Effect of valproic acid through regulation of NMDA receptor-ERK signaling in sleep deprivation rats

Downregulation of microRNA-330-5p induces manic-like behaviors in REM sleep-deprived rats by enhancing tyrosine hydroxylase expression

AIM

In our pilot study, we found an increase in tyrosine hydroxylase (Th) mRNA expression in the prefrontal cortex of 72-h REM sleep-deprived (SD) rats, a mania model. Additionally, the expression levels of miR-325-3p, miR-326-3p, and miR-330-5p, the predicted target miRNAs on TH, were significantly decreased. Based on these results, in this study, we investigated whether miRNA-325-3p, miR-326-3p, and miR-330-5p modulate TH and manic-like behaviors in SD rats.

METHODS

Manic-like behaviors were assessed using the open field test (OFT) and elevated plus-maze (EPM) test. The direct binding activity of miRNAs to the 3'-untranslated region (3'-UTR) of the Th gene was measured in HEK-293 cells using a luciferase reporter system. We also examined mRNA and protein expression of TH after intracerebroventricular (ICV) injection of miR-330-5p agomir to SD rats, along with manic-like behaviors.

RESULTS

We observed an upregulation in mRNA and protein expression of TH and downregulation in miRNA-325-3p, miR-326-3p, and miR-330-5p expressions in the prefrontal cortex of SD rats, together with increased manic-like behaviors. The luciferase reporter assay showed that miR-330-5p could repress TH expression through direct binding to its target site in the 3'-UTR of Th, whereas miR-326-3p and miR-330-5p could not. In addition, ICV injection of miR-330-5p agomir alleviated the increase in TH expression in the prefrontal cortex of SD rats and manic-like behaviors.

CONCLUSIONS

TH expression regulation through miR-330-5p may be implicated in the pathophysiology of mania in SD rats.

Combined cell grafting and VPA administration facilitates neural repair through axonal regeneration and synaptogenesis in traumatic brain injury

Neuronal regeneration and functional recovery are severely compromised following traumatic brain injury (TBI). Treatment options, including cell transplantation and drug therapy, have been shown to benefit TBI, although the underlying mechanisms remain elusive. In this study, neural stem cells (NSCs) are transplanted into TBI-challenged mice, together with olfactory ensheathing cells (OECs) or followed by valproic acid (VPA) treatment. Both OEC grafting and VPA treatment facilitate the differentiation of NSCs into neurons (including endogenous and exogenous neurons) and significantly attenuate neurological functional defects in TBI mice. Combination of NSCs with OECs or VPA administration leads to overt improvement in axonal regeneration, synaptogenesis, and synaptic plasticity in the cerebral cortex in TBI-challenged mice, as shown by retrograde corticospinal tract tracing, electron microscopy, growth-associated protein 43 (GAP43), and synaptophysin (SYN) analyses. However, these beneficial effects of VPA are reversed by local delivery of N-methyl-D-aspartate (NMDA) into tissues surrounding the injury epicenter in the cerebral cortex, accompanied by a pronounced drop in axons and synapses in the brain. Our findings reveal that increased axonal regeneration and synaptogenesis evoked by cell grafting and VPA fosters neural repair in a murine model of TBI. Moreover, VPA-induced neuroprotective roles are antagonized by exogenous NMDA administration and its concomitant decrease in the number of neurons of local brain, indicating that increased neurons induced by VPA treatment mediate axonal regeneration and synaptogenesis in mice after TBI operation. Collectively, this study provides new insights into NSC transplantation therapy for TBI.

