Light-induced phase shifts in tau mutant hamsters.
Phase shifts produced by single 1-hr light pulses were compared in homozygous tau mutant and wild-type hamsters after several different kinds of pretreatment regimens. There was a dramatic increase in the magnitude of phase delays in the mutant hamsters as they were kept for progressively longer times in constant darkness (DD), and a smaller increase in the magnitude of phase advances. Under the same conditions a small increase in the magnitude of phase delays and no significant increase in phase advances occurred in the wild-type hamsters. After only 7 days in DD the phase response curves (PRCs) of mutant and wild-type hamsters were both type 1 and were indistinguishable from each other, whereas after 49 days in DD the PRCs of mutant hamsters had become type O. Mutant hamsters were entrained to eight different T-cycles (1 hr of light per cycle), released into DD, and given a phase delaying light pulse 7 days later. T-cycles which entrained the animals so that the 1 hr of light fell between 6 and 9 hours after the onset of activity suppressed the amplitude of phase delays, whereas T-cycles which entrained the animals so that the 1 hr of light fell at other times did not suppress phase delays. The implications of the data for entrainment theory and the mechanism of action of the tau gene are discussed.
Shimomura
K
K
NSF Center for Biological Timing, University of Virginia, Charlottesville 22903.
Menaker
M
M
D000818:Animals; D002940:Circadian Rhythm / Q000235:genetics* / Q000502:physiology / Q000528:radiation effects*; D006224:Cricetinae; D003624:Darkness; D006720:Homozygote; D008027:Light; D008297:Male; D008647:Mesocricetus; D009154:Mutation; D010775:Photic Stimulation; D017440:Photoperiod; D011930:Reaction Time