Showing papers in "Neuroendocrinology in 1997"
TL;DR: Treatment of the ob/ob mouse with recombinant leptin was found to markedly upregulate side chain cleavage and 17 alpha-hydroxylase mRNA levels in the ovary, demonstrating that leptin, acting either through a direct or indirect mechanism, can regulate gene expression in reproductive tissues.
Abstract: The obese gene (ob) product, leptin, has recently been shown to be produced by adipocytes and to circulate in the plasma acting as a hormone to modulate appetite and metabolism. Intriguingly, the ob/o
320 citations
TL;DR: The results show that the POMC neurons are targets for NPY, which is presumably present in, and released from, fibres originating in the ventromedial arcuate nucleus and which may play a role in NPY-induced feeding.
Abstract: The arcuate nucleus of the hypothalamus houses a number of neurochemically different cell populations. Among these, a dense cluster of small neuropeptide-Y (NPY)-expressing neurons is located in its ventromedial subdivision and a pro-opiomelanocortin (POMC)-expressing neuron population in its ventrolateral part. Furthermore, both neuropeptide Y Y1 and Y2 receptors (Y1-Rs and Y2-Rs) are expressed in the arcuate nucleus. Here we analyse the co-expression of NPY and POMC/adrenocorticotropic hormone with the Y1-R and Y2-R in arcuate neurons using immunohistochemistry and in situ hybridization. Many, but not all, POMC neurons expressed Y1-R mRNA and protein. Conversely, several Y1-R-positive, POMC-negative neurons were found. NPY-positive nerve terminals were found in close apposition to Y1-R-like immunoreactivity localized close to the dendritic and somatic cell membranes. Y2-R mRNA was found in almost all NPY mRNA-expressing neurons, but also in a group of NPY mRNA-negative cells. These results show that the POMC neurons are targets for NPY, which is presumably present in, and released from, fibres originating in the ventromedial arcuate nucleus and which may play a role in NPY-induced feeding. Release of NPY, and possible coexisting messengers, may be controlled by presynaptic Y2-R expressed in NPY neurons. Taken together, the findings support the division of Y1-Rs and Y2-Rs into post- and presynaptic receptors, respectively.
309 citations
TL;DR: The data presented here are the first to describe the distribution of estrogen receptor-beta (ER beta)-like immunoreactivity in brain tissue and suggest that ER beta mediates estrogen's actions in a subset of hypothalamic and limbic neurons.
Abstract: The data presented here are the first to describe the distribution of estrogen receptor-beta (ER beta)-like immunoreactivity in brain tissue. We employed an affinity purified rabbit antiserum made against a portion of the C-terminal of the ER beta protein. The majority of ER beta-like immunoreactive (ER beta-ir) neurons were found in the following regions: lateral septum, bed nucleus of the stria terminalis, paraventricular nucleus, supraoptic nucleus, medial amygdala, the dentate gyrus and the CA1 and CA2 fields of the hippocampus. A few ER beta-ir neurons were noted in the anterior hypothalamus, periventricular nucleus, medial preoptic area, and in the arcuate nucleus. All of the immunoreactivity appeared nuclear in its subcellular distribution, with the exception of the cells in the lateral septum, CA1 and CA2. In these areas immunoreactivity was noted throughout the perikarya and in cell processes. The data suggest that ER beta mediates estrogen's actions in a subset of hypothalamic and limbic neurons.
267 citations
TL;DR: Strain differences in HPA axis responsivity, observed under conditions of acute stress, are further amplified during prolonged or repeated stress, which may magnify the behavioral and immunological differences observed under basal as well as challenged conditions.
Abstract: Sprague-Dawley (SD), Fischer 344 (F344) and Lewis (LEW) rats are used in a wide variety of laboratory studies. Compared to SD and LEW rats, F344 rats show significantly greater activation of the hypothalamic-pituitary-adrenal (HPA) axis in response to acute stress, or to immunologic challenge. These differences in HPA axis responsivity have been the basis for numerous studies investigating strain differences in immunological and behavioral parameters. However, strain differences in the adaptation of the HPA axis response to prolonged stress, or to repeated stress, have not been investigated. This series of studies demonstrates that F344 rats maintain significantly higher ACTH and corticosterone levels than SD and LEW rats during a single prolonged stress session. Furthermore, F344 rats show virtually no habituation or adaptation of the corticosterone stress response during a single prolonged (4 h) stress session, or during stress sessions repeated over a period of 10 days. In contrast, SD and LEW rats show habituation both within and across stress sessions. Strain differences in HPA axis responsivity are also reflected in the significant adrenal hypertrophy observed in F344 rats (but not in SD or LEW rats) following repeated stress. These results show that strain differences in HPA axis responsivity, which are observed under conditions of acute stress, are further amplified during prolonged or repeated stress. These differences under prolonged or repeated stress conditions may consequently magnify the behavioral and immunological differences observed between strains under basal as well as challenged conditions.
258 citations
TL;DR: Subcutaneous IL-6 administration induced synchronized dose-dependent increases in the RMR and hypothalamic-pituitary-adrenal axis activity, suggesting that hypothalamic corticotropin-releasing hormone may mediate both of these functions in humans.
