Effects of afferent firing frequency on the amplitude of the monosynaptic EPSP elicited by trigeminal spindle afferents on trigeminal motoneurones.

We have examined the effect of changes in afferent firing frequency on the monosynaptic EPSP elicited by trigeminal muscle spindle afferents in elevator motoneurones, using both paired pulse and repetitive activation of the masseter nerve. Both modes of stimulation resulted in significant facilitation of EPSP amplitude over intervals of 5-19 ms, but no significant change in EPSP amplitude at either longer or shorter intervals. The facilitation obtained stands in contrast to the predominant depression of EPSP amplitude reported in hindlimb motoneurones following stimulation at decreasing intervals.