Table 3.

Results from combination tests of the D₄ dopamine receptor agonist ABT-724 (0.08 mg/kg; 0.2μmol/kg), and two selective D₄ receptor antagonists A-381393 (3.93 mg/kg; 10 μmol/kg) and L-745870 (3 mg/kg; 6.88 μmol/kg), with different doses of (+)-amphetamine, tested in rats trained to discriminate (+)-amphetamine (1 mg/kg; 5.45 μmol/kg, i.p.) from saline. N – number of rats tested; %D – percentage of rats disrupted; %SDL – percentage of rats selecting the drug appropriate level. The ED50 was calculated according to the method of Litchfield and Wilcoxon (1949).

TEST DRUG	DOSE OF COMBINED DRUG		DOSE OF (+)-AMPHETAMINE		N	% D	% SDL	ED50 (95% C.I.)
	mg/kg	μmole/kg	mg/kg	μmole/kg				mg/kg	μmole/kg
saline	0	0	0.13	0.68	11	0	18	0.24 (0.17–0.36)	1.34 (0.93–1.95)
	0	0	0.25	1.35	11	0	55
	0	0	0.50	2.70	11	0	73
	0	0	1.00	5.40	11	0	100
ABT-724	0.08	0.2	0.13	0.68	7	0	71	0.09 (0.04–0.22)	0.49 (0.22–1.19)
	0.08	0.2	0.25	1.35	9	33	100
	0.08	0.2	0.50	2.70	10	10	100
	0.08	0.2	1.00	5.40	12	17	100
L-745870	3.0	6.88	0.13	0.68	11	0	0
	3.0	6.88	0.25	1.35	10	0	20
	3.0	6.88	0.50	2.70	10	0	30
	3.0	6.88	1.00	5.40	11	9	40
A-381393	3.93	10	0.13	0.68	11	0	27
	3.93	10	0.25	1.35	11	0	36
	3.93	10	0.50	2.70	11	27	38
	3.93	10	1.00	5.40	11	18	67