RESUMO
BACKGROUND: Male testosterone levels decline by 1% per year from the age of 40 years. Whilst a primary testicular deficit occurs, hypothalamic or pituitary dysregulation may also coexist. This study aimed to compare the hypothalamic response to kisspeptin-54 and the pituitary response to gonadotropin-releasing hormone (GnRH) of older men with those of young men. METHODS: Following 1 h of baseline sampling, healthy older men (n = 5, mean age 59.3 ± 2.9 years) received a 3-h intravenous infusion of either vehicle, kisspeptin-54 0.1, 0.3, or 1.0 nmol/kg/h or GnRH 0.1 nmol/kg/h, on five different study days. Serum gonadotropins and total testosterone were measured every 10 min and compared to those of young men (n = 5/group) (mean age 28.9 ± 2.0 years) with a similar body mass index (24 kg/m2) who underwent the same protocol. RESULTS: Kisspeptin-54 and GnRH significantly stimulated serum gonadotropin release in older men compared to vehicle (p < 0.001 for all groups). Gonadotropin response to kisspeptin-54 was at least preserved in older men when compared to young men. At the highest dose of kisspeptin-54 (1.0 nmol/kg/h), a significantly greater luteinising hormone (LH) (p = 0.003) response was observed in older men. The follicle-stimulating hormone (FSH) response to GnRH was increased in older men (p = 0.002), but the LH response was similar (p = 0.38). Serum testosterone rises following all doses of kisspeptin-54 (p ≤ 0.009) were reduced in older men. CONCLUSIONS: Our data suggest that healthy older men without late-onset hypo-gonadism (LOH) have preserved hypothalamic response to kisspeptin-54 and pituitary response to GnRH, but impaired testicular response. Further work is required to investigate the use of kisspeptin-54 to identify hypothalamic deficits in men with LOH.
Assuntos
Envelhecimento/metabolismo , Gonadotropinas/sangue , Hipotálamo/metabolismo , Hipófise/inervação , Testosterona/sangue , Adulto , Hormônio Liberador de Gonadotropina/farmacologia , Humanos , Hipotálamo/efeitos dos fármacos , Kisspeptinas/farmacologia , Masculino , Pessoa de Meia-Idade , Hipófise/efeitos dos fármacos , Hipófise/metabolismoRESUMO
The influence of chronic stress, induced by food deprivation (FD) and/or high stocking density (HSD), was assessed on stress, vasotocinergic and isotocinergic pathways of the gilthead sea bream (Sparus aurata). Fish were randomly assigned to one of the following treatments: (1) fed at low stocking density (LSD-F; 5kg·m-3); (2) fed at high stocking density (HSD-F, 40kg·m-3); (3) food-deprived at LSD (LSD-FD); and (4) food-deprived at HSD (HSD-FD). After 21days, samples from plasma, liver, hypothalamus, pituitary and head-kidney were collected. Both stressors (FD and HSD) induced a chronic stress situation, as indicated by the elevated cortisol levels, the enhancement in corticotrophin releasing hormone (crh) expression and the down-regulation in corticotrophin releasing hormone binding protein (crhbp) expression. Changes in plasma and liver metabolites confirmed a metabolic adjustment to cope with energy demand imposed by stressors. Changes in avt and it gene expression, as well as in their specific receptors (avtrv1a, avtrv2 and itr) at central (hypothalamus and pituitary) and peripheral (liver and head-kidney) levels, showed that vasotocinergic and isotocinergic pathways are involved in physiological changes induced by FD or HSD, suggesting that different stressors are handled through different stress pathways in S. aurata.
