摘要:

AbstractIn the present study, the dendritic organisation of neurones in the normal human basal forebrain was analysed as a prerequisite for the evaluation of pathological changes occurring in Alzheimer's disease and related conditions (see other Arendt et al. papers in this issue).Neurones in the basal nucleus of Meynert (NbM), the nucleus of the vertical limb of the diagonal band, and the medial septal nucleus were examined after Golgi impregnation. Cells were classified according to the dendritic branching pattern and soma shape as either reticular neurones or multipolar giant neurones. The reticular type of neurones constitutes more than 90% of neurones in the NbM. Cholinergic neurones also belong to this cell type. Reticular neurones were further subdivided into four subtypes. Morphological features and arrangement of reticular basal forebrain neurones were identical to those described for “reticular formation cells” or “isodendritic” neurones. Dendritic trees of reticular neurones show a spatial orientation perpendicular to passing fibres as well as a high degree of overlap, both of which are hallmarks of “open nuclei.”The qualitative classification of Golgi‐impregnated basal forebrain neurones was substantiated by a computer‐based three‐dimensional analysis. Topologic and metric parameters of the dendritic tree were calculated for each type of neurone to characterise the degree of dendritic branching, the shape and orientation of the dendritic arborisation, the spatial extension of the dendritic tree, and soma size. The classification criteria were evaluated according to their power of discrimination between different cell types by means of a discriminant analysis. The quantitative approach applied in the present study not only provides an objective measure for the description and comparison of the structure of various types of neurones but also makes it possible to elucidate fine structural changes that might occur under pathologic conditions and that are not evident during qualitative studies alone. © 19

ISSN:0092-7317    

DOI:10.1002/cne.903510202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractChanges in the dendritic arborisation of Golgi‐impregnated basal forebrain neurones with respect to size, shape, orientation, and topology of branching were quantitatively investigated in ageing, Alzheimer's disease (AD), Korsakoff's disease (KD), and Parkinson's disease (PD). A reorganisation of the whole dendritic tree characterized by an increase in both the total dendritic length and the degree of dendritic arborisation as well as by changes in the shape of the dendritic field was found during ageing, in KD, PD, and AD. Dendritic growth under these conditions was related to the extent of cell loss in basal forebrain nuclei. There appeared to be major differences, however, with respect to the overall pattern of dendritic reorganisation between AD on one side and ageing, KD, and PD on the other side. In both ageing and KD, dendritic growth was largely restricted to the terminal dendritic segments, resulting in an increase of the size of the dendritic field (pattern of “extensive growth”). In AD, aberrant growth processes were frequently observed in the perisomatic area or on distal dendritic segments of basal forebrain neurones of the reticular type. Neurones with aberrant growth profiles were typically located in the direct vicinity of deposits of β/A4 amyloid. Perisomatic growth profiles were covered by the low‐affinity receptor of nerve growth factor p75NGFR. Aberrant growth processes were not present in ageing, KD, and PD. On the basis of the present study, it is concluded that under certain degenerative conditions, reticular basal forebrain neurones undergo a compensatory reorganisation of their dendritic arborisation, a process that has become defective in AD, thereby converting a physiological signal into a cascade of events contributing to the pathology of the disease. © 1995 Willy

