Control of spasticity in a multiple sclerosis model is mediated by CB1, not CB2, cannabinoid receptors

Abstract

Background and purpose: There is increasing evidence to suggest that cannabis can ameliorate muscle-spasticity in multiple sclerosis, as was objectively shown in experimental autoimmune encephalomyelitis models. The purpose of this study was to investigate further the involvement of CB1 and CB2)cannabinoid receptors in the control of experimental spasticity.

Experimental approach: Spasticity was induced in wildtype and CB1-deficient mice following the development of relapsing, experimental autoimmune encephalomyelitis. Spastic-hindlimb stiffness was measured by the resistance to flexion against a strain gauge following the administration of CB1 and CB2 agonists.

Key results: As previously suggested, some CB2-selective agonists (RWJ400065) could inhibit spasticity. Importantly, however, the anti-spastic activity of RWJ400065 and the therapeutic effect of non-selective CB1/CB2 agonists (R(+)WIN55,212-2 and CP55, 940) was lost in spastic, CB1-deficit mice.

Conclusions and implications: The CB1 receptor controls spasticity and cross-reactivity to this receptor appears to account for the therapeutic action of some CB2 agonists. As cannabinoid-induced psychoactivity is also mediated by the CB1 receptor, it will be difficult to truly dissociate the therapeutic effects from the well-known, adverse effects of cannabinoids when using cannabis as a medicine. The lack of knowledge on the true diversity of the cannabinoid system coupled with the lack of total specificity of current cannabinoid reagents makes interpretation of in vivo results difficult, if using a purely pharmacological approach. Gene knockout technology provides an important tool in target validation and indicates that the CB1 receptor is the main cannabinoid target for an anti-spastic effect.

Figure 1

Inhibition of spasticity, with CB₂ agonists is CB₁-mediated. Following the development of spasticity ABH mice were injected i.v. with either: (a) the non-selective agonist RWJ35320 or the CB₂-selective agonist JWH056 or (b) the CB₂-selective agonist, RWJ400065. These received 0.2 mg kg⁻¹ (n=17 limbs), 0.01 mg kg⁻¹ (n=13 limbs) RWJ353203 or 10 mg kg⁻¹ JWH056 (n=7 limbs) or 0.01 mg kg⁻¹ (n=12 limbs), 1 mg kg⁻¹ (n=16 limbs) or 10 mg kg⁻¹ (n=16 limbs) RWJ400065 in wild-type or CB₁-deficient mice (n=12 limbs) in intralipid. The resistance to flexion was measured against a strain gauge. ^**P<0.01, ^***P<0.001 compared to baseline.

Figure 2

Hypothermia induced by cannabinoids. Wild-type or CB₁-deficient mice were injected either i.v. or i.p. with the non-selective agonist RWJ35320 or CB₂-selective agonist RWJ400065 in intralipid. The change in body temperature (mean±s.e.mean (vertical lines)) 20 min following injection compared to baseline was assessed. ^**P<0.01, ^***P<0.001 compared to baseline by paired t tests.

Figure 3

Spasticity is controlled by the CB₁ receptor. Wild-type or CB₁-deficient mice (Cnr1−/−) were injected intraperitoneally with the full CB₁/CB₂ agonists CP-55,940 (n=8/group) or R(+)WIN-55,212–2 (n=14/group). To facilitate visualization of differences between groups, results are expressed as the mean±s.e.mean (vertical lines) percentage change in the resistance to hindlimb flexion compared to baseline, 10 min after the injection of compound. ^***P<0.001 compared to baseline by paired t tests.