ANTIDROMIC RESPONSE LATENCY DISTRIBUTION OF CAT PYRAMIDAL TRACT CELLS - 3 GROUPS WITH RESPECTIVE EXTRACELLULAR SPIKE PROPERTIES

The antidromic extracellular action potentials of 470 pyramidal tract (PT) neurons were recorded after stimulation of the ipsilateral medullary pyramid in pentobarbital-anesthetized cats. The amplitude of the antidromic action potentials of PT cells was inversely related to their antidromic spike latencies. The duration of the antidromic spike was a linear function of the antidromic latency. There was a negative correlation between the amplitude of antidromic spike and its duration. Three groups were distinguished in the latency histogram, indicating that the PT neurons can be separated into three groups: group I (F-fast, large), group II (SI-intermediate, medium size), and group III (SII-very slow, small). The latencies and conduction velocities of neurons in groups I, II, and III were respectively 0.45 to 1.9 (25.26 to 106.7), 2.09 to 4.2 (11.16 to 22.97), and 4.24 to 7.95 ms (6.05 to 11.14 m/s). Two waves were recorded from the cortical surface before insertion of the microelectrode into the cerebral cortex. Three waves appeared as the microelectrode was advanced into the cortex to the depth of 150 or 200 μm. The time course of these three waves coincided with that of three PT cell groups in each particular experiment. We suggest that cortical, spinal, and muscular motor units may be interrelated with regard to size and function. © 1979.