Calcineurin contributes to spatial memory impairment induced by rapid eye movement sleep deprivation

Synaptophysin and GSK-3beta activity in the prefrontal cortex may underlie the effects of REM sleep deprivation and lithium on behavioral functions and memory performance in male rats

Rapid-eye movement (REM) stage of sleep serves a critical role in processing cognitive and behavioral functions. Evidence shows that REM sleep deprivation (REM SD) strongly affects the mood state and cognitive abilities. However, there are many inconsistent reports. Although the exact molecular mechanisms underlying REM SD effects have not well been discovered, however, molecular factors including those affected synaptic plasticity and mood state may be involved. There are two important molecular factors that have not been well studied: synaptophysin and glycogen synthase kinase-3 beta (GSK-3beta). The present study aimed to investigate the role of synaptophysin and GSK-3beta in the modulation of memory and behavioral changes induced by REM SD and lithium (as a potent GSK-3beta inhibitor and mood stabilizer). Multiple platform apparatus was used to induce REM SD for 48 h. Lithium was injected at the dose of 50 mg/kg, intraperitoneal (i.p.). Locomotor activity, anxiety-like behavior, pain threshold, novel object recognition memory, and synaptophysin and GSK-3beta level in the prefrontal cortex were evaluated. Results showed REM SD increased locomotor activity, decreased pain threshold, impaired novel object recognition memory, decreased synaptophysin and increased GSK-3beta levels. Lithium reversed these effects. Anxiety-like behavior was unaffected. For the first time, the present study showed that GSK-3beta and synaptophysin may be involved in the modulation of behavior and cognition induced by REM SD and lithium. In conclusion, we suggested that GSK-3beta upregulation and synaptophysin downregulation may underlie the deleterious effects of REM SD, while lithium may counteract REM SD effects via restoring the level of both.

REM sleep deprivation induced by the modified multi-platform method has detrimental effects on memory: A systematic review and meta-analysis

The modified multi-platform method (MMPM) is used to induce animal models of paradoxical sleep deprivation and impairs memory in rodents. However, variations in MMPM protocols have contributed to inconsistent conclusions across studies. This meta-analysis aimed to assess the variations of the MMPM and their effects on memory in rats and mice. A comprehensive search identified 60 studies, and 50 were included in our meta-analysis. Overall, the meta-analysis showed that the MMPM significantly reduced the percentage of time spent in target quadrants (I2 = 54 %, 95 % confidence interval [CI] = [-1.83, -1.18]) and the number of platform-area crossings (I2 = 26 %, 95 % CI = [-1.71, -1.07]) in the Morris water maze (MWM) and shortened the latency to entering the dark compartment in the passive avoidance task (I2 = 68 %, 95 % CI = [-1.36, -0.57]), but it increased the number of errors in the radial arm water maze (RAWM) (I2 = 59 %, 95 % CI = [1.29, 2.07]). Additionally, mice performed worse on the MWM, whereas rats performed worse on the passive avoidance task. More significant memory deficits were found in cross-learning and post-learning MMPM in the MWM and RAWM, respectively. This study provided evidence that the MMPM can be used in preclinical studies of memory deficits induced by paradoxical sleep deprivation.

Relationship between circadian genes and memory impairment caused by sleep deprivation

Background

Sleep deprivation (SD)-induced cognitive impairment is highly prevalent worldwide and has attracted widespread attention. The temporal and spatial oscillations of circadian genes are severely disturbed after SD, leading to a progressive loss of their physiological rhythms, which in turn affects memory function. However, there is a lack of research on the role of circadian genes and memory function after SD. Therefore, the present study aims to investigate the relationship between circadian genes and memory function and provide potential therapeutic insights into the mechanism of SD-induced memory impairment.

Methods

Gene expression profiles of GSE33302 and GSE9442 from the Gene Expression Omnibus (GEO) were applied to identify differentially expressed genes (DEGs). Subsequently, both datasets were subjected to Gene Set Enrichment Analysis (GSEA) to determine the overall gene changes in the hippocampus and brain after SD. A Gene Oncology (GO) analysis and Protein-Protein Interaction (PPI) analysis were employed to explore the genes related to circadian rhythm, with their relationship and importance determined through a correlation analysis and a receiver operating characteristic curve (ROC), respectively. The water maze experiments detected behavioral changes related to memory function in SD rats. The expression of circadian genes in several critical organs such as the brain, heart, liver, and lungs and their correlation with memory function was investigated using several microarrays. Finally, changes in the hippocampal immune environment after SD were analyzed using the CIBERSORT in R software.

