Automated measurement of age-related changes in the locomotor response to environmental novelty and home-cage activity

The likelihood to explore in an open-field environment decreases with age. Older animals tend to be less active and explore less both in novel and hom e-cage environments. The locomotor performance (fine movements, ambulatory movements, and rearing) of male Fischer 344 (17344) rats that were 6 (n=6) or 22 (n=6) months of age was evaluated by continuous automated counting of photobeam interruptions, every 30 min, during 60 consecutive hours, in sta ndard polycarbonate cages. Novel environment performance was determined by photobeam interruption counting during the first hour in the new cage. The remaining 59 h were evaluated as home-cage activity. A significant age-rela ted decrease in ambulatory and fine motor activity was seen during the firs t hour of testing (novel environment). In addition, aged rats showed a decr eased number of ambulatory and fine movements in home-cage activity, predom inately during the dark portion of the light cycle and during or around bot h light-switch periods (05:00 and 17:00). No differences were seen in reari ng behavior. These findings provide a more detailed analysis and additional evidence of the activity decreases and rhythmic changes seen in aged F344 rats under uninterrupted testing conditions. Published by Elsevier Science Ireland Ltd.