Neuroprotective effects of sodium valproate on hippocampal cell and volume, and cognitive function in a rat model of focal cerebral ischemia

Valproate (VPA) as a histone deacetylase (HDAC) inhibitor has shown neuroprotective effects in neurodegenerative diseases. This study evaluated whether VPA treatment ameliorated the synaptic plasticity dysfunction, hippocampal neuronal loss, and spatial memory deficits induced by cerebral ischemia in the middle cerebral artery occlusion (MCAO) model. Thirty-two male Sprague-Dawley rats were randomly divided into 4 groups control, sham, cerebral ischemia+vehicle (MCAO+V), and MCAO+VPA. The right common carotid artery was occluded for 1 hour. VPA (300 mg/kg) or vehicles were injected intraperitoneally on days 0,1,2 and 3 of the reperfusion. After 7 days of reperfusion the Morris water maze, passive avoidance, and open field tests were performed. Hippocampal synaptic plasticity in the CA1 area was recorded by field potential recording. We used the term neuronal Input-Output (I/O) function and paired-pulse ratio (PPR) to refer to basal synaptic transmission and presynaptic neurotransmitter release probability respectively. After that, the brains were removed for assaying stereological parameters of the CA1 neurons. Our results showed the VPA administration significantly reduced the total infarct volume, improved MCAO-induced spatial learning -memory, fear memory, and anxiety compared to the MCAO+V group. In addition, the field potential recording showed that VPA significantly ameliorated the impaired the long- term potentiation (LTP) induced by MCAO, without any effects on basal synaptic transmission and neurotransmitter release probability. Therefore, it seems that a decrease in total infarct volume and induction of long-term potentiation via postsynaptic mechanisms is responsible for improving MCAO-induced cognitive impairment.

REM-Sleep Deprivation Induces Mitochondrial Biogenesis in the Rat Hippocampus

BACKGROUND/AIM

Sleep loss is proposed as a trigger for manic episodes in bipolar disorder in humans. It has been shown that sleep and wakefulness can affect changes in mitochondrial gene expression, oxidative phosphorylation (OXPHOS) activity, and morphology in the brain. In this study, we investigated alterations in mitochondrial bioenergetic function in the brain of rats after 72-h rapid eye movement sleep deprivation (REM-SD).

MATERIALS AND METHODS

Alterations in the mitochondrial DNA (mtDNA) copy number were detected in the prefrontal cortex and hippocampus through amplification of mitochondrially encoded NADH dehydrogenase 1 (mt-Nd1) gene using quantitative real-time polymerase chain reaction. The expression levels of mitochondrial biogenesis-related proteins such as peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PPARGC1A), cytochrome c oxidase subunit 4I1 (COX4I1) and sirtuin 3 (SIRT3) were assessed using western blot analysis and immunohistochemistry.

RESULTS

We found that REM-SD significantly increased the mtDNA copy number in the hippocampus but not in the prefrontal cortex. In addition, REM-SD increased the protein expression of COX4I1 in the hippocampus. Furthermore, we observed manic-like behaviors in rats exposed to 72-h REM-SD. REM-SD increased locomotion in the open-field test and the time spent in open arms in the elevated plus-maze test.

CONCLUSION

REM-SD may induce mitochondrial dysfunction in the brain, which may be involved in the induction of mania.

Jujuboside A prevents sleep loss-induced disturbance of hippocampal neuronal excitability and memory impairment in young APP/PS1 mice

Sleep deprivation (SD) is the hallmark of modern society and may increase risk of Alzheimer's disease (AD). However, it is unclear how SD facilitates early cognitive impairments observed in AD models, as the underlying molecular mechanism is largely unknown. Here, we aim to investigate SD-induced cellular and molecular alterations in hippocampus of young APP/PS1 mice and whether jujuboside A (JuA) treatment could negate these alterations. Our results reveal that although SD causes spatial memory impairments in both genotypes, SD decreases frequency and amplitude of mEPSCs and pCREB levels in WT, but increases frequency and amplitude of mEPSCs, NMDAR, GluR1, pCaMKII (β, α) and decreases CREB levels in APP/PS1 mice, implicating that SD may facilitate abnormalities in young APP/PS1 mice via enhancing neuronal excitability. Moreover, JuA suppresses SD-induced enhancement of mEPSCs and prevents memory impairment in APP/PS1 mice. Further, whole-cell puff experiment suggests that JuA may function to activate GABAergic inhibition to reduce SD-induced enhancement of excitatory synaptic transmission in APP/PS1 mice. The present study reveals that sleep loss induces spatial memory impairment in an AD mouse model by disrupting the excitatory signaling pathway, and JuA prevents this via GABAergic mechanism.

