cynomolgus monkeys

A polyclonal antibody, PA1, raised in a rabbit against fusion proteins containing fragments of the human prostatic androgen receptor (AR) was used to map the distribution of AR-like immunoreactivity in the brains of adult male and female cynomolgus monkeys. PA1 AR-immunoreactive (ARir) labeling occurred in the cell nuclei and, more weakly, in the cytoplasm of brain cells. The PA1 ARir labeling occurred primarily in brain regions previously shown on the basis of gonadal steroid autoradiography to contain androgen receptors. However, the distribution of PA1 ARir staining was substantially more restricted than that of autoradiographic labeling using 3H-androgens. The pattern of PA1 ARir labeling was closely similar between animals and occurred in the lateral septum, medial preoptic area, bed nucleus of stria terminalis, anterior, cortical, accessory basal and medial amygdala, several hypothalamic nuclei including the supraoptic, anterior, paraventricular, ventromedial and arcuate nuclei, and the premammillary nucleus. No significant sex differences were observed. With the exception of the supraoptic nucleus, reported not to be labeled by autoradiography, earlier autoradiographic findings and the current immunocytochemical results, although not congruent, have noteworthy similarities.

Androgen-dependent and -independent aromatase activity coexists with androgen receptors in male Guinea-pig brain

Abstract Using a microdissection technique we localized androgen receptors and aromatase activity (AA) in the brain of male guinea-pigs. In addition, we evaluated the effects of castration and androgen replacement on androgen receptor dynamics and induction of AA. In the castrate animal, cytosolic androgen receptor content was highest in the basal hypothalamus, specifically in the median eminence-arcuate nucleus (> 15 fmol mg protein (1)), while lesser levels were found in the preoptic regions and amygdala. Nuclear receptor content was highest (> 150 fmol mg DNA (-1)) in the median eminence-arcuate nucleus, periventricular region of the preoptic area and cortical amygdala. All regions investigated showed a significant decrease in nuclear receptors following castration and an increase with androgen replacement. However, reciprocal changes in cytosolic androgen receptors were not always evident. Aromatase activity was high in the cortical amygdala, medial amygdala, periventricular region of the preoptic area and bed nucleus of the stria terminalis. Castration and androgen replacement had significant stimulatory effects on AA in the ventral medial hypothalamus, median eminence-arcuate nucleus, cortical amygdala and periventricular regions of the preoptic area and anterior hypothalamus. Thus, androgen receptors and AA are unevenly distributed throughout the subcortical regions of the male guinea-pig brain and respond differently to endocrine stimuli. Our data demonstrate that AA is androgen-dependent in some subcortical regions which contain androgen receptors. Even though nuclear receptors in all brain regions were affected by castration and dihydrotestosterone treatment, the events were not always linked to AA regulation. Due to this difference in regulation, AA may serve divergent functions in guinea-pig brain.

The leptomenix in normal baboon brain contain receptors for dihydrotestosterone but not estradiol

There exists a sexual dimorphism in the occurrence of meningiomas. Biochemical binding assays conducted on samples of meningiomas have indicated a high incidence of progesterone and androgen receptors in these tumors. However, similar studies have been very controversial as to the existence of estrogen receptors in these tumors. The present study was conducted to determine whether the normal leptomenix contains estrogen and androgen receptors in a primate model, namely the baboon. Three male and three female baboons were injected with either 3H-dihydrotestosterone (3H-DHT) or 3H-estradiol. One animal from each group received 3H-steroid + 100-fold unlabeled corresponding steroid to serve as control. One hour after injection of the 3H-steroids the animals were sacrificed. Their brains were removed and processed for autoradiography. Nuclear uptake and retention of 3H-DHT and/or one of its metabolites was found in 25-50% of the cells in pieces of the arachnoid adhering to the brain, cells of the glial membrane, cells in large fiber bundles, presumably oligodendroglia, and cells lining the Virchow-Robins spaces. No such localization was found with 3H-estradiol. This study provides the first anatomical evidence for the presence of androgen receptors in the normal leptomenix and glial cells of the baboon. These findings are discussed in relation to the possible clinical significance of the use of steroids to modulate the growth of meningiomas.

Distribution of androgen receptor in microdissected brain areas of the female baboon (Papio cynocephalus)

We measured androgen receptors in the brain and pituitary of 4 female baboons (Papio cynocephalus) by the in vitro binding of methyltrienolone (R1881) to cytosols from 17 brain subregions as well as anterior and posterior pituitaries. High levels of AR were detected in anterior (22.1 +/- 7.1 (S.E.M.) fmol/mg protein) and posterior pituitary (12.6 +/- 3.3 fmol/mg protein). In brain tissue, the highest androgen receptor levels were found in the infundibular nucleus/median eminence (9.4 +/- 2.3 fmol/mg protein), ventromedial nucleus (6.3 +/- 1.7 fmol/mg protein) and periventricular area (4.9 +/- 1.3 fmol/mg protein). Saturation analysis of anterior pituitary and brain tissue (pool of hypothalamic, preoptic area, amygdala and septum remaining after microdissection of brain nuclei) showed that [3H]R1881 binds to the androgen receptor with high specificity and affinity (Kd = 1.25 x 10(-10) M, 0.45 x 10(-10) M, in anterior pituitary and HPA cytosol, respectively). Serum testosterone levels were low in all animals (0.59 +/- 0.26 ng/ml). With these data we described the quantitative distribution of androgen receptor in the pituitary and in specific brain nuclei in a species of nonhuman primate. The distribution is similar in many respects to that described in the male rat and the data suggest a conservation of androgen receptor distribution across species.

