Recurrent Facilitation in Cat Pyramidal Tract Cells

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Abstract
Intracellular techniques were employed in a study of 166 pyramidal tract [PT] cells (130 fast and 36 slow PT cells) of the postcruciate tyrus of the cat in the deeply pentobarbitalized state, in order to study the characteristics of the pyramidally evoked antidromic excitatory post-synaptic potentials (PD-EPSP) and to determine the linkage among the PT cells, the PD-EPSP appeared after 3.8 msec, latency from the pyramid stimulation and had a rise time of 4.5 - 11.5 msec, followed by a linear decay phase of 50-70 msec. Out of a total of 166 cells, the PD-EPSP was found in 36 cells (23.5%). A PD-EPSP was found in cells with an antidromic latency of less than 2.5 msec, i.e., in cells with an axonal velocity of more than 20 m./sec. Conduction velocities of the pyramidal tract fibers which give rise to the PD-EPSP recurrently are less than 20 m/sec. The PD-EPSP is found in the fast type of the PT cell and is transmi?ted through the axons of the slow type PT cell. Evidence is presented which suggests a mono-synaptic activation of the PD-EPSP.

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