Nitric oxide synthase distribution in the cat superior colliculus and co-localization with choline acetyltransferase

Nitric oxide and acetylcholine are important neuromodulators implicated in brain plasticity and disease. We have examined the cellular and fiber local ization of nitric oxide in the cat superior colliculus (SC) and its degree of co-localization with ACh using nicotinamide adenine dinucleotide phospha te diaphorase (NADPHd) histochemistry and an antibody to neuronal nitric ox ide synthase. ACh was localized using an antibody against choline acetyltra nsferase. We also made injections of biocytin into the region of the parabr achial brainstem to confirm that this region is a source of nitric oxide co ntaining fibers in SC. NADPHd labeled neurons within the superficial layers of the superior colliculus included pyriform, vertical fusiform, and horiz ontal morphologies. Labeled neurons in the intermediate gray layer were sma ll to medium in size, and mostly of stellate morphology. Neurons in the dee pest layers had mostly vertical or stellate morphologies. NADPHd labeled fi bers formed dense patches of terminal boutons within the intermediate gray layer and streams of fibers within the deepest layers of SC. Choline acetyl transferase antibody labeling in adjacent sections indicated that many fibe rs must contain both labels. Over 94% of neurons in the pedunculopontine te gmental and lateral dorsal tegmental nuclei were also labeled by both NADPH d and choline acetyltransferase. In addition, biocytin labeled fibers from this region were localized in the NADPHd labeled patches. We conclude that nitric oxide is contained in a variety of cell types in SC and that both ni tric oxide and ACh likely serve as co-modulators in this midbrain structure . (C) 2000 Elsevier Science B.V. All rights reserved.