RESUMEN
The hippocampal formation is essential for spatial navigation and episodic memory. The anatomical structure is largely similar across mammalian species, apart from the deep polymorphic layer of the dentate gyrus and the adjacent part of cornu ammonis 3 (CA3) which feature substantial variations. In rodents, the polymorphic layer has a triangular cross-section abutting on the end of the CA3 pyramidal layer, while in primates it is long and band-shaped capping the expanded CA3 end, which here lacks a distinct pyramidal layer. This structural variation has resulted in a confusing nomenclature and unclear anatomical criteria for the definition of the dentate-ammonic border. Seeking to clarify the border, we present here a light microscopic investigation based on Golgi-impregnated and Timm-thionin-stained sections of the Artiodactyla sheep and domestic pig, in which the dentate gyrus and CA3 end have some topographical features in common with primates. In short, the band-shaped polymorphic layer coincides with the Timm-positive mossy fiber collateral plexus and the Timm-negative subgranular zone. While the soma and excrescence-covered proximal dendrites of the mossy cells are localized within the plexus, the peripheral mossy cell dendrites extend outside the plexus, both into the granular and molecular layers, and the CA3. The main mossy fibers leave the collateral plexus in a scattered formation to converge gradually through the CA3 end in between the dispersed pyramidal cells, which are of three subtypes, as in monkey, with the classical apical subtype dominating near the hidden blade, the nonapical subtype near the exposed blade, and the dentate subtype being the only pyramidal cells that extend dendrites into the dentate gyrus. In agreement with our previous study in mink, the findings show that the border between the dentate gyrus and the CA3 end can be more accurately localized by the mossy fiber system than by cyto-architecture alone.
Asunto(s)
Oveja Doméstica , Sus scrofa , Animales , Región CA3 Hipocampal , Giro Dentado , Hipocampo , Ovinos , PorcinosRESUMEN
The mammalian auditory system comprises a complex network of brain regions. Interpretations and comparisons of experimental results from this system depend on appropriate anatomical identification of auditory structures. The Waxholm Space (WHS) atlas of the Sprague Dawley rat brain (Papp et al., Neuroimage 97:374-86, 2014) is an open access, three-dimensional reference atlas defined in an ex-vivo magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI) volume. Version 2.0 of the atlas (Kjonigsen et al., Neuroimage 108:441-9, 2015) includes detailed delineations of the hippocampus and several major subcortical regions, but only few auditory structures. To amend this, we have delineated the complete ascending auditory system from the cochlea to the cerebral cortex. 40 new brain structure delineations have been added, and the delineations of 10 regions have been revised based on the interpretation of image features in the WHS rat brain MRI/DTI volumes. We here describe and validate the new delineations in relation to corresponding cell- and myelin-stained histological sections and previous literature. We found it possible to delineate all main regions and the majority of subregions and fibre tracts of the ascending auditory pathway, apart from the auditory cortex, for which delineations were extrapolated from a conventional two-dimensional atlas. By contrast, only parts of the descending pathways were discernible in the template. Version 3.0 of the atlas, with altogether 118 anatomical delineations, is shared via the NeuroImaging Tools and Resources Collaboratory (www.nitrc.org).
Asunto(s)
Corteza Auditiva/anatomía & histología , Tronco Encefálico/anatomía & histología , Cóclea/anatomía & histología , Nervio Coclear/anatomía & histología , Imagen de Difusión Tensora/métodos , Cuerpos Geniculados/anatomía & histología , Colículos Inferiores/anatomía & histología , Imagen por Resonancia Magnética/métodos , Animales , Atlas como Asunto , Corteza Auditiva/diagnóstico por imagen , Tronco Encefálico/diagnóstico por imagen , Cóclea/diagnóstico por imagen , Nervio Coclear/diagnóstico por imagen , Cuerpos Geniculados/diagnóstico por imagen , Humanos , Colículos Inferiores/diagnóstico por imagen , Ratas , Ratas Sprague-DawleyRESUMEN
Detailed knowledge about the neural circuitry connecting the hippocampus and entorhinal cortex is necessary to understand how this system contributes to spatial navigation and episodic memory. The two principal cell types of the dentate gyrus, mossy cells and granule cells, are interconnected in a positive feedback loop, by which mossy cells can influence information passing from the entorhinal cortex via granule cells to hippocampal pyramidal cells. Mossy cells, like CA3 pyramidal cells, are characterized by thorny excrescences on their proximal dendrites, postsynaptic to giant terminals of granule cell axons. In addition to disynaptic input from the entorhinal cortex and perforant path via granule cells, mossy cells may also receive monosynaptic input from the perforant path via special dendrites ascending to the molecular layer. We here report qualitative and quantitative descriptions of Golgi-stained hippocampal mossy cells in mink, based on light microscopic observations and three-dimensional reconstructions. The main focus is on the location, branching pattern, and length of dendrites, particularly those ascending to the granular and molecular layers. In mink, the latter dendrites are more numerous than in rat, but fewer than in primates. They form on average 12% (and up to 29%) of the total dendritic length, and appear to cover the terminal fields of both the lateral and medial perforant paths. In further contrast to rat, the main mossy cell dendrites in mink branch more extensively with distal dendrites encroaching upon the CA3 field. The dendritic arbors extend both along and across the septotemporal axis of the dentate gyrus, not conforming to the lamellar pattern of the hippocampus. The findings suggest that the afferent input to the mossy cells becomes more complex in species closer to primates.