Assuntos
Fenômenos Fisiológicos da Nutrição Animal , Proteínas de Peixes/metabolismo , Modelos Neurológicos , Ocitocina/análogos & derivados , Dourada/fisiologia , Estresse Fisiológico , Vasotocina/metabolismo , Animais , Biomarcadores/sangue , Biomarcadores/metabolismo , Restrição Calórica/efeitos adversos , Aglomeração , Proteínas de Peixes/sangue , Proteínas de Peixes/genética , Regulação da Expressão Gênica no Desenvolvimento , Rim Cefálico/crescimento & desenvolvimento , Rim Cefálico/inervação , Rim Cefálico/metabolismo , Hipotálamo/crescimento & desenvolvimento , Hipotálamo/metabolismo , Fígado/crescimento & desenvolvimento , Fígado/metabolismo , Masculino , Neurônios/metabolismo , Ocitocina/sangue , Ocitocina/metabolismo , Hipófise/crescimento & desenvolvimento , Hipófise/inervação , Hipófise/metabolismo , Distribuição Aleatória , Dourada/sangue , Dourada/crescimento & desenvolvimento , Vasotocina/sangueRESUMO
This review aims at synthesizing the most relevant information regarding the neuroendocrine circuits controlling reproduction, mainly gonadotropin release, in teleost fish. In teleosts, the pituitary receives a more or less direct innervation by neurons sending projections to the vicinity of the pituitary gonadotrophs. Among the neurotransmitters and neuropeptides released by these nerve endings are gonadotrophin-releasing hormones (GnRH) and dopamine, acting as stimulatory and inhibitory factors (in many but not all fish) on the liberation of LH and to a lesser extent that of FSH. The activity of the corresponding neurons depends on a complex interplay between external and internal factors that will ultimately influence the triggering of puberty and sexual maturation. Among these factors are sex steroids and other peripheral hormones and growth factors, but little is known regarding their targets. However, very recently a new actor has entered the field of reproductive physiology. KiSS1, first known as a tumor suppressor called metastin, and its receptor GPR54, are now central to the regulation of GnRH, and consequently LH and FSH secretion in mammals. The KiSS system is notably viewed as instrumental in integrating both environmental cues and metabolic signals and passing this information onto the reproductive axis. In fish, there are two KiSS genes, KiSS1 and KiSS2, expressed in neurons of the preoptic area and mediobasal hypothalamus. Pionneer studies indicate that KiSS and GPR54 expression seem to be activated at puberty. Although precise information as to the physiological effects of KiSS1 in fish, notably on GnRH neurons and gonadotropin release, is still limited, KiSS neurons may emerge as the "gatekeeper" of puberty and reproduction in fish as in mammals.
Assuntos
Peixes/fisiologia , Hormônio Liberador de Gonadotropina/fisiologia , Hipotálamo/fisiologia , Hipófise/fisiologia , Reprodução/fisiologia , Animais , Feminino , Peixes/metabolismo , Hormônios Esteroides Gonadais/metabolismo , Hormônios Esteroides Gonadais/fisiologia , Hormônio Liberador de Gonadotropina/metabolismo , Gonadotropinas/metabolismo , Gonadotropinas/fisiologia , Hipotálamo/metabolismo , Kisspeptinas , Masculino , Neuroendocrinologia , Neuropeptídeo Y/metabolismo , Neuropeptídeo Y/fisiologia , Hipófise/inervação , Hipófise/metabolismo , Receptores Acoplados a Proteínas G/genética , Receptores Acoplados a Proteínas G/metabolismo , Receptores Acoplados a Proteínas G/fisiologia , Maturidade Sexual/genética , Maturidade Sexual/fisiologia , Proteínas de Peixe-Zebra/genética , Proteínas de Peixe-Zebra/metabolismo , Proteínas de Peixe-Zebra/fisiologia , Ácido gama-Aminobutírico/metabolismo , Ácido gama-Aminobutírico/fisiologiaRESUMO
Interoceptive feedback signals from the body are transmitted to hypothalamic neurons that control pituitary hormone release. This review article describes the organization of central neural pathways that convey ascending visceral sensory signals to endocrine neurons in the paraventricular (PVN) and supraoptic nuclei (SON) of the hypothalamus in rats. A special emphasis is placed on viscerosensory inputs to corticotropin releasing factor (CRF)-containing PVN neurons that drive the hypothalamic-pituitary-adrenal axis, and on inputs to magnocellular PVN and SON neurons that release vasopressin (AVP) or oxytocin (OT) from the posterior pituitary. The postnatal development of these ascending pathways also is considered.