Abstract: Interleukin-6 (IL-6), the main circulating cytokine, is putatively a major mediator of the effects of the immune system on several endocrine axes and intermediate metabolism. We performed dose-response studies of recombinant human IL-6 on pituitary hormone secretion in 15 healthy male volunteers, using 5 single, escalating subcutaneous doses of IL-6 (0.1, 0.3, 1.0, 3.0 and 10.0 micrograms/kg body weight), each in 3 volunteers. We measured resting metabolic rate (RMR) with indirect calorimetry and plasma anterior pituitary hormones and vasopressin (AVP) at baseline and half-hourly over 4 h after the injection. All doses examined were tolerated well and produced no significant adverse effects. Dose-dependent RMR increases were observed in response to the 3.0- and 10.0-microgram/kg doses of IL-6, beginning at 60 min and slowly peaking between 180 and 240 min. Plasma adrenocorticotropic-hormone concentrations increased dramatically and dose-dependently in all the patients who received the 3.0- and 10.0-microgram/kg doses of IL-6, respectively, peaking to 150 and 255 pg/ml at 60 min, and slowly returning to normal by 4 h. Corresponding plasma cortisol levels peaked dose-dependently between 90 and 150 min, but remained elevated throughout the sampling period. In contrast, the growth hormone (GH) dose-response was bell-shaped, with maximum (approximately 100-fold) stimulation achieved by 3.0 micrograms/kg IL-6. Prolactin (PRL) showed a similar but less pronounced response pattern. Thyroid-stimulating hormone (TSH) dose-dependently and progressively decreased over the 240 min, while gonadotropins showed no clear-cut changes. In conclusion, subcutaneous IL-6 administration induced synchronized dose-dependent increases in the RMR and hypothalamic-pituitary-adrenal axis activity, suggesting that hypothalamic corticotropin-releasing hormone may mediate both of these functions in humans. IL-6 also acutely stimulated GH and PRL secretion and suppressed TSH secretion. The dose of 3.0 micrograms/kg could be used safely in the study of patients with disturbances of the hypothalamic-pituitary unit or of thermogenesis.
223 citations
TL;DR: The reported data here are consistent with the hypothesis that an altered GR capacity or function underlies the exaggerated HPA activity in depression.
Abstract: Decreased feedback control of the hypothalamic-pituitary-adrenocortical (HPA) system as revealed by the combined dexamethasone and corticotropin-releasing hormone (DEX-CRH) test has been documented in the vast majority of patients with affective disorders. This finding was interpreted as a failure at the level of the glucocorticoid receptor (GR)-mediated feedback action, which apparently fails to restrain HPA activity in the presence of elevated plasma corticosteroid levels. To test this hypothesis we conducted the DEX/CRH test using increasing doses of DEX in order to establish a dose-response relationship. We used three different DEX doses (0.75, 1.5, 3.0 mg) in three groups of depressed patients and controls. As expected, increasing DEX doses were associated with decreasing amounts of adrenocorticotropin (ACTH) and cortisol being released after CRH injection. However, dose-response curves for both plasma ACTH and cortisol concentrations were shifted to higher area under the curve (AUC) values among patients compared to controls. Pretreatment with 0.75 and 1.5 mg DEX produced significantly higher AUC values for both plasma ACTH and cortisol values among patients. These differences became less obvious with the higher DEX doses, indicating that the dose of 1.5 mg used in the majority of clinical studies so far is well suited to differentiate between healthy controls and patients. The reported data here are consistent with the hypothesis that an altered GR capacity or function underlies the exaggerated HPA activity in depression.
211 citations
TL;DR: First evidence to indicate the specific localization of the OB-R in the brain of lean, obese and NIDDM subjects is presented.
Abstract: Leptin (OB protein), the product of the adipose-specific ob gene, exerts important effects in the regulation of food intake and energy expenditure. Based upon results from animal studies, several groups have suggested that this action may be exerted in the brain, specifically in the hypothalamic region. However, to date, the localization of the OB-R in the human brain has not been described. One aim of this study was to contribute to a better understanding of the role that the central nervous system plays in the pathogenesis of obesity in humans. A first stage was to determine the OB-R expression in the human brain by means of immunohistochemistry and Western blotting. Several brain regions from 17 lean, 14 obese, and 4 diabetic (NIDDM) subjects, obtained from archival autopsy material, were sampled. Brain samples from neocortex, hypothalamus, medualla, limbic system, pineal and cerebellum were routinely processed in paraffin and analyzed with the avidin-biotin immunoperoxidase and diaminobenzidine detection method. Western blotting (WB) analysis was done on fresh brain tissue from an obese patient. Specific OB-R immunoreactivity was localized in the choroid plexus epithelium, ependymal lining, and neurons of the hypothalamic nuclei (arcuate, suprachiasmatic, mamillary, paraventricular, dorsomedial, supraoptic and posterior), nucleus basalis of Meynert, inferior olivary nuclei and cerebellar Purkinje cells. No differences in OB-R immunoreactivity were found among the three groups examined. WB analysis yielded 97- and 125-kD bands in the hypothalamus and cerebellum. In summary, this paper presents the first evidence to indicate the specific localization of the OB-R in the brain of lean, obese and NIDDM subjects.
209 citations
TL;DR: Evidence is provided for reduced responsiveness to glucocorticoid feedback inhibition in human aging by the latency to and extent of decline of plasma ACTH concentration during and following the cortisol infusion.
Abstract: Aging-related reduction in the sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis to glucocorticoid feedback inhibition has been demonstrated in rodents, but aging effects on glucocorticoid
176 citations
TL;DR: The data show that leptin markedly influences LH secretion and the estrous cycle in the female rat and an impairment of reproductive function is shown.
Abstract: Recent data indicate that leptin may well play an important regulatory role in the hypothalamo-pituitary-gonadal axis. In order to further unravel the mechanisms by which leptin acts, we have studied the effect of treatment (8 days) of leptin antiserum (5 microl daily; i.c.v.) on LH pulsatility and estrous cycle in adult female rats. The administration of leptin antiserum led to a marked decrease in LH pulsatility as assessed by the area under the curve (13.5 +/- 4.7 ng/ml) in comparison to rats treated with normal rabbit serum (114 f 53 ng/ml; p < 0.01). Furthermore, rats treated with leptin antiserum showed an impairment of reproductive function as shown by the fact that all rats remained in anestrus. In conclusion, these data show that leptin markedly influences LH secretion and the estrous cycle in the female rat.
