Group I inhibition in Ib excited ventral spinocerebellar tract neurones.

Abstract

AbstractThe convergence of inhibition and excitation from muscle spindle Ia and Golgi tendon organ Ib afferents was investigated in ventral spinocerebellar tract (VSCT) neurones monosynaptically excited from Ib afferents. Although most cells received Ib excitation from several nerves, the dominating excitation was supplied from nerves to synergistic muscles acting as either flexors or extensors at one joint. Disynaptic Ia lPSPs from the nemc to the knee extensor were common in cells with their main Ib excitation from the nerves to either hip, knee or ankle extensors or to knee flexors. The Ia IPSPs in cells excited from hip extensors and knee flexors were depressed by antidromic impulses in motor axons, while no such effect occurred on Ia IPSPs in the other cells. The Ia IPSPs in Ib VSCT neurones thus seem to be mediated by two different groups of Ia inhibitory interneurones, with and without recurrent inhibition from motor axon collaterals through Renshaw cells. Disynaptic Ib IPSPs from nerves to thigh muscles were rare while presumed Ib IPSPs from nerves to ankle and toe muscles were more common. In some cells there were indications of convergence of monosynaptic EPSPs and disynaptic IPSPs from Ib afferents in the same nerve. The results are discussed in relation to the hypothesis that the VSCT relays information about interneuronal transmission in the spinal cord.