Localization of NADPH-diaphorase and nitric oxide synthase activity in the eyestalk of the crayfish, Procambarus clarkii

The distribution of nitric oxide synthase (NOS) in the eyestalk tissues of the crayfish, Procambarus clarkii, was studied using NADPH-diaphorase (NADPH-d) histochemistry and an NOS biochemical assay. In the retina, NADPH-d activity was detected in the rhabdom of the ommatidium and axons of retinular cells that terminate in the lamina ganglionaris. In the eyestalk ganglia, NADPH-d was localized to the fibers in the 1st chiasma that connect the lamina ganglionaris and medulla externa, and 2 prominent fiber tracts that appear to originate from the medulla terminalis, project distally, and terminate in the synaptic layers of the medulla interna. In addition, NIADPH-d-positive somata were found in the periphery of the medulla externa. Specific staining of NADPH-d activity was eliminated by DPIP, an inhibitor of NOS-associated NADPH-d. The distribution pattern of NADPH-d activity described above is much broader than that of NOS-immunoreactivity reported in a previous study (Lee et al. 2000). Biochemical analysis revealed that the regions (the medulla interna and medulla terminalis) where only NADPH-d activity (but not NOS-immunoreactivity) was detected also contained significant levels of NOS activity, suggesting that the observed NADPH-d activity is associated with NOS. The combined results indicate that, in contrast to a highly restricted pattern suggested by immunohistochemical data, NOS is widely distributed in the crayfish eyestalk and implicates NO in the processing of visual information.