Phase-delay in the light-dark cycle impairs clock gene expression and levels of serotonin, norepinephrine, and their metabolites in the mouse hippocampus and amygdala.
OBJECTIVE
A number of animal studies have implicated circadian clock genes in the regulation of mood, anxiety, and reward. However, the effect of misalignment of the environmental light-dark and internal circadian clock on the monoamine system is not fully understood. In the present study, we examined whether an abnormal light-dark schedule would affect behavior-, circadian clock-, and monoamine-related gene expressions, along with monoamine contents in the amygdala and hippocampus of mice.


METHODS
Mice were subjected to an 8-hour phase delay in the light-dark cycle (Shift) every two days for four weeks, and locomotor activity was continuously measured. We examined the circadian expression of clock genes (Per1, Per2, and Bmal1) and genes of the NE/5HT uptake transporters (Net and Sert). In addition, the levels of NE/5HT and their metabolites MHPG/5HIAA were analyzed in the amygdala and hippocampus.


RESULTS
Locomotor activity showed a free-running phenotype with a longer period (>24 hours) and showed misalignment between the light-dark and inactive-active cycles. The amplitude of the day-night fluctuation of Bmal1 expression was reduced in the amygdala and hippocampus of light-dark-shifted mice. Net gene expression in the Shift group showed different profiles compared with the Control group. In addition, NE and 5HT levels in the amygdala of the Shift group increased during the active period.


CONCLUSIONS
The present results suggest that misalignment of the internal and external clocks by continuous shifting of the light-dark cycle affects the circadian clocks and monoamine metabolism in the amygdala and hippocampus of mice.
Laboratory of Physiology and Pharmacology, School of Advanced Science and Engineering, Waseda University, Shinjuku-ku, Tokyo, Japan; Department of Psychiatry, School of Medicine, Tokyo Women's Medical University, Shinjuku-ku, Tokyo, Japan.
Shunpei
S
Moriya
Laboratory of Physiology and Pharmacology, School of Advanced Science and Engineering, Waseda University, Shinjuku-ku, Tokyo, Japan.
Yu
Y
Tahara
Laboratory of Physiology and Pharmacology, School of Advanced Science and Engineering, Waseda University, Shinjuku-ku, Tokyo, Japan.
Hiroyuki
H
Sasaki
Department of Psychiatry, School of Medicine, Tokyo Women's Medical University, Shinjuku-ku, Tokyo, Japan.
Jun
J
Ishigooka
Laboratory of Physiology and Pharmacology, School of Advanced Science and Engineering, Waseda University, Shinjuku-ku, Tokyo, Japan. Electronic address: shibatas@waseda.jp.
Shigenobu
S
Shibata
D056930:ARNTL Transcription Factors / Q000378:metabolism; D000679:Amygdala / Q000378:metabolism*; D000818:Animals; D001522:Behavior, Animal; D056926:CLOCK Proteins / Q000235:genetics; D057906:Circadian Clocks / Q000502:physiology; D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology*; D015870:Gene Expression / Q000502:physiology*; D006624:Hippocampus / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009638:Norepinephrine / Q000378:metabolism*; D056950:Period Circadian Proteins / Q000378:metabolism; D017440:Photoperiod; D010805:Physical Conditioning, Animal / Q000502:physiology; D012701:Serotonin / Q000378:metabolism*
D056930:ARNTL Transcription Factors; C538961:Bmal1 protein, mouse; C539023:Per1 protein, mouse; D056950:Period Circadian Proteins; D012701:Serotonin; D056926:CLOCK Proteins; C538944:Clock protein, mouse; D009638:Norepinephrine
Amygdala; Circadian rhythm; Locomotor activity; Monoamine; Phase delay