The action of microelectrophoretically applied L-3,4-dihydroxyphenylalanine (DOPA) on single cortical neurones.

The technique of microelectrophoresis was used in order to compare the actions of L-3,4-dihydroxyphenylalanine (DOPA) and noradrenaline on single neurones in the cerebral cortices of cats and rats. DOPA could both excite and depress cortical neurones. Cells excited by DOPA were also excited by noradrenaline and cells depressed by DOPA were also depressed by noradrenaline. In the case of both excitatory and depressant responses, DOPA appeared to be less potent than noradrenaline. Responses to DOPA and noradrenaline could be antagonized by phentolamine and propranolol. Responses to acetylcholine were not affected. Responses to acetylcholine, but not responses to DOPA, were antagonized by atropine. The results indicate that locally applied DOPA may mimic the actions of noradrenaline on cortical neurones. Possible mechanisms for these effects of DOPA are discussed.