Expression of cannabinoid and opioid receptors in nervous as well as immune systems of Macaca mulatta and Tupaia belangeri

To make Macaca mulatta and Tupaia belangeri as experimental animals for studying functions of opioid and cannabinoid receptors in drug addiction, we examined expression of the opioid and cannabinoid receptors in nervous and immune system of the two animals. We dissected normal adult M. mulatta and T. belangeri, collected tissues of cortex, cerebellum, brain stem, hippocampus, spinal cord, and spleen, and then applied the semi-quantitative PCR and real-time quantitative PCR methods to investigate the mRNA expression levels of the opioid and cannabinoid receptors in these tissues. In M. mulatta, the cannabinoid receptor 1 (CNR1) mRNA was expressed in the all tissues; in contrast, the cannabinoid receptor 2 (CNR2) mRNA was only present in the spleen. The mu opioid receptor (MOPR) was detected in all tissues, and the kappa opioid receptor (KOPR) was found in the cortex, cerebellum, brain stem, and spinal cord, but not in hippocampus and spleen. However, the delta opioid receptor (DOPR) was restrictively expressed in the hippocampus. In T. belangeri, CNR1 and CNR2 were expressed in the five regions of the brain. CNR2, but no CNR1, was also detected in the spleen. MOPR was expressed in all examined tissues, and its expression levels in the brain were higher than that in the spleen. DOPR and KOPR were not found in all tissues. Taken together, the expression profiles of cannabinoid receptors in human being, M. mulatta, T. belangeri, and rat were similar, and the expression patterns of the opioid receptors in M. mulatta were more close to human beings. The opioid and cannabinoid receptors were expressed in the tissues of nervous and immune systems of M. mulatta and T. belangeri, and both animals could be used for studying drug addiction. Macaca mulatta is still the best experimental animal for drug addiction research because it shows very similar expression profiles of these receptors to human beings.