The binding of serotonergic ligands to the porcine choroid plexus: characterization of a new type of serotonin recognition site

The kinetic and pharmacological characteristics of the binding of 3H]5-HT (serotonin), 3H]8-OH-DPAT (8-OH-2-di-n-propylaminotetraline), 3H]LSD, 3H]ketanserin and 3H]mesulergine to membranes from frontal cortex, hippocampus and choroid plexus of pig brain were studied. The binding of these ligands to frontal cortex and hippocampus demonstrated the presence of 5-HT1 and 5-HT2 sites in both tissues, although hippocampus was richer in 5-HT1 (subtype 5-HT1A) sites. 3H]5-HT, 3H]mesulergine and 3H]LSD labeled the pig choroid plexus with high affinity. The pharmacological profiles of 3H]5-HT and 3H]mesulergine binding to this tissue were closely comparable. Ligands reported as selective for 5-HT1A, 5-HT1B or 5-HT2 subtypes did not show high affinity for these binding sites. Therefore, these 5-HT binding sites in pig choroid plexus could be named 5-HT1C. Other drugs with a high affinity for these sites were methysergide and mianserine. In pig frontal cortex, 3H]5-HT labeled the different subtypes of 5-HT1 sites. In contrast, 3H]mesulergine bound in pig frontal cortex to a small population of sites with pharmacological properties similar to those of the choroid plexus 5-HT1C sites. Possible physiological functions in which these sites might be involved are discussed.