Perspectives in affective disorders: Clocks and sleep

Mood disorders are often characterised by alterations in circadian rhythms, sleep disturbances and seasonal exacerbation. Conversely, chronobiological treatments utilise zeitgebers for circadian rhythms such as light to improve mood and stabilise sleep, and manipulations of sleep timing and duration as rapid antidepressant modalities. Although sleep deprivation ("wake therapy") can act within hours, and its mood-elevating effects be maintained by regular morning light administration/medication/earlier sleep, it has not entered the regular guidelines for treating affective disorders as a first-line treatment. The hindrances to using chronotherapeutics may lie in their lack of patentability, few sponsors to carry out large multi-centre trials, non-reimbursement by medical insurance and their perceived difficulty or exotic "alternative" nature. Future use can be promoted by new technology (single-sample phase measurements, phone apps, movement and sleep trackers) that provides ambulatory documentation over long periods and feedback to therapist and patient. Light combinations with cognitive behavioural therapy and sleep hygiene practice may speed up and also maintain response. The urgent need for new antidepressants should hopefully lead to reconsideration and implementation of these non-pharmacological methods, as well as further clinical trials. We review the putative neurochemical mechanisms underlying the antidepressant effect of sleep deprivation and light therapy, and current knowledge linking clocks and sleep with affective disorders: neurotransmitter switching, stress and cortico-limbic reactivity, clock genes, cortical neuroplasticity, connectomics and neuroinflammation. Despite the complexity of multi-system mechanisms, more insight will lead to fine tuning and better application of circadian and sleep-related treatments of depression.

Cellular and Molecular Mechanisms of REM Sleep Homeostatic Drive: A Plausible Component for Behavioral Plasticity

Homeostatic regulation of REM sleep drive, as measured by an increase in the number of REM sleep transitions, plays a key role in neuronal and behavioral plasticity (i.e., learning and memory). Deficits in REM sleep homeostatic drive (RSHD) are implicated in the development of many neuropsychiatric disorders. Yet, the cellular and molecular mechanisms underlying this RSHD remain to be incomplete. To further our understanding of this mechanism, the current study was performed on freely moving rats to test a hypothesis that a positive interaction between extracellular-signal-regulated kinase 1 and 2 (ERK1/2) activity and brain-derived neurotrophic factor (BDNF) signaling in the pedunculopontine tegmentum (PPT) is a causal factor for the development of RSHD. Behavioral results of this study demonstrated that a short period (<90 min) of selective REM sleep restriction (RSR) exhibited a strong RSHD. Molecular analyses revealed that this increased RSHD increased phosphorylation and activation of ERK1/2 and BDNF expression in the PPT. Additionally, pharmacological results demonstrated that the application of the ERK1/2 activation inhibitor U0126 into the PPT prevented RSHD and suppressed BDNF expression in the PPT. These results, for the first time, suggest that the positive interaction between ERK1/2 and BDNF in the PPT is a casual factor for the development of RSHD. These findings provide a novel direction in understanding how RSHD-associated specific molecular changes can facilitate neuronal plasticity and memory processing.

Short-term sleep deprivation disrupts the molecular composition of ionotropic glutamate receptors in entorhinal cortex and impairs the rat spatial reference memory

Numerous studies reported that sleep deprivation (SD) causes impairment in spatial cognitive performance. However, the molecular mechanisms affected by SD underlying this behavioral phenomenon remain elusive. Here, we focused on the entorhinal cortex (EC), the gateway of the hippocampus, and investigated how SD affected the subunit expression of AMPARs and NMDARs, the main ionotropic glutamategic receptors serving a pivotal role in spatial cognition. In EC, we found 4h SD remarkably reduced surface expression of GluA1, while there was an increase in the surface expression of GluA2 and GluA3. As for NMDARs, SD with short duration significantly reduced the surface expression levels of GluN1 and GluN2B without effect on the GluN2A. In parallel with the alterations in AMPARs and NMDARs, we found the 4h SD impaired rat spatial reference memory as assessed by Morris water maze task. Overall, these data indicate that brief SD differently affects the AMPAR and NMDAR subunit expressions in EC and might consequently disrupt the composition and functional properties of these receptors.

