THE N-METHYL-D-ASPARTATE RECEPTOR ANTAGONIST DEXTROMETHORPHAN SELECTIVELY REDUCES TEMPORAL SUMMATION OF 2ND PAIN IN MAN

Oral doses of dextromethorphan (DM), a common cough suppressant and N- methyl-D-aspartate (NMDA) receptor antagonist, and their vehicle contr ol were given on a double-blind basis to normal Volunteer human subjec ts who rated intensities of first and second pain in response to repea ted painful electric shocks and repeated 52 degrees C heat pulses. Dos es of 30 and 45 mg, but not 15 mg, were effective in attenuating tempo ral summation of second pain, a psychophysical correlate of temporal s ummation of C afferent-mediated responses of dorsal horn nociceptive n eurons, termed 'wind-up'. By contrast, neither first nor second pain e voked by the first stimulus in a train of stimuli were affected by any of these doses of DM. These results further confirm temporal summatio n of second pain as a psychophysical correlate of wind-up by providing evidence that DM selectively reduces temporal Summation of second pai n, as has been shown for wind-up.