SUPPRESSION BY DIPHENYLHYDANTOIN OF AFFERENT DISCHARGES ARISING IN MUSCLE SPINDLES OF THE TRICEPS SURAE OF THE CAT

¹ Department of Pharmacology, Georgetown University, Schools of Medicine and Dentistry, Washington, D.C.
² Department of Pharmacology, Georgetown University, Schools of Medicine and Dentistry, Washington, D. C.

Cats anesthetized with ketamine hydrochloride and -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 enhancement 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; with 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 increased 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 consistent with earlier data which suggest that DPH acts in nerve terminal structures by suppressing generator potentials. The observed reduction in somatosensory perception capability may account, in part, for the ataxia and incoordination associated with DPH intoxication.