Mature and developing visual system of Ceratitis capitata (Diptera, Tephritidae): histochemical evidence of nitric oxide synthase in the wild type and the white eye mutant strains

Nitric oxide (NO) is acknowledged as a messenger molecule in the nervous sy stem. It has a role in the modulation of the chemosensory information and s eems implicated also in visual processes and visually guided behaviour of s ome insects. In the present study, we used two different strains of the med fly Ceratitis capitata (Diptera, Tephritidae), a wild type eye colour and a white eye mutant line, as models to clarify the involvement of NO in the m ature and developing visual system. The comparison between the pattern of e nzyme histochemical localization of NO synthase (NOS), through NADPH diapho rase (NADPHd) staining, in the optic lobes of the two strains revealed fur adults a stronger intensity of reaction in all the neuropiles and the sub-r etinic monopolar cell layer of the wild type flies, with respect to the whi te eye mutant correspondent areas. Anti-NOS immunocytochemistry correlated with these results, underlying reactivity both in fine fibres and varicosit ies and in cell bodies and supporting the idea of presence of NOS also in t he retina of the medfly optic lobes. NADPHd reactivity was present in the f irst developmental stages of the white eye mutant also, but at lower intens ity than wild type, and it decreased in some areas during the transition to adult fly stage both in the wild type and in the white eve mutant. All the se observations together indicate that changes in the NO system of C. capit ata could be related to the visual information processing, when the visual response or discrimination are altered. Furthermore, NO may be involved in the establishment of the retinal projection pattern and in the control of o ptic lobes morphogenesis. (C) 1999 Elsevier Science B.V. All rights reserve d.