EVIDENCE THAT CHOLINERGIC AXONS FROM THE PARABRACHIAL REGION OF THE BRAIN-STEM ARE THE EXCLUSIVE SOURCE OF NITRIC-OXIDE IN THE LATERAL GENICULATE-NUCLEUS OF THE CAT

We investigated the source of axons and terminals in the cat's lateral geniculate nucleus that stain positively for NADPH-diaphorase. The fu nctional significance of such staining is that NADPH-diaphorase is ide ntical to the enzyme nitric oxide synthetase, and thus it is thought t o reveal cells and axons that use nitric oxide as a neuromodulator. Wi thin the lateral geniculate and adjacent perigeniculate nuclei, a dens e network of axons and terminals is labeled for NADPH-diaphorase. The pattern of NADPH-diaphorase staining here is remarkably similar to tha t of choline acetyltransferase (ChAT) staining, suggesting that the so urce of these axons and terminals might be the parabrachial region of the brainstem because this provides the major cholinergic input to the lateral geniculate nucleus. In other areas of the brain to which para brachial axons project, there is also a similar staining pattern for N ADPH-diaphorase and ChAT. Furthermore, the patterns of cell staining w ithin the parabrachial region for NADPH-diaphorase and ChAT are virtua lly identical. However, the relationship between ChAT and NADPH-diapho rase staining for the parabrachial region is not a general property of cholinergic neurons. Other cholinergic cells and axons, such as the t rochlear nerve, the oculomotor nerve and nucleus, and the parabigemina l nucleus, which all label densely for ChAT, stain poorly or not at al l for NADPH-diaphorase. It is significant that the parabigeminal nucle us, which provides a cholinergic input to the lateral geniculate nucle us, has no cells that label for NADPH-diaphorase. We used double label ing methods to identify further the source of NADPH-diaphorase stainin g in the lateral geniculate nucleus. We found that parabrachial cells co-localize NADPH-diaphorase and ChAT. Noradrenergic and serotoninergi c cells in the brainstem also innervate the lateral geniculate nucleus , but we found that none of these co-localize NADPH-diaphorase. Finall y, by combining NADPH-diaphorase histochemistry with retrograde labeli ng of cells that project to the lateral geniculate nucleus, we found t hat the cholinergic cells of the parabrachial region are essentially t he sole source of NADPH-diaphorase in the lateral geniculate nucleus. We thus conclude that cells from the parabrachial region that innervat e the lateral geniculate nucleus use both acetylcholine and nitric oxi de for neurotransmission, and that this is virtually the only afferent input to this region that uses nitric oxide. (C) 1993 Wiley-Liss, Inc .