Relationship between interhemispheric nigrostriatal projections and the direction of rotational behavior induced by amphetamine.

This experiment dealth with the relationship between the direction of amphetamine-induced turning and the distribution of crossed nigrostriatal projections in the rat. Animals that showed a high degree of asymmetry, as indicated by the consistency and amount of turning behavior elicited by repeated amphetamine administration, were implanted with horseradish peroxidase (HRP) in the striatum either ipsilateral or contralateral to their dominant direction of rotation. Microscopic analysis revealed a relationship between the direction of amphetamine-induced asymmetry and the number of HRP-labeled cells found in the substantia nigra contralateral to the striatum into which the tracer was implanted; i.e., animals with the HRP applied contralateral to their dominant turning direction had more labeled cells in the caudal part of the substantia nigra of the opposite hemisphere than those animals implanted ipsilaterally. There was no relationship between the direction and the number of labeled cells found in the ventral tegmental area and retrorubral area contralateral to the tracer implantation site. Moreover, there was no association between the direction of amphetamine-induced turning and the number of labeled cells found in the homolateral substantia nigra, or ventral tegmental and retrorubral areas.