Nitric oxide synthase-dependent NADPH-diaphorase activity in the optic lobes of male and female Ceratitis capitata mutants

Nitric oxide (NO) is acknowledged as a messenger molecule in the nervous system with a pivotal role in the modulation of the chemosensory information. It has been shown to be present in the optic lobes of several insect species. In the present study, we used males and females from four different strains of the medfly Ceratitis capitata (Diptera, Tephritidae): or; or,wp (both orange eyed); w,M360 and w,Heraklion (both white eyed), as models to further clarify the involvement of NO in the mutants’ visual system and differences in its activity and localization in the sexes. Comparison of the localization pattern of NO synthase (NOS), through NADPH-diaphorase (NADPHd) staining, in the optic lobes of the four strains, revealed a stronger reaction intensity in the retina and in the neuropile region lamina than in medulla and lobula. Interestingly, the intensity of NADPHd staining differs, at least in some strains, in the optic lobes of the two sexes; all the areas are generally strongly labelled in the males of the or and w,M360 strains, whereas the w,Heraklion and or,wp mutants do not show evident sexdependent NADPHd staining. Taken as a whole, our data point to NO as a likely transmitter candidate in the visual information processes in insects, with a possible correlation among NOS distribution, eye pigmentation and visual function in C. capitata males. Moreover, NO could influence behavioural differences linked to vision in the two sexes.