DORSAL SPINOCEREBELLAR TRACT NEURONS ARE NOT SUBJECTED TO POSTSYNAPTIC INHIBITION DURING CARBACHOL-INDUCED MOTOR INHIBITION

Dorsal spinocerebellar tract (DSCT) neurons in Clarke's column in the lumbar spinal cord of cats anesthetized with alpha-chloralose were rec orded intracellularly. The membrane potential activity and electrophys iological properties of these neurons were examined before and during the state of active-sleep-like motor inhibition induced by the injecti on of carbachol into the nucleus pontis oralis. The synaptic activity of DSCT neurons during carbachol-induced motor inhibition did not chan ge compared with that during control conditions. In particular, there was an absence of inhibitory postsynaptic potentials (IPSPs) in high-g ain recordings from DSCT neurons and the resting membrane potential of DSCT neurons was not significantly hyperpolarized during carbachol-in duced motor inhibition. The mean amplitude of both monosynaptic excita tory postsynaptic potentials and disynaptic IPSPs evoked in DSCT neuro ns following stimulation of group I muscle afferents after the injecti on of carbachol was similar to that evoked before the injection of car bachol. There were no significant changes in the mean input resistance and membrane time constant of DSCT neurons during carbachol-induced m otor inhibition. We conclude that, in contrast to lumbar motoneurons, DSCT neurons in Clarke's column are not postsynaptically inhibited dur ing carbachol-induced motor inhibition. Therefore the population of sp inal cord Ib interneurons that inhibit both DSCT neurons and lumbar mo toneurons is not likely to be the interneurons that are responsible fo r the postsynaptic inhibition of motoneurons that occurs during carbac hol-induced motor inhibition. The present findings also indicate that transmission through the DSCT is not modulated by postsynaptic inhibit ion at the level of DSCT neurons during carbachol-induced motor inhibi tion.