Effects of diphenylhydantoin on synaptic transmission

The effect of diphenylhydantoin (Dilantin) on various aspects of synaptic transmission in the spinal cord and stellate ganglion of cats has been investigated by electrophysiological technics. Dilantin has a slight depressant effect upon transmission of isolated impulses in the spinal cord, and the effect upon activity in polysynaptic pathways in somewhat more pronounced. No effect of Dilantin on facilitation in either the spinal cord or. ganglion has been observed; primary inhibition has not been thoroughly studied. The principal effects of Dilantin on synaptic transmission were found to be qualitatively identical for the monosynaptic pathways of the spinal cord and ganglion. Dilantin deepens depression following transmission of a single impulse and hastens fatigue during repetitive stimulation. Post-tetanic potentiation is strikingly reduced by Dilantin. The doses employed in all studies were in the anticonvulsant, nontoxic range for cats. In view of the anatomical and functional differences of the two synaptic systems studied and of the strikingly similar effects of Dilantin on transmission at these sites, it appears likely that the drug exerts similar effects upon synaptic transmission at sites in the central nervous system concerned with convulsive activity. The possible significance of the observed effects in relation to the anticonvulsant action of the drug is discussed.