Effect of extreme light/dark cycles on monoamine levels, physiological indices, and emotional behaviors in rats — The Association Specialists
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Effect of extreme light/dark cycles on monoamine levels, physiological indices, and emotional behaviors in rats (21500)

Takayuki Ishiwata 1 2 3 , Akira Kawata 3 , Yuta Kaneda 3 , Daisuke Matsunaga 4 , Hikaru Nakagawa 1 , Fumiharu Togo 5 , Mikinobu Yasumatsu 1 2 3
  1. Department of Sport and Wellness, RIkkyo University, Niiza, Saitama, Japan
  2. Graduate School of Sport and Wellness, Rikkyo University, Niiza, Saitama, Japan
  3. Graduate School of Community & Human Services, Rikkyo University, Niiza, Saitama, Japan
  4. Department of Health-Promotion & Sports Science, Osaka Electro-Communication University, Shijonawate, Osaka, Japan
  5. Graduate School of Education, The University of Tokyo, Bunkyo, Tokyo, Japan

Aberrant light/dark (LD) cycles are prevalent in modern society due to the widespread use of electric lights, causing mood disorders due to circadian disruption. This study investigated the potential effects of an extreme LD cycle on body weight (BW), core body temperature (Tcore), locomotor activity (ACT), emotional behaviors, and the levels of monoamines in several brain regions of rats, including noradrenaline (NA), dopamine (DA), and serotonin (5-HT). Male Wistar rats were kept in conventional physical parameters apart from their exposure to one month of either long light phase (Long-LP; 20 h:4 h), long dark phase (Long-DP; 4 h:20 h), or normal (Norm-LD; 12 h:12 h) LD cycles. Compared to Norm-LD rats, the Long-LP and Long-DP rats showed distinct differences in Tcore and ACT rhythms with increments in BW gain. The NA and 5-HT levels of the Long-LP rats decreased in the suprachiasmatic nucleus and amygdala, respectively. Long-DP rats showed increased DA and 5-HT levels in the caudate putamen and dorsomedial hypothalamus, respectively. In the emotional behavior tests, both the Long-LP and Long-DP rats showed anxiety-like behaviors in both the open field test and social interaction test. These results suggest that an extreme LD cycle affects Tcore and ACT circadian rhythms and monoamine levels across brain regions and induces anxiogenic responses.