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

Neurobiology of puberty and its disorders

Puberty, which in humans is considered to include both gonadarche and adrenarche, is the period of becoming capable of reproducing sexually and is recognized by maturation of the gonads and development of secondary sex characteristics. Gonadarche referring to growth and maturation of the gonads is fundamental to puberty since it encompasses increased gonadal steroid secretion and initiation of gametogenesis resulting from enhanced pituitary gonadotropin secretion, triggered in turn by robust pulsatile GnRH release from the hypothalamus. This chapter reviews the development of GnRH pulsatility from before birth until the onset of puberty. In humans, GnRH pulse generation is restrained during childhood and juvenile development. This prepubertal hiatus in hypothalamic activity is considered to result from a neurobiological brake imposed upon the GnRH pulse generator resident in the infundibular nucleus. Reactivation of the GnRH pulse generator initiates pubertal development. Current understanding of the genetics and physiology of the brake will be discussed, as will hypotheses proposed to account for timing the resurgence in pulsatile GnRH and initiation of puberty. The chapter ends with a discussion of disorders associated with precocious or delayed puberty with a focus on those with etiologies attributed to aberrant GnRH neuron anatomy or function. A pediatric approach to patients with pubertal disorders is provided and contemporary treatments for both precocious and delayed puberty outlined.

Father absence, age at menarche, and genetic confounding: A replication and extension using a polygenic score

Father absence has a small but robust association with earlier age at menarche (AAM), likely reflecting both genetic confounding and an environmental influence on life history strategy development. Studies that have attempted to disambiguate genetic versus environmental contributions to this association have shown conflicting findings, though genomic-based studies have begun to establish the role of gene-environment interplay in the father absence/AAM literature. The purpose of this study was to replicate and extend prior genomic work using the Avon Longitudinal Study of Parents and Children (ALSPAC), a prospective longitudinal cohort study (N = 2,685), by (a) testing if an AAM polygenic score (PGS) could account for the father absence/AAM association, (b) replicating G×E research on lin-28 homolog B (LIN28B) variation and father absence, and (c) testing the G×E hypothesis using the PGS. Results showed that the PGS could not explain the father absence/AAM association and there was no interaction between father absence and the PGS. Findings using LIN28B largely replicated prior work that showed LIN28B variants predicted later AAM in father-present girls, but this AAM-delaying effect was absent or reversed in father-absent girls. Findings are discussed in terms genetic confounding, the unique biological role of LIN28B, and using PGSs for G×E tests.

Neuroendocrine mechanisms of puberty in non-human primates

An increase in pulsatile release of gonadotropin releasing hormone (GnRH) initiates puberty in mammalian species. While mutations in KISS1 and TAC3 and their receptors, KISS1R and NK3R, respectively, result in the absence or abnormal timing of puberty, the neurocircuitry and precise role of kisspeptin and neurokinin B (NKB) in regulation of the GnRH neurosecretory system in primate puberty remain elusive. This review discusses how kisspeptin and NKB signaling contributes to the pubertal increase in GnRH release in non-human primates and how remodeling of the NKB and kisspeptin signaling circuitry controlling GnRH neurons takes place during the progress of puberty. Importantly, the pubertal remodeling of kisspeptin and NKB signaling ensures efficient functions of the GnRH neurosecretory system that regulates sex-specific reproduction in primates.

Prepubertal overexposure to manganese induce precocious puberty through GABAA receptor/nitric oxide pathway in immature female rats

Gamma-aminobutyric acid (GABA) plays a critical role in regulation of gonadotropin-releasing hormone (GnRH) through GABA_A receptor (GABA_AR). Nitric oxide (NO) production has correlation with GABA and regulates GnRH secretion. This study was performed to examine the mechanisms by which manganese (Mn) accelerate puberty onset involves GABA_AR/NO pathway in the preoptic area-anterior hypothalamus (POA-AH) in immature female rats. First, female rats received daily dose of MnCl₂ 0 (saline), 2.5, 5 and 10 mg/kg b.w by oral gavage during postnatal day (PND) 21-32. Animals administered with 10 mg/kg MnCl₂ exhibited earlier puberty onset age and advanced ovary and uterus development than these in saline-treatment group. Furthermore, we found that decrease of GABA_AR result in elevated production of nitric oxide synthase1 (NOS1), NO and GnRH in the POA-AH. Second, we recorded the neuronal spikes alternation after perfusion with GABA_AR inhibitor bicuculline (BIC), GABA_AR agonist isoguvacine (isog), and MnCl₂ from the POA-AH in acute brain slices of PND21 rats. Spontaneous firing revealed a powerful GABA_AR-mediated action on immature POA-AH and confirm that MnCl₂ has a significant effect on GABA_AR. Third, we revealed that decrease in NOS1 and NO production by treatment with isog-alone or isog+MnCl₂ contribute to the decrease of GnRH in the POA-AH and a delayed puberty onset age compared to treatment with MnCl₂-alone. Together, these results suggested that excessive exposure to MnCl₂ stimulates NO production through decreased GABA_AR in the POA-AH to advance puberty onset in immature female rats.

Emerging Genetic and Epigenetic Mechanisms Underlying Pubertal Maturation in Adolescence

The adolescent transition begins with the onset of puberty which, upstream in the brain, is initiated by the gonadotropin-releasing hormone (GnRH) pulse generator that activates the release of peripheral sex hormones. Substantial research in human and animal models has revealed a myriad of cellular networks and heritable genes that control the GnRH pulse generator allowing the individual to begin the process of reproductive competence and sexual maturation. Here, we review the latest knowledge in neuroendocrine pubertal research with emphasis on genetic and epigenetic mechanisms underlying the pubertal transition.

Changes in the Responsiveness of the Hypothalamic-Pituitary-Gonadal Axis to Kisspeptin-10 Administration during Pubertal Transition in Boys

In human, no studies are available regarding changes in kisspeptin1 receptor (KISS1R) sensitivity during pubertal transition. In this study, healthy boys were classified into 5 Tanner stages of puberty (n = 5/stage). Human kisspeptin-10 was administered to boys at each Tanner stage and to adult men (n = 5) as an IV bolus for comparison. Serial blood samples were collected for 30 min pre- and 120 min post-kisspeptin injection periods at 30 min interval for measuring plasma LH and testosterone levels. There was insignificant effect of kisspeptin on LH and testosterone levels in boys of Tanner stages I-III. At Tanner stage IV, the effect of kisspeptin on plasma LH was insignificant. However, a paired t-test on a log-transformed data showed a significant (P < 0.05) increase in mean peak post-kisspeptin testosterone level. In Tanner stage V, a significant (P < 0.05) increase was observed in mean post-kisspeptin peak LH level as compared to the mean basal LH value. Post-kisspeptin plasma testosterone levels were also significantly (P < 0.05) increased as compared to the pre-kisspeptin level in Tanner stage V. Our data suggest that sensitivity of KISS1R on GnRH neurons with reference to LH stimulation in boys develops during the later part of puberty reaching to adult level at Tanner stage V. This trial is registered with WHO International Clinical Trial Registration ID NCT03286517.

