Developmental expression of the genes encoding transforming growth factor alpha and its receptor in the hypothalamus of female rhesus macaques

Identification of EGFR in pearl oyster (Pinctada fucata martensii) and correlation analysis of its expression and growth traits

Marine pearl production is directly influenced by the growth speed of Pinctada fucata martensii. However, the slow growth rate of this organism remains the main challenge in aquaculture production. Epidermal growth factor receptor (EGFR), an important receptor of tyrosine kinases in animals, plays versatile functions in development, growth and tissue regeneration. In this study, we described the characteristic and function of an EGFR gene identified from P. f. martensii (PmEGFR). PmEGFR possesses a typical EGFR structure and is expressed in all studied tissues, with the highest expression level in adductor muscle. PmEGFR expression level is significantly higher in the fast-growing group than that in the slow-growing one. Correlation analysis represents that shell height and shell weight show positive correlation with PmEGFR expression (p < 0.05), and total weight and tissue weight exhibit positive correlation with it (p < 0.01). This study indicates that PmEGFR is a valuable functional gene associated with growth traits.

Manganese protects against the effects of alcohol on hypothalamic puberty-related hormones

AIMS

Since manganese (Mn) is capable of stimulating the hypothalamic-pituitary unit and advancing female puberty, we assessed the possibility that this element might overcome some of the detrimental effects of prepubertal alcohol (ALC) exposure on the hypothalamic control of pituitary function.

MAIN METHODS

Rats received either saline or Mn (10mg/kg) daily by gastric gavage from day 12 to day 31. After weaning, all rats were provided Lab Chow diet ad libitum until day 27 when they began receiving either the Bio Serv control or ALC diet regime. On day 31, the medial basal hypothalamus (MBH) was collected to assess luteinizing hormone-releasing hormone (LHRH) and cyclooxygenase 2 (COX2) protein levels. Release of prostaglandin-E2 (PGE2), LHRH and serum luteinizing hormone (LH) were also assessed. Other animals were not terminated on day 31, but remained in study to assess timing of puberty.

KEY FINDINGS

Short-term ALC exposure caused elevated hypothalamic LHRH content, suggesting an inhibition in peptide release, resulting in a decrease in LH. Both actions of ALC were reversed by Mn supplementation. COX2 synthesis, as well as PGE2 and LHRH release were suppressed by ALC exposure, but Mn supplementation caused an increase in COX2 synthesis and subsequent PGE2 and LHRH release in the presence of ALC. Mn supplementation also ameliorated the action of ALC to delay puberty.

SIGNIFICANCE

These results suggest that low level Mn supplementation acts to protect the hypothalamus from some of the detrimental effects of ALC on puberty-related hormones.

Alcohol alters hypothalamic glial-neuronal communications involved in the neuroendocrine control of puberty: In vivo and in vitro assessments

The onset of puberty is the result of the increased secretion of hypothalamic luteinizing hormone-releasing hormone (LHRH). The pubertal process can be altered by substances that can affect the prepubertal secretion of this peptide. Alcohol is one such substance known to diminish LHRH secretion and delay the initiation of puberty. The increased secretion of LHRH that normally occurs at the time of puberty is due to a decrease of inhibitory tone that prevails prior to the onset of puberty, as well as an enhanced development of excitatory inputs to the LHRH secretory system. Additionally, it has become increasingly clear that glial-neuronal communications are important for pubertal development because they play an integral role in facilitating the pubertal rise in LHRH secretion. Thus, in recent years attempts have been made to identify specific glial-derived components that contribute to the development of coordinated communication networks between glia and LHRH cell bodies, as well as their nerve terminals. Transforming growth factor-α and transforming growth factor-β1 are two such glial substances that have received attention in this regard. This review summarizes the use of multiple neuroendocrine research techniques employed to assess these glial-neuronal communication pathways involved in regulating prepubertal LHRH secretion and the effects that alcohol can have on their respective functions.

Spatiotemporal dynamics of the postnatal developing primate brain transcriptome

Developmental changes in the temporal and spatial regulation of gene expression drive the emergence of normal mature brain function, while disruptions in these processes underlie many neurodevelopmental abnormalities. To solidify our foundational knowledge of such changes in a primate brain with an extended period of postnatal maturation like in human, we investigated the whole-genome transcriptional profiles of rhesus monkey brains from birth to adulthood. We found that gene expression dynamics are largest from birth through infancy, after which gene expression profiles transition to a relatively stable state by young adulthood. Biological pathway enrichment analysis revealed that genes more highly expressed at birth are associated with cell adhesion and neuron differentiation, while genes more highly expressed in juveniles and adults are associated with cell death. Neocortex showed significantly greater differential expression over time than subcortical structures, and this trend likely reflects the protracted postnatal development of the cortex. Using network analysis, we identified 27 co-expression modules containing genes with highly correlated expression patterns that are associated with specific brain regions, ages or both. In particular, one module with high expression in neonatal cortex and striatum that decreases during infancy and juvenile development was significantly enriched for autism spectrum disorder (ASD)-related genes. This network was enriched for genes associated with axon guidance and interneuron differentiation, consistent with a disruption in the formation of functional cortical circuitry in ASD.

Role of glia in the regulation of gonadotropin-releasing hormone neuronal activity and secretion

Gonadotropin-releasing hormone (GnRH) neurons are the final common pathway for the central control of reproduction. The coordinated and timely activation of these hypothalamic neurons, which determines sexual development and adult reproductive function, lies under the tight control of a complex array of excitatory and inhibitory transsynaptic inputs. In addition, research conducted over the past 20 years has unveiled the major contribution of glial cells to the control of GnRH neurons. Glia use a variety of molecular and cellular strategies to modulate GnRH neuronal function both at the level of their cell bodies and at their nerve terminals. These mechanisms include the secretion of bioactive molecules that exert paracrine effects on GnRH neurons, juxtacrine interactions between glial cells and GnRH neurons via adhesive molecules and the morphological plasticity of the glial coverage of GnRH neurons. It now appears that glial cells are integral components, along with upstream neuronal networks, of the central control of GnRH neuronal function. This review attempts to summarize our current knowledge of the mechanisms used by glial cells to control GnRH neuronal activity and secretion.

Hypothalamic glial-to-neuronal signaling during puberty: influence of alcohol

Mammalian puberty requires complex interactions between glial and neuronal regulatory systems within the hypothalamus that results in the timely increase in the secretion of luteinizing hormone releasing hormone (LHRH). Assessing the molecules required for the development of coordinated communication networks between glia and LHRH neuron terminals in the basal hypothalamus, as well as identifying substances capable of affecting cell-cell communication are important. One such pathway involves growth factors of the epidermal growth factor (EGF) family that bind to specific erbB receptors. Activation of this receptor results in the release of prostaglandin-E₂ (PGE₂) from adjacent glial cells, which then acts on the nearby LHRH nerve terminals to elicit release of the peptide. Another pathway involves novel genes which synthesize adhesion/signaling proteins responsible for the structural integrity of bi-directional glial-neuronal communication. In this review, we will discuss the influence of these glial-neuronal communication pathways on the prepubertal LHRH secretory system, and furthermore, discuss the actions and interactions of alcohol on these two signaling processes.

