As per a new Nature Reviews Neuroscience research highlight , conditioning in zebrafish happened better during subjective daytime (SD) as compared to subjective nighttime (SN) and this effect was mediated by the release of Melatonin during nighttime. the authors conclude that Melatonin suppresses memory formation in Zebrafish.
Learning and memory are known to be influenced by the time of day, but the nature and mechanism of this modulation has been elusive. Now, a new study shows that melatonin, a hormone released in a circadian fashion, affects memory consolidation in zebrafish.
Melatonin release peaks during the night and falls during the day, and melatonin has been shown to affect neuronal firing in the hippocampus. The authors therefore decided to investigate whether melatonin mediates the effects of the circadian system on memory formation. They found that bathing the zebrafish in 50 M melatonin prior to SD conditioning significantly suppressed memory formation, whereas administration after conditioning or prior to testing had no effect. Furthermore, administration of a melatonin-receptor antagonist prior to SN conditioning significantly improved memory retention, as did removal of the pineal gland, the site of melatonin release.
Taken together, these results show that memory formation in zebrafish is inhibited during the night relative to the day, and that this modulation is mediated at least in part by circadian melatonin release. This might direct future research into improving mental performance in humans.
While extending the research results from zebrafish to humans may be premature, some simple studies with human subjects can confirm the effect of melatonin on human learning. and memory formation.