Acute light exposure suppresses circadian rhythms in clock gene expression.
Light can induce arrhythmia in circadian systems by several weeks of constant light or by a brief light stimulus given at the transition point of the phase response curve. In the present study, a novel light treatment consisting of phase advance and phase delay photic stimuli given on 2 successive nights was used to induce circadian arrhythmia in the Siberian hamster ( Phodopus sungorus). We therefore investigated whether loss of rhythms in behavior was due to arrhythmia within the suprachiasmatic nucleus (SCN). SCN tissue samples were obtained at 6 time points across 24 h in constant darkness from entrained and arrhythmic hamsters, and per1, per2 , bmal1, and cry1 mRNA were measured by quantitative RT-PCR. The light treatment eliminated circadian expression of clock genes within the SCN, and the overall expression of these genes was reduced by 18% to 40% of entrained values. Arrhythmia in per1, per2, and bmal1 was due to reductions in the amplitudes of their oscillations. We suggest that these data are compatible with an amplitude suppression model in which light induces singularity in the molecular circadian pacemaker.
Department of Biology, Stanford University, Stanford, CA, USA.
Brian P
BP
Grone
Doris
D
Chang
Patrice
P
Bourgin
Vinh
V
Cao
Russell D
RD
Fernald
H Craig
HC
Heller
Norman F
NF
Ruby
D000818:Animals; D001145:Arrhythmias, Cardiac; D001683:Biological Clocks; D056926:CLOCK Proteins / Q000235:genetics*; D002940:Circadian Rhythm; D006224:Cricetinae; D005786:Gene Expression Regulation; D006801:Humans; D008027:Light; D009991:Oscillometry; D017111:Phodopus; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013493:Suprachiasmatic Nucleus / Q000502:physiology*; D013997:Time Factors
D012333:RNA, Messenger; D056926:CLOCK Proteins