Prepubertal ethanol exposure alters hypothalamic transforming growth factor-α and erbB1 receptor signaling in the female rat

Glial-derived transforming growth factor alpha (TGFα) activates the erbB1/erbB2 receptor complex on adjacent glial cells in the medial basal hypothalamus (MBH). This receptor activation stimulates the synthesis and release of prostaglandin-E(2) (PGE(2)) from the glial cells, which then induces the release of prepubertal luteinizing hormone-releasing hormone (LHRH) secretion from nearby nerve terminals; thus, showing the importance of glial-neuronal communications at the time of puberty. Ethanol (EtOH) is known to cause depressed prepubertal LHRH secretion and delayed pubertal development. In this study, we assessed whether short-term EtOH exposure could alter the hypothalamic glial to glial signaling components involved in prepubertal PGE(2) secretion. Immature female rats began receiving control or EtOH diets beginning when 27 days old. The animals were killed by decapitation after 4 and 6 days of treatment and confirmed to be in the late juvenile stage of development. Blood and brain tissues were collected for gene, protein, and hormonal assessments. Real-time polymerase chain reaction (PCR) analysis demonstrated that EtOH did not affect basal levels of erbB1 gene expression in the MBH. Expression of total erbB1 protein was also unaffected; however, the EtOH caused suppressed phosphorylation of erbB1 protein in the MBH at both 4 and 6 days (P<.01) as revealed by Western blotting. Phosphorylation and total protein levels of erbB2 receptor were not affected by EtOH exposure. Because this receptor is critical for PGE(2) synthesis/release, which mediates the secretion of LHRH, we assessed whether in vivo EtOH exposure could affect the release of PGE(2). EtOH exposure for 6 days suppressed (P<.01) basal levels of PGE(2) released into the medium. The effects of 4- and 6-day EtOH exposure on gene and protein expressions of TGFα, an upstream component in the activation of erbB1/erbB2, were also studied. The levels of TGFα mRNA were increased markedly at 4 days (P<.001), but declined to near basal levels by 6 days in the EtOH-treated animals. The EtOH caused increases in TGFα protein expression at both 4 (P<.001) and 6 (P<.01) days; hence, suggesting that the EtOH inhibited release of the peptide. We confirmed this inhibition by showing decreased (P<.01) TGFα released from MBHs incubated in vitro following 6 days of EtOH exposure in vivo. Thus, these results demonstrate that EtOH is capable of interfering with hypothalamic glial to glial signaling processes involved in prepubertal PGE(2) secretion.

FXYD1, a modulator of Na,K-ATPase activity, facilitates female sexual development by maintaining gonadotrophin-releasing hormone neuronal excitability

The excitatory tone to gonadotrophin-releasing hormone (GnRH) neurones is a critical component underlying the pubertal increase in GnRH secretion. However, the homeostatic mechanisms modulating the response of GnRH neurones to excitatory inputs remain poorly understood. A basic mechanism of neuronal homeostasis is the Na(+),K(+)-ATPase-dependent restoration of Na(+) and K(+) transmembrane gradients after neuronal excitation. This activity is reduced in a mouse model of Rett syndrome (RTT), a neurodevelopmental disorder in which expression of FXYD1, a modulator of Na(+),K(+)-ATPase activity, is increased. We now report that the initiation, but not the completion of puberty, is advanced in girls with RTT, and that, in rodents, FXYD1 may contribute to the neuroendocrine regulation of female puberty by modulating GnRH neuronal excitability. Fxyd1 mRNA abundance reaches maximal levels in the female rat hypothalamus by the fourth postnatal week of life (i.e., around the time when the mode of GnRH secretion acquires an adult pattern of release). Although Fxyd1 mRNA expression is low in the hypothalamus, approximately 50% of GnRH neurones contain Fxyd1 transcripts. Whole-cell patch recording of GnRH-EGFP neurones revealed that the neurones of Fxyd1-null female mice respond to somatic current injections with a lower number of action potentials than wild-type cells. Both the age at vaginal opening and at first oestrous were delayed in Fxyd1(-/-) mice, but adult reproductive capacity was normal. These results suggest that FXYD1 contributes to facilitating the advent of puberty by maintaining GnRH neuronal excitability to incoming transsynaptic stimulatory inputs.

[Advances on related genes with sexual precocity in mammals]

In mammals and humans, reproductive capacity is attained at puberty as the end-point of a complex series of developmental and neuroendocrine events that lead to true sexual maturity. As for humans, sexual precocity looks like a pathologic status. While for some animals, sexual precocity may be a valuable quantitative character. For some species, the character of sexual precocity was developed in the evolutionary process and stably transmitted to future generations. Sexual precocity is a complex character determined by polygenes. This review introduced the association between KiSS-1, GPR54, LHR, FSHR, CYP, ER, TGFa, IGF-, GNAS1, HSD3B2, SHBG, VDR genes and sexual precocity in mammals.

Behavioral effects of systemic transforming growth factor-alpha in Syrian hamsters

The growth factor, transforming growth factor-alpha (TGF-alpha) is strongly expressed in the hypothalamic circadian pacemaker, the suprachiasmatic nucleus (SCN). TGF-alpha is one of several SCN peptides recently suggested to function as a circadian output signal for the regulation of locomotor activity rhythms in nocturnal rodents. When infused in the brain, TGF-alpha suppresses activity. TGF-alpha suppresses other behaviors as well including feeding, resulting in weight loss. Elevated TGF-alpha is correlated with some cancers, and it is possible the TGF-alpha and its receptor, the epidermal growth factor receptor (EGFR), mediate fatigue and weight loss associated with cancer. If true for cancers outside of the brain, then systemic TGF-alpha should also affect behavior. We tested this hypothesis in hamsters with intraperitoneal injections or week-long subcutaneous infusions of TGF-alpha. Both treatments suppressed activity and infusions caused reduced food consumption and weight loss. To identify areas of the brain that might mediate these effects of systemic TGF-alpha, we used immunohistochemistry to localize cells with an activated MAP kinase signaling pathway (phosphorylated ERK1). Cells were activated in two hypothalamic areas, the paraventricular nucleus and a narrow region surrounding the third ventricle. These sites could not only be targets of TGF-alpha produced in the SCN but could also mediate effects of elevated TGF-alpha from tumors both within and outside the central nervous system.

Neurobiology of stress-induced reproductive dysfunction in female macaques

It is now well accepted that stress can precipitate mental and physical illness. However, it is becoming clear that given the same stress, some individuals are very vulnerable and will succumb to illness while others are more resilient and cope effectively, rather than becoming ill. This difference between individuals is called stress sensitivity. Stress sensitivity of an individual appears to be influenced by genetically inherited factors, early life (even prenatal) stress, and by the presence or absence of factors that provide protection from stress. In comparison to other stress-related diseases, the concept of sensitivity versus resilience to stress-induced reproductive dysfunction has received relatively little attention. The studies presented herein were undertaken to begin to identify stable characteristics and the neural underpinnings of individuals with sensitivity to stress-induced reproductive dysfunction. Female cynomolgus macaques with normal menstrual cycles either stop ovulating (stress sensitive) or to continue to ovulate (stress resilient) upon exposure to a combined metabolic and psychosocial stress. However, even in the absence of stress, the stress-sensitive animals have lower secretion of the ovarian steroids, estrogen and progesterone, have higher heart rates, have lower serotonin function, have fewer serotonin neurons and lower expression of pivotal serotonin-related genes, have lower expression of 5HT2A and 2C genes in the hypothalamus, have higher gene expression of GAD67 and CRH in the hypothalamus, and have reduced gonadotropin-releasing hormone transport to the anterior pituitary. Altogether, the results suggest that the neurobiology of reproductive circuits in stress-sensitive individuals is compromised. We speculate that with the application of stress, the dysfunction of these neural systems becomes exacerbated and reproductive function ceases.

