Intracranial self-stimulation effects along the route of the nigro-striatal bundle.

Recent evidence suggesting a possible dopaminergic nigro-striatal substrate of self-stimulation led us to map this route for both self-stimulation and stimulus-bound motor effects. The results of 128 electrode placements show that the route of the nigro-striatal projection supports strong self-stimulation effects from the substantia nigra to the ento-peduncular nucleus. Beyond this level, such effects disappear. Our results indicate that the striatum itself is neutral with regard to reinforcement, and suggest that such apparent neutrality cannot be ascribed to motor or other artifacts. These findings require a reappraisal of the hypothesis of a dopaminergic self-stimulation system, although they are not in conflict with the idea that dopaminergic manipulations may affect self-stimulation through some more general regulatory influence on operant responding.