Fig. 3. Representative fluorescence photomicrographs of rainbow trout PCV cross-sections demonstrating (A) the presence of nNOS immuno-positive cells (red) in chromaffin cells [green; areas of colocalization (arrows) appear as orange/yellow] or in close proximity to the chromaffin cells as identified by aldehyde-induced fluorescence. Cell nuclei are indicated by blue fluorescence (DAPI staining). (B) A representative western blot of trout PCV tissue demonstrating the presence of a single immunoreactive band at approximately 150 kDa (lane 1) that was absent after preabsorption of the nNOS antibody with blocking peptide (lane 2). There was no detectable red fluorescence in sections where the primary antibody was omitted (C).