Results

The quality of the two datasets was very good. After SD, changes were seen primarily in genes related to memory impairment and immune function. Genes related to circadian rhythm were highly correlated with engagement in muscle structure development and circadian rhythm. Seven circadian genes showed their potential therapeutic value in SD. Water maze experiments confirmed that SD exacerbates memory impairment-related behaviors, including prolonged escape latencies and reduced numbers of rats crossing the platform. The expression of circadian genes was verified, while some genes were also significant in the heart, liver, and lungs. All seven circadian genes were also associated with memory markers in SD. The contents of four immune cells in the hippocampal immune environment changed after SD. Seven circadian genes were related to multiple immune cells.

Conclusions

In the present study, we found that SD leads to memory impairment accompanied by changes in circadian rhythm-related genes. Seven circadian genes play crucial roles in memory impairment after SD. Naïve B cells and follicular helper T cells are closely related to SD. These findings provide new insights into the treatment of memory impairment caused by SD.

Cytomorphological Analysis and Interpretation of Nitric Oxide-Mediated Neurotoxicity in Sleep-Deprived Mice Model

Background:

Sleep deprivation (SD) is a biological stress condition for the brain, and the pathogenesis of SD is closely related to elevated oxidative stress, mitochondrial dysfunction, a major cause of neurodegeneration. This oxidative stress-mediated cell death is attributed to rise in calcium ion influx which further excites or alters the neurotransmitters level by activating neuronal nitric oxide (NO) synthase (nNOS) release of NO in mouse SD model. This study indicates that the nitrergic neurons are possible therapeutic targets for the amelioration of SD-induced cognitive dysfunction and behavioral alterations.

Purpose:

SD is considered as a risk factor for various neurodegenerative diseases. SD leads to biochemical, behavioral, and neurochemical alterations in animals. This study was designed to explore the possible involvement of a nitrergic neuron system in six days SD-induced morphological and neurodegenerative changes in mice.

Methods:

Using nNOS immunohistochemistry, we have investigated the effects of SD on nNOS positive neurons. Immunohistochemical study for the distribution of nNOS positive neuronal cell bodies was carried out in the hippocampus, prefrontal cortex (PFC), and amygdaloid nuclei of mice brain.

Results:

Sleep-deprived animals showed a significantly increased number of nNOS positive neurons and altered neuronal cytomorphology as compared with the control group.

Conclusion:

These results indicate that total SD may induce morphological changes in nNOS positive neurons in the brain, thus increasing NO synthesis, which is implicated in SD-induced neuronal cell death.

Inconsistent effects of sleep deprivation on memory function

In this review article, we aimed to discuss the role of sleep deprivation (SD) in learning and memory processing in basic and clinical studies. There are numerous studies investigating the effect of SD on memory, while most of these studies have shown the impairment effect of SD. However, some of these studies have reported conflicting results, indicating that SD does not impair memory performance or even improves it. So far, no study has discussed or compared the conflicting results of SD on learning and memory. Thus, this important issue in the neuroscience of sleep remains unknown. The main goal of this review article is to compare the similar mechanisms between the impairment and the improvement effects of SD on learning and memory, probably leading to a scientific solution that justifies these conflicting results. We focused on the inconsistent effects of SD on some mechanisms involved in learning and memory, and tried to discuss the inconsistent effects of SD on learning and memory.

Sleep Deprivation Aggravates Cognitive Impairment by the Alteration of Hippocampal Neuronal Activity and the Density of Dendritic Spine in Isoflurane-Exposed Mice

