Development of the cholinergic, nitrergic, and GABAergic innervation of the cat dorsal lateral geniculate nucleus

Cholinergic projections from the brainstem have been shown to be important modulators of visual activity in the dorsal lateral geniculate nucleus (dLG N) of the adult, but little is known about the role of these modulatory inp uts during development. We examined the postnatal development of the cholin ergic innervation of the dLGN by using an monoclonal antibody against choli ne acetyl transferase (ChAT), We also investigated the development of GABAe rgic interneurons in the dLGN by using an antibody against glutamic acid de carboxylase (GAD), and the developmental expression of brain nitric oxide s ynthase (BNOS) by using an antibody against this enzyme. We found that brai nstem cells surrounding the brachium conjunctivum express ChAT at birth, al though axons in the dLGN do not express ChAT until the end of the first pos tnatal week. Cholinergic synaptic contacts were observed as early as the se cond postnatal week. The number of axons stained with the ChAT antibody inc reased slowly during the subsequent weeks in the dLGN and reached adult lev els by the eighth postnatal week. GABAergic interneurons were present at bi rth and reached their adult soma size by the third postnatal week. GABAergi c fibers are dense at birth but change during development from a diffuse pa ttern to clustered arrangements that can be recognized as distinct rings of GAD staining by P35. Cellular expression of BNOS was seen within all dLGN laminae during development. The BNOS-stained cells are tentatively identifi ed as interneurons because their soma sizes were similar to those of CAD-st ained cells. Although cellular BNOS staining remained robust in the C1-3 la minae through adulthood, cellular expression of BNOS in the A laminae decli ned during the first five postnatal weeks and remains sparse in the adult. As cellular BNOS staining declined, there was a steady increase in BNOS-sta ined fibers, which paralleled the increase of ChAT-stained fibers that are known to colocalize BNOS in the adult. Our results emphasize the continued transformations of intrinsic as well as extrinsic innervation patterns that occur during the development of the dLGN. (C) 2000 Wiley-Liss, Inc.