ISSN:0092-7317    

DOI:10.1002/cne.903510203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe distribution of the reticular neuronal type in the human brain and its involvement in both degeneration and dendritic reorganisation under the conditions of ageing, Korsakoff's disease (KD), Alzheimer's disease (AD), and Parkinson's disease (PD) was comparatively investigated after Golgi impregnation. Reticular neurones are distributed throughout different areas along the brain axis. The cholinergic basal forebrain nuclei, i.e., the basal nucleus of Meynert, the nucleus of the diagonal band, and the medial septal nucleus form the most rostral part of this network of “open nuclei,” which is collectively referred to as the “reticular core.” Reticular neurones of the following areas were quantitatively investigated by a computer‐based three‐dimensional analysis: caudate nucleus, globus pallidus, medial septal nucleus, nucleus of the vertical limb of the diagonal band, basal nucleus, medial amygdaloid nucleus, reticular thalamic nucleus, lateral hypothalamic area, subthalamic nucleus, substantia nigra, locus coeruleus, pedunculopontine tegmental nucleus, and raphe magnus nucleus. There are three major findings. First, neurones that were found to be susceptible to degeneration in AD were largely part of the same neuronal populations prone to degeneration during ageing, in KD and PD. Thus, areas could be classified according to their overall degree of vulnerability under the present degenerative conditions as being highly vulnerable (basal forebrain nuclei, caudate nucleus, locus coeruleus), moderately vulnerable (medial amygdaloid nucleus, raphe magnus nucleus, lateral hypothalamic area, substantia nigra, pedunculopontine tegmental nucleus), or marginally vulnerable (globus pallidus, subthalamic nucleus, reticular thalamic nucleus). Second, neuronal populations that are particularly vulnerable to degenerative changes show a high degree of structural plasticity. Third, the degree of this dendritic plasticity is inversely related to the complexity of dendritic arborisation of the neurone. It is concluded that the sparsely ramified reticular type of neurone forms a pool of pluripotent neurones that have retained their plastic capacity throughout life, which makes them vulnerable to a variety of perturbations. © 1995 Wil

ISSN:0092-7317    

DOI:10.1002/cne.903510204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractSynapse are complex arrangements of pre‐and postsynaptic differentiations involved in neural communication. A key element in this synaptic transmission is the presynaptic active zone where the release of neurotransmitter occurs. Active zones can be visualized and analyzed after staining with ethanolic phosphotungstic acid (EPTA) on semithin (0.5μm) sections. This staining has been used in association with postembedding immunogold labeling for the neurotransmitters glycine or GABA, to investigate the organization of chemically defined inhibitory active zones, viewed in their full extent, on different regions of the goldfish Mauthner (M−) cell.With this approach, a marked variability in size and shape was observed for the release sites contacting the different parts of the postsynaptic neuron. In the axon cap and on the soma, glycinergic afferent terminals have small presynaptic grids (0.066 ± 0.029 μm2, n = 30 and 0.076 ± 0.037 μm2, n = 46, respectively). These grids are quite circular and they include 12 to 13 presynaptic dense projections (PDPs). The situation is different on the lateral dendrite, where glycinergic and GABAergic active zones display a greater variability in their surface areas (mean = 0.147 ± 0.100 μm2, n =115 and 0.139 ± 0.080 μm2, n = 125, respectively), and their number of PDPs (mean = 19 ± 9) per individual grid. Similarly, the shape of the release sites over the dendrite is more complex (annular, horseshoe‐shaped) when compared to those on the soma. These differences of dendritic versus somatic release sites could represent a structural basis to maximize the shunting effect of glycinergic and GABAergic inhibitory junctions, i.e., close to excitatory inputs.We also observed that the proportion of endings containing 1 or more active zones also varies. More precisely, 96% and 82% of glycinergic terminals in the axon cap and on the soma, respectively, display only one active zone. On the dendrite, their proportion falls to 65.5% for both glycine‐ and GABA‐containing boutons. The remaining inhibitory terminals contain 2 (30%) and 3 to 4 (4.5%) presynaptic grids. These results reveal a greater variability of morphology and organization of the inhibitory release sites at dendritic versus somatic locations. The functional significance of this observation for the synaptic transmission is discussed. ©