163 citations
TL;DR: These results suggest that (1) TN-GnRH cells are involved in the control of the threshold for nest-building behavior initiation and (2) TNs are not a prerequisite for other aspects of reproductive behavior in the male gouramis.
Abstract: Functions of the terminal nerve (TN) are largely unknown. To examine whether gonadotropin-releasing hormone (GnRH)-immunoreactive TN cells (TN-GnRH cells) are involved in the control of reproductive b
162 citations
TL;DR: Taken as a whole, the current data suggest that the diffusible gases, NO and CO, act as novel transmitters in the neuroendocrine axis and mediate a variety of important neuro endocrine functions.
Abstract: Recent work has demonstrated that the brain has the capacity to synthesize impressive amounts of the gases nitric oxide (NO) and carbon monoxide (CO). There is growing evidence that these gaseous mole
TL;DR: The findings suggest that the estrogenic regulation of oxytocin receptor binding in both CNS and uterine tissues may in part be mediated by de novo synthesis of oxy hostage receptor mRNA or by alterations in the stability of Oxytocin receptors gene transcripts.
Abstract: Oxytocin receptors are regulated during parturition and lactation. Gonadal steroids are thought to be key players in this regulation. It is not well documented how oxytocin receptor gene expression is regulated in the CNS. In this study we analyzed potential estrogen effects on the oxytocin receptor mRNA levels in some areas integral to the limbic-hypothalamic system, namely the ventromedial nucleus of the hypothalamus (VMH), posterior medial nucleus of amygdala (MeAmyg), and arcuate nucleus (ARC), as well as the caudate putamen (CPu), CA1 region of the hippocampus, anterior pituitary, and uterine tissue of ovariectomized (OVX) female rats. By in situ hybridization we observed a 4.4-fold increase in oxytocin receptor mRNA levels in the VMH after 48 h of estrogen treatment when compared to OVX rats. Smaller increases were observed in the MeAmyg, hippocampus, and anterior pituitary (3.18, 1.76, and 2.55, respectively). No changes in oxytocin receptor mRNA levels were observed in the CPu or ARC after estrogen treatment. A similar finding resulted from slot-blot analysis of total mRNA extracts. In uterine tissue, 48 h of estrogen treatment increased oxytocin receptor mRNA level in the myometrium (3.13-fold). No changes in oxytocin receptor mRNA levels were observed after 12 and 24 h of estrogen treatment. These findings suggest that the estrogenic regulation of oxytocin receptor binding in both CNS and uterine tissues may in part be mediated by de novo synthesis of oxytocin receptor mRNA or by alterations in the stability of oxytocin receptor gene transcripts.
TL;DR: Results show that MCH has a stimulatory effect on LH release when administered into the pre-optic area, median eminence (ME) and MPOA, and that alpha-MSH has an inhibitory effect in the MPOA and ME.
Abstract: Alpha-melanocyte-stimulating hormone (alpha-MSH) and melanin-concentrating hormone (MCH) are two peptide neurotransmitters widely distributed in the mammalian brain, the former originating mainly from cell bodies in the arcuate nucleus and the latter from cell bodies in the zona incerta and lateral hypothalamus. Within the hypothalamus they innervate the pre-optic area, median eminence (ME) and ventromedial nucleus (VMN). Both peptides stimulate sexual behaviour and in this report we have investigated their effect on another gonadal steroid-dependent function, luteinising hormone (LH) release. alpha-MSH, MCH or a combination of the two were injected bilaterally (100 ng/side) into either the medial pre-optic area (MPOA), ME, or VMN of anaesthetised (Saffan 3 ml/kg i.p.) rats that had previously been ovariectomised and adrenalectomised (O+A) and then primed with 5 microg/rat s.c. oestradiol benzoate (OB), 48 h before peptide administration. MCH stimulated LH release when applied to the MPOA and ME; alpha-MSH was inhibitory in the ME and in this model was ineffective in the MPOA. Neither peptide was effective in the VMN. The two peptides were then injected into the MPOA of O+A rats primed with OB followed 48 h later by 0.5 mg/rat s.c. progesterone, which normally induces an LH surge. alpha-MSH, but not MCH, inhibited this induced rise in LH. Administration of anti-MCH antiserum (0.5 microg/side neat serum) also had an inhibitory effect on LH release in this model. These results show that MCH has a stimulatory effect on LH release when administered into the ME and MPOA. In the MPOA, this may be physiologically significant since blocking endogenous MCH with an anti-MCH antiserum inhibits LH release. On the other hand, alpha-MSH has an inhibitory effect on LH release in the MPOA and ME. In the teleost skin these two peptides are functionally antagonistic; it seems that a similar antagonism exists between their effects on LH release.
TL;DR: Transgenic mice with impaired GR function show major disturbances in HPA axis regulation which seem to be caused by the primary defect in conjunction with secondary modifications in, amongst others, pituitary CRH receptor system(s), sympathetic output and adrenal development.
