CB1-cannabinoid and μ-opioid receptor co-localization on postsynaptic target in the rat dorsal horn

Cannabinoids and opioids interact in the control of nociception at the spinal level. Likely, several mechanisms are involved, with one of them being co-localization of cannabinoid and opioid receptors. In order to validate this hypothesis, a double labeling study of CB1 cannabinoid receptors and mu-opioid receptors in the dorsal horn of the rat spinal cord was performed. A strong co-localization of CB1 and mu-opioid receptors was observed in lamina II interneurons at the ultrastructural level. The physiological consequences of the co-localization are discussed.