Indoleacetaldehydes: Serotonin-like Effects on the Central Nervous System

Abstract

SEROTONIN (5HT) and tryptamine are metabolized primarily by monoamine oxidase (MAO)¹ with the formation of the corresponding aldehyde derivatives 5-hydroxyindole-3-acetaldehyde (5HIAAld) and indoleacetaldehyde (IAAld). These aldehydes are unstable and reactive and are promptly oxidized to corresponding acids², are firmly bound to acid-insoluble fractions of brain homogenates^2–3 or follow other metabolic routes^2,4,5, but they are not significantly reconverted to the corresponding amines³. Little attention has been paid to the possible pharmacological activity of these aldehydes because they are inactive in smooth muscle preparations⁶. We now wish, however, to present evidence that indoleacetaldehydes are biologically active and that to some extent their effects mimic the action of serotonin in visual evoked responses⁷ and sleep induction⁹, two functions known to be affected selectively by serotonin probably because the corresponding pathways are normally modulated by the endogenous amine. Our 5HIAAld was prepared enzymatically from 5HT⁶ and its concentration determined by the 2,4-dinitrophenylhydrazine method⁹. Its purity was determined by a combination of electrophoretic separation and subsequent autoradiography³; serotonin was not detectable.