Abstract

Conventional electro electrophysiologic techniques were used to study the effects of coniine on contractions of the nictitating membrane, ganglionic and neuromuscular transmission and spinal reflexes and inhibition. Coniine blocked transmission through the superior cervical ganglion and the neuromuscular junction. The drug was given by slow intravenous infusion, and little evidence of stimulation prior to blockade was seen with this mode of administration. The responses of the normal and chronically denervated nictitating membranes to injected acetylcholine (ACh) were blocked by coniine and restored by physostigmine. The responses of these membranes to injected epinephrine were not affected. Studies on the frog neuromuscular junction in vitro revealed that coniine first reduced the amplitude of the endplate potential and then caused a depolarization of the membrane. Coniine produced both depressant and excitatory effects on the spinal cord of the cat. Depressant effects were manifested by a decrease in the monosynaptic response and depression of posttetanic potentiation. The excitatory effects resembled those of strychnine and consisted of the production of spontaneous waves and discharges recorded from the ventral root and blockade of direct and recurrent postsynaptic inhibition. Presynaptic inhibition was not affected by coniine.