Behavioral Responses of Vipr2^–/– Mice to Light

May 20, 2008Journal of biological rhythms

Behavioral responses to light in mice lacking the Vipr2 receptor

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Abstract

Mice lacking VPAC2 receptors show altered circadian rhythms but may still respond behaviorally to light cues.

Mice without VPAC2 receptors (Vipr2-/-) exhibit impaired synchronization to environmental light.
Light exposure increases certain protein and gene activity in the SCN of Vipr2-/- mice.
Behavioral analysis reveals that Vipr2-/- mice have disrupted locomotor patterns.
In some Vipr2-/- mice, light can reset the timing of activity rhythms during the subjective night.
These findings indicate that the circadian clock in Vipr2-/- mice remains responsive to light.

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Vasoactive intestinal polypeptide and its receptor, VPAC2, play important roles in the functioning of the dominant circadian pacemaker, located in the hypothalamic suprachiasmatic nuclei (SCN). Mice lacking VPAC2 receptors (Vipr2-/-) show altered circadian rhythms and impaired synchronization to environmental lighting cues. However, light can increase phosphoprotein and immediate early gene expression in the Vipr2-/- SCN demonstrating that the circadian clock is readily responsive to light in these mice. It is not clear whether these neurochemical responses to light can be transduced to behavioral changes as seen in wild-type (WT) animals. In this study we investigated the diurnal and circadian wheel-running profile of WT (C57BL/6J) and Vipr2-/- mice under a 12-h light:12-h complete darkness (LD) lighting schedule and in constant darkness (DD) and used 1-h light pulses to shift the activity of mice in DD. Unlike WT mice, Vipr2-/- mice show grossly altered locomotor patterns making the analysis of behavioral responses to light problematic. However, analyses of both the onset and the offset of locomotor activity reveal that in a subset of these mice, light can reset the offset of behavioral rhythms during the subjective night. This suggests that the SCN clock of Vipr2-/- mice and the rhythms it generates are responsive to photic stimulation and that these responses can be integrated to whole animal behavioral changes.

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Behavioral Responses of Vipr2^–/– Mice to Light

Abstract

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