Binding sites for melanin-concentrating hormone in the human brain.

Binding sites for melanin-concentrating hormone (MCH) in human brain were investigated and characterized by radioligand binding. Specific binding sites for MCH were present in every region of human brain (cerebral cortex, cerebellum, thalamus, hypothalamus, pons, and medulla oblongata) obtained at autopsy. alpha-Melanocyte stimulating hormone or ACTH was a poor inhibitor of (125)I-MCH binding (IC(50) 1 microM) compared with MCH (IC(50) = 0.3 +/- 0.07 nM, mean +/- SEM, n = 3). Scatchard plots of (125)I-MCH binding in human brain (thalamus) gave a dissociation constant of 0.2 +/- 0.06 nM and maximal binding of 5.8 +/- 0.3 fmol/mg protein (n = 3). These findings suggest that specific MCH binding sites that differ from the melanocortin receptors exist in human brain.