Gene x environment effects: stress and memory dysfunctions caused by stress and gonadal factor irregularities during puberty in control and TGF-alpha hypomorphic mice

The maturation of many neural functions occurs during puberty. An abnormal development of these processes, in the context of genetic vulnerability, may result in sex- and age-dependent penetrance of neuropsychiatric disorders. Reduced transforming growth factors-alpha (TGF-alpha) expression in Waved-1 (Wa-1) mice impairs the stress response and fear memory in adult males, but are absent or far less prominent in adult females and in pubertal males. Gonadectomy around the onset of puberty, when the mutant anatomical and behavioral phenotypes are undetectable, results in significant gene x environment effects. Adult control males show reduced physiological stress response as a result of gonadectomy, but not adult Wa-1 males. In females, pubertal gonadectomy elevates specific anxiety parameters only in adult control mice. There also are general sex-specific effects of pubertal gonadectomy on adult stress and fear memory. Surgical stress alone also induces sex- and genotype-dependent effects, albeit in different behavioral parameters than those affected by gonadectomy. We conclude that normal development of stress and memory processes is reliant on the levels of stress and gonadal factors during puberty, the effects of which are modulated by genetic factors and sex.

Expression of a tumor-related gene network increases in the mammalian hypothalamus at the time of female puberty

Much has been learned in recent years about the central mechanisms controlling the initiation of mammalian puberty. It is now clear that this process requires the interactive participation of several genes. Using a combination of high throughput, molecular, and bioinformatics strategies, in combination with a system biology approach, we singled out from the hypothalamus of nonhuman primates and rats a group of related genes whose expression increases at the time of female puberty. Although these genes [henceforth termed tumor-related genes (TRGs)] have diverse cellular functions, they share the common feature of having been earlier identified as involved in tumor suppression/tumor formation. A prominent member of this group is KiSS1, a gene recently shown to be essential for the occurrence of puberty. Cis-regulatory analysis revealed the presence of a hierarchically arranged gene set containing five major hubs (CDP/CUTL1, MAF, p53, YY1, and USF2) controlling the network at the transcriptional level. In turn, these hubs are heavily connected to non-TRGs involved in the transcriptional regulation of the pubertal process. TRGs may be expressed in the mammalian hypothalamus as components of a regulatory gene network that facilitates and integrates cellular and cell-cell communication programs required for the acquisition of female reproductive competence.

A contactin-receptor-like protein tyrosine phosphatase beta complex mediates adhesive communication between astroglial cells and gonadotrophin-releasing hormone neurones

Although it is well established that gonadotrophin-releasing hormone (GnRH) neurones and astrocytes maintain an intimate contact throughout development and adult life, the cell-surface molecules that may contribute to this adhesiveness remain largely unknown. In the peripheral nervous system, the glycosylphosphatidyl inositol (GPI)-anchored protein contactin is a cell-surface neuronal protein required for axonal-glial adhesiveness. A glial transmembrane protein recognised by neuronal contactin is receptor-like protein tyrosine phosphatase beta (RPTP beta), a phosphatase with structural similarities to cell adhesion molecules. In the present study, we show that contactin, and its preferred in cis partner Caspr1, are expressed in GnRH neurones. We also show that the RPTP beta mRNA predominantly expressed in hypothalamic astrocytes encodes an RPTP beta isoform (short RPTP beta) that uses its carbonic anhydrase (CAH) extracellular subdomain to interact with neuronal contactin. Immunoreactive contactin is most abundant in GnRH nerve terminals projecting to both the organum vasculosum of the lamina terminalis and median eminence, implying GnRH axons as an important site of contactin-dependent cell adhesiveness. GT1-7 immortalised GnRH neurones adhere to the CAH domain of RPTPbeta, and this adhesiveness is blocked when contactin GPI anchoring is disrupted or contactin binding capacity is immunoneutralised, suggesting that astrocytic RPTP beta interacts with neuronal contactin to mediate glial-GnRH neurone adhesiveness. Because the abundance of short RPTP beta mRNA increases in the female mouse hypothalamus (but not in the cerebral cortex) before puberty, it appears that an increased interaction between GnRH axons and astrocytes mediated by RPTP beta-contactin is a dynamic mechanism of neurone-glia communication during female sexual development.

Hypothalamic gonadotrophin-releasing hormone expression in female monkeys with different sensitivity to stress

Psychosocial stress, combined with mild dieting and moderate exercise, are observed in women seeking treatment for hypothalamic amenorrhea. Using female cynomolgus macaques, we previously reported that the same combination of mild stresses suppressed reproductive hormone secretion and menstrual cycles in some individuals (stress-sensitive, SS), but not in others (highly stress-resilient, HSR). Compared to HSR monkeys, SS monkeys exhibited lower oestradiol and progesterone levels at the midcycle peak and decreased gene expression in the central serotonergic system during nonstressed cycles. Because steroids and serotonin impinge upon the hypothalamic-pituitary-gonadal (HPG) axis, we hypothesised that the differences between SS and HSR monkeys in the sensitivity of the HPG axis to stress may ultimately manifest in differences in the gonadotrophin-releasing hormone (GnRH) system. GnRH in situ hybridisation and immunohistochemistry were performed with hypothalamic sections from SS and HSR animals, euthanised in the early follicular phase of a nonstressed menstrual cycle. Compared to HSR monkeys, SS monkeys exhibited a significantly higher number and density of GnRH cell bodies, as well as a higher number of soma with extremely robust expression of GnRH mRNA, but SS monkeys exhibited a lower density of immunostained GnRH fibres in the median eminence. We suggest that neuronal mechanisms involved in the control of GnRH synthesis, transport and release differ in SS compared to HSR animals.

Waved-1 mutant mice are hypersensitive to the locomotor actions of cocaine

Transforming growth factor-alpha (TGFalpha) is a well-known regulator of many developmental processes, and is expressed heavily in basal forebrain and striatal regions. When TGFalpha is reduced in Waved-1 (Wa-1) mutant mice, brain anatomy, biogenic amines, stress response, and behavior are normal prior to, but altered following puberty. As an initial screen for possible alterations in nigrostriatal and mesolimbic dopamine (DA) systems, we tested adult Wa-1 mutant mice in an open field, following acute injection with cocaine (15 mg/kg). Wa-1 mice exhibited significantly greater ambulatory distance, number of ambulatory episodes, and cocaine-induced motor stereotypies than do controls. These data indicate that adult Wa-1 mice are hypersensitive to the locomotor effects of cocaine and provide a new potential link between neurodevelopmental processes and adult psychostimulant responsiveness.

An increase in in vivo release of LHRH and precocious puberty by posterior hypothalamic lesions in female rhesus monkeys (Macaca mulatta)

We have previously shown that a decrease in gamma-aminobutyric acid (GABA) tone and a subsequent increase in glutamatergic tone occur in association with the pubertal increase in luteinizing hormone releasing hormone (LHRH) release in primates. To further determine the causal relationship between developmental changes in GABA and glutamate levels and the pubertal increase in LHRH release, we examined monkeys with precocious puberty induced by lesions in the posterior hypothalamus (PH). Six prepubertal female rhesus monkeys (17.4 +/- 0.1 mo of age) received lesions in the PH, three prepubertal females (17.5 +/- 0.1 mo) received sham lesions, and two females received no treatments. LHRH, GABA, and glutamate levels in the stalk-median eminence before and after lesions were assessed over two 6-h periods (0600-1200 and 1800-2400) using push-pull perfusion. Monkeys with PH lesions exhibited external signs of precocious puberty, including significantly earlier menarche in PH lesion animals (18.8 +/- 0.2 mo) than in sham/controls (25.5 +/- 0.9 mo, P<0.001). Moreover, PH lesion animals had elevated LHRH levels and higher evening glutamate levels after lesions, whereas LHRH changes did not occur in sham/controls until later. Changes in GABA release were not discernible, since evening GABA levels already deceased at 18-20 mo of age in both groups and morning levels remained at the prepubertal levels. The age of first ovulation in both groups did not differ. Collectively, PH lesions may not be a good tool to investigate the mechanism of puberty, and, taking into account the recent findings on the role of kisspeptins, the mechanism of the puberty onset in primates is more complex than we initially anticipated.

