CIRCADIAN MODULATION OF COMPLEX LEARNING IN DIURNAL AND NOCTURNAL APLYSIA
Lisa C. Lyons *, Oliver Rawashdeh *, Ayelet Katzoff †, Abraham J. Susswein †, and Arnold Eskin * , ‡
Understanding modulation of memory, as well as the mechanisms underlying memory formation, has become a key issue in neuroscience research. Previously, we found that the formation of long-term, but not short-term, memory for a nonassociative form of learning, sensitization, was modulated by the circadian clock in the diurnal Aplysia californica. To define the scope of circadian modulation of memory, we examined an associative operant learning paradigm, learning that food is inedible (LFI). Significantly greater long-term memory of LFI occurred when A. californica were trained and tested during the subjective day, compared with animals trained and tested in the subjective night. In contrast, animals displayed similar levels of short-term memory for LFI when trained in either the subjective day or night. Circadian modulation of long-term memory for LFI was dependent on the time of training, rather than the time of testing. To broaden our investigation of circadian modulation of memory, we extended our studies to a nocturnal species, Aplysia fasciata. Contrary to the significant memory observed during the day with the diurnal A. californica, A. fasciata showed no long-term memory for LFI when trained during the day. However, A. fasciata demonstrated significant long-term memory when trained and tested during the night. Thus, the circadian clock modulates memory formation in phase with the animals' activity period. The results from our studies of circadian modulation of long-term sensitization and LFI suggest that circadian modulation of memory formation may be a general phenomenon with potentially widespread implications for many types of long-term learning.
NON-OCULAR CIRCADIAN OSCILLATORS AND PHOTORECEPTORS MODULATE LONG TERM MEMORY FORMATION IN APLYSIA
Lisa C. Lyons *, Oliver Rawashdeh *, and Arnold Eskin
* equall contribution
In Aplysia californica, memory formation for long-term sensitization (LTS) and for a more complex type of associative learning, learning that food is inedible (LFI), is modulated by a circadian clock. For both types of learning, formation of long-term memory occurs during the day and significantly less during the night. Aplysia eyes contain a well-characterized circadian oscillator that is strongly coupled to the locomotor activity rhythm. Thus, the authors hypothesized that the ocular circadian oscillator was responsible for the circadian modulation of LFI and LTS. To test this hypothesis, they investigated whether the eyes were necessary for circadian modulation of LFI and LTS. Eyeless animals trained during the subjective day and tested 24 h later demonstrated robust long-term memory for both LFI and LTS, while eyeless animals trained and tested during the subjective night showed little or no memory for LFI or LTS. The amplitude of the rhythm of modulation in eyeless animals was similar to that of intact Aplysia, suggesting that extraocular circadian oscillators were mainly responsible for the circadian rhythms in long-term memory formation. Next, the authors investigated whether the eyes played a role in photic entrainment for circadian regulation of long-term memory formation. Eyeless animals were exposed to a reversed LD cycle for 7 days and then trained and tested for long-term memory using the LFI paradigm. Eyeless Aplysia formed significant long-term memory when trained during the projected shifted day but not during the projected shifted night. Thus, the extraocular circadian oscillator responsible for the rhythmic modulation of long-term memory formation can be entrained by extraocular photoreceptors.
MELATONIN SUPPRESSES NIGHTTIME MEMORY FORMATION IN ZEBRAFISH
Oliver Rawashdeh, Nancy Hernandez de Borsetti, Gregg Roman*, Gregory M. Cahill
* corresponding Author
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.
