Effects of orchidectomy on levels of the mRNAs encoding gonadotropin-releasing hormone and other hypothalamic peptides in the adult male rhesus monkey (Macaca mulatta)

Testosterone and Zinc Supplementations on Renal Ischemia-Reperfusion Injury in Orchiectomized Rats

Background

Renal ischemia-reperfusion (IR) injury has numerous deleterious effects on the kidney function. An experimental investigation was conducted to determine the possible protective role of testosterone (TES) and zinc (Zn) supplementations on the kidney function after IR injury in orchiectomized rats.

Methods

Orchiectomized rats (n = 32) were divided into the five groups as sham operated (Group 1), IR (Group 2), IR pretreatment with TES (IR + TES, Group 3), Zn (IR + Zn, Group 4), and TES + Zn (IR + TES + Zn, Group 5). Twenty-four hours' post-IR injury, the animals were sacrificed and the required parameters were measured.

Results

The results revealed that there were not any significant difference in serum levels of creatinine (Cr), nitrite and malondialdehyde (MDA), Cr clearance (ClCr), renal sodium (Na) load, and percentage of Na excretion (ENa%) between sham and IR groups. The pretreatment with TES and Zn either alone or combine did not alter the serum levels of Cr, nitrite and MDA, and ClCr, Na load, and ENa%. However, pretreatment with Zn, TES, or combined altered kidney weight, kidney tissue levels of nitrite and MDA, and urine flow in IR groups.

Conclusions

The orchiectomy itself performed protective effect against renal IR injury. However, pretreatment with Zn or TES may not alter kidney function against renal IR in orchiectomized rats.

Mapping GABA and glutamate inputs to gonadotrophin-releasing hormone neurones in male and female mice

Gonadotrophin-releasing hormone (GnRH) neurone function is dependent upon gonadal steroid hormone feedback, which is communicated in large part through an afferent neuronal network. The classical neurotransmitters GABA and glutamate are important regulators of GnRH neurone activity and are implicated in mediating feedback signals. In the present study, we aimed to determine whether GABAergic or glutamatergic input to GnRH neurones differs between males and females and/or exhibits morphological plasticity in response to steroid hormone feedback in females. Tissue collected from GnRH-green fluorescent protein (GFP) male and female mice in dioestrus underwent immunofluorescence labelling of GFP and either the vesicular GABA transporter (VGAT) or the vesicular glutamate transporter 2 (VGLUT2). No differences in the densities or absolute numbers of VGAT-immunoreactive (-IR) or VGLUT2-IR puncta apposed to GnRH neurones were identified between males and females. The most significant input from either neurotransmitter was to the proximal dendritic region and 80% of VGAT-IR puncta apposed to GnRH neurones co-localised with synaptophysin. Putative inputs were also assessed in ovariectomised (OVX) female mice treated with negative (OVX+E) or positive (OVX+E+E) feedback levels of oestrogen, and OVX+E+E mice were killed during the expected GnRH/luteinising hormone surge. No differences in VGLUT2-IR contacts to GnRH neurones were identified between animals under the negative-feedback influence of oestrogen (OVX+E) or the positive influence of oestrogen (OVX+E+E), regardless of cFos activation status. By contrast, a significant elevation in putative GABAergic inputs to GnRH neurones at the time of the preovulatory surge was found in the cFos-negative subset of GnRH neurones, both at the level of the soma and at the proximal dendrite. Taken together, these data suggest that, although GABAergic and glutamatergic innervation of GnRH neurones is not sexually differentiated, cyclic fluctuations in steroid hormone feedback over the female oestrous cycle result in plastic changes in GABAergic inputs to a subpopulation of GnRH neurones.

Estradiol Upregulates Kisspeptin Expression in the Preoptic Area of both the Male and Female Rhesus Monkey (Macaca mulatta): Implications for the Hypothalamic Control of Ovulation in Highly Evolved Primates

The aim of this immunohistochemical study was to evaluate the distribution of kisspeptin neurons in the preoptic area (POA) of gonadally intact adult male and female rhesus monkeys, and to determine whether imposition of an estradiol (E2)-positive feedback signal in the castrate male increased kisspeptin in the POA. Additionally, kisspeptin in the POA of the intact female was examined during an LH surge induced prematurely by E2 administered in the early follicular phase. The number of kisspeptin neurons in the POA of males and females was similar. Immunoactive kisspeptin perikarya were not observed in the POA of castrate adult males, but such neurons in these animals were present within 12 h of imposing an increment in circulating E2 concentrations that in a screening study conducted 4-6 weeks earlier had elicited an LH surge. As expected, premature induction of an LH surge by E2 early in the follicular phase was associated with upregulation of kisspeptin in the POA. These results represent the first description of immunoreactive kisspeptin cell bodies in the POA of the macaque brain and provide further support for the view that (1) kisspeptin neurons in the POA of the female monkey are a target for the positive feedback action of E2 and (2) the hypothalamic mechanism which mediates this action of E2 in primates is not subjected to perinatal programming by testicular testosterone. Moreover, our findings indicate that maintenance of the kisspeptin content in the POA of intact male monkeys requires the action of E2, presumably generated by aromatization of testicular testosterone at the hypothalamic level.

Epigenetic regulation of puberty via Zinc finger protein-mediated transcriptional repression

In primates, puberty is unleashed by increased GnRH release from the hypothalamus following an interval of juvenile quiescence. GWAS implicates Zinc finger (ZNF) genes in timing human puberty. Here we show that hypothalamic expression of several ZNFs decreased in agonadal male monkeys in association with the pubertal reactivation of gonadotropin secretion. Expression of two of these ZNFs, GATAD1 and ZNF573, also decreases in peripubertal female monkeys. However, only GATAD1 abundance increases when gonadotropin secretion is suppressed during late infancy. Targeted delivery of GATAD1 or ZNF573 to the rat hypothalamus delays puberty by impairing the transition of a transcriptional network from an immature repressive epigenetic configuration to one of activation. GATAD1 represses transcription of two key puberty-related genes, KISS1 and TAC3, directly, and reduces the activating histone mark H3K4me2 at each promoter via recruitment of histone demethylase KDM1A. We conclude that GATAD1 epitomizes a subset of ZNFs involved in epigenetic repression of primate puberty.