Abstract: A transgene expressing antisense RNA complementary to a fragment of the glucocorticoid receptor cDNA was incorporated into the mouse genome and resulted in a transgenic animal that has decreased glucocorticoid receptor function. The transgenic mice showed basal plasma ACTH and corticosterone levels similar to those of the normal control animals. We have further investigated changes in HPA axis regulation by use of different neuroendocrine challenge tests including a dexamethasone suppression test (DST). In comparison to normal mice, a tenfold higher dose of dexamethasone (i.e. 20 µg/100 g body weight) was required to suppress the basal corticosterone levels of transgenic mice. Dexamethasone (2 µg/100 g body weight) produced a long-lasting suppression of plasma ACTH and corticosterone levels in control mice, whereas in transgenic animals only a short-lasting decrease in ACTH levels was apparent. Corticotropin-releasing hormone (CRH) administration resulted in an enhanced response in plasma ACTH levels in transgenic mice, whereas the corticosterone response was markedly reduced. The discrepancy between ACTH and corresponding corticosterone secretions in transgenic mice could be attributed, in part, to a reduced sensitivity of the adrenal gland to stimulation by ACTH. Pituitaries of transgenic mice contained about 50% less proopiomelanocortin (POMC) mRNA than those of control animals. No significant differences were noted in the ACTH or protein contents of normal and transgenic mice pituitary glands although a slight increase in protein content of the transgenic mouse adrenal gland was apparent. In conclusion, transgenic mice with impaired GR function show major disturbances in HPA axis regulation which seem to be caused by the primary defect in conjunction with secondary modifications in, amongst others, pituitary CRH receptor system(s), sympathetic output and adrenal development. This mouse is therefore a useful model to study the consequences of life-long defective GR function and HPA axis regulation in general.
TL;DR: The results demonstrate that food deprivation is capable of generating in obese Zucker rats a stress-like response that translates into a particularly striking activation of the hypothalamic-pituitary-adrenal axis.
Abstract: The time course of the action of food deprivation on the functional activation of corticotropin-releasing hormone (CRH) neurons and on the expression of the genes encoding CRH and its receptors of typ
TL;DR: The present findings suggest that MK-677 may simultaneously improve sleep quality and correct the relative hyposomatotropism of senescence in healthy young and older adults.
Abstract: Previous studies have indicated the existence of common mechanisms regulating sleep and somatotropic activity. In the present study, we investigated the effects of prolonged treatment with a novel, orally active, growth hormone secretagogue (MK-677) on sleep quality in healthy young and older adults. Eight young subjects (18-30 years) followed a double-blind, placebo-controlled, three-period crossover design. Each subject participated in three 7-day treatment periods (with bedtime drug administration), presented in random (Latin square) order, and separated by at least 14 days. Doses were 5 and 25 mg MK-677 and matching placebo. Six older subjects, ages 65-71 years, each participated in two 14-day treatment periods (with bedtime drug administration) separated by a 14-day washout. Doses were 2 and 25 mg MK-677 during the first and second periods, respectively. Baseline sleep and hormonal data were obtained on the 2 days preceding the beginning of the first 14-day treatment period. In young subjects, high-dose MK-677 treatment resulted in an approximately 50% increase in the duration of stage IV and in a more than 20% increase in REM sleep as compared to placebo (p < 0.05). The frequency of deviations from normal sleep decreased from 42% under placebo to 8% under high-dose MK-677 (p < 0.03). In older adults, treatment with MK-677 was associated with a nearly 50% increase in REM sleep (p < 0.05) and a decrease in REM latency (p < 0.02). The frequency of deviations from normal sleep also decreased (p < 0.02). The present findings suggest that MK-677 may simultaneously improve sleep quality and correct the relative hyposomatotropism of senescence.
TL;DR: The findings suggest that CRH has an inhibitory effect on the pineal secretion of melatonin in normal man, which may extend the knowledge of neuroendocrine alterations mediating the adaptive response to stress and the eventual involvement in the pathogenesis of depression.
Abstract: Interactions between the hypothalamic-pituitary-adrenocortical (HPA) system and melatonin secretion have been demonstrated, but only the effects of melatonin on the activity of the HPA system have bee
TL;DR: Results indicate that the GAL-R1 mRNA is not only expressed in anterior hypothalamic nuclei but also in the mediobasal hypothalamus and periventricular region, which represents the morphological substrate for GAL roles in the hypothalamic regulation of neuroendocrine, behavioral and autonomic functions.
Abstract: The semiquantitative distribution of mRNA encoding for rat galanin receptor (GAL-R1) was examined by in situ hybridization in the rat hypothalamus using a 35S-riboprobe. Most hypothalamic nuclei expressed GAL-R1 mRNA. In the anterior hypothalamus, high levels of expression were found in the medial preoptic area, paraventricular and supraoptic nuclei. Numerous cells also expressed the GAL-R1 mRNA with a moderate level of expression in the periventricular region. Very few GAL-R1-expressing cells were present in the suprachiasmatic nucleus. In the medial hypothalamus, numerous expressing cells were detected in the dorsomedial and ventromedial nuclei. The arcuate nucleus was moderately labeled throughout its rostrocaudal extent; labeled cell bodies were visible in the ventromedial and ventrolateral subdivisions as well. These results indicate that the GAL-R1 mRNA is not only expressed in anterior hypothalamic nuclei but also in the mediobasal hypothalamus and periventricular region. This hypothalamic distribution correlates well with that of 125I-GAL-binding sites and GAL-immunoreactive fibers. This distribution represents the morphological substrate for GAL roles in the hypothalamic regulation of neuroendocrine, behavioral and autonomic functions.
TL;DR: Evidence is provided that the neuroendocrine events regulating the reproductive cyclicity influence the endotoxin-induced activation of the early gene c-fos in selective structures of the brain and the stimulation of neurons directly involved in the regulation of the HPA axis.