CYCLING BEHAVIOR AND MEMORY FORMATION
Jason R. Gerstner, Lisa C. Lyons, Kenneth P. Wright Jr, Dawn H. Loh, Oliver Rawashdeh, Kristin L. Eckel-Mahan, and Gregg W. Roman
Circadian research has spent considerable effort in the determining clock output pathways, including identifying both physiological and behavioral processes that demonstrate significant time-of-day variation. Memory formation and consolidation represent notable processes shaped by endogenous circadian oscillators. To date, very few studies on memory mechanisms have considered potential confounding effects of time-of-day and the organism's innate activity cycles (e.g., nocturnal, diurnal, or crepuscular). The following studies highlight recent work describing this interactive role of circadian rhythms and memory formation, and were presented at a mini-symposium at the 2009 annual meeting of the Society for Neuroscience. The studies illustrate these time-of-day observations in a variety of behavioral paradigms and model organisms, including olfactory avoidance conditioning in Drosophila, long-term sensitization in Aplysia, active-avoidance conditioning in Zebrafish, and classical fear conditioning in rodents, suggesting that the circadian influence on memory behavior is highly conserved across species. Evidence also exists for a conserved mechanistic relationship between specific cycling molecules and memory formation, and the extent to which proper circadian cycling of these molecules is necessary for optimal cognitive performance. Studies describe the involvement of the core clock gene period, as well as vasoactive intestinal peptide, melatonin, and the cAMP/MAPK (cAMP/mitogen-activated protein kinase) cascade. Finally, studies in humans describe evidence for alterations in cognitive performance based on an interaction between sleep–wake homeostasis and the internal circadian clock. Conservation of a functional relationship between circadian rhythms with learning and memory formation across species provides a critical framework for future analysis of molecular mechanisms underlying complex behavior.
AGEING OR NOT, CLOCK GENES ARE IMPORTANT FOR MEMORY PROCESSES; AN INTERESTING HYPOTHESIS RAISING MANY QUESTIONS
Oliver Rawashdeh, and Joerg H. Stehle
Commentary on: Kondratova et al. Circadian clock proteins control adaptation to novel environment and memory formation Aging. 2010
CIRCADIAN PERIODS OF SENSITIVITY FOR RAMELTEON ON THE ONSET OF RUNNING-WHEEL ACTIVITY ON THE PEAK OF SUPRACHIASMATIC NUCLEUS FIRING RHYTHMS IN C3H/HEN MICE
Oliver Rawashdeh, Randall L. Hudson, Iwona Stepien, and Margarita L. Dubocovich
Ramelteon, an MT1/MT2 melatonin receptor agonist, is used for the treatment of sleep-onset insomnia and circadian sleep disorders. Ramelteon phase shifts circadian rhythms in rodents and humans when given at the end of the subjective day; however, its efficacy at other circadian times is not known. Here, the authors determined in C3H/HeN mice the maximal circadian sensitivity for ramelteon in vivo on the onset of circadian running-wheel activity rhythms, and in vitro on the peak of circadian rhythm of neuronal firing in suprachiasmatic nucleus (SCN) brain slices. The phase response curve (PRC) for ramelteon (90 µg/mouse, subcutaneous [sc]) on circadian wheel-activity rhythms shows maximal sensitivity during the late mid to end of the subjective day, between CT8 and CT12 (phase advance), and late subjective night and early subjective day, between CT20 and CT2 (phase delay), using a 3-day-pulse treatment regimen in C3H/HeN mice. The PRC for ramelteon resembles that for melatonin in C3H/HeN mice, showing the same magnitude of maximal shifts at CT10 and CT2, except that the range of sensitivity for ramelteon (CT8–CT12) during the subjective day is broader. Furthermore, in SCN brain slices in vitro, ramelteon (10 pM) administered at CT10 phase advances (5.6 ± 0.29 h, n = 3) and at CT2 phase delays (−3.2 ± 0.12 h, n = 6) the peak of circadian rhythm of neuronal firing, with the shifts being significantly larger than those induced by melatonin (10 pM) at the same circadian times (CT10: 2.7 ± 0.15 h, n = 4, p < .05; CT2: −1.13 ± 0.08 h, n = 6, p < .001, respectively). The phase shifts induced by both melatonin and ramelteon in the SCN brain slice at either CT10 or CT2 corresponded with the period of sensitivity observed in vivo. In conclusion, melatonin and ramelteon showed identical periods of circadian sensitivity at CT10 (advance) and CT2 (delay) to shift the onset of circadian activity rhythms in vivo and the peak of SCN neuronal firing rhythms in vitro.
THE HORMONAL ZEITGEBER MELATONIN: ROLE AS A CIRCADIAN MODULATOR IN MEMORY PROCESSING
Oliver Rawashdeh, and Erik Maronde
The neuroendocrine substance melatonin is a hormone synthesized rhythmically by the pineal gland under the influence of the circadian system and alternating light/dark cycles. Melatonin has been shown to have broad applications, and consequently becoming a molecule of great controversy. Undoubtedly, however, melatonin plays an important role as a time cue for the endogenous circadian system. This review focuses on melatonin as a regulator in the circadian modulation of memory processing. Memory processes (acquisition, consolidation, and retrieval) are modulated by the circadian system. However, the mechanism by which the biological clock is rhythmically influencing cognitive processes remains unknown. We also discuss, how the circadian system by generating cycling melatonin levels can implant information about daytime into memory processing, depicted as day and nighttime differences in acquisition, memory consolidation and/or retrieval.
