Post‐Session Activation, but not Blockade, of Dopamine D2‐like Receptors Disrupts Instrumental Behavior

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Rats will reduce their responding for flavored solutions if these solutions are paired with administration of the indirect dopamine receptor (DAR) agonist amphetamine or the nonselective direct DAR agonist apomorphine. The present studies sought to further characterize the effects of pairing DAR activation or blockade with instrumental behavior and its outcomes. Rats were trained in daily sessions to respond for access to unflavored tap water. Immediate post‐session administration of the D3‐preferring agonist quinpirole (QNP) or the D2‐preferring agonist sumanirole (SUM) produced progressive declines in responding across days that were characterized by orderly shifts of responding away from the ends of sessions. When control animals were given QNP or SUM on a quasirandom schedule that included an equal number of pre‐ and post‐session administrations, pre‐session administrations significantly decreased responding, whereas responding was unchanged by post‐session administrations. Thus, the progressive declines observed above result from learned associations between sessions and drug administration, not from drug accumulation. Similar results were obtained with food‐reinforced animals. In contrast to the effects of D2‐like DAR agonists, post‐session treatment with the D2‐like DAR antagonist haloperidol (HAL) did not disrupt water‐reinforced responding. These results are consistent with studies showing HAL fails to produce place‐ or taste‐avoidance, two other effects of associative learning. Supported by USPHS/NIDA grant R01 DA020669 and an NSF Graduate Research Fellowship.