RESUMO
In this work we report the existence of several evaginations extending out of the third ventricle within the mediobasal hypothalamus of the rat. In coronal sections, these evaginations appear as very narrow canaliculi integrating a canalicular system, which increases the contact surface between the ventricular lining and the nervous tissue. Consequently these evaginations enlarge the ventricular route for the transport of active principles present in the cerebrospinal fluid, such as (neuro)hormones and neurotransmitters. The mediobasal hypothalamus includes the arcuate nucleus and the median eminence (both involved in neuroendocrine mechanisms and in the regulation of pituitary function). A possible implication of our finding is that the neuroactive substance-containing ventricular cerebrospinal fluid may reach the intercellular spaces of the surrounding neuropil of the arcuate nucleus. According to literature these substances cross the ependyma of the lateral wall of the infundibular recess of the third ventricle. We suggest that such substances might also pass through the ependymal lining of the canalicular system, which displays the same ultrastructural characteristics as the rest of the ependyma of the lateral wall of the third ventricle. Therefore, the arcuate neurons may be influenced not only by synaptic inputs (afferent fibers) but also by non-synaptic diffusion neurotransmission (by means of neuroactive substances present in the cerebrospinal fluid).
Assuntos
Ventrículos Cerebrais/anatomia & histologia , Ventrículos Cerebrais/fisiologia , Hipotálamo Médio/anatomia & histologia , Hipotálamo Médio/fisiologia , Animais , Núcleo Arqueado do Hipotálamo/anatomia & histologia , Núcleo Arqueado do Hipotálamo/fisiologia , Ventrículos Cerebrais/ultraestrutura , Líquido Cefalorraquidiano/fisiologia , Feminino , Hipotálamo Médio/ultraestrutura , Masculino , Microvilosidades/ultraestrutura , Modelos Neurológicos , Ratos , Ratos Sprague-DawleyRESUMO
Diazepam-binding inhibitor (DBI) is the precursor of a family of peptides, including an octadecaneuropeptide (ODN), that share with DBI the ability to specifically displace benzodiazepines (BZD) from their receptors. An association of ODN with the peripheral type BZD receptors (PBR) has been reported in the brain and a few peripheral tissues. In order to investigate whether DBI and PBR are present in ovarian tissue, we have localized DBI by means of immunocytochemistry, in situ hybridization and autoradiography of PBR in the rat ovary. Immunocytochemical localization was achieved by means of rabbit antibodies developed against rat ODN. Immunostaining was located in the cytoplasm of the theca interna, corpus luteum and interstitial gland cells, but not in the granulosa cells. Hybridization signal obtained following in situ hybridization with a [35S]-labelled single-stranded RNA probe complementary to DBI mRNA was observed in all the steroid-secreting cells, including granulosa cells of developing and mature follicles. Autoradiographic localization of PBR obtained by incubating ovary sections with [3H] PK11195, a ligand selective for PBR, revealed the presence of specific labelling in all the steroid-secreting cells. These results, which demonstrate for the first time that the ovarian steroid-secreting cells contain both PBR and its endogenous ligand, suggest that the BZD receptor might be involved in the regulation of ovarian function.
Assuntos
Proteínas de Transporte/análise , Ovário/química , Receptores de GABA-A/análise , Animais , Autorradiografia , Sítios de Ligação , Corpo Lúteo/química , Corpo Lúteo/ultraestrutura , Citoplasma/química , Inibidor da Ligação a Diazepam , Diestro , Feminino , Células da Granulosa/química , Células da Granulosa/ultraestrutura , Técnicas Imunoenzimáticas , Hibridização In Situ , Oócitos/química , Oócitos/ultraestrutura , Ovário/citologia , Ovário/fisiologia , Proestro , RNA Complementar , Ratos , Ratos Sprague-Dawley , Células Tecais/química , Células Tecais/ultraestruturaRESUMO
The morphological features of the ependymal surface and supraependymal elements of the fourth ventricle of the rat were examined by scanning electron microscopy (SEM) and by the transmission electron microscopy (TEM). The results confirm the following aspects: 1) The presence of supraependymal elements and microvilli in the ependymal territories, including the sites where the cilia completely cover the ependymal surface; 2) The existence of cilia with oval or spherical thickenings together with supraependymal bulbs similar in size to those of the larger ciliary swellings; 3) Identification of the long supraependymal fibres with intermittent fusiform dilations observed under the SEM with the nerve fibres seen under the TEM; 4) The existence of intraventricular axodendritic synapses.
