Electrophysiological study of the effects of D1 and D2 dopamine antagonists on the interaction of converging inputs from the sensory-motor cortex and substantia nigra neurons in the rat.

The interaction of stimulation of the cerebral cortex and of the substantia nigra on the activity of neostriatal neurons was investigated in urethane-anesthetized rats. Neurons of the dorsal striatum were activated by single pulse stimulation of the sensory-motor cortex. The effects of nigral conditioning stimulation on this excitatory response of striatal neurons to cortical stimulation were studied in a series of parametric experiments in which the length of the train of pulses and the intensity of the nigral stimulation were varied. One and five pulses of nigral conditioning stimulation had little or no effect. Ten pulses of nigral conditioning stimulation reduced the excitatory response, the magnitude of the reduction being greater with higher current intensities. In another series of experiments, the effects of dopaminergic receptor antagonists on the interaction of cortical and nigral inputs to striatal neurons were studied. Sulpiride, a D2 antagonist, reversed the attenuating effects of nigral conditioning stimulation on the excitatory response of striatal neurons to cortical stimulation, whereas SCH 23390 a D1 antagonist, had no effect. The present findings support the hypothesis that the nigrostriatal dopaminergic pathway modulates the excitatory response of striatal neurons to cortical stimulation by means of dopamine D2 receptors.