Rhythm chronotypes in a diurnal rodent, octodon degus.
Labyak, Susan E., Theresa M. Lee, and Namni Goel.
School of Nursing and Department of Psychology, University of
Michigan, 525 E., University Ave., Ann Arbor, MI 48109-1109
APStracts 4:0208R, 1997.
Interindividual variations in entrained human circadian rhythms and
their relationship to differences in ease of adjustment to phase
-shifts have been well described. Humans classified as `morning type'
(MT) display phase advanced temperature minimum, onset of daily
activity and onset of sleep, whereas `evening type' (ET) individuals
demonstrate the opposite pattern with a later phase angle of
entrainment for these measures. We examined 15 variables of circadian
activity and temperature for diurnal Octodon degus (n=49; 28 male, 21
female), and noted similar chronotype variations as described for
humans. Individuals with extreme MT and ET chronotypes were
identified as those that differed from the entire population mean by
one or more standard deviations. Compared with MTs (n=5) and ITs
(`intermediate chronotype', n=34), ETs (n=10) displayed a significant
delay in the phase of temperature minimum, rise in temperature above
the daily mean, and decline in activity and temperature below the
daily mean, and had longer elevated activity and temperature
durations ([alpha]), and higher levels of mean daily activity and
activity amplitude. MTs also displayed a significant phase advance in
the morning temperature rise compared with ITs and ETs. This is the
first description of variation in entrained circadian rhythms similar
to that described for humans in both an outbred animal population and
a diurnal rodent.
Received 16 August 1996; accepted in final form 30 April 1997.
APS Manuscript Number R501-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 11 June 1997