TABLE 3

Calculated E_max and EC₅₀ values from agonist-stimulated GTPgS binding experiments in CB1 (+/+) and (+/−) membranes from cerebellum and spinal cord tissue

Agonist	CB1 (+/+)		CB1 (+/−)		(+/−) E_max/(+/+) E_max
Agonist	E_max	EC₅₀	E_max	EC₅₀	(+/−) E_max/(+/+) E_max
Cerebellum^{^a}
A-834,735D	211.1 ± 11.4	22.3 ± 5.6	164.9 ± 14.1*^#	29.4 ± 11.9	0.78
WIN55,212-2	202.5 ± 7.6	39.4 ± 7.6	152.6 ± 4.9**^#	50.4 ± 8.0	0.75
CP55,940	198.7 ± 5.2	4.1 ± 0.6	166.3 ± 7.6*^#	6.1 ± 1.4	0.84
JWH-073	185.5 ± 1.7	25.6 ± 1.2	95.5 ± 3.9^****	38.3 ± 7.1	0.51
CP47,497	212 ± 8.6	102.1 ± 18.2	133.3 ± 7.6***	94.5 ± 22.8	0.63
THC	119.9 ± 4.6^	24.3 ± 4.7	73.8 ± 8.7**^	52.4 ± 29.0	0.62
Spinal cord^{^b}
A-834,735D	57.8 ± 2.4	15.0 ± 3.0	35.0 ± 3.0**	24.1 ± 9.6	0.61
WIN55,212-2	56.3 ± 3.8	65.4 ± 22.0	36.9 ± 2.4**	84.8 ± 21.6	0.66
CP55,940	49.6 ± 5.9	8.61 ± 5.1	30.4 ± 4.3*	9.5 ± 6.9	0.61
JWH-073	41.3 ± 3.5	77.8 ± 29.9	20.6 ± 7.7^#	46.6 ± 91.0	0.49
CP47,497	41.2 ± 3.9	93.2 ± 38.1	17.1 ± 2.2**^#^$	45.9 ± 24.2	0.42
THC	11.4 ± 2.3^	6.1 ± 11.2	ND	ND	ND

ND, not determined; ^indicates significant differences versus all other ligands within (+/+) E_max values. *P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001 for (+/+) versus (+/−) samples within tissue. ^P < 0.05 for THC versus other wild-type E_max values. #P < 0.05 for JWH-073 versus other (+/−) E_max values. ^$P < 0.05 for CP47,497 versus other (+/−) E_max values. No significant differences in EC₅₀ were detected across brain region or genotype for each drug.
↵^a In cerebellum, all agonists elicited significantly lower [³⁵S]GTPγS binding in (+/−) membranes than in (+/+) membranes. Comparison of CB₁ (+/+) E_max values across drugs revealed that THC elicited the least stimulation of all ligands tested in (+/+) and (+/−) tissue.
↵^b Spinal cord membranes showed a similar pattern of results in which stimulation was significantly reduced in tissue from (+/−) mice compared with (+/+) mice, although the E_max value of JWH073 in CB₁ (+/−) mice did not statistically differ from its E_max value in CB₁ (+/+) mice (P = 0.052). The lack of detectable stimulation by THC in spinal cord tissue from CB₁ (+/−) mice precluded the calculation of the E_max and EC₅₀ values of this compound, although the moderate efficacy agonists CP47,497 and JWH-073 differed from WIN,55,212-2 in (+/−) spinal cord. In CB₁ (+/+) spinal cord tissue, the E_max value of THC was significantly reduced compared with each of the other ligands. This loss of efficacy is expressed additionally as the CB₁ (+/−) E_max/ CB₁ (+/+) E_max to show relative differences between high receptor conditions of cerebellum and low receptor conditions of spinal cord.