Live imaging of altered period1 expression in the suprachiasmatic nuclei of Vipr2−/− mice1

Vasoactive intestinal polypeptide and its receptor, VPAC(2), play important roles in the functioning of the brain's circadian clock in the suprachiasmatic nuclei (SCN). Mice lacking VPAC(2) receptors (Vipr2(-/-)) show altered circadian rhythms in locomotor behavior, neuronal firing rate, and clock gene expression, however, the nature of molecular oscillations in individual cells is unclear. Here, we used real-time confocal imaging of a destabilized green fluorescent protein (GFP) reporter to track the expression of the core clock gene Per1 in live SCN-containing brain slices from wild-type (WT) and Vipr2(-/-) mice. Rhythms in Per1-driven GFP were detected in WT and Vipr2(-/-) cells, though a significantly lower number and proportion of cells in Vipr2(-/-) slices expressed detectable rhythms. Further, Vipr2(-/-) cells expressed significantly lower amplitude oscillations than WT cells. Within each slice, the phases of WT cells were synchronized whereas cells in Vipr2(-/-) slices were poorly synchronized. Most GFP-expressing cells, from both genotypes, expressed neither vasopressin nor vasoactive intestinal polypeptide. Pharmacological blockade of VPAC(2) receptors in WT SCN slices partially mimicked the Vipr2(-/-) phenotype. These data demonstrate that intercellular communication via the VPAC(2) receptor is important for SCN neurons to sustain robust, synchronous oscillations in clock gene expression.