Interdependence of the nigrostriatal dopaminergic systems on the two sides of the brain in the cat.

The release of [3H]dopamine in vivo was estimated in the left and right caudate nuclei of the cat during the continuous superfusion of the two structures with L-[3,5-3H]tyrosine by means of two "push-pull" cannulas. A lesion made in the left substantia nigra interrupted the release of [3H]dopamine in the ipsilateral caudate nucleus and was associated with a simultaneous increase in the release of [3H]dopamine on the contralateral side. The release of [3H]dopamine also decreased in the left caudate nucleus and increased in the right structure when dopamine was applied to the left substantia nigra which reduces the activity of the left dopaminergic pathway. A total of 120 estimations of the spontaneous release of [3H]dopamine were made simultaneously in the left and right caudate nuclei during periods characterized by a stable physiological state of the animals, and 76% of the estimations showed that an increase in the release of [3H]dopamine on one side corresponded to a decrease in the release of [3H]dopamine on the other side, and vice versa. These results demonstrate a close relation between the two nigrostriatal dopaminergic systems.