Assuntos
Tronco Encefálico/ultraestrutura , Cerebelo/ultraestrutura , Epêndima/ultraestrutura , Animais , Cílios/ultraestrutura , Feminino , Masculino , Microscopia Eletrônica , Microscopia Eletrônica de Varredura , Microvilosidades/ultraestrutura , Ratos , Sinapses/ultraestruturaRESUMO
Ultrastructural studies of the ependyma of the tuberoinfundibular region of the rat hypothalamus have revealed the existence of intraventricular axonal endings and of cytoplasmic blebs and bulbs that project from the apical surface of the ependymal cells to the ventricular lumen. All these structures account for the processes of ependymal apocrine secretion and the neuroventriculocrinia, and hence the release of biologically active substances into the cerebrospinal fluid (CSF). These substances contained in the CSF must act on the nervous nuclei of the tuberoinfundibular region, such as the arcuate nucleus, which is very important in the neuroendocrine regulation of the anterior pituitary gland. Dilated intercellular spaces among neighbouring ependymocytes of this region, small intraependymal cisternae and, in particular, a lateral prolongation of the infundibular recess, which courses through the nervous tissue between the arcuate nucleus and the median eminence from the vertex of the lateral angle of the infundibular recess, may be the route followed by the CSF from the third ventricle to the tissue compartment of the tuberoinfundibular region. Also studied are the cisternae of the region and the relationships of these with the lateral prolongation of the infundibular recess. Some of these cisternae may be filled by the CSF through the prolongation. In this way, the tissue compartment of CSF would be enlarged, and hence the ventricular route for the secretion and transport of biologically active substances would be potentiated.
Assuntos
Hipotálamo Médio/metabolismo , Hipotálamo Médio/ultraestrutura , Animais , Líquido Cefalorraquidiano , Feminino , Hipotálamo Médio/anatomia & histologia , Masculino , Microscopia Eletrônica , Ratos , Ratos Sprague-DawleyRESUMO
Ultrastructural studies of the ependyma of the tuberoinfundibular region of the rat hypothalamus have revealed the existence of intraventricular axonal endings and of cytoplasmic blebs and bulbs that project from the apical surface of the ependymal cells to the ventricular lumen. All these structures account for the processes of ependymal apocrine secretion and the neuroventriculocrinia, and hence the release of biologically active substances into the cerebrospinal fluid (CSF). These substances contained in the CSF must act on the nervous nuclei of the tuberoinfundibular region, such as the arcuate nucleus, which is very important in the neuroendocrine regulation of the anterior pituitary gland. Dilated intercellular spaces among neighbouring ependymocytes of this region, small intraependymal cisternae and, in particular, a lateral prolongation of the infundibular recess, which courses through the nervous tissue between the arcuate nucleus and the median eminence from the vertex of the lateral angle of the infundibular recess, may be the route followed by the CSF from the third ventricle to the tissue compartment of the tuberoinfundibular region. Also studied are the cisternae of the region and the relationships of these with the lateral prolongation of the infundibular recess. Some of these cisternae may be filled by the CSF through the prolongation. In this way, the tissue compartment of CSF would be enlarged, and hence the ventricular route for the secretion and transport of biologically active substances would be potentiated
Assuntos
Animais , Feminino , Masculino , Ratos , Hipotálamo Médio/metabolismo , Líquido Cefalorraquidiano , Hipotálamo Médio/anatomia & histologia , Hipotálamo Médio , Microscopia Eletrônica , Ratos Sprague-DawleyRESUMO
An endogenous peptide, named diazepam-binding inhibitor (DBI) capable of displacing benzodiazepines from binding sites has been recently fully characterized. In order to clearly identify the cell types responsible for the biosynthesis of DBI in the rat central nervous system, we have performed high resolution in situ hybridization in the area postrema, hypothalamus and cerebellum, using a [35S]-labeled single stranded RNA probe. Hybridization signal was detected in both semithin and ultrathin sections. In all the brain areas examined, specific labeling was exclusively observed in non-neuronal cells including ependymal and subependymal cells bordering the third ventricle. The results obtained clearly establish that DBI is synthesized by non-neuronal cells in the rat brain.
