Printed in SUPPRESSION BY DIPHENYLHYDANTOIN OF AFFER- ENT DISCHARGES ARISING IN MUSCLE SPINDLES OF TILE TRICEPS SURAE OF THE CAT1’2

ANDERSON, REBECCA J. AND ARTHUR RAINE5: Suppression by diphenyihydantoin of afferent discharges arising in muscle spindles of the triceps surae of the cat. J. Pharmacol. Exp. Tluer. 191: 290-299, 1974. Cats anesthetized withu ketamine hydrochloride auud a-chloralose were prepared for multiple- and single-fiber recordings of discharges from muscle spindle afferents of the triceps surae. Unit fiber conduction velocity, spontaneous firing frequency and its euu-hancement evoked by muscle stretch, as well as the poststretch silent period duration, were measured. Diphenylhydantoin (DPH) suppressed all aspects of muscle spindle afferent discharges. DPH in doses as low as 2.5 mg/kg prolonged the silent period; witlu 5 mg of DPH per kilogram, both the spontaneous and stretch-evoked spindle discharge frequencies were suppressed. Suppression of these latter aspects of spindle behavior in-creased with increasing DPH dose, 20 mg/kg abolishing the spontaneous discharges and 40 mg/kg of DPH abolishing those which were stretch evoked. These results are con-sistent witlu earlier data which suggest that DPH acts in nerve terminal structures by suppressing generator potentials. The observed reduction in somatosensory perceptiouu capability may account, in part, for the ataxia and incoordination associated with DPH intoxication. Peripheral nerve preparations have served as models for central nervous system (CNS) actions of diphenylhydantoin (DPH) for man