ISSN:0092-7317    

DOI:10.1002/cne.903510205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe present investigation was designed to determine the number and internal organization of somatosensory fields in monotremes. Microelectrode mapping methods were used in conjunction with cytochrome oxidase and myelin staining to reveal subdivisions and topography of somatosensory cortex in the platypus and the short‐billed echidna. The neocortices of both monotremes were found to contain four representations of the body surface. A large area that contained neurons predominantly responsive to cutaneous stimulation of the contralateral body surface was identified as the primary somatosensory area (SI). Although the overall organization of SI was similar in both mammals, the platypus had a relatively larger representation of the bill. Furthermore, some of the neurons in the bill representation of SI were also responsive to low amplitude electrical stimulation. These neurons were spatially segregated from neurons responsive to pure mechanosensory stimulation. Another somatosensory field (R) was identified immediately rostral to SI. The topographic organization of R was similar to that found in SI; however, neurons in R responded most often to light pressure and taps to peripheral body parts. Neurons in cortex rostral to R were responsive to manipulation of joints and hard taps to the body. We termed this field the manipulation field (M). The mediolateral sequence of representation in M was similar to that of both SI and R, but was topographically less precise. Another somatosensory field, caudal to SI, was adjacent to SI laterally at the representation of the face, but medially was separated from SI by auditory cortex. Its position relative to SI and auditory cortex, and its topographic organization led us to hypothesize that this caudal field may be homologous to the parietal ventral area (PV) as described in other mammals. The evidence for the existence of four separate representations in somatosensory cortex in the two species of monotremes indicates that cortical organization is more complex in these mammals than was previously thought. Because the two monotreme families have been separate for at least 55 million years (Richardson, B. J. [1987] Aust. Mammal. 11:71–73), the present results suggest either that the original differentiation of fields occurred very early in mammalian evolution or that the potential for differentiation of somatosensory cortex into multiple fields is highly constrained in evolution, so that both species arrived at the same solution independently. © 1995 Willy‐Lis

ISSN:0092-7317    

DOI:10.1002/cne.903510206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

摘要:

AbstractThe hedgehog, a macrosomatic insectivore with an extraordinary development of the olfactory structures, has a crucial value for any phylogenetic or comparative study in mammals. The distribution pattern and morphology of NADPH‐diaphorase‐active and calbindin D‐28k‐immunoreactive neurons were studied in the main and accessory olfactory bulbs of the hedgehog. NADPH‐diaphorase (ND) staining was carried out by a direct histochemical method, and the calbindin D‐28k (CaBP) immunoreaction by using a monoclonal antibody and the avidin‐biotin‐immunoperoxidase method. The possible coexistence of both markers was determined by sequential histochemical‐immunohistochemical double labeling of the same sections. Specific neuronal populations were positive for both ND and CaBP markers. No cell colocalized both stains in the hedgehog olfactory bulb. A subpopulation of olfactory fibers, and a subpopulation of olfactory glomeruli, located on the medial side, were positive for ND. Surrounding both the ND‐positive and ND‐negative glomeruli, there were ND‐ and CaBP‐positive periglomerular cells, the latter group being much more abundant. A subpopulation of superficial short‐axon cells was CaBP positive but, contrary to what is observed in rodents, this neuronal type was always ND negative. In addition, three neuronal types were observed in the GL‐EPL border after CaBP immunostaining. These neuronal types have not been previously described either in the hedgehog or in the rodent olfactory bulb. Horizontal cells and vertical cells of Cajal were also observed after both ND and CaBP labeling. Distinct groups of ND‐ and CaBP‐positive cells, differing in size, shape, dendritic branching pattern, and staining intensity, were distinguished in the granule cell layer and in the white matter. The large and medium‐sized cells were identified as a very heterogeneous population of deep short‐axon cells, whereas a subpopulation of granule cells was ND positive. The accessory olfactory bulb showed ND staining in all vomeronasal fibers and glomeruli, and in subpopulations of periglomerular cells, granule cells, and deep short‐axon cells. The CaBP immunolabeling was more restricted and located in subpopulations of periglomerular cells and in deep short‐axon cells. These results indicate different and more complex ND and CaBP staining patterns in the hedgehog olfactory bulb than those previously described in rodents, including the presence of specific, chemically and morphologically defined n

ISSN:0092-7317    

DOI:10.1002/cne.903510207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.903510208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.903510201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1995

数据来源: WILEY