Metagenomic Sequencing Indicates That the Oropharyngeal Phageome of Individuals With Schizophrenia Differs From That of Controls

Mucosal sites such as the oropharynx contain a wide range of microorganisms, collectively designated as the microbiome. The microbiome can affect behavior through a number of neurobiological and immunological mechanisms. Most previous studies have focused on the bacterial components of the microbiome. However, the microbiome also includes viruses such as bacteriophages, which are viruses that infect bacteria and alter their metabolism and replication. We employed metagenomic analysis to characterize bacteriophage genomes in the oral pharynx of 41 individuals with schizophrenia and 33 control individuals without a psychiatric disorder. This analysis was performed by the generation of more than 100,000,000 sequence reads from each sample and the mapping of these reads to databases. We identified 79 distinct bacteriophage sequences in the oropharyngeal samples. Of these, one bacteriophage genome, Lactobacillus phage phiadh, was found to be significantly different in individuals with schizophrenia (P < .00037, q < 0.03 adjusted for multiple comparisons). The differential levels of Lactobacillus phage phiadh remained significant when controlling for age, gender, race, socioeconomic status, or cigarette smoking (P < .006). Within the group of individuals with schizophrenia, the level of Lactobacillus phage phiadh correlated with the prevalence of immunological disorders as well as with the administration of valproate, which has been shown in animal models to alter the microbiome. The bacteriophage composition of the oropharynx in individuals with schizophrenia differs from that of controls. The biological consequences of this difference and the potential effects of altering bacteriophage levels through therapeutic interventions are worthy of further investigation.

Successful antidepressant chronotherapeutics enhance fronto-limbic neural responses and connectivity in bipolar depression

The identification of antidepressant response predictors in bipolar disorder (BD) may provide new potential enhancements in treatment selection. Repeated total sleep deprivation combined with light therapy (TSD+LT) can acutely reverse depressive symptoms and has been proposed as a model antidepressant treatment. This study aims at investigating the effect of TSD+LT on effective connectivity and neural response in cortico-limbic circuitries during implicit processing of fearful and angry faces in patients with BD. fMRI and Dynamic Causal Modeling (DCM) were combined to study the effect of chronotherapeutics on neural responses in healthy controls (HC, n = 35) and BD patients either responder (RBD, n = 26) or non responder (nRBD, n = 11) to 3 consecutive TSD+LT sessions. Twenty-four DCMs exploring connectivity between anterior cingulate cortex (ACC), dorsolateral prefrontal cortex (DLPFC), Amygdala (Amy), fusiform gyrus and visual cortex were constructed. After treatment, patients significantly increased their neural responses in DLPFC, ACC and insula. nRBD showed lower baseline and endpoint neural responses than RBD. The increased activity in ACC and in medial prefrontal cortex, associated with antidepressant treatment, was positively associated with the improvement of depressive symptomatology. Only RBD patients increased intrinsic connectivity from DLPFC to ACC and reduced the modulatory effect of the task on Amy-DLPFC connection. A successful antidepressant treatment was associated with an increased functional activity and connectivity within cortico-limbic networks, suggesting the possible role of these measures in providing possible biomarkers for treatment efficacy.

