Binding sites for 125I-cholecystokinin in primate spinal cord are of the CCK-A subclass.

Cholecystokinin (CCK) receptor binding was measured in sections of human, monkey and rat spinal cord using autoradiographical techniques. In each species, high levels of specific 125I-Bolton-Hunter CCK binding were detected in the superficial layers of the dorsal horn (the substantia gelatinosa). In monkey and human but not rat spinal cord, 125I-CCK binding was dose-dependently inhibited by low concentrations of the selective CCK-A antagonist L-364,718. Binding of [3H]L-364,718, which was saturable (Bmax = 29.0 +/- 0.95 pmol/g wet wt.) and of high affinity (pKd) = 9.92 +/- 0.16) was also detected in sections of monkey spinal cord and had a similar localization to that of specific 125I-CCK binding. These data indicate that in striking contrast to CCK receptors in rat spinal cord, those in the primate cord are of the CCK-A receptor subclass.