Assuntos
Hipotálamo/anatomia & histologia , Neurônios Aferentes/fisiologia , Hipófise , Vísceras/inervação , Animais , Neurônios/citologia , Neurônios/metabolismo , Neurônios Aferentes/citologia , Neuropeptídeos/metabolismo , Hipófise/inervação , Hipófise/fisiologiaRESUMO
Genistein is a phytoestrogen, particularly abundant in soybeans that can bind estrogen receptors and sex hormone binding proteins, exerting both estrogenic and antiestrogenic activity. In this study we used the Japanese quail embryo as a test end-point to investigate the effects of early embryonic exposure to genistein on male copulatory behavior and on vasotocin parvocellular system. Both differentiate by the organizational effects of estradiol during development and may therefore represent an optimal model to study the effects of xenoestrogens. We injected two doses of genistein (100 and 1000 microg) into the yolk of 3-day-old Japanese quail eggs. Other eggs were treated with either 25 microg of estradiol benzoate or sesame oil as positive and negative controls. At the age of 6 weeks, behavioral tests revealed a significant decrease of all aspects of copulatory behavior (in comparison to the control group) in estradiol-treated birds. In contrast, genistein-treated animals demonstrated various degrees of decrease in the mean frequencies of some aspects of the sexual behavior. The computerized analysis of vasotocin innervation in medial preoptic, stria terminalis and lateral septum nuclei revealed a statistically significant decreased immunoreactivity in treated animals compared to control ones. These results demonstrate that genistein, similarly to estradiol, has an organizational effect on quail parvocellular vasotocin system and on copulatory behavior. In conclusion, present results confirm, in this avian model, that embryonic exposure to phytoestrogens may have life-long effects on sexual differentiation of brain structures and behaviors.
Assuntos
Copulação/efeitos dos fármacos , Genisteína/toxicidade , Hipotálamo/efeitos dos fármacos , Hipófise/efeitos dos fármacos , Vasotocina/metabolismo , Animais , Coturnix/embriologia , Estradiol/análogos & derivados , Estradiol/toxicidade , Feminino , Hipotálamo/anatomia & histologia , Masculino , Modelos Animais , Hipófise/inervação , Hipófise/metabolismo , Diferenciação Sexual/efeitos dos fármacosRESUMO
Recent studies have localized the glutamatergic cell marker type-2 vesicular glutamate transporter (VGLUT2) to distinct peptidergic neurosecretory systems that regulate hypophysial functions in rats. The present studies were aimed to map the neuronal sources of VGLUT2 in the median eminence and the posterior pituitary, the main terminal fields of hypothalamic neurosecretory neurons. Neurons innervating these regions were identified by the uptake of the retrograde tract-tracer Fluoro-Gold (FG) from the systemic circulation, whereas glutamatergic perikarya of the hypothalamus were visualized via the radioisotopic in situ hybridization detection of VGLUT2 mRNA. The results of dual-labeling studies established that the majority of neurons accumulating FG and also expressing VGLUT2 mRNA were located within the paraventricular, periventricular and supraoptic nuclei and around the organum vasculosum of the lamina terminalis and the preoptic area. In contrast, only few FG-accumulating cells exhibited VGLUT2 mRNA signal in the arcuate nucleus. Dual-label immunofluorescent studies of the median eminence and posterior pituitary to determine the subcellular location of VGLUT2, revealed the association of VGLUT2 immunoreactivity with SV2 protein, a marker for small clear vesicles in neurosecretory endings. Electron microscopic studies using pre-embedding colloidal gold labeling confirmed the localization of VGLUT2 in small clear synaptic vesicles. These data suggest that neurosecretory neurons located mainly within the paraventricular, anterior periventricular and supraoptic nuclei and around the organum vasculosum of the lamina terminalis and the preoptic area secrete glutamate into the fenestrated vessels of the median eminence and posterior pituitary. The functional aspects of the putative neuropeptide/glutamate co-release from neuroendocrine terminals remain to be elucidated.