Bipolar disorder and antibodies against the N-methyl-d-aspartate receptor: A gate to the involvement of autoimmunity in the pathophysiology of bipolar illness

The high prevalence of comorbidity between bipolar disorder (BD) and other medical conditions, including autoimmune diseases, supports the hypothesis of the nature of BD as a biological illness category. Hence, an immune dysregulation process may play an important role in the development of at least certain subtypes of BD. Increasing evidence also suggests that the N-methyl-d-aspartate receptor (NMDAR) may be relevant in the pathophysiology of BD. A possible key mechanism underlying the physiopathology of certain autoimmune diseases that may present with affective symptoms might be the production of anti-NMDAR auto-antibodies (auto-Abs). The best characterized autoimmune anti-NMDAR disease is the anti-NMDAR encephalitis. It has been found that 4% of these patients present isolated, mostly affective, psychiatric manifestations during their illness. An interesting suggestion emerged from this overview is that the same mechanisms that trigger affective symptoms in patients with increased anti-NMDAR auto-Abs levels could be involved in the physiopathology of at least a subgroup of BD. Future studies are needed to characterize the relationship between anti-NMDAR auto-Abs and BD.

Short-term sleep deprivation impairs spatial working memory and modulates expression levels of ionotropic glutamate receptor subunits in hippocampus

Hippocampus-dependent learning memory is sensitive to sleep deprivation (SD). Although the ionotropic glutamate receptors play a vital role in synaptic plasticity and learning and memory, however, whether the expression of these receptor subunits is modulated by sleep loss remains unclear. In the present study, western blotting was performed by probing with specific antibodies against the ionotropic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunits GluA1, GluA2, GluA3, and against the N-methyl-d-aspartate (NMDA) glutamate receptor subunits GluN1, GluN2A, GluN2B. In hippocampus, down regulation of surface GluA1 and GluN2A surface expression were observed in both SD groups. However, surface expression level of GluA2, GluA3, GluN1 and GluN2B was significantly up-regulated in 8h-SD rats when compared to the 4h-SD rats. In parallel with the complex changes in AMPA and NMDA receptor subunit expressions, we found the 8h-SD impaired rat spatial working memory in 30-s-delay T-maze task, whereas no impairment of spatial learning was observed in 4h-SD rats. These results indicate that sleep loss alters the relative expression levels of the AMPA and NMDA receptors, thus affects the synaptic strength and capacity for plasticity and partially contributes to spatial memory impairment.

Transiently increasing cAMP levels selectively in hippocampal excitatory neurons during sleep deprivation prevents memory deficits caused by sleep loss

The hippocampus is particularly sensitive to sleep loss. Although previous work has indicated that sleep deprivation impairs hippocampal cAMP signaling, it remains to be determined whether the cognitive deficits associated with sleep deprivation are caused by attenuated cAMP signaling in the hippocampus. Further, it is unclear which cell types are responsible for the memory impairments associated with sleep deprivation. Transgenic approaches lack the spatial resolution to manipulate specific signaling pathways selectively in the hippocampus, while pharmacological strategies are limited in terms of cell-type specificity. Therefore, we used a pharmacogenetic approach based on a virus-mediated expression of a Gαs-coupled Drosophila octopamine receptor selectively in mouse hippocampal excitatory neurons in vivo. With this approach, a systemic injection with the receptor ligand octopamine leads to increased cAMP levels in this specific set of hippocampal neurons. We assessed whether transiently increasing cAMP levels during sleep deprivation prevents memory consolidation deficits associated with sleep loss in an object-location task. Five hours of total sleep deprivation directly following training impaired the formation of object-location memories. Transiently increasing cAMP levels in hippocampal neurons during the course of sleep deprivation prevented these memory consolidation deficits. These findings demonstrate that attenuated cAMP signaling in hippocampal excitatory neurons is a critical component underlying the memory deficits in hippocampus-dependent learning tasks associated with sleep deprivation.

