Effects of haloperidol and d-amphetamine on in vivo 3H-spiroperiodol binding in the rat forebrain(1)

Specific (3)H-spiroperidol ((3)H-Sp) binding was demonstrated to occur, in vivo, throughout the rat forebrain. The highest concentrations of (3)H-Sp were found in regions known to contain dopamine neuron terminals. Acute and repeated administration of low does of haloperidol decreased in vivo (3)H-Sp in subcortical but not cortical regions. Repeated administration of high does of haloperidol followed by washout periods up to 8 days did not lead to an increase in in vivo (3)H-Sp binding; however, a single dose of d-amphetamine caused substantial increases. Analysis of the alterations induced by haloperidol and d-amphetamine suggest that the dopamine receptor changes configuration upon excessive exposure to agonists or antagonists in such a way as to favor the counterpart ligand.