Assuntos
Ácido Glutâmico/metabolismo , Hipotálamo/metabolismo , Eminência Mediana/inervação , Vias Neurais/metabolismo , Neuro-Hipófise/inervação , Proteína Vesicular 2 de Transporte de Glutamato/metabolismo , Animais , Biomarcadores/metabolismo , Hipotálamo/ultraestrutura , Hibridização In Situ , Masculino , Eminência Mediana/irrigação sanguínea , Eminência Mediana/ultraestrutura , Glicoproteínas de Membrana/metabolismo , Microcirculação/citologia , Microcirculação/fisiologia , Microscopia Imunoeletrônica , Proteínas do Tecido Nervoso/metabolismo , Vias Neurais/ultraestrutura , Neurônios/citologia , Neurônios/metabolismo , Sistemas Neurossecretores/metabolismo , Sistemas Neurossecretores/ultraestrutura , Hipófise/irrigação sanguínea , Hipófise/inervação , Hipófise/fisiologia , Neuro-Hipófise/irrigação sanguínea , Neuro-Hipófise/ultraestrutura , Terminações Pré-Sinápticas/metabolismo , Terminações Pré-Sinápticas/ultraestrutura , RNA Mensageiro/metabolismo , Ratos , Ratos Wistar , Estilbamidinas , Vesículas Sinápticas/metabolismo , Vesículas Sinápticas/ultraestrutura , Proteína Vesicular 2 de Transporte de Glutamato/genéticaRESUMO
L1 is a murine multidomain glycoprotein implicated in cell aggregation, fasciculation. neurite outgrowth and synaptogenesis. Laminin, a trimeric polypeptide, is implicated in neuronal survival, growth cone guidance, neurite outgrowth and cell differentiation. Laminin can also interact with the cell adhesion molecule L1. Their expressions were investigated from embryonic day 15 (E15) to adult in the rat hypophysis, and in adult neurohemal zones. Detected in the neural lobe from E17, the L1 immunoreactivity increased during prenatal development and persisted in adulthood mainly related to the neuropeptidergic fibers. Pituicytes were only labelled on the plasmalemma apposed to axons. In the intermediate lobe, L1 appeared at birth on folliculo-stellate cells extensions, constituting a network which densified during postnatal development. L1 is also expressed in all neurohemal areas on neuronal profiles. Laminin was clearly detectable in the hypophysis at E15 before the first blood vessels penetrate the Rathke pouch. At E20, all the basal membranes of the blood vessels were stained. In the intermediate lobe, a spotted laminin immunoreactivity was detected at E21. At this stage, we observed the staining of intercellular spaces and the intracellular labelling of melanotrophs, concerning reticulum or vesicles. The staining of melanotrophs seemed to maintain during adulthood. In contrast with blood vessels of the adult cerebral tissue, adult capillaries of the neural lobe and the others neuro-hemal zones were intensely labelled with the anti-laminin antibody. These results suggest that neurite outgrowth and neurite guidance could be promoted by L1 and laminin in the neurointermediate lobe. The "intercellular tunnels" could also be an important guidance cue for migrating cells in the intermediate lobe. These data also demonstrate that melanotrophic cells. secreting the laminin, have a role in the ontogenesis of the gland. Finally, we suggest that L1 and laminin can collaborate to reinforce "neurons-capillaries" interactions in neurohemal zones.
Assuntos
Proteínas Fetais/biossíntese , Regulação da Expressão Gênica no Desenvolvimento , Laminina/biossíntese , Glicoproteínas de Membrana/biossíntese , Proteínas do Tecido Nervoso/biossíntese , Moléculas de Adesão de Célula Nervosa/biossíntese , Sistemas Neurossecretores/embriologia , Hipófise/embriologia , Animais , Movimento Celular , Proteínas Fetais/genética , Idade Gestacional , Hipotálamo/embriologia , Hipotálamo/crescimento & desenvolvimento , Hibridização In Situ , Laminina/genética , Complexo Antígeno L1 Leucocitário , Glicoproteínas de Membrana/genética , Neovascularização Fisiológica , Proteínas do Tecido Nervoso/genética , Moléculas de Adesão de Célula Nervosa/genética , Neuritos/fisiologia , Sistemas Neurossecretores/crescimento & desenvolvimento , Sistemas Neurossecretores/metabolismo , Hipófise/irrigação sanguínea , Hipófise/crescimento & desenvolvimento , Hipófise/inervação , Hipófise/metabolismo , Ratos , Ratos WistarRESUMO
The neuroanatomical organization of neurons projecting to the pituitary and the origin of pituitary dopamine and nonapeptides were investigated in the brain of the Atlantic salmon (Salmo salar). Carbocyanine tract tracing in combination with tyrosine hydroxylase, arginine vasotocin and isotocin immunocytochemistry for double labelling revealed a previously unknown organization of hypophysiotrophic cell groups and their extrahypothalamic projections, and provide the first direct identification in a teleost fish of the origin of the dopaminergic and nonapeptidergic innervation of the pituitary. The present data include identification of (1) hypophysiotrophic neurons in the ventral telencephalon and in the periventricular preoptic nucleus, (2) large (magnocellular) vasotocinergic hypophysiotrophic neurons in the most rostral extension of the preoptic area, (3) a distinct neuronal group located in a supraoptic/suprachiasmatic position in the anterior periventricular nucleus, that seems to be the major source of dopaminergic innervation of the pituitary, (4) the nonapeptidergic hypophysiotrophic neurons in the preoptic nucleus, (5) hypophysiotrophic neurons in the ventral and posterior hypothalamus of which some are of liquor-contacting type, (6) projections from hypophysiotrophic and non-hypophysiotrophic neurons in the preoptic nucleus to extrahypothalamic areas such as thalamic and periventricular pretectal nuclei, and (7) subdivisions within the preoptic nucleus that exhibit different combinations of hypophysiotrophic and extrahypothalamic efferent connections. Together with previous studies of retinohypothalamic projections and neurochemical organization of hypothalamic/preoptic areas, the present data suggest that the preoptic nucleus and the anterior periventricular nucleus in teleosts possess functional subdivisions with features that resemble those of the paraventricular, supraoptic and suprachiasmatic nuclei of other vertebrates. In the Atlantic salmon, specific dopaminergic and nonapeptidergic neuronal subdivisions are proposed to play a role for photoperiod control of endocrine activity.
