ORIGIN OF CCK-LIKE IMMUNOREACTIVE NERVE-FIBERS IN THE NEUROHYPOPHYSISOF THE RAT

Wheatgerm agglutin (WGA) conjugated horseradish peroxidase (HRP) retro grade tracing technique was combined with immunohistochemistry to stud y the origin of cholecystokinin (CCK)-like immunoreactive (ir) nerve f ibers in the neurohypophysis of the rat. The CCK-ir neurons projecting to the neurohypophysis were localized mainly in the magnocellular par aventricular nuclei (mPVN), periventricular PVN, medial parvocelullar PVN, medial preoptic area and dorsal accessory nuclei in region betwee n the stria medullaris and fornix. Double-labeled cells were also obse rved in small amounts in the dorsal parts of supraoptic nuclei, the ve ntral parts of anterior hypothalamic regions and lateral hypothalamic areas. In addition, a few double-labeled cells were seen in the subepe ndymal 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 a reas than generally assumed. The fact that some CCK-ir neurons project ing to the posterior pituitary were located close to cerebrospinal flu id suggests that they may play. a role in monitoring and controlling c hanges of cerebrospinal fluid.