The NK3 Receptor Antagonist ESN364 Interrupts Pulsatile LH Secretion and Moderates Levels of Ovarian Hormones Throughout the Menstrual Cycle

Women's health disorders such as uterine fibroids and endometriosis are currently treated by GnRH modulators that effectively suppress the hypothalamic-pituitary-gonadal axis. The neurokinin-3 receptor (NK3R) is an alternative target with an important role in the modulation of this axis. In this report, we demonstrate that systemic administration of an NK3R antagonist (ESN364) prolongs the LH interpulse interval in ovarectomized ewes and significantly lowers plasma LH and FSH concentrations in castrated nonhuman primates (Macaca fascicularis). Moreover, daily oral dosing of ESN364 throughout the menstrual cycle in M fascicularis lowered plasma estradiol levels in a dose-dependent manner, although nadir levels of estradiol were maintained well above menopausal levels. Nevertheless, estradiol levels during the follicular phase were sufficiently inhibited at all doses to preclude the triggering of ovulation as evidenced by the absence of the LH surge and failure of a subsequent luteal phase rise in plasma progesterone concentrations, consistent with the absence of normal cycle changes in the uterus. Apart from the point at surge, FSH levels were not altered over the course of the menstrual cycle. These effects of ESN364 were reversible upon cessation of drug treatment. Together these data support the proposed role of neurokinin B-NK3R signaling in the control of pulsatile GnRH secretion. Furthermore, in contrast to GnRH antagonists, NK3R antagonists induce a partial suppression of estradiol and thereby offer a viable therapeutic approach to the treatment of ovarian sex hormone disorders with a mitigated risk of menopausal-like adverse events in response to long-term drug exposure.

A Reevaluation of the Question: Is the Pubertal Resurgence in Pulsatile GnRH Release in the Male Rhesus Monkey (Macaca mulatta) Associated With a Gonad-Independent Augmentation of GH Secretion?

A somatic signal has been posited to trigger the pubertal resurgence in pulsatile GnRH secretion that initiates puberty in highly evolved primates. That GH might provide such a signal emerged in 2000 as a result of a study reporting that circulating nocturnal GH concentrations in castrated juvenile male monkeys increased in a 3-week period immediately preceding the pubertal resurgence of LH secretion. The present study was conducted to reexamine this intriguing relationship, again in an agonadal model. Four castrated juvenile male monkeys were implanted with indwelling jugular catheters, housed in remote sampling cages, and subjected to 24 hours of sequential blood sampling (every 30 min) every 2 weeks from 19.5 to 22 months of age. Twenty-four-hour profiles of circulating GH concentrations were analyzed using the pulse detection algorithm, PULSAR, and developmental changes in pulsatile GH release with respect to the initiation of the pubertal rise of LH secretion (week 0; observed between 22.5 and 32 mo of age) were examined for significance by a repeated-measures ANOVA. Changes in the parameters of pulsatile GH secretion, including mean 24-hour GH concentration and GH pulse frequency and pulse amplitude for 3 (n = 4) and 6 (n = 3) months before week 0 were unremarkable and nonsignificant. These findings fail to confirm those of the earlier study and lead us to conclude that the timing of the pubertal resurgence of GnRH release in the male monkey is not dictated by GH. Reasons for the discrepancy between the two studies are unclear.

Emerging association between androgen deprivation therapy and male meningioma: significant expression of luteinizing hormone-releasing hormone receptor in male meningioma

BACKGROUND

There is emerging data suggesting a potential risk for meningioma growth stimulation in patients on luteinizing hormone-releasing hormone (LHRH) analogs for prostate cancer. We examined the expression of LHRH receptor (LHRH-R), progesterone receptor (PR) and Ki67 labeling index (LI) in specimens from male meningioma (MM) and female meningioma (FM) patients.

METHODS

A total of 24 MM and 24 FM paraffin blocks were retrieved from our institution between 1991 and 2008. Sections from the paraffin blocks were stained with mouse monoclonal antibodies against LHRH-R, PR and Ki67. All male patients had no previous history of prostate cancer (PCa) or previous history of hormone therapy.

RESULTS

LHRH-R positivity was extensive in 92% of MM and 88% of FM samples, with both showing strong intensity (67% and 79%, respectively). PR was positive in 20 of 24 (83%) MM and 23 of 24 (96%) FM samples. MM is less likely to exhibit Ki67 LI >4% compared with FM.

CONCLUSIONS

The majority of MM and FM samples were strongly positive for LHRH-R expression and PR expression. The emerging association of androgen deprivation therapy and meningioma growth should be recognized in urological practice. Caution should be taken when considering LHRH agonist administration for patients with PCa and concurrent meningioma or previous history of meningioma.

Ovarian regulation of kisspeptin neurones in the arcuate nucleus of the rhesus monkey (macaca mulatta)

Tonic gonadotrophin secretion throughout the menstrual cycle is regulated by the negative-feedback actions of ovarian oestradiol (E₂) and progesterone. Although kisspeptin neurones in the arcuate nucleus (ARC) of the hypothalamus appear to play a major role in mediating these feedback actions of the steroids in nonprimate species, this issue has been less well studied in the monkey. In the present study, we used immunohistochemistry and in situ hybridisation to examine kisspeptin and KISS1 expression, respectively, in the mediobasal hypothalamus (MBH) of adult ovariectomised (OVX) rhesus monkeys. We also examined kisspeptin expression in the MBH of ovarian intact females, and the effect of E₂, progesterone and E₂ + progesterone replacement on KISS1 expression in OVX animals. Kisspeptin or KISS1 expressing neurones and pronounced kisspeptin fibres were readily identified throughout the ARC of ovariectomised monkeys but, on the other hand, in intact animals, kisspeptin cell bodies were small in size and number and only fine fibres were observed. Replacement of OVX monkeys with physiological levels of E₂, either alone or with luteal phase levels of progesterone, abolished KISS1 expression in the ARC. Interestingly, progesterone replacement alone for 14 days also resulted in a significant down-regulation of KISS1 expression. These findings support the view that, in primates, as in rodents and sheep, kisspeptin signalling in ARC neurones appears to play an important role in mediating the negative-feedback action of E₂ on gonadotrophin secretion, and also indicate the need to study further their regulation by progesterone.