A SURVEY OF MOLECULAR DETAILS IN THE HUMAN PINEAL GLAND IN THE LIGHT OF PHYLOGENY, STRUCTURE, FUNCTION AND CHRONOBIOLOGICAL DISEASES
Jörg H. Stehle, Anastasia Saade, Oliver Rawashdeh, Katrin Ackermann, Antje Jilg, Tamás Sebestény and Erik Maronde
The human pineal gland is a neuroendocrine transducer that forms an integral part of the brain. Through the nocturnally elevated synthesis and release of the neurohormone melatonin, the pineal gland encodes and disseminates information on circadian time, thus coupling the outside world to the biochemical and physiological internal demands of the body. Approaches to better understand molecular details behind the rhythmic signalling in the human pineal gland are limited but implicitly warranted, as human chronobiological dysfunctions are often associated with alterations in melatonin synthesis. Current knowledge on melatonin synthesis in the human pineal gland is based on minimally invasive analyses, and by the comparison of signalling events between different vertebrate species, with emphasis put on data acquired in sheep and other primates. Together with investigations using autoptic pineal tissue, a remnant silhouette of premortem dynamics within the hormone’s biosynthesis pathway can be constructed. The detected biochemical scenario behind the generation of dynamics in melatonin synthesis positions the human pineal gland surprisingly isolated. In this neuroendocrine brain structure, protein-protein interactions and nucleo-cytoplasmic protein shuttling indicate furthermore a novel twist in the molecular dynamics in the cells of this neuroendocrine brain structure. These findings have to be seen in the light that an impaired melatonin synthesis is observed in elderly and/or demented patients, in individuals affected by Alzheimer’s disease, Smith–Magenis syndrome, autism spectrum disorder and sleep phase disorders. Already, recent advances in understanding signalling dynamics in the human pineal gland have significantly helped to counteract chronobiological dysfunctions through a proper restoration of the nocturnal melatonin surge.
LONG-TERM EFFECTS OF MATERNAL SEPARATION ON THE RESPONSIVENESS OF THE CIRCADIAN SYSTEM TO MELATONIN IN THE DIURNAL NONHUMAN PRIMATE (MACACA MULATTA)
Oliver Rawashdeh and Margarita L. Dubocovich
Depression is often linked to early-life adversity and circadian disturbances. Here, we assessed the long-term impact of early-life adversity, particularly preweaning mother–infant separation, on the circadian system's responsiveness to a time giver or synchronizer (Zeitgeber). Mother-reared (MR) and peer-reared (PR) rhesus monkeys were subjected to chronic jet-lag, a forced desynchrony protocol of 22 hr T-cycles [11:11 hr light:dark (LD) cycles] to destabilize the central circadian organization. MR and PR monkeys subjected to the T-cycles showed split locomotor activity rhythms with periods of ~22 hr (entrained) and ~24 hr (free-running), simultaneously. Continuous melatonin treatment in the drinking water (20 μg/mL) gradually increased the amplitude of the entrained rhythm at the expense of the free-running rhythm, reaching complete entrainment by 1 wk. Upon release into constant dim light, a rearing effect on anticipation for both the predicted light onset and food presentation was observed. In MR monkeys, melatonin did not affect the amplitude of anticipatory behavior. Interestingly, however, PR macaques showed light onset and food anticipatory activities in response to melatonin treatment. These results demonstrate for the first time a rearing-dependent effect of maternal separation in macaques, imprinting long-term plastic changes on the circadian system well into late adulthood. These effects could be counteracted by the synchronizer molecule melatonin. We conclude that the melatonergic system is targeted by early-life adversity of maternal separation and that melatonin supplementation ameliorates the negative impact of stress on the circadian system.
