Immunocytochemical Localization of Growth Hormone-Releasing Factor in the Rat Hypothalamus*

The distribution of GRF-immunoreactive structures in the rat hypothalamus was studied after colchicine treatment with peroxidase-antiperoxidase immunocytochemistry in vibratome sections. The majority of the GRF-immunoreactive cell bodies were found in the arcuate nucleus and the medial perifornical region of the lateral hypothalamus. Scattered cells were seen in the lateral basal hypothalamus, the medial and lateral portions of the ventromedial nucleus, and the dorsomedial and paraventricular nuclei. Fibers from the perifornical cell bodies formed a fan-like projection to the median eminence, where a dense accumulation of GRF-containing processes and terminals was found. GRF terminals were located in the central regions of the median eminence. The localization of GRF-immunoreactive structures in the hypothalamus and median eminence reinforces the view that GRF plays a physiological role in the regulation of pituitary function.