Neural Inhibition in a Bird : Effect of Strychnine and Picrotoxin

Abstract

SEVERAL convulsant drugs have been shown to act by impairing specific inhibitory processes in the brain, and there is a clear-cut contrast between crustacean and mammal in this respect. In the crayfish, picrotoxin produces convulsions and it blocks several inhibitory mechanisms as well as the inhibitory action which Florey's Factor I exerts on these synapses^1–3. Strychnine does not cause convulsions in the crayfish nor does it interfere with these inhibitory processes^1,2. In the cat both drugs act as convulsants; but only strychnine antagonizes the inhibitory post-synaptic potentials of spinal motoneurones^4,5 and the centrifugal inhibition mediated by the Rasmussen's olivocochlear fibres, both crossed⁶ and uncrossed⁷. The mode of action of picrotoxin in the mammalian brain is less clear and it may involve an activation of excitatory synapses⁸. The pharmacological approach just sketched clearly provides useful tools for the investigation of neural inhibition and of convulsive states, and it seemed worth extending it to the bird, using as a physiological test the inhibition produced by the efferent cochlear bundle⁹, which can be successfully stimulated as follows¹⁰.