Adrenal androgen concentrations increase during infancy in male rhesus macaques (Macaca mulatta)

This study investigated adrenal androgens (AA), gonadotropins, and cortisol in castrated and gonad-intact male rhesus macaques from birth through infancy. Blood samples were collected longitudinally from castrated (n = 6; weekly, 1-40 wk) and intact (n = 4; every other week, 1-17 wk) males. Plasma concentrations of AA were determined by liquid chromatography-tandem mass spectrometry, and plasma concentrations of cortisol and gonadotropins were determined by RIA. Dehydroepiandrosterone sulfate (DHEAS) concentrations increased almost threefold (to 8 wk), dehydroepiandrosterone (DHEA) increased more than eightfold (to 11 wk), and androstenedione doubled (to 15 wk) in five castrated infant males and declined continuously thereafter. A sixth castrated male had markedly different temporal patterns and concentrations (many times more than 2 SDs from the cohort mean) of AA and gonadotropins from first sampling (3 wk) and was excluded from analysis. Cortisol increased over 16 wk but correlated poorly with DHEAS. Luteinizing and follicle-stimulating hormones increased to peaks at 3 and 7 wk, respectively. Testis-intact males exhibited similar profiles, but with earlier peaks of DHEAS (5 wk) and DHEA and androstenedione (7 wk). Peak concentrations of DHEAS were lower and those of DHEA and androstenedione were higher in intact than castrated infants. Testosterone was undetectable in castrated males and >0.5 ng/ml in intact males but was not correlated with DHEA or DHEAS. These are the first data documenting a transient increase in AA secretion during infancy in an Old World primate and are consistent with the previously documented time course of zona reticularis development that accompanies increases in androgen synthetic capacity of the adrenal. The rhesus is a promising model for androgen secretion from the human adrenal cortex.

Evidence from the agonadal juvenile male rhesus monkey (Macaca mulatta) for the view that the action of neurokinin B to trigger gonadotropin-releasing hormone release is upstream from the kisspeptin receptor

Human genetics have revealed that kisspeptin signaling and neurokinin B (NKB) signaling are both required for robust pulsatile gonadotropin-releasing hormone (GnRH) release, and therefore for puberty and maintenance of adult gonadal function. How these two peptides interact to affect GnRH pulse generation remains a mystery. To address the hierarchy of the NKB and kisspeptin signaling pathways that are essential for GnRH release, two experiments were conducted using agonadal, juvenile male monkeys. Pituitary responsiveness to GnRH was first heightened by a pulsatile GnRH infusion to use the in situ pituitary as a bioassay for GnRH release. In the first experiment (n = 3), the kisspeptin receptor (KISS1R) was desensitized by a continuous 99-hour i.v. infusion of kisspeptin-10 (100 μg/h). During the last 4 h of continuous kisspeptin-10 infusion, desensitization of KISS1R was confirmed by failure of an i.v. bolus of kisspeptin-10 to elicit GnRH release. Desensitization of KISS1R was associated with a markedly blunted GnRH response to senktide. The response to senktide was progressively restored during the 72 h following termination of continuous kisspeptin-10. An analogous design was employed in the second experiment (n = 2) to desensitize the NKB receptor (neurokinin 3 receptor, NK3R) by administration of a continuous 48-hour i.v. infusion of senktide (200 μg/h). While a bolus of senktide during the last 3 h of continuous senktide administration failed to elicit GnRH release, thus confirming desensitization of NK3R, the ability of kisspeptin to stimulate GnRH was unimpaired. The foregoing findings support the view that NKB stimulation of GnRH release is upstream from KISS1R.

Neurokinin B stimulates GnRH release in the male monkey (Macaca mulatta) and is colocalized with kisspeptin in the arcuate nucleus

Human genetics indicate that kisspeptin and neurokinin B (NKB) signaling are necessary for generating pulsatile LH release and therefore for initiation of puberty and maintaining gonadal function. In the present study, male monkeys were employed to examine 1) whether activation of the NKB receptor (NK3R) is associated with GnRH release, and 2) hypothalamic localization of these peptides using immunofluorescence histochemistry. Agonadal juveniles, in which pituitary responsiveness to GnRH was heightened by GnRH priming, were employed to indirectly examine GnRH-releasing actions of NK3R and kisspeptin receptor agonists by tracking LH after their i.v. injection. Castrated adults were used for immunohistochemistry. Single i.v. injections of NKB or senktide (an NK3R agonist) elicited robust LH discharges that were abolished by GnRH receptor antagonism (acyline) confirming the ligands' hypothalamic action. Intermittent infusion of senktide (1-min pulse every hour for 4 h), in contrast to that of kisspeptin, failed to sustain pulsatile GnRH release. Repetitive senktide injections did not compromise the GnRH-releasing action of kisspeptin. NKB and kisspeptin were colocalized in perikarya of the arcuate nucleus and in axonal projections to the median eminence, confirming earlier findings in sheep. These results are consistent with the human genetics, and indicate that although brief activation of NK3R stimulates GnRH release, repetitive stimulation of this pathway, in contrast to that of kisspeptin receptor, fails to sustain pulsatile GnRH release. In addition, the data provide a platform for future elucidation of the interactions between NKB and kisspeptin that are required for generating pulsatile GnRH release in primates.

