Contribution of Polysynaptic Pathways to the Tonic Vibration Reflex

1) Unit discharges produced by either muscle vibration (the tonic vibration reflex, TVR) or electric stimulation of muscle nerve (the monosynaptic reflex, MSR) were recorded on the ventral root filament in the unanesthetized spinal or decerebrate preparation. The effect of tetanization of synergist and contralateral sural nerve was studied and the TVR was compared with the MSR under thiopental anesthesia.2) Tetanization (250/sec, 10 sec) of synergist nerve produced potentiation of the TVR for a few minutes in both decerebrated and spinal preparations.3) Tetanization of the contralateral sural nerve also potentiated the TVR in decerebrate preparations but not in the spinal preparations.4) A small dose of thiopental sodium (2-10 mg/kg, i. v.) markedly suppressed the TVR, whereas production of the MSR was facilitated.5) When the muscle was stimulated by repeated vibratory bursts, reflex discharges gradually increased as the trials were repeated in both decerebrate and spinal preparations.6) On the basis of these facts, it was suggested that polysynaptic pathway through GIa activation, which was at least partly segmental, plays an important role in generating the TVR.