PERIOD1 COORDINATES HIPPOCAMPAL RHYTHMS AND MEMORY PROCESSING WITH DAYTIME
Oliver Rawashdeh, Antje Jilg, Peter Jedlicka, Jolanta Slawska, Lukas Thomas, Anastasia Saade, Stephan W. Schwarzacher and Jörg H. Stehle
In species ranging from flies to mammals, parameters of memory processing, like acquisition, consolidation, and retrieval are clearly molded by time of day. However, mechanisms that regulate and adapt these temporal differences are elusive, with an involvement of clock genes and their protein products suggestive. Therefore, we analyzed initially in mouse hippocampus the daytime-dependent dynamics of parameters, known to be important for proper memory formation, like phosphorylation of the “memory molecule” cyclic adenosine monophosphate (cAMP) responsive element binding protein (CREB) and chromatin remodeling. Next, in an effort to characterize the mechanistic role of clock genes within hippocampal molecular dynamics, we compared the results obtained from wildtype (WT) -mice and mice deficient for the archetypical clock gene Period1 (Per1-/--mice). We detected that the circadian rhythm of CREB phosphorylation in the hippocampus of WT mice disappeared completely in mice lacking Per1. Furthermore, we found that the here for the first time described profound endogenous day/night rhythms in histone modifications in the hippocampus of WT-mice are markedly perturbed in Per1-/--mice. Concomitantly, both, in vivorecorded LTP, a cellular correlate for long-term memory, and hippocampal gene expression were significantly altered in the absence of Per1. Notably, these molecular perturbations in Per1-/--mice were accompanied by the loss of daytime-dependent differences in spatial working memory performance. Our data provide a molecular blueprint for a novel role of PER1 in temporally shaping the daytime-dependency of memory performance, likely, by gating CREB signaling, and by coupling to downstream chromatin remodeling.
RIBOSOMAL RNA - A TAIL WAGGING THE DOG?
Jörg H. Stehle and Oliver Rawashdeh
It is an intriguing hypothesis that the complex organization of neuronal dynamics important for a memory engram is largely underpinned by the regulation of nucleolar functioning. This Editorial highlights a study by Capitano and coworkers in this issue of the Journal of Neurochemistry, in which the authors tackle this hypothesis with a behavioral approach. The study investigates the role of axo-dendritic mRNAs within learning-induced plasticity and in vivo modulation of rRNA transcription in response to spatial learning. The authors confirm with their in vivo approach what is known from many earlier in vitro experiments: efficient learning and memory requires a proper homeostasis of hippocampal neurons in general, which, however, depends crucially on proper integrity of the nucleolus.
PERIOD1 GATES THE CIRCADIAN MODULATION OF MEMORY-RELEVANT SIGNALING IN MOUSE HIPPOCAMPUS BY REGULATING THE NUCLEAR SHUTTLING OF THE CREB KINASE pP90RSK
Oliver Rawashdeh, Antje Jilg, Erik Maronde, Jan Fahrenkrug and Jörg H. Stehle
Memory performance varies over a 24-h day/night cycle. While the detailed underlying mechanisms are yet unknown, recent evidence suggests that in the mouse hippocampus, rhythmic phosphorylation of mitogen-activated protein kinase (MAPK) and cyclic adenosine monophosphate response element-binding protein (CREB) are central to the circadian (~ 24 h) regulation of learning and memory. We recently identified the clock protein PERIOD1 (PER1) as a vehicle that translates information encoding time of day to hippocampal plasticity. We here elaborate how PER1 may gate the sensitivity of memory-relevant hippocampal signaling pathways. We found that in wild-type mice (WT), spatial learning triggers CREB phosphorylation only during the daytime, and that this effect depends on the presence of PER1. The time-of-day-dependent induction of CREB phosphorylation can be reproduced pharmacologically in acute hippocampal slices prepared from WT mice, but is absent in preparations made from Per1-knockout (Per1(-/-) ) mice. We showed that the PER1-dependent CREB phosphorylation is regulated downstream of MAPK. Stimulation of WT hippocampal neurons triggered the co-translocation of PER1 and the CREB kinase pP90RSK (pMAPK-activated ribosomal S6 kinase) into the nucleus. In hippocampal neurons from Per1(-/-) mice, however, pP90RSK remained perinuclear. A co-immunoprecipitation assay confirmed a high-affinity interaction between PER1 and pP90RSK. Knocking down endogenous PER1 in hippocampal cells inhibited adenylyl cyclase-dependent CREB activation. Taken together, the PER1-dependent modulation of cytoplasmic-to-nuclear signaling in the murine hippocampus provides a molecular explanation for how the circadian system potentially shapes a temporal framework for daytime-dependent memory performance, and adds a novel facet to the versatility of the clock gene protein PER1. We provide evidence that the circadian clock gene Period1 (Per1) regulates CREB phosphorylation in the mouse hippocampus, sculpturing time-of-day-dependent memory formation. This molecular mechanism constitutes the functional link between circadian rhythms and learning efficiency. In hippocampal neurons of wild-type mice, pP90RSK translocates into the nucleus upon stimulation with forskolin (left), whereas in Period1-knockout (Per1(-/-) ) mice (right) the kinase is trapped at the nuclear periphery, unable to efficiently phosphorylate nuclear CREB. Consequently, the presence of PER1 in hippocampal neurons is a prerequisite for the time-of-day-dependent phosphorylation of CREB, as it regulates the shuttling of pP90RSK into the nucleus.
