Toshikazu Nagato

A Scanning Electron Microscope Study of Myoepithelial Cells in Exocrine Glands

SummaryBy removing connective tissue components with enzymatic digestion followed by HCl-hydrolysis, myoepithelial cells (MECs) of the terminal portion in a variety of exocrine glands of the rat were examined with the scanning electron microscope.The profile of MECs varied considerably from gland to gland; MECs in the lactating mammary gland have a few long cytoplasmic processes in close contact with those of adjacent cells forming a continuous network around the terminal portion. Those of the exorbital lacrimal gland are stellate with many thin radiating processes with tapered ends that terminate freely. MECs in the sublingual gland are characterized by a number of broad and extensive cellular processes. MECs in the submandibular gland are similar in appearance to those of the exorbital lacrimal gland, but with more extensive cellular processes that form a more or less continuous network with those of the adjacent cells. No MECs were observed on the terminal portion of the parotid gland where the cells appear to be lodged on the intercalated duct.The relative surface area covered by MECs per terminal portion was also found to vary significantly, being 24% in the lactating mammary, 17% in the exorbital lacrimal, 48% in the sublingual, and 25% in the submandibular glands.The findings are discussed in relation to the physical properties of secretions in different glands.

Effect of parasympathectomy on the histochemical maturation of myoepithelial cells of the rat sublingual salivary gland

This effect of parasympathectomy was assessed by fluorescent microscopy using nitrobenzoxadiazole-phallacidin, which is known for its specific binding to actin filaments. Resection of the chorda tympani within 48 h after birth inhibited the normal formation of actin in the myoepithelial cells and the maturation of myoepithelial cells. The effect of denervation decreased progressively if the operation was delayed. Denervation 30 days after birth had no effect on development and differentiation of myoepithelial cells. Moreover, the procedure produced no histochemical changes in the myoepithelial cells in mature rats, even two months later. These findings suggest that the parasympathetic innervation is closely involved in the maturation of myoepithelial cells. Further, its involvement is limited to the first 48 h after birth, during which it exerts its neurotrophic effect on the myoepithelial cells present in all the acinar buds.

Lipid droplet accumulation and lipoprotein lipase activity in the rat salivary gland during the perinatal period

The submandibular and sublingual glands of foetal and newborn rats aged 21 days in utero to 7 days after birth were examined morphologically and biochemically. Lipid droplets tended to be localized in secretory cells, especially in their basal cytoplasm. The degree of droplet accumulation varied with the age of the rat. No droplets were observed before and immediately after birth. The number of accumulated droplets peaked 24-48 h after birth, then gradually decreased and reached normal levels by 5 days. In the salivary glands of fasted newborn rats, no lipid droplets were observed throughout the experiment. The amount of triacylglycerol reached its maximum level 1 day after birth; it then decreased gradually until 5 days and after that did not change. The amount of cholesterol did not change during postnatal development. Lipase activity attained its maximum level in the salivary glands immediately after birth and then decreased rapidly. It was higher in the glands of fasted than fed 1-day-old rats. Antiserum against lipoprotein lipase inhibited the salivary gland lipase activity in a dose-dependent manner, with 5 microliters of antiserum producing 60-70% inhibition. Non-immune serum had little effect. It was concluded that (1) accumulated lipid in the secretory cell cytoplasm of the salivary glands originates from ingested milk; (2) the principal component of accumulated lipid droplets is triacylglycerol; (3) 60-70% of the total lipase activity represents lipoprotein lipase; (4) an increase of lipoprotein lipase activity is recognizable before the accumulation of triacylglycerol.

Morphological changes in the myoepithelial cells of the rat sublingual salivary gland during differentiation as shown by the nitrobenzoxadiazole-phallacidin fluorescent method

Changes in myoepithelial cells (MECs) during perinatal development were examined by using the fluorescent probe for actin, nitrobenzoxadiazole (NBD)-phallacidin. By the twentieth day of gestation, there was no distinct fluorescent pattern suggestive of MECs. In newborn and 1-day-old rats, cells with diffuse fluorescence occurred around the acini, representing incipient MECs. Between 3 and 4 days after birth, actin staining was concentrated in strands which were arranged parallel to the long axis of the cell processes. MECs had developed further by the tenth day after birth with an increased number and thickness of their processes. Fully developed MECs were found between the thirtieth and fortieth day. These were stellate and encompassed individual acini.

Scanning electron microscopy of 7,12-dimethylbenz(a)-anthracene-induced mammary carcinoma in the female Sprague-Dawley rat

SummaryThe surface morphology of normal mammary glands and mammary carcinomas was examined under the scanning electron microscope after digestion of connective tissue and the basal lamina with collagenase, hyaluronidase and hydrochloric acid (HC1).Two types of cells were clearly identified in the acini of normal glands; granular epithelial cells and stellate myoepithelial cells. Spindle-shaped myoepithelial cells lying longitudinally along the mammary ducts were also recognized.7, 12-dimethylbenz(a)anthracene-induced mammary carcinomas consisted or irregular masses of cells which had polypoid or columnar processes with rounded heads; the masses appeared to be composed of a single type of rhomboid cell. The tumors lacked the stellate or spindle-shaped myoepithelial cells found in normal acini and ducts.