alpha 2-Adrenergic receptors in human spinal cord: specific localized expression of mRNA encoding alpha 2-adrenergic receptor subtypes at four distinct levels.

alpha 2-Adrenergic receptor (AR) subtype mRNA (alpha 2a, alpha 2b, alpha 2c) neuronal localization in human spinal cord has not been described. We therefore performed in situ hybridization to identify cell bodies at four levels of human spinal cord (cervical, thoracic, lumbar, sacral) containing alpha 2AR subtype specific mRNA. alpha 2AR mRNA is present in gray matter only (ventral > dorsal; sacral > cervical > thoracic = lumbar). In addition to alpha 2AR mRNA in cell bodies in thoracic and lumbar intermediolateral (sympathetic) and sacral intermediate (parasympathetic) cell columns (lamina VII), all levels in dorsal horn laminae I, II, V, and ventral horn lamina IX, we demonstrate alpha 2AR mRNA in dorsal horn laminae III and IV, and dorsal nucleus of Clarke, where alpha 2ARs have not been described. Previously unreported heterogeneity in alpha 2AR subtype distribution (alpha 2a and alpha 2bAR mRNA present, alpha 2cAR mRNA virtually absent) is found at all sites of alpha 2AR mRNA expression in human spinal cord, including locations known to mediate effects of alpha 2AR agonist drugs on nociception, autonomic function and motor tone. Cervical spinal cord demonstrates a predominance of alpha 2a mRNA signal, while thoracic, lumbar, and sacral spinal cord demonstrate an increasing predominance of alpha 2bAR mRNA. If confirmed at a protein level, these findings have profound implications for therapeutic strategies in managing human pain.