Assuntos
Química Encefálica/fisiologia , Neurônios/química , Sistemas Neurossecretores/fisiologia , Hipófise/inervação , Salmão/anatomia & histologia , Animais , Carbocianinas , Dopamina/análise , Corantes Fluorescentes , Hipotálamo/química , Técnicas Imunoenzimáticas , Neuropeptídeos/análise , Oligopeptídeos/análise , Hipófise/citologia , Área Pré-Óptica/química , Salmão/metabolismo , Telencéfalo/químicaRESUMO
The hypothalamic hypophysiotrophic neurones are densely innervated by adrenergic and noradrenergic nerve terminals. Activation of alpha 1-adrenoceptors located in the brain stimulates the secretion of ACTH, prolactin and TSH. The effects of the alpha 1-adrenoceptors seem to be exerted on hypothalamic neurones that secrete vasopressin, CRH-41 and TRH. These mechanisms are important in the physiological control of the secretion of ACTH and TSH in humans. alpha 2-Adrenoceptors are not involved in the control of secretion of these hormones under basal conditions in humans. However, alpha 2-adrenoceptors exert an inhibitory effect that acts as a negative feedback mechanism, limiting excessive secretion of these hormones. There is no convincing evidence for the involvement of beta-adrenoceptors in the control of the secretion of these three hormones in humans. Studies on cultured anterior pituitary cells suggested that adrenaline and noradrenaline may influence the secretion of ACTH, prolactin and TSH directly at the level of the pituitary. However, these effects are not demonstrable in humans, and are likely to be due to alterations in the pituitary adrenoceptors during culture. In the case of growth hormone, activation of alpha 2-adrenoceptors located in the brain stimulates secretion of this hormone both by increasing the secretion of GHRH and by inhibiting the secretion of somatostatin. Activation of beta-adrenoceptors inhibits the secretion of growth hormone via an increase in the secretion of somatostatin. The effects of the central alpha 2- and beta-adrenoceptors are important in the physiological control of growth hormone secretion in humans. A considerable amount of evidence implicates brain alpha 1-adrenoceptors in the control of secretion of the gonadotrophins in experimental animals, but, despite intensive study, no convincing evidence has been found in humans of reproductive age.
Assuntos
Epinefrina/fisiologia , Norepinefrina/fisiologia , Hormônios Adeno-Hipofisários/metabolismo , Humanos , Hipotálamo/fisiologia , Hipófise/inervação , Hipófise/fisiologia , Receptores Adrenérgicos alfa/fisiologia , Receptores Adrenérgicos beta/fisiologiaRESUMO
The activities of periventricular-hypophysial dopaminergic (DA) neurons were compared in male and female rats by measuring dopamine synthesis (accumulation of 3,4-dihydroxyphenylalanine [DOPA] after inhibition of L-aromatic amino acid decarboxylase) and metabolism (concentrations of 3,4-dihydroxyphenylacetic acid [DOPAC]) in terminals of these neurons in the intermediate lobe of the pituitary. For comparison, the synthesis and metabolism of dopamine in the neural lobe of the pituitary and median eminence were also determined. The concentrations of DOPAC and accumulation of DOPA were higher in females than in males in both the intermediate lobe and median eminence, revealing a sexual difference in the basal activity of periventricular-hypophysial and tuberoinfundibular DA neurons. In contrast, there were no differences between male and female rats in activity of DA neurons terminating in the neural lobe. One week following gonadectomy, DOPA accumulation in the median eminence was decreased in females and increased in males, but remained unchanged in the intermediate lobe. These results indicate that sexual differences in the activity of periventricular-hypophysial DA neurons terminating in the intermediate lobe are not dependent upon the presence of circulating gonadal steroids, and in this respect, these neurons differ from tuberoinfundibular DA neurons.
