Descending modulation of dorsal horn biogenic amines as determined by in vivo dialysis.

Bipolar concentric stimulating electrodes were placed medially within the nucleus raphe magnus and laterally within the nucleus gigantocellularis. The levels of norepinephrine (NE), serotonin (5-HT), and 5-hydroxyindolacetic acid (5-HIAA) within the dorsal horn of the spinal cord were measured before and after electrical stimulation of these brainstem nuclei using in vivo dialysis coupled with high pressure liquid chromatography and electrochemical detection. Stimulation medially significantly increased the levels of all three amines. While simulation laterally also increased NE, both 5-HT and 5-HIAA were significantly reduced. The relevance of these findings to descending modulation of ascending nociceptive neural activity within the dorsal horn is discussed.