TABLE 2

Percentage of N₂O lever responding (± S.E.M.) and response rate (± S.E.M.) produced by morphine, U-50488H, SNC-80, ethanol, mCPP, and 8-OH-DPAT

Values in [brackets] indicate number of subjects earning at least one reinforcer (first value) and subjects tested (second value).

Test Drug	Drug Dose	Percentage of N₂O Lever Responding (± S.E.M.)	Response Rate in Responses per Second (± S.E.M.)
	mg/kg
Morphine (n = 8)	O₂ + vehicle	2.4 (1.6)	1.8 (0.1)
	N₂O + vehicle	96.1 (2.5)	1.6 (0.1)
	1	2.4 (1.6)	1.7 (0.1)
	3	15.1 (12.2)	1.3 (0.2)
	10	3.3 (2.2)	0.9 (0.2)^*
	30	33.3 (33.3) [3/8]	0.1 (0.0)^*
U-50488H (n = 8)	O₂ + vehicle	2.4 (1.5)	1.5 (0.1)
	N₂O + vehicle	95.8 (2.4)	1.3 (0.1)
	1	2.4 (1.6)	1.7 (0.1)
	3.2	1.6 (1.6) [5/8]	0.9 (0.3)^*
	7	10.7 (10.7) [3/8]	0.1 (0.1)^*
SNC-80 (n = 8)	O₂ + vehicle	1.9 (1.3)	1.7 (0.1)
	N₂O + vehicle	93.0 (0.8)	1.5 (0.2)
	1	1.4 (0.8)	1.7 (0.1)
	10	10.3 (2.9)	1.2 (0.1)^*
	17	7.9 (3.0)	1.1 (0.2)^*
	30	8.7 (1.8) [7/8]	0.8 (0.2)^*
	56	6.8 (1.8) [5/8]	0.5 (0.2)^*
Ethanol (n = 9)	O₂ + vehicle	2.3 (1.5)	1.6 (0.1)
	N₂O + vehicle	96.6 (1.5)	1.3 (0.2)
	1000	9.6 (6.6)	1.4 (0.1)^*
	1500	11.6 (5.5)	1.3 (0.1)^*
	2000	44.9 (15.3)	0.8 (0.1)^*
	2500	55.0 (13.2)	0.4 (0.1)^*
mCPP (n = 8)	O₂ + vehicle	2.6 (1.7)	1.7 (0.1)
	N₂O + vehicle	96.9 (1.7)	1.6 (0.1)
	0.1	1.9 (1.1)	1.8 (0.1)
	1	2.0 (1.3)	1.6 (0.1)
	5.6	3.4 (1.7)	0.9 (0.2)^*
	10	20.6 (17.0) [5/8]	0.4 (0.2)^*
8-OH DPAT (n = 8)	O₂ + vehicle	1.6 (1.6)	1.6 (0.1)
	N₂O + vehicle	98.3 (1.5)	1.5 (0.1)
	0.1	1.6 (1.6)	1.4 (0.1)
	0.3	1.4 (1.1)	1.1 (0.1)^*
	1	1.1 (1.1) [7/8]	0.5 (0.1)^*
	1.56	4.3 (2.4) [6/8]	0.4 (0.1)^*

↵* Statistically significant (P < 0.05) difference in response rates compared with the oxygen + vehicle control condition.