Assuntos
Dopamina/metabolismo , Hipotálamo/fisiologia , Neurônios/fisiologia , Hipófise/inervação , Ácido 3,4-Di-Hidroxifenilacético/metabolismo , Animais , Castração , Di-Hidroxifenilalanina/metabolismo , Dopamina/biossíntese , Dopamina/fisiologia , Feminino , Gônadas/metabolismo , Gônadas/fisiologia , Hipotálamo/citologia , Hipotálamo/metabolismo , Masculino , Neurônios/metabolismo , Ratos , Ratos Endogâmicos , Fatores Sexuais , Esteroides/sangueRESUMO
Immunostaining of brain and pituitary sections of teleost fishes (eels, salmonidae, cyprinidae, gourami, sculpin, mullet) with anti porcine galanin (GAL) revealed the presence of immunoreactive (ir) perikarya and a rich network of fibers. Ir-perikarya were located rostrodorsally to the recessus preopticus, and in the posterior tuberal hypothalamus. Ir-fibers were abundant in basal telencephalon and around diencephalic ventricular recesses but never contacted their lumen. Furthermore, they were observed in basal hypothalamus, brainstem and ventral medulla. Ir-fibers passed along corticotropic (ACTH), gonadotropic cells and somatotropes (GH cells) in eel and trout pars distalis, but rarely ended in caudal neurohypophysis. In goldfish pituitary ir-fibers occurred in neural digitations and among different cell types which however did not contain a GAL-like peptide. The relation GAL fibers/GH cells appeared more evident in species with a high growth rate. The other species showed a similar distribution of brain GAL. In eels and trout, ir-perikarya were not observed in areas containing somatostatin, GH- and ACTH-releasing factor, and ACTH-like perikarya, suggesting that GAL did not coexist with these peptides. The widespread distribution of a GAL-like peptide in teleost brain suggests that it could play a role of neurotransmitter and/or neuromodulator and regulate the secretion of adenohypophysial hormone(s).
Assuntos
Química Encefálica , Peixes/metabolismo , Neuropeptídeos/análise , Peptídeos/análise , Peptídeos/imunologia , Hipófise/inervação , Animais , Tronco Encefálico/química , Cyprinidae/metabolismo , Enguias/metabolismo , Feminino , Galanina , Hipotálamo/química , Imuno-Histoquímica , Masculino , Neuropeptídeos/imunologia , Hipófise/química , Salmonidae/metabolismo , Coloração e RotulagemRESUMO
Retrograde transport of horseradish peroxidase (HRP) was used to identify supraependymal neurons projecting to the pituitary gland in the hamster. Supraependymal neurons overlying the median eminence were labeled by HRP injections into the neural and intermediate lobes of the pituitary gland; no neurons were labeled following HRP injections confined to the anterior lobe. Supraependymal neurons innervating the pituitary gland may provide a means whereby cerebrospinal fluid-borne substances modulate neuro-intermediate lobe function.
Assuntos
Ventrículos Cerebrais/citologia , Hipotálamo/citologia , Hipófise/inervação , Animais , Cricetinae , Feminino , Peroxidase do Rábano Silvestre , Mesocricetus , Vias Neurais/anatomia & histologia , Conjugado Aglutinina do Germe de Trigo-Peroxidase do Rábano Silvestre , Aglutininas do Germe de TrigoRESUMO
Short-term in vitro incubation of hypothalamo-hypophyseal tissue from young rats was undertaken to discern more clearly the functional relationship between putative dopaminergic neural projections in the pars intermedia and the secretory activity of melanophore stimulating hormone (MSH). This explant consisted of a portion of the mediobasal hypothalamus containing the dopamine neurone cell bodies of interest, with the attached pituitary neuro-intermediate lobe (n.i.l.). The n.i.l. was inserted into the end of a 1 mm diameter tube attached to a perfusion pump which allowed uninterrupted sampling of medium neighbouring the n.i.l. A 'real-time' analysis of hormone secretion was obtained by immediately and continuously bioassaying for MSH. A bipolar stimulating electrode was placed on the ventral floor of the mediobasal hypothalamus either directly on the arcuate nucleus, median eminence or infundibular stalk. Electrical stimulation for 5 min (0.1-20.0 Hz) caused a transient inhibition of basal MSH secretion, while continuous stimulation (0.1-5.0 Hz) led to a much greater, long-term, reversible inhibition. In the latter, the degree of inhibition was generally dependent on stimulation rate up to a maximum at 5 Hz. Application of the dopamine D2 receptor antagonist, 1-sulpiride (0.001-0.1 microM) to the perfusion medium not only completely and reversibly blocked the stimulus-induced inhibition of MSH release but by itself, significantly increased the basal secretion rate. Applied to the isolated n.i.l., 1-sulpiride did not alter release but did prevent the inhibitory response caused by exogenously applied dopamine (0.1 microM). The gamma-aminobutyric acid receptor antagonist, bicuculline (0.01-1.0 microM), had no effect on any of the parameters studied. In explants, cutting the infundibular stalk linking the mediobasal hypothalamus with the n.i.l., mimicked the effects of 1-sulpiride by interrupting impulse flow to the gland. Thus, electrical stimulation of hypothalamic neurones in these explants apparently causes a release of dopamine from nerve terminals in the pars intermedia to inhibit MSH secretion and perhaps other pro-opiomelanocortin-derived peptides as well.