Isoflurane contributes to cognitive deficits when used as a general anesthetic, and so does sleep deprivation (SD). Patients usually suffer from insomnia before an operation due to anxiety, fear, and other factors. It remains unclear whether preoperative SD exacerbates cognitive impairment induced by isoflurane. In this study, we observed the effects of pretreated 24-h SD in adult isoflurane-exposed mice on the cognitive behaviors, the Ca²⁺ signals of dorsal hippocampal CA1 (dCA1) neurons in vivo with fiber photometry, and the density of dendritic spines in hippocampal neurons. Our results showed that in cognitive behavior tasks, short-term memory damages were more severe with SD followed by isoflurane exposure than that with SD or isoflurane exposure separately, and interestingly, severe long-term memory deficits were induced only by SD followed by isoflurane exposure. Only the treatment of SD followed by isoflurane exposure could reversibly decrease the amplitude of Ca²⁺ signals when mice were freely moving and increase the duration of Ca²⁺ signals during the long-term memory behavior test. The density of dendritic spines with both SD and isoflurane exposure was lower than that with SD alone. This study suggests that SD should be avoided preoperatively in patients undergoing elective surgery under isoflurane anesthesia.

Sleep Deprivation and Neurological Disorders

Sleep plays an important role in maintaining neuronal circuitry, signalling and helps maintain overall health and wellbeing. Sleep deprivation (SD) disturbs the circadian physiology and exerts a negative impact on brain and behavioural functions. SD impairs the cellular clearance of misfolded neurotoxin proteins like α-synuclein, amyloid-β, and tau which are involved in major neurodegenerative diseases like Alzheimer's disease and Parkinson's disease. In addition, SD is also shown to affect the glymphatic system, a glial-dependent metabolic waste clearance pathway, causing accumulation of misfolded faulty proteins in synaptic compartments resulting in cognitive decline. Also, SD affects the immunological and redox system resulting in neuroinflammation and oxidative stress. Hence, it is important to understand the molecular and biochemical alterations that are the causative factors leading to these pathophysiological effects on the neuronal system. This review is an attempt in this direction. It provides up-to-date information on the alterations in the key processes, pathways, and proteins that are negatively affected by SD and become reasons for neurological disorders over a prolonged period of time, if left unattended.

Short-term REM deprivation does not affect acquisition or reversal of a spatial learning task

Although there is a general belief that rapid eye movement sleep (REM) is essential for spatial memory tasks such as the Morris water maze (MWM), there is conflicting evidence for this assertion. This study investigated the effects of short-term REM deprivation on acquisition and reversal of the MWM by varying the timing of REM deprivation and the degree of task acquisition in three separate experiments. There was no evidence for a detrimental effect of REM deprivation on acquisition, retention, or reversal in the MWM. These data add to a growing body of evidence that although REM is important for certain types of learning and memory, spatial memory, as assessed by the MWM, is not among them.

Role of normal sleep and sleep apnea in human memory processing

A fundamental problem in the field of obstructive sleep apnea (OSA) and memory is that it has historically minimized the basic neurobiology of sleep's role in memory. Memory formation has been classically divided into phases of encoding, processing/consolidation, and retrieval. An abundance of evidence suggests that sleep plays a critical role specifically in the processing/consolidation phase, but may do so differentially for memories that were encoded using particular brain circuits. In this review, we discuss some of the more established evidence for sleep's function in the processing of declarative, spatial navigational, emotional, and motor/procedural memories and more emerging evidence highlighting sleep's importance in higher order functions such as probabilistic learning, transitive inference, and category/gist learning. Furthermore, we discuss sleep's capacity for memory augmentation through targeted/cued memory reactivation. OSA - by virtue of its associated sleep fragmentation, intermittent hypoxia, and potential brain structural effects - is well positioned to specifically impact the processing/consolidation phase, but testing this possibility requires experimental paradigms in which memory encoding and retrieval are separated by a period of sleep with and without the presence of OSA. We argue that such paradigms should focus on the specific types of memory tasks for which sleep has been shown to have a significant effect. We discuss the small number of studies in which this has been done, in which OSA nearly uniformly negatively impacts offline memory processing. When periods of offline processing are minimal or absent and do not contain sleep, as is the case in the broad literature on OSA and memory, the effects of OSA on memory are far less consistent.

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.