Expression of Tgfα in the suprachiasmatic nuclei of nocturnal and diurnal rodents

Transforming growth factor alpha (TGFalpha) in the suprachiasmatic nuclei (SCN) has been proposed as an inhibitory signal involved in the control of daily locomotor activity. This assumption is based mainly on studies performed in nocturnal hamsters. To test whether the transcriptional regulation of Tgfalpha can be correlated with the timing of overt activity in other species, we compared Tgfalpha expression in the SCN of nocturnal Swiss mice and of diurnal Arvicanthis housed under a light/dark cycle (LD) or transferred to constant darkness (DD). In agreement with data on hamsters, Tgfalpha mRNA levels in the mouse SCN showed peak and trough levels around (subjective) dawn and dusk, respectively, roughly corresponding to the period of rest and activity in this species. In contrast, in Arvicanthis housed in DD, the circadian rhythm of SCN Tgfalpha was similar to that of the mice in spite of opposite phasing of locomotor activity. Furthermore, in Arvicanthis exposed to LD, Tgfalpha mRNA levels were constitutively high throughout the day. A tonic role of light in the regulation of Tgfalpha in Arvicanthis was confirmed by an increased expression of Tgfalpha in response to a 6-h exposure to light during daytime in animals otherwise kept in DD. In conclusion, this study shows that, contrary to what is observed in mice, Tgfalpha mRNA levels in the SCN of Arvicanthis do not match timing of locomotor activity and are modulated by light.

Deletion of the Ttf1 gene in differentiated neurons disrupts female reproduction without impairing basal ganglia function

Thyroid transcription factor 1 (TTF1) [also known as Nkx2.1 (related to the NK-2 class of homeobox genes) and T/ebp (thyroid-specific enhancer-binding protein)], a homeodomain gene required for basal forebrain morphogenesis, remains expressed in the hypothalamus after birth, suggesting a role in neuroendocrine function. Here, we show an involvement of TTF1 in the control of mammalian puberty and adult reproductive function. Gene expression profiling of the nonhuman primate hypothalamus revealed that TTF1 expression increases at puberty. Mice in which the Ttf1 gene was ablated from differentiated neurons grew normally and had normal basal ganglia/hypothalamic morphology but exhibited delayed puberty, reduced reproductive capacity, and a short reproductive span. These defects were associated with reduced hypothalamic expression of genes required for sexual development and deregulation of a gene involved in restraining puberty. No extrapyramidal impairments associated with basal ganglia dysfunction were apparent. Thus, although TTF1 appears to fulfill only a morphogenic function in the ventral telencephalon, once this function is satisfied in the hypothalamus, TTF1 remains active as part of the transcriptional machinery controlling female sexual development.

The role of KiSS-1 in the regulation of puberty in higher primates

Puberty in higher primates is triggered by resurgence in the pulsatile secretion of hypothalamic GnRH after a hiatus in the robust release of this hypophysiotropic signal during childhood and juvenile development. Interestingly, the prepubertal decline in GnRH release is not associated with a marked reduction in the expression of either the gene that codes for GnRH (GnRH-1) or the decapeptide itself, and the network of GnRH neurons in the hypothalamus of the juvenile may by activated prematurely and with surprising ease by intermittent neurochemical stimulation with N-methyl-d-aspartate (NMDA), a glutamate receptor agonist. KiSS-1, a gene that encodes for kisspeptin-121, which is proteolytically cleaved to a 54 amino acid peptide, metastin, was initially studied in the context of tumor suppression. In 2003, however, inactivating mutations in the metastin receptor, GPR54, were reported to be associated with hypogonadotropic hypogonadism and absent puberty in man. Subsequent studies in the rhesus monkey have shown that GPR54 and KiSS-1 are expressed in the mediobasal hypothalamus (MBH), KiSS-1 expression in the MBH increases at the time of the pubertal resurgence in GnRH release and pulsatile, but not continuous, i.v. administration of metastin 45-54 in the juvenile male monkey elicits sustained GnRH release precociously. The significance of these findings in the context of the initiation of the onset of puberty is discussed.

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.

Transforming growth factor-α induces sex-specific neurochemical imbalance in the stress- and memory-associated brain structures

Transforming growth factor-alpha (TGFalpha) is a well-known regulator of many developmental processes. However, its role in adult nervous system is yet unclear. Studies have shown that TGFalpha can regulate stress and memory behavior in adult mice. When TGFalpha is reduced in Waved-1 (Wa-1) mutant mice, the stress response and memory are impaired predominantly in males and only after puberty. To determine the neurochemical changes resulting from the reduced TGFalpha levels that could explain the reported behavioral outcomes, biogenic amine and amino acid levels were determined in the brain regions associated with stress and memory. Interestingly, sex-specific alterations in neurochemical levels were detected, including elevated noradrenaline and reduced glutamate levels in striatum of Wa-1 males, increased noradrenaline and reduced serotonin metabolite levels in hippocampus of Wa-1 females, reduced serotonin metabolite levels in cortex and amygdala of Wa-1 females, and reduced noradrenaline, dopamine, serotonin, glutamate and glycine levels in hypothalamus of Wa-1 females compared to their respective controls. Increased dopamine turnover in cortex and reduced dopamine and serotonin turnover in amygdala were observed in both male and female Wa-1 mice. The data indicate sex-specific alterations of specific neurochemicals as a result of reduced TGFalpha expression, which may underlie sex-dependent stress response and memory impairment in Wa-1 mice.

Hypothalamic tumor necrosis factor-alpha converting enzyme mediates excitatory amino acid-dependent neuron-to-glia signaling in the neuroendocrine brain

Glial erbB1 receptors play a significant role in the hypothalamic control of female puberty. Activation of these receptors by transforming growth factor alpha (TGFalpha) results in production of prostaglandin E2, which then stimulates luteinizing hormone releasing hormone (LHRH) neurons to secrete LHRH, the neuropeptide controlling sexual development. Glutamatergic neurons set in motion this glia-to-neuron signaling pathway by transactivating erbB1 receptors via coactivation of AMPA receptors (AMPARs) and metabotropic glutamate receptors (mGluRs). Because the metalloproteinase tumor necrosis factor alpha converting enzyme (TACE) releases TGFalpha from its transmembrane precursor before TGFalpha can bind to erbB1 receptors, we sought to determine whether TACE is required for excitatory amino acids to activate the TGFalpha-erbB1 signaling module in hypothalamic astrocytes, and thus facilitate the advent of puberty. Coactivation of astrocytic AMPARs and mGluRs caused extracellular Ca2+ influx, a Ca2+/protein kinase C-dependent increase in TACE-like activity, and enhanced release of TGFalpha. Within the hypothalamus, TACE is most abundantly expressed in astrocytes of the median eminence (ME), and its enzymatic activity increases selectively in this region at the time of the first preovulatory surge of gonadotropins. ME explants respond to stimulation of AMPARs and mGluRs with LHRH release, and this response is prevented by blocking TACE activity. In vivo inhibition of TACE activity targeted to the ME delayed the age at first ovulation, indicating that ME-specific changes in TACE activity are required for the normal timing of puberty. These results suggest that TACE is a component of the neuron-to-glia signaling process used by glutamatergic neurons to control female sexual development.