Species Comparison of Postnatal Development of the Female Reproductive System

The postnatal development of the female reproductive system in laboratory animals and humans is reviewed. To enable a meaningful species comparison of the developing female reproductive system, common definitions of developmental processes were established with a focus made on aspects that are similar across species. A species comparison of the key endocrine, morphologic, and functional (onset of ovarian cycles and ability to reproduce) features of postnatal development of the female reproductive system is provided for human, nonhuman primate, dog, rat, and also mouse, minipig, and rabbit where possible. Species differences in the timing and control of female sexual maturation are highlighted. Additionally, a species comparison of the type and timing of female reproductive ovarian cycles was compiled. Human development provided the frame of reference, and then other common laboratory species were compared. The comparison has inherent challenges because the processes involved and sequence of events can differ greatly across species. Broad strokes were taken to assign a particular average age to an event and are to be used with caution. Methods of evaluation of postnatal female reproductive development in laboratory animals are discussed. Lastly, control rodent data from one of the author's laboratory on vaginal opening, first estrus, estrous cyclicity, and the histopathology involved with the developing female rat and mouse are presented. The information provided in this review is intended to be a resource for the design and interpretation of juvenile animal toxicity testing and ultimately, the relevance of the data to characterize potential risks for women and girls. Birth Defects Research 110:163-189, 2018. © 2017 Wiley Periodicals, Inc.

Altered Gene Expression Profiles of the Hypothalamic Arcuate Nucleus of Male Mice Suggest Profound Developmental Changes in Peptidergic Signaling

Neuropeptides of the hypothalamic arcuate nucleus (ARC) regulate important homeostatic and endocrine functions and also play critical roles in pubertal development. The altered peptidergic and aminoacidergic neurotransmission accompanying pubertal maturation of the ARC is not fully understood. Here we studied the developmental shift in the gene expression profile of the ARC of male mice. RNA samples for quantitative RT-PCR studies were isolated from the ARC of 14-day-old infantile and 60-day-old adult male mice with laser capture microdissection. The expression of 18 neuropeptide, 15 neuropeptide receptor, 4 sex steroid receptor and 6 classic neurotransmitter marker mRNAs was compared between the two time points. The adult animals showed increased mRNA levels encoding cocaine- and amphetamine-regulated transcripts, galanin-like peptide, dynorphin, kisspeptin, proopiomelanocortin, proenkephalin and galanin and a reduced expression of mRNAs for pituitary adenylate cyclase-activating peptide, calcitonin gene-related peptide, neuropeptide Y, substance P, agouti-related protein, neurotensin and growth hormone-releasing hormone. From the neuropeptide receptors tested, melanocortin receptor-4 showed the most striking increase (5-fold). Melanocortin receptor-3 and the Y1 and Y5 neuropeptide Y receptors increased 1.5- to 1.8-fold, whereas δ-opioid receptor and neurotensin receptor-1 transcripts were reduced by 27 and 21%, respectively. Androgen receptor, progesterone receptor and α-estrogen receptor transcripts increased by 54-72%. The mRNAs of glutamic acid decarboxylases-65 and -67, vesicular GABA transporter and choline acetyltransferase remained unchanged. Tyrosine hydroxylase mRNA increased by 44%, whereas type-2 vesicular glutamate transporter mRNA decreased by 43% by adulthood. Many of the developmental changes we revealed in this study suggest a reduced inhibitory and/or enhanced excitatory neuropeptidergic drive on fertility in adult animals.

Neuroendocrine control of the onset of puberty

This chapter is based on the Geoffrey Harris Memorial Lecture presented at the 8th International Congress of Neuroendocrinology, which was held in Sydney, August 2014. It provides the development of our understanding of the neuroendocrine control of puberty since Harris proposed in his 1955 monograph (Harris, 1955) that "a major factor responsible for puberty is an increased rate of release of pituitary gonadotrophin" and posited "that a neural (hypothalamic) stimulus, via the hypophysial portal vessels, may be involved." Emphasis is placed on the neurobiological mechanisms governing puberty in highly evolved primates, although an attempt is made to reverse translate a model for the timing of puberty in man and monkey to non-primate species.

Rhesus monkey brain development during late infancy and the effect of phencyclidine: a longitudinal MRI and DTI study

Early brain development is a complex and rapid process, the disturbance of which may cause the onset of brain disorders. Based on longitudinal imaging data acquired from 6 to 16 months postnatal, we describe a systematic trajectory of monkey brain development during late infancy, and demonstrate the influence of phencyclidine (PCP) on this trajectory. Although the general developmental trajectory of the monkey brain was close to that of the human brain, the development in monkeys was faster and regionally specific. Gray matter volume began to decrease during late infancy in monkeys, much earlier than in humans in whom it occurs in adolescence. Additionally, the decrease of gray matter volume in higher-order association regions (the frontal, parietal and temporal lobes) occurred later than in regions for primary functions (the occipital lobe and cerebellum). White matter volume displayed an increasing trend in most brain regions, but not in the occipital lobe, which had a stable volume. In addition, based on diffusion tensor imaging, we found an increase in fractional anisotropy and a decrease in diffusivity, which may be associated with myelination and axonal changes in white matter tracts. Meanwhile, we tested the influence of 14-day PCP treatment on the developmental trajectories. Such treatment tended to accelerated brain maturation during late infancy, although not statistically significant. These findings provide comparative information for the understanding of primate brain maturation and neurodevelopmental disorders.