Prevention by Regular Exercise of Acute Sleep Deprivation-Induced Impairment of Late Phase LTP and Related Signaling Molecules in the Dentate Gyrus

The dentate gyrus (DG) and CA1 regions of the hippocampus are intimately related physically and functionally, yet they react differently to insults. The purpose of this study was to determine the protective effects of regular treadmill exercise on late phase long-term potentiation (L-LTP) and its signaling cascade in the DG region of the hippocampus of rapid eye movement (REM) sleep-deprived rats. Adult Wistar rats ran on treadmills for 4 weeks then were acutely sleep deprived for 24 h using the modified multiple platform method. After sleep deprivation, the rats were anesthetized and L-LTP was induced in the DG region. Extracellular field potentials from the DG were recorded in vivo, and levels of L-LTP-related signaling proteins were assessed both before and after L-LTP expression using immunoblot analysis. Sleep deprivation reduced the basal levels of phosphorylated cAMP response element-binding protein (P-CREB) as well as other upstream modulators including calcium/calmodulin kinase IV (CaMKIV) and brain-derived neurotrophic factor (BDNF) in the DG of the hippocampus. Regular exercise prevented impairment of the basal levels of P-CREB and total CREB as well as those of CaMKIV in sleep-deprived animals. Furthermore, regular exercise prevented sleep deprivation-induced inhibition of L-LTP and post-L-LTP downregulation of P-CREB and BDNF levels in the DG. The current findings show that our exercise regimen prevents sleep deprivation-induced deficits in L-LTP as well as the basal and poststimulation levels of key signaling molecules.

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.

Experimental sleep deprivation as a tool to test memory deficits in rodents

Paradigms of sleep deprivation (SD) and memory testing in rodents (laboratory rats and mice) are here reviewed. The vast majority of these studies have been aimed at understanding the contribution of sleep to cognition, and in particular to memory. Relatively little attention, instead, has been devoted to SD as a challenge to induce a transient memory impairment, and therefore as a tool to test cognitive enhancers in drug discovery. Studies that have accurately described methodological aspects of the SD protocol are first reviewed, followed by procedures to investigate SD-induced impairment of learning and memory consolidation in order to propose SD protocols that could be employed as cognitive challenge. Thus, a platform of knowledge is provided for laboratory protocols that could be used to assess the efficacy of drugs designed to improve memory performance in rodents, including rodent models of neurodegenerative diseases that cause cognitive deficits, and Alzheimer's disease in particular. Issues in the interpretation of such preclinical data and their predictive value for clinical translation are also discussed.

Loss of calcineurin in the spinal dorsal horn contributes to neuropathic pain, and intrathecal administration of the phosphatase provides prolonged analgesia

Calcineurin (protein phosphatase 3) regulates synaptic plasticity in the brain. The development of neuropathic pain appears dependent on some of the same mechanisms that underlie brain synaptic plasticity. In this study, we examined whether calcineurin regulates chronic constriction injury (CCI)-elicited plasticity in the spinal dorsal horn. CCI animals exhibited mechanical and thermal hypersensitivity 7 days after ligation of the sciatic nerve. Neither control uninjured nor sham-operated animals exhibited pain behavior. Calcineurin activity and content of its Aα isoform were significantly decreased in the ipsilateral postsynaptic density (PSD) of dorsal horn neurons in CCI animals. Calcineurin activity and content in the contralateral PSD of CCI animals or either side of the dorsal horn in sham animals were not modified. The pain behavior in CCI animals was attenuated by intrathecal application of exogenous calcineurin. The treatment was long-lasting as a single injection provided analgesia for 4 days by restoring the phosphatase's activity and Aα content in the PSD. No signs of toxicity were detected up to 14 days after the single intrathecal injection. Intrathecal application of the calcineurin inhibitor FK-506 elicited pain behavior in control uninjured animals and significantly reduced calcineurin activity in the PSD. CCI may elicit neuropathic pain at least in part as a result of the loss of calcineurin-mediated dephosphorylation in the dorsal horn. Addition of the phosphatase by intrathecal injection reverses the injury-elicited loss and provides prolonged pain relief. Clinical therapy with calcineurin may prove to be a novel, effective, and safe approach in the management of well-established neuropathic pain.

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.

