Fibroma (myxoma) molle in a hamster (Mesocricetus auratus).

An adult female Syrian hamster (Mesocricetus auratus) presented with a large, ulcerated lesion in its right cheek pouch; this wound interfered with the animal's ability to masticate. As a result, the hamster became inappetant and lethargic and lost about 25% of its original body weight within 6 to 9 weeks of presentation. The mass was surgically excised and submitted for histopathological evaluation. Microscopically, the mass was characterized as a neoplastic process partially encapsulated with fibrous connective tissue in the submucosa. Loosely arranged bundles of spindle to stellate cells with round to oval hyperchromatic nuclei and amphophilic cytoplasm were abundant. Some cells had multiple nucleoli, and some mitotic figures were observed. Special stains were used to definitively diagnose fibroma (myxoma) molle, a rare spontaneous neoplastic lesion in the hamster.

Subchronic sodium chlorate exposure in drinking water results in a concentration-dependent increase in rat thyroid follicular cell hyperplasia.

Chlorine dioxide (ClO2) is an effective drinking water disinfectant, but sodium chlorate (NaClO3) has been identified as a potentially harmful disinfection by-product. Studies were performed to describe the development of thyroid lesions in animals exposed to NaClO3 in the drinking water. Male and female F344 rats and B6C3F1 mice were exposed to 0, 0.125, 0.25, 0.5, 1.0, or 2.0 g/L NaClO3 for 21 days. Additional male F344 rats were exposed to 0, 0.001. 0.01. 0.1, 1.0. or 2.0 g/L NaClO3 for 90 days. Female F344 rats were exposed to 0, 0.5, 1.0, 2.0, 4.0, or 6.0 g/L of NaClO3 for 105 days. Thyroid tissues were processed by routine methods for light microscopic examination, and follicular cell hyperplasia was diagnosed using a novel method. Thyroid hormone levels were altered significantly after 4 and 21 days. NaClO, treatment induced a concentration-dependent increase in the incidence and severity of thyroid follicular cell hyperplasia. Male rats are more sensitive to the effects of NaClO3 treatment than females. Follicular cell hyperplasia was not present in male or female B6C3F1 mice. These data can be used to estimate the human health risk that would be associated with using ClO2, rather than chlorine, to disinfect drinking water.

Husbandry factors and the prevalence of age-related amyloidosis in mice.

A retrospective study of the prevalence of amyloidosis in mice from several facilities was done. Amyloid deposition is an age-related lesion. The influence of common laboratory factors on the occurrence of this lesion was analyzed. This study documented genotypic difference in susceptibility to amyloidosis and showed that caging and pathogen status both impact on the number of cases of amyloidosis seen in a population. The lowest percentage of affected mice was seen when the animals were individually caged in a specific pathogen-free facility where conditions of stress were minimized.

Pulmonary tumor colony formation following i.v. inoculation of six human colorectal carcinoma xenografts in young gnotobiotic athymic mice.

The lung colonizing potential of 6 xenografted human colorectal adenocarcinomas following tail vein inoculation of tumor cell suspensions into gnotobiotic 3-4-week-old congenitally athymic mice was investigated. One of the lines, CRCo2, was of particular interest, as apparently distinctive lung colonizing phenotypes, large (greater than 2.5 mm diameter) and small (less than 1 mm diameter) colonies were identified, and variant lines with greater, equal, or lesser ability to grow in the lungs relative to the sc tumor of origin were observed. Another line, CRCo1, was also able to grow well in the lungs following tail vein inoculation, but subsequent cycles of lung tumor recovery and reinoculation i.v. did not result in an enhancement of the tumor's lung colonizing ability relative to the initial i.v. inoculation of the sc carried tumor. Scattered lung colonies were observed following i.v. inoculation of sc carried xenografts in three of the four other lines, but we could not consistently recover lung colonies with these tumors. The data are in accord with the clinical observation that pulmonary metastasis is not a high frequency event in human colorectal carcinoma, illustrating the selective nature and experimental utility of this model of metastasis. Further, there were indications of the inefficient and/or random nature of the metastatic process in some of the tumors, while in others, evidence for both effectively higher and lower metastatic variants were found, as might be predicted in heterogeneous tumor cell populations.

