RESUMO
The posterodorsal medial amygdala (MePD) has an adapted synaptic organization that dynamically modulates reproduction and other social behaviors in rats. Discrete gap junctions between glial cells were previously reported in the MePD neuropil. Connexins (Cx) are components of gap junctions and indicative of cellular electrical coupling. Here, we report the ultrastructural occurrence of gap junctions between neurons in the MePD and demonstrate the expression and immunofluorescent labeling of Cx36, Cx43 and Cx45 in this subcortical area of adult male rats. Few neuronal gap junctions were found in the MePD and, when identified, occurred between dendrites. On the other hand, there is a diffuse presence and distribution of punctate labelling for the tested Cxs. Puncta were visualized isolated or forming clusters in the same focal plane of cell bodies or along the MePD neuropil. The Cx36 puncta were found in neurons, Cx43 in astrocytes and Cx45 in both neurons and astrocytes. Our data indicate the presence of few gap junctions and different Cxs composition in the MePD. Because Cxs can assemble, form hemichannel units and/or serve as transcriptional regulator, it is likely that additional modulation of intercellular communication can occur besides the chemical transmission in the MePD of adult rats.
Assuntos
Tonsila do Cerebelo/ultraestrutura , Conexinas/biossíntese , Junções Comunicantes/ultraestrutura , Neurônios/ultraestrutura , Tonsila do Cerebelo/metabolismo , Animais , Conexina 43/biossíntese , Junções Comunicantes/metabolismo , Masculino , Microscopia Eletrônica de Transmissão , Neurônios/metabolismo , Ratos , Ratos Wistar , Proteína delta-2 de Junções ComunicantesRESUMO
The posterodorsal medial amygdala (MePD) is a sex-steroid-sensitive area that modulates reproductive behavior in rats. The volume of the neuronal cell body, density of dendritic spines, and glial fibrillary acidic protein immunoreactivity are sexually dimorphic or affected by gonadal hormones in the MePD. Here we add new data to this panorama and describe the ultrastructure of the glial and axonal coverage of the perikaryal membrane and the somatic spines in the MePD of males and cycling females (in diestrus, early proestrus, late proestrus, and estrus). Transmission electron microscopy data (mean values from seven to 11 neurons per rat, five or six animals per group) showed that the rat MePD has most of the perikaryal membrane covered by glial processes and a relatively large amount (up to 40%) of axonal processes contacting the neuronal cell body. No statistically significant difference was found between groups for these somatic coverages (P > 0.5). However, the density of somatic spines along the length of the perikaryal membrane was higher in the late proestrus than in estrus (P < 0.05), and somatic spines in early and late proestrus showed variable shapes with stubby/wide, thin, mushroom-like, ramified, transitional or atypical aspects. These findings add to the rapid adjustable synaptic changes in the MePD and in the integrated neural circuits that control neuroendocrine secretion and the hormonally modulated timely display of social behaviors in rats.
Assuntos
Tonsila do Cerebelo/ultraestrutura , Axônios/ultraestrutura , Espinhas Dendríticas/ultraestrutura , Ciclo Estral/fisiologia , Neuroglia/ultraestrutura , Caracteres Sexuais , Tonsila do Cerebelo/fisiologia , Animais , Axônios/fisiologia , Espinhas Dendríticas/fisiologia , Feminino , Masculino , Microscopia Eletrônica de Transmissão , Neuroglia/fisiologia , Ratos WistarRESUMO
The rat posterodorsal medial amygdala (MePD) is a brain area in which gonadal hormones induce notable plastic effects in the density of dendritic spines. Dendritic spines are post-synaptic specializations whose shape and spacing change neuronal excitability. Our aim was to obtain new data on the dendritic spines morphology and density from MePD neurons using the carbocyanine dye DiI under confocal microscopy. In adult male rats, the dendritic spine density of the medial branches of the left MePD (mean+/-SD) was 1.15+/-0.67spines/dendritic microm. From the total sampled, approximately 53% of the spines were classified as thin, 22.5% as "mushroom-like", and 21.5% as stubby/wide. Other spine shapes (3%) included those ramified, with a filopodium-like or a gemule appearance, and others with a protruding spinule. Additional experiment joining DiI and synaptophysin (a pre-synaptic protein) labeling suggested synaptic sites on dendritic shafts and spines. Dendritic spines showed synaptophysin puncta close to their head and neck, although some spines had no evident labeled puncta on them or, conversely, multiple puncta appeared upon one spine. These results advance previous light microscopy results by revealing features and complexities of the dendritic spines at the same time that give new insight on the possible synaptic organization of the adult rat MePD.