Postpubertal sex differentiation of forebrain structures and functions depend on transforming growth factor-alpha

Sex- and age-associated deficits in brain structure and behavior are reported in a number of neuropsychiatric disorders. Although genetic and environmental factors are thought to contribute to the pathogenesis, there are only few examples in clinical or experimental systems that have identified specific causes. Here, we report that transforming growth factor-alpha (TGFalpha) may regulate sex- and age-dependent development of forebrain structures and associated neural functions after puberty. Waved-1 (Wa-1) mice inherit an autosomal recessive, spontaneous mutation that results in a postnatal reduction in TGFalpha gene expression. The assessment of forebrain structures using a three-dimensional magnetic resonance microscopy indicated ventricular enlargement and striatal reduction in both male and female Wa-1 adult mice, with Wa-1 males exhibiting a more severe phenotype. In contrast, the hippocampal volume was reduced only in adult Wa-1 males. Similarly, behavioral analyses showed impaired auditory and contextual fear learning in adult Wa-1 males only, whereas abnormal stress response was expressed by both male and female adult Wa-1 mice. Interestingly, all behavioral deficits were absent before full sexual maturation, despite some slight forebrain structural abnormalities. These results suggest that TGFalpha may regulate postpubertal, sex differentiation in ventricular and periventricular anatomy and associated behavior, affecting predominantly males. In particular, the adult male-specific reduction in hippocampal volume may reflect an age- and sex-specific regulation of stress homeostasis and fear learning. Furthermore, a lack of a behavioral phenotype, despite anatomical alterations in peripubertal Wa-1 mice, suggests that analysis of certain neuroanatomical features at puberty may predict neurobehavioral deficits in adulthood.

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.

A study of gene expression of cyclophilin in childhood refractory nephrotic syndrome and its clinical significance

AIM

The purpose of this study was to investigate the clinical significance of gene expression of cyclophilin (CyP) in children with refractory nephrotic syndrome (NS).

METHODS

The levels of leukocyte mRNA expression in 33 cases of childhood refractory NS were determined by reverse transcription polymerase chain reaction (RT-PCR). The CyP levels in these children were compared with those of a healthy control groups.

RESULTS

Cyclophilin (408 bp) and beta-actin bands (234 bp) were distinct on electrophoresis. The levels of leukocyte CyP mRNA expression were higher in children with mesangio-proliferative glomerulonephritis (MsPGN) and focal segmental glomerulosclerosis (FSGS) than in minimal-change nephrotic syndrome (MCNS), whereas in membrano-proliferative glomerulonephritis (MPGN) they were found to be lower. The levels of leukocyte CyP mRNA were increased with exacerbation of clinical disease. Determination of the levels of leukocyte CyP mRNA expression in children with different clinical types showed that there was no difference in the levels of CyP mRNA expression in children with prednisone-dependent, frequent relapsing or prednisone-resistant types. The level of leukocyte CyP mRNA expression was found to be higher in acute stage groups than in convalescent stage or control groups.

CONCLUSIONS

Determination of the levels of leukocyte CyP mRNA may be of assistance in cyclosporine A therapy.

Expression of three gene families encoding cell-cell communication molecules in the prepubertal nonhuman primate hypothalamus

Transsynaptic and glial-neuronal communication are important components of the mechanism underlying the pubertal activation of luteinizing hormone-releasing hormone (LHRH) secretion. The molecules required for the architectural organization of these cell-cell interactions have not been identified. We now show that the hypothalamus of the prepubertal female rhesus monkey expresses a multiplicity of genes encoding three families of adhesion/signalling proteins involved in the structural definition of both neurone-to-neurone and bi-directional neurone-glia communication. These include the neurexin/neuroligin (NRX/NRL) and protocadherin-alpha (PCDHalpha) families of synaptic specifiers/adhesion molecules, and key components of the contactin-dependent neuronal-glial adhesiveness complex, including contactin/F3 itself, the contactin-associated protein-1 (CASPR1), and the glial receptor protein tyrosine phosphatase beta. Prominently expressed among members of the NRX family is the neurexin isoform involved in the specification of glutamatergic synapses. Although NRXs, PCDHalphas and CASPR1 transcripts are mostly detected in neurones, the topography of expression appears different. NRX1 mRNA-containing neurones are scattered throughout the hypothalamus, PCDHalpha mRNA transcripts appear more abundant in neurones of the arcuate nucleus and periventricular region, and neurones positive for CASPR1 mRNA exhibit a particularly striking distribution pattern that delineates the hypothalamus. Examination of LHRH neurones, using the LHRH-secreting cell line GT1-7, showed that these cells contain transcripts encoding NRXs and one of their ligands (NRL1), at least one PCDHalpha (CNR-8/PCDHalpha10), and the CASPR1/contactin complex. The results indicate that the prepubertal female monkey hypothalamus contains a plethora of adhesion/signalling molecules with different but complementary functions, and that an LHRH neuronal cell line expresses key components of this structural complex. The presence of such cell-cell communication machinery in the neuroendocrine brain suggests an integrated participation of their individual components in the central control of female sexual development.

Central administration of transforming growth factor-alpha and neuregulin-1 suppress active behaviors and cause weight loss in hamsters

Transforming growth factor-alpha (TGF-alpha) is a candidate output signal of the hypothalamic circadian pacemaker. TGF-alpha is expressed in the suprachiasmatic nucleus (SCN) of rats, hamsters, and rhesus macaques [A. Kramer, F.C. Yang, P. Snodgrass, X. Li, T.E. Scammell, F.C. Davis and C.J. Weitz, Regulation of daily locomotor activity and sleep by hypothalamic EGF receptor signaling, Science, 294 (2001) 2511-5., X. Li, N. Sankrithi and F.C. Davis, Transforming growth factor-alpha is expressed in astrocytes of the suprachiasmatic nucleus in hamster: role of glial cells in circadian clocks, Neuroreport, 13 (2002) 2143-7., Y.J. Ma, M.E. Costa and S.R. Ojeda, Developmental expression of the genes encoding transforming growth factor alpha and its receptor in the hypothalamus of female rhesus macaques, Neuroendocrinology, 60 (1994) 346-59., Y.J. Ma, M.P. Junier, M.E. Costa and S.R. Ojeda, Transforming growth factor-alpha gene expression in the hypothalamus is developmentally regulated and linked to sexual maturation, Neuron, 9 (1992) 657-70.]. TGF-alpha reversibly inhibits wheel-running activity during long-term infusions into the third ventricle of hamsters (2 weeks, intracerebroventricular or ICV) [A. Kramer, F.C. Yang, P. Snodgrass, X. Li, T.E. Scammell, F.C. Davis and C.J. Weitz, Regulation of daily locomotor activity and sleep by hypothalamic EGF receptor signaling, Science, 294 (2001) 2511-5.], and this effect appears to be mediated by the epidermal growth factor receptor (EGFR or ErbB-1) [A. Kramer, F.C. Yang, P. Snodgrass, X. Li, T.E. Scammell, F.C. Davis and C.J. Weitz, Regulation of daily locomotor activity and sleep by hypothalamic EGF receptor signaling, Science, 294 (2001) 2511-5.]. Here, we demonstrate that this inhibitory effect is not restricted to wheel-running behavior or to mediation by the EGFR. Using direct observation, we found the effects of long-term TGF-alpha infusion (ICV, 12 microl/day, 3.3 microM) to be more general than previously reported. Other active behaviors such as grooming and feeding were reversibly inhibited and hamsters showed dramatic weight loss as a result of reduced feeding (34% of body weight over 19 days). TGF-alpha did not disrupt a non-behavioral rhythm, the rhythm in pineal melatonin. Wheel-running activity was also inhibited by another epidermal growth factor-like (EGF-like) peptide, neuregulin (NRG-1), that binds to different ErbB receptors. Like TGF-alpha, NRG-1 caused a significant weight loss. We also show that an acute injection of TGF-alpha inhibits activity (ICV, 5 microl, 3.3 microM over 2 min), with inhibition and recovery occurring over a few hours. Although the results are consistent with the proposed [A. Kramer, F.C. Yang, P. Snodgrass, X. Li, T.E. Scammell, F.C. Davis and C.J. Weitz, Regulation of daily locomotor activity and sleep by hypothalamic EGF receptor signaling, Science, 294 (2001) 2511-5.] role for EGF-like peptides in the daily regulation of activity, the actions of these peptides might also contribute to the behavioral etiology of diseases in which EGF-like peptides are expressed.

