Abstract
In 1953, Twarog and Page (1) demonstrated that 5-hydroxytryptamine (serotonin) is present in relatively high concentrations in the brain. At about the same time Gaddum (2) and Woolley and Shaw (3) observed that LSD is a highly potent serotonin antagonist in such tissues as rat uterus and hypothesized that the hallucinogenic effect of LSD might be due to interference in the action of serotonin.