Effects of lighting condition on circadian behavior in 5-HT1A receptor knockout mice

Dec 3, 2014Physiology & behavior

How light affects daily activity patterns in mice lacking the 5-HT1A receptor

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Abstract

5-HT1A receptor knockout mice show lower activity levels during the first 8 hours of the night compared to wildtype mice under light and constant light conditions.

These knockout mice exhibit later activity onsets during transient days when re-entraining to new light-dark cycles.
They demonstrate shorter free-running periods in constant light when housed with running wheels.
Knockout mice show smaller phase shifts in response to dark pulses compared to wildtype mice.
No significant differences were observed in activity levels during constant darkness or other circadian properties.

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Serotonin (5-HT) is an important regulator of the mammalian circadian system, and has been implicated in modulating entrained and free-running rhythms, as well as photic and non-photic phase shifting. In general, 5-HT appears to oppose the actions of light on the circadian system of nocturnal rodents. As well, 5-HT mediates, at least in part, some non-photic responses. The 5-HT1A, 1B and 7 receptors regulate these acute responses to zeitgebers. 5-HT also regulates some entrained and free-running properties of the circadian clock. The receptors that contribute to these phenomena have not been fully examined. Here, we use 5-HT1A receptor knockout (KO) mice to examine the response of the mouse circadian system to a variety of lighting conditions, including a normal light-dark cycle (LD), T-cycles, phase advanced LD cycles, constant darkness (DD), constant light (LL) and a 6 hour dark pulse starting at CT5. Relative to wildtype mice, the 5-HT1A receptor KO mice have lower levels of activity during the first 8h of the night/subjective night in LD and LL, later activity onsets on transient days during re-entrainment, shorter free-running periods in LL when housed with wheels, and smaller phase shifts to dark pulses. No differences were noted in activity levels during DD, alpha under any light condition, free-running period in DD, or phase angle of entrainment in LD. While the 5-HT1A receptor plays an important role in regulating photic and non-photic phase shifting, its contribution to entrained and free-running properties of the circadian clock is relatively minor.

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Effects of lighting condition on circadian behavior in 5-HT1A receptor knockout mice

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