Infra-additivity of combined treatments with selective D1 and D2 receptor antagonists for inhibiting sucrose reinforcement.

Selective antagonists of either the D1 receptor (SCH 23390) or of the D2 receptor (raclopride) produce a dose-related inhibition of sucrose sham feeding in the rat. We investigated the effect of combined treatments with these antagonists on sucrose sham feeding and observed infra-additivity of inhibition across a range of doses. On the basis of this observed occlusive relationship, we conclude that the relevant D1 and D2 receptor mechanisms mediating sweet taste reward do not function independently.