SLOW AND FAST GROUPS OF PYRAMIDAL TRACT CELLS AND THEIR RESPECTIVE MEMBRANE PROPERTIES

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Abstract
Pyramidal tract cells (PTcells) of the cat were activated antidromically and responses were recorded with glass microelectrodes extracellularly and intracellularly. In the depths of the postcruclate gyrus, stimulation of the pyramid elicited field potentials with 2 successive negative deflections. Similar responses were also elicited by stimulation of the cerebral peduncle, but with shorter latencies. These deflections were attributed to the 2 groups of PT cells, fast and slow, with different conduction velocities. PT cells of both groups were impaled with microelectrodes. They responded to pyramidal stimulation by generating antidromic spike potentials. The latency of invasion varied from 0.5 to 5.0 msec. These antidromic spikes and the peak time of the after-hyperpolarization following the intracellularly-induced spikes were both found to positively correlated with the latency of the pyramid-induced antidromic activation. Measurements with intracellularly-passed rectangular current pulses further revealed that the values of membrane resistance tended to be higher in the cells having slower axonal conduction velocities.

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