Asunto(s)
Dendritas/fisiología , Fibras Musgosas del Hipocampo/fisiología , Neocórtex/citología , Neocórtex/fisiología , Animales , Femenino , Hipocampo/citología , Hipocampo/fisiología , Masculino , Visón , Vías Nerviosas/citología , Vías Nerviosas/fisiologíaRESUMEN
The transition between the central (CNS) and peripheral nervous system (PNS) in cranial and spinal nerve roots, referred to here as the CNS-PNS border, is of relevance to nerve root disorders and factors that affect peripheral-central regeneration. Here, this border is described in the cat cochlear nerve using light microscopical sections, and scanning electron microscopy of the CNS-PNS interfaces exposed by fracture of the nerve either prior to or following critical point drying. The CNS-PNS border represents an abrupt change in type of myelin, supporting elements, and vascularization. Because central myelin is formed by oligodendrocytes and peripheral myelin by Schwann cells, the myelinated fibers are as a rule equipped with a node of Ranvier at the border passage. The border is shallower and smoother in cat cochlear nerve than expected from other nerves, and the borderline nodes are largely in register. The loose endoneurial connective tissue of the PNS compartment is closed at the border by a compact glial membrane, the mantle zone, of the CNS compartment. The mantle zone is penetrated by the nerve fibers, but is otherwise composed of astrocytes and their interwoven processes like the external limiting membrane of the brain surface with which it is continuous. The distal surface of the mantle zone is covered by a fenestrated basal lamina. Only occasional vessels traverse the border. From an anatomical point of view, the border might be expected to be a weak point along the cochlear nerve and thus vulnerable to trauma. In mature animals, the CNS-PNS border presents a barrier to regrowth of regenerating nerve fibers and to invasion of the CNS by Schwann cells. An understanding of this region in the cochlear nerve is therefore relevant to head injuries that lead to hearing loss, to surgery on acoustic Schwannomas, and to the possibility of cochlear nerve regeneration.
Asunto(s)
Sistema Nervioso Central/ultraestructura , Nervio Coclear/ultraestructura , Microscopía Electrónica de Rastreo , Sistema Nervioso Periférico/ultraestructura , Animales , Astrocitos/ultraestructura , Gatos , Sistema Nervioso Central/citología , Nervio Coclear/citología , Disección , Femenino , Técnicas de Preparación Histocitológica , Masculino , Fibras Nerviosas/ultraestructura , Neuroglía/ultraestructura , Sistema Nervioso Periférico/citología , Células de Schwann/ultraestructura , Raíces Nerviosas Espinales/ultraestructuraRESUMEN
The inferior colliculus (IC) is the main auditory nucleus in the midbrain. This auditory center is made of a central nucleus (CNIC) characterized by a distinct laminar organization that is surrounded by cortical regions. The neuronal types in the CNIC are well established but thus far, the neuronal composition and functional roles of the cortical regions are not fully appreciated. As dendritic architecture is critical for the synaptic integrative properties of neurons, a detailed analysis of the dendritic architecture of the neurons in the collicular cortical regions should shed light on our understanding of their roles in collicular function. In the present study, we have used the del Rio-Hortega Golgi procedure to impregnate individual neurons within the IC. Rat brains were embedded in resin and sectioned serially to allow quantitative 3-D analyses of single neurons or groups of neurons. Our results demonstrate that the cortical regions of the IC are made up of unique sets of neuronal types and that there is an interdigitation of dendrites at the cortical borders. This latter feature may have led to difficulty in delineating a sharp border between the CNIC and cortical regions in previous studies. The quantitative analysis further demonstrates that there are significant differences in many of the dendritic parameters tested when compared to the neurons from the CNIC. Moreover, we observed that the neuronal populations of the cortical regions vary from the laminar pattern of the CNIC and from each other. Since the main organizing principle of the CNIC is the laminar organization of 'flat' neurons, evidence that cortical IC regions lack flat neurons supports the subdivision schema presented here.
