Characterization and quantification of (125)I-bolton hunter substance P binding sites in human brain

(125)I-Bolton Hunter substance P (BHSP) specific binding sites in human brain synaptosomal membrane preparations were studied with respect to binding characteristics and regional distribution. Specific binding of (125)I-BHSP, which constituted 75% of total binding, and 7% of the total radioactivity added to the incubation medium, was saturable and stable at 20 degrees C. Scatchard analysis of data from equilibrium studies revealed the existence of a single class of binding sites (K(D) = 0.37 nM, B(MAX) = 47.3 fmol/mg tissue protein) in human nucleus caudatus. Competitive studies of (125)I-BHSP binding in human nucleus caudatus gave the following rank order of potencies among tachykinins: substance P > physalaemin > neurokinin A ? neurokinin B ? kassinin ? eledoisin. Measurements of (125)I-BHSP receptor binding densities in different regions of autopsy human brain revealed highest densities in the corpus of nucleus caudatus and the putamen. Moderately high binding densities were detected in the amygdala, hypothalamus, caput of nucleus caudatus and certain parts of the frontal lobe, whereas other regions showed only low levels of binding.