Table 3.

Opioid analgesia in wild-type and exon 11 knockout mice

Drug	ED50, mg/kg (s.c.)			Fold shift	P
	Wild type (+/+)	Heterozygote (+/−)	Homozygote (−/−)
Morphine	1.58 ± 0.17	1.30 ± 0.20	2.58 ± 0.52	1.6	0.07
Methadone	1.53 ± 0.06	1.56 ± 0.08	1.8 ± 0.14	1.2	0.11
M6G	0.92 ± 0.12	0.97 ± 0.25	19.3 ± 4.2	21	0.0005
Heroin	0.58 ± 0.11	0.48 ± 0.05	3.2 ± 0.8	5.5	0.0005
Fentanyl	0.024 ± 0.002	0.020 ± 0.001	0.23 ± 0.09	9.7	0.024

Analgesia was assessed in cumulative dose–response studies with at least 8 animals/groups using the radiant heat tail-flick assay and was defined quantally as a doubling or greater of the baseline latency with a maximal latency of 10 sec to minimize tissue damage, as previously described (28). ED₅₀ values were determined using probit analysis. Results are the means ± SEM of the ED₅₀ values determined from independent dose–response studies for morphine (n = 5), methadone (n = 5), heroin (n = 7), M6G (n = 7), and fentanyl (n = 4). Differences among groups for each drug were determined by ANOVA.