LEARNED MOTIVATION DRIVES CIRCADIAN PHYSIOLOGY IN THE ABSENCE OF THE MASTER CIRCADIAN CLOCK
Oliver Rawashdeh, Shannon Clough, Randal Hudson and Margarita Dubocovich
The suprachiasmatic nucleus (SCN)-often referred to as the master circadian clock-is essential in generating physiologic rhythms and orchestrating synchrony among circadian clocks. This study tested the hypothesis that periodic motivation induced by rhythmically pairing 2 reinforcing stimuli [methamphetamine (Meth) and running wheel (RW)] restores autonomous circadian activity in arrhythmic SCN-lesioned (SCNX) C3H/HeN mice. Sham-surgery and SCNX mice were treated with either Meth (1.2 mg/kg, i.p.) or vehicle in association, dissociation, or absence of an RW. Only the association of Meth treatment and restricted RW access successfully reestablished entrained circadian rhythms in mice with SCNX. RW-likely acting as a link between the circadian and reward systems-promotes circadian entrainment of activity. We conclude that a conditioned drug response is a powerful tool to entrain, drive, and restore circadian physiology. Furthermore, an RW should be recognized as a potent input signal in addition to the conventional use as an output signal.
THE HIPPOCAMPAL AUTOPHAGIC MACHINERY IS DEPRESSED IN THE ABSENCE OF THE CIRCADIAN CLOCK PROTEIN PER1 THAT MAY LEAD TO VULNERABILITY DURING CEREBRAL ISCHEMIA
Abdelhaq Rami, Julia Fekadu and Oliver Rawashdeh
Autophagy is an intracellular bulk self-degrading process in which cytoplasmic contents of abnormal proteins and excess or damaged organelles are sequestered into autophagosomes, and degraded upon fusion with lysosomes. Although autophagy is generally considered to be pro-survival, it also functions in cell death processes. We recently reported on the hippocampal, higher vulnerability to cerebral ischemia in mice lacking the circadian clock protein PERIOD1 (PER1), a phenomenon we found to be linked to a PER1-dependent modulation of the expression patterns of apoptotic/autophagic markers.
To exclude the contribution of vascular or glial factors to the innate vulnerability of Per1 knockout-mice (Per1-/- mice) to cerebral ischemia in vivo, we compared the autophagic machinery between primary hippocampal cultures from wild-type (WT)- and Per1-/--mice, using the lipophilic macrolide antibiotic, Rapamycin to induce autophagy.
Development of autophagy in WT cells involved an increased LC3-II-to-LC3-I ratio (microtubule-associated protein 1 light chain 3) and an overall increase in the level of LC3-II. In addition, immunostaining of LC3 in WT cells revealed the typical transformation of LC3 localization from a diffused staining to a dot- and ring-like pattern. In contrast, Per1-/- hippocampal cells were resistant to Rapamycin induced alterations of autophagy hallmarks.
Our in vitro data suggests that basal activity of autophagy seems to be modulated by PER1, and confirms the in vivo data by showing that the autophagic machinery is depressed in Per1-/-hippocampal neurons.The implication of both autophagy and circadian dysfunction in the pathogenesis of cerebral ischemia suggests that a functional connection between the two processes may exist.
