摘要:

AbstractSynapses have been counted by electron microscopy and neurones by light microscopy through the depth of the visual cortex in a series of cats from 37 days gestation to adulthood. A few definite synapses are present as early as three weeks before birth, but there is then a latent period of four weeks before synapses increase rapidly in number 8–37 days after birth. The synapses occur just above and just below the cell plate at first, but in the adult cat they become evenly distributed in the depth of the cortex. The gradual separation of neurones by neuropil during development precedes a parallel increase in the density of synapses by about one week. The average number of synapses associated with one neurone rises to a peak of about 13,000 at seven weeks after birth. The densities of synapses and of neurones subsequently fall to slightly lower values in adult cats as the glial cells continue to develop.The timing of synaptic development in the visual cortex has been compared quantitatively with that in the L. G. N. and qualitatively with synaptogenesis in the retina. Synapses develop in the L. G. N. and cortex in a parallel fashion, and the L. G. N. precedes the cortex by a short interval of about two days. In the cell plate of the retina a few receptor synapses are present nine days before birth. Inner plexiform synapses are also present at this time, but ribbon‐containing synapses do not appear until birth. Very few receptors possess outer segments with discs at birth, but five days later disc‐bearing outer segments have developed.Thus synaptic development starts before afferent impulses can enter the visual system, but the main increase in synapses in the L. G. N. and cortex takes place four weeks after the start of synapse formation while the visual system is being

ISSN:0092-7317    

DOI:10.1002/cne.901600202

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe structure of the first somatic sensory area (areas 3,1 and 2), of the motor area (area 4) and the intervening transitional field (area 3a) is described in the squirrel monkey (Saimiri sciureus) using Nissl, Bodian, Weil and Golgi preparations. The laminar arrangement of both cells and axons is briefly described and this is correlated with the Nauta and autoradiographic techniques. The latter method was used particularly in order to assess quantitative differences in the density of thalamic projections to the five cytoarchitectonic fields.In the somatic sensory areas thalamic afferents terminate not only in layer IV but to a large extent also in a recognizable part of layer III (layer IIIb). In area 4 thalamic terminals fill much of layer III, reaching almost to layer II. In area 3a the extent is intermediate between that seen in areas 3 and 4. It is thought that the extensive spread of thalamic terminals is related to the elongated form of a particular class of spine‐bearing cell whose somata are situated in layer IV (Jones, 1975). In all areas a small proportion of thalamic afferents end also in layer I. Evidence is presented to indicate that specific afferent fibers emanating from the ventrobasal and ventrolateral complexes of the thalamus terminate in both the deep and superficial parts of layer I While “non‐specific” afferents from other thalamic sources end in the superficial part.The autoradiographic studies indicate that there are considerable differences between the number of thalamic afferents ending in area 3 on the hand and in areas 1 and 2 on the other. Given this and the nature of the degenerating thalamic afferents observed in Nauta preparations, it is possible to identify thalamic afferents in normal Golgi preparations and significant differences are detectable in areas 4, 3 and 1 and 2. It is yet uncertain whether the slightly thinner, more sparsely distributed thalamic afferents ending in areas 1 and 2 are branches of those directed primarily to

ISSN:0092-7317    

DOI:10.1002/cne.901600203

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

年代:1975

数据来源: WILEY

摘要:

AbstractThe morphology and distribution of cells which do not conform to the conventional pyramidal pattern have been investigated in rapid Golgi, Golgi‐Kopsch and Golgi‐Cox preparations fromn cortical areas 3, 1 and 2 of juvenile and mature squirrel monkeys. The material has been analyzed qualitatively and quantitatively by means of a computer program which permits cells to be roatated so as to display their three‐dimensional architecture.Nine non‐pyramidal types are identified of which one is a rare giant cell and another, forming a major proportion of the cells in layer VI, is considered to be a modified form of pyramidal cell. Of the other seven types, two have horizontally distributed axons, one esseentially confined to layer II, is the other sending long (up to 1 mm) branches antero‐posteriorly through all layers.Two types have vertical axons. One, corresponding to the “double bouquet dendritique” cell of Cajal, is mainly situated in layer II or the upper part of layer III and has a cluster of large axone branches which descend to layers IV and V and which enclose and terminate on the apical dendrites of pyramidal cells. The other type is the only non‐pyramidal cell which has a relatively high concentration of dendritic spines in the adult animal. Its soma lies in layer IV and it has several strongly recurrent, thick axonal branches ascending to layer II, also enclosing the apical dendrites of pyramidal cells. The dendritic field is not truly stellate but is drawn out into a pronounced ascending tuft which ascends cends into lalyer IIIb. The cell thus resembles a “star‐pyramid” of Lorente de Nó. Nevertheless such cells have many features, notably the distribution of their axons and the distribution of dendritic spines which are identical to those of the well‐known “spiny stellate” cell of the visual cortex. Conversely the same features both in these cells and in the spiny stellate cells of the visual cortex. Conversely the same features both in these cells and in the spiny stellate cells of the visual cortex (which were also examined) differ markedly fromn those of small pyramidal cells with somata of similar dimensions.The three remaining non‐pyramidal cell types have locally ramifying axons which appear to terminate predominantly on pyramidal cells. In one, the axon forms smoothly curving arcades in layer III, in another it is intensely tangled in layer in layer IV and in the third it is bush‐like in layers II–IV.There are morphological changes in certain of the cell types associated with the thinning of the cortex as it is folded into the central sulcus. For examplle, the spiny cells of layer IV become much more stellate‐like in the floor of the sulcus. It is thought that the changes in the shape of these cells can be correlated with the concomitant changes in the superificial to deep extent of the thalamic afferent plexus. Certain differences were also detected between the juvenile and adult animals. Certain differences were also detectex between the thalamic afferent plxus. Certain differences were also detecd between the In the juvenile, many more dendritic spines were seen on cells which in the adults normally possess few or none and the axonal plexusesscs of some cell were were less oraganized.In discussing the reusults, attempts are made toof correlate the these findings with those of other workers and to suggest possible morphological correlatessates of the elecotrophysiologically iden

ISSN:0092-7317    

DOI:10.1002/cne.901600204

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

年代:1975

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901600201

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

年代:1975

数据来源: WILEY