Increasing LH pulsatility in women with hypothalamic amenorrhoea using intravenous infusion of Kisspeptin-54

BACKGROUND

Hypothalamic amenorrhea (HA) is the one of the most common causes of period loss in women of reproductive age and is associated with deficient LH pulsatility. High-dose kisspeptin-54 acutely stimulates LH secretion in women with HA, but chronic administration causes desensitization. GnRH has paradoxical effects on reproductive activity; we therefore hypothesized that a dose-dependent therapeutic window exists within which kisspeptin treatment restores the GnRH/LH pulsatility in women with HA.

AIM

The aim of the study was to determine whether constant iv infusion of kisspeptin-54 temporarily increases pulsatile LH secretion in women with HA.

METHODS

Five patients with HA each underwent six assessments of LH pulsatility. Single-blinded continuous iv infusion of vehicle or kisspeptin-54 (0.01, 0.03, 0.10, 0.30, or 1.00 nmol/kg/h) was administered. The LH pulses were detected using blinded deconvolution.

RESULTS

Kisspeptin increased LH pulsatility in all patients with HA, with peak responses observed at different doses in each patient. The mean peak number of pulses during infusion of kisspeptin-54 was 3-fold higher when compared with vehicle (number of LH pulses per 8 h: 1.6 ± 0.4, vehicle; 5.0 ± 0.5, kisspeptin-54, P < .01 vs vehicle). The mean peak LH pulse secretory mass during kisspeptin-54 was 6-fold higher when compared with vehicle (LH pulse secretory mass in international units per liter: 3.92 ± 2.31, vehicle; 23.44 ± 12.59, kisspeptin-54; P < .05 vs vehicle).

CONCLUSIONS

Kisspeptin-54 infusion temporarily increases LH pulsatility in women with HA. Furthermore, we have determined the dose range within which kisspeptin-54 treatment increases basal and pulsatile LH secretion in women with HA. This work provides a basis for studying the potential of kisspeptin-based therapies to treat women with HA.

Working memory performance and neural activity in prefrontal cortex of peripubertal monkeys

The dorsolateral prefrontal cortex matures late into adolescence or early adulthood. This pattern of maturation mirrors working memory abilities, which continue to improve into adulthood. However, the nature of the changes that prefrontal neuronal activity undergoes during this process is poorly understood. We investigated behavioral performance and neural activity in working memory tasks around the time of puberty, a developmental event associated with the release of sex hormones and significant neurological change. The developmental stages of male rhesus monkeys were evaluated with a series of morphometric, hormonal, and radiographic measures. Peripubertal monkeys were trained to perform an oculomotor delayed response task and a variation of this task involving a distractor stimulus. We found that the peripubertal monkeys tended to abort a relatively large fraction of trials, and these were associated with low levels of task-related neuronal activity. However, for completed trials, accuracy in the delayed saccade task was high and the appearance of a distractor stimulus did not impact performance significantly. In correct trials delay period activity was robust and was not eliminated by the presentation of a distracting stimulus, whereas in trials that resulted in errors the sustained cue-related activity was significantly weaker. Our results show that in peripubertal monkeys the prefrontal cortex is capable of generating robust persistent activity in the delay periods of working memory tasks, although in general it may be more prone to stochastic failure than in adults.

A single injection of kisspeptin-54 temporarily increases luteinizing hormone pulsatility in healthy women

BACKGROUND

Kisspeptin is a novel hypothalamic peptide which stimulates endogenous gonadotrophin releasing hormone (GnRH) secretion. A single subcutaneous bolus injection of kisspeptin-54 increases circulating luteinizing hormone (LH) levels in women, but its acute effects on LH pulsatility are not known.

AIMS

To investigate the effects of a single subcutaneous (sc) injection of kisspeptin-54 administration on LH pulsatility in healthy female volunteers.

METHODS

Six healthy female adult volunteers underwent 10-minute blood sampling for serum LH measurement for 8 h during the follicular phase of menstrual cycle. Sc bolus injection of saline or kisspeptin-54 (0·15, 0·30 or 0·60 nmol/kg) was administered 4 h after commencing the study. A previously described, blinded deconvolution method was used to detect LH pulses.

RESULTS

Mean number of LH pulses was increased significantly following 0·30 and 0·60 nmol/kg kisspeptin-54 when compared with saline (mean increase in number of LH pulses per 4 h, following injection: -0·17 ± 0·54, saline; +2·33 ± 0·56, 0·30 nmol/kg kisspeptin-54, P < 0·05 vs saline; +2·33 ± 0·80, 0·60 nmol/kg kisspeptin-54, P < 0·05 vs saline). LH pulse secretory mass increased following injection of 0·60 nmol/kg in five of six subjects, but the mean change in all subjects was non-significant when compared with saline (mean increase in pulse secretory mass in IU/l following injection: +0·35 ± 0·40, saline; +2·61 ± 1·17, 0·60 nmol/kg kisspeptin-54, P = 0·10 vs saline).

CONCLUSIONS

A single injection of kisspeptin-54 temporarily stimulates the number of LH pulses in healthy women. Further studies are required to investigate the therapeutic potential of kisspeptin-54 injection to restore LH pulsatility in patients with reproductive disorders caused by impaired GnRH secretion.

Environmental and social influences on neuroendocrine puberty and behavior in macaques and other nonhuman primates

This article is part of a Special Issue "Puberty and Adolescence". Puberty is the developmental period when the hypothalamic-pituitary-gonadal (HPG) axis is activated, following a juvenile quiescent period, and reproductive capacity matures. Although pubertal events occur in a consistent sequence, there is considerable variation between individuals in the onset and timing of pubertal events, with puberty onset occurring earlier in girls than in boys. Evidence in humans demonstrates that social and environmental context influences the timing of puberty onset and may account for some of the observed variation. This review analyzes the nonhuman primate literature, focusing primarily on rhesus macaques (Macaca mulatta), to examine the social and environmental influences on puberty onset, how these factors influence puberty in males and females, and to review the relationship between puberty onset of adult neuroendocrine function and sexual behavior. Social and environmental factors influence the timing of puberty onset and pubertal events in nonhuman primates, as in humans, and the influences of these factors differ for males and females. In nonhuman primates, gonadal hormones are not required for sexual behavior, but modulate the frequency of occurrence of behavior, with social context influencing the relationship between gonadal hormones and sexual behavior. Thus, the onset of sexual behavior is independent of neuroendocrine changes at puberty; however, there are distinct behavioral changes that occur at puberty, which are modulated by social context. Puberty is possibly the developmental period when hormonal modulation of sexual behavior is organized, and thus, when social context interacts with hormonal state to strongly influence the expression of sexual behavior.

