AUTORADIOGRAPHIC MAPPING OF SEROTONIN 5-HT1A, 5-HT1D, 5-HT2A AND 5-HT3 RECEPTORS IN THE AGED HUMAN SPINAL-CORD

Quantitative autoradiography with selective radioligands was used to e stablish the respective distribution of serotonin 5-HT1A, 5-HT1D, 5-HT 2A and 5-HT3 receptors at the cervical, thoracic and lumbar levels of the spinal cord from subjects who died at 81-94 years. A high density of 5-HT1A receptors, labeled by [H-3]8-hydroxy-2-(di-n-propylamino)tet ralin ([H-3]8-OH-DPAT), was found in the superficial layers of the dor sal horn, with a significant enrichment (similar to 20%) in the lumbar vs. the thoracic and cervical segments. In contrast, only very low sp ecific labeling by [H-3]8-OH-DPAT (i.e. less than 10% of that measured in the dorsal horn), was detected in the ventral horn. 5-HT1D sites l abeled by serotonin-O-carboxymethyl-glycyl-iodo-tyrosinamide ([I-125]G TI) were also mainly located within the superficial layers of the dors al horn, but no difference in their relative density was noted at the three levels of the spinal cord examined. 5-HT2A sites labeled by [H-3 ]ketanserin were found in the dorsal horn of the cervical segments but no specific binding of this radioligand could be detected at any othe r level of the spinal cord of such aged subjects. Finally, a high dens ity of [H-3]S-zacopride-labeled 5-HT3 receptors was noted especially i n the most superficial layer (lamina I) of the dorsal horn at all segm ents examined. These data provide anatomical support for a role of spi nal serotonin especially in nociception processing.