Cannabis in movement disorders.

Central cannabinoid receptors are densely located in the output nuclei of the basal ganglia (globus pallidus, substantia nigra pars reticulata), suggesting their involvement in the regulation of motor activity. Furthermore, there is evidence that endogenous cannabinoid transmission plays a role in the manipulation of other transmitter systems within the basal ganglia by increasing GABAergic transmission, inhibiting glutamate release and affecting dopaminergic uptake. Most hyperkinetic and hypokinetic movement disorders are caused by a dysfunction of basal ganglia-thalamo-cortical loops. It has been suggested that an endogenous cannabinoid tone participates in the control of movements and, therefore, the central cannabinoid system might play a role in the pathophysiology of these diseases. During the last years in humans a limited number of clinical trials demonstrated that cannabinoids might be useful in the treatment of movement disorders. Despite the lack of controlled studies there is evidence that cannabinoids are of therapeutic value in the treatment of tics in Tourette syndrome, the reduction of levodopa-induced dyskinesia in Parkinson s disease and some forms of tremor and dystonia. It can be speculated that cannabinoid antagonists might be useful in the treatment of chorea in Huntington s disease and hypokinetic parkinsonian syndromes.