The relationship between lesion site, dopamine neurons, and turning behavior in the rat

The phenomenon of turning after administration of amphetamine to rats with unilateral lesions in the midbrain has been studied to determine the anatomical locus of the lesion site in relation to turning behavior. Lesions which encroached upon the substantia nigra to a significant extent were always effective; lesions in a large number of structures dorsal to the substantia nigra were not. These data are consistent with the hypothesis that destruction of part of the nigrostriatal tract is essential for the behavior. On the other hand, six rats with lesions medial to and not encroaching upon the substantia nigra also showed clear-cut turning behavior. This finding is consistent with other observations which suggest that the nigrostriatal pathway courses medially to the substantia nigra before turning rostrally towards the striatum.