INHIBITION OF DISCHARGES INTO THE DORSAL AND VENTRAL SPINOCEREBELLAR TRACTS

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Abstract
Mass discharges in the dorsal spinocerebellar tract (DSCT) were evoked by Group I muscle volleys and were inhibited for more than 100 msec by brief repetitive trains of Group I muscle afferent volleys, and also by single cutaneous volleys. The excitability of the presynaptic fibers in the region of DSCT cells showed that there was a primary afferent depolarization with a similar time course, which is the characteristic test for presynaptic inhibition. Mass discharges in the ventral spino-cerebellar tract of the contralateral side were also evoked by Group I muscle afferent volleys and likewise were similarly inhibited, but usually the inhibitory curve was briefer than for the DSCT discharge. Sometimes the inhibition reyersed to a late facilitation; otherwise it may have had the characteristic duration of presynaptic inhibition.