Transmitters involved in antinociception in the spinal cord

The possible physiological and pathophysiological role of monoamines-adrene rgic transmitter (norepinephrine), serotonin; cholinergic transmitter (acet ylcholine); inhibitory (gamma-aminobutyric acid) and excitatory (glutamate) amino acids; opioid and nonopioid peptides, enkephalins, beta-endorphin an d substance P, neurokinin-A, neurokinin-B, neurotensin, cytokines, calciton ine gene-related peptide, galanin, neuropeptide Y, nerve growth factor, cho lecystokinin; purines; nitric oxide; vanilloid receptor agonists (capasaici n); and nociceptin-in spinal transmission of pain is reviewed, The role of substance P, neurokinin-A and neurokinin-B in the dorsal horn has been iden tified. These were suggested to be primary afferent transmitters mediating or facilitating the expression of nociceptive inputs. Pronociceptive modula tors will be discussed later. Recent findings showing that N-methyl-D-aspar tate (NMDA) receptor activation generates nitric oxide and prostanoids that enhance pain transmission whereas adenosine release acts to control these NMDA-mediated events are also mentioned. The clinical importance of central ly acting alpha(2)-adrenoceptor agonists (clonidine and dexmedetomidine) is also discussed. Antinociceptive and morphine-potentiating drugs are ideal adjuvants for anesthesia; their application in spinal anesthesia is highlig hted. The recent development in understanding the importance of noradrenerg ic transmission and subtypes of alpha(2)-adrenoceptors (alpha(2A) and alpha (2B)) for the first time is reviewed. (C) 1999 Elsevier Science Inc.