Blockade by frontocortical lesion of reciprocal regulation between the two nigrostriatal dopaminergic pathways.

Tritiated dopamine synthesized from tritiated tyrosine was estimated simultaneously in the two caudate nuclei and the two substantia nigra of cats anaesthesized with halothane. In control animals, the electrical stimulation of the right forelimb enhanced dopamine release in the right caudate nucleus and decreased dopamine release in the right substantia nigra. Opposite effects were observed in the contralateral structures. Left nigral application of d-amphetamine produced the same effect. However in cats with extensive lesions of the left pericruciate cortex, an increase in the release of dopamine in the left substantia nigra was the only detectable effect of these two treatments. These results suggest that the cortical structures are involved not only in the transfer of information between the two dopaminergic pathways but are also involved with regulation of the release of dopamine in the striatum originating in the substantia nigra. With regard to the role of the thalamic structures in this transfer of information, it is proposed that the thalamostriatal control of the release of dopamine previously suggested is closely dependent on cortical activity.