Abstract
Vasoactive polypeptide (VIP) immunoreactivity is present in varicosities and fibers in the hypothalamic paraventricular nucleus (PVN) in normal control animals [rats]. Adrenalectomy and lactation combined with colchicine treatment results in the appearance of a large population of VIP-immunopositive cell bodies in the parvocellular part of the PVN. Adrenalectomy, as well as lactation, significantly increases the number of VIP-positive fibers in the external zone of the median eminence. The VIP-immunopositive neurons in the PVN may participate in regulating prolactin and corticotropin secretion.