CNR1 and Parkinson disease: Although one study did find an increase in CB1R mRNA levels in the striatum in 6-OHDA lesioned rats chronically treated with levodopa (Zeng et al. 1999), levodopa has since then been found to consistently reverse both the elevation of endocannabinoid levels (Maccarrone et al. 2003; van der Stelt et al. 2005) and the PD-related increase in CB1R density and binding (Lastres-Becker et al. 2001).