RESUMO
Energy homeostasis is achieved by the integration of peripheral metabolic signals by neural circuits. The organisation and function of neural circuits regulating energy homeostasis has been the subject of intense investigation and has led to the definition of a core circuitry in the hypothalamus that interacts with key regions in the brain stem, which appear to mediate many of the effects of the adipocyte-derived hormone leptin on feeding and energy balance. Recent data on the ontogeny of these pathways indicate that, in rodents, these feeding circuits primarily form during neonatal life and remain structurally and functionally immature until 3 weeks of life. Our understanding of the mechanisms promoting the formation of these critical circuits has been advanced significantly by recent evidence showing that neonatal leptin acts as a neurotrophic factor promoting the development of projections from the arcuate nucleus of the hypothalamus. Together with an expanding literature on the role of nutritional factors to affect health, these discoveries may contribute to our understanding on perinatally acquired predisposition to later disease, such as obesity and diabetes.
Assuntos
Metabolismo Energético/fisiologia , Leptina/fisiologia , Vias Neurais/embriologia , Vias Neurais/fisiologia , Animais , Núcleo Arqueado do Hipotálamo/citologia , Núcleo Arqueado do Hipotálamo/efeitos dos fármacos , Núcleo Arqueado do Hipotálamo/embriologia , Tronco Encefálico/embriologia , Tronco Encefálico/metabolismo , Comportamento Alimentar/efeitos dos fármacos , Comportamento Alimentar/fisiologia , Humanos , Hipotálamo/embriologia , Hipotálamo/metabolismo , Leptina/deficiência , Leptina/farmacologia , Modelos Biológicos , Modelos Neurológicos , Vias Neurais/metabolismo , Neurônios/efeitos dos fármacosRESUMO
The hypothalamus plays a critical role in the regulation of food intake and body weight, and recent work has defined a core circuitry in the hypothalamus that appears to mediate many of the effects of the adipocyte-derived hormone leptin on feeding and glucose homeostasis. However, until recently, little was known about the development of these critical pathways. This review summarizes recent advances regarding the post-natal development of 'metabolic' projections from the arcuate nucleus of the hypothalamus. Evidence accumulated primarily in mice indicates that these circuits develop after birth and remain both structurally and functionally immature until the second week of life. Recent studies have begun to identify cues governing development of these pathways, and leptin appears to play a crucial neurotrophic role in the development of the hypothalamic circuits regulating food intake and adiposity. The neurodevelopmental actions of leptin appear specifically to be restricted to a neonatal critical period that coincides with the naturally occurring surge in leptin. In addition, the timing and amplitude of the post-natal leptin surge has important consequences for normal body weight regulation and glucose homeostasis later in life. Ultimately, these data promise to provide new insight into the mechanisms by which alteration of perinatal nutrition may have long-term consequences on body weight regulation and adiposity in the offspring.
Assuntos
Regulação do Apetite/fisiologia , Comportamento Alimentar/fisiologia , Hipotálamo/fisiologia , Leptina/fisiologia , Adiposidade/fisiologia , Animais , Núcleo Arqueado do Hipotálamo/crescimento & desenvolvimento , Núcleo Arqueado do Hipotálamo/fisiologia , Humanos , Hipotálamo/crescimento & desenvolvimento , Camundongos , Obesidade/patologia , Obesidade/fisiopatologiaRESUMO
It has become apparent that galanin as well as proopiomelanocortin-derived peptides, such as beta-endorphin, play an important role in the hypothalamic circuitry that regulates neuroendocrine functions and appetite behavior. We have recently shown that GalR1 and GalR2 galanin receptor mRNAs are expressed in proopiomelanocortin neurons of the arcuate nucleus, suggesting a direct modulatory action of galanin on the proopiomelanocortin neuronal system. In the present study, we investigated the effect of galanin on beta-endorphin release and proopiomelanocortin mRNA expression from male rat mediobasal hypothalamic fragments incubated ex vivo. Galanin induced a decrease of spontaneous beta-endorphin release within the first 30-60 min of incubation and this effect was blocked by the galanin receptor antagonist galantide. Co-incubation of galanin with FK-506 (tacrolimus), a calcineurin inhibitor, suppressed the inhibitory effect of galanin on beta-endorphin release, suggesting that calcineurin is involved in the galanin-evoked decrease in beta-endorphin release. Measurement of beta-endorphin levels in the tissues at the end of the incubation period (120 min) revealed that galanin caused a two-fold increase of beta-endorphin peptide concentration in the mediobasal hypothalamic tissues. Concurrently, galanin induced an increase in the mean density of silver grains overlying proopiomelanocortin neurons after 60 min of incubation, an effect antagonized by galantide. Finally, reverse transcription-polymerase chain reaction analysis revealed that the mRNAs for the three galanin receptor subtypes (i.e. GalR1, GalR2, and GalR3) were expressed in the incubated mediobasal hypothalamic fragments. Taken as a whole, our results indicate that galanin plays a modulatory role on proopiomelanocortin neurons and this interrelation contributes to the elucidation of the neural circuitry that controls, among others, gonadotropin-releasing hormone function.