Assuntos
Dopamina/fisiologia , Sistema Hipotálamo-Hipofisário/fisiologia , Hormônios Estimuladores de Melanócitos/metabolismo , Hipófise/inervação , Animais , Bicuculina/farmacologia , Dopamina/farmacologia , Hipotálamo/citologia , Técnicas In Vitro , Masculino , Neurônios/fisiologia , Ratos , Ratos Endogâmicos , Sulpirida/farmacologiaRESUMO
Control of the secretion of ACTH appears to involve several mechanisms. It is dependent upon the release, from neurones in the hypothalamus, of corticotrophin releasing factor, which is probably a complex including CRF-41 and vasopressin. The secretion of the complex is influenced by various central inhibitory and excitatory nervous pathways. The releasing factor is conveyed by the hypophyseal portal vessels to the adenohypophysis where it stimulates the secretion of ACTH. The corticosteroids exert a profound control over the basal secretion of ACTH, but only modulate the pituitary adrenocorticotrophic response to stress. The mechanisms which may be involved are summarized in figure 8.
Assuntos
Sistema Hipotálamo-Hipofisário/fisiologia , Sistema Hipófise-Suprarrenal/fisiologia , Corticosteroides/biossíntese , Corticosteroides/fisiologia , Hormônio Adrenocorticotrópico/metabolismo , Animais , Hormônio Liberador da Corticotropina/metabolismo , Hormônio Liberador da Corticotropina/fisiologia , Humanos , Hipotálamo/fisiologia , Hipófise/irrigação sanguínea , Hipófise/inervação , Estresse Fisiológico/fisiopatologiaRESUMO
The distribution of immunoreactive substance P (IR-SP) neurons was examined in the hypothalamus and pituitary gland of the rhesus monkey by using the peroxidase-antiperoxidase immunocytochemical technique. Immunoreactive SP cell bodies were observed in the arcuate nucleus, in the region lateral to the arcuate nucleus, and in the median eminence (ME). Immunoreactive SP cells were also seen in the periventricular area of the dorsal tuberal region. A rich network of SP fibers was concentrated in the arcuate region, and the fiber stain was particularly dense in the external zone of the median eminence and in the external layer of the infundibular stalk. Also, substance P fibers were seen in the internal layer of the pituitary stalk and in the neural lobe of the pituitary gland. Outside the hypothalamus a dense network of IR-SP fibers was observed in the globus pallidus.
Assuntos
Hipotálamo/anatomia & histologia , Hipófise/inervação , Substância P/metabolismo , Animais , Núcleo Arqueado do Hipotálamo/anatomia & histologia , Castração , Ventrículos Cerebrais/anatomia & histologia , Feminino , Hipotálamo Médio/anatomia & histologia , Técnicas Imunoenzimáticas , Macaca mulatta , Masculino , Eminência Mediana/anatomia & histologia , Fibras Nervosas/ultraestrutura , Neurônios/ultraestruturaRESUMO
With the aid of lesion experiments and the Falck-Hillarp fluorescence technique, it is shown that the aminergic nerves of the hypophysis, including pars distalis, originate in the caudal hypothalamus and reach the gland via a fibre tract in the floor of tuber cinereum. However, some contribution to the eminentia mediana from the preoptic area could not be excluded. A vasomotor function of the pars distalis nerves is unlikely. Based on a comparative survey the hypothesis is put forward, that the pars distalis nerves, which disappear during the metamorphic climax, are remnants of an aminergic innervation existing together with a hypophyseal portal system as a functional link between brain and pituitary in the fish-like ancestor of amphibians. Aspects are given on the problem of why a direct pars distalis innervation has neither been retained nor evolved during evolution of tetrapods.
