Summary: Researchers unveiled the intricate mechanisms through which melatonin enhances memory. They investigated how melatonin and its derivatives influence the phosphorylation levels of key memory proteins.
By focusing on male mice, they found that specific compounds facilitate the formation of long-term memory by modulating certain proteins’ phosphorylation levels. These breakthrough findings may pave the way for novel treatments for age-related memory impairment.
Melatonin and its derivatives, AMK and ramelteon, impact the phosphorylation levels of memory-related proteins, revealing their role in memory enhancement.
The study used the novel object recognition task (NORT) to gauge long-term memory formation in male mice.
Results showed that melatonin promotes long-term memory formation by modulating protein phosphorylation, offering potential for developing new memory-enhancing drugs.
Source: Sophia University
Multiple studies have demonstrated the memory-enhancing effects of melatonin and its derivatives in animal models. It is also known that forming both short- and long-term memories require the phosphorylation of certain memory-related proteins. However, the molecular mechanisms underlying melatonin-induced memory enhancement have remained elusive.
Medical researchers from Sophia University, Japan, have made important findings that contribute significantly to elucidating the underlying mechanisms in a recent article in NeuroReport .
Regarding the premise of the study, lead author Professor Atsuhiko Chiba from the Department of Materials and Life Sciences, Faculty of Science and Technology, Sophia University, says, “Our study aimed to investigate the effects of melatonin, ramelteon, and N1-acetyl-5-methoxyquinuramine on the relative phosphorylation levels of memory-related proteins in order to explore candidate signaling pathways associated with the receptor- and nonreceptor-mediated memory-enhancing effects of melatonin.”
In simpler terms, the research team, which included Dr. Masahiro Sano (currently affiliated with Tohoku University) and Dr. Hikaru Iwashita (currently affiliated with Kansai Medical University), examined the effects of three compounds on memory formation; these compounds were melatonin, a hormone secreted by the pineal gland located in the brain; N1-acetyl-5-methoxyquinuramine (AMK), melatonin’s biological metabolite; and ramelteon, a drug that binds and activates the melatonin receptor.
In addition, they examined “phosphorylation,” or the biochemical addition of phosphate groups to protein structures, in five key proteins involved in memory formation. These included the protein extracellular signal-regulated kinase (ERK), calcium/calmodulin-dependent kinase IIα (CaMKIIα), CaMKIIβ, CaMKIV, and the cAMP-response element binding protein (CREB).
Initial experiments conducted on male mice clearly showed that the administration of melatonin, ramelteon, or AMK at a dose of 1 mg/kg facilitated the formation of long-term memory.
The researchers did not investigate the effects of the three compounds on female mice to avoid any likely data variability resulting from the reproductive cycles occurring in female mammals.
Long-term memory formation in male mice was assessed by conducting a series of experiments based on the novel objection recognition task or “NORT.” In this study, laboratory mice under investigation were first acclimated to an experimental arena for 5 minutes per day for three consecutive days.
On the fourth day, two identical objects were placed in the experimental arena and mice were allowed to explore these objects for 5 minutes (training phase). Twenty-four hours after the cessation of the training phase, the male mice were subjected to testing. During the testing phase, one out of the two familiar objects was replaced with a new or unfamiliar object.
The amount of time spent by the mice exploring each object—a good measure of object recognition memory—was recorded by a trained observer. It is a known fact that mice spend more time exploring novel objects they encounter and less near familiar objects.
The researchers then studied the effects of ramelteon and AMK on the phosphorylation of ERK, CaMKIIα, CaMKIIβ, CaMKIV, and CREB in the male mouse brain after sacrificing the rodents using standard protocols.
In the hippocampus, which is the learning and memory center of the mammalian brain, treatment with ramelteon/AMK significantly increased the phosphorylation of both ERK and CREB.
However, these drugs significantly decreased CaMKIIα/β phosphorylation in the same brain region. In the perirhinal cortex (PRC), which is also associated with memory functions, both ramelteon and AMK significantly increased ERK, and only ramelteon significantly increased CaMKIIβ phosphorylation. In the hippocampus/PRC, ramelteon/AMK did not affect the phosphorylation of CaMKIV.
Talking about the study’s results, Prof. Chiba concludes, “Our findings suggest that melatonin is involved in promoting the formation of long-term object recognition memory by modulating the phosphorylation levels of memory-related proteins such as ERK, CaMKIIs, and CREB in both receptor-mediated and nonreceptor-mediated signaling pathways.”
What implications could these study findings have on humans? The researchers believe that the results of their study will contribute to the development of new drugs that can improve memory function in people suffering from age-related memory impairment with fewer side effects. For a steadily aging global society, this is indeed a remarkable discovery.
Effects of Melatonin on Phosphorylation of Memory-Related Proteins in the Hippocampus and the Perirhinal Cortex in Male Mice
We recently demonstrated that a single post-training administration of either melatonin, an MT1/MT2 melatonin receptor agonist ramelteon, or a brain melatonin metabolite N1-acetyl-5-methoxyquinuramine (AMK) enhanced object recognition memory.
The present study aims to investigate the effects of melatonin, ramelteon, and AMK on relative phosphorylation levels of memory-related proteins in order to explore candidate signaling pathways associated with the receptor-mediated and nonreceptor-mediated memory-enhancing effects of melatonin.
We first confirmed that post-training administration of either melatonin, ramelteon, or AMK at 1 mg/kg promoted long-term memory formation, using the novel object recognition task.
Next, the effects of the same doses of these drugs on relative phosphorylation levels of the extracellular signal-regulated kinase (ERK) and calcium/calmodulin-dependent kinases (CaMKs) in the hippocampus and the perirhinal cortex (PRC) were examined by western blot analysis.
In the hippocampus, treatment with ramelteon or AMK significantly increased and decreased phosphorylation levels of ERK and cAMP-response element binding protein (CREB) and those of CaMKIIα and β, respectively.
In the PRC, phosphorylation levels of ERK and those of CaMKIIβ were significantly increased by both ramelteon and AMK and by ramelteon, respectively. Neither ramelteon nor AMK altered the phosphorylation levels of CaMKIV in either hippocampus or PRC.
These results suggest that melatonin may be involved in promoting the formation of long-term object recognition memory in a similar, if not identical, manner by modulating the phosphorylation levels of memory-related proteins such as ERK, CaMKIIs, and CREB in both receptor-mediated and nonreceptor-mediated signaling pathways.