CNR1 and Parkinson disease: Previous studies in experimental PD showed enhanced eCB activity in the basal ganglia, including increased CB1 mRNA levels, CB1 activity, AEA levels, and decreased CB clearance.9,10,27,49–52 Accordingly, increased level of AEA has been shown in the cerebrospinal fluid of untreated PD patients.11 Also, increased expression of CB1 receptors in the basal ganglia has been reported.51 These changes are associated with movement suppression and may be reversed by chronic levodopa treatment.9,51,53