The recent genetics of hypogonadotrophic hypogonadism - novel insights and new questions

The complex organization and regulation of the human hypothalamic-pituitary-gonadal axis render it susceptible to dysfunction in the face of a variety of genetic insults, leading to different degrees of hypogonadotrophic hypogonadism (HH). Although the genetic basis of some HH was recognized more than 60 years ago the first specific pathogenic defect, in the KAL1 gene, was only identified within the last 20 years. In the past decade, the rate of genetic discovery has dramatically accelerated, with defects in more than 10 genes now associated with HH. Several themes have emerged as the genetic basis of HH has gradually been uncovered, including the association of some genes such as FGFR1, FGF8, PROK2 and PROKR2, both with HH in association with hyposmia/anosmia (Kallmann syndrome) and with normosmic HH, thus blurring the clinical distinction between ontogenic and purely functional defects in the axis. Many examples of digenic inheritance of HH have also been reported, sometimes producing variable reproductive and accessory phenotypes within a family with non-Mendelian inheritance patterns. In strictly normosmic HH, human genetics has made a particularly dramatic impact in the past 6 years through homozygosity mapping in consanguineous families, first through identification of a key role for kisspeptin in triggering GnRH release, and very recently through demonstration of a critical role for neurokinin B in normal sexual maturation. This review summarises current understanding of the genetic architecture of HH, as well as its diagnostic and mechanistic implications.

Pubertal development and behavior: hormonal activation of social and motivational tendencies

Adolescence is a time of dramatic changes including rapid physical growth, the onset of sexual maturation, the activation of new drives and motivations, and a wide array of social and affective changes and challenges. This review focuses on behavioral changes in this interval and is organized by the claim that a key set of these adolescent changes are part of a more general re-orientation of social behavior. More specifically we hypothesize that pubertal maturation is associated with the activation of social and motivational tendencies, which in turn influence behavior and emotion in adolescence depending upon interactions with social context. We focus on evidence for two examples of these motivational changes: (1) increases in sensation-seeking (motivational tendency to want to experience high-intensity, exciting experiences) and (2) stronger natural interest in--and pursuit of--contact with peers and potential romantic partners. We consider how these motivational changes contribute to the broader social re-orientation of adolescence, including exploration of social experiences, development of skills and knowledge relevant to taking on adult social roles, individuation from family, and establishment of an individual identity, all of which represent core developmental tasks during this period in the life span (Blakemore, 2008; Dahl & Spear, 2004; Steinberg & Morris, 2000). The paper also emphasizes the importance of investigating and understanding the direct influences of puberty on behavior and disentangling these from the broader set of changes during adolescent development.

Kisspeptin and the regulation of the hypothalamic-pituitary-gonadal axis in the rhesus monkey (Macaca mulatta)

The present article reviews recent studies of monkeys and, in some cases, humans that have been conducted to examine the role of kisspeptin-GPR54 signaling in the regulation of the hypothalamic-pituitary-gonadal axis in higher primates. This area of peptide biology was initiated in 2003 by the discovery that loss of function mutations of GPR54 in man were associated with hypogonadotropic hypogonadism and absent or delayed puberty. Puberty in the monkey, an experimental model commonly used to study this fundamental developmental stage, is first described. This is followed by a review of the role of kisspeptin in the regulation of the postnatal ontogeny of GnRH pulsatility. The roles of kisspeptin in GnRH pulse generation and in the feedback loops governing gonadotropin secretion in primates are then discussed. A brief section on kisspeptin-GPR54 signaling at the pituitary and gonadal levels is also included. The review concludes with a discussion of the phenomenon of GPR54 downregulation by continuous exposure to kisspeptin and its therapeutic implications.

Kisspeptins and the control of gonadotropin secretion in humans

The kisspeptin hormones are a family of peptides encoded by the KiSS-1 gene, which bind to the G-protein coupled receptor-54 (GPR54). Interactions between kisspeptin and GPR54 are thought to play a critical role in reproduction. In agreement with animal data, kisspeptin-54 administration acutely stimulates the release of gonadotrophins in both male and female healthy subjects, with no observed adverse effects. Furthermore, its potency is comparable to those of other gonadotrophin secretagogues studied. The kisspeptin-GPR54 system thus offers a novel means of therapeutically manipulating the hypothalamo-pituitary-gonadal (HPG) axis in humans. This article aims to provide a focused review of the experimental data which inform us how kisspeptin influences the HPG axis in humans.

Kisspeptin: a novel regulator of reproductive function

The UK and international neuroendocrine community was deeply shocked and saddened the unbelievably premature death of Michael Harbuz in Bristol in 2006. Mick was a superb friend and colleague, and played a huge part in the development and activities of the British Neuroendocrine Group/British Society for Neuroendocrinology (BSN), serving as both Membership Secretary and Treasurer between 1999 and 2004. Mick was a leader in the field of neuroendocrine-immune interactions, and brought a great deal of charisma, humour and ability to meetings and conferences. He was also a passionate and committed supporter of the progress of young researchers and of their participation in neuroendocrine events. He recognised that today's postgraduate students and postdoctoral research fellows are tomorrow's neuroendocrine researchers, be it in academia, the health services or industry. To recognise Mick's great commitment to and enthusiasm for postgraduate education both in the University of Bristol and in the BSN, we decided to honour and remember him by instituting the 'Michael Harbuz Young Investigator Prize Lecture' to be delivered annually. Dr Waljit Dhillo from Imperial College London was the inaugural recipient of this award, and presented his lecture at the Annual Meeting of the BSN in Nottingham in September 2007, upon which this review is based. Recent evidence demonstrates that the neuropeptide kisspeptin and its receptor, GPR54, have a fundamental role in initiating the onset of puberty and are important in regulating reproductive function. This review discusses the evidence available from animals and humans demonstrating that kisspeptin potently stimulates the release of gonadotrophins by stimulating the release of gonadotrophin-releasing hormone and that a lack of kisspeptin or GPR54 results in reproductive failure.

Review. Do hormonal control systems produce evolutionary inertia?

