Nitric oxide synthase expression in the opossum superior colliculus: A histochemical, immunohistochemical and biochemical study

The expression of neuronal nitric oxide synthase (nNOS) in the superior col liculus (SC) of the opossum Didelphis marsupialis was studied by NADPH diap horase (NADPH-d) histochemistry and nNOS immunohistochemistry. In addition, the activity of nNOS was quantified by measurement of [H-3]-L-arginine con version to [H-3]-L-citrulline in tissue extracts from SC superficial layers in opossums and rats. Our results show that the number of NADPH-d stained cells was small and virtually identical in stratum opticum (SO) and stratum griseum superficiale (SGS) and their staining was very light, particularly in SGS, Neuropil staining was heavier in the stratum zonale (SZ) than in S GS or SO, The intermediate and deep layers contained heavily stained cells and moderate neuropil staining. Surprisingly, nNOS-immunoreactive cells wer e far more numerous than NADPH-d+ cells in every layer. The production of [ H-3]-L-citrulline from [H-3]-L-arginine in tissue extracts enriched in supe rficial layers indicated that nNOS specific activity is as high in the opos sum as in the rat. Our results suggest that the location of nNOS-expressing neurons in retino-receptive layers may be related to inter-specific differ ences in the processing of visual information. Copyright (C) 2000 S. Karger AG, Basel.