This study tested the possible involvement of nitric oxide (NO) in light-adaptive morphological changes in the outer retina of a cyprinid fish, the roach. Isolated retinae were treated in the dark by either of two NO-donor compounds (S-nitroso-n-acetylpenicillamine and sodium nitroprusside) and then studied by light and electron microscopy; similar results were obtained in both cases. Application of NO induced contraction of cone photo-receptor myoids (i.e. retinomotor movements) and formation of horizontal cell spinules. Accordingly the cone index and the spinule/ribbon ratio showed 15-20% and 49-95% change, respectively, compared with controls. These results are consistent with involvement of NO in the light adaptation process in the outer retina of teleost fish.
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Greenstreet et al. (1994) studied this question.