A new study in mice has suggested an explanation for how the sleep hormone melatonin may help enhance memory.
The study by Japanese researchers at Tokyo’s Sophia University and published in NeuroReport found melatonin – naturally produced by the pineal gland in the brain’s centre to induce sleep and regulate the circadian cycle – promoted long-term memory formation through the regulation of phosphorylation of proteins in parts of the brain responsible for memory.
In a study designed to measure long- term memory formation by using the ‘novel object recognition task’ (NORT), male mice were first trained to find a ceramic object they hadn’t seen before, while being exposed to a ‘12-hour light’ and ‘12-hour dark’ cycle. (Females were avoided due to concerns their fertility cycle would affect results.)
The mice were familiarised with an experimental arena over 3 days. On the fourth day, 2 objects were introduced for a training phase. After 24 hours, one familiar object was replaced with a new object for the testing phase.
Researchers recorded the duration of object exploration, which serves as an ‘indicator of object recognition memory’.
Following the initial memory test, the mice were administered either melatonin, a drug that binds to the melatonin receptor called ramelteon, a metabolic metabolite to melatonin called AMK, or a control treatment – with effectiveness of these treatments on memory performance assessed after a day.
Researchers found ‘novel object recognition’ increased in mice administered melatonin, AMK and ramelteon compared to controls.
The researchers then euthanised the mice and examined ‘phosphorylation’ of proteins associated with memory formation in parts of their brains associated with memory creation – the hippocampus and perirhinal cortex.
Phosphorylation is the addition of a chemical group to a protein, which affects its activity levels in biochemical reactions. The researchers found phosphorylation of memory-associated proteins increased in the presence of AMK and ramelteon.
The findings suggest ‘melatonin is involved in promoting the formation of long-term object recognition memory by modulating the phosphorylation levels of memory-related proteins’, summed up medicalnewestoday.com.
