Transgenic approach reveals expression of the VPAC₂ receptor in phenotypically defined neurons in the mouse suprachiasmatic nucleus and in its efferent target sites

Circadian rhythms in mammals depend on the properties of cells in the suprachlasmatic nucleus (SCN). The retino-recipient core of the mouse SCN is characterized by vasoactive intestinal peptide (VIP) neurons. Expression within the SCN of VPAC₂, a VIP receptor, is required for circadian rhythmicity Using transgenlc mice with β-galactosidase as a marker for VPAC2, we have phenotyped VPAC₂, expressing cells within the SCN and investigated expression of the VPAC₂ marker at sites previously shown to receive VIP-containing SCN efferents. In situ hybridization and immunohistochemistry demonstrated identical distributions for VPAC₂ mRNA and β-galactosidase and coexpression of the two signals in the SCN. Double-label confocal immunofluorescence identified β-galactosidase in 32% of the VIP and 31% of the calretinin neurons In the SCN core. Of the arginine-vasopressin neurons that characterize the SCN shell, 45% expressed β-galactosidase. In contrast, this marker was not apparent in astrocytes within the SCN core or shell. Cell bodies containing β-galactosidase were detected at sites reportedly receiving VIP-containing SCN efferents, including the subparaventricular zone and lateral septum and the anteroventral periventricular, preoptic suprachiasmatic, medial preoptic and paraventricular hypothalamic nuclei. The detection of a marker for VPAC₂ expression in the SCN in almost one-third of the VIP and calretinin core neurons and nearly half of the arginine-vasopressin shell neurons and also in cell bodies at sites receiving VIP-immunoreactive projections from the SCN indicates that VPAC ₂ may contribute to autoregulation and/or coupling within the SCN core and to the control of the SCN shell and sites distal to this nucleus.