ALTERED LIGHT DARK ACTIVITY DIFFERENCE WITH AGING IN 2 RAT STRAINS

The daily activity rhythm of adult and senescent male rats of two different strains (Iva:SDIV and Emd:Wi-AF/Han) was evaluated over several days with a capacitance-induction motility monitor. The Iva:SDIV rats were 6 to 9 or 29 to 32 months old and the Emd:Wi-AF/Han rats were 3 to 5, 16 to 18, or 31 to 39 months old at the time of testing. The rats were maintained in individual cages under a 12:12 hr light/dark regimen prior to and during this experiment. Senescent rats were much less active during the dark phase and somewhat more active during the light phase than same-strain young adult rats. This pattern of results was found for measurement of gross and fine movements combined (high sensitivity setting) and to a lesser extent for gross movements alone (low sensitivity setting). Furthermore, in the senescent rats the absolute magnitude of the light/dark activity difference was found to be positively related to the subsequent survival time.