Phase-response and Aschoff illuminance curves for locomotor activity rhythm of the rat.
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.
D000818:Animals; D002940:Circadian Rhythm; D005260:Female; D008954:Models, Biological; D009043:Motor Activity / Q000502:physiology*; D051381:Rats / Q000502:physiology*; D011919:Rats, Inbred Strains