Milk Collected at Night Induces Sedative and Anxiolytic-Like Effects and Augments Pentobarbital-Induced Sleeping Behavior in Mice

Milk has long been known and used to promote sleep. The sleep-promoting effect of milk has been attributed to its psychological associations (i.e., the memory of a mother giving milk at bedtime) and its rich store of sleep-promoting constituents (e.g., tryptophan). Studies have shown that milk harvested at night (Night milk) contains exceptionally high amounts of tryptophan and melatonin. In the present study, we evaluated the psychopharmacological properties of Night milk, particularly its probable sleep-promoting/enhancing, and anxiolytic effects. Night milk was orally administered to ICR mice at various concentrations (100, 200, or 300 mg/kg). An hour after administration, assessment of its sedative (open-field and rotarod tests) and sedative sleep-potentiating effects (pentobarbital-induced sleeping test) was conducted. For comparison, the effects of Day milk (daytime milking) were also assessed. In addition, the effects of Night milk on anxiety behavior (elevated plus maze [EPM] test) and electroencephalographic (EEG) waves were evaluated. Night milk-treated animals exhibited decreased spontaneous locomotion (open-field test) and impaired motor balance and coordination (rotarod test). Furthermore, Night milk shortened the sleep onset and prolonged the sleep duration induced by pentobarbital sodium. These effects were comparable to that of diazepam. In addition, Night milk significantly increased the percentage of time spent and entries into the open arms of the EPM, indicating that it also has anxiolytic effects. No significant changes in EEG waves were observed. Altogether, these findings suggest that Night milk is a promising natural aid for sleep- and anxiety-related disturbances.