A note on the termination of commissural fibers in the neocortex.
ABSTRACT A study of callosal fiber degeneration in the rat and opossum by the aid of the Fink-Heimer silver technique has led to the conclusion that the intracortical distribution of the corpus callosum involves all cortical layers. Evidence was found of regional differences in the intracortical distribution pattern; in some regions a stratified mode of callosal fiber termination was apparent.
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ABSTRACT: Thermal lesions were made in layers I, II, and upper part of layer III of rat visual cortex. The distribution of degenerating axons and axon terminals in layers IV, V, and VI was studied using electron microscopic techniques.Following supragranular thermal lesions, the majority of degenerating axon terminals were found in layer V, with extension into the adjacent part of layer VI. Neural profiles postsynaptic to degenerating axon terminals were found in these layers in the following distribution: 81.7% on spines of small to medium size dendrites; 18.2% on dendrite shafts; and <1% on neuronal perikarya. Few degenerating terminals were found on or near apical dendrites. Degenerating terminals were identified on shafts of stellate-type dendrites found in the upper part of layer V.Degenerating axons oriented parallel to the cortical surface were found most often in deep layer IV and upper layer V. Degenerating axons were also seen in axon bundles coursing vertically through layer IV.Approximately 10% of the terminals within a grid square have undergone degeneration; no clustering of degenerating terminals was found in vertical or transverse sections through layers V and VI.We suggest that most axon terminals arising from pyramidal neurons in layers II and upper III synapse with spines and shafts of dendrite branches originating from pyramidal neurons in layer V and perhaps VI.The Journal of Comparative Neurology 10/2004; 174(3):521 - 533. · 3.66 Impact Factor
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ABSTRACT: We have examined callosal-axon neurons giving rise to homotopic and heterotopic callosal projections to caudal inferior parietal lobule (area PG) in Macaca mulatta, identifying these neurons by means of retrograde axonal transport of horseradish peroxidase. The labeled neurons in the homotopic region occur predominantly in layers IIIB and V. A moderate number are seen also in layer VI, a smaller number in layer IV, and rare cells occur in layer II. These neurons occupy a region very similar in outline to the injection area, and though variable in density in the horizontal plane are continuously distributed in this plane.The heterotopic neurons are seen in the contralateral cingulate gyrus, continuing caudally into medial parietal cortex, in the cortex of the superior temporal and occipitotemporal sulci, in the caudal superior temporal gyrus, and in the caudal inferior parietal lobule, behind the homotopic area. These same regions on the ipsilateral side contain labeled neurons of origin of ipsilateral association projections to area PG. For other ipsilateral association regions (e.g., frontal lobe), no corresponding contralateral heterotopic labeling was found. A review of the literature on heterotopic callosal connections allows tentative generalization of this conclusion: The callosal heterotopic connections of a particular cortical area are made with regions which on the ipsilateral side have association connections with that area, though usually not with all of such regions.The Journal of Comparative Neurology 04/1981; 197(4):605 - 621. · 3.66 Impact Factor
- Annals of the New York Academy of Sciences 12/2006; 167(1):241 - 257. · 4.38 Impact Factor