Pre-optic and hypothalamic neurons accumulate [3H]medroxyprogesterone acetate in male cynomolgus monkeys

Medroxyprogesterone acetate (MPA) is a synthetic progestin that is reported to be effective in the treatment of paraphilic behavior, including paraphilic aggression, in men. The mechanisms and sites of action for its behavioral effects are not known. Thaw-mount autoradiography was used to help identify sites in the brain at which MPA may act in a male primate. Two adult, castrated male cynomolgus monkeys were administered [3H]MPA and killed one hour later. Radioactivity was concentrated in the nuclei of many neurons in the medial preoptic nucleus (n.), anterior hypothalamic area, ventromedial hypothalamic n., and arcuate n. Virtually no labeled cells were observed in the bed n. of the stria terminalis, lateral septal n., or amygdala. Analysis by high performance liquid chromatography of brain samples from the same animals demonstrated that 84% of the extractable radioactivity in cell nuclei from the hypothalamus and preoptic area was in the form of unmetabolized [3H]MPA. The localization of MPA-concentrating neurons in regions of the brain known to be implicated in regulating both sexual behavior and pituitary function suggests that, among other sites of action, MPA may act directly upon the brain.

Neurons in the brain of fetal rhesus monkeys accumulate 3H-testosterone or its metabolites

Autoradiography was used to map sites in the primate brain at which testosterone may have sexual differentiating actions on brain function and behavior during fetal development. Two female rhesus monkey fetuses were injected in utero on days 112 and 114 of gestation respectively with 3H-testosterone, and were killed 30 and 60 minutes later. Thaw-mount autoradiography of the brains revealed the accumulation of radioactivity, representing 3H-testosterone or its metabolites, in neurons of the medial preoptic-anterior hypothalamic area, bed nucleus (n.) of the stria terminalis, ventromedial hypothalamic n., and corticomedial amygdala. Thus, it appears that steroid receptors are present in a circumscribed system in the brain of the primate fetus at this stage of development.

The distribution, nuclear uptake and metabolism of [3H]dihydrotestosterone in the brain, pituitary gland and genital tract of the male rhesus monkey

Three adult male rhesus monkeys were castrated and administered 2 mCi [3H]dihydrotestosterone ([3H]DHT) intravenously. Brain and peripheral organs were removed after 60 min and were examined either by thaw-mount autoradiography or by subcellular fractionation and high performance liquid chromatography. Neurons that accumulated radioactivity in their nuclei were distributed widely in many regions of the brain including the preoptic area, hypothalamus, septal area-bed nucleus, amygdala, thalamus, and brain stem. Several brain areas which were labeled after [3H]DHT injection had not been labeled in earlier experiments after [3H]testosterone ([3H]T) injection. The major metabolite of [3H]DHT in extranuclear fractions from brain was [3H]androstanediol, but [3H]DHT alone was detected in cell nuclei. There was no evidence of any [3H]estradiol in cell nuclei, confirming that DHT can also be regarded as a non-aromatizable androgen in the primate brain. Since the nuclear concentrations of androgens were 2-3 times higher in the brain following [3H]DHT than they were in the earlier [3H]T experiments, the relative lack of effectiveness of DHT in restoring the sexual behavior of male castrates cannot be related to an inability of DHT to enter brain cell nuclei.

Localization of the synthetic progestin 3H-ORG 2058 in neurons of the primate brain: evidence for the site of action of progestins on behavior

The location of neurons that concentrate progestin in the brains of female cynomolgus monkeys was mapped by autoradiography using the specific synthetic progestin receptor ligand 3H-ORG 2058. Three females were ovariectomized and treated with estrogen (20 micrograms estradiol benzoate daily for 7 days), and one of them was also pretreated with progesterone. Each received an i.v. injection of 1 mCi 3H-ORG 2058 and was killed 1 hour later. Thaw-mount autoradiograms revealed intense accumulation of radioactivity in the nuclei of many neurons in the mediobasal hypothalamus, particularly in the ventromedial nucleus (n.), arcuate n., and premammillary n. Neuronal labeling was also observed frequently in the medial preoptic n., and occasionally in the anterior hypothalamic area, paraventricular n., and organum vasculosum of the lamina terminalis. In the pituitary gland, about 5% of cells in the pars distalis were intensely labeled. In the female pretreated with progesterone, however, labeling was almost completely blocked. Analysis of samples by high-performance liquid chromatography demonstrated that the radioactivity extracted from brain and pituitary gland cell nuclei was almost entirely unmetabolized 3H-ORG 2058. The nuclear concentration of progestin was much greater in the pituitary gland than in the brain, and was greater in the hypothalamus than in any other brain area. These results revealed well-localized groups of progestin-concentrating neurons in the primate brain which presumably mediate the effects of progesterone on both gonadotropin secretion and female sexual behavior.