Hormonal control systems are complex in design and well integrated. Concern has been raised that these systems might act as evolutionary constraints when animals are subject to anthropogenic environmental change. Three systems are examined in vertebrates, especially birds, that are important for assessing this possibility: (i) the hypothalamic-pituitary-gonadal (HPG) axis, (ii) the activational effects of sex steroids on mating effort behaviour, and (iii) sexual differentiation. Consideration of how these systems actually work that takes adequate account of the brain's role and mechanisms suggests that the first two are unlikely to be impediments to evolution. The neural and molecular networks that regulate the HPG provide both phenotypic and evolutionary flexibility, and rapid evolutionary responses to selection have been documented in several species. The neuroendocrine and molecular cascades for behaviour provide many avenues for evolutionary change without requiring a change in peripheral hormone levels. Sexual differentiation has some potential to be a source of evolutionary inertia in birds and could contribute to the lack of diversity in certain reproductive (including life history) traits. It is unclear, however, whether that lack of diversity would impede adaptation to rapid environmental change given the role of behavioural flexibility in avian reproduction.

Hypothalamic control of the pituitary-gonadal axis in higher primates: key advances over the last two decades

This review provides a brief historical background to the foundation of primate reproductive neuroendocrinology that was laid by Ernst Knobil during the late 1960s and early 1970s. This is followed by a discussion of studies conducted over the last two decades that I view as having contributed to the current understanding of the field of primate reproductive neuroendocrinology. The review concludes with a short summary of key questions that remain to be addressed.

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.

Molecular analysis of the neuropeptide Y1 receptor gene in human idiopathic gonadotropin-dependent precocious puberty and isolated hypogonadotropic hypogonadism

OBJECTIVE

To investigate the role of mutations or polymorphisms in the NPY-Y1R gene in human idiopathic central pubertal disorders.

DESIGN

Molecular studies.

SETTING

University hospital.

PATIENT(S)

Thirty-three patients with gonadotropin-dependent precocious puberty, 22 with hypogonadotropic hypogonadism, and 50 controls.

INTERVENTION(S)

Genomic DNA extraction, NPY-Y1R gene sequence analysis, cell-surface expression, and functional activity of an identified receptor variant.

MAIN OUTCOME MEASURE(S)

Results of sequencing, cell-surface receptor expression, and receptor function.

RESULT(S)

A heterozygous substitution of lysine (K) by threonine (T) at position 374 in the carboxyl terminal region of NPY-Y1R was identified in a girl with familial GDPP. Her mother, who had pubertal developmental at appropriate age, carried the same genetic variant. Introduction of the K374T variant into an expression vector containing the human NPY-Y1R complementary DNA led to a partial reduction in cell-surface expression of NPY-Y1R in transiently transfected HEK293 cells. This mutation did not lead to a significant reduction in NPY-stimulated activity of the receptor in this heterologous expression system. No other allelic variants of the NPY-Y1R gene were identified in patients or controls.

CONCLUSION(S)

We have identified an inherited heterozygous variant of the NPY-Y1R gene in a girl with precocious puberty; however, this most likely did not contribute to her phenotype. Mutations of the highly conserved NPY-Y1R gene do not appear to represent a frequent mechanism underlying human idiopathic central pubertal disorders.

Puberty and depression

Unipolar depression only becomes more common in girls than boys after the age of 13, as a result of an increased incidence of depressive episodes in girls at that time. This article reviews evidence that links multiple dimensions of maturation in the hypothalamo-pituitary-gonadal axis with this phenomenon. Effects of developmental status and timing have been implicated, but few studies have deployed either the measurement strategies or the statistical power needed to provide a satisfactory answer to the question regarding which components of puberty are most responsible.

Development of GnRH cells: Setting the stage for puberty

Cells containing gonadotropin-releasing hormone (GnRH) are essential not only for reproduction but also for neuromodulatory functions in the adult animal. A variety of studies have hinted at multiple origins for GnRH-containing cells in the developing embryo. We have shown, using zebrafish as a model system, that GnRH cells originate from precursors lying outside the olfactory placode: the region of the anterior pituitary gives rise to hypothalamic GnRH cells and the cranial neural crest gives rise to the GnRH cells of the terminal nerve and midbrain. Cells of both the forming anterior pituitary and cranial neural crest are closely apposed to the precursors of the olfactory epithelium during early development. Disruption of kallmann gene function results in loss of the hypothalamic but not the terminal nerve GnRH cells during early development. The GnRH proteins are expressed early in development and this expression is mirrored by the onset of GnRH receptor (GnRH-R) expression during early development. Thus the signaling of the GnRH neuronal circuitry is set up early in development laying the foundation for the GnRH network that is activated at puberty leading to reproductive function in the mature animal.

Development of GABA and glutamate signaling at the GnRH neuron in relation to puberty

The gonadotropin-releasing hormone (GnRH) neurons represent the critical cell type activated to induce puberty in mammals. However, the mechanisms underlying their activation remain unclear. As the principal amino acid neurotransmitters in the brain, GABA and glutamate are known to have critical roles in the development of neuronal networks. This review provides an update on what is known about GABA and glutamate signaling at the GnRH neuron across development. An examination of morphological, receptor subunit expression, and electrophysiological data suggest that GABAA receptor signaling develops in advance of glutamatergic signaling. However, compared with other networks, the switch from GABAA receptor depolarization to hyperpolarization of GnRH neurons is delayed until the time of puberty. These observations suggest that developing GnRH neurons exhibit a sequence of GABA-->glutamate signaling similar to that of other neuronal networks but that it is significantly elongated so as to only be complete by the time of puberty onset.

The male monkey as a model for the study of the neurobiology of puberty onset in man

This chapter is based on the material that was presented in the Symposium titled "Puberty in mechanistic perspective: animal models" at Sixth International Conference on the Control of the Onset of Puberty held in Evian, May 2005.

