Melatonin Suppresses Nighttime Memory Formation in Zebrafish

Abstract

Memory processes are modulated by the biological clock, although the mechanisms are unknown. Here, we report that in the diurnal zebrafish both learning and memory formation of an operant conditioning paradigm occur better during the day than during the night. Melatonin treatment during the day mimics the nighttime suppression of memory formation. Training in constant light improves nighttime memory formation while reducing endogenous melatonin concentrations. Treatment with melatonin receptor antagonists at night dramatically improves memory. Pinealectomy also significantly improves nighttime memory formation. We adduce that melatonin is both sufficient and necessary for poor memory formation during the night.

Circadian modulation of short-term memory in Drosophila

“…(Tapp and Holloway 1981;Fekete et al 1985). Finally, the circadian clock modulates learning such that greater memory is formed or recalled at a particular circadian phase as has been well characterized in Aplysia and zebrafish (Fernandez et al 2003;Lyons et al 2005Lyons et al , 2006Rawashdeh et al 2007). In contrast, how time of day affects short-term memory is considerably less well understood and often dismissed as having little or no impact.…”

“…Given the widespread effect of the circadian clock on physiology and behavior, it is not surprising that the circadian clock also affects learning and memory. In the past several years, circadian modulation of long-term memory formation has been observed in many invertebrate and vertebrate model systems including Aplysia (Fernandez et al 2003;Lyons et al 2005), zebrafish (Rawashdeh et al 2007), mice (Valentinuzzi et al 2001;Chaudhury and Colwell 2002), and rats (Rudy and Pugh 1998;Valentinuzzi et al 2004;Hasher 1999, 2004). More recently, investigations into the mechanism through which the circadian clock regulates long-term memory formation in Aplysia, have suggested that the circadian clock modulates memory formation in the presynaptic sensory neurons by regulating the induction of kinase activity and learning induced gene transcription (Lyons et al 2006).…”

Melatonin improves memory acquisition under stress independent of stress hormone release

“…Under non-stress conditions, melatonin reduced rather than improved induction of long term potentiation (LTP) in hippocampal slices from mice, i.e., a synaptic plastic process believed to underlie the encoding of novels stimuli (Ozcan et al 2006;Wang et al 2005). Moreover, a recent study in zebrafish describes a suppressive effect of administration of a very high melatonin dose on nighttime memory formation under nonstress conditions (Rawashdeh et al 2007). However, it is unknown whether these animal findings apply to daytime memory formation under resting conditions in humans.…”

Synchrony and desynchrony in circadian clocks: impacts on learning and memory

“…Melatonin, a circulating hormone rhythmically secreted by the pineal gland, functions in the circadian system through the SCN and also functions in neural plasticity (for review, see Rawashdeh and Maronde 2012). In pharmacological studies, acute administration of melatonin inhibits long-term potentiation ) and affects hippocampal neuronal plasticity (El-Sherif et al 2002; whereas melatonin receptor antagonists phase-specifically enhance nighttime memory in diurnal animals (Rawashdeh et al 2007). In rats, melatonin phase-specifically enhances memory during the day and impairs memory at night ).…”