Assuntos
Química Encefálica , Neuropeptídeos/genética , RNA Mensageiro/análise , Animais , Autorradiografia , Sítios de Ligação , Cerebelo/química , Cerebelo/ultraestrutura , Inibidor da Ligação a Diazepam , Epêndima/química , Epêndima/ultraestrutura , Hipotálamo/química , Hipotálamo/ultraestrutura , Masculino , Neuropeptídeos/química , Hibridização de Ácido Nucleico , RNA Mensageiro/genética , Ratos , Ratos EndogâmicosRESUMO
An electron-microscopic study was carried out on the median eminence of cats during post-natal development. From the moment of birth (observations performed 12 hours later) Herring bodies were seen in the fibrillary layer of the median eminence. At 45 days after birth, myelinated nerve fibres could be observed, some of them containing neurosecretory granules. The number of myelinated fibres in the median eminence increased with age and at 90 days some Herring bodies appeared surrounded by myelin sheaths; these mainly contained neurosecretory granules and a few mitochondria.
Assuntos
Sistema Hipotálamo-Hipofisário/citologia , Corpos de Inclusão/ultraestrutura , Eminência Mediana/ultraestrutura , Bainha de Mielina/ultraestrutura , Fibras Nervosas/ultraestrutura , Animais , Gatos , Grânulos Citoplasmáticos/ultraestrutura , Feminino , Masculino , Microscopia Eletrônica , Mitocôndrias/ultraestruturaRESUMO
The fine modulation of gonadotropin gene expression and secretion is well recognized to be regulated by sex steroids through their direct action both at the anterior pituitary level and on the pulsatile pattern of GnRH secretion at the hypothalamic level. Since the influence of sex steroids on hypothalamic GnRH mRNA levels remains to be elucidated, quantitative in situ hybridization was used to study the effect of sex steroids on cellular levels of pro-GnRH mRNA in adult rats of both sexes. The effects of 14-day gonadectomy as well as administration of 17 beta-estradiol (E2, 0.25 micrograms) or dihydrotestosterone (DHT, 100 micrograms) twice a day during 14 days to gonadectomized animals were evaluated. In addition, the effect of progesterone (P, 2 mg, twice daily) alone or in the presence of E2 was also studied in ovariectomized animals. Hybridization was performed using a 35S-labeled cDNA probe encoding rat pro-GnRH and the corresponding mRNA levels were assessed by counting the number of silver grains overlying labeled neurons. In male rats, castration induced a highly significant 65% increase (compared to intact rats) in the mean number of grains per neuron. Administration of E2 or DHT to castrated animals completely prevented the post castration rise in pro-GnRH mRNA levels. In female animals, the effect of ovariectomy was less striking than in the male, a 25% increase (P less than 0.001) being observed. Treatment with E2 or DHT also completely prevented the increase in pro-GnRH mRNA levels induced by ovariectomy. Moreover, treatment with P in ovariectomized animals markedly potentiated the inhibitory effect of E2 on pro-GnRH mRNA levels.(ABSTRACT TRUNCATED AT 250 WORDS)