Immunolocalization of CB1 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 (CB1) mRNA has been observed in medium-sized spiny neurons of the striatum, a description of the precise localization of CB1 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 CB1 and to assess the distribution of the receptor within these neurons. In our single label light microscopy study, CB1 was observed in most medium-sized neurons of the caudate-putamen. However, CB1 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 CB1, and that 56.4% of projection neurons in patch are labeled for CB1. To investigate the presence of CB1 among the different subclasses of striatal interneurons we performed a double-labeling study matching CB1 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 CB1. Calretinin-immunolabeled neurons were devoid of CB1. (C) 2004 Wiley-Liss, Inc.