An investigation of local actions of ionophoretically applied DOPA in the spinal cord.

Methyl-L-DOPA (L-beta-3,4-dihydroxy-phenylalanine methyl ester, hydrochloride) was applied ionophoretically to investigate its effects on neurones at various locations in the cat spinal cord. Its actions were tested on monosynaptic field potentials evoked from group I and group II muscle afferents in midlumbar segments. Methyl-L-DOPA has been found to depress field potentials evoked from group II afferents in the ventral horn and in the intermediate zone but not in the dorsal horn, nor field potentials evoked from group I afferents. Its effects were the same as those of systemically applied L-DOPA (L-beta-3,4-dihydroxyphenylalanine), although weaker.