Recurrent Inhibition from Motor Axon Collaterals of Ventral Spinocerebellar Tract Neurones



Recurrent inhibition from motor axon collaterals was searched for in intracellularly recorded ventral spinocerebellar tract (VSCT) neurones in the cat. A small proportion of the investigated cells received inhibition on antidromic stimulation of ventral roots. The IPSP was evoked by a-fibres, had a segmental latency indicating a disynaptic linkage from motor axon collaterals and a duration of about 50 ms. The inhibited cells received monosynaptic excitation from group Ia muscle spindle afferents. The inhibition could be demonstrated also on the VSCT mass discharge evoked by stimulation of Ia afferents. The ventral roots, giving rise to the inhibition in a given VSCT cell, were the same as the ventral roots which give recurrent inhibition in a-motoneurones and Ia inhibitory interneurones excited by Ia afferents of the same muscle as the VSCT cell. The results indicate that Renshaw cells, terminating on a-motoneurones and Ia inhibitory interneurones, also send collaterals to some VSCT neurones. This finding strongly supports the idea that the VSCT relays information about the transmission in intemeuronal inhibitory reflex pathways to motoneurones (Lundberg 1971).