PILOCARPINE BLOCKADE OF SPINAL INHIBITION IN CATS

¹ Department of Pharmacology, University of Utah College of Medicine, Salt Lake City, Utah

The effects of pilocarpine (40 to 160 mg/kg) on evoked monosynaptic and polysynaptic potentials in spinal cats are generally similar to those of strychnine. Spontaneous ventral root discharges were invariably seen with 160 mg/kg of the drug, and larger doses produced prolonged asynchronous discharges and recurring waves of activity resembling those seen after strychnine. these effects of pilocarpine were not altered by administration of atropine in one-tenth of the pilocarpine dosage.

Pilocarpine blocks "direct," indirect, and recurrent inhibition. Recurrent inhibition was abolished by doses of the drug which did not affect Renshaw cell discharges. In the "direct" pathway pilocarpine blocked inhibition evoked by stimuli at intervals too short to activate complex interneuronal systems. This indicates that the drug interferes directly with inhibitory processes and not merely with transmission in systems whose function may be predominantly inhibitory.

The pattern of peripheral and central blocking actions of piocarpine, taken together with other pharmacological evidence, points to a cholinergic link in the transmission of inhibitory impulses.