Changes in CB1 receptors in motor-related brain structures of chronic relapsing experimental allergic...

Recent studies have examined the changes in the activity of cannabinoid signaling system in multiple sclerosis (MS), as a way to explain the efficacy of cannabinoid compounds to alleviate spasticity, pain, tremor and other signs of this autoimmune disease. In the present study, we have further explored this issue by examining density, mRNA expression and activation of GTP-binding proteins for the cannabinoid CB1 receptor subtype in several brain structures of mice with chronic relapsing experimental allergic encephalomyelitis (CREAE), a chronic model of MS that reproduces many of the pathological hallmarks of the human disease. CREAE animals were used at different phases in the progression of the disease (acute, remission and chronic) and compared to control mice. We observed several changes in the status of CB1 receptors that were region-specific and mainly circumscribed to motor-related regions, which is compatible with the symptomatology described for these animals that is preferentially of motor nature. We found a moderate decrease in the density of CB1 receptors in the caudate-putamen during the acute phase of CREAE. These reductions disappeared during the remission phase, but they were again observed, to a more marked extent, in the chronic phase. The same pattern for CB1 receptor density was observed in the cerebellum which, in this case, was accompanied by a progressive decrease in the capability of these receptors to activate GTP-binding proteins that was maximal in the chronic phase. The decrease in the density of CB1 receptors in the acute phase was also found in the globus pallidus but, in this case, the reduction was maintained during the further phases. No changes were observed in CB1 receptor-mRNA levels in any of the different regions examined. Finally, by contrast with the observations in motor structures, the status of CB1 receptors remained unaltered in cognition-related regions, such as the cerebral cortex and the hippocampus, during the different phases of CREAE. In summary, CB1 receptors were affected by the development of CREAE in mice exhibiting always down-regulatory responses that were circumscribed to motor-related regions and that were generally more marked during the acute and chronic phases. These observations may explain the efficacy of cannabinoid agonists to improve motor symptoms (spasticity, tremor, ataxia) typical of MS in both humans and animal models.