Assuntos
Tonsila do Cerebelo/ultraestrutura , Forma Celular/fisiologia , Espinhas Dendríticas/ultraestrutura , Neurônios/ultraestrutura , Sinapses/ultraestrutura , Tonsila do Cerebelo/citologia , Tonsila do Cerebelo/fisiologia , Animais , Carbocianinas/farmacocinética , Espinhas Dendríticas/metabolismo , Corantes Fluorescentes/farmacocinética , Masculino , Microscopia Confocal/métodos , Neurônios/citologia , Neurônios/fisiologia , Ratos , Ratos Wistar , Sinapses/metabolismoRESUMO
Repeated seizures induce permanent alterations of the brain in experimental models and patients with intractable temporal lobe epilepsy (TLE), which is a common form of epilepsy in humans. Together with cell loss and gliosis in many brain regions, synaptic reorganization is observed principally in the hippocampus. However, in the amygdala this synaptic reorganization has been not studied. The changes in Zn density, synaptophysin and MAP(2) as markers of reactive synaptogenesis in medial extended amygdala induced by kainic acid (KA) as a model of TLE was studied. Adult male rats (n=6) were perfused at 10 days, 1, 2, 3 and 4 months after KA i.p. injection (9 mg/kg). Controls were injected with saline. The brains were processed by the Timm's method to reveal synaptic Zn and analyzed by densitometry. Immunohistochemistry was used to reveal synaptophysin and MAP(2) expression. A two-way ANOVA was used for statistics, with a P<0.05 as a significance limit. Normal dark staining was seen in all medial extended amygdala subdivisions of control animals. At 10 days post KA injection a dramatic loss of staining was observed. A slow but steady recovery of Zn density can be followed in the 4 month period studied. Parallel, from 10 days to 2 months stronger synaptophysin expression could be observed, whereas MAP(2) expression increased from 1 month with peak levels at 3-4 months. The results suggest that a process of sprouting exists in surviving neurons of medial extended amygdala after status epilepticus and that these neurons might be an evidence of a reactive synaptogenesis process.
Assuntos
Tonsila do Cerebelo/metabolismo , Epilepsia/metabolismo , Plasticidade Neuronal/fisiologia , Terminações Pré-Sinápticas/metabolismo , Zinco/metabolismo , Tonsila do Cerebelo/fisiopatologia , Tonsila do Cerebelo/ultraestrutura , Animais , Biomarcadores/metabolismo , Convulsivantes , Modelos Animais de Doenças , Epilepsia/fisiopatologia , Epilepsia do Lobo Temporal/metabolismo , Epilepsia do Lobo Temporal/fisiopatologia , Cones de Crescimento/metabolismo , Cones de Crescimento/ultraestrutura , Histocitoquímica , Imuno-Histoquímica , Ácido Caínico , Masculino , Proteínas Associadas aos Microtúbulos/metabolismo , Ratos , Ratos Wistar , Núcleos Septais/metabolismo , Núcleos Septais/fisiopatologia , Núcleos Septais/ultraestrutura , Coloração e Rotulagem , Sinaptofisina/metabolismoRESUMO
The volumes of the neuronal nucleus and the cell body in the left posterodorsal medial amygdala (MePD) of adult ovariectomized (OVX) female rats submitted to different hormonal therapies were studied here, aiming to reveal possible influence of substitutive sex steroids in these morphological parameters. One week following ovariectomy and at the end of treatments, brains were cut to semi-thin sections (1 microm) and stained with 1% toluidine blue for stereological estimations, carried out using the Cavalieri method and the technique of point counting. Both the volume of the neuronal nucleus and the soma showed a statistically significant difference when comparing the data among OVX females treated with vehicle (V), estradiol (EB) alone, EB plus progesterone (EB+P) or P alone [n=5 rats in each group; one-way ANOVA test, P<0.01 in both cases]. The Tukey test showed that OVX and EB+P treated females had higher mean neuronal nucleus and somatic volumes when compared to V (P<0.01) or EB alone (P<0.01). Also, OVX females treated with P alone showed larger mean neuronal nucleus and somatic volumes when compared to V (P<0.05). These results suggest that the neuronal nucleus and the somatic volumes can be modulated by substitutive ovarian hormones administered to OVX females, for which P can lead to higher results. These findings reveal additional epigenetic actions of the sex steroids in the MePD and new neuronal morphological features in adult female rats.
