Noxious thermal stimulation of c-fos activity induced in rat lumbar spinal cord is reduced by AP-5 but not by Glycine

The effects of intrathecal administration of NMDA (N-methyl-D-aspartic acid) receptor antagonist AP-5 (2-Amino-5-phosphonopentanoic acid), a competitive and specific NMDA antagonist, and glycine on the neuronal expression of c-fos protein (Fos) in the dorsal neurons lumbar segments four and five were studied after noxious heat stimulation. Heat (52 degrees C, 3 s per application, repeated 10 times) was applied to the hindpaws of rats. NMDA receptor antagonist AP-5 (0.1 mmol/10 mi, i.t.) suppressed the noxious heat-induced Fos immunoreactivity by 65% as compared to animals pre-treated with saline. In contrast, glycine (0.1 mu mol/10 mu l, it.) did not influence Fos expression induced by the noxious heat stimulation. This study suggests that excitatory amino acids, e.g. glutamate but not the inhibitory aminos acid, glycine, plays a role in thermal nociception which in turn is mediated, in part, by c-fos activity. (C) 1999 Published by Elsevier Science Ireland Ltd. All rights reserved.