Cannabinoid Receptor Type 1 in Parkinson's Disease: A Positron Emission Tomography Study with [ (18)F]FMPEP‐d (2)

BACKGROUND: The endocannabinoid system is a widespread neuromodulatory system affecting several biological functions and processes. High densities of type 1 cannabinoid (CB1) receptors and endocannabinoids are found in basal ganglia, which makes them an interesting target group for drug development in basal ganglia disorders such as Parkinson's disease (PD). OBJECTIVE: The aim of this study was to investigate CB1 receptors in PD with [(18)F]FMPEP‐d (2) positron emission tomography (PET) and the effect of dopaminergic medication on the [(18)F]FMPEP‐d (2) binding. METHODS: The data consisted of 16 subjects with PD and 10 healthy control subjects (HCs). All participants underwent a [(18)F]FMPEP‐d (2) high‐resolution research tomograph PET examination for the quantitative assessment of cerebral binding to CB1 receptors. To investigate the effect of dopaminergic medication on the [(18)F]FMPEP‐d (2) binding, 15 subjects with PD underwent [(18)F]FMPEP‐d (2) PET twice, both on and off antiparkinsonian medication. RESULTS: [(18)F]FMPEP‐d (2) distribution volume was significantly lower in the off scan compared with the on scan in basal ganglia, thalamus, hippocampus, and amygdala (P < 0.05). Distribution volume was lower in subjects with PD off than in HCs globally (P < 0.05), but not higher than in HCs in any brain region. CONCLUSIONS: Subjects with PD have lower CB1 receptor availability compared with HCs. PD medication increases CB1 receptor toward normal levels. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society