Studies of the localisation of kisspeptin within the pituitary of the rhesus monkey (Macaca mulatta) and the effect of kisspeptin on the release of non-gonadotropic pituitary hormones

Kisspeptin neurones in the arcuate nucleus play a pivotal role in the regulation of hypothalamic gonadotrophin-releasing hormone (GnRH) secretion in higher primates. To examine whether kisspeptin also influences the function of the primate pituitary directly, two experiments were performed in adult male rhesus monkeys. First, the distribution of kisspeptin-containing cells in the pituitary was described using fluorescence immunohistochemistry. Second, the secretion of non-gonadotrophin adenohypophysial hormones [growth hormone (GH), prolactin and thyroid-stimulating hormone (TSH)] and cortisol in response to i.v. kisspeptin administration was examined. Eight animals were deeply anaesthetised and transcardially perfused with 4% paraformaldehyde. Fluorescence immunohistochemistry was performed on 25-microm thick free-floating pituitary sections to localise immunopositive kisspeptin cells and to examine their relationship with immunostaining for luteinising hormone (LH), follicle-stimulating hormone, GH, prolactin, alpha-melanocyte-stimulating hormone (MSH), adrenocorticotrophic hormone (ACTH) and GnRH. Kisspeptin cells were found in the intermediate lobe of all animals and, in four monkeys, this neuropeptide was also observed in cells scattered in the periphery of the anterior lobe. Kisspeptin colocalised with alpha-MSH-immunopositive cells in the intermediate lobe and, in 50% of the monkeys, with ACTH-immuunopositive cells in the periphery of the adenohypophysis. There was no evidence for colocalisation of kisspeptin with gonadotrophs, somatotrophs or lactotrophs. Beaded kisspeptin axons were observed in the neural lobe. In addition, assay of plasma samples that had been collected for a previous study documenting kisspeptin-10-induced LH release in male monkeys revealed that kisspeptin administration failed to influence circulating concentrations of GH, prolactin, TSH and cortisol. Release of all four of these non-gonadotrophic hormones, however, was stimulated markedly by NMDA, which is considered to act centrally. Although the morphological findings obtained in the present study are consistent with the notion that kisspeptin may act directly at the level of the pituitary, the nature of such an action remains to be defined.

Leptin is associated with blood pressure and hypertension in women from the National Heart, Lung, and Blood Institute Family Heart Study

Leptin is a key neuroendocrine hormone regulating food intake, metabolism, and fat accumulation, and it may also affect blood pressure and contribute to hypertension through sympathetic activation in the vasculature or at the renal level. Although previous studies have shown that the distribution of leptin is significantly different between males and females, as is the risk of hypertension between males and females, results regarding the role of leptin in the gender-specific regulation of blood pressure are controversial. Thus, we performed family-based association analyses in the National Heart, Lung, and Blood Institute Family Heart Study to test the hypothesis that LEPTIN gene variants and the plasma leptin level influence variability in blood pressure and the risk of hypertension differently by gender. We identified significant associations between LEPTIN single nucleotide polymorphisms with blood pressure and hypertension, but in postmenopausal women only. We also identified significant associations between plasma leptin levels and both blood pressure and hypertension in women. The current study supports a role for LEPTIN and plasma leptin levels in blood pressure regulation in women. It also provides insight into the gender differences in hypertension, as well as the differential distribution and activity of leptin in men and women.

Postmenopausal increase in KiSS-1, GPR54, and luteinizing hormone releasing hormone (LHRH-1) mRNA in the basal hypothalamus of female rhesus monkeys

The G-protein coupled receptor, GPR54, and its ligand, kisspeptin-54 (a KiSS-1 derived peptide) have been reported to be important players in control of LHRH-1 release. However, the role of the GPR54 signaling in primate reproductive senescence is still unclear. In the present study we investigated whether KiSS-1, GPR54, and LHRH-1 mRNA in the brain change after menopause in female rhesus monkeys using quantitative real-time PCR. Results indicate that KiSS-1, GPR54, and LHRH-1 mRNA levels in the medial basal hypothalamus (MBH) in postmenopausal females (28.3+/-1.1 years of age, n=5) were all significantly higher than that in eugonadal adult females (14.7+/-2.1 years of age, n=9), whereas KiSS-1, GPR54, and LHRH-1 mRNA levels in the preoptic area (POA) did not have any significant changes between the two age groups. To further determine the potential contribution by the absence of ovarian steroids, we compared the changes in KiSS-1, GPR54, and LHRH-1 mRNA levels in young adult ovarian intact vs. young ovariectomized females. Results indicate that KiSS-1 and LHRH-1 mRNA levels in the MBH, not POA, in ovariectomized females were significantly higher than those in ovarian intact females, whereas GPR54 mRNA levels in ovariectomized females had a tendency to be elevated in the MBH, although the values were not quite statistically significant. Collectively, in the primate the reduction in the negative feedback control by ovarian steroids appears to be responsible for the aging changes in kisspeptin-GPR54 signaling and the elevated state of the LHRH-1 neuronal system.

The recreational drug ecstasy disrupts the hypothalamic-pituitary-gonadal reproductive axis in adult male rats

Reproductive function involves an interaction of three regulatory levels: hypothalamus, pituitary, and gonad. The primary drive upon this system comes from hypothalamic gonadotropin-releasing hormone (GnRH) neurosecretory cells, which receive afferent inputs from other neurotransmitter systems in the central nervous system to result in the proper coordination of reproduction and the environment. Here, we hypothesized that the recreational drug (+/-)-3,4-methylenedioxymethamphetamine (MDMA; 'ecstasy'), which acts through several of the neurotransmitter systems that affect GnRH neurons, suppresses the hypothalamic-pituitary-gonadal reproductive axis of male rats. Adult male Sprague-Dawley rats self-administered saline or MDMA either once (acute) or for 20 days (chronic) and were euthanized 7 days following the last administration. We quantified hypothalamic GnRH mRNA, serum luteinizing hormone concentrations, and serum testosterone levels as indices of hypothalamic, pituitary, and gonadal functions, respectively. The results indicate that the hypothalamic and gonadal levels of the hypothalamic-pituitary-gonadal axis are significantly altered by MDMA, with GnRH mRNA and serum testosterone levels suppressed in rats administered MDMA compared to saline. Furthermore, our finding that hypothalamic GnRH mRNA levels are suppressed in the context of low testosterone concentrations suggests that the central GnRH neurosecretory system may be a primary target of inhibitory regulation by MDMA usage.

