Identification of 5-hydroxytryptamine binding site subtypes in rat spinal cord.

High-affinity, specific [3H]5-hydroxytryptamine (5-HT) binding was analyzed in rat spinal cord homogenates. Drug competition studies were performed using 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) to compete selectively for 5-HT1A sites, RU 24969 to compete for 5-HT1B sites and mesulergine to compete for 5-HT1C sites. Competition data were analyzed by computer-assisted iterative curve-fitting analysis. The results demonstrate that 5-HT1A, 5-HT1B and 5-HT1C binding sites are present in rat spinal cord. In addition, approximately 33% of total 5-HT1 sites do not appear to represent either 5-HT1A, 5-HT1B or 5-HT1C binding sites. Therefore, 5-HT1D and/or some other 5-HT1 binding site subtype may also be present in rat spinal cord.