alone, as shown at the left side of panels A and B, respectively. Response rates following administration of any of the doses of THC did not significantly differ from rates obtained after vehicle injection for either discrimination group (Fig. 1, panels C and D). In contrast, significant decreases in response rates (compared to vehicle) were observed with each of the endocannabinoids [anandamide: F(6,42)=25.23, P<0.05; 2-AG: F(7,63)=23.38, P<0.05]. Significant attenuation of responding was noted at the 3 and 10 mg/kg doses of anandamide and the 3–30 mg/kg doses of 2-AG (Fig. 1, panels C and D, respectively). Compared to response rates after vehicle injection, the combination of 0.3 mg/kg URB597 and lower doses of anandamide did not significantly affect response rates (Fig. 1, panel C) whereas the combination of 1 mg/kg NAM and the 1 mg/kg dose of 2-AG significantly suppressed responding [F(4,24)=8.84, P<0.05] (Fig. 1, panel D).
