AUTORADIOGRAPHIC LOCALIZATION OF RECEPTORS FOR NEUROPEPTIDE FF, FLFQPQRFAMIDE, IN HUMAN SPINAL SENSORY SYSTEM

The regional distribution of FLFQPQRFamide binding sites on fresh unfi xed cryostat sections from post mortem specimens of human spinal cord and lower medulla oblongata was studied by quantitative autoradiograph ic methods using [I-125]YLFQPQRFamide as ligand. Samples were taken fr om fives cases who had died with no history of neurological disease at ages ranging from 5 months to 66 years. The biochemical and pharmacol ogical characteristics of [I-125]YLFQPQRFamide binding to mounted tiss ue sections were comparable to those reported for the rat in a previou s study. [I-125]YLFQPQRFamide appeared to interact reversibly with hig h affinity binding sites (K-d = 0.06 nM), distinct from opiate recepto rs. Sites labelled with [I-125]YLFQPQRFamide were distributed unevenly within the human spinal cord and lower medulla oblongata, with the hi ghest density in the superficial layers of the dorsal horn and the spi nal trigeminal nucleus. Although moderate labelling was observed in th e ventral part of spinal grey matter, dense labelling appeared in the gracile and cuneate nuclei. No binding sites were detected in white ma tter. These results show that, as in the rat, FLFQPQRFamide receptors in the human spinal cord and lower medulla oblongata, are mainly conce ntrated within spinal areas implicated in the analgesic action of opia tes. The possible role of these receptors in modulating spinal nocicep tive information is discussed with respect to the pharmacological effe cts of substances acting on FLFQPQRFamide receptors in animals.