Animal studies on the role of sleep in memory: from behavioral performance to molecular mechanisms

Although the exact functions of sleep remain a topic of debate, several hypotheses propose that sleep benefits neuronal plasticity, which ultimately supports brain function and cognition . For over a century, researchers have applied a wide variety of behavioral, electrophysiological, biochemical, and molecular approaches to study how memory processes are promoted by sleep and perturbed by sleep loss. Interestingly, experimental studies indicate that cognitive impairments as a consequence of sleep deprivation appear to be most severe with learning and memory processes that require the hippocampus , which suggests that this brain region is particularly sensitive to the consequences of sleep loss. Moreover, recent studies in laboratory rodents indicate that sleep deprivation impairs hippocampal neuronal plasticity and memory processes by attenuating intracellular cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling. Attenuated cAMP-PKA signaling can lead to a reduced activity of the transcription factor cAMP response element binding protein (CREB) and ultimately affect the expression of genes and proteins involved in neuronal plasticity and memory formation. Pharmacogenetic experiments in mice show that memory deficits following sleep deprivation can be prevented by specifically boosting cAMP signaling in excitatory neurons of the hippocampus. Given the high incidence of sleep disturbance and sleep restriction in our 24/7 society, understanding the consequences of sleep loss and unraveling the underlying molecular mechanisms is of great importance.

The role of NMDA receptors in the pathophysiology and treatment of mood disorders

Mood disorders such as major depressive disorder and bipolar disorder are chronic and recurrent illnesses that cause significant disability and affect approximately 350 million people worldwide. Currently available biogenic amine treatments provide relief for many and yet fail to ameliorate symptoms for others, highlighting the need to diversify the search for new therapeutic strategies. Here we present recent evidence implicating the role of N-methyl-D-aspartate receptor (NMDAR) signaling in the pathophysiology of mood disorders. The possible role of NMDARs in mood disorders has been supported by evidence demonstrating that: (i) both BPD and MDD are characterized by altered levels of central excitatory neurotransmitters; (ii) NMDAR expression, distribution, and function are atypical in patients with mood disorders; (iii) NMDAR modulators show positive therapeutic effects in BPD and MDD patients; and (iv) conventional antidepressants/mood stabilizers can modulate NMDAR function. Taken together, this evidence suggests the NMDAR system holds considerable promise as a therapeutic target for developing next generation drugs that may provide more rapid onset relief of symptoms. Identifying the subcircuits involved in mood and elucidating the role of NMDARs subtypes in specific brain circuits would constitute an important step toward the development of more effective therapies with fewer side effects.

Spontaneous sleep-wake cycle and sleep deprivation differently induce Bdnf1, Bdnf4 and Bdnf9a DNA methylation and transcripts levels in the basal forebrain and frontal cortex in rats

Brain-derived neurotrophic factor (Bdnf) regulates neuronal plasticity, slow wave activity and sleep homeostasis. Environmental stimuli control Bdnf expression through epigenetic mechanisms, but there are no data on epigenetic regulation of Bdnf by sleep or sleep deprivation. Here we investigated whether 5-methylcytosine (5mC) DNA modification at Bdnf promoters p1, p4 and p9 influences Bdnf1, Bdnf4 and Bdnf9a expression during the normal inactive phase or after sleep deprivation (SD) (3, 6 and 12 h, end-times being ZT3, ZT6 and ZT12) in rats in two brain areas involved in sleep regulation, the basal forebrain and cortex. We found a daytime variation in cortical Bdnf expression: Bdnf1 expression was highest at ZT6 and Bdnf4 lowest at ZT12. Such variation was not observed in the basal forebrain. Also Bdnf p1 and p9 methylation levels differed only in the cortex, while Bdnf p4 methylation did not vary in either area. Factorial analysis revealed that sleep deprivation significantly induced Bdnf1 and Bdnf4 with the similar pattern for Bdnf9a in both basal forebrain and cortex; 12 h of sleep deprivation decreased 5mC levels at the cortical Bdnf p4 and p9. Regression analysis between the 5mC promoter levels and the corresponding Bdnf transcript expression revealed significant negative correlations for the basal forebrain Bdnf1 and cortical Bdnf9a transcripts in only non-deprived rats, while these correlations were lost after sleep deprivation. Our results suggest that Bdnf transcription during the light phase of undisturbed sleep-wake cycle but not after SD is regulated at least partially by brain site-specific DNA methylation.

