AJP - Regulatory, Integrative and Comparative Physiology, Vol 246, Issue 3 299-R304, Copyright © 1984 by American Physiological Society
Phase-response and Aschoff illuminance curves for locomotor activity rhythm of the rat
T. L. Summer, J. S. Ferraro and C. E. McCormack
A phase-response curve (PRC) for the circadian rhythm of locomotor activity
was constructed for female Sprague-Dawley-derived rats kept in continuous
darkness (DD) except when given a 1-h light pulse (150 lx) once each 2 wk.
By use of the circadian onset of wheel running as the phase-reference
point, the free-running period (tau) in DD was 24.09 h. Maximum phase
delays and phase advances occurred in response to light pulses given during
the first 5 and last 6 h of activity, respectively. The delay-to-advance
ratio (D/A) of the PRC was 1.5. In a separate group of rats exposed to
continuous light, tau increased by 1.45 h as illuminance was increased in
log steps from 0.1 to 10 lx, thus demonstrating the Aschoff effect in rats.
This increase in tau was large, considering the relatively low D/A of the
PRC, suggesting that factors in addition to the D/A contribute to the
Aschoff effect.
