Indoloquinolizidines, formal derivatives of tetrahydro-beta-carbolines, show selective affinity for benzodiazepine, tryptamine and serotonin binding sites in rat brain.

Beta-carbolines and indoloquinolizidines occur in plants, and some of the former compounds also in mammalian tissues. Many beta-carbolines cause tremor or convulsions, and they are among the most potent known endogenous compounds to bind to benzodiazepine, tryptamine and serotonin binding sites. In this study seven indoloquinolizidines which are formal derivatives of 1,2-disubstituted 1,2,3,4-tetrahydro-beta-carbolines were assayed for their affinity for benzodiazepine, tryptamine and serotonin binding sites in rat brain in vitro. Three of them exhibited significant affinity for tryptamine receptors: Ki values ranged from 0.97 microM upwards. The affinity spectra towards different receptors greatly varied from compound to compound showing selectivity to one or several of the binding sites now studied. These derivatives of beta-carbolines may be useful tools when assessing the physiological functions of the tryptamine and other binding sites.