Prevention of a Mental Defect of Phenylketonuria with Serotonin Congeners such as Melatonin or Hydroxytryptophan

Mice made phenylketonuric from birth until maturity by continuous administration of phenylalanine plus tyrosine had a subnormal maze-learning ability which was largely prevented when serotonin congeners such as melatonin or 5-hydroxytryptophan were administered continuously from birth to maturity. These results were interpreted to mean that the mental failure of experimental phenylketonuria is attributable to the serotonin deficiency imposed by it in infancy.