Effects of the unilateral nigral application of dopaminergic drugs on the in vivo release of dopamine in the two caudate nuclei of the cat.

The effects of the unilateral application of d-amphetamine, benztropine, haloperidol and thioproperazine to one substantia nigra on the release of 3H-dopamine (3H-DA) in the two caudate nuclei were examined in halothane-anesthetized cats. For this purpose animals were implanted with push-pull cannulae and 3H-DA was estimated in superfusates during the continuous delivery of L-3,5-3H-tyrosine. The nigral application of d-amphetamine (10-6 M) or benztropine (10-6 M) reduced the release of 3-H-DA in in the ipsilateral caudate nucleus and induced an opposite effect in the contralateral side. In contrast, the nigral application of haloperidol (10-6 M) or thioproperazine (10-6 M) slightly increased the release of 3H-DA in the ipsilateral caudate nucleus and induced a reduction of 3H-transmitter release in the contralateral side. These results emphasize the role of the dendritic release of DA in the control of the activity of dopaminergic neurons and confirm our previous findings concerning the existence of a reciprocal control in the activity of the two dopaminergic pathways.