Effect of continuous intravenous administration of human metastin 45-54 on the neuroendocrine activity of the hypothalamic-pituitary-testicular axis in the adult male rhesus monkey (Macaca mulatta)

In agonadal juvenile male monkeys, continuous administration of human metastin 45-54 (hu metastin 45-54) leads to desensitization of its receptor, G protein-coupled receptor 54 (GPR54), and decreased LH. The present study extended this observation to the adult male monkey, a more preclinically relevant model in which robust activity in the hypothalamic-pituitary-testicular axis is present. Continuous iv infusion of hu metastin 45-54 at either 200 or 400 microg/h elicited a marked rise in circulating LH that peaked 2-3 h after initiation of treatment. Thereafter, levels declined, and by 24 h, LH in metastin 45-54-infused animals was similar to control. LH release in response to an iv bolus of hu metastin 45-54 (10-30 microg) during the final 3 h of continuous infusion was truncated or abolished (low and high peptide dose, respectively). GPR54 desensitization by the high-dose metastin 45-54 infusion was associated with compromised pituitary response to a bolus GnRH injection (0.3 microg). LH pulse amplitude and pulse frequency were markedly suppressed during high-dose metastin 45-54 treatment. Surprisingly, the fidelity of the relationship between circulating testosterone (T) and LH was distorted during the high-dose peptide infusion. Thus, for a given concentration of LH, T levels were invariably higher during the high-dose metastin 45-54 infusion than during vehicle, suggesting that the peptide may exert direct actions on the testis to amplify T production. These findings support the notion that GPR54 is desensitized by continuous exposure to ligand, and they raise the possibility of an intratesticular role of GPR54.

Evidence that down regulation of hypothalamic KiSS-1 expression is involved in the negative feedback action of testosterone to regulate luteinising hormone secretion in the adult male rhesus monkey (Macaca mulatta)

In the male monkey, luteinising hormone (LH) secretion is regulated by a negative feedback action of testicular testosterone that is exerted indirectly at the hypothalamic level to decelerate pulsatile gonadotrophin-releasing hormone release (GnRH). The purpose of the present experiment was to investigate whether the kisspeptin-G protein-coupled receptor 54 (GPR54) signalling pathway is involved in mediating the action of testosterone to suppress GnRH release in the monkey, as has been indicated by studies of nonprimates. To this end, 12 castrated adult male rhesus monkeys were implanted with either testosterone containing or empty Silastic capsules. Testosterone treatment produced a square wave increment in circulating testosterone levels within the physiologic range. After suppression of LH and follicle-stimulating hormone secretion was established at 5-6 weeks of testosterone exposure, the animals were killed and expression of the genes encoding for kisspeptin, GPR54 and GnRH determined in the mediobasal hypothalamus and preoptic area of both treated and control animals using RNase protection assays. The suppression in pituitary gonadotrophin secretion was associated with a reduction in kisspeptin mRNA levels in the mediobasal hypothalamus, but not the preoptic area. GPR54 mRNA levels, on the other hand, were not influenced by testosterone treatment. These results are consistent with those previously reported for the rodent, and suggest that the neurobiology of the negative feedback action of testicular testosterone on LH secretion in the monkey, a representative higher primate, may be mediated by kisspeptinergic neurones upstream to the GnRH network.

Neuroendocrine regulation of prolactin secretion in adult female rhesus monkeys during different phases of the menstrual cycle: role of neuroexcitatory amino acid (NMA)

The present study attempts to examine the role of N-methyl-D, L-aspartate (NMDA) receptors in the central regulation of prolactin (PRL) secretion, which may be involved in ovarian function and its alteration by glutamate in various phases of the menstrual cycle of female rhesus monkeys (Macaca mulatta). The results suggest that the glutaminergic component of the control system, which governs PRL secretion by utilizing NMDA receptors, may have an important role in regulating changes in PRL secretion. The response of PRL during the luteal phase of the cycle was different from that observed in follicular and menstrual phases. Steroids may influence the NMDA-dependent drive to release PRL. N-methyl-D-aspartic acid (NMA) involvement in the regulation of PRL secretion may occur through activation of the PRL-stimulating system depending on the physiological state or steroidal milieu. It is possible, therefore, that the NMA-induced release of PRL-releasing factors (PRF) and PRL are enhanced in the presence of ovarian feedback.

Continuous human metastin 45-54 infusion desensitizes G protein-coupled receptor 54-induced gonadotropin-releasing hormone release monitored indirectly in the juvenile male Rhesus monkey (Macaca mulatta): a finding with therapeutic implications

The effect of continuous administration of the C-terminal fragment of metastin, the ligand for the G protein-coupled receptor, GPR54, on GnRH-induced LH secretion was examined in three agonadal, juvenile male monkeys whose responsiveness to GnRH was heightened by pretreatment with a chronic pulsatile iv infusion of synthetic GnRH. After bolus injection of 10 microg human (hu) metastin 45-54 (equivalent to kisspeptin 112-121), the GPR54 agonist was infused continuously at a dose of 100 microg/h and elicited a brisk LH response for approximately 3 h. This rise was then followed by a precipitous drop in LH despite continuous exposure of GPR54 to metastin 45-54. On d 4, during the final 3 h of the infusion, single boluses of hu metastin 45-54 (10 microg), N-methyl-DL-aspartic acid (NMDA) (10 mg/kg) and GnRH (0.3 microg) were administered to interrogate each element of the metastin-GPR54-GnRH-GnRH receptor cascade. Although the NMDA and GnRH boluses were able to elicit LH pulses, that of hu metastin 45-54 was not, demonstrating functional integrity of GnRH neurons (NMDA) and GnRH receptors (NMDA and GnRH) but desensitization of GPR54. The desensitization of GPR54 by continuous hu metastin 45-54 administration has therapeutic implications for a variety of conditions currently being treated by GnRH and its analogs, including restoration of fertility in patients with abnormal GnRH secretion (i.e. idiopathic hypogonadotropic hypogonadism and hypothalamic amenorrhea) and selective, reversible suppression of the pituitary-gonadal axis to achieve suppression of gonadal steroids (i.e. precocious puberty, endometriosis, uterine fibroids, and prostate cancer).

