Effects of ethosuximide on transmission of repetitive impulses and apparent rates of transmitter turnover in the spinal monosynaptic pathway

R Capek and B Esplin

The effects of ethosuximide on spinal monosynaptic transmission were studied in cats. The drug in doses of 200 or 400 mg/kg deepened the decline of monosynaptic response amplitude evoked by trains of 10 stimuli to a motor nerve at 2, 5 or 10 Hz, without affecting the transmission of single isolated impulses. The patterns of decline were analyzed under the assumption that they reflect a partial depletion of the apparent transmitter stores in the presynaptic terminals, each incoming volley releasing a constant fraction of the store while a constant fraction of the instant size of the depleted part is being replenished per second. Ethosuximide increased the fractional release without a consistent effect on the fractional rate of replenishment. It is suggested that the resulting more rapid and more profound depletion of the apparent transmitter store could account for the observed preferential depression of repetitive transmission in the spinal monosynaptic pathway by this drug.

Volume 201, Issue 2, pp. 320-325, 05/01/1977
Copyright © 1977 by American Society for Pharmacology and Experimental Therapeutics