Age-Associated Behavioral Alterations in Laboratory-Housed Octodon degus

Octodon degus are long-lived, diurnal, and highly social rodents increasingly used in studies of aging and neurodegeneration. However, behavioral profiles of aged laboratory-housed degus remain incompletely characterized, limiting the interpretation of aging-associated functional and molecular phenotypes in this species. Here, we evaluated age-associated changes in locomotor activity, open-field exploration, social novelty behavior, and manually scored ethological responses in young and old degus maintained under long-term laboratory housing conditions. Automated behavioral tracking was performed during open-field testing and three-chamber social behavior testing. During open-field testing, old degus showed increased locomotor activity compared with young animals, including greater total distance moved, higher mean velocity, increased moving frequency, and longer cumulative movement duration. Old degus also showed increased center-zone duration and reduced thigmotaxis score. Manual ethological scoring revealed increased rearing and fecal boli in old animals during open-field exposure. In the three-chamber social behavior assay, young degus showed higher investigation frequency toward the novel intruder than toward the familiar cagemate, whereas old degus showed a lower social novelty discrimination index compared with young animals. Exploratory sex-stratified analyses identified selective differences in center-border exploration in the young cohort: young males spent more time in the center zone and showed lower thigmotaxis than young females, whereas no significant sex-associated differences were detected in the other open-field or social novelty measures examined. Together, these findings indicate that aging in laboratory-housed degus is associated with a mixed behavioral profile involving increased stress-related ethological responses and reduced social novelty discrimination, affecting behavioral domains relevant to dementia and neurodegenerative aging. This behavioral framework provides a practical reference for future studies examining behavioral heterogeneity and molecular or neuropathological correlates of brain aging in degus.