Morphological differences between fast and slow pyramidal tract neurons in the monkey motor cortex as revealed by intracellular injection of horseradish peroxidase by pressure

Abstract Morphological differences between 4 fast and 3 slow pyramidal tract neurons (PTNs) in the monkey motor cortex were studied by intracellular injection of horseradish peroxidase (HRP). Fast PTNs had larger soma and thicker axons than slow PTNS and had two to three tap root basal dendrites. An apical dendrite of fast PTNs had a narrow dendritic field with fewer branches, and was free of spines in layers I and II. Axon collaterals of both PTNs did not reach layer III. The narrow apical dendritic field of fast PTN may be important to the reception of restricted inputs and to perform skillful movement.

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