Fig 2: Transmission electron microscopy of nNOS immunostaining in human salivary glands, visualized using the immunogold technique (a–c). a High-magnification image of the apical portion of striated ductal cells in the parotid gland. b, c High-magnification details of the basal portion of striated ductal cells in the parotid gland, showing gold particles associated with basal folds and mitochondria. L, lumen; P, parotid. Scale bar 1 µm (a–c)

Fig 3: Transmission electron microscopy of nNOS immunostaining in human submandibular glands (SM), visualized using the immunogold technique (a, b). a High-magnification image of the apical portion of the epithelial lining of striated ducts, showing heterogeneous labeling. Some cells show sparse immunolabeling (asterisks). b Basal portion of striated ductal cells with immunogold labeling observed in mitochondria and nuclei. N, nucleus. Scale bar 1 µm (a, b)

Fig 4: Light microscopy of nNOS immunostaining in human salivary glands. a, b Parotid gland (P); e–h Submandibular gland (SM). nNOS immunolabeling is present in serous acinar cells of the parotid (c, d) and submandibular glands (e–h), as well as in submandibular serous demilunes (e, f) (arrowheads) and ducts (c–f, h) (asterisks). nNOS-immunostained nerve fibers (arrows) are observed as bundles of varying caliber running in the stroma (e), as individual fibers (e), or as coarse terminals near serous (d, g) and mucous (g) secretory cells, or as arrays of thin dot-like terminals placed against the duct walls (h). a, b Hematoxylin and eosin staining and f Carazzi’s hematoxylin counterstaining. i Negative control for immunostaining. Scale bars: 100 µm (a, b, c, e); 50 µm (d, f, h, i); 20 µm (g)