Disruption of circadian rhythms due to chronic constant light leads to depressive and anxiety-like behaviors in the rat

May 30, 2013Behavioural brain research

Constant light disrupting daily body rhythms may cause depression and anxiety-like behaviors in rats

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Abstract

Exposure to constant light for 8 weeks resulted in loss of circadian patterns in rats.

Circadian disruption is linked to increased signs of depression and anxiety in rats.
Rats exposed to constant light showed changes in activity, melatonin, and corticosterone levels.
Behavioral tests indicated anhedonia and heightened anxiety in rats under constant light.
Decreased cellular activation in the suprachiasmatic nucleus was observed following constant light exposure.
In contrast, rats in constant darkness maintained some circadian patterns but showed mild depressive and anxiety-like behaviors.

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Depression is strongly associated with the circadian system, disruption of the circadian system leads to increased propensity to disease and to mood disorders including depression. The present study explored in rats the effects of circadian disruption by constant light on behavioral and hormonal indicators of a depressive-like condition and on the biological clock, the suprachiasmatic nucleus (SCN). Exposure to constant light for 8 weeks resulted in loss of circadian patterns of spontaneous general activity, melatonin and corticosterone. Moreover these rats exhibited anhedonia in a sucrose consumption test, and increased grooming in the open-field test, which reflects an anxiety-like condition. In the SCN decreased cellular activation was observed by c-Fos immunohistochemistry. In rats exposed to constant darkness, circadian behavioral and hormonal patterns remained conserved, however mild depressive-like indicators were observed in the anhedonia test and mild anxiety-like behaviors were observed in the open field test. Data indicate that chronic conditions of LL or DD are both disruptive for the activity of the SCN leading to depression- and anxiety-like behavior. Present results point out the main role played by the biological clock and the risk of altered photoperiods on affective behavior.

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Disruption of circadian rhythms due to chronic constant light leads to depressive and anxiety-like behaviors in the rat

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