Live imaging of altered period1 expression in the suprachiasmatic nuclei of Vipr2-/- mice

Vasoactive intestinal polypeptide and its receptor, VPAC2, play important roles in the functioning of the brain's circadian clock in the suprachiasmatic nuclei (SCN). Mice lacking VPAC2 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 VPAC2 receptors in WT SCN slices partially mimicked the Vipr2 -/- phenotype. These data demonstrate that intercellular communication via the VPAC2 receptor is important for SCN neurons to sustain robust, synchronous oscillations in clock gene expression. © 2008 The Authors.