Submitted to: Experimental Gerontology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/17/2001
Publication Date: 10/1/2001
Citation: Casadesus, G., Shukitt-Hale, B., and Joseph, J.A. Automated measurement of age-related changes in the locomotor response to environmental novelty and home-cage activity. Mech. Ageing Develop. 2001, 122: 1887 1897. Interpretive Summary: It probably goes without saying that as we age, we tend to move around less than when were young, but interestingly, what has not been studied to any great extent is what aspects of the activity tend to be reduced and how that might relate to light changes. In other words, what are the "fine grained" changes? In order to better understand this we studied various aspects of motor performance (fine movements, walking around, and rearing up) of young (6 mo) or old (22 mo) rats for 60 hours in standard cages. In the first two hours we made the assumption that this was a "new" environment and the next 58 hrs. were identified as "home cage". As might be expected activity declined in both groups in the first two hours in a new environment. But in addition, the aged rats showed decreases in fine movements during the dark portion of the 12hr/12hr cycle and during the periods from dark to light or light to dark. No age-differences were seen in rearing behavior. Thus, this study provides a more detailed analysis o the age-related declines in activity, especially as it relates to the light cycle.
Technical Abstract: The capacity to explore in an open-field environment decreases with age. Older animals tend to be less active and explore less both in novel and home-cage environments. The locomotor performance (fine movements, ambulatory movements, and rearing) of male Fischer 344 (F344)rats that were 6 (n=6) or 22 (n=6) months of age was evaluated by continuous automated counting of photobeam interruptions, every 30 minutes, during 60 consecutive hours, in standard polycarbonate cages. Novel environment performance was determined by photobeam interruption counting during the first 2 hours in the new cage. The remaining 58 hours were evaluated as home-cage activity. A significant age-related decrease in ambulatory activity was seen during the first 2 hours of the testing (novel environment). In addition, aged rats showed a decreased number of ambulatory and fine movements in home-cage activity, predominately during the dark portion of the light cycle and during both light-switch periods (5:00 am and 5:00 pm). No differences were seen in rearing behavior. These findings provide a more detailed analysis and additional evidence of the activity decreases and circadian rhythm changes seen in aged F344 rats under uninterrupted testing conditions.