Abstract: The purpose of this study was to investigate whether the ovulatory cycle interferes with the effect of the acute-phase response of a systemic immune activation on the transcription of the immediate early gene c-fos and the stress-related neuropeptide corticotropin-releasing hormone (CRH) in the brains of female rats. Throughout the day of proestrus and diestrus-2 (09.00, 12.00, 15.00 h), adult rats received either a single intraperitoneal injection of the endotoxin lipopolysaccharide (LPS, 200 micrograms/100 g body weight) or the vehicle solution and were killed 3 h later (12.00, 15.00, 18.00 h). Frozen brains were mounted on a microtome, cut in 30-micron slices and then processed for the detection of c-fos mRNA and CRH primary transcript (heteronuclear [hnRNA]) by means of in situ hybridization histochemistry using 35S-labeled exonic and intronic probes, respectively. LPS injection induced a profound expression of c-fos mRNA in the several nuclei and areas of the brain, such as the organum vasculosum of the lamina terminalis/medial preoptic area, supraoptic nucleus, parvo- and magnocellular divisions of the hypothalamic paraventricular nucleus (PVN), arcuate nucleus/median eminence, central nucleus of the amygdala, locus coeruleus, nucleus of the solitary tract, area postrema and ventrolateral medulla. Interestingly, the intensity of expression of c-fos mRNA depended on the phase of the estrous cycle and/or the time of the day. Indeed, in several of the structures described above, LPS induced a more pronounced c-fos signal in the morning of proestrus than the afternoon and diestrus-2. CRH primary transcript was significantly increased by LPS treatment selectively in the parvocellular division of the PVN and the highest hybridization signal was observed in the morning of proestrus, a period where a large number of c-fos-positive cells were colocalized in CRH-immunoreactive neurons. A significant increase in the levels of AVP hnRNA was also observed in the parvocellular PVN of animals sacrificed at noon and early afternoon of both pro- and diestrus days. These results provide evidence that the neuroendocrine events regulating the reproductive cyclicity influence the endotoxin-induced activation of the early gene c-fos in selective structures of the brain and the stimulation of neurons directly involved in the regulation of the HPA axis. It is possible that the gonadal status of female mammals plays a crucial role in the integration of the organism in the presence of foreign material in preventing an exaggerated immune response during particular phases of the ovulatory cycle. The capacity of female animals to modulate the intensity through which the neuronal circuitry activated during immunogenic processes is likely to be an elegant sexual dimorphism participating in the adjustment of the responses in line with the physiological demand.
TL;DR: It is demonstrated that glucocorticoids suppress CREB phosphorylation in hypophysiotropic CRH neurons and suggested that prevention of CREBosphorylation is a possible mechanism for feedback inhibition of CRH biosynthesis by glucocORTicoids.
Abstract: The corticotropin-releasing hormone (CRH) gene contains a perfect palindromic motif in its promoter region that allows binding of the cyclic adenosine monophosphate response element binding protein, CREB. Since previous studies suggest that the CRH gene can be activated by cyclic adenosine monophosphate, we determined whether stress and feedback inhibition by glucocorticoids in CRH-producing neurons in the hypothalamic paraventricular nucleus could be mediated by changes in the phosphorylation of CREB. Antisera to CREB and phospho-CREB Ser133 (PCREB), the active phosphorylated form of CREB, were used for immunohistochemical studies on rat brain. In nonstressed animals CREB immunostaining was confined to the nucleus of cells ubiquitously throughout the hypothalamus, while PCREB immunostaining was discretely localized in magnocellular neurons and only a few cells in the medial parvocellular subdivision of the paraventricular nucleus. Ether and handling stress markedly increased the number of PCREB-labeled neurons in the parvocellular subdivision. Double immunolabeling with CRH antiserum revealed that the majority of hypophysiotropic CRH neurons in stressed animals expressed PCREB. Following systemic administration of dexamethasone (100 micrograms/day) for 2.5 days, PCREB immunostaining was completely abolished in parvocellular CRH-producing neurons after ether or handling stress. Dexamethasone had no apparent effect on CREB immunostaining. These results demonstrate that glucocorticoids suppress CREB phosphorylation in hypophysiotropic CRH neurons and suggest that prevention of CREB phosphorylation is a possible mechanism for feedback inhibition of CRH biosynthesis by glucocorticoids.
TL;DR: A physiological role for AMPA receptors in the production of the steroids-induced LH surge was suggested, based on the finding that central administration of the selective AMPA receptor antagonist, NBQX, into the third cerebroventricle significantly attenuated the steroid- induced LH surge in the ovariectomized adult female rat.
Abstract: Recent work has demonstrated that glutamate functions as a major transmitter involved in the regulation of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) secretion in female animals, although the specific receptors and mechanisms mediating its effects have not been completely worked out. The purpose of the present study, therefore, was to examine the role of the AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid)-type glutamate receptor in the control of GnRH and LH secretion in female animals. Toward this end, the dose- and steroid-dependent effects of AMPA on GnRH and LH secretion in female rats were investigated using both in vitro and in vivo approaches, and the role of AMPA receptors in the production of the steroid-induced LH surge was also assessed. The results of the study revealed that central administration of AMPA resulted in a stimulation of LH release in the estrogen-primed ovariectomized adult rat. AMPA was also found to potently stimulate GnRH release in vitro from mediobasal hypothalamic (MBH) fragments obtained from estrogen-primed ovariectomized adult rats, and this effect was blocked by the selective AMPA receptor antagonist, NBQX. The mechanism of action of AMPA appeared to differ from that of N-methyl-D-aspartate (NMDA) as AMPA, in contrast to NMDA, failed to elevate nitric oxide synthase activity in the hypothalamus. The effect of AMPA on LH secretion was demonstrated to be steroid dependent, as central administration of AMPA stimulated LH release in estrogen-primed ovariectomized rats, but was inhibitory to LH release in non-estrogen-primed ovariectomized rats. In contrast, AMPA stimulated GnRH release equally well from MBH fragments obtained from estrogen-primed or non-estrogen-primed ovariectomized rats. The different effects of AMPA on LH release may be due to different pituitary sensitivities between the two models, or alternatively, AMPA may stimulate the release of LH inhibitory factors in the ovariectomized rat in the absence of estrogen. Finally, a physiological role for AMPA receptors in the production of the steroid-induced LH surge was suggested, based on the finding that central administration of the selective AMPA receptor antagonist, NBQX, into the third cerebroventricle significantly attenuated the steroid-induced LH surge in the ovariectomized adult female rat.
