The action of local anaesthetics on the spinal cord of the cat.

The effects of intravenously injected lignocaine, procaine and amethocaine on the monosynaptic and polysynaptic reflexes and the cord dorsum potentials elicited by selective electrical stimulation of appropriate afferent fibres have been investigated in decerebrate cats before and after strychnine. The three drugs depress the amplitude of the reflex responses in the basal preparation for 40 to 50 min. Smaller doses eliminate the reflex augmentation produced by strychnine for comparable periods. Very small doses selectively abolish the augmentation of the P component of the cord dorsum response induced by strychnine. The drugs have no effect on post-tetanic potentiation of the monosynaptic reflex response evoked from the gastrocnemius muscle in the cat. Their activity on the spinal cord is roughly proportional to their local anaesthetic potency. The ratios of the doses which produce the same central activity are amethocaine 3: lignocaine 10: procaine 20.