Asunto(s)
Aparato de Golgi/fisiología , Colículos Inferiores/anatomía & histología , Neuronas/fisiología , Algoritmos , Animales , Vías Auditivas/fisiología , Mapeo Encefálico/métodos , Biología Computacional/métodos , Dendritas/metabolismo , Dendritas/fisiología , Femenino , Procesamiento de Imagen Asistido por Computador/métodos , Imagenología Tridimensional , Colículos Inferiores/fisiología , Modelos Estadísticos , Neuronas/metabolismo , Ratas , Programas InformáticosRESUMEN
It has been suggested that astrocytic glutamate release or perturbed glutamate metabolism contributes to the proneness to epileptic seizures. Here we investigated whether astrocytic contents of the major glutamate degrading enzymes glutamine synthetase (GS) and glutamate dehydrogenase (GDH) decreases on moving from the latent phase (prior to seizures) to the chronic phase (after onset of seizures) in the kainate (KA) model of temporal lobe epilepsy. Western blotting and immunogold analysis of hippocampal formation indicated similar levels of GDH in the latent and chronic phases of KA injected rats and in corresponding controls. In contrast, the level of GS was increased in the latent phase compared with controls, as assessed by Western blots of whole hippocampal formation and subregions. The increase in GS paralleled that of glial fibrillary acidic protein (GFAP). Compared with the latent phase, the chronic phase revealed a lower level of GS (approaching control levels) but an unchanged GFAP content. The decrease in GS from latent to chronic phase was significant in whole hippocampal formation, dentate gyrus and CA3. It is concluded that kainate treated rats show an initial increase in GS, pari passu with the increase in GFAP, and a secondary decrease in GS that is not accompanied by a similar loss of GFAP. In a situation where glutamate catabolism is in high demand the secondary reduction in GS level may be sufficient to contribute to the seizure proneness that develops between the latent and chronic phases.
Asunto(s)
Epilepsia del Lóbulo Temporal/enzimología , Regulación Enzimológica de la Expresión Génica/fisiología , Glutamato Deshidrogenasa/metabolismo , Glutamato-Amoníaco Ligasa/metabolismo , Animales , Conducta Animal , Modelos Animales de Enfermedad , Epilepsia del Lóbulo Temporal/inducido químicamente , Epilepsia del Lóbulo Temporal/patología , Epilepsia del Lóbulo Temporal/fisiopatología , Transportador 2 de Aminoácidos Excitadores/metabolismo , Regulación Enzimológica de la Expresión Génica/efectos de los fármacos , Proteína Ácida Fibrilar de la Glía/metabolismo , Hipocampo/efectos de los fármacos , Hipocampo/metabolismo , Hipocampo/fisiología , Hipocampo/ultraestructura , Ácido Kaínico , Masculino , Microscopía Inmunoelectrónica/métodos , Ratas , Ratas Sprague-Dawley , Factores de TiempoRESUMEN
Glutamine is involved in a variety of metabolic processes, including recycling of the neurotransmitters glutamate and gamma-aminobutyric acid (GABA). The system N transporter SN1 mediates efflux as well as influx of glutamine in glial cells [Chaudhry et al. (1999), Cell, 99, 769-780]. We here report qualitative and quantitative data on SN1 protein expression in rat. The total tissue concentrations of SN1 in brain and in kidney are half and one-quarter, respectively, of that in liver, but the average concentration of SN1 could be higher in astrocytes than in hepatocytes. Light and electron microscopic immunocytochemistry shows that glutamatergic, GABAergic and, surprisingly, purely glycinergic boutons are ensheathed by astrocytic SN1 laden processes, indicating a role of glutamine in the production of all three rapid transmitters. A dedication of SN1 to neurotransmitter recycling is further supported by the lack of SN1 immunoreactivity in oligodendrocytes (cells rich in glutamine but without perisynaptic processes). All neuronal structures appear unlabelled implying that a different protein mediates glutamine uptake into nerve endings. In several regions, SN1 immunoreactivity is higher in association with GABAergic than glutamatergic synapses, in agreement with observations that exogenous glutamine increases output of transmitter glutamate but not GABA. Nerve terminals with low transmitter reuptake or high prevailing firing frequency are associated with high SN1 immunoreactivity in adjacent glia. Bergmann glia and certain other astroglia contain very low levels of SN1 immunoreactivity compared to most astroglia, including retinal Müller cells, indicating the possible existence of SN isoforms and alternative mechanisms for transmitter recycling.