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. · 3.51 Impact Factor
- Annals of the New York Academy of Sciences 12/2006; 167(1):241 - 257. · 4.38 Impact Factor
- Trends in Neurosciences 01/1981; 4:142-144. · 12.90 Impact Factor