TL;DR: The data suggest that suppressed GH secretion in food-deprived rats may reflect a general downregulation of the neuroendocrine and pituitary GH axis.
Abstract: Neuroendocrine mechanisms governing growth hormone (GH) secretion are sensitive to nutritional status since the normal pulsatile pattern of GH release is disrupted during conditions of food deprivation or malnutrition. A reasonable hypothesis for this occurrence is the alteration of somatostatin and GH-releasing hormone (GHRH) synthesis, storage and secretion. In this study, we investigated the effects of food deprivation on GH, GHRH, hypothalamic and pituitary galanin (GAL), and somatostatin through immunocytochemical and mRNA analysis. Adult male rats were subjected to 72 h of food deprivation, during which an average of 18% total body weight was lost. ICC studies were performed on brain sections from the rostral, middle and caudal regions of the median eminence of the hypothalamus using the avidin-biotin-peroxidase method. Immunocytochemical results were generated for the percent area and optical density (intensity) of immunostaining in the median eminence. Messenger RNA analyses were performed using sense and antisense riboprobes produced from cDNA clones for GH, GHRH, somatostatin and GAL. Food deprivation decreased somatostatin immunostaining in middle and caudal regions of the median eminence; similarly, food deprivation resulted in decreased GHRH immunostaining in rostral and middle sections of the median eminence of the hypothalamus. mRNA levels for somatostatin, GHRH and GH and GAL were also reduced by food deprivation. Our data suggest that suppressed GH secretion in food-deprived rats may reflect a general downregulation of the neuroendocrine and pituitary GH axis.
TL;DR: It is concluded that pulsatile GnRH secretion occurs in the virtual absence of GnRH cell bodies but does not occur from GnRH terminals in the isolated median eminence, indicating that a mechanism of Gn RH pulsatility is located in the retrochiasmatic hypothalamus and involves neurons different from the GnRH neurons.
Abstract: Gonadotropin-releasing hormone (GnRH) is typically secreted in a pulsatile manner. It is still unclear whether pulsatility depends on a GnRH pulse generator residing in the GnRH neurons or in other neurons. Since the cell bodies of GnRH neurons are located rostrally to the optic chiasm and the majority of GnRH terminals in the median eminence of the rat hypothalamus, we have compared GnRH secretion from individual preoptic, retrochiasmatic and median eminence explants using a static incubation system. GnRH is released from the three different types of explant in response to depolarization with veratridine or glutamate receptor stimulation using the agonist N-methyl-D-aspartate. Only the retrochiasmatic explants, however, show a characteristic pulsatile secretion of GnRH. The mean (+/- SD) interpulse interval is respectively 37 +/- 5, 25 +/- 4 and 12 +/- 1 min when the fractions are collected at 7.5-, 5.0- and 2.5-min intervals. The immunocytochemically stained GnRH cell bodies are normally distributed in the preoptic explants (n = 212-420) while only 3 GnRH cell bodies can be visualized in 7 retrochiasmatic explants. Semi-quantitative RT-PCR shows that GnRH mRNA is present in the retrochiasmatic explant in a ratio of about 1:600 relative to the preoptic explant. We conclude that pulsatile GnRH secretion occurs in the virtual absence of GnRH cell bodies but does not occur from GnRH terminals in the isolated median eminence. These data further indicate that a mechanism of GnRH pulsatility is located in the retrochiasmatic hypothalamus and involves neurons different from the GnRH neurons.
TL;DR: Glu and GABA neurons which become sensitive to steroid hormones may help regulate GnRH neurohormone release and promote the onset of puberty as well as insights into the specific neuronal events involved in the peripubertal transition in primates.
Abstract: We have previously reported direct glutamate (Glu) synapses upon GnRH-containing neurons in the primate hypothalamus, and extensive interactions between Glu and aminobutyric acid (GABA) neurons in areas associated with reproductive function. Both Glu and GABA are known to affect peripubertal GnRH neurohormone release, but their relative roles remain unclear. In a developmental survey, estrogen receptors (ER) and progesterone receptors (PR) were virtually undetectable after immunostaining the hypothalamus of prepubertal monkeys, but were clearly evident in neurons of adults. We hypothesized, therefore, that Glu and GABA neurons which develop ER or PR expression during puberty may participate in reactivation of the hypothalamic-pituitary-gonadal axis. To identify those neurons in midpubertal female cynomolgus monkeys, we performed immunofluorescence staining for ER or for PR in separate sets of hypothalamic sections, and then immunostained for Glu or for glutamate decarboxylase (GAD, to identify GABA neurons) using a contrasting fluorophore. ER and PR were localized in the cytoplasm and nuclei of Glu and GAD neurons in nine hypothalamic and related brain regions. Quantitation revealed intranuclear ER in an average of 80% of the Glu neurons in all regions analyzed, and an average of 84% of the GAD neurons in all regions except the supraoptic nucleus (28%). Intranuclear PR expression was more variable, occurring in an average of 93% of the Glu neurons in seven regions, but in only 41% in the medial preoptic area, and 0% in the arcuate-periventicular zone. In addition, while intranuclear PR was seen in 96% of the GAD neurons in the septum, it appeared in 67% of the GAD neurons in the paraventricular nucleus, 47% in the medial preoptic area, 40% in the periventricular zone, and was absent from neurons in the supraoptic nucleus and mammillary bodies. In summary, certain subpopulations of Glu and GABA neurons in principal hypothalamic regions of the female monkey express ER and PR at midpuberty. Taken together with previous findings, these results suggest that Glu and GABA neurons which become sensitive to steroid hormones may help regulate GnRH neurohormone release and promote the onset of puberty. Since neuronal expression of ER or PR connotes sensitivity to gonadal feedback, and intranuclear translocation signals transcriptional activation, these results provide insights into the specific neuronal events involved in the peripubertal transition in primates.
