Subcellular distribution of corticotropin-releasing factor in the medio-basal hypothalamus of the rat.

Subcellular fractionation of the mediobasal hypothalamus (MBH) and frontal cerebral cortex was performed by differential and discontinuous sucrose gradient centrifugation. Corticotropin-releasing factor (CRF) activity of the different fractions was evaluated by bioassay. Significant CRF activity was found in acidic extracts of the MBH but not of the cerebral cortex. About 80% of the MBH effect on adrenocorticotropic hormone release was recovered in the crude mitochondrial pellet (P2) which contains synaptosomes. After further fractionation, distribution of CRF activity paralleled that of lactate dehydrogenase activity, a marker of the soluble cytoplasm. It is concluded that most CRF in the MBH is located in nerve endings as already shown for several other neurohormones.