dorsal spinocerebellar tract neurons are not subjected to postsynaptic inhibition during carbachol-induced motor inhibition. Ming-Chu Xi, Jack Yamuy, Rong-Huan Liu, Francisco R. Morales, and Michael H. Chase. Department of Physiology and the Brain Research Institute, UCLA School of Medicine, Los Angeles, CA 90024.
APStracts 4:0071N, 1997.
ABSTRACT
Dorsal spinocerebellar tract (DSCT) neurons in Clarke's column in the lumbar spinal cord of cats anesthetized with à-chloralose were recorded intracellularly. The membrane potential activity and electrophysiological properties of these neurons were examined before and during the state of active sleep-like motor inhibition induced by the injection of carbachol into the nucleus pontis oralis (NPO). The synaptic activity of DSCT neurons during carbachol-induced motor inhibition did not change compared with that during control conditions. In particular, there was an absence of inhibitory postsynaptic potentials (IPSPs) in high-gain recordings from DSCT neurons and the resting membrane potential of DSCT neurons was not significantly hyperpolarized during carbachol-induced motor inhibition. The mean amplitude of both monosynaptic excitatory postsynaptic potentials (EPSPs) and disynaptic IPSPs evoked in DSCT neurons following stimulation of group I muscle afferents after the injection of carbachol was similar to that evoked before the injection of carbachol. There were no significant changes in the mean input resistance and membrane time constant of DSCT neurons during carbachol-induced motor inhibition. We conclude that, in contrast to lumbar motoneurons, DSCT neurons in ClarkeOs column are not postsynaptically inhibited during carbachol-induced motor inhibition. Therefore, the population of spinal cord Ib interneurons which inhibit both DSCT neurons and lumbar motoneurons are not likely to be the interneurons which are responsible for the postsynaptic inhibition of motoneurons that occurs during carbachol-induced motor inhibition. The present findings also indicate that transmission through the DSCT is not modulated by postsynaptic inhibition at the level of DSCT neurons during carbachol-induced motor inhibition. 

Received 23 August 1996; accepted in final form 6 March 1997.
APS Manuscript Number J684-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 3 April 1997