Journal of Neuroscience, Vol 5, 1246-1261, Copyright © 1985 by Society for Neuroscience
Forebrain origins and terminations of the medial forebrain bundle metabolically activated by rewarding stimulation or by reward-blocking doses of pimozide
CR Gallistel, Y Gomita, E Yadin and KA Campbell
Using [14C]-2-deoxyglucose autoradiography, we determined which forebrain
and diencephalic areas showed metabolic alterations in response to
unilateral electrical stimulation of the posterior medial forebrain bundle
at parameters chosen to produce a just-submaximal rewarding effect. At
these parameters, only a few areas were activated. There was no detectable
activation anterior or dorsal to the genu of the corpus callosum. Just
anterior to the anterior commissure, there was strong activation of the
vertical limb of the diagonal band of Broca, with a focus in the nucleus of
the diagonal band. Just posterior to the anterior commissure, there was
strong activation of compartment "c" of the medial forebrain bundle (MFB),
with weaker activation of the bed nucleus of the stria terminalis and the
medial preoptic area. At midhypothalamic levels, the dorsolateral,
dorsomedial, and ventral MFB all showed activation. There was bilateral
suppression of activity in the lateral habenula. Activation appeared to end
in the anterior ventral tegmental area of Tsai. Reward-blocking doses of
the neuroleptic pimozide activated the caudate and the lateral habenula but
did not alter any of the unilateral effects of stimulation. Using longer
pulse durations and/or shifting the site of stimulation to the substantia
nigra activated many of the systems not activated in the first experiment,
including all of the major dopaminergic projection systems, proving the
capacity of the technique to reveal activation of these systems. The
results permit one to define a discrete projection system that merits
electrophysiological investigation as a likely substrate for the rewarding
effect of MFB stimulation. They also suggest that dopaminergic projection
systems may not form part of the reward pathway itself.