Activation of gonadotropin-releasing hormone neurons by kisspeptin as a neuroendocrine switch for the onset of puberty

We examined the role of kisspeptin and its receptor, the G-protein-coupled receptor GPR54, in governing the onset of puberty in the mouse. In the adult male and female mouse, kisspeptin (10-100 nM) evoked a remarkably potent, long-lasting depolarization of >90% of gonadotropin-releasing hormone (GnRH)-green fluorescent protein neurons in situ. In contrast, in juvenile [postnatal day 8 (P8) to P19] and prepubertal (P26-P33) male mice, kisspeptin activated only 27 and 44% of GnRH neurons, respectively. This developmental recruitment of GnRH neurons into a kisspeptin-responsive pool was paralleled by an increase in the ability of centrally administered kisspeptin to evoke luteinizing hormone secretion in vivo. To learn more about the mechanisms through which kisspeptin-GPR54 signaling at the GnRH neuron may change over postnatal development, we performed quantitative in situ hybridization for kisspeptin and GPR54 transcripts. Approximately 90% of GnRH neurons were found to express GPR54 mRNA in both juvenile and adult mice, without a detectable difference in the mRNA content between the age groups. In contrast, the expression of KiSS-1 mRNA increased dramatically across the transition from juvenile to adult life in the anteroventral periventricular nucleus (AVPV; p < 0.001). These results demonstrate that kisspeptin exerts a potent depolarizing effect on the excitability of almost all adult GnRH neurons and that the responsiveness of GnRH neurons to kisspeptin increases over postnatal development. Together, these observations suggest that activation of GnRH neurons by kisspeptin at puberty reflects a dual process involving an increase in kisspeptin input from the AVPV and a post-transcriptional change in GPR54 signaling within the GnRH neuron.

Isolated gonadotropic deficiency with and without anosmia: a developmental defect or a neuroendocrine regulation abnormality of the gonadotropic axis

Hypogonadotropic hypogonadism has been described in several human genetic diseases. Congenital isolated hypogonadotropic hypogonadism is classified into two categories: one that is associated with anosmia (Kallmann syndrome) and one that is apparently isolated. Mutations and deletions of the KAL1 gene, which encodes for a protein involved in cell adhesion, have been observed in many cases of the X-linked form of Kallmann syndrome. Recently, loss-of-function mutations of fibroblast growth factor receptor-1 (FGFR1) were associated with an autosomal dominant form of Kallmann syndrome. Genotype-phenotype correlations confirm the large spectrum of the phenotype due to FGFR1 mutations. Cases of isolated hypogonadotropic hypogonadism were considered to be idiopathic until the description of mutations of the gonadotropin releasing hormone receptor, luteinizing hormone and follicle stimulating hormone genes. However, defects in these genes only account for a small percentage of familial cases, which suggests that other proteins may be involved in regulation of the gonadotropic axis. We recently described GPR54 as one of these proteins by genome mapping in a very informative family. In vivo studies and genotype-phenotype correlations indicate that gonadotropic axis regulation by GPR54 occurs mainly at the level of the hypothalamus.

Pubertal hormones organize the adolescent brain and behavior

Maturation of the reproductive system during puberty results in elevated levels of gonadal steroid hormones. These hormones sculpt neural circuits during adolescence, a time of dramatic rewiring of the nervous system. Here, we review the evidence that steroid-dependent organization of the adolescent brain programs a variety of adult behaviors in animals and humans. Converging lines of evidence indicate that adolescence may be a sensitive period for steroid-dependent brain organization and that variation in the timing of interactions between the hormones of puberty and the adolescent brain leads to individual differences in adult behavior and risk of sex-biased psychopathologies.

The neuroendocrine timing of puberty

Puberty is the attainment of fertility, a process encompassing morphological, physiological and behavioural development. The increased hypothalamic secretion of the gonadotrophin-releasing hormone decapeptide (GnRH) is essential for the activation of the pituitary-gonadal axis at puberty. The GnRH secretory network initially develops and is temporarily active during species-specific periods of fetal/neonatal development, so puberty is the secondary reactivation of an existing system. From a neurobiological perspective, the timing of puberty is therefore a function of changes in the neural systems controlling GnRH release. The large variability between individuals in the onset and progression of puberty indicates that the timing of puberty is not simply a function of chronological age. Rather, the neurotransmitter and neuromodulatory systems that impact upon the GnRH secretory network convey information about metabolic fuels, energy stores and somatic development and, for many species, information about season and social environment. The clear links demonstrated between metabolic fuel availability and reproductive function in many animal models provides evidence that the earlier onset of pubertal development observed in girls in certain US study populations is likely to relate to the increasing prevalence of overweight and obesity in adolescents.

The neural basis of puberty and adolescence

The pubertal transition to adulthood involves both gonadal and behavioral maturation. A developmental clock, along with permissive signals that provide information on somatic growth, energy balance and season, time the awakening of gonadotropin releasing hormone (GnRH) neurons at the onset of puberty. High-frequency GnRH release results from disinhibition and activation of GnRH neurons at puberty onset, leading to gametogenesis and an increase in gonadal steroid hormone secretion. Steroid hormones, in turn, both remodel and activate neural circuits during adolescent brain development, leading to the development of sexual salience of sensory stimuli, sexual motivation, and expression of copulatory behaviors in specific social contexts. These influences of hormones on reproductive behavior depend in part on changes in the adolescent brain that occur independently of gonadal maturation. Reproductive maturity is therefore the product of developmentally timed, brain-driven and recurrent interactions between steroid hormones and the adolescent nervous system.

Reduced Growth Hormone Secretion Prolongs Puberty But Does Not Delay the Developmental Increase in Luteinizing Hormone in the Absence of Gonadal Negative Feedback1

Previous studies have shown that the growth hormone (GH) axis is important for timing the later stages of puberty in female monkeys. However, it is not clear whether these growth-related signals are important for the initiation of puberty and early pubertal events. The present study, using female rhesus monkeys, used two approaches to answer this question. Experiment 1 tested the hypothesis that reduced GH secretion would blunt the rise in nocturnal LH secretion in young (17 mo; n = 7) but not older adolescent ovariectomized females (29 mo; n = 6). Reduced GH secretion was induced by treating females with the sustained release somatostatin analogue formulation, Sandostatin LAR (625 microg/kg). Morning (0900-0930 h) and evening (2200-2230 h) concentrations of bioactive LH were higher in older adolescent compared to young adolescent females. However, diurnal concentrations were not affected by the inhibition of GH secretion in either age group when compared to the placebo-treated, control condition. Experiment 2 tested the hypothesis that reduced GH secretion induced in young juvenile females would delay the initial increase in nocturnal LH secretion and subsequent early signs of puberty. In order to examine this hypothesis, puberty in control females (n = 7) was compared to those in which puberty had been experimentally arrested until a late adolescent age (29 mo) by the use of a depot GnRH analogue, Lupron (750 microg kg(-1) mo(-1); n = 7). Once the analogue treatment was discontinued, the progression of puberty was compared to a group treated in a similar fashion but made GH deficient by continuous treatment with Sandostatin LAR (n = 6). Puberty occurred as expected in control females with the initial rise in evening LH at 21 mo, menarche at 22 mo, and first ovulation at 30 mo. As expected, Lupron arrested reproductive maturation, but elevations in morning and evening LH and menarche occurred within 2 mo of the cessation of Lupron in both Lupron and Lupron-GH-suppressed females. In contrast, first ovulation was delayed significantly in the Lupron-GH-suppressed females (41 mo) compared to the Lupron-only females (36 mo). These data indicate that within this experimental model, reduced GH secretion does not perturb the early stages of puberty but supports previous observations that the GH axis is important for timing the later stages of puberty and attainment of fertility. Taken together, the data indicate that factors that reduce GH secretion may have a deleterious effect on the completion of puberty.