Repetitive activation of hypothalamic G protein-coupled receptor 54 with intravenous pulses of kisspeptin in the juvenile monkey (Macaca mulatta) elicits a sustained train of gonadotropin-releasing hormone discharges

The purpose of the present study was to further examine the hypothesis that activation of G protein-coupled receptor 54 (GPR54) signaling at the end of the juvenile phase of primate development is responsible for initiation of gonadarche and the onset of puberty. Accordingly, we determined whether repetitive iv administration of the GPR54 receptor agonist kisspeptin-10 (2 microg as a brief 1-min infusion once every hour for 48 h) to the juvenile male rhesus monkey would prematurely elicit sustained, pulsatile release of hypothalamic GnRH, the neuroendocrine trigger for gonadarche. GnRH release was monitored indirectly by measuring LH secretion from the in situ pituitary, the GnRH responsiveness of which had been heightened before the experiment with an intermittent iv infusion of synthetic GnRH. Agonadal animals (n = 4) were employed to eliminate any confounding and secondary effects of changing feedback signals from the testis. The first brief infusion of kisspeptin-10 evoked an LH discharge that mimicked those produced by GnRH priming, and this was followed by a train of similar LH discharges in response to hourly activation of GPR54 by repetitive kisspeptin-10 administration. Concomitant treatment with a GnRH receptor antagonist, acyline, abolished kisspeptin-10-induced LH release. Repetitive kisspeptin-10 administration also provided a GnRH-dependent signal to FSH secretion. These findings are consistent with the notion that, in primates, the transition from the juvenile (attenuated GnRH release) to pubertal (robust GnRH release) state is controlled by activation of GPR54 resulting from increased expression of hypothalamic KiSS-1 and release of kisspeptin in this region of the brain.

Increased expression of forebrain GnRH mRNA and changes in testosterone negative feedback following pubertal maturation

Pubertal development is associated with increased activity of the gonadotropin releasing hormone (GnRH) neuronal system and rising gonadal steroid levels. The purpose of this study was to determine whether different circulating levels of testosterone affect GnRH mRNA and luteinizing hormone (LH) to the same degree prior to and following pubertal maturation. Pre- and post-pubertal male Syrian hamsters were gonadectomized and treated with timed-release testosterone pellets (0, 0.5, 1.5, or 2.5mg) for one week. Following treatment, three separate brain tissue dissections containing the majority of GnRH cell bodies, tenia tecta and medial septum (TT/MS), diagonal band of Broca/organum vasculosum of the lamina terminalis (DBB/OVLT), and preoptic area (POA), were analyzed for GnRH mRNA levels by RNase protection assay and terminal plasma luteinizing hormone concentrations were determined by radioimmunoassay. Pre-pubertal animals were more sensitive to testosterone negative feedback on LH. Conversely, the ability of testosterone to reduce GnRH mRNA was much greater after pubertal development. Specifically, GnRH mRNA in the TT/MS was considerably higher in adults, and testosterone reduced GnRH mRNA in a dose-dependent manner only in adults. These data indicate that although testosterone is a powerful suppressor of LH release before puberty, it does not have appreciable control over GnRH mRNA until after puberty. Furthermore, the pubertal increase in GnRH mRNA appears to occur via steroid feedback-independent mechanisms in the male Syrian hamster.

Neuropeptide Y gene expression in male sheep: influence of photoperiod and testosterone

The frequency of pulsatile release of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) is high in the breeding season and low in the nonbreeding season. These alterations in the patterns of GnRH and LH release are due to an interaction of daylength and gonadal steroid negative feedback. A vast amount of data indicates that steroid-responsive neural systems may play a role in regulating seasonal changes in GnRH release. One candidate system is neuropeptide Y (NPY). To determine the independent and interactive influences of photoperiod and steroid exposure on NPY mRNA levels, we used hypothalamic tissue from four groups (n = 4 per group) of castrated male sheep that were simultaneously housed in photochambers and exposed to: (1) a 16L:8D photoperiod (LD); (2) LD and implanted with testosterone (LD + T); (3) a 10L:14D photoperiod (SD), and (4) SD + T. Circulating levels of T averaged 2.8 +/- 0.2 ng/ml in implanted animals, but were undetectable in nonimplanted males. Mean LH levels were significantly reduced (p < 0.01) in the LD + T group as compared with the other groups which did not differ from each other. The silver grain area per NPY neuron in the arcuate nucleus, as assessed by in situ hybridization, was inversely related to mean LH values, with the grain area per cell being significantly greater (p < 0.05) for LD + T males than for all other groups which did not differ from each other. NPY cell numbers were not significantly different (p > 0.10) among the treatment groups. These results show that NPY mRNA expression is increased in male sheep during a LD photoperiod in a T-dependent manner. Our data are consistent with the idea that NPY is involved in the seasonal regulation of GnRH and LH release in the male sheep.

