The distribution and cells of origin of ACTH(1-39)-stained varicosities in the paraventricular and supraoptic nuclei.

ACTH(1-39)-immunoreactive fibers and varicosities were localized using indirect immunofluorescence histochemistry in normal rats, and were found to be distributed in specific parts of the parvocellular division of the paraventricular nucleus, and in regions of the magnocellular division of the paraventricular and supraoptic nuclei in which oxytocinergic cells predominate. A combined retrograde transport-immunohistochemical method was used to confirm that these projections arise from a group of ACTH(1-39)-stained cells in the arcuate nucleus (and in adjacent regions along the base of the hypothalamus), and to describe their distribution within this region.