Age-related disruptions in circadian timing: Evidence for "split" activity rhythms in the SAMP8

J. Devin McAuley, Jonathan P. Miller, Eric Beck, Z. Michael Nagy, Kevin C.H. Pang

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23 Scopus citations


In the senescence-accelerated mouse of the P8 line (SAMP8), age-related changes in circadian timing include a decrease in amplitude of the rhythm, a slower rate of re-entrainment following a phase advance, and a longer free-running period (τ). The present study extends previous research by investigating possible split activity rhythms in the SAMP8. Running wheel activity was examined in 2-, 7-, and 12-month SAMP8. Consistent with previous research, rhythms of older SAMP8 were decreased in amplitude and showed high levels of activity during the light phase of the light-dark cycle. Contrary to previous reports, lengthening of τ in constant darkness was not observed. Additionally, activity rhythms were "split" in older SAMP8, demonstrated by 1) the appearance of a secondary peak in the periodogram at approximately half the value of τ and 2) the perceptual classification of actograms by naïve observers. This result differs from previous studies in hamsters demonstrating an age-related decrease in the incidence of rhythm splitting. Overall, the present findings provide further evidence for age-related disruption of circadian timing in SAMP8.

Original languageEnglish (US)
Pages (from-to)625-632
Number of pages8
JournalNeurobiology of Aging
Issue number4
StatePublished - Jan 1 2002
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Neuroscience(all)
  • Aging
  • Clinical Neurology
  • Developmental Biology
  • Geriatrics and Gerontology


  • Aging
  • Circadian rhythms
  • SAMP8
  • Senescence-accelerated mouse
  • Split activity rhythms

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