Activation by diphenylthiohydantoin of inhibitory influences on spinal motor activity

The effect of diphenylthiohydantoin (DPTH) on spinal reflex activity (mono- and polysynaptic mass reflexes) in cervical and lumbar segments was studied in precollicularly decerebrate cats. DPTH (20 mg/kg) depressed the reflex activity in preparations with an intact spinal cord. It increased the reflex activity after removal of the anterior lobe of the cerebellum and after low spinalization; in the latter preparation, diphenylhydantoin produced an effect similar to that of DPTH but a longer duration. Reciprocal inhibition as well as ascending and descending intraspinal inhibition was increased by DPTH. From the results it is concluded that DPTH, apart from activating spinal reflexes, stimulates inhibition. Stimulation of inhibition may also account for the anticonvulsive action of the drug.