Antidepressant-Like Effect of β-Lactolin, a Glycine-Threonine-Tryptophan-Tyrosine Peptide.

The number of patients with mental illnesses, including depression, is rapidly increasing, and daily lifestyle is closely associated with the development of symptoms. Consequently, corrective measures, such as diet-based treatment for diseases, are receiving great attention. We previously showed that beta-lactolin, a beta-lactopeptide of glycine-threonine-tryptophan-tyrosine peptide, inhibits monoamine oxidase and improves memory impairment in mice, but the effects on depression have not been investigated. Here we showed that beta-lactolin improved depression-like behavior via dopamine-D1-like receptor. Orally administered beta-lactolin reduced immobility time in tail suspension test (TST). Pretreatment with SCH23390, dopamine D1-like receptor antagonist, attenuated the reduction in TST by beta-lactolin. These effects were observed by the treatment with whey digest rich in beta-lactolin. In addition, beta-lactolin increased the levels of dopamine in the frontal cortex associated with the depression-like behavior. The present study suggests that supplements or nutraceutical compounds in whey digests (such as beta-lactolin) show antidepressant-like effect.