Central nervous system receptors involved in mediating the inhibitory action of neuropeptide Y on luteinizing hormone secretion in the male rhesus monkey (Macaca mulatta)

An earlier finding that gonadotropin-releasing hormone (GnRH) secretion may be triggered prematurely in the juvenile male monkey by central administration of 1229U91, a Y1 receptor antagonist, contributed to our current hypothesis that neuropeptide Y (NPY) is a major component of the brake that holds pulsatile GnRH release in check during prepubertal development in primates. However, 1229U91 is also a Y4 receptor agonist, and the present study was conducted to further examine the role of the Y1 receptor in mediating the putative inhibitory action of NPY on GnRH release. Agonadal juvenile and postpubertal male monkeys were implanted with i.v. and i.c.v. cannulae to gain continuous access to the venous and cerebroventricular circulations without sedation. Luteinizing hormone (LH) secretion was measured to provide an indirect index of GnRH release. The specific Y1 antagonists, VD-11 (476 microg; n = 4) and isopropyl 3-chloro-5-[1-((6-[2-(5-ethyl-4-methyl-1,3-thiazol-2-yl)ethyl]-4-morpholin-4-ylpyridin-2-yl)amino)ethyl]phenylcarbamate (Compound A, 300 microg; n = 4), did not mimic the stimulatory action of 1229U91 on GnRH secretion in the juvenile male monkey. Additionally, neither NPY (200 microg; n = 2), a general Y receptor agonist, nor rPP (100 microg; n = 4), a Y4 agonist, mimicked the action of 1229U91 in stimulating GnRH release. Moreover, previous exposure of the hypothalamus of juvenile monkeys (n = 5) to NPY (660 microg) failed to block 1229U91-induced (200 microg) GnRH release. However, the action of NPY (364 microg) in inhibiting GnRH release postpubertally was attenuated by 1229U91 (300 microg). We conclude that, although the action of exogenous NPY to suppress GnRH release from the postpubertal hypothalamus appears to be mediated, at least in part, by the Y1 receptor, the existence of a Y1 receptor pathway inhibitory to GnRH release in the prepubertal hypothalamus remains to be substantiated.

Sex differences in estrogen-dependent transcription of gonadotropin-releasing hormone (GnRH) gene revealed in GnRH transgenic mice

The mechanisms through which gonadal steroids exert feedback actions on the activity of the GnRH neurons are not understood. Using a series of GnRH-LacZ transgenic mice we have examined the manner in which gonadal steroids suppress GnRH mRNA expression in male and female mice. The long-term gonadectomy of 5.5-GNZ-3.5 transgenic mice resulted in significant increases in cellular GnRH mRNA expression (P < 0.05) and plasma LH concentrations (P < 0.01) in both sexes. However, cellular levels of LacZ mRNA and beta-galactosidase, which provide an index of GnRH gene transcription, were only elevated in males after gonadectomy. This sexually differentiated response was also observed in mice gonadectomized for 2 wk. Estrogen replacement in gonadectomized males returned transgene expression to intact levels. Experiments in transgenic mice with 3' and 5' deleted GnRH-LacZ constructs revealed that the suppressive influence of estrogen on LacZ transcription in the male required a critical element located between -5.2 and -1.7 kb of the GnRH promoter. These studies show that the suppression of GnRH mRNA expression by estrogen in the male involves a decrease in GnRH gene transcription that is dependent on a distal GnRH promoter element. The same mechanism does not exist in females, indicating that gonadal steroids suppress GnRH mRNA levels in a sexually dimorphic manner.

Ovarian steroids differentially modulate the gene expression of gonadotropin-releasing hormone neuronal subtypes in the ovariectomized cynomolgus monkey

In the present study, we compared the morphology and distribution of neurons expressing GnRH gene transcripts in the hypothalamus and forebrain of the cynomolgus monkey to that of the human. As in the human, three subtypes of GnRH neurons were identified. Type I GnRH neurons were small, oval cells with high levels of gene expression and were located within the basal hypothalamus. Type II GnRH neurons were small and sparsely labeled and were widely scattered in the hypothalamus, midline nuclei of the thalamus, and extended amygdala. Type III neurons displayed magnocellular morphology and intermediate labeling intensity and were located in the nucleus basalis of Meynert, caudate, and amygdala. In a second experiment, we determined the effect of estrogen or estrogen plus progesterone on the gene expression of GnRH neurons in the brains of young, ovariectomized cynomolgus monkeys. We report that hormone treatment resulted in a significant decrease in GnRH mRNA in type I neurons within the basal hypothalamus of ovariectomized monkeys. In contrast, there was no effect of hormone treatment on the gene expression of type III GnRH neurons in the nucleus basalis of Meynert. The present findings provide evidence that the increase in gene expression of type I GnRH neurons in postmenopausal women is secondary to the ovarian failure of menopause. The differential responses of type I and III GnRH neurons to hormone treatment provide additional evidence that distinct subpopulations of neurons expressing GnRH mRNA exist in the primate hypothalamus.

Leptin's sexual dimorphism results from genotype by sex interactions mediated by testosterone

OBJECTIVE

Recent studies have reported the existence of marked sexual dimorphism in serum leptin levels in humans, with women having approximately three times the levels of men. As we have shown for other measures of adiposity, such sexual dimorphism can arise from a special case of genotype by environment interaction, that of genotype by sex interaction.

RESEARCH METHODS AND PROCEDURES

Using maximum likelihood-based variance decomposition techniques, we examined the genetic and environmental architecture of sexual dimorphism in serum leptin levels in 1147 Mexican Americans from the San Antonio Family Heart Study.

RESULTS

Both the genetic and environmental variances for this trait differed significantly between the sexes (p < 0.001 and p < 0.01, respectively), with women displaying larger values for both components. We found significant evidence that different genes influence variation in serum leptin levels between the two sexes (p = 0.05). Furthermore, this pattern of sexual dimorphism in serum leptin levels persisted even after accounting for the effects of either the percentage of body fat or total body fat. However, this pattern of sexual dimorphism was eliminated after accounting for the effects of testosterone.

DISCUSSION

These findings suggest that the sexual dimorphism seen in leptin levels is not simply explained as differences in total adiposity between the sexes. We conclude that the genes, which influence variation in serum leptin levels, are differentially expressed depending on sex, and that the sexes also show differences in response of the expression of this obesity-related trait to unmeasured residual effects.

Are POMC neurons targets for sex steroids in the arcuate nucleus of the rat?

