Distribution of corticotropin-releasing factor in rat brain.

Corticotropin-releasing factor (CRF) has been measured in 70 brain nuclei and in the posterior pituitary of the rat by radioimmunoassay (RIA) developed against synthetic rat CRF. CRF-like immunoreactivity was detected in 32 brain areas in concentrations higher than 0.3 ng/mg protein. Most of the CRF in the brain was in the hypothalamus, where the highest level was found in the median eminence. Several limbic nuclei, such as the lateral septal nucleus, central amygdaloid nucleus, periventricular thalamic nuclei, and bed nucleus of the stria terminalis, contained CRF in moderate to low concentrations. CRF was detected in a number of lower brain-stem nuclei, including the ventral tegmental area, central gray matter, dorsal raphe, parabrachial nuclei, and locus ceruleus. Surprisingly, the highest extrahypothalamic CRF level was found in the inferior olive. Our RIA data are, in general, fairly consistent with immunohistochemical findings.