Origin of CCK-like immunoreactive nerve fibers in the neurohypophysis of the rat.

Wheatgerm agglutin (WGA) conjugated horseradish peroxidase (HRP) retrograde tracing technique was combined with immunohistochemistry to study the origin of cholecystokinin (CCK)-like immunoreactive (ir) nerve fibers in the neurohypophysis of the rat. The CCK-ir neurons projecting to the neurohypophysis were localized mainly in the magnocellular paraventricular nuclei (mPVN), periventricular PVN, medial parvocelullar PVN, medial preoptic area and dorsal accessory nuclei in region between the stria medullaris and fornix. Double-labeled cells were also observed in small amounts in the dorsal parts of supraoptic nuclei, the ventral parts of anterior hypothalamic regions and lateral hypothalamic areas. In addition, a few double-labeled cells were seen in the subependymal area of the interventricular foramen (IVF) and in the floor of the 3rd ventricle. Our results demonstrate that CCK-ir nerve fibers in the posterior pituitary originate from more widespread hypothalamic areas than generally assumed. The fact that some CCK-ir neurons projecting to the posterior pituitary were located close to cerebrospinal fluid suggests that they may play a role in monitoring and controlling changes of cerebrospinal fluid.