Figure 4. Distribution of CRF receptors in the brain-pituitary-immune axis. A, B and C illustrate darkfield photomicrographs demonstrating the total distribution of [125I] Tyr0-oCRF binding sites in mouse pituitary, brain and spleen, respectively. In darkfield illumination, the bright areas represent high densities of CRF receptors. In A (horizontal section of pituitary), note the higher density of CRF receptors in the intermediate lobe of the pituitary, compared with the anterior lobe. CRF binding sites are conspicuously absent in the posterior lobe. In B (horizontal section of brain), note the higher densities of binding sites in cerebral cortex, olfactory bulb, cerebellum and in a variety of limbic areas. In C (sagittal section of spleen), note the diffuse density of CRF binding sites localized to the red pulp regions and the high density of CRF binding sites in the marginal zone surrounding the white pulp zone. There was a notable absence of CRF binding in the white pulp regions, which contain high concentrations of T and B lymphocytes. D, E and F are darkfield photomicrographs showing the absence of specific binding in adjacent sections of all three tissues in which 1 mM unlabeled rat/human CRF was included in the incubation medium.