Decreased expression of N-methyl-D-aspartate (NMDA) receptors in rat dorsal root ganglion following complete Freund's adjuvant-induced inflammation: an immunocytochemical study for NMDA NR1 subunit.

The changes in expression of NMDA NR1, an essential functional subunit of N-methyl-D-aspartate (NMDA) receptors, were examined in the rat lumbar dorsal root ganglion (DRG) by immunocytochemical technique following injection of complete Freund's adjuvant (CFA) into the unilateral hindpaw. The results showed that there appeared a significant and several days-lasting down-regulation in expression of NMDA NR1 in the lumbar DRG following CFA injection, and especially, this change mainly appeared in the small and medium sized DRG neurons. It is suggested that a long-lasting flow of nociceptive inputs in nociceptors will elicit a decreased expression of NMDA receptors on primary afferent neurons and this plastic change would act as a factor leading towards the hyposensitization for nociception at the nociceptor level.