N-METHYL-D-ASPARTATE (NMDA) AND NON-NMDA GLUTAMATE-RECEPTOR ANTAGONISTS DIFFERENTIALLY SUPPRESS DORSAL HORN NEURON RESPONSES TO MECHANICAL STIMULI IN RATS WITH PERIPHERAL-NERVE INJURY

The effects of iontophoretically ejected glutamate receptor antagonist s on mechanically evoked responsiveness were examined on wide dynamic range (WDR) dorsal horn neurons in anesthetized rats that received a u nilateral ligation of the L5 and L6 spinal nerves 10-15 days previousl y. Both brush- and pinch-evoked responses of dorsal horn neurons on th e nerve-injured side were enhanced. N-Methyl-D-aspartate (NMDA) recept or antagonist, 2-amino-5-phosphonopentanoic acid (AP5), preferentially suppressed the enhanced pinch-evoked response, whereas ha-amino-3-hyd roxy-5-methyl-4-isoxazole-propionate (AMPA) receptor selective antagon ist, 6-nitro-7-sulphamoylbenzo(f)quinoxaline-2,3 (NBQX), preferentiall y attenuated the enhanced brush-evoked response. The results indicate that the enhanced responses to noxious and non-noxious peripheral inpu ts induced in WDR dorsal horn neurons following the nerve injury are m ediated by activation of NMDA and AMPA receptors, respectively.