CLOCKING IN TIME TO GATE MEMORY PROCESSES: THE CIRCADIAN CLOCK IS PART OF THE INS AND OUTS OF MEMORY
Oliver Rawashdeh, Rex Parsons and Erik Maronde
Learning, memory consolidation, and retrieval are processes known to be modulated by the circadian (circa: about; dies: day) system. The circadian regulation of memory performance is evolutionarily conserved, independent of the type and complexity of the learning paradigm tested, and not specific to crepuscular, nocturnal, or diurnal organisms. In mammals, long-term memory (LTM) formation is tightly coupled to de novo gene expression of plasticity-related proteins and posttranslational modifications and relies on intact cAMP/protein kinase A (PKA)/protein kinase C (PKC)/mitogen-activated protein kinase (MAPK)/cyclic adenosine monophosphate response element-binding protein (CREB) signaling. These memory-essential signaling components cycle rhythmically in the hippocampus across the day and night and are clearly molded by an intricate interplay between the circadian system and memory. Important components of the circadian timing mechanism and its plasticity are members of the Period clock gene family (Per1, Per2). Interestingly, Per1 is rhythmically expressed in mouse hippocampus. Observations suggest important and largely unexplored roles of the clock gene protein PER1 in synaptic plasticity and in the daytime-dependent modulation of learning and memory. Here, we review the latest findings on the role of the clock gene Period 1 (Per1) as a candidate molecular and mechanistic blueprint for gating the daytime dependency of memory processing.
EARLY POSTNATAL DEVELOPMENT OF THE VISUAL CORTEX IN MICE WITH RETINAL DEGENERATION
Dominique Himmelhan, Oliver Rawashdeh, and Helmut Ölschläger
This study characterizes the early postnatal development of the visual neocortex in C3H/HeNRj mice. These mice are homozygous for the Pde6brd1 mutation, which causes retinal degeneration starting from postnatal day 7 (P7). To monitor the development of the visual cortex between P3 and P28 we used eight antigens known to be expressed at different developmental stages (Nestin, tau3, β3- Tubulin, Calbindin, Doublecortin, MAP2, Parvalbumin and NeuN). Using semiquantitative analysis we traced the expression and localization of different developmental markers throughout the layers of the visual cortex. Cortical tissue sections corresponding to the first postnatal week (P3-P6) stained positively for Nestin, tau3, β3-Tubulin and Calbindin. These proteins are known to be involved in the migration of neural progenitor cells (NPCs) within the cortical plate. At the time of eye-opening (P14), Doublecortin, MAP2 and NeuN, markers for developing and maturing neurons involved in NPC differentiation are present. Between P9 and P21 Nestin and Calbindin disappear while NeuN and Parvalbumin expression increases in the course of visual neocortex development. The findings of this study provide a snapshot of the dynamic changes in cortex formation during early postnatal development. So far, it is the first investigation on the postnatal development of the mouse visual cortex. Our results indicate that in C3H/HeNRj mice retinal degeneration during these early stages may not influence the maturation of the visual cortex. Until P28 in this mouse strain, the development of the visual neocortex is in accordance with data from other mice (C57BL/6) without retinal degeneration. Whether in older individuals of the C3H/HeNRj strain the visual neocortex will show signs of functional impairment has to be shown by future work.
PERICONCEPTIONAL MATERNAL ALCOHOL CONSUMPTION LEADS TO BEHAVIOURAL CHANGES IN ADULT AND AGED OFFSPRING AND ALTERS THE EXPRESSION OF HIPPOCAMPAL GENES ASSOCIATED WITH LEARNING AND MEMORY AND REGULATORS OF THE EPIGENOME
D. Lucia, D. Burgess, C.L. Cullen, E.S. Dorey, Oliver Rawashdeh, and K.M. Moritz
Maternal alcohol consumption throughout pregnancy can result in long term behavioural deficits in offspring. However, less is known about the impact of alcohol during the periconceptional period (PC). The aim of this study was to examine the effect of PC ethanol (PC:EtOH) exposure on long term cognitive function; including memory and anxiety. Rats were exposed to a liquid diet containing ethanol (EtOH) (12.5% vol;vol) or a control diet from 4 days prior to mating until day 4 of pregnancy.