TL;DR: Findings suggest that endogenous chicken GnRH II may play a role in synaptic transmission in the sympathetic ganglia via a receptor specific for chicken Gn RH II.
Abstract: Amphibia, like most vertebrate species, have two forms of GnRH, namely [Arg8]GnRH (mammalian GnRH) and [His5,Trp7,Tyr8] GnRH (chicken GnRH II). The differential distribution of the two peptides in the amphibian brain suggests that they may play different roles. Mammalian GnRH, which is found predominantly in the hypothalamus, is most likely the prime regulator of gonadotropin release, while chicken GnRH II, which occurs predominantly in the midbrain and hindbrain, may play a neuromodulatory role. In amphibian sympathetic ganglia, GnRH has been demonstrated to be a neurotransmitter where its release from the presynaptic nerve terminals reversibly inhibits M current, a time- and voltage-dependent potassium current. The occurrence of GnRH in sympathetic ganglia extracts from two amphibian species was investigated. Chicken GnRH II-like immunoreactivity was detected in extracts of bullfrog (Rana catesbeiana) and platanna (Xenopus laevis) sympathetic ganglia after high performance liquid chromatography. Under the chromatographic conditions used, a second unknown peptide co-eluted with synthetic mammalian GnRH, but showed no cross-reactivity with specific mammalian GnRH antisera. To test the possibility of the presence of a chicken GnRH II receptor in sympathetic ganglion neurones, competition binding of membranes extracted from the sympathetic ganglia of the two amphibian species was investigated with 125I-labelled GnRH agonists. The binding of 125-I-[His5,D-Arg6,Trp7,Tyr8]GnRH (a chicken GnRH II agonist) to membranes from the sympathetic ganglia of both amphibian species was specific and had a higher affinity than chicken GnRH II, mammalian GnRH and a mammalian GnRH agonist [D-Ala6,NMe-Leu7,Pro9-NHEt]GnRH. These findings suggest that endogenous chicken GnRH II may play a role in synaptic transmission in the sympathetic ganglia via a receptor specific for chicken GnRH II.
TL;DR: It is suggested that glutamate, acting through KA2 receptors directly on GnRH neurons is, at least in part, an important factor in the excitatory regulation of the postnatal sexual development of the female rat.
Abstract: Excitatory amino acids, particularly glutamate, are thought to be important for the maturation of the brain-pituitary-gonadal axis and the induction of puberty in the rat. We have previously shown tha
TL;DR: The anxiolytic effects observed after central and peripheral administration support the idea that atrial natriuretic peptide, which is increased in panic-anxiety, may be involved in the tapering of anxiety-related behavior.
Abstract: The effects of the central and peripheral administration of atriopeptin II, a 23-amino acid residue peptide of atrial natriuretic peptide (Ser103-Arg125) on anxiety-related behavior and on locomotor activity, was studied in male Wis-tar rats. Their behavior on the elevated plus-maze after social defeat stress indicated that intracerebroventricular (2.5 and 5 µg) and intraperitoneal (50 µg) administration of atriopeptin II produced anxiolysis. A low dose of 0.25 µg atriopeptin II administered bilaterally into the central nucleus of the amygdala was also found to be anxiolytic. Because intracerebroventricular administration of 5 µg atriopeptin II did not affect locomotor activity in the open-field test, the possibility that the anxiolytic effect was secondary to sedation could be ruled out. The anxiolytic effects observed after central and peripheral administration support the idea that atrial natriuretic peptide, which is increased in panic-anxiety, may be involved in the tapering of anxiety-related behavior.
TL;DR: It is demonstrated that GHRPs, beside their well-known GH-re releasing activity, possess a remarkable ACTH-releasing activity, overlapping with that of AVP and similar to that of hCRH, two neurohormones which are known to play the major role in the control of the pituitary-adrenal axis.
