COLOCALIZATION OF IONOTROPIC GLUTAMATE-RECEPTOR SUBUNITS WITH NADPH-DIAPHORASE-CONTAINING NEURONS IN THE RAT MESOPONTINE TEGMENTUM

Tegmental cholinergic neurons vary their discharge patterns across the sleep-wake cycle, and glutamate is suggested to play an important rol e in determining these firing patterns. Cholinergic and noncholinergic neurons in the mesopontine tegmentum have different susceptibilities to various excitotoxins, presumably because of heterogeneity in the ex pression of glutamate receptor subtypes in this area. By using a doubl e-labeling procedure that combines nicotinamide adenine dinucleotide p hosphate diaphorase (NADPH-diaphorase) histochemistry and avidin-bioti n-peroxidase immunocytochemistry with diaminobenzidine as the chromoge n, we compared the colocalization of AMPA receptor subunits GluR1, Glu R2/3, and GluR4, kainate receptor subunits GluR5/6/7, and an NMDA rece ptor subunit NMDAR1 on NADPH-diaphorase-positive (cholinergic) neurons in the mesopontine tegmentum. Throughout the brainstem, neurons immun oreactive for GluR2/3 and NMDAR1 were most numerous, whereas neurons l abeled for GluR1, GluR4, and GluR5/6/7 were less common. Specifically within the mesopontine tegmentum, the proportion of double-labeled neu rons in the diaphorase-containing cell population was highest with Glu R1 (43%) and lowest with GluR5/6/7 (12%). Regardless of the receptor s ubunit type, the greatest numbers of double-labeled neurons were obser ved in the pedunculopontine tegmental nucleus pars compacta and the fe west in the dorsal aspect of the laterodorsal tegmental nucleus. In ad dition, there were regional differences in the relative expression of receptor subunits and diaphorase-positive neurons across the subdivisi ons of the tegmental cholinergic column. Because each ionotropic subun it confers distinctive properties to a receptor channel, the present r esults suggest that mesopontine cholinergic neurons have nonuniform re sponses to glutamate and are also discriminable from basal forebrain c holinergic neurons in terms of glutamate receptor configuration. (C) 1 996 Wiley-Liss, Inc.