EFFECTS OF EXCITATORY TRANSMITTER CANDIDATES ON FROG SPINAL MOTOR FUNCTION

Abstract

The propriospinal motor function of the frog spinal cord was investigated pharmacologically in the isolated spinal cord-nerve-muscle preparation. In the preparation with a pair of antagonistic muscles, the tissues showed reciprocal contractions in response to the spontaneous discharges from the ventral root. M. [musculus] tibialis anterior responded to the discharges from the ventral root and showed slow contractions. Contractions of the m. gastrocnemius were much less frequent but the movement was rapid and strong. The addition of acetylcholine (10-4-10-3 M) to the medium, perfusing the spinal cord, resulted in a predominant excitation of m. tibialis anterior. Carbamylcholine (10-5 M) and bethanechol (10-4 M) induced rhythmical contractions in m. tibialis anterior and depressed the movement of m. gastrocnemius. These effects were blocked by atropine (10-5 M). Serotonin (10-5 M) exerted a strong facilitatory effect on both muscles which contracted reciprocally during this treatment. L-Glutamate (10-4-10-3 M) induced a transient synchronous contraction in both muscles. By the sucrose-gap method, cholinomimetics and serotonin had no direct effect on the motoneuron, while L-glutamate had a direct effect. Apparently, propriospinal controlling mechanisms, regulated via serotonergic and cholinergic pathways, exist and drive co-ordinate muscle movement.