Localization of N-methyl-D-aspartate NR2B subunits on primary sensory neurons that give rise to small-caliber sciatic nerve fibers in rats

In the present study we have used immunohistochemical staining and retrogra de tracing techniques to investigate the relationship between the N-methyl- D-aspartate receptor NR2B subunits and small-diameter primary afferent dors al root ganglion neurons that give rise to the sciatic nerve fibers. Three days after an intra-sciatic nerve injection of tetramethyl rhodamine isothi ocyanate-conjugated wheat germ agglutinin which labels small-diameter prima ry afferents, many NR2B and wheat germ agglutinin-double-labeled cells (sim ilar to 70% of wheat germ agglutinin-labeled neurons) were observed in the L5 dorsal root ganglia. Three days after an intra-sciatic nerve injection o f fluorescein isothiocyanate-conjugated Bandeiraea simplicifolia agglutinin isolectin B4 which labels predominantly non-peptidergic C-fiber primary af ferents, NR2B and Bandeiraea simplicifolia agglutinin isolectin B4 double-l abeled neurons (similar to 90% of Bandeiraea simplicifolia agglutinin isole ctin B4-labeled neurons) were also observed in the L5 dorsal root ganglion. Three days after an intra-sciatic nerve injection of fluorescein isothiocy anate-conjugated cholera toxin B subunit, only similar to 40% of cholera to xin B subunit-labeled neurons were NR2B positive and those labeled neurons tended to be small-sized. When calcitonin gene-related peptide and NR2B wer e labeled by a double immunofluorescent staining technique, we found that t he majority of calcitonin gene-related peptide-positive neurons was NR2B im munoreactive (>90% of calcitonin gene-related peptide-positive neurons, and similar to 60% of NR2B-positive neurons) as well. Size frequency analysis also demonstrated that NR2B subunits were predominantly localized on the sm all and medium-sized neurons. These results suggest that NR2B subunits are predominantly expressed on sma ll diameter primary afferents, and these NR2B containing N-methyl-D-asparta te receptors may play a role in the modulation of neurotransmitter release from primary afferent terminals. (C) 2000 IBRO. Published by Elsevier Scien ce Ltd. All rights reserved.