Effect of kai xin san on learning and memory in a rat model of paradoxical sleep deprivation

The present study aimed to evaluate the effect of kai xin san (KXS, at doses of 500, 250, and 125 mg/kg body weight per day), a well-known traditional Chinese medicine, on learning and memory in paradoxical sleep deprivation (PSD)-induced cognition deficit rats. Two behavior tests (the Open Field test and the Morris water maze task) were used for testing the effects of KXS on a PSD-induced learning and memory deficit model. Furthermore, its effect on the glutamic acid (GLU) and γ-amino-butyric acid (GABA) levels in the brain tissue, brain-derived neurotrophic factor (BDNF), cyclic AMP response element binding protein (CREB), and phosphorylated-CREB (p-CREB) expression in the hippocampus was also tested. KXS exerted the greatest cognition against the 48 h PSD-induced cognitive deficit and these effects may be mediated by decreasing the GLU and GABA levels and increasing the levels of BDNF, CREB, and p-CREB. This study indicates that the effect of KXS on learning and memory in a rat model of PSD could be associated with the modulation of neurotransmitter levels and the expression of some genes in the brain that contribute to memory functions.

The impact of sleep deprivation on neuronal and glial signaling pathways important for memory and synaptic plasticity

Sleep deprivation is a common feature in modern society, and one of the consequences of sleep loss is the impairment of cognitive function. Although it has been widely accepted that sleep deprivation affects learning and memory, only recently has research begun to address which molecular signaling pathways are altered by sleep loss and, more importantly, which pathways can be targeted to reverse the memory impairments resulting from sleep deprivation. In this review, we discuss the different methods used to sleep deprive animals and the effects of different durations of sleep deprivation on learning and memory with an emphasis on hippocampus-dependent memory. We then review the molecular signaling pathways that are sensitive to sleep loss, with a focus on those thought to play a critical role in the memory and synaptic plasticity deficits observed after sleep deprivation. Finally, we highlight several recent attempts to reverse the effects of sleep deprivation on memory and synaptic plasticity. Future research building on these studies promises to contribute to the development of novel strategies to ameliorate the effects of sleep loss on cognition.

The beneficial effects of regular exercise on cognition in REM sleep deprivation: behavioral, electrophysiological and molecular evidence

Inadequate sleep is prevalent in modern societies and is known to profoundly impair cognitive function. We examined the impact of 4 weeks of regular treadmill exercise on sleep deprivation induced spatial learning and memory, synaptic plasticity and related signaling molecules in area CA1 of the rat hippocampus. Rats were exercised on a treadmill and subsequently sleep-deprived for 24h using the modified multiple platform technique. Testing of learning and short-term memory performance in the radial arm water maze showed that although sedentary sleep deprived rats were severely impaired, exercised sleep deprived rats' performance was normal. Extracellular recording from area CA1 of anesthetized rats revealed that early phase LTP (E-LTP) was markedly impaired in the sedentary sleep deprived animals, but was normal in the exercised sleep deprived group. Additionally, immunoblot analysis of CA1 area before (basal) and after expression of E-LTP indicated that the significant down-regulation of the brain derived neurotrophic factor (BDNF) and phosphorylated calcium-calmodulin dependent protein kinase II (P-CaMKII) levels in sleep deprived animals was prevented by the regular exercise regimen. The results suggest that the regular exercise protocol prevents the sleep deprivation induced impairments in short-term memory and E-LTP by preventing deleterious changes in the basal and post-stimulation levels of P-CaMKII and BDNF associated with sleep deprivation.

Spatial and reversal learning in the Morris water maze are largely resistant to six hours of REM sleep deprivation following training

This first test of the role of REM (rapid eye movement) sleep in reversal spatial learning is also the first attempt to replicate a much cited pair of papers reporting that REM sleep deprivation impairs the consolidation of initial spatial learning in the Morris water maze. We hypothesized that REM sleep deprivation following training would impair both hippocampus-dependent spatial learning and learning a new target location within a familiar environment: reversal learning. A 6-d protocol was divided into the initial spatial learning phase (3.5 d) immediately followed by the reversal phase (2.5 d). During the 6 h following four or 12 training trials/day of initial or reversal learning phases, REM sleep was eliminated and non-REM sleep left intact using the multiple inverted flowerpot method. Contrary to our hypotheses, REM sleep deprivation during four or 12 trials/day of initial spatial or reversal learning did not affect training performance. However, some probe trial measures indicated REM sleep-deprivation-associated impairment in initial spatial learning with four trials/day and enhancement of subsequent reversal learning. In naive animals, REM sleep deprivation during normal initial spatial learning was followed by a lack of preference for the subsequent reversal platform location during the probe. Our findings contradict reports that REM sleep is essential for spatial learning in the Morris water maze and newly reveal that short periods of REM sleep deprivation do not impair concurrent reversal learning. Effects on subsequent reversal learning are consistent with the idea that REM sleep serves the consolidation of incompletely learned items.

