Abstract

The monosynaptic (2N) reflex was recorded electrically from the seventh lumbar or first sacral ventral roots of 37 unanesthetized spinal cats. In i.v. doses of 0.3 to 0.6 mg/kg, the convulsant barbiturate, 5-(2-cyclohexylideneëthyl)-5-ethyl barbituric acid, produced a prominent increase in the 2N response. Accompanying changes in presynaptic and postsynaptic inhibition did not account adequately for the increase in the 2N response. Pentobarbital Na in low i.v. doses (2 mg/kg) produced an increase in the 2N response of lesser extent and duration; after pentobarbital, the effect of the convulsant barbiturate was markedly diminished. The antagonism was reversible, and depression of the 2N response produced by larger doses of pentobarbital was reversed by larger doses of the convulsant barbiturate.