Phase angle changes of photically entrained circadian rhythms following a single nonphotic stimulus.
Syrian hamsters entrained to a light-dark (LD) cycle of 14:10 h were given the opportunity to run in novel wheels for 3 h in the middle of the light phase. This manipulation transiently altered the phase angle of entrainment to the LD cycle: activity onset was significantly advanced (by about 0.5 h) on the day after the pulse and gradually drifted back toward its prepulse time. When animals were held in LD 11.5:12.5 h, a photoperiod in which onset time occurs later relative to the time of lights-off, they again advanced about 0.5 h in response to the pulse of wheel running, but many animals retained an advanced phase angle for at least 7 days, and some for more than 21 days. Individual changes in phase angle were highly correlated with the prepulse phase angle: the more negative the phase angle, the greater the advance subsequent to the novel wheel pulse. These results show that a single, short-duration, nonphotic manipulation can produce long-lasting alterations in the phase angle of entrainment to a LD cycle.
Janik
D
D
Department of Zoology, University of Toronto, Canada.
Godfrey
M
M
Mrosovsky
N
N
D000818:Animals; D001245:Association Learning; D002940:Circadian Rhythm; D006224:Cricetinae; D004193:Discrimination Learning; D008027:Light; D008297:Male; D008647:Mesocricetus; D009043:Motor Activity; D012931:Social Environment; D013998:Time Perception