Aim of this study was to investigate, with the aid of a recently developed immunofluorescence technique, cellular colocalization of vasoactive intestinal peptide (VIP) with arginine-vasopressin (AVP) in the paraventricular nucleus (PVN), the supraoptic nucleus (SON) and the suprachiasmatic nucleus (SCN) of the human hypothalamus. To this end, six hypothalami resected from patients who had died suddenly served as material of research. After formaldehyde fixation and subsequent storage in 30% sucrose, 25-microm thick cryosections were cut of one half of each hypothalamus. These sections were double-immunolabeled with primary antibodies against AVP and VIP followed by fluorophore-conjugated secondary antibodies. Autofluorescence, mainly caused by lipofuscin granules in neurons and glial cells, was blocked by a specially developed procedure consisting of incubating the immunolabeled sections in a Sudan Black B solution. Quantitative analysis with a confocal laser scanning microscope showed that of all stained cellular profiles the percentages of profiles immunoreactive exclusively for AVP or VIP or for both neuropeptides (colocalization) were for the SCN approximately 76.5%, 19.6% and 3.9%, for the SON 97.7%, 0.2% and 2. 1% and for the PVN 93.2%, 1.6% and 5.2%, respectively. These data illustrate that colocalization between AVP and VIP is not only present in neurons of the PVN and SON, but also in neurons of the SCN. This unexpected finding illustrates that the human SCN may also use a highly differentiated language to transmit its circadian signal to the rest of the brain.
Copyright 1999 Elsevier Science B.V.