RESUMO
Substance P (SP) was recently reported to be expressed in human kisspeptin/neurokinin B/dynorphin (KNDy) neurons and to enhance KNDy neuron excitability in the mouse hypothalamus. We therefore examined (1) interactions of SP and kisspeptin in the mediobasal hypothalamus of adult male rhesus monkeys using immunofluorescence, and (2) the ability of SP to induce LH release in GnRH-primed, agonadal juvenile male monkeys. SP cell bodies were observed only occasionally in the arcuate nucleus (Arc), but more frequently dorsal to the Arc in the region of the premammillary nucleus. Castration resulted in an increase in the number of SP cell bodies in the Arc but not in the other regions. SP fibers innervated the Arc, where they were found in close apposition with kisspeptin perikarya in the periphery of this nucleus. Beaded SP axons projected to the median eminence, where they terminated in the external layer and intermingled with beaded kisspeptin axons. Colocalization of the two peptides, however, was not observed. Although close apposition between SP fibers and kisspeptin neurons suggest a role for SP in modulating GnRH pulse generator activity, i.v. injections of SP failed to elicit release of GnRH (as reflected by LH) in the juvenile monkey. Although the finding of structural interactions between SP and kisspeptin neurons is consistent with the notion that this tachykinin may be involved in regulating pulsatile GnRH release, the apparent absence of expression of SP in KNDy neurons suggests that this peptide is unlikely to be a fundamental component of the primate GnRH pulse generator.
Assuntos
Hormônio Liberador de Gonadotropina/metabolismo , Hipotálamo Médio , Kisspeptinas/metabolismo , Hormônio Luteinizante/metabolismo , Peptídeos/administração & dosagem , Substância P/metabolismo , Administração Intravenosa , Animais , Castração , Relação Dose-Resposta a Droga , Hipotálamo Médio/citologia , Hipotálamo Médio/efeitos dos fármacos , Hipotálamo Médio/metabolismo , Macaca mulatta , Masculino , Neurônios/efeitos dos fármacos , Neurônios/metabolismoRESUMO
The pars tuberalis (PT) is the only pituitary region in close contact with the medial-basal hypothalamus and bathed by cerebrospinal fluid (CSF). Although PT has long been recognized as an endocrine gland, certain aspects of its structure remain obscure. The present investigation has been designed to gain information concerning (1) the cellular organization of PT, (2) the PT/median eminence spatial relationship and (3) the exposure of various cell compartments of PT to CSF. Non-endocrine cells (S100-reactive) appear as the organizer of the PT architecture. The apical poles of these cells line large cistern-like cavities and the processes of these cells establish a close spatial relationship with PT-specific secretory cells, portal capillaries and tanycytes. The cisterns are also endowed with clusters of ciliated cells and with a highly electron-dense and PAS-reactive content. The unique spatial organization of endocrine and non-endocrine cells of the PT supports a functional relationship between both cell populations. PT endocrine cells display a hallmark of PT-specific cells, namely, the paranuclear spot, which is a complex structure involving the Golgi apparatus, a large pool of immature secretory granules and a centriole from which originates a single 9+0 cilium projecting to the intercellular channels. Horseradish peroxidase (HRP) injected into the CSF readily reaches the intercellular channels of PT and the inner channel of the single cilium and is incorporated by the endocytic machinery of the secretory cells. The PT endocrine cells, through their single 9+0 cilium, may act as sensors of the CSF. HRP also reaches the lumen of the cisterns, indicating that this PT compartment is also exposed to CSF. PT endocrine cells establish direct cell-to-cell contacts with hypothalamic beta(1) tanycytes, suggesting a second means of brain-PT communication.