Metastatic potential of four human melanoma xenografts in young athymic mice following tail vein inoculation.

We have investigated the lung colonizing ability of four newly established human metastatic melanoma xenografts, designated CRML1, CRML2, CRML3, and CRML4 following i.v. tail vein inoculation into 3- to 4-week-old gnotobiotic CD-1 athymic mice. The experimental metastatic potential of the tumors was assessed from the primary tumor samples through eight progressively growing s.c. passages. CRML1 and 2 were investigated in detail; five sublines (two from CRML1 and three from CRML2) were established from these tumors with various growth rates and lung colonizing abilities. The histopathologies of the patients' biopsies and the s.c. passaged parental lines were compared with these i.v.-derived sublines as one measure of tumor heterogeneity, in conjunction with the kinetics of lung tumor formation. The frequency and distribution of extrapulmonary tumor growth was also investigated after i.v. inoculation. In general, it reflected the clinical distribution of metastases, although their frequency of appearance was reduced. While CRML3 was the most aggressive disease clinically, it did not demonstrate the reproducible experimental metastasis of the other lines. CRML4 produced lung colonies routinely, but with latency periods of 20 weeks or more. On the other hand, the most rapidly growing sublines of CRML1 and CRML2 essentially replaced the normal lung tissue within 4 to 6 weeks following inoculation of 10(5) cells. The two sublines of CRML1 with higher effective metastatic potential were maximally able to colonize the lungs within only two i.v. cycles in one case, while the other line required six i.v. to i.v. passages to reach its maximum ability. In CRML2, two sublines were identified that rapidly increased in their lung colonizing ability, while another line remained effectively equal to the parental s.c. line over four cycles of reinoculation i.v. These results demonstrated that the athymic mouse can serve as a model for experimental metastasis of human tumors, and that aspects of the metastatic heterogeneity of these tumors can be investigated by using this system.

Pathogenesis of feline gastric chlamydial infection.

Studies were conducted to determine whether the gastric chlamydiae that have been observed recently in cats are of pathologic significance. Chlamydiae were isolated in mouse L cell cultures from the homogenized pooled gastric mucosa of 3 cats that had been identified, by histopathologic examination, to have gastric chlamydiosis. Ten specific-pathogen-free kittens were exposed by aerosol and oral inoculation to the harvested feline gastric chlamydiae cell-culture media. In general, the clinical signs and lesions were conjunctivitis, rhinitis, and mild gastritis. The clinical signs and lesions were most severe in 2 chlamydia-infected kittens that had received methylprednisolone acetate (50 mg/kg of body weight). Chlamydiae were demonstrated in epithelial cells of conjunctival and nasal smears in 10 of 10 infected kittens from postexposure days 7 through 35. In addition, chlamydiae were isolated in L cell cultures from a variety of antemortem and postmortem specimens from infected kittens. The present study provided evidence that feline gastric chlamydiae, under appropriate conditions, were capable of inducing, in cats, clinical signs and lesions similar to those induced by the feline pneumonitis agent.

Chlamydial infection of the gastric mucosa in twelve cats.

Twelve cats, all from research or commercial breeding colonies, had unidentified, intracellular organisms in the gastric mucosa. Histochemical staining and ultrastructural features provided the basis for identification of the organism as a Chlamydia sp. Ultrastructural observations were restricted to one of the 12 infected cats. There was no consistent association of gastric chlamydial infection and clinical disease. The infection was present in apparently healthy cats as well as those with a variety of clinical signs and lesions, especially weight loss of undetermined origin. None of the cats with gastric chlamydial infection had lesions compatible with feline pneumonitis. The significance of gastric chlamydial infection has yet to be established.