THE COMBINATION OF NMDA ANTAGONISM AND MORPHINE PRODUCES PROFOUND ANTINOCICEPTION IN THE RAT DORSAL HORN

Dorsal horn nociceptive neurones exhibit wind up, a frequency dependent potentiation of their responses to repeated C-fibre stimulation. Intrathecal morphine (5-mu-g) significantly reduces the initial responses of the neurones but not wind up whereas the reverse is true for N-methyl-D-aspartate (NMDA) antagonists. The combination of intrathecal morphine (5-mu-g) and 7-chlorokynurenate (2.5-mu-g), an antagonist at the glycine site of the NMDA receptor, abolishes both the input and wind up of these neurones.