Autoradiographic localization of estrogen and androgen receptors in the sexually dimorphic area and other regions of the gerbil brain

Autoradiography was used to localize sex hormone-accumulating cells in the gerbil brain. Some areas had a high density of both androgen and estrogen receptors. These areas included the lateral septum, the bed nucleus of the stria terminalis, the medial and cortical amygdaloid nuclei, the medial preoptic area (MPOA), the arcuate nucleus, the ventromedial hypothalamus, and the periventricular central gray. This distribution of hormone receptors agrees closely with that seen in other mammals. In contrast to what has been reported for other species, the distribution of estradiol-accumulating cells in the gerbil MPOA is different in males and females. Estradiol uptake in the posterior MPOA followed the morphology of a sexually dimorphic area (SDA) and was therefore sexually dimorphic. Moreover, the percentage of SDA cells that accumulated estradiol appeared to be higher in males than in females. The pattern of androgen accumulation also followed the morphology of the SDA but differed from the pattern of estrogen accumulation in one way. The uptake of 5 alpha-dihydrotestosterone in the SDA pars compacta (pc), a component of the SDA, was much greater than in the rest of the SDA. This was not true for estradiol. Since most females lack the SDApc, androgen uptake in the gerbil SDA may also be sexually dimorphic. Androgen uptake was more widespread than estrogen uptake in the brainstem. Brainstem nuclei that accumulated 5 alpha-dihydrotestosterone included the locus ceruleus, the dorsal raphe, the hypoglossal nucleus, the area postrema, the nucleus of the solitary tract, and the dorsal nucleus of the vagus.

Aromatization of testosterone to estrogen varies between strains of mice

The nuclear uptake and retention of [3H]testosterone or one of its metabolites and the aromatization of testosterone to estrogen were examined in the Swiss--Webster mouse. Castrated male mice were injected with 0.2 micrograms of either [1 alpha, 2 alpha-3H(N)]testosterone or [1 beta, 2 beta-3H(N)]testosterone per 100 g of body weight and killed one and one-half hours later. The brains were removed and processed for autoradiography. A nuclear localization of testosterone or one of its metabolites was found in the nucleus (n) interstitialis striae terminalis, n. preopticus medialis, n. premamillaris ventralis and n. amygdaloideus medialis in animals injected with [1 alpha, 2 alpha-3H(N)]testosterone. In animals injected with [1 beta, 2 beta-3H(N)]testosterone a nuclear localization was found in only n. interstitialis striae terminalis, n. premamillaris ventralis and n. amygdaloideus medialis. The results suggest testosterone is aromatized to estrogen in n. preopticus medialis ventralis in the Swiss--Webster mouse. Together with previous data, these data suggest (1) the uptake and retention of testosterone or one of its androgenic metabolites and the aromatization of testosterone to estrogen varies between strains of mice and (2) there are two separate uptake and retention systems (receptors?) for testosterone and dihydrotestosterone in the brain in all animals studied thus far with autoradiographic techniques.

Characterization by high performance liquid chromatography of nuclear metabolites of testosterone in the brains of male rhesus monkeys

Testosterone (T) restores the potency of castrated male rhesus monkeys, and our autoradiographic data have demonstrated that 3H-T or its metabolites concentrate in cell nuclei in the corticomedial amygdala, bed nucleus of stria terminalis, preoptic area, and hypothalamus. In rat, 3H-estradiol (3H-E2) is a major nuclear metabolite of 3H-T in areas of the limbic system, but comparable data are lacking for the primate. We have therefore developed an improved technique using high performance liquid chromatography for investigating metabolites of 3H-T that accumulate in cell nuclei in small amounts of tissue obtained from the brain of the rhesus monkey. Two castrated male rhesus monkeys were injected with 5 mCi of 3H-T and were killed 30 min later. In amygdala, preoptic area-bed nucleus of stria terminalis, and hypothalamus, 48-70% of the nuclear radioactivity was in the form of 3H-E2 (Type I tissues). In six other brain areas and in pituitary, 35-85% of the nuclear radioactivity was in the form of 3H-T (Type II tissues), whereas in genital tract tissues, 86-99% of the nuclear radioactivity was in the form of 3'-dihydrotestosterone (3H-DHT) (Type III tissues). In plasma and in supernatants from both Type I and Type II tissues, the proportions of 3H-T were high, and 3H-E2 did not exceed 10% of the total extractable radioactivity. These data suggest that, as in rodents, some of the central actions of T in primates may be mediated by estrogen target neurons.