The invention provides a novel amino acid, neo-tryptophan, as well as polypeptides containing this novel amino acid such as neurotensin analogs. In addition, the invention provides neo-tryptophan derivatives, serotonin-like neo-tryptophan derivatives, and polypeptides containing such derivatives. The invention also provides methods for making neo-tryptophan, neo-tryptophan derivatives, serotonin-like neo-tryptophan derivatives, and compositions containing these compounds. Further, the invention provides methods for inducing a neurotensin response in a mammal as well as methods for treating a mammal having a serotonin recognition molecule.