[A study of excitability changes in DSCT neurons of the cat (author's transl)]

Excitability changes in the dorsal spinocerebellar tract (DSCT) neurons of the cat were extracellularly studied with correlation analysis. Most of the interval histograms were classifed as normal distribution, and occasionally bimodal distributions were observed, which resulted from an occasional "double spiking" in the spontaneous background discharge (BD). The conduction velocity was measured in 72 DSCT fibers. The histogram showed a peak at 40-50 M/S. The majority of the units had BD with coefficient of variation less than 0.2, which suggest BD with regular firing. Based on cross-correlelograms, DSCT responses to electrical stimulation of the muscle nerves of the hind leg were classified into at least three types. Type 1 response, constituted approximately one-fifth of the total, is monosynaptic activation. Type 2 response, observed most frequently (47%), is inhibition of DSCT cells with a short latency. Type 3 responses, observed nearly as often as type 2 (34%), is a long latency excitation, undoubtedly polysynaptic. Changes in stimulation intensity showed complex changes in the pattern of response. Type 1 and 2 responses were unaffected by increasing stimulus rate. Peak correlations in type 3 response were reduced by increase in stimulus rate. There were no data demonstrating feedback circuitry associated with collaterals of DSCT axons. This suggest that axon collaterals have no direct effect on the activity of Dsct cells.