Iezo Nakao

Induction of mammary carcinomas by the direct application of crystalline N-methyl-N-nitrosourea onto rat mammary gland

The effectiveness of the direct application of crystalline N-methyl-N-nitrosourea (MNU) onto the mammary gland was compared with the systemic intraperitoneal (i.p.) administration method for the induction of mammary carcinomas in female Sprague-Dawley (S-D) rats. The effectiveness was also tested in genetically resistant female Copenhagen (Cop) rats. The 10 mg crystalline MNU was dusted directly onto the right-inguinal mammary gland, or 50 mg/kg body weight MNU solution was given i.p. at 50 days of age. Animals were palpated for tumor detection twice weekly and killed when the tumor reached 1-2 cm in diameter or were necropsied 30 weeks after carcinogen treatment. In S-D rats, all of the 78 tumors produced by dusting were adenocarcinomas. By contrast, 40 tumors produced i.p. were adenocarcinomas, 1 was fibroadenoma, and 5 were lactating adenomas. The cumulative incidence of mammary carcinoma was high in the dusting and the i.p. groups (12/12; 100% and 11/13; 84%, respectively). However, the dusting groups showed a high number of carcinoma per rats (6.5 vs. 3.6; P < 0.01) and short cancer latency (13.8 weeks v.s. 28.1 weeks; P < 0.001) than the i.p. groups. In Cop rats, although low (4/11; 36%), adenocarcinomas were developed by the dusting method. In both strains, adenocarcinomas displayed various degrees of differentiation but no evidence was found for metastasis. For MNU-administration, the direct dusting technique is an effective method and offers added advantages of ease for the induction of mammary carcinomas in rats.

A Mixture of Paraphenylenediamine and Imidazole: Its Effect on the Extraction of Lipid Droplets during Electron Microscopy Staining

To prevent extraction of lipids during a double staining procedure for electron microscopy, the tissue slices, double fixed with glutaraldehyde and osmium tetroxide to preserve microvesicular lipid droplets in the cytoplasm, were immersed for 2 hr in veronal buffer (pH 9.0) containing 0.5% p-phenylenediamine and 0.5% imidazole immediately after postfixation. The stained sections of the immersed tissue slice showed blackened, well circumscribed lipid droplets similar to those in corresponding unstained sections. Moreover, highly contrasting features of the cellular architecture could be visualized with the double stained, as well as routinely prepared sections.

Improved Lipid Visualization with a Modified Osmium Tetroxide Method Using Ultrasonic Treatment and Intensification with Imidazole or Triazole

Formalin fixed autopsy tissue containing lipids were cut into 1-5 mm thick blocks, washed well, then postfixed in 2% OsO4 in 0.03 M veronal acetate buffer for 30, 60, 90, 120, or 180 min with or without ultrasonic treatment. Tissues exposed to ultrasound for 90 min showed superior penetration of OsO4 and well preserved histological architecture. Tissues also were immersed for 1 hr in veronal acetate buffer (pH 7.4) containing 0.5% imidazole or triazole and compared with untreated controls. Paraffin sections, 4 microns thick, were examined under a light microscope with an image analyzer. Both intensity and percentage area of osmium blackening were significantly higher in samples immersed in imidazole or triazole than in untreated controls. No difference was observed between imidazole- and triazole-immersed samples. The OsO4 method, modified by ultrasound treatment and imidazole- or triazole-immersion, can be applied to routine formalin fixed autopsy materials for improved lipid visualization.