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ABSTRACT. The histological characteristics of 9 cases of granular cell tumors (GCTs) observed in B6C3F 1 mice were examined to determine their cellular origin. Seven of the 9 cases were found in the uterus and other 2 cases were in the subcutaneous tissue. Tumor cells had abundant granules in the cytoplasm which were stained with PAS and were resistant to diastase treatment. Ultrastructurally, the granules were identified as lysosomes. The cell surface had cytoplasmic processus showing interdigitation with adjacent cells. A character feature of the tumor cells was the presence of a desmosome-like structure on their cell surface but no basal lamina was demonstrated. Although GCTs have been considered to be derived from Schwann cells on the basis of their ultrastructural features and S-100 proteinimmunopositive findings, the absence of basal lamina in the present cases may raise a controversy as to their origin. KEY WORDS: B6C3F 1 mouse, granular cell tumor.

Morphogenesis of craniopharyngeal derivatives of the neurohypophysis found in 14 Fischer 344 (F344) rats was studied. The incidence of the craniopharyngeal derivatives was 0.17% in male (7 out of 4,200) and 0.16% in female (7 out of 4,450) F344 rats. Neither a sexrelated difference in their incidence nor a strain-related difference in their morphological features was observed. Craniopharyngeal derivatives were composed of aberrant epithelial structures consisting of serous acinar and tubular and fusiform cell structures, and most of these derivatives were associated with Rathke's cleft cysts, which are suggestive of a congenital background. The acinar structures were positive for periodic acid-Schiff reaction and negative for Alcian blue stain. Immunohistochemically, cells forming these structures were positive for cytokeratin, and basal cells of the acinar or tubular structures and some of the fusiform cells showed positive staining for alpha-smooth muscle actin. Electron microscopically, these spindle-shaped basal cells had intracytoplasmic myofilaments with focal density in their cytoplasm, and they were regarded to be myoepithelial cells. These findings strongly indicate that the craniopharyngeal derivatives are not a neoplastic lesion but rather are a developmental aberration derived from the stomatodeum, which is known to be the origin of both nasal and oral epithelial tissues, including the parotid glands, other than Rathke's pouch.

The genotoxicity of multi-walled carbon nanotubes (MWCNTs) was evaluated in vivo with comet assays using the lung cells of rats given MWCNTs. The MWCNTs were intratracheally instilled as a single dose at 0.2 or 1.0 mg kg(-1) or a repeated dose at 0.04 or 0.2 mg kg(-1) , once a week for 5 weeks, to male rats. The rats were sacrificed 3 or 24 h after the single instillation and were sacrificed 3 h after the last instillation in the repeated instillation groups. Histopathological examinations of the lungs revealed that MWCNTs caused inflammatory changes including the infiltration of macrophages and neutrophils after a single instillation and repeated instillation at both doses. In comet assays using rat lung cells, no changes in % Tail DNA were found in any group given MWCNTs. These findings indicate that MWCNTs do not have the potential to cause DNA damage in comet assays using the lung cells of rats given MWCNTs at doses causing inflammatory responses.

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