Assuntos
Líquido Cefalorraquidiano , Epêndima/citologia , Eminência Mediana/citologia , Adeno-Hipófise/citologia , Animais , Capilares , Centríolos/ultraestrutura , Cílios/ultraestrutura , Células Endócrinas/metabolismo , Células Endócrinas/ultraestrutura , Endocitose , Espaço Extracelular , Complexo de Golgi/metabolismo , Complexo de Golgi/ultraestrutura , Hipotálamo Médio/citologia , Adeno-Hipófise/metabolismo , Ratos , Proteínas S100/metabolismo , Vesículas Secretórias/ultraestrutura , Terceiro Ventrículo/citologiaRESUMO
Tanycytes are bipolar cells bridging the cerebrospinal fluid (CSF) to the portal capillaries and may link the CSF to neuroendocrine events. During the perinatal period a subpopulation of radial glial cells differentiates into tanycytes, a cell lineage sharing some properties with astrocytes and the radial glia, but displaying unique and distinct morphological, molecular, and functional characteristics. Four populations of tanycytes, alpha(1,2) and beta(1,2), can be distinguished. These subtypes express differentially important functional molecules, such as glucose and glutamate transporters; a series of receptors for neuropeptide and peripheral hormones; secretory molecules such as transforming growth factors, prostaglandin E(2), and the specific protein P85; and proteins of the endocytic pathways. This results in functional differences between the four subtypes of tanycytes. Thus, alpha(1,2) tanycytes do not have barrier properties, whereas beta(1,2) tanycytes do. Different types of tanycytes use different mechanisms to internalize and transport cargo molecules; compounds internalized via a clathrin-dependent endocytosis would only enter tanycytes from the CSF. There are also differences in the neuron-tanycyte relationships; beta(1,2) tanycytes are innervated by peptidergic and aminergic neurons, but alpha(1,2) tanycytes are not. Important aspects of the neuron-beta(1) tanycyte relationships have been elucidated. Tanycytes can participate in the release of gonadotropin-releasing hormone (GnRH) to the portal blood by expressing estrogen receptors, absorbing molecules from the CSF, and providing signal(s) to the GnRH neurons. Removal of tanycytes prevents the pulse of GnRH release into the portal blood, the peak of luteinizing hormone, and ovulation. The discovery in tanycytes of new functional molecules is opening a new field of research. Thus, thyroxine deiodinase type II, an enzyme generating triiodothyronine (T(3)) from thyroxine, appears to be exclusively expressed by tanycytes, suggesting that these cells are the main source of brain T(3). Glucose transporter-2 (GLUT-2), a low-affinity transporter of glucose and fructose, and ATP-sensitive K(+) channels are expressed by tanycytes, suggesting that they may sense CSF glucose concentrations.
Assuntos
Hipotálamo Médio/citologia , Hipotálamo Médio/fisiologia , Sistemas Neurossecretores/fisiologia , Animais , Astrócitos/citologia , Astrócitos/metabolismo , Astrócitos/fisiologia , Barreira Hematoencefálica/citologia , Barreira Hematoencefálica/fisiologia , Encéfalo/citologia , Encéfalo/fisiologia , Líquido Cefalorraquidiano/fisiologia , Glândulas Endócrinas/citologia , Glândulas Endócrinas/fisiologia , Endocitose/fisiologia , Epêndima/química , Epêndima/citologia , Feminino , Hormônio Liberador de Gonadotropina/sangue , Hormônio Liberador de Gonadotropina/líquido cefalorraquidiano , Hipotálamo Médio/metabolismo , Masculino , Neuroglia/citologia , Neuroglia/metabolismo , Neuroglia/fisiologia , Neurônios/fisiologia , Sistemas Neurossecretores/citologia , Ratos , Células-Tronco/citologia , Células-Tronco/fisiologiaRESUMO
The connections of the precomissural nucleus (PRC) have been examined with anterograde and retrograde axonal tracing methods in the rat. Experiments with cholera toxin B subunit (CTb) indicate that the PRC shares a number of common afferent sources with the dorsolateral periaqueductal gray (PAG). Thus, we have shown that the nucleus receives substantial inputs from the prefrontal cortex, specific domains of the rostral part of the lateral septal nucleus, rostral zona incerta, perifornical region, anterior hypothalamic nucleus, ventromedial hypothalamic nucleus, dorsal premammillary nucleus, medial regions of the intermediate and deep layers of the superior colliculus, and cuneiform nucleus. Moreover, the PRC also receives inputs from several PAG regions and from neural sites involved in the control of attentive or motivational state, including the laterodorsal tegemental nucleus and the ventral tegmental area. The efferent projections of the PRC were analyzed by using the Phaseolus vulgaris-leucoagglutinin (PHA-L) method. Notably, the PRC presents a projection pattern that resembles in many ways the pattern described previously for the rostral dorsolateral PAG in addition to projections to a number of targets that also are innervated by neighboring pretectal nuclei, including the rostrodorsomedial part of the lateral dorsal thalamic nucleus, the ventral part of the lateral geniculate complex, the medial pretectal nucleus, the nucleus of the posterior commissure, and the ventrolateral part of the subcuneiform reticular nucleus. Overall, the results suggest that the PRC might be viewed as a rostral component of the PAG, and the possible functional significance of the nucleus is discussed in terms of its connections.
