Cannabinoid mechanisms of pain suppression.

A large body of literature indicates that cannabinoids suppress behavioral responses to acute and persistent noxious stimulation in animals. This review examines neuroanatomical, behavioral, and neurophysiological evidence supporting a role for cannabinoids in suppressing pain at spinal, supraspinal, and peripheral levels. Localization studies employing receptor binding and quantitative autoradiography, immunocytochemistry, and in situ hybridization are reviewed to examine the distribution of cannabinoid receptors at these levels and provide a neuroanatomical framework with which to understand the roles of endogenous cannabinoids in sensory processing. Pharmacological and transgenic approaches that have been used to study cannabinoid antinociceptive mechanisms are described. These studies provide insight into the functional roles of cannabinoid CB1 (CB1R) and CB2 (CB2R) receptor subtypes in cannabinoid antinociceptive mechanisms, as revealed in animal models of acute and persistent pain. The role of endocannabinoids and related fatty acid amides that are implicated in endogenous mechanisms for pain suppression are discussed. Human studies evaluating therapeutic potential of cannabinoid pharmacotherapies in experimental and clinical pain syndromes are evaluated. The potential of exploiting cannabinoid antinociceptive mechanisms in novel pharmacotherapies for pain is discussed.