摘要:

AbstractThe first order projections of the trigeminal nerve were studied in four species of snakes, three of which are infrared sensitive, utilizing silver degeneration and cobalt iontophoresis techniques. The trigeminal nerve projected ipsilaterally to a main sensory nucleus, descending spinal nucleus, ventral trigeminal field and solitary nucleus with a contralateral projection to the base of the descending spinal nucleus in all four species. A major additional projection to the lateral nucleus of the trigeminal was present in all three infrared sensitive species but absent in the other. Iontophoresis of cobalt chloride into a trigeminal branch composed entirely of infrared sensitive fibers and into a trigeminal branch containing no infrared fibers indicated that the lateral nucleus of the trigeminal nerve was the sole first order target of the infrared system.

ISSN:0092-7317    

DOI:10.1002/cne.901690102

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

年代:1976

数据来源: WILEY

摘要:

AbstractA quantitative study of synapse formation in the mouse olfactory bulb has been carried out using serial sections. Volumetric synaptic density as well as absolute number of synapses per olfactory bulb for eight distinct synaptic types have been determined at 15 different ages, from the beginning of synapse formation at embryonic day 14 (E14) to postnatal day 44 (P44). Synapses are first found in appreciable numbers at E15 when both axo‐dendritic and a few dendrodendritic synapses occur in the presumptive glomerular layer. Initial synapse formation correlates closely with the reorientation of mitral cells from a primitive tangential to a defintive radial direction. Synapse formation by mitral cell dendrites occurs after mitral cell axons have grown into the future olfactory cortical areas, either simultaneous with or before synapse formation by these axons.Virtually all synaptic types detected in adults have been found on the day of birth, consistent with the idea that olfaction is an important sensory modality for newborn mice. Volumetric density of a given synaptic type generally increases 50–100 times during development while the absolute number increases about 1,000 times. Synapses in glomeruli develop more precociously than those in the external plexiform and internal granular layers, which correlates well with the time of origin and differentiation of the principal postsynaptic elements of these two divisions (mitral cells and internal granule cells) Correlation of the time of synapse formation of various synaptic types with their putative excitatory or inhibitory role determined in adult studies suggests that excitatory synapses generally form somewhat earlier, although throughout nearly all of synaptic development, both excitatory and inhibitory synapses are present.Reciprocal dendro‐dendritic synapses in the external plexiform layer appear to have a special mode of formation. It is suggested that a granule‐to‐mitral dendro‐dendritic synapse only forms next to an already existing mitral‐to‐granule synapse on t

ISSN:0092-7317    

DOI:10.1002/cne.901690103

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

年代:1976

数据来源: WILEY

摘要:

AbstractSerial thin sections of the mouse olfactory bulb from the fourteenth day of gestation (E14) to postnatal day 44 (P44) have been examined in order to study morphogenesis of individual synaptic junctions. At the initiation of synapse formation structures are found that resemble postsynaptic densities but are facing extracellular space or unmodified processes. Transition forms between these isolated postsynaptic densities and undoubted synapses have been found. These observations as well as quantitative studies support the hypothesis that isolated postsynaptic densities can form independently and be converted to synapses when a presynaptic specialization develops opposite them.Detailed studies of olfactory axodendritic synaptogenesis throughout the entire developmental period suggests strongly that these asymmetrical synapses pass through an immature symmetrical phase: (1) symmetrical olfactory axodendritic synapses are found in significantly higher concentration on axonal and dendritic growth cones than on more mature processes; (2) the number of symmetrical synapses is correlated with the rate of formation of new synapses determined previously. The time for a recognizable symmetrical synapse to be transformed into a recognizable asymmetrical one has been calculated to be 9–10 hours.A scheme of synapse formation in the CNS has been proposed in which a postsynaptic structure forms independently followed by aggregation of pre‐existing presynaptic components into a presynaptic specialization. Different morphogenetic sequences of synapse formation from region to region are attributed simply to different relative rates in the development of the postsynaptic density and the presynaptic specializat

ISSN:0092-7317    

DOI:10.1002/cne.901690104

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe laminar and cellular structure of retrosplenial cortex in the rhesus monkey was studied with Nissl stained and rapid Golgi impregnated tissue and the results were used to evaluate morphological features of a cortical transition zone. The granular layer of retrosplenial granular cortex is composed primarily of small, densely packed, star pyramidal cells. These cells branch within the granular layer itself, while the apical dendrite enters layer I where it branches infrequently or not at all. This cell type is similar to the star pyramid first described by Lorente de Nó except in its areal and laminar distribution.Cytoarchitectonic observations of retrosplenial agranular cortex show that, although this area is relatively “agranular” in comparison to other cortical areas, it does possess an incipient layer II and layer IV. These layers are composed mainly of small and medium sized pyramidal cells, but many non‐pyramidal cell types were found in these and other layers in this area in rapid Golgi preparations. Stellate cells with beaded or smooth, lightly spinous dendrites were found throughout layers I–IV, while fusiform cells with smooth or very lightly spinous dendrites appear in layers III–VI.Areas surrounding retrosplenial cortex in the posterior cingulate region were also evaluated in Nissl and Golgi preparations including the indusium griseum, subiculum (dorsal to the corpus callosum) and area 23. The laminar and cellular constituents of retrosplenial cortex were then evaluated in the context of cortical architectonic transition. The transition from one cellular layer in the indusium griseum to five cellular layers in area 23 is made by the addition of layers II, III, IV and VI in retrosplenial cortex to the one ganglionic layer of the indusium griseum and subiculum. Besides the addition and subdivision of layers in retrosplenial cortex, two aspects of cell morphology were found to change in this region. First, the structure of pyramidal cells progressively changes from those in the indusium griseum which have predominently round or oval somata and a preponderance of apical and few basal dendrites to those in layer V of retrosplenial cortex and area 23 which have pyramidal shaped somata and a great number of basal dendrites which branch frequently and spread horizontally for hundreds of microns. Second, there is a change in the number and distribution of non‐pyramidal cell types. Evidence was not found that the indusium griseum, dorsal subiculum or layer V of retrosplenial granular cortex contain a significant number of stellate or fusiform cells. At the retrosplenial granular/agranular border, though, these cells gradually begin to constitute a greater proportion of the cell population and in area 23 form a major component of layer IV. Since these laminar and cellular changes are similar, in part, to those observed by previous investigators as characteristic of ascending phylogenetic and ontogenetic development, cortical architectonic transition represents another dimension along which the cortex progressivel

ISSN:0092-7317    

DOI:10.1002/cne.901690105

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

年代:1976

数据来源: WILEY

摘要:

AbstractThe properties of ganglion cells in the visual streak of the cat's retina have been investigated. Evidence is presented that the streak is formed principally, but not entirely, by a concentration of small‐bodied ganglion cells with the receptive field properties and slow‐conducting axons typical of W‐

ISSN:0092-7317    

DOI:10.1002/cne.901690106

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

年代:1976

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901690101

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

年代:1976

数据来源: WILEY