Fig. 4.

Effects of the adenosine A₁ receptor antagonist DPCPX (0.31, 1.25, and 5 mg/kg) on the antidepressant-like effects of the adenosine A₁ receptor agonist CHA (0.0625 mg/kg) in rats performing on a DRL 72-s schedule. Rats were tested using a with-in subject design with drugs administered at weekly intervals in the order shown (n = 13) via an intraperitoneal route of administration. Open bar, vehicle–vehicle; solid black bars, vehicle–CHA (0.0625 mg/kg); blue hatched bars, DPCPX (0.31 mg/kg)–CHA (0.0625 mg/kg).; green cross-hatched bars, DPCPX (1.25 mg/kg)–CHA (0.0625 mg/kg); red hatched bars, DPCPX (5 mg/kg)–CHA (0.0625 mg/kg). ***, p < 0.001 compared with the vehicle–vehicle condition. ###, p ≤ 0.001 compared with the vehicle–CHA (0.0625 mg/kg) condition. The significant effects of the combination of vehicle–CHA (0.0625 mg/kg) administered a second time compared with the vehicle–vehicle condition are not shown.