Evidence for biogenic amine receptors in toad sciatic nerves

Serotonin, l-epinephrine, histamine and other neurotropic drugs increase spike amplitude in toad sciatics. The biogenic amines, pentolinium, nicotine and arecoline antagonized nerve block induced by cocaine, procaine, chlorpromazine, imipramine, strychnine, LSD, etc. Reversal of conduction block (without removal of blocker) showed that the antagonism did not result from interference with penetration. The action of the biogenic amines seems related to interactions with specific receptors rather than to general ionic effects since (a) they antagonized both Na-dependent threshold raisers (cocaine) and Na-independent blockers (chlorpromazine); (b) specific competitive-like antagonisms were observed (serotonin vs. imipramine block; antihistaminics vs. histamine protection against cocaine). The presence of scattered synaptic-like receptors on the axonal membrane is discussed.