Dopaminergic modulation of transcallosal activity of cat motor cortical neurons

The effects of dopamine (DA) and its antagonists on the transcallosal activity of pyramidal tract neurons (PTNs) and non-PTNs in the anesthetized cat motor cortex were studied with iontophoretic applications; dopamine, SCH 23390 (D1 antagonist), sulpiride (D2 antagonist) and haloperidol. Neuronal activity was recorded with a multi-barreled glass microelectrode. Transcallosal neuronal activity was evoked by stimulation of the contralateral motor cortex. The number of spikes thus activated was counted for the control and test conditions after application of each drug: (1) dopamine application decreased the number of spikes evoked by transcallosal stimulation; (2) application of SCH 23390, sulpiride and haloperidol restored these decreased spike numbers to the control level; (3) latency of neuronal response to transcallosal stimulation was not affected by the application of either DA, SCH 23390, sulpiride or haloperidol; and (4) there was no significant difference between PTNs and non-PTNs in the manner of response to DA and its antagonist applications. Our conclusion is that dopamine modulated the transcallosal neuronal response in the cat motor cortex in a suppressive manner. This fact suggested that interhemispheric neuronal communications could be subjected to suppressive modification by the dopaminergic system.