Increased hypothalamic GPR54 signaling: a potential mechanism for initiation of puberty in primates

To further study the role of GPR54 signaling in the onset of primate puberty, we used the monkey to examine the ability of kisspeptin-10 to elicit the release of gonadotropin-releasing hormone (GnRH) precociously, and we describe the expression of GPR54 and KiSS-1 in the hypothalamus during the peripubertal period. Agonadal juvenile male monkeys were implanted with a lateral cerebroventricular cannula and a jugular vein catheter. The responsiveness of the juvenile pituitary to endogenous GnRH release was heightened with a chronic pulsatile i.v. infusion of synthetic GnRH before kisspeptin-10 (112-121) injection. Intracerebroventricular (30 microg or 100 microg) or i.v. (100 microg) bolus injections of kisspeptin-10 elicited a robust GnRH discharge, as reflected by luteinizing hormone secretion, which was abolished by pretreatment with a GnRH-receptor antagonist. RNA was isolated from the hypothalamus of agonadal males before (juvenile) and after (pubertal) the pubertal resurgence of pulsatile GnRH release and from juvenile, early pubertal, and midpubertal ovary-intact females. KiSS-1 mRNA levels detected by real-time PCR increased with puberty in both male and female monkeys. In intact females, but not in agonadal males, GPR54 mRNA levels in the hypothalamus increased approximately 3-fold from the juvenile to midpubertal stage. Hybridization histochemistry indicated robust KiSS-1 and GPR54 mRNA expression in the region of the arcuate nucleus. These findings are consistent with the hypothesis that GPR54 signaling by its cognate ligand in the primate hypothalamus may be activated at the end of the juvenile phase of development and may contribute to the pubertal resurgence of pulsatile GnRH release, the central drive for puberty.

Compromised reproductive function in adult female mice selectively expressing mutant ErbB-1 tyrosine kinase receptors in astroglia

The ErbB-1 tyrosine kinase receptor plays critical roles in regulating physiological functions. This receptor-mediated signaling in astroglia has been implicated in controlling female sexual development via activating neurons that release LH-releasing hormone (LHRH), the neuropeptide required for the secretion of LH. It remains unknown whether astroglial ErbB-1 receptors are necessary for maintaining normal adult reproductive function. Here we provide genetic evidence that astroglia-specific and time-controlled disruption of ErbB-1 receptor signaling by expressing mutant ErbB-1 receptors leads to compromised reproduction due to alteration in LHRH neuron-controlled secretion of LH in adult female mice. Therefore, astroglial ErbB-1 receptors are required for controlling LHRH neuronal function and thus maintaining adult reproduction, suggesting that compromised astroglial ErbB-1 signaling may also contribute to reproductive abnormalities in aging females.

Novel putative nonprotein-coding RNA gene from 11q14 displays decreased expression in brains of patients with schizophrenia

A modified method of differential display was employed to identify a novel gene (named PSZA11q14), the expression of which was reduced in brains from patients with schizophrenia. Decreased expression of PSZA11q14 was identified initially in Brodmann's area (BA) 21 from a small group of patients with schizophrenia (n = 4) and normal controls (n = 6) and was confirmed subsequently using independent RT-PCR assay in BA 21, 22, and 9, and in hippocampus from a larger group of patients with schizophrenia (n = 36) and controls (n = 35). PSZA11q14 is located on chromosome 11q14, an area shown previously to co-segregate with schizophrenia and related disorders in several families. Decreased expression of PSZA11q14 in patients with schizophrenia and its location on 11q14 provide converging lines of evidence indicating that PSZA11q14 may be involved in at least some cases of schizophrenia. PSZA11q14 shows no significant homology with any known gene. It has no introns and produces two RNA transcripts of approximately 4.5 and approximately 7.0 kb. The largest open reading frame (ORF) in the PSZA11q14 transcripts may potentially encode for a short polypeptide of 71 amino acids. High frequency of rare codons, the short size of this ORF, and low homology with mouse sequences, however, indicate that PSZA11q14 may instead represent a novel member of a family of nonprotein-coding RNA genes that are not translated and that function at the RNA level. PSZA11q14 is located within the first intron of the DLG-2 gene and transcribed in the opposite direction to DLG-2. These results suggest that PSZA11q14 may be considered a candidate gene for schizophrenia acting as an antisense regulator of DLG-2, which controls assembling functional N-methyl-D-aspartate (NMDA) receptors.

Immobilization stress rapidly modulates BDNF mRNA expression in the hypothalamus of adult male rats

We demonstrated that short times (15 min) of immobilization stress application induced a very rapid increase in brain-derived neurotrophic factor (BDNF) mRNA expression in rat hypothalamus followed by a BDNF protein increase. The early change in total BDNF mRNA level seems to reflect increased expression of the BDNF transcript containing exon III, which was also rapidly (15 min) modified. The paraventricular and supraoptic nuclei, two hypothalamic nuclei closely related to the stress response and known to express BDNF mRNA, were analyzed by in situ hybridization following immobilization stress. In the parvocellular region of the paraventricular nucleus, BDNF mRNA levels increased very quickly as early as 15 min. In contrast, in the two other regions examined, the lateral and ventral magnocellular regions of the paraventricular nucleus, as well as in the supraoptic nucleus, signals above control were increased later, at 60 min. After stress application, plasma adrenocorticotropic hormone and corticosterone levels were strongly and significantly increased at 15 min. These studies demonstrated that immobilization stress challenge very rapidly enhanced BDNF mRNA levels as well as the protein, suggesting that BDNF may play a role in plasticity processes related to the stress response.

Growth factors and steroid hormones: a complex interplay in the hypothalamic control of reproductive functions

The mechanisms through which LHRH-secreting neurons are controlled still represent a crucial and debated field of research in the neuroendocrine control of reproduction. In the present review, we have specifically considered two potential signals reaching these hypothalamic neurons: steroid hormones and growth factors. Examples of the relevant physiological role of the interactions between these two families of biologically acting molecules have been provided. In many cases, these interactions occur at the level of hypothalamic astrocytes, which are presently accepted as functional partners of the LHRH-secreting neurons. On the basis of the observations here summarized, we have formulated the hypothesis that a functional co-operation of steroid hormones and growth factors occurring in the hypothalamic astrocytic compartment represents a key factor in the neuroendocrine control of reproductive functions.

Functional integrity of ErbB-4/-2 tyrosine kinase receptor complex in the hypothalamus is required for maintaining normal reproduction in young adult female rats

ErbB-1 tyrosine kinase receptors are necessary for maintaining female reproduction by modulating the release of LH-releasing hormone (LHRH). Changes in ErbB-1 signaling capacity in aging rats are linked to compromised reproduction. The interactive and synergistic nature of different members of ErbB receptors in mediating signal transduction exists in many cellular systems. Particularly, the interactions among ErbB-1 and ErbB-2 or ErbB-4 and ErbB-2 are known to be involved in the stimulation of LHRH secretion during sexual maturation. Thus, ErbB-4/-2 receptors may also play a role in maintaining reproduction during adulthood, and consequently, alteration in ErbB-4/-2 signaling capacity may contribute to compromised reproductive competence during aging. By in situ hybridization histochemistry, ErbB-4/-2 mRNAs were detected in the preoptic area (POA) and arcuate nucleus, which are important areas involved in the control of LHRH neuronal activity. RT-PCR analyses showed that levels of ErbB-4/-2 mRNA increased to a maximal value in the POA of young adult animals before the LH surge. However, no such increase was found in middle-aged female rats. The timing of the decrease in ErbB-4 mRNA in the median eminence-arcuate nucleus of middle-aged rats was delayed compared with that in young adult animals. Disruption of functional ErbB-4/-2 receptor complex by blocking ErbB-2 receptor synthesis in the hypothalamus via an infusion of ErbB-2 antisense oligodeoxynucleotide resulted in an estrous acyclicity in young adult rats. These results indicate that changes in ErbB-4/-2 gene expression and functional integrity of this ErbB-4/-2 receptor complex in the hypothalamus of middle-aged female animals may lead to an altered preovulatory LH release. Thus, the ErbB-4/-2 receptor complex is a physiological component necessary for maintaining female reproduction.

