Intracranial self-stimulation in relation to the ascending dopaminergic systems of the midbrain: a moveable electrode mapping study.

Chronically implanted moveable electrodes were used to map the midbrain and caudal diencephalon for intracranial self-stimulation in relation to the ascendindg dopamine systems as revealed by fluorescence histochemistry. In the diencephalon the lowest self-stimulation thresholds and the highest response rates were in the areas traversed by the dopamine fiber bundles. In the midbrain, self-stimulation was restricted to the layer of dopamine containing cell bodies. Self-stimulation current thresholds and responses rates were proportional to the density of dopaminergic elements surrounding the electrode tip; the lowest thresholds and highest response rates were associated with the densest packing of dopaminergic neurons. However, not all portions of the dopamine cell groups supported self-stimulation. Self-stimulation was not obtained from the caudal poles of the A9 and A10 groups, nor from the A8 cell group. These findings suggest that a certain population of dopaminergic neurons directly participates in what is probably a multiple-link circuitry subserving positive reinforcement.