INHIBITION OF NITRIC-OXIDE SYNTHASE FAILS TO DISRUPT THE DEVELOPMENT OF CHOLINERGIC FIBER PATCHES IN THE RAT SUPERIOR COLLICULUS

in the developing nervous system. Whether this action is dependent upo n glutamate and the N-methyl-D-aspartate receptor is not yet establish ed. We have used the patch-cluster system in the intermediate gray lay er (IGL) of the rat Nitric oxide may serve as a retrograde messenger t o refine or stabilize synapses superior colliculus (SC), a system rece iving both glutamatergic and cholinergic input, to study this question . The normal distribution and development of nitric oxide synthase (NO S) in SC was examined using nicotinamide adenine dinucleotide phosphat e diaphorase (NADPH-d) histochemistry in Sprague-Dawley rats aged P4 t o adulthood. Fibers containing acetylcholine (ACh) were identified usi ng choline acetyltransferase (ChAT) immunocytochemistry. In addition, N omega-nitro-L-arginine, an inhibitor of NOS, was injected intraperit oneally from birth until P10, P14, P18, or P21-22 to determine if NOS inhibition would disrupt the formation of the ACh patches. Control ani mals were studied from the same age groups. Our results show NADPH-d-l abeled cells within the periaqueductal gray and the deep gray layer of SC by P4, the earliest age examined. By P8-P9, cells in the IGL were well labeled by NADPH-d, while few in the superficial layers (SL) were labeled. SL cells were visible by P10 and were intensely labeled by P 14. IGL cells transiently expressed NADPH-d in that the number of labe led cells increased from P8 to P35, then decreased in the adult. ChAT- labeled fibers first appeared in the IGL at P10: formed a characterist ic two-tier pattern by P14, and established obvious patches by P21. In hibition of NOS from birth produced no qualitative differences in the distribution or density of either ChAT-labeled fibers or NADPHd-labele d cells and fibers at any of the ages examined. We therefore conclude that NO does not contribute to the refinement of cholinergic fiber pat ches in the rat SC, probably because the fiber system is not glutamate rgic.