Valproate improves memory deficits in an Alzheimer's disease mouse model: investigation of possible mechanisms of action

Alzheimer's disease (AD) is a very common progressive neurodegenerative disorder affecting the learning and memory abilities in the brain. Key findings from recent studies of epigenetic mechanisms of memory suggest chromatin remodeling disorders via histone hypoacetylation of the lysine residue contribute to the cognitive impairment in AD. Therefore, the deinhibition of histone acetylation induced by histone deacetylases (HDACs) inhibitors contributes to recovery of learning and memory. We show here that the antiepileptic drug sodium valproate (VPA) potently enhanced long-term recognition memory and spatial learning and memory in AD transgenic mice. Possible mechanisms showed VPA could significantly elevate histone acetylation through HDACs activity inhibition and increase plasticity-associated gene expression within the hippocampi of mice. Our study suggests that VPA, serving as a HDACs inhibitor, can be considered as a potential pharmaceutical agent for the improvement of cognitive function in AD.

Sleep, plasticity and memory from molecules to whole-brain networks

Despite the ubiquity of sleep across phylogeny, its function remains elusive. In this review, we consider one compelling candidate: brain plasticity associated with memory processing. Focusing largely on hippocampus-dependent memory in rodents and humans, we describe molecular, cellular, network, whole-brain and behavioral evidence establishing a role for sleep both in preparation for initial memory encoding, and in the subsequent offline consolidation of memory. Sleep and sleep deprivation bidirectionally alter molecular signaling pathways that regulate synaptic strength and control plasticity-related gene transcription and protein translation. At the cellular level, sleep deprivation impairs cellular excitability necessary for inducing synaptic potentiation and accelerates the decay of long-lasting forms of synaptic plasticity. In contrast, rapid eye movement (REM) and non-rapid eye movement (NREM) sleep enhance previously induced synaptic potentiation, although synaptic de-potentiation during sleep has also been observed. Beyond single cell dynamics, large-scale cell ensembles express coordinated replay of prior learning-related firing patterns during subsequent NREM sleep. At the whole-brain level, somewhat analogous learning-associated hippocampal (re)activation during NREM sleep has been reported in humans. Moreover, the same cortical NREM oscillations associated with replay in rodents also promote human hippocampal memory consolidation, and this process can be manipulated using exogenous reactivation cues during sleep. Mirroring molecular findings in rodents, specific NREM sleep oscillations before encoding refresh human hippocampal learning capacity, while deprivation of sleep conversely impairs subsequent hippocampal activity and associated encoding. Together, these cross-descriptive level findings demonstrate that the unique neurobiology of sleep exerts powerful effects on molecular, cellular and network mechanisms of plasticity that govern both initial learning and subsequent long-term memory consolidation.

The impact of sleep loss on hippocampal function

Hippocampal cellular and molecular processes critical for memory consolidation are affected by the amount and quality of sleep attained. Questions remain with regard to how sleep enhances memory, what parameters of sleep after learning are optimal for memory consolidation, and what underlying hippocampal molecular players are targeted by sleep deprivation to impair memory consolidation and plasticity. In this review, we address these topics with a focus on the detrimental effects of post-learning sleep deprivation on memory consolidation. Obtaining adequate sleep is challenging in a society that values "work around the clock." Therefore, the development of interventions to combat the negative cognitive effects of sleep deprivation is key. However, there are a limited number of therapeutics that are able to enhance cognition in the face of insufficient sleep. The identification of molecular pathways implicated in the deleterious effects of sleep deprivation on memory could potentially yield new targets for the development of more effective drugs.

