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Abstract
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.