Assuntos
Tonsila do Cerebelo/citologia , Estradiol/fisiologia , Neurônios/citologia , Progesterona/fisiologia , Tonsila do Cerebelo/efeitos dos fármacos , Tonsila do Cerebelo/ultraestrutura , Animais , Núcleo Celular/ultraestrutura , Tamanho Celular , Estradiol/farmacologia , Terapia de Reposição de Estrogênios , Feminino , Neurônios/efeitos dos fármacos , Neurônios/ultraestrutura , Ovariectomia , Progesterona/farmacologia , Ratos , Ratos WistarRESUMO
Several evidences suggest that the posterodorsal medial amygdala (MePD) can be a relevant part of the rat neural circuitry for the regulation of hypothalamic neuroendocrine secretion and for ontogenetically different behavioral displays. The dendritic spine density of Golgi-impregnated neurons from the MePD was evaluated in young rats following acute or chronic restraint stress and in aged animals (24 months old). Compared to the control group, a single 1 h restraint stress session promoted a decreased spine density (p<0.01) whereas a single 6 h restraint stress session or daily 6-h restraint sessions for 28 consecutive days did not lead to the same effect (p>0.05). Aged rats showed no difference in this dendritic spine parameter when compared to young adults (p>0.05). These results indicate that short-term stress (1 h) can affect MePD dendritic spines and that neural plasticity is involved with adaptive responses onwards in restrained rats. On the other hand, brain structural modifications related with ageing appear not to influence the number of certain postsynaptic sites in the MePD of rats.
Assuntos
Envelhecimento/patologia , Tonsila do Cerebelo/patologia , Espinhas Dendríticas/patologia , Estresse Psicológico/patologia , Adaptação Fisiológica/fisiologia , Tonsila do Cerebelo/fisiopatologia , Tonsila do Cerebelo/ultraestrutura , Animais , Espinhas Dendríticas/ultraestrutura , Hipotálamo/metabolismo , Hipotálamo/fisiopatologia , Masculino , Vias Neurais/fisiopatologia , Plasticidade Neuronal/fisiologia , Sistemas Neurossecretores/patologia , Sistemas Neurossecretores/fisiopatologia , Sistemas Neurossecretores/ultraestrutura , Ratos , Ratos Wistar , Restrição Física , Estresse Psicológico/fisiopatologiaRESUMO
The aim of the present study was to describe the ultrastructure of neurons (from eight animals) and to analyse the synaptic terminal distribution (from two animals) in the posterodorsal subnucleus of the medial amygdala (MePD) of adult male rats. Using transmission electron microscopy, it was possible to identify many spiny and aspiny dendrites, unmyelinated axonal bundles, single axonal processes, a few myelinated axons, blood vessels and glial processes in the neuropil. Axodendritic synapses were the most frequently observed (67.5%), appearing to be of either the inhibitory or the excitatory types. The presynaptic region contained round or flattened vesicles that occurred either singly or with dense-cored vesicles (DCVs). The dendrites often received many synapses on a single shaft, and axon terminals displayed synaptic contacts with one or more postsynaptic structures. Dendritic spines showed different morphologies and the synapses on them (23.1%) formed a single and apparently excitatory synaptic contact with round, electron-lucid vesicles alone or, less frequently, with DCVs. Inhibitory and excitatory axosomatic synapses (8.2%) and excitatory axoaxonic synapses (1.2%) were also identified. The present report provides new findings relevant to the study of the MePD cellular organization and could be combined with other morphological data in order to reveal the functional activity of this area in male rats.
Assuntos
Tonsila do Cerebelo/ultraestrutura , Neurônios/ultraestrutura , Terminações Pré-Sinápticas/ultraestrutura , Animais , Masculino , Microscopia Eletrônica , Microtomia , Ratos , Ratos WistarRESUMO
The medial amygdala (MeA) has receptors for gonadal hormones and is a sexually dimorphic area in rats. The aims of the present work were (1) to look at sex differences and the effect of gonadal hormone withdrawal in males castrated as offspring or at adulthood on neuronal soma area in the anterior and posterior MeA and (2) to study the dendritic branching and the density of dendritic spines in neurons from the MeA of intact males and females. Animals were adult rats, for which the single-section Golgi method was used. Stellate and bitufted cells were found in the MeA. Comparing data among groups, no significant difference in cell body area was found. Dendrites divide sparingly and have very different lengths, and a statistical difference (p < 0.001, males higher than females) in the spine density in the anterior MeA, but not in the posterior MeA, was found. These results suggest that castration does not alter the somal area in males submitted to gonadectomy during the early postnatal period or at adulthood. In addition, the already described sex difference in this nucleus may be more related to the neuropil than the neuronal somal area, which may be relevant for the function of the MeA.