We investigated the source of axons and terminals in the cat's lateral geniculate nucleus that stain positively for NADPH-diaphorase. The functional significance of such staining is that NADPH-diaphorase is identical to the enzyme nitric oxide synthetase, and thus it is thought to reveal cells and axons that use nitric oxide as a neuromodulator. Within the lateral geniculate and adjacent perigeniculate nuclei, a dense network of axons and terminals is labeled for NADPH-diaphorase. The pattern of NADPH-diaphorase staining here is remarkably similar to that of choline acetyltransferase (ChAT) staining, suggesting that the source 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 parabrachial axons project, there is also a similar staining pattern for NADPH-diaphorase and ChAT. Furthermore, the patterns of cell staining within the parabrachial region for NADPH-diaphorase and ChAT are virtually identical. However, the relationship between ChAT and NADPH-diaphorase staining for the parabrachial region is not a general property of cholinergic neurons. Other cholinergic cells and axons, such as the trochlear nerve, the oculomotor nerve and nucleus, and the parabigeminal nucleus, which all label densely for ChAT, stain poorly or not at all for NADPH-diaphorase. It is significant that the parabigeminal nucleus, which provides a cholinergic input to the lateral geniculate nucleus, has no cells that label for NADPH-diaphorase. We used double labeling methods to identify further the source of NADPH-diaphorase staining in the lateral geniculate nucleus. We found that parabrachial cells co-localize NADPH-diaphorase and ChAT. Noradrenergic and serotoninergic cells in the brainstem also innervate the lateral geniculate nucleus, but we found that none of these co-localize NADPH-diaphorase. Finally, by combining NADPH-diaphorase histochemistry with retrograde labeling of cells that project to the lateral geniculate nucleus, we found that the cholinergic cells of the parabrachial region are essentially the sole source of NADPH-diaphorase in the lateral geniculate nucleus. We thus conclude that cells from the parabrachial region that innervate the lateral geniculate nucleus use both acetylcholine and nitric oxide for neurotransmission, and that this is virtually the only afferent input to this region that uses nitric oxide.

We examined the projection from the basal forebrain to thalamic and cortical regions of the visual system in cats, with particular reference to the visual sector of the thalamic reticular nucleus, the lateral geniculate nucleus, and the striate cortex. First, we made injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the visual sector of the thalamic reticular nucleus and found cells labeled by retrograde transport in the lateral nucleus basalis magnocellularis. Injection of biocytin into the basal forebrain resulted in the anterograde labeling of a dense band of fibers and terminals within the entire thalamic reticular nucleus; this labeling extended through the visual sector including the perigeniculate nucleus. No orthograde labeling was found in the lateral geniculate nucleus. Next, we addressed the issue of putative neurotransmitters used by this pathway using a variety of immunocytochemical and histochemical markers. In this fashion, we identified two populations of cells in the nucleus basalis magnocellularis of the cat; large cholinergic cells that contain choline acetyltransferase, NADPH-diaphorase, and calbindin and that project to striate cortex and smaller cells that contain gamma-aminobutyric acid (GABA), glutamic acid decarboxylase, and parvalbumin and that project to the visual sector of the thalamic reticular nucleus. We also examined at the electron microscopic level terminals in the visual sector of the thalamic reticular nucleus that were labeled from a biocytin injection in the basal forebrain. Most of these terminals form symmetric contacts onto dendrites and were revealed by postembedding immunocytochemical staining to be positive for GABA.

We investigated the changes in NADPH-diaphorase staining that occur in the lateral geniculate nucleus of cats following rearing with monocular lid suture. This staining allows visualization of the synthesizing enzyme of nitric oxide, a neuromodulator associated with plasticity. In the lateral geniculate nucleus of normally reared cats, NADPH-diaphorase exclusively labels the axons and terminals of an input from the parabrachial region of the brainstem; no geniculate cells in the A-laminae are labeled. Early monocular lid suture has no obvious effect on the NADPH-diaphorase staining of parabrachial axons. However, this lid suture results in the abnormal appearance of NADPH-diaphorase staining for geniculate somata. These cells are located primarily in the nondeprived laminae. Double-labeling experiments indicate that these cells with abnormal NADPH-diaphorase reactivity are Y relay cells: NADPH-diaphorase staining is found in cells retrogradely labeled from visual cortex; it is found in cells labeled with a monoclonal antibody for CAT-301, which selectively targets Y cells; it is not found in cells labeled with an anti-GABA antibody, which targets interneurons. Also, NADPH-diaphorase labeled cells are among the largest cells in the nondeprived laminae, again suggesting that they are Y relay cells. We cannot suggest a specific mechanism for this induction of NADPH-diaphorase labeling, but it does not seem to be due to abnormal binocular competition induced by the monocular lid suture.