Differential expression of the "C" and "T" alleles of the 5-HT2A receptor gene in the temporal cortex of normal individuals and schizophrenics

A genetic association between schizophrenia and a silent C/T(102) polymorphism in the 5-HT2A receptor gene (5-HT2AR) has been previously reported; however, the mechanisms underlying this association remain unknown. Here we developed an improved quantitative assay for measurements of allele ratios, which revealed that the expression of allele "C" in the temporal cortex of normal heterozygous individuals was significantly lower than the expression of allele "T" (allele "C" to allele "T" ratio of approximately 0.8, P < 0.0001). Confirming decreased expression of allele "C," total levels of 5-HT2AR mRNA and protein in normal individuals with the C/C genotype were lower than in individuals with the T/T genotype. Similarly to normal individuals, allele "C" to allele "T" ratio in heterozygous schizophrenics was reduced (approximately 0.8, P < 0001). This ratio was independent of neuroleptic treatment history. By contrast, total levels of 5-HT2AR mRNA correlated inversely with neuroleptic free interval prior to death (r = -0.67, P < 0.001) suggesting a reversible neuroleptic effect. Total levels 5-HT2AR mRNA in neuroleptic free (> 26 weeks) schizophrenics (n = 11) were significantly lower than in controls (P = 0.03). The data suggest that increased prevalence of allele "C" among schizophrenics may be due to intrinsically low expression of this allele, which may contribute to a deficit in 5-HT2AR expression in some schizophrenics.

Altered gene activity of epidermal growth factor receptor (ErbB-1) in the hypothalamus of aging female rat is linked to abnormal estrous cycles

Activation of the ErbB-1 receptor is necessary for initiating mammalian female puberty by stimulating the release of LH-releasing hormone. It remains unclear whether ErbB-1 is also required in governing reproduction during adulthood and whether altered ErbB-1 signaling is linked to changes in gonadotropin secretion in aging females. The present study examined these issues. RT-PCR was employed to determine changes in ErbB-1 mRNA levels during proestrus in both young adult (YA) and middle-aged (MA) female rats. Before the LH surge, expression levels in the preoptic area of YA rats increased to a maximal value. No such increase in ErbB-1 mRNA was found in MA rats. This difference was confirmed by the analysis of in situ hybridization histochemistry, where a stronger mRNA signal was observed in the preoptic area of YA rats compared with MA females. ErbB-1 protein levels measured by Western blot reflected this difference. A peak level of ErbB-1 mRNA in the median eminence-arcuate nucleus was detected at 0800 h in YA rats, but it was delayed in MA animals. There were intense ErbB-1 mRNA-positive cells in the arcuate nucleus. Pharmacological blockade of ErbB-1 receptor-mediated signal transduction resulted in the disruption of estrous cyclicity in YA rats. These results indicate that ErbB-1 receptors are necessary for maintaining normal estrous cycles. Consequently, age-related alterations in hypothalamic ErbB-1 gene activity may contribute to a delayed preovulatory LH secretion in aging females. Thus, the ErbB-1 signaling system plays an important role in the control of female reproduction during adulthood.

Regulation of brain-derived neurotrophic factor transcripts by neuronal activation in rat hypothalamic neurons

Brain-derived neurotrophic factor (BDNF) belongs to the neurotrophin family and regulates the survival, differentiation, and maintenance of function in different neuronal populations. BDNF is strongly expressed in hypothalamic neurons, where it exerts long- or short-lasting actions. Because glutamate has been associated with regulations of hypothalamic hormones, we examined the regulation of the four promoters of the BDNF gene by glutamate in fetal hypothalamic neurons. The expression levels of BDNF transcripts were investigated using semiquantitative RT-PCR. BDNF protein was determined by enzyme immunoassay, and BDNF and Trk B (BDNF receptor) gene variations were determined by RNAse protection assay. By RT-PCR, we showed that, under basal conditions, BDNF transcripts from exons I, II, and III but not from IV were expressed in the hypothalamic neurons. Glutamate increased expression of both the protein and the four transcripts via N-methyl-D-aspartate receptors, with maximal stimulations after 3 hr of application for exon I and II mRNAs and after 1 hr for exon III and IV mRNAs. Actinomycin D blocked the increase of all transcripts, whereas cycloheximide treatment inhibited stimulation only of exon I and II mRNAs. Trk B mRNA was rapidly and transiently reduced after glutamate application. Our results demonstrate that glutamate 1) regulates BDNF mRNA expression at an early developmental stage in hypothalamic neurons and 2) exerts a differential regulation of BDNF transcripts.

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.

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.

Neurobiological mechanisms of the onset of puberty in primates

An increase in pulsatile release of LHRH is essential for the onset of puberty. However, the mechanism controlling the pubertal increase in LHRH release is still unclear. In primates the LHRH neurosecretory system is already active during the neonatal period but subsequently enters a dormant state in the juvenile/prepubertal period. Neither gonadal steroid hormones nor the absence of facilitatory neuronal inputs to LHRH neurons is responsible for the low levels of LHRH release before the onset of puberty in primates. Recent studies suggest that during the prepubertal period an inhibitory neuronal system suppresses LHRH release and that during the subsequent maturation of the hypothalamus this prepubertal inhibition is removed, allowing the adult pattern of pulsatile LHRH release. In fact, y-aminobutyric acid (GABA) appears to be an inhibitory neurotransmitter responsible for restricting LHRH release before the onset of puberty in female rhesus monkeys. In addition, it appears that the reduction in tonic GABA inhibition allows an increase in the release of glutamate as well as other neurotransmitters, which contributes to the increase in pubertal LHRH release. In this review, developmental changes in several neurotransmitter systems controlling pulsatile LHRH release are extensively reviewed.

