Cognitive, Behavioral, and Systems NeuroscienceResearch PaperNighttime dim light exposure alters the responses of the circadian system
Section snippets
Animals
Male CD1 mice (28 days old) were purchased from Charles River and were randomly assigned to one of two groups. The control group was housed in a 12:12 h light: dark (LD, 300 lux: 1 lux) cycle. Light phase illumination was produced by cool white fluorescent bulbs. A red safety light, with a maximum light intensity of 1 lux, was on during the dark phase to allow for animal care and maintenance. The experimental group was housed in a 12:12 h light: dim light (LdimL 300 lux: 20 lux) condition, in
Effect of nighttime dim light on the daily oscillation of the SCN
PER1 expression was high at ZT12 and low at ZT23 under both lighting condition (Fig. 1). At ZT12 (Fig. 1A, left column), densely packed PER1-ir nuclei were seen throughout the SCN in both LD and LdimL. At ZT23, scattered PER1-ir nuclei were seen at the center to dorsal but absent in the ventral region of the SCN in LD, showing the distribution characteristic to this time as previously reported (King et al., 2003). However, for the animals housed in LdimL, PER1-ir nuclei were distributed in both
Discussion
The results from the present study revealed that both the time-keeping and entrainment functions of the SCN were altered by a brighter night and that these changes had consequences downstream, in the form of changes in the overt behavioral rhythms of the animals. One of the main findings of the present study was an elevated baseline expression of clock genes in the SCN. At ZT23, which is the trough time for PER1 expression, the number of PER1-ir cells in the LdimL group was significantly higher
Acknowledgments
We would like to thank Drs. Antonio Nunez and Laura Smale for critical reading of previous drafts of this manuscript. We also thank Ashley Tomczak, Madison Operacz, Mona Shah and Kathleen Thomas for assisting the experiment and data analysis. We would also like to thank Drs. Matthew Blanchard, Taosheng Liu, Jie Huang at MSU and Dr. Arnold Wilkins at University of Essex for their help in characterizing and interpreting the light conditions. This work was supported by Psychology Department
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