Separate cohorts of animals were tested at 6 months (adult) or 15–18 months of age (aged). Offspring underwent a series of behavioural tests to assess anxiety, spatial and recognition memory. The hippocampus was collected, and mRNA expression of epigenetic modifiers and genes implicated in learning and memory were examined. PC:EtOH exposure resulted in a subtle anxiety like behaviour in adult female offspring with a significant reduction in directed exploring/head dipping behaviour during holeboard testing. In aged male offspring, PC:EtOH exposure resulted in a tendency for increased directed exploring/head dipping behaviour during holeboard testing. No differences between treatments were observed in the elevated plus maze. Aged female offspring exposed to PC:EtOH demonstrated short term spatial memory impairment (P < 0.05). PC:EtOH resulted in an upregulation of hippocampal mRNA expression of bdnf, grin2a and grin2b at 18 months of age along with increased expression of epigenetic modifiers (dnmt1, dnmt3a and hdac2). In conclusion, PC:EtOH can lead to sex specific anxiety-like behaviour and impairments in spatial memory and altered hippocampal gene expression.
COUPLING THE CIRCADIAN CLOCK TO HOMEOSTASIS: THE ROLE OF PERIOD IN TIMING PHYSIOLOGY
Pureum Kim, Henrik Oster, Hendrik Lehnert, Sebastian M Schmid, Nicole Salamat, Johanna L Barclay, Erik Maronde, Warrick Inder, Oliver Rawashdeh
A plethora of physiological processes show stable and synchronized daily oscillations that are either driven or modulated by biological clocks. A circadian pacemaker located in the suprachiasmatic nucleus of the ventral hypothalamus coordinates 24-hour oscillations of central and peripheral physiology with the environment. The circadian clockwork involved in driving rhythmic physiology is composed of various clock genes that are interlocked via a complex feedback loop to generate precise yet plastic oscillations of ∼24 hours. This review focuses on the specific role of the core clockwork gene Period1 and its paralogs on intra-oscillator and extra-oscillator functions, including, but not limited to, hippocampus-dependent processes, cardiovascular function, appetite control, as well as glucose and lipid homeostasis. Alterations in Period gene function have been implicated in a wide range of physical and mental disorders. At the same time, a variety of conditions including metabolic disorders also impact clock gene expression, resulting in circadian disruptions, which in turn often exacerbates the disease state.
AT THE INTERSECTION OF MICROBIOTA AND CIRCADIAN CLOCK: ARE SEXUAL DIMORPHISM AND GROWTH HORMONES THE MISSING LINK TO PATHOLOGY?
Benjamin D. Weger, Oliver Rawashdeh, Frederic Gachon
Reciprocal interactions between the host circadian clock and the microbiota are evidenced by recent literature. Interestingly, dysregulation of either the circadian clock or microbiota is associated with common human pathologies such as obesity, type 2 diabetes, or neurological disorders. However, it is unclear to what extent a perturbation of pathways regulated by both the circadian clock and microbiota is involved in the development of these disorders. It is speculated that these perturbations are associated with impaired growth hormone (GH) secretion and sexual development. The GH axis is a broadly neglected pathway and could be the main converging point for the interaction of both circadian clock and microbiota. Here, the links between the circadian clock and microbiota are reviewed. Finally, the effects of chronodisruption and dysbiosis on physiology and pathology are discussed and it is speculated whether a common deregulation of the GH pathway could mediates those effects.
CircaCompare: A METHOD TO ESTIMATE AND STATISTICALLY SUPPORT DIFFERENCES IN MESOR, AMPLITUDE, AND PHASE, BETWEEN CIRCADIAN RHYTHMS
Rex Parsons, Richard Parsons, Nicholas Garner, Henrik Oster, Oliver Rawashdeh
A fundamental interest in chronobiology is to compare patterns between groups of rhythmic data. However, many existing methods are ill-equipped to derive statements concerning the statistical significance of differences between rhythms that may be visually apparent. This is attributed to both the form of data used (longitudinal versus cross-sectional) and the limitations of the statistical tests used to draw conclusions.
To address this problem, we propose that a cosinusoidal curve with a particular parametrization be used to model and compare data of two sets of observations collected over a 24-h period. The novelty of our test is in the parametrization, which allows the explicit estimation of rhythmic parameters [mesor (the rhythm-adjusted mean level of a response variable around which a wave function oscillates), amplitude and phase], and simultaneously testing for statistical significance in all three parameters between two or more groups of datasets. A statistically significant difference between two groups, regarding each of these rhythmic parameters, is indicated by a P-value. The method is evaluated by applying the model to publicly available datasets, and is further exemplified by comparison to the currently recommended method, DODR. The results suggest that the method proposed may be highly sensitive to detect rhythmic differences between groups in phase, amplitude and mesor.
Availability and implementation