Localization of Cannabinoid Receptors Using Immunoperoxidase Methods

Two cannabinoid receptors have been identified to date. The first of these, designated CB₁ , is localized primarily in the central nervous system but is also present at lower levels in other tissues. The second receptor, CB₂ , has been found natively in cells of the immune system. Both receptors have an extracellular amine-terminal domain, seven transmembrane domains, an intracellular carboxy-terminal domain, and are coupled through G proteins to adenylate cyclase and mitogen-activated protein kinase. In this chapter, a series of experimental protocols is presented that allows for the systematic identification and localization of cannabinoid receptors in tissues and cells. Immunoperoxidase staining for light microscopy is complemented with correlative application for electron microscopy. This approach is followed by that using immunogold labeling for high-resolution definition of cannabinoid receptor distribution at the ultrastructural level.