Direct effects of nerve growth factor on thecal cells from antral ovarian follicles

TrkA, the nerve growth factor (NGF) tyrosine kinase receptor, is expressed not only in the nervous system, but also in nonneural cells, including discrete cellular subsets of the endocrine and immune system. In the rat ovary, trkA receptor abundance increases strikingly in thecal-interstitial cells during the hours preceding the first ovulation. Blockade of either trkA transducing capacity or NGF biological activity inhibited ovulation, suggesting a role for NGF in the ovulatory process of this species. To identify some of the processes that may be affected by trkA activation in the thecal compartment, we used purified thecal cells/thecal fibroblasts from bovine ovaries (heretofore referred to as thecal cells). Ribonuclease protection assays employing bovine-specific cRNA probes demonstrated the presence of the messenger RNAs (mRNAs) encoding NGF and its receptors, p75 NTR and trkA, in the thecal compartment of small, medium, and large antral follicles and showed that trkA mRNA is also expressed in granulosa cells. In situ hybridization and immunohistochemical examination of intact ovaries confirmed these cellular sites of NGF and trkA synthesis. TrkA mRNA, but not NGF mRNA, was lost within 48 h of placing thecal cells in culture. Thus, to study trkA-mediated actions of NGF on these cells we transiently expressed the receptor by transfection with a vector containing a full-length rat trkA complementary DNA under transcriptional control of the cytomegalovirus promoter. Because ovulation is preceded by an LH-dependent increase in androgen and progesterone production, the ability of NGF to modify the release of these steroids was determined in freshly plated cells still containing endogenous trkA receptors and in cells undergoing luteinization in culture that were transiently transfected with the trkA-encoding plasmid. NGF stimulated both androgen and progesterone release in freshly plated thecal cells, but not in luteinizing cells provided with trkA receptors. As ovulation in rodents requires an increased formation of PGE2 and has been shown to be antedated by proliferation of thecal fibroblasts, we determined the ability of NGF to affect these parameters in trkA-transfected thecal cells. The neurotrophin rapidly stimulated PGE2 release and amplified the early steroidal response to hCG in trkA-expressing cells, but not in cells lacking the receptor. Likewise, NGF stimulated [3H]thymidine incorporation into trkA-containing cells, but not into cells that had lost the receptor in culture. Induction of ovulation in immature rats by gonadotropin treatment verified that an increased cell proliferation in the thecal compartment, determined by the incorporation of bromodeoxyuridine into cell nuclei, occurs 4-5 h before ovulation in this species. These results suggest that the contribution of NGF to the ovulatory process includes a stimulatory effect of the neurotrophin on steroidogenesis, PGE2 formation, and proliferative activity of thecal compartment cells.

What role(s) for TGFalpha in the central nervous system?

Transforming growth factor alpha (TGFalpha) is a member of the epidermal growth factor (EGF) family with which it shares the same receptor, the EGF receptor (EGFR or erbB1). Identified since 1985 in the central nervous system (CNS), its functions in this organ have started to be determined during the past decade although numerous questions remain unanswered. TGFalpha is widely distributed in the nervous system, both glial and neuronal cells contributing to its synthesis. Although astrocytes appear as its main targets, mediating in part TGFalpha effects on different neuronal populations, results from different studies have raised the possibility for a direct action of this growth factor on neurons. A large array of experimental data have thus pointed to TGFalpha as a multifunctional factor in the CNS. This review is an attempt to present, in a comprehensive manner, the very diverse works performed in vitro and in vivo which have provided evidences for (i) an intervention of TGFalpha in the control of developmental events such as neural progenitors proliferation/cell fate choice, neuronal survival/differentiation, and neuronal control of female puberty onset, (ii) its role as a potent regulator of astroglial metabolism including astrocytic reactivity, (iii) its neuroprotective potential, and (iv) its participation to neuropathological processes as exemplified by astroglial neoplasia. In addition, informations regarding the complex modes of TGFalpha action at the molecular level are provided, and its place within the large EGF family is precised with regard to the potential interactions and substitutions which may take place between TGFalpha and its kindred.

Levels of mRNAs encoding synaptic vesicle and synaptic plasma membrane proteins in the temporal cortex of elderly schizophrenic patients

BACKGROUND

Electron microscopy and biochemical studies indicate that developmental abnormalities in synaptic organization may be present in brains of schizophrenic patients. This study determined whether these synaptic abnormalities are reflected in differential or uniform alterations in the expression of various synaptic protein genes in the left superior temporal gyrus of schizophrenic patients.

METHODS

Levels of mRNAs encoding four synaptic vesicle proteins (synaptotagmin I [p65], rab3a, synaptobrevin 1, and synaptobrevin 2) and two synaptic plasma membrane proteins (syntaxin 1A and SNAP-25) were measured postmortem in the left superior temporal gyrus from elderly (58-95 years) schizophrenic patients (n = 14) and age-matched control subjects (n = 9).

RESULTS

There were significant negative correlations between age and levels of synaptotagmin I (p65), rab3a, synaptobrevin 1, SNAP-25, and syntaxin 1A mRNAs in schizophrenic patients (-.692 < r < -.517,.003 < p <.030) but not in control subjects. Levels of all six synaptic mRNAs studied were increased in the younger (58-79 years) subgroup of schizophrenic patients compared to control subjects and older (80-95 years) subgroup of schizophrenic patients.

CONCLUSIONS

That similar abnormalities were found for mRNAs encoding different synaptic vesicle and synaptic plasma membrane proteins suggests that they reflect overall neurodevelopmental abnormalities in synaptic connectivity in the temporal cortex of schizophrenic patients rather than changes in the number of synaptic vesicles per synapse or abnormalities in a specific synaptic function.

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.

Two molecular forms of gonadotropin-releasing hormone (GnRH-I and GnRH-II) are expressed by two separate populations of cells in the rhesus macaque hypothalamus

Gonadotropin-releasing hormone represents the primary neuroendocrine link between the brain and the reproductive axis, and at least two distinct molecular forms of this decapeptide (GnRH-I and GnRH-II) are known to be expressed in the forebrain of rhesus macaques (Macaca mulatta). Although the distribution pattern of the two corresponding mRNAs is largely dissimilar, their expression appears to show some overlap in specific regions of the hypothalamus; this raises the possibility that some cells express both molecular forms of GnRH. To resolve this issue, double-label histochemistry was performed on hypothalamic sections from six male rhesus macaques, using a monoclonal antibody to GnRH-I and a riboprobe to monkey GnRH-II mRNA. In total, more than 2000 GnRH neurons were examined but in no instance were GnRH-I peptide and GnRH-II mRNA found to be coexpressed. This finding emphasizes that GnRH-I and GnRH-II are synthesized by two distinct populations of hypothalamic neurons, and suggests that they may be regulated by different neuroendocrine pathways.

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

The testicular regulation of luteinizing hormone (LH) secretion in the adult rhesus monkey is mediated by an indirect action of testosterone to decelerate pulsatile gonadotrophin releasing hormone (GnRH) release. Whether this negative feedback action of testosterone involves regulation of GnRH gene expression is unknown. Therefore, the effect of bilateral orchidectomy on hypothalamic levels of the mRNA encoding this hypophysiotropic factor was examined. The feedback action of testosterone is generally considered to be mediated through non-GnRH cells, and the present experiment provided the opportunity to also examine testicular influences on mRNAs encoding putative hypothalamic factors implicated in the testicular regulation of LH secretion. Adult male rhesus monkeys were orchidectomized (n=5) or sham-orchidectomized (n=5) and killed 6 weeks later, after a castration-induced hypersecretion of LH was established. Separate preoptic and mediobasal hypothalamus containing areas were collected, and levels of GnRH mRNA, as well as those of mRNAs encoding pro-opiomelanocortin (POMC), the gamma-aminobutyric acid (GABA) synthesizing enzymes (glutamic acid decarboxylase 65 and 67; GAD65 and GAD67, respectively), neuropeptide Y, galanin and transforming growth factor (TGF)alpha, were quantified using RNase protection assay. Values were expressed in terms of optical density relative to that of cyclophilin mRNA levels. Bilateral orchidectomy produced a significant increase in GnRH mRNA levels that was restricted to the mediobasal hypothalamus and that was associated with a significant decrease in POMC, GAD65 and GAD67 mRNA levels in this region of the hypothalamus. In contrast, neuropeptide Y, galanin and TGFalpha mRNA levels were not affected by castration. These results indicate that, in the monkey, the deceleration of pulsatile GnRH release that is imposed by the testis, and presumably mediated by testosterone, is associated with a concomitant down regulation of GnRH gene expression in the mediobasal hypothalamus. They also support the notion that this hypothalamic feedback action may be mediated by POMC-and GABA-producing neurones in the mediobasal hypothalamus.