Caudate nucleus neurones: correlation of the effects of substantia nigra stimulaton with iontophoretic dopamine.

1. Extracellular recordings were made from caudate nucleus neurones in decerebrate cats using five-barrel micropipette electrodes.2. Electrical stimulation of the substantia nigra caused spike rate depressions in 121 of 260 caudate neurones as evidenced by changes in the post-stimulus histograms of their firing patterns. Spike rate facilitation occurred with forty-two caudate units.3. Neurones depressed by nigral stimuli were consistently depressed by micro-iontophoretic dopamine.4. Alpha-methyldopamine, administered iontophoretically, antagonized the depressant responses induced by both nigral stimulation and iontophoretic dopamine.5. The data are compatible with the concept that the caudate neuronal depressant responses produced by nigral stimulation are mediated by a direct dopaminergic nigro-neostriatal pathway. The possibility of mediation via polysynaptic pathways cannot, however, be completely excluded.