Interrelationships between Hormones, Behavior, and Affect during Adolescence: Understanding Hormonal, Physical, and Brain Changes Occurring in Association with Pubertal Activation of the Reproductive Axis. Introduction to Part III

This paper summarizes the goals of this section and considers current knowledge about the association between hormonal changes that occur over pubertal development and the changes in behavior and brain function over the adolescent period. It reviews the cascade of neural and hormonal changes that occur with puberty; discusses mechanisms by which these changes can affect higher-order brain processes; reviews the current limited state of knowledge about links between puberty and changes in affect regulation in the adolescent period; identifies hurdles that have made progress in our understanding of these relationships difficult; and suggests areas for future investigation that will allow us to obtain a much more comprehensive understanding of these interrelationships. This overview of the physiological processes occurring at puberty indicates that puberty (1) encompasses changes in a number of neural systems; (2) results in altered secretion of a number of hormones; (3) involves hormones that are secreted in a pulsatile manner so that collection of a single blood sample does not clearly delineate hormone profiles; and (4) shows considerable individual variation in the rate of progression and in hormone secretion during progression. The important role that gonadal steroid hormones play throughout development and adulthood in regulating plastic changes in neuronal structure and function is noted, highlighting the need for further studies to determine the extent to which the dramatic increases in circulating steroid hormones at puberty modulate brain circuits that underlie changes in social behaviors, risk-taking behaviors, and cognitive function at adolescence.

In boys with abnormal developmental tempo, maturation of the skeleton and the hypothalamic-pituitary-gonadal axis remains synchronous

The primary mechanism that initiates puberty is unknown. One possible clue is that pubertal maturation often parallels skeletal maturation. Conditions that delay skeletal maturation also tend to delay the onset of puberty, whereas conditions that accelerate skeletal maturation tend to hasten the onset of puberty. To examine this relationship, we studied boys with congenital adrenal hyperplasia (n = 13) and familial male-limited precocious puberty (n = 22), two conditions that accelerate maturational tempo, and boys with idiopathic short stature (n = 18) in which maturational tempo is sometimes delayed. In all three conditions, the onset of central puberty generally occurred at an abnormal chronological age but a normal bone age. Boys with the greatest skeletal advancement began central puberty at the earliest age, whereas boys with the greatest skeletal delay began puberty at the latest age. Furthermore, the magnitude of the skeletal advancement or delay matched the magnitude of the pubertal advancement or delay. This synchrony between skeletal maturation and hypothalamic-pituitary-gonadal axis maturation was observed among patients within each condition and also between conditions. In contrast, the maturation of the hypothalamic-pituitary-gonadal axis did not remain synchronous with other maturational processes including weight, height, or body mass index. We conclude that in boys with abnormal developmental tempo, maturation of the skeleton and the hypothalamic-pituitary-gonadal axis remains synchronous. This synchrony is consistent with the hypothesis that in boys, skeletal maturation influences hypothalamic-pituitary-gonadal axis maturation.

Leptin signaling in the hypothalamus: emphasis on energy homeostasis and leptin resistance

Leptin, the long-sought satiety factor of adipocytes origin, has emerged as one of the major signals that relay the status of fat stores to the hypothalamus and plays a significant role in energy homeostasis. Understanding the mechanisms of leptin signaling in the hypothalamus during normal and pathological conditions, such as obesity, has been the subject of intensive research during the last decade. It is now established that leptin action in the hypothalamus in regulation of food intake and body weight is mediated by a neural circuitry comprising of orexigenic and anorectic signals, including NPY, MCH, galanin, orexin, GALP, alpha-MSH, NT, and CRH. In addition to the conventional JAK2-STAT3 pathway, it has become evident that PI3K-PDE3B-cAMP pathway plays a critical role in leptin signaling in the hypothalamus. It is now established that central leptin resistance contributes to the development of diet-induced obesity and ageing associated obesity. Central leptin resistance also occurs due to hyperleptinimia produced by exogenous leptin infusion. A defective nutritional regulation of leptin receptor gene expression and reduced STAT3 signaling may be involved in the development of leptin resistance in DIO. However, leptin resistance in the hypothalamic neurons may occur despite an intact JAK2-STAT3 pathway of leptin signaling. Thus, in addition to defective JAK2-STAT3 pathway, defects in other leptin signaling pathways may be involved in leptin resistance. We hypothesize that defective regulation of PI3K-PDE3B-cAMP pathway may be one of the mechanisms behind the development of central leptin resistance seen in obesity.

The neuropeptide Y Y1 receptor mediates NPY‐induced inhibition of the gonadotrope axis under poor metabolic conditions

Hypothalamic neuropeptide Y (NPY) plays a central role in the control of food intake, energy balance, and modulation of neuroendocrine functions. In particular, an increase in NPY expression participates in the inhibition of the reproductive activity under poor nutritional conditions. The present study was designed to evaluate further the involvement of the Y1 subtype of NPY receptors in these effects. Food intake, body weight gain, and the onset of puberty were studied in groups of wild-type and Y1 deficient mice that were either fed ad libitum or subjected to a 30% restriction in food intake. This moderate feeding restriction induced a similar deficit in body weight gain in wild-type and in Y1 knockout mice. However, although wild-type mice experienced the expected delay of puberty, all mice in the food restriction group and lacking Y1 could go through puberty over the time of the experiment despite decreases in circulating leptin levels and increases in hypothalamic NPY expression. This observation demonstrates that the absence of Y1 impairs the perception of decreasing energy stores by the gonadotrope axis, demonstrating a physiological role for Y1 in the sensing of endogenous metabolic parameters by the hypothalamus.