Changes in calcineurin message, enzyme activity and protein content in the spinal dorsal horn are associated with chronic constriction injury of the rat sciatic nerve

Plasticity in the spinal dorsal horn is thought to underlie the development of neuropathic pain. Calcineurin (protein phosphatase 3) plays an important role in plasticity in the brain. Here we examined whether chronic constriction injury (CCI) of the sciatic nerve modifies calcineurin expression in the spinal dorsal horn. Male rats were assigned to control (uninjured), sham-operated or CCI groups. CCI animals exhibited both a shift in weight bearing and a reduction in paw withdrawal latencies as signs of pain behavior. At 3 days (3D) the pain behavior was associated with a significant increase in calcineurin gene expression, enzyme activity and content of its Aα isoform in the ipsilateral spinal dorsal horn. In contrast, while the pain behavior persisted at 7 days (7D) calcineurin gene expression returned to control levels and activity and protein content decreased. A single intrathecal injection of MK-801 15 min before the ligation attenuated both signs of pain behavior in 3D but not 7D CCI animals. The same pre-treatment also prevented the CCI-associated increases in calcineurin in these animals. These data suggested an involvement of calcineurin in CCI-elicited neuropathic pain. The time-dependent divergent changes in calcineurin expression may underlie the different phases of neuropathic pain development.

Sleep deprivation prevents stimulation-induced increases of levels of P-CREB and BDNF: protection by caffeine

It is well known that caffeine and sleep deprivation have opposing effects on learning and memory; therefore, this study was undertaken to determine the effects of chronic (4wks) caffeine treatment (0.3g/l in drinking water) on long-term memory deficit associated with 24h sleep deprivation. Animals were sleep deprived using the modified multiple platform method. The results showed that chronic caffeine treatment prevented the impairment of long-term memory as measured by performance in the radial arm water maze task and normalized L-LTP in area CA1 of the hippocampi of sleep-deprived anesthetized rats. Sleep deprivation prevents the high frequency stimulation-induced increases in the levels of phosphorylated-cAMP response element binding protein (P-CREB) and brain-derived neurotrophic factor (BDNF) seen during the expression of late phase long-term potentiation (L-LTP). However, chronic caffeine treatment prevented the effect of sleep-deprivation on the stimulated levels of P-CREB and BDNF. The results suggest that chronic caffeine treatment may protect the sleep-deprived brain probably by preserving the levels of P-CREB and BDNF.

Neuropeptide S mitigates spatial memory impairment induced by rapid eye movement sleep deprivation in rats

Rapid eye movement (REM) sleep deprivation causes learning and memory deficits. Neuropeptide S, a newly discovered neuropeptide, has been shown to regulate arousal, anxiety, and may enhance long-term memory formation and spatial memory. However, it is unknown whether neuropeptide S could improve the REM sleep deprivation-induced memory impairment. Here, we report that 72-h REM sleep deprivation in rats resulted in spatial memory impairment and reduced phosphorylation level of cAMP-response element binding protein in the hippocampus, both of which were reversed by central administration of neuropeptide S. The results suggest that neuropeptide S mitigates spatial memory impairment in rats induced by 72-h REM sleep deprivation, possibly through activating cAMP-response element binding protein phosphorylation in the hippocampus.

Low-frequency stimulation of the hippocampus following fear extinction impairs both restoration of rapid eye movement sleep and retrieval of extinction memory

Post-learning rapid eye movement (REM) sleep deprivation has often been shown to impair hippocampal functioning, which results in deficit in retrieval of some types of memory. However, it remains to be determined whether post-learning alteration of hippocampal functioning affects, in turn, REM sleep. Recent studies have shown that both post-extinction REM sleep deprivation and post-extinction application of hippocampal low-frequency stimulation (LFS) impair memory of fear extinction, indicating possible bidirectional interactions between hippocampal functioning and REM sleep. To analyze the potential effect of post-extinction alteration of hippocampal functioning on REM sleep, rats were implanted with stimulating electrodes in the dorsal hippocampