Abstract
Affective disorders have been linked to abnormal biological rhythms. Depression- and anxiety-related behaviors can be altered following changes of daily periods of environmental light. The aim of this study was to investigate the effect of daily light cycle on both anxiety- and depressive-like behaviors of rats. Wistar male rats were exposed to constant dark or constant light during one week and compared to control animals exposed to 12/12h light/dark cycle regarding to anxiety-like behaviors and general activity on open field test and depressive-like behaviors on the forced swimming test. Data showed that rats exposed to one week of constant light exhibited increased number of quadrants crossed in the open field. No change on anxiety-like behaviors (time and quadrants crossed in the center of apparatus) was observed in the open field test. One week of constant dark increased the time of immobility behavior in the forced swimming test relative to control 12/12h light/dark treatment. Therefore, one week of continuous light induced locomotor hyperactivity and one week of continuous dark induced depressive-like behaviors following reestablishment of normal 12/12h light/dark cycle. Such data demonstrate the importance of light/dark environmental rhythm on mood changes and the significance of light/dark cycle control on behavioral studies.
Highlights
The rotation of Earth around itself and around the Sun causes daily and seasonal rhythms in light intensity, temperature, humidity, and more
Affective disorders had been linked to abnormal biological rhythms for many years and diurnal and seasonal variations of mood had been incorporated into the diagnostic system of affective disorders and many sleep and rhythm-related changes were identified in patients suffering from depression and anxiety disorders (WIRZ-JUSTICE, 2007)
Light/Dark cycle alteration Animals were separated into three treatment groups: Light/dark 12h/12h, Light 24h/day and Dark 24h/day
Summary
The rotation of Earth around itself and around the Sun causes daily and seasonal rhythms in light intensity, temperature, humidity, and more. Affective disorders had been linked to abnormal biological rhythms for many years and diurnal and seasonal variations of mood had been incorporated into the diagnostic system of affective disorders and many sleep and rhythm-related changes were identified in patients suffering from depression and anxiety disorders (WIRZ-JUSTICE, 2007). Unipolar depression is described by an unpleasant (dysphoric) mood that is present most of the day as well as intense mental anguish, the inability to experience pleasure (anhedonia), and a generalized loss of interest in the world. The key feature of generalized anxiety disorder is unrealistic or excessive worry, lasting not minutes but continuously for six months or longer.
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