Changes of estrous cycles with aging in female F344/n rats.

Changes of estrous cycles with aging of F344/N rats between 1 and 30 months of age (M) were monitored by vaginal smear cytology. The vaginal opening and first cornified cell phase were identified at 1.3 +/- 0.1 M and 1.5 +/- 0.2 M, respectively. Thereafter, estrous cycles showed about 5-day intervals, and ceased at 16.4 +/- 1.2 M. Thereafter irregular appearance of single cornified cell phases without the preceding of nucleated cell phases interspersed with a predominant leukocyte phase was seen in vaginal smears until 26.9 +/- 0.5 M. Growing and mature follicles as well as corpora lutea persisted until at least 30 M, and characterized the post reproductive aging of F344/N females. The F344/N rats seem to resemble humans in that the cessation of estrous cycles occurs at approximately half their entire lifespan. However, other aging characteristics are unknown in postmenopausal women. Therefore, we must be careful when extrapolating the aging changes of reproduction in F344/N rats to human beings.

Aging changes in the periodontal bone of F344/N rat.

The aim of this research was to determine whether a rat was an adequate laboratory animal model for periodontal research on elderly humans. Thirty-two F344/NSlc female rats ranged between 30 and 1000 days of age were used. The alveolar bone loss around the molars was assessed by a morphometric method. A significant correlation was found between age and the amount of alveolar bone loss. For further analysis, the rats were grouped into four by age; 30-60 days, 220-430 days, 640-850 days, and more than 850 days. The means of alveolar bone loss were compared between age groups. It was found that the resorption of the alveolar bone around the molars of the rats continued until they were 1000-days-old, and this trend was stronger in the mandible than the maxilla. It was suggested that rats could be used as adequate laboratory animals for periodontal research.

Effects of diet on the incidence of dental pathology in free living caviomorph rodents.

Examinations of dental pathology in five genera of caviomorph rodents found caries and periodontal disease in both grazers and frugivores, although the prevalence differed between the two groups. Caries was more prevalent in the frugivores (10.5-19.8%) than in the grazers (1.1-8.7%); mild periodontal disease occurred occasionally in the grazers (5.6-8.7%), but was almost absent in the frugivores (0.0-1.3%). The consistent findings of caries and periodontal disease suggest that ecological differences between the two related groups, and the subsequent dietary differences, are important in determining the incidence of dental pathology.

Dental and skull anomalies in feral coypu, Myocastor coypus.

The study of dental and skull abnormalities of wild animals can provide useful information for comparative studies. Although studies of captive and laboratory rodents have been published, there are few reports on wild populations. We examined anomalous and pathological conditions in the skulls of feral coypus, Myocastor coypus, from Aichi Prefecture, Japan, and identified the types of abnormality. Of the 203 coypu skulls of various ages examined, 19 specimens (9.4%) had abnormalities. A total of 23 anomalies were divisible into three categories: dental diseases, dental injuries and skull injuries. Seven specimens (3.4%) had evidence of periodontal disease in the cheek teeth, and one specimen (0.5%) had caries. Seven specimens (3.4%) had broken upper or lower incisors. Four specimens (2.0%) had injured cranial bones and three (1.4%) had fractures near the zygomatic arch. A single specimen (0.5%) had a deformed rostrum. No statistically significant differences between the genders were found in any category (chi2 test: P < 0.05). The incidence of dental disease appeared to be related to the biological characteristics of this species, i.e., long lifespan, herbivorous diet and molar crown morphology. By contrast, dental and skull injuries appeared to be due to trauma caused when farmers attacked feral coypus.