Disorders of pubertal development

Puberty is the period of life during which reproductive capability is acquired. It is characterized clinically by the acquisition of secondary sexual characteristics associated with a growth spurt, and on average takes 3-4 years. Early maturation is defined as the development of sexual characteristics before the age of 8 years in girls and 9 years in boys. Delayed puberty is defined when there are no signs of puberty at the age of 13.4 years in girls and 14 years in boys (2 SD above the mean of chronological age for the onset of puberty). There are many forms of premature sexual maturation: gonadotrophin-dependent (central, or 'idiopathic' or 'true' precocious puberty) and gonadotrophin-independent precocious puberty (McCune-Albright syndrome in girls, testotoxicosis in boys); isolated premature thelarche (in the forms of classical, atypical and variant); premature adrenarche (characterized by the production of significant quantities of androgens between 5 and 8 years of age); premature menarche. The differential diagnosis of delayed puberty is between constitutional delay of growth and puberty, pubertal delay secondary to chronic disease and hypogonadotrophic hypogonadism.

Pubertal and gender-related changes in the sympathoadrenal system in healthy children

A critical amount of body fat is necessary for the initiation of puberty, and leptin, an adipocyte-derived hormone, is necessary for pubertal development. The sympathoadrenal system modulates body fat stores and leptin secretion and interacts with adrenocortical androgen production, suggesting a possible role in sexual maturation. We studied sympathetic nerve and adrenomedullary activity at rest in 80 healthy children (ages, 5-17 yr; 37 boys and 43 girls) in relation to age, pubertal stage, gender, physical activity, body mass index, and serum levels of sex steroids, dehydroepiandrosterone sulfate, cortisol, leptin, and insulin. Plasma concentrations of the adrenomedullary hormone, epinephrine (E), and its metabolite metanephrine (MN), decreased significantly with advancing puberty and were higher in boys than in girls. E and MN correlated significantly and inversely with dehydroepiandrosterone sulfate, estradiol, testosterone, leptin, and insulin. Plasma norepinephrine, which is primarily derived from sympathetic nerve endings, increased significantly with advancing puberty and increasing testosterone levels in boys. Stepwise multiple regression analysis revealed that E was best predicted by pubertal stage and leptin, and MN by estradiol and leptin. Our data suggest that sympathoadrenal hormones may play a role in the complex process of sexual maturation. Further studies are needed to investigate a possible modulatory role of the adrenal medulla in the body weight-related timing of adrenarche and/or gonadarche.

Distribution of neurons containing leptin receptors in the hypothalamus of the pig

Leptin, secreted by white adipocytes, has profound feeding, metabolic, and neuroendocrine effects. Leptin acts on the brain, but specific anatomical sites and pathways responsible for mediating these effects are still unclear. We have systematically examined the distribution of leptin receptor containing neurons in the porcine hypothalamus by means of immunohistochemical staining methods. Leptin receptor immunoreactivity (OBR-IR) was observed in both the preoptic area and anterior hypothalamic area. No immunoreactive structures were found in the median eminence. Only single, small neurons were observed in the arcuate nucleus. The most abundant OBR-IR cell bodies were located in the supraoptic nucleus. In the paraventricular nucleus, OBR-IR neurons were moderate in number. Single, dispersed neurons were found in the ventromedial nucleus. These findings indicate that there are distinct OBR-IR neuronal populations in the porcine hypothalamus and leptin not only plays an integrative role in feeding behavior, but also in neuroendocrine activity.

Organochlorine pesticides directly regulate gonadotropin-releasing hormone gene expression and biosynthesis in the GT1-7 hypothalamic cell line

Environmental toxicants profoundly affect growth and developmental processes. In the present study, we hypothesized that hypothalamic gonadotropin-releasing hormone (GnRH) neurons, which regulate the reproductive axis, are targets of environmental endocrine disrupting chemicals. Two organochlorine pesticides (methoxychlor and chlorpyrifos) were tested for their effects on GnRH gene expression and biosynthesis in the immortalized hypothalamic GT1-7 cells, which synthesize and secrete GnRH. GT1-7 cells were treated with methoxychlor or chlorpyrifos for 24 h in dose-response experiments, and GnRH gene expression and peptide levels were quantified. In order to examine whether these pesticides affect GnRH biosynthesis through the estrogen receptor (ER), in other experiments their effects were compared to those of estrogen, or they were co-administered with the ER antagonist, ICI 182,780 (ICI). Both methoxychlor and chlorpyrifos had significant effects on GnRH gene transcription and GnRH mRNA levels. These effects were not consistently blocked by ICI, nor did the effects of these pesticides consistently mimic those of estrogen, suggesting a mechanism independent of the ER. Chlorpyrifos and methoxychlor slightly stimulated peptide levels, and this effect was blocked by ICI, suggesting that the ER may mediate effects of pesticides on GnRH release. These results indicate that chlorpyrifos and methoxychlor alter GnRH biosynthesis in this hypothalamic cell line in vitro, suggesting that they may have endocrine disrupting effects on GnRH neurons in vivo.

Delayed puberty

Puberty is the acquisition of secondary sexual characteristics associated with a growth spurt and resulting in the attainment of reproductive function. Delayed puberty is diagnosed when there is no breast development by 13.4 years of age in a girl and no testicular enlargement by 14.0 years in a boy. The aetiologies are: (i) pubertal delay, either with constitutional delay of growth and puberty or secondary to chronic illness, and (ii) pubertal failure, with hypogonadotrophic (defect in the hypothalamo-pituitary region) or hypergonadotrophic (secondary to gonadal failure) hypogonadism, or both (secondary to radio/chemotherapy). The investigation includes: history, auxological data and pubertal development examination. Boys usually require treatment and, if they do not respond, investigation. In girls it is appropriate to measure the thyroid function and karyotype first and, if necessary, to offer treatment. If they present with dysmorphic features, or positive familial history, an assessment is required before treatment.

Neural mechanisms underlying the pubertal increase in LHRH release in the rhesus monkey

Puberty is triggered by an increase in pulsatile release of luteinizing hormone-releasing hormone (LHRH) from the hypothalamus. Although the LHRH neurosecretory system is mature well before the onset of puberty, a central inhibitory mechanism restrains LHRH release in juvenile primates. Recent studies suggest that this central inhibition is primarily because of GABAergic neurotransmission. A reduction of GABAergic restraint appears to be essential for the initiation of puberty, but the mechanism that underlies the disinhibition process remains to be elucidated. Future research into the regulation of central inhibition should provide more effective treatments for the prevention of disease associated with abnormal pubertal development.