New features of the locust optic lobe: evidence of a role for nitric oxide in insect vision

The enzyme nitric oxide synthase can be localised by NADPH-diaphorase histochemistry. Here we have applied this technique to the optic lobe of the locust Schistocerca gregaria and revealed new features of the insect visual system. Extensive but locally intense staining is associated with identified tracts, distinct neuropiles and cell body groups, and a detailed analysis of stained elements is provided here. The most striking staining occurs in the anterior lobe of the lobula complex and its connection with the medulla by means of the dorsal uncrossed bundle. Eleven groups of cell bodies are identified and their contribution to fibre tracts and neuropile areas is described. Diaphorase-positive fibre tracts pass between all major subdivisions of the optic lobe, but there are no conspicuous fibre connections from the optic lobe to the brain. The widespread distribution of NADPH-diaphorase staining in the optic lobe suggests that nitric oxide is likely to play an important role in information processing in insect vision.