Circadian modulation of short-term memory in Drosophila

Abstract

Endogenous biological clocks are widespread regulators of behavior and physiology, allowing for a more efficient allocation of efforts and resources over the course of a day. The extent that different processes are regulated by circadian oscillators, however, is not fully understood. We investigated the role of the circadian clock on short-term associative memory formation using a negatively reinforced olfactory-learning paradigm in Drosophila melanogaster. We found that memory formation was regulated in a circadian manner. The peak performance in short-term memory (STM) occurred during the early subjective night with a twofold performance amplitude after a single pairing of conditioned and unconditioned stimuli. This rhythm in memory is eliminated in both timeless and period mutants and is absent during constant light conditions. Circadian gating of sensory perception does not appear to underlie the rhythm in short-term memory as evidenced by the nonrhythmic shock avoidance and olfactory avoidance behaviors. Moreover, central brain oscillators appear to be responsible for the modulation as cryptochrome mutants, in which the antennal circadian oscillators are nonfunctional, demonstrate robust circadian rhythms in short-term memory. Together these data suggest that central, rather than peripheral, circadian oscillators modulate the formation of short-term associative memory and not the perception of the stimuli.Circadian clocks operate in organisms ranging from single-celled prokaryotes to humans. Intracellular circadian oscillators maintain 24 h cycles through circadian gene expression and autoregulatory, negative feedback loops (reviewed in Bell-Pedersen et al. 2005;Hardin 2005). Circadian regulation impacts almost every aspect of an animal's life including gene expression, enzyme activity, cell division, cell metabolism, as well as physiological and behavioral processes. 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).In contrast, it is more difficult to draw conclusions about the impact of the circadian clock on short-term memory (STM). In studies emphasizing short-term memory or working memory tasks in humans, time of day appears to influence memory and performance (reviewed in Schmidt et al. 20...

The FlyBar: Administering Alcohol to Flies

“…In Drosophila, continuous light (LL) conditions result in circadian dysfunction with dampened or abolished molecular oscillations of core circadian genes and disruption of behavioral circadian rhythms as evidenced by arrhythmic locomotor activity [18][19][20][21] and arrhythmic short-term memory 17 . The protocol is optimized for circadian studies and can be simplified for other experiments.…”

“…For that reason, no anesthesia (CO 2 or alternatives) is used during any of the following steps of the protocol. Furthermore, flies should be age matched across experiments and time points to minimize variability as is standard for other behavioral analyses including learning and memory experiments 17 .…”

Regulation of Drosophila circadian rhythms by miRNA let-7 is mediated by a regulatory cycle

“…A lmost all animals display a wide range of circadian rhythms in behaviour and physiology, such as locomotor activity, sleep, learning and memory, mating and endocrine function [1][2][3][4] . The circadian system includes an input pathway, a core clock system and an output pathway 5 .…”

<em>Drosophila</em> Adult Olfactory Shock Learning

“…As well as determination of the effect of circadian rhythms 18 , sleep 19 , diet 20,21 , senescence [11][12][13] , neurodegenerative disease 5 and drug treatments 5,6,19 on memory.…”

“…The length of the adult stage accommodates longer-term genetic, behavioral, dietary and pharmacological manipulations of memory, in addition to determining the effect of aging and neurodegenerative disease on memory [3][4][5][6][11][12][13][15][16][17][18][19][20][21] . Classical conditioning is induced by the simultaneous presentation of a neutral odor cue (conditioned stimulus, CS + ) and a reinforcement stimulus, e.g., an electric shock or sucrose, (unconditioned stimulus, US), that become associated with one another by the animal 1,16 .…”