Abstract
Although type 1 cannabinoid receptors (CB1Rs) are expressed abundantly throughout the brain, the presence of type 2 cannabinoid receptors (CB2Rs) in neurons is still somewhat controversial. Taking advantage of newly designed CB1R and CB2R mRNA riboprobes, we demonstrate by PCR and in situ hybridization that transcripts for both cannabinoid receptors are present within labeled pallidothalamic-projecting neurons of control and MPTP-treated macaques, whereas the expression is markedly reduced in dyskinetic animals. Moreover, an in situ proximity ligation assay was used to qualitatively assess the presence of CB1Rs and CB2Rs, as well as CB1R-CB2R heteromers within basal ganglia output neurons in all animal groups (control, parkinsonian and dyskinetic macaques). A marked reduction in the number of CB1Rs, CB2Rs and CB1R-CB2R heteromers was found in dyskinetic animals, mimicking the observed reduction in CB1R and CB2R mRNA expression levels. The fact that chronic levodopa treatment disrupted CB1R-CB2R heteromeric complexes should be taken into consideration when designing new drugs acting on cannabinoid receptor heteromers.