Convergent serotonin and GABA innervation of VIP neurons in the suprachiasmatic nucleus demonstrated by triple labeling in the rat.

By means of a combination of serotonin (5-HT) uptake radioautography and dual immunocytochemistry, vasoactive intestinal polypeptide (VIP) neurons in the suprachiasmatic nucleus are demonstrated to simultaneously receive both 5-HT and GABA afferents at their somatic and dendritic levels. These data constitute a further step towards the improved characterization of the morphological substrate of the integrative function of these neurons, which are known to play an important role in the delivery of light-mediated rhythmic signals to other parts of the brain.