Testosterone alters the expression of proopiomelanocortin (POMC) mRNA in the neurons of the arcuate nucleus. While observations suggest that both estrogen and androgen receptors (AR) can mediate this action, only a negligible number of POMC neurons has previously been shown to contain estrogen receptor (ER)-alpha. To determine whether the putative action of testosterone is mediated via ER-beta or AR we double immuno- labeled hypothalamic sections from colchicine-pretreated male rats. Only few cells were immunostained for ER-beta and they were never found to co-localize POMC. In spite of the overlap in the anatomical distribution, only 3% of POMC cells appeared to contain AR. These results suggest that sex steroids have an indirect effect on most POMC neurons.

Androgen depletion activates telomerase in the prostate of the nonhuman primate, Macaca mulatta

BACKGROUND

The activity of telomerase, an enzyme that synthesizes telomeric repeats at the ends of chromosomes, is not detectable in normal human prostate. However, the majority of human prostate cancers exhibit telomerase activity. Since androgens play a major role in prostate tumorigenesis, we investigated the effect of androgen-depletion on the expression of telomerase activity in the prostate.

METHODS

Adult male rhesus monkeys were either bilaterally castrated or subjected to sham surgery (n = 5 each). Approximately 6 weeks later, the animals were killed and the different regions of the prostate gland were removed and frozen immediately. Telomerase activity was assayed using the telomeric repeat amplification protocol.

RESULTS

All five regions of the prostate from sham operated control animals failed to exhibit telomerase activity. In the castrated monkey, all regions of the prostate, except for the anterior lobe, expressed high levels of telomerase activity.

CONCLUSIONS

Our results indicate that in monkeys, androgen-ablation leads to up-regulation of telomerase activity. The negative-regulation of telomerase activity by androgens is probably lost during prostate tumorigenesis.

Pituitary follistatin and activin gene expression, and the testicular regulation of FSH in the adult Rhesus monkey (Macaca mulatta)

In rats, FSHbeta gene expression and FSH secretion are increased and decreased, respectively, by pituitary activin and follistatin. Because little information is available on the paracrine control of FSH secretion in the primate, follistatin and activin/inhibin beta(B) messenger RNA (mRNA) levels were measured in pituitaries of adult male rhesus monkeys 6 weeks after castration or sham surgery (n = 5/group). Follistatin mRNA was determined by quantitative RT-PCR assay using oligonucleotide primers designed to span exons 3-5 of the human follistatin gene. Activin/inhibin beta(B) mRNA levels were measured by ribonuclease protection. Orchidectomy resulted in a 100-fold increase in plasma FSH concentrations and a 60-fold rise in those of LH. In castrated monkeys, levels of mRNA encoding FSHbeta, LHbeta, alpha- subunit, and GnRH receptor (GnRH-R) were increased 21-, 2.1-, 1.7-, and 1.7-fold, respectively (P < 0.01). Levels of pituitary follistatin and activin/inhibin beta(B) mRNAs, however, were similar in castrated and intact animals. These data suggest that the paracrine control of FSH secretion in the male differs substantially in primates and rodents. Specifically, the relatively greater postcastration rise in FSHbeta gene expression and FSH secretion in the adult male monkey may result because in this species pituitary follistatin gene expression does not increase after orchidectomy, as it does in the rat.

Neurobiological bases underlying the control of the onset of puberty in the rhesus monkey: a representative higher primate

The purpose of this article is to discuss our understanding of the neurobiological mechanisms that govern the timing of the onset of puberty in the rhesus monkey, a representative higher primate, and, whenever possible, to place findings obtained from studies of this macaque in perspective with those for the human situation. Specifically, the dynamics in the postnatal ontogeny of hypothalamic GnRH gene expression and release are described, and the roles of neuropeptide Y and gamma-aminobutyric acid in imposing the restraint on pulsatile GnRH release during juvenile development are examined. Finally, the hypothesis that circulating leptin provides the signal that times the reaugmentation of pulsatile GnRH release at the termination of juvenile development, and therefore triggers the onset of primate puberty, is discussed.

Gonadal steroids and energy homeostasis in the leptin era

Gonadal steroids influence food intake and body weight. Although the specific mechanisms underlying these effects are not clear, a consideration of their effects in the context of current models of energy homeostasis may ultimately lead to the identification of these mechanisms. When compared with leptin, the prototypical humoral signal of energy balance, sex steroids share many common properties related to food intake and body weight. Specifically, gonadal steroids circulate in proportion to fat mass and current energy balance, and administration of these compounds influences food intake, energy expenditure, body weight, and body composition. Moreover, both estrogens and androgens modulate central nervous system effectors of energy homeostasis that are targets for the action of leptin, including pathways that contain neuropeptide Y, pro-opiomelanocortin, or melanin-concentrating hormone. Sex steroids and leptin also regulate one another's production. Although gonadal steroids, unlike leptin, are clearly not critical to the maintenance of normal energy homeostasis, they do appear to function as physiologic modulators of this process. Identifying the specific central mediators of their effects will contribute to our understanding of their role in energy homeostasis.

Neuropeptide Y: A hypothalamic brake restraining the onset of puberty in primates

The adult reproductive axis is driven by an intermittent discharge of gonadotropin-releasing hormone (GnRH) generated by a network of hypothalamic neurons known as the GnRH pulse generator. Although this signal generator is operational in infant primates, puberty in these species is delayed by activation shortly after birth of a central neural mechanism that holds GnRH release in check during juvenile development. Here, we show that, in the male rhesus monkey, the postnatal pattern in GnRH pulse generator activity is inversely related to that in neuropeptide Y (NPY) gene and protein expression in the mediobasal hypothalamus and that central administration of an NPY Y(1) receptor antagonist to juvenile animals elicits precocious GnRH release. Cell imaging indicated that the developmentally regulated NPY neurons may be located in regions dorsal to the arcuate nucleus. These findings lead us to propose that NPY is a fundamental component of the neurobiological brake restraining the onset of puberty in primates.