Assuntos
Galanina/farmacologia , Hipotálamo/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Pró-Opiomelanocortina/metabolismo , Animais , Inibidores de Calcineurina , Relação Dose-Resposta a Droga , Galanina/antagonistas & inibidores , Hipotálamo/química , Hipotálamo/citologia , Hipotálamo/fisiologia , Hibridização In Situ , Técnicas In Vitro , Masculino , Neurônios/química , Neurônios/citologia , Neurônios/fisiologia , RNA Mensageiro/análise , RNA Mensageiro/biossíntese , Ratos , Ratos Wistar , Receptores de Galanina , Receptores de Neuropeptídeos/biossíntese , Receptores de Neuropeptídeos/genética , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Tacrolimo/farmacologia , beta-Endorfina/análise , beta-Endorfina/metabolismoRESUMO
In a attempt to improve the sensitivity of the simultaneous use of immunohistochemistry (IHC) with estrogen receptor (ER) and in situ hybridization (ISH) with a neuropeptide receptor, we first applied an existing microwave (MW) irradiation protocol for immunohistochemical detection of the estrogen receptor in frozen brain sections. Regions of interest were the preoptic area and the arcuate nucleus of the hypothalamus. ER signal was effective only after MW heating of sections in the two regions. Control sections without pretreatment exhibited no staining for ER. Second, the MW protocol was applied in a novel procedure that consists of evaluation of the expression of the galanin receptor mRNA with a radioactive riboprobe after MW pretreatment. The galanin receptor mRNA signal intensity obtained after heating was quantitatively at least as good or significantly increased according to the region, with no discernible loss of tissue morphology. Finally, we describe a novel application of MW pretreatment on the same frozen section processed with ER antibody and a radioactive galanin receptor riboprobe. The stainings for estrogen and galanin receptors were intense in many cells of the preoptic area, with very low background. These results show that both IHC and ISH can be significantly improved by subjecting frozen sections to MW heating before the double labeling. This approach may provide a potential method to answer the important question of whether or not estrogen has a direct action on the expression of a peptide receptor. (J Histochem Cytochem 49:901-910, 2001)
Assuntos
Hipotálamo/metabolismo , RNA Mensageiro/metabolismo , Receptores de Estrogênio/metabolismo , Receptores de Neuropeptídeos/metabolismo , Animais , Feminino , Secções Congeladas , Hipotálamo/anatomia & histologia , Imuno-Histoquímica/métodos , Hibridização In Situ/métodos , Micro-Ondas , Ratos , Ratos Wistar , Receptores de GalaninaRESUMO
The forebrain and pituitary sites of synthesis of growth hormone secretagogue-receptor mRNA were identified in four adult lemurs (Microcebus murinus) by in situ hybridisation performed with a radiolabeled cRNA probe transcribed from human Growth Hormone Secretagogue-Receptor cDNA. The cRNA sense and antisense probes were hybridised to cryostat sections containing structures extending from the rostral hypothalamus to its caudal limit as defined by the mammillary bodies. The pituitary gland and areas adjacent to the hypothalamus were also analyzed. For comparative purposes, sections from five adult rats containing these structures were hybridised with the same probes. The results point to a widespread distribution of Growth Hormone Secretagogue-Receptor mRNA in the hypothalamus, hippocampal formation, and cerebellar cortex of both lemurs and rats. As in the rat, specific hybridisation was particularly dense in the arcuate nucleus. Significant species differences were observed in the periventricular nucleus, the ventromedial nucleus, the lateral hypothalamic area, and the pituitary gland. In contrast to the rat, the lemur exhibited marked labelling in the infundibular nucleus, the periventricular nucleus and the pars tuberalis of the pituitary gland, whereas no labeling was detectable in the ventromedial nucleus and the lateral hypothalamic area. These results are discussed in terms of difference between the control of growth hormone secretion, feeding behaviour and seasonal rhythmicity among murine species and primates.
