Fig. 7. Immunocytochemical localization of NO synthase in Y-organ, gill and ovary. Sections were incubated with a universal anti-NOS rabbit antibody (1:1000 dilution; A, B and D) or no primary antibody (C); detection used Vector Red (see Materials and methods). (A) Y-organ (YO). NOS was localized in cytoplasm and nuclei of YO cells. Connective tissue (CT) showed little or no staining. BC, branchial chamber. (B) Gill. The field includes a portion of the central axis (CA) and transverse sections through three lamellae. NOS was localized in the epithelium and pillar cells (arrowheads). The epithelium lining the central axis stained more intensely (arrows). Control sections of Y-organ and gill incubated with either non-immune primary antibody or no primary antibody showed no specific staining (data not shown). Cuticular ridges (CR) keep lamellar surfaces from touching, creating a space for air circulation between gill lamellae. (C) Ovary control (no primary antibody), showing weak non-specific staining in the perinuclear region of oocytes (arrowhead). (D) Ovary. NOS was confined to the perinuclear cytoplasm of oocytes (arrowheads). Scale bars: 400 µm in A, 50 µm in B, and 200 µm in C and D.