Abstract: Hexarelin (HEX) is a synthetic growth-hormone-releasing peptide (GHRP) which acts via specific receptors at both the pituitary and the hypothalamic level to stimulate GH release both in animals and in man. Like other GHRPs, HEX possesses also significant prolactin- and adrenocorticotropin (ACTH) cortisol-releasing activity, but the mechanisms underlying these effects are even less clear. To clarify the mechanisms by which HEX stimulates the pituitary-adrenal axis in man, in 7 healthy young volunteers we studied the effects of HEX (2.0 microg/kg i.v.) and/or human corticotropin-releasing hormone (hCRH; 2.0 microg/kg i.v.) and/or arginine vasopressin (AVP; 0.17 U/kg i.m.) on ACTH and cortisol secretion. The GH responses to HEX alone and combined with hCRH and/or AVP were also studied. HEX increased ACTH and cortisol secretion (peak, mean +/- SEM: 26.3 +/- 5.1 vs. 15.8 +/- 3.1 pg/ml and 145.0 +/- 11.4 vs. 131.7 +/- 11.7 microg/l, p < 0.01, respectively) to levels overlapping with those induced by AVP (27.9 +/- 6.1 vs. 13.1 +/- 3.5 pg/ml and 167.6 +/- 16.2 vs. 113.3 +/- 9.4 microg/l, p < 0.01, respectively) and similar to those elicited by hCRH (28.1 +/- 4.6 vs. 17.4 +/- 3.1 pg/ml and 182.7 +/- 22.8 vs. 114.8 +/- 12.3 microg/l, p < 0.02, respectively). The ACTH but not the cortisol response to hCRH was higher (p < 0.02) than those to HEX when evaluated as area under the curve. The co-administration of HEX and AVP had no significant interaction on ACTH and cortisol peak levels (40.7 micro 5.3 pg/ml and 168.8 +/- 13.5 microg/l, respectively). On the other hand, the co-administration of HEX and hCRH had a less than additive effect on ACTH and cortisol secretion (53.3 +/- 11.2 pg/ml and 204.0 +/- 13.7 microg/l, respectively). CRH and AVP had a true synergistic effect on ACTH (104.9 +/- 14.2 pg/ml, p < 0.01) and an additive effect on cortisol secretion (281.3 +/- 10.8 microg/l, p < 0.02). HEX did not modify the effect of CRH + AVP on both ACTH (135.5 +/- 22.0 pg/ml) and cortisol secretion (261.1 +/- 13.2 microg/l). The GH response to HEX (55.7 +/- 19.8 vs. 2.7 +/- 1.9 microg/l, p < 0.005) was unaffected by the administration of CRH alone (53.5 +/- 21.0 microg/l) and/or AVP co-administration (60.2 +/- 21.2 and 45.9 +/- 10.6 microg/l, respectively). In conclusion, the results of this study demonstrate that GHRPs, beside their well-known GH-releasing activity, possess a remarkable ACTH-releasing activity, overlapping with that of AVP and similar to that of hCRH, two neurohormones which are known to play the major role in the control of the pituitary-adrenal axis. It is noteworthy that HEX shows no synergistic effect with either AVP or hCRH which, on the other hand, truly synergize. This evidence suggests the hypothesis that the ACTH-releasing activity of GHRPs could be, at least partially, independent of both CRH- and AVP-mediated actions in humans.
TL;DR: The responsiveness of these cells to ANG supports the conclusion that their properties are similar to those in vivo, and suggests that use of this technique will permit systematic analysis of the membrane events underlying the actions of multiple ligands on this uniquely specialised group of CNS neurons.
Abstract: We have utilised standard dissociation techniques to obtain a preparation of subfornical organ (SFO) cells that have been maintained in tissue culture for up to 1 week. Stable (>15 min) whole cell rec
TL;DR: The findings suggest that the 5-HT2 system in the POA has a stimulatory role in the control of female sexual behaviour and in receptive animals there is an increase in both5-HT turnover and 5- HT2A receptors in thePOA and ME.
Abstract: In a previous study we have shown that a positive correlation exists between 5-hydroxytryptamine (5-HT) activity and female sexual receptivity in the pre-optic area (POA) and median eminence (ME) and that there is a negative correlation in the ventromedial nucleus (VMN), zona incerta (ZI) and arcuate nucleus (ARC). In this report, the possibility that 5-HT receptor density and affinity alter with sexual receptivity has been investigated. Micropunches of the POA, VMN, ARC, ME and the anterior hypothalamus were dissected from ovariectomised rats primed with a submaximal steroid regime (2 microg oestradiol benzoate, OB, followed at 48 h by 0.05 mg progesterone) which induced receptivity (lordosis quotient, LQ, 80-100%) in approximately half the animals, the remaining half usually exhibiting an LQ <20%. Binding studies were carried out using 3H-ketanserin (5-HT2A ligand) and 3H-8-hydroxy-2-(di-n-propylamine)tetraline (8-OHDPAT; 5-HT1A ligand) and pooled (n = 5) micropunch samples. The Bmax of 5-HT2A receptors in the sexually receptive groups was significantly (p < 0.05) greater in the POA and ME and significantly lower in the VMN, ARC and ZI when compared with values in the non-receptive animals. The KD values of the 5-HT2A receptors did not differ in the two groups (except the ZI, where the KD was lower in receptive rats). Neither the Bmax nor KD of the 5-HT1A receptors differed in the two groups in any area investigated. Administration of the 5-HT2 agonists dimethoxyiodophenylaminopropane and m-chlorophenyl piperazine into the POA resulted in enhanced sexual activity in animals exhibiting a low level of receptivity, after 5 microg OB given alone while ketanserin (5-HT2A antagonist) in the POA inhibited sexual activity in receptive animals primed with the submaximal steroid regime given above. In the same models, neither the 5-HT2 agonists nor the 5-HT2A antagonist affected behaviour when applied to the VMN. The 5-HT1A agonist 8-OHDPAT exerted an inhibitory effect in the VMN. These findings, together with earlier results, show that in receptive animals there is an increase in both 5-HT turnover and 5-HT2A receptors in the POA and ME. Additionally 5-HT2 agonists and an antagonist applied to the POA enhance and reduce sexual activity, respectively. This suggests that the 5-HT2 system in the POA has a stimulatory role in the control of female sexual behaviour. Both 5-HT activity and 5-HT2 receptors are decreased in the VMN, ARC and ZI of receptive animals. 5-HT2 agonists and a 5-HT2A antagonist have no effect in the VMN indicating that there is no 5-HT2-stimulatory or -inhibitory effect in this area, at least in the animal models used in these experiments. However, the VMN is a site of an inhibitory action mediated by the 5-HT1A receptors.