revision preference src: Activation of 5-HT may be particularly important for hallucinogenic activity. However, repeated exposure to hallucinogens leads to rapid tolerance, likely through down-regulation of these receptors in specific target cells. <SEP> tgt: Activation of 5-HT may be particularly important for hallucinogenic activity. Repeated exposure to hallucinogens leads to rapid tolerance, likely through down-regulation of these receptors in specific target cells.