Ketamine, magnesium and major depression--from pharmacology to pathophysiology and back

The glutamatergic mechanism of antidepressant treatments is now in the center of research to overcome the limitations of monoamine-based approaches. There are several unresolved issues. For the action of the model compound, ketamine, NMDA-receptor block, AMPA-receptor activation and BDNF release appear to be involved in a mechanism, which leads to synaptic sprouting and strengthened synaptic connections. The link to the pathophysiology of depression is not clear. An overlooked connection is the role of magnesium, which acts as physiological NMDA-receptor antagonist: 1. There is overlap between the actions of ketamine with that of high doses of magnesium in animal models, finally leading to synaptic sprouting. 2. Magnesium and ketamine lead to synaptic strengthening, as measured by an increase in slow wave sleep in humans. 3. Pathophysiological mechanisms, which have been identified as risk factors for depression, lead to a reduction of (intracellular) magnesium. These are neuroendocrine changes (increased cortisol and aldosterone) and diabetes mellitus as well as Mg(2+) deficiency. 4. Patients with therapy refractory depression appear to have lower CNS Mg(2+) levels in comparison to health controls. 5. Experimental Mg(2+) depletion leads to depression- and anxiety like behavior in animal models. 6. Ketamine, directly or indirectly via non-NMDA glutamate receptor activation, acts to increase brain Mg(2+) levels. Similar effects have been observed with other classes of antidepressants. 7. Depressed patients with low Mg(2+) levels tend to be therapy refractory. Accordingly, administration of Mg(2+) either alone or in combination with standard antidepressants acts synergistically on depression like behavior in animal models.

CONCLUSION

On the basis of the potential pathophysiological role of Mg(2+)-regulation, it may be possible to predict the action of ketamine and of related compounds based on Mg(2+) levels. Furthermore, screening for compounds to increase neuronal Mg(2+) concentration could be a promising instrument to identify new classes of antidepressants. Overall, any discussion of the glutamatergic system in affective disorders should consider the role of Mg(2+).

Neurobiological consequences of sleep deprivation

Although the physiological function of sleep is not completely understood, it is well documented that it contributes significantly to the process of learning and memory. Ample evidence suggests that adequate sleep is essential for fostering connections among neuronal networks for memory consolidation in the hippocampus. Sleep deprivation studies are extremely valuable in understanding why we sleep and what are the consequences of sleep loss. Experimental sleep deprivation in animals allows us to gain insight into the mechanism of sleep at levels not possible to study in human subjects. Many useful approaches have been utilized to evaluate the effect of sleep loss on cognitive function, each with relative advantages and disadvantages. In this review we discuss sleep and the detrimental effects of sleep deprivation mostly in experimental animals. The negative effects of sleep deprivation on various aspects of brain function including learning and memory, synaptic plasticity and the state of cognition-related signaling molecules are discussed.

Therapeutic potential of mood stabilizers lithium and valproic acid: beyond bipolar disorder

The mood stabilizers lithium and valproic acid (VPA) are traditionally used to treat bipolar disorder (BD), a severe mental illness arising from complex interactions between genes and environment that drive deficits in cellular plasticity and resiliency. The therapeutic potential of these drugs in other central nervous system diseases is also gaining support. This article reviews the various mechanisms of action of lithium and VPA gleaned from cellular and animal models of neurologic, neurodegenerative, and neuropsychiatric disorders. Clinical evidence is included when available to provide a comprehensive perspective of the field and to acknowledge some of the limitations of these treatments. First, the review describes how action at these drugs' primary targets--glycogen synthase kinase-3 for lithium and histone deacetylases for VPA--induces the transcription and expression of neurotrophic, angiogenic, and neuroprotective proteins. Cell survival signaling cascades, oxidative stress pathways, and protein quality control mechanisms may further underlie lithium and VPA's beneficial actions. The ability of cotreatment to augment neuroprotection and enhance stem cell homing and migration is also discussed, as are microRNAs as new therapeutic targets. Finally, preclinical findings have shown that the neuroprotective benefits of these agents facilitate anti-inflammation, angiogenesis, neurogenesis, blood-brain barrier integrity, and disease-specific neuroprotection. These mechanisms can be compared with dysregulated disease mechanisms to suggest core cellular and molecular disturbances identifiable by specific risk biomarkers. Future clinical endeavors are warranted to determine the therapeutic potential of lithium and VPA across the spectrum of central nervous system diseases, with particular emphasis on a personalized medicine approach toward treating these disorders.