EFFECT OF CLOZAPINE UPON SCHEDULE-INDUCED-POLYDIPSIA (SIP) RESEMBLES NEITHER THE ACTIONS OF DOPAMINE D1 NOR D2 BLOCKADE

The effects of clozapine (CLOZ) upon acquired schedule-induced polydipsia in rats were compared to the effects of the dopamine (DA) D-1 antagonist SCH 23390 (SCH) and the DA D-2 antagonist raclopride (RAC). Ah three compounds suppressed water consumption, but only SCH and RAC decreased drinking efficiency. SCH was the only compound with an effect on panel pressing (PP), causing suppression even at a dose without effect upon water intake. SCH also affected the temporal pattern of licking (TPL) at all doses, while clozapine, 10 mg/kg, only affected the pattern acutely, and raclopride was without effect. In conclusion, PP and the TPL are more sensitive to D-1 than D-2 blockade. While PP and the TPL are more sensitive than water intake to D-1 blockade, the opposite is true for D-2 blockade. It is possible to differentiate between DA D-1/D-2 antagonists and CLOZ in this model, focusing upon reduction in water consumption, with and without reduction in drinking efficiency. Furthermore, it is possible to differentiate between D-1 and D-2 blockade by analyzing water consumption, PP and the TPL.