Neuropeptides and NADPH-diaphorase activity in the ascending cholinergic reticular system of the rat.

A major group of cholinergic neurons is present in the midbrain and pontine tegmentum. These cells could be selectively stained using either monoclonal antibodies to choline acetyltransferase, the pharmacohistochemical acetylcholinesterase procedure, or reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase histochemistry. Using these three techniques, the precise distribution of this cell group was determined. By combining these techniques with immunohistochemical staining for various neuropeptides, examples of peptide-cholinergic coexistence could be demonstrated in this cell group. Approximately 30% of these cholinergic neurons displayed substance P immunoreactivity. Most of these cells also showed corticotropin-releasing factor immunoreactivity and bombesin/gastrin-releasing peptide immunoreactivity. These results therefore provide evidence for the coexistence of various neuropeptides together with NADPH-diaphorase activity in the ascending cholinergic reticular system.