Galanin and NADPH-diaphorase coexistence in cholinergic neurons of the rat basal forebrain

The distribution of the enzyme NADPH-diaphorase in the rat basal forebrain was examined in relation to the neuropeptide galanin and the neurotransmitter synthetic enzyme choline acetyltransferase. Immunoperoxidase staining permitted camera lucida mapping of galanin and choline acetyltransferase distributions in serial sections through the basal forebrain for comparison with adjacent sections prepared for NADPH-diaphorase histochemistry. Photographs of sections subjected to indirect immunofluorescence for galanin and choline acetyltransferase were compared to photographs of the same sections taken after NADPH-diaphorase histochemistry. This permitted the direct investigation of co-localization within the cholinergic basal forebrain. The distributions of choline acetyltransferase- and galanin-immunoreactive neurons in the basal forebrain agreed with previous descriptions. NADPH-diaphorase histochemistry selectively stained a population of magnocellular basal forebrain neurons with a distribution similar to that observed with galanin immunohistochemistry. Double and triple staining experiments indicated that NADPH-diaphorase labels a majority of the magnocellular cholinergic neurons in the medial septum and diagonal band nuclei. Most of these neurons also contain galanin immunoreactivity. However, small populations of galanin-positive/diaphorase-negative or diaphorase-positive/galanin-negative cholinergic neurons were also observed. In the more caudal portions of the cholinergic basal forebrain, very few galanin or NADPH-diaphorase-positive neurons were observed. Thus, galanin and NADPH-diaphorase coexist in the majority of cholinergic basal forebrain neurons in the regions innervating limbic structures. The neocortically projecting cholinergic cells in the caudal basal forebrain appear to lack these other neurochemical markers.