Assuntos
Hipotálamo/anatomia & histologia , Neurotransmissores/metabolismo , Filogenia , Hipófise/inervação , Rana temporaria/anatomia & histologia , Animais , Larva , Metamorfose Biológica , Microscopia de Fluorescência , Fibras Nervosas/ultraestrutura , Vias Neurais/anatomia & histologiaRESUMO
The horseradish-peroxidase (HRP) technique was used to visualize the cell bodies of axons projecting to the goldfish pituitary. Following intravenous injections of HRP, HRP reaction products were observed in axons of the rostral pars distalis, proximal pars distalis, neurointermediate lobe, pituitary stalk and in axons coursing from the pituitary into the hypothalamus. HRP-labelled cells in the brain were localized in two regions only - the nucleus preopticus (NPO) pars magnocellularis and pars parvocellularis, and the nucleus lateralis tuberis (NLT) of the hypothalamus. These observations suggest that the NPO and NLT are the source of the neurosecretory innervation of the goldfish pituitary.
Assuntos
Cyprinidae/anatomia & histologia , Carpa Dourada/anatomia & histologia , Hipotálamo/citologia , Hipófise/inervação , Animais , Transporte Axonal , Feminino , Peroxidase do Rábano Silvestre , Masculino , Vias Neurais , Adeno-Hipófise/inervação , Neuro-Hipófise/inervação , Área Pré-Óptica/citologiaRESUMO
The peptidergic nature of most of the fibres of the neurosecretory system of Scyliorhinus caniculus has been demonstrated with the oxidation method of Naumann and Sterba (1976). Some of the fibres of this peptidergic system terminate on capillaries in the hypothalamic floor, some on neurointermediate cells. The evolutionary aspects of these observations are discussed.
Assuntos
Evolução Biológica , Cação (Peixe)/anatomia & histologia , Hipotálamo/ultraestrutura , Fibras Nervosas/ultraestrutura , Hipófise/inervação , Área Pré-Óptica/ultraestrutura , Tubarões/anatomia & histologia , Animais , Capilares/inervação , Vias Neurais , Neurofisinas/análise , Sistemas Neurossecretores/ultraestrutura , Peptídeos/fisiologiaRESUMO
Experiments using two retrogradely transported fluorescent dyes (bisbenzimide-true blue, and Evans blue-granular blue) were performed in order to determine whether the same or different populations of neurons of the paraventricular nucleus of the hypothalamus (PVH) project to the pituitary gland, dorsal vagal complex, and spinal cord in the rat. The results suggest that cells projecting to the pituitary gland are concentrated in the magnocellular core of the nucleus, while the descending connections arise primarily from the surrounding parvocellular division. The occurrence of neurons double-labeled with both dyes further indicate that at lease 10-15% of the labeled cells in the parvocellular division send divergent axon collaterals to the dorsal vagal complex and to the spinal cord. Cell counts suggest that at least 1,500 cells in the PVH project to the medulla and/or spinal cord. These results, combined with a cytoarchitectonic analysis, show that the PVH consists of eight distinct subdivisions, three magnocellular and five parvocellular. The lateral hypothalamic area and zona incerta also contain a large number of cells projecting to the dorsomedial medulla and spinal cord; approximately 15% of such cells are the double-labeled following injections of separate tracers into these two regions of the same animal.
Assuntos
Hipotálamo/citologia , Bulbo/citologia , Núcleo Hipotalâmico Paraventricular/citologia , Hipófise/inervação , Medula Espinal/citologia , Animais , Axônios/ultraestrutura , Corantes Fluorescentes , Masculino , Neurônios/citologia , RatosRESUMO
Double labeling experiments with the retrogradely transported fluorescent tracers bisbenzimide and True blue indicate that separate populations of cells in the paraventricular nucleus of the hypothalamus project to the median eminence and to the dorsomedial medulla or spinal cord in the rat. The cell populations giving rise to each projection are, however, at least partially intermixed in different parts of the nucleus.