DEVELOPMENTAL-CHANGES IN THE PATTERN OF NADPH-DIAPHORASE STAINING IN THE CATS LATERAL GENICULATE-NUCLEUS

We examined the pattern of NADPH-diaphorase (NADPH-d) staining in the lateral geniculate nucleus (LGN) of dorsal thalamus in fetal and newbo rn kittens, and adult cats. This staining Visualizes the synthesizing enzyme of nitric oxide (NO), a neuromodulator associated with central nervous system (CNS) development and synaptic plasticity. In the adult , very few LGN cells stained for NADPH-d, and these were restricted to interlaminar zones and ventral C layers. NADPH-d labeled a dense netw ork of fibers and axon terminals throughout the LGN and adjacent thala mic nuclei. The source of such labelling has been reported to be choli nergic neurons from the parabrachial region of the brain stem (Bickfor d et al., 1993). A very different pattern of staining was observed in prenatal and early postnatal kittens. Between embryonic (E) day 46-57, lightly stained cells appeared throughout the LGN. From this age, thr ough about the first month of life, the number of stained cells in the LGN rose rapidly. The density (cells/mm(2)) of labeled cells peaked a t postnatal day (P) 28 (P28), and was about 150 times greater than the level measured in the adult LGN. After P28, cell staining declined ra pidly, and fell to adult levels at P41. The reduction in cell staining that occurred between P35-41 was accompanied by the appearance of fin e-caliber fiber staining, similar to that observed in the adult LGN. N ADPH-d staining, which reveals the presence of nitric oxide synthase ( NOS), and thus NO activity, may reflect two processes. In the adult LG N, the labeling of cholinergic axons arising from the brain-stem parab rachial region coupled with a paucity of the LGN cellular staining sug gests that NO operates in an orthograde manner, being co-released with ACh to influence the gain and efficacy of retinogeniculate transmissi on. By contrast, in developing kitten, NADPH-d staining of LGN cells s uggests that NO acts in a retrograde fashion, perhaps playing a role i n maintaining associative processes underlying activity-dependent refi nement of retinogeniculate connections.