Assuntos
Hipotálamo Anterior/citologia , Hipotálamo Médio/citologia , Vias Neurais/anatomia & histologia , Animais , Axônios/ultraestrutura , Tronco Encefálico/citologia , Hipotálamo Anterior/ultraestrutura , Hipotálamo Médio/ultraestrutura , Masculino , Ratos , Ratos Wistar , Telencéfalo/citologiaRESUMO
Release of luteinizing hormone (LH)-releasing hormone (LHRH), the hypothalamic peptide that controls release of LH from the adenohypophysis, is controlled by NO. There is a rich plexus of nitric oxide synthase (NOS)-containing neurons and fibers in the lateral median eminence, intermingled with terminals of the LHRH neurons. To study relations between NOS and LHRH in this brain region, we measured NOS activity in incubated medial basal hypothalamus (MBH). NOS converts [14C]arginine to equimolar quantities of [14C]citrulline plus NO, which rapidly decomposes. The [14C]citrulline serves as an index of the NO produced. NOS basal activity was suppressed by incubation of the tissue with an inhibitor of NOS, nitroarginine methyl ester (NAME) (10(-5) M). Furthermore, incubation of MBH explants for 30 min with norepinephrine (NE) increased NOS activity and the increase was prevented by prazosine (10(-5) M), an alpha 1-adrenergic receptor blocker; however, direct addition of NE to the tissue homogenate or to a preparation of MBH synaptosomes did not alter enzyme activity, which suggested that NE increased the content of NOS during incubation with the tissue. After purification of NOS, the increase in enzyme content induced by NE was still measurable. This indicates that within 30 min NE increased the synthesis of NOS in vitro. Incubation of MBH or the MBH homogenate with various concentrations of sodium nitroprusside (NP), a releaser of NO, reduced NOS activity at high concentrations (> or = 0.9 mM), which were associated with either a reduction of stimulation or a plateau of LHRH release. Finally, incubation of either MBH or the homogenate with cGMP, a major mediatior of NO action, at concentrations that increased LHRH release also reduced NOS activity. These results indicate that NO at high concentrations can inactivate NOS and that cGMP can also inhibit the enzyme directly. Therefore, the increased NOS activity induced by activation of alpha 1 receptors by NE is inhibited by NO itself and a principal product of its activity, cGMP, providing negative feedback on NOS. In central nervous system (CNS) infections with high concentrations of inducible NOS produced by glial elements, the high concentrations of NO and cGMP produced may suppress LHRH release, resulting in decreased gonadotropin and gonadal steroid release.
Assuntos
GMP Cíclico/farmacologia , Hipotálamo Médio/enzimologia , Neurônios/enzimologia , Óxido Nítrico Sintase/metabolismo , Nitroprussiato/farmacologia , Norepinefrina/farmacologia , Animais , Arginina/metabolismo , Radioisótopos de Carbono , Citrulina , Hormônio Liberador de Gonadotropina/metabolismo , Hipotálamo Médio/citologia , Hipotálamo Médio/efeitos dos fármacos , Cinética , Masculino , Modelos Neurológicos , Fibras Nervosas/enzimologia , Neurônios/citologia , Neurônios/efeitos dos fármacos , Técnicas de Cultura de Órgãos , Ratos , Ratos WistarRESUMO
c-fos immunoreactivity was used to map brain areas in which neurons reacted either to electrical stimulation or to microinjection of the excitatory amino acid kainate and of the GABAA antagonist, SR-95531, applied to the medial hypothalamus of freely moving rats. All these stimulations induced flight behavior of moderate intensity. Immunoreactive cells were found within a radius of 0.5 mm around the stimulated area. Distally, clusters of labeled cells were found ipsilaterally in the piriform and entorhinal cortices, in several amygdaloid nuclei, in the bed nucleus of the stria terminalis, in the septo-hypothalamic nucleus, in the paraventricular, anterior and dorsomedial hypothalamic nuclei, the the paraventricular thalamic nucleus, in the dorsal periaqueductal gray extending to the cuneiform nucleus, and bilaterally in the supramammillary decussation and the locus coeruleus. The specificity of the brain areas thus labeled was indicated by the unilateral pattern of activation as well as by the different pattern obtained after control microinjection of saline. Therefore, these results are likely to provide sound information about the brain structures involved in defensive-aversive behavior evoked from the medial hypothalamus.
Assuntos
Química Encefálica/efeitos dos fármacos , Química Encefálica/fisiologia , Hipotálamo Médio/efeitos dos fármacos , Hipotálamo Médio/fisiologia , Proteínas Proto-Oncogênicas c-fos/metabolismo , Animais , Comportamento Animal/efeitos dos fármacos , Comportamento Animal/fisiologia , Mapeamento Encefálico , Estimulação Elétrica , Antagonistas de Receptores de GABA-A , Hipotálamo Médio/citologia , Imuno-Histoquímica , Ácido Caínico/farmacologia , Masculino , Piridazinas/farmacologia , Ratos , Estimulação QuímicaRESUMO
Estrogen stimulates the neurite outgrowth response of medial basal hypothalamic neurons maintained in culture. We show here that one effect of estrogen is to promote an increase in tau, but not in tubulin, microtubule-associated protein 1a (MAP-1a), or MAP-2 protein levels. This response precedes and accompanies an increase in stable microtubules and in neurite length. Taken collectively, our data suggest that estrogen-enhanced neurite growth is mediated by a selective induction of microtubule-stabilizing factors, namely, the tau proteins.