Lead-induced decrements in waiting behavior: Involvement of D-2-like dopamine receptors

Some behavioral changes produced by chronic postweaning lead (Pb) exposure have been linked to mesolimbic dopamine (DA) system alterations. This study sought to determine the role of DA systems in Pb-induced changes in a fixe d ratio (FR) waiting-for-reward paradigm. Rats exposed chronically from wea ning to 0, 50, or 150 ppm Pb acetate drinking solutions earned free reinfor cers for waiting after completion of an FR, with increasing time between su ccessive free reinforcers. Responses during the waiting period reset the FR requirement. Once performance stabilized, the effects of acute TP administ ration of the D-1 agonist SKF82958, the D-2 agonist quinpirole, the D-1 ant agonist SCH23390, and the D-2 antagonist eticlopride were determined. Pb it self increased FR response rates and decreased mean waiting time, a pattern of behavior that increased the number of earned reinforcers, but doubled t he number of responses/reinforcer. None of the DA compounds mimicked Pb eff ects when administered to controls. Only DA agonists altered waiting behavi or and responses per reinforcer. Quinpirole, in particular, appeared to rev erse Pb effects on the FR wait baseline by increasing waiting time and decr easing FR resets to control levels. These findings point to a particular ro le for D-2 DA function in Pb's detrimental effects on waiting. (C) 1999 Els evier Science Inc.