Immunolocalization of CB 1 receptor in rat striatal neurons: A confocal microscopy study

Several lines of evidence indicate that cannabinoids, among other functions, are involved in motor control. Although cannabinoid receptors (CB 1 ) mRNA has been observed in medium‐sized spiny neurons of the striatum, a description of the precise localization of CB 1 at a protein level among striatal cells is still lacking. Therefore, we performed immunohistochemical studies with light and confocal microscopy to identify neuronal subpopulations that express CB 1 and to assess the distribution of the receptor within these neurons. In our single label light microscopy study, CB 1 was observed in most medium‐sized neurons of the caudate‐putamen. However, CB 1 was also present in large‐sized neurons scattered throughout the striatum. Our dual‐label study showed that 89.3% of projection neurons in matrix contain CB 1 , and that 56.4% of projection neurons in patch are labeled for CB 1 . To investigate the presence of CB 1 among the different subclasses of striatal interneurons we performed a double‐labeling study matching CB 1 and each of the striatal interneuron markers, namely, choline acetyl‐transferase, parvalbumin, calretinin, and nitric oxide synthase. Our double‐label study showed that most parvalbumin immunoreactive interneurons (86.5%), more than one‐third (39.2%) of cholinergic interneurons, and about one‐third (30.4%) of the NOS‐positive neurons are labeled for CB 1 . Calretinin‐immunolabeled neurons were devoid of CB 1 . Synapse 53:159–167, 2004. © 2004 Wiley‐Liss, Inc.