Assuntos
Hipotálamo/metabolismo , Hipófise/metabolismo , RNA Mensageiro/metabolismo , Receptores de Superfície Celular/metabolismo , Receptores Acoplados a Proteínas G , Animais , Hibridização In Situ , Lemur , Masculino , Ratos , Ratos Sprague-Dawley , Receptores de GrelinaRESUMO
The present study was designed to determine whether transforming growth factor (TGF)beta and/or activin participate in the regulation of the gonadotropin releasing hormone (GnRH) neuroendocrine axis in vivo. Single-label in situ hybridization histochemistry was used to determine the anatomical distribution of a TGFbeta and activin type I receptor (B1) mRNA, in the adult female rat hypothalamic areas that are known to be important sites for the regulation of reproduction. Dual-label in situ hybridization histochemistry was performed to determine whether B1 mRNA was expressed in GnRH neurones. The results of these studies revealed an extensive distribution of B1 mRNA in the hypothalamic regions, including diagonal bands of Broca, preoptic area, arcuate nucleus and median eminence. In the median eminence, B1 mRNA was detected in tanycytes and in the endothelial cells of the pituitary portal blood capillaries. Dual-label in situ hybridization histochemistry showed that 31+/-5% of GnRH neurones expressed B1 mRNA, thus providing evidence that TGFbeta and/or activin can act directly on GnRH neurones to modulate their activity. Taken together, these data provide morphological arguments in favour of a participation of TGFbeta and/or activin in the regulation of reproduction at the hypothalamic level.
Assuntos
Hormônio Liberador de Gonadotropina/metabolismo , Família Multigênica/fisiologia , Sistemas Neurossecretores/fisiologia , Proteínas Serina-Treonina Quinases , Receptores de Fatores de Crescimento Transformadores beta , Fator de Crescimento Transformador beta/genética , Fator de Crescimento Transformador beta/metabolismo , Ativinas , Animais , Feminino , Hipotálamo/citologia , Hipotálamo/metabolismo , Inibinas/metabolismo , Neurônios/metabolismo , RNA Mensageiro/metabolismo , Ratos , Ratos Wistar , Receptores de Fatores de Crescimento/metabolismoRESUMO
The distribution of galanin receptor subtype 2 (Gal-R2) mRNA-expressing cells was examined by in situ hybridization in the rat hypothalamus using a full-length rat 35S-riboprobe. Gal-R2 receptor mRNA-expressing cells were found at moderate to high levels of expression in most nuclei and regions of hypothalamus. The labeling was observed within well-defined anatomical nuclei: preoptic, suprachiasmatic, periventricular, paraventricular, arcuate, dorsomedial, mammillary nuclei. The supraoptic and ventromedial nuclei were almost devoid of labeling. Some scattered labeled cells were also observed in the pituitary. This distribution of Gal-R2 mRNA-expressing cells corresponds well with that of galanin binding sites studies. As compared to the distribution of the galanin receptor subtype 1 (Gal-R1), our results indicate that the Gal-R2 type is differentially distributed, although a significant overlap exists in some regions such the preoptic area, arcuate and dorsomedial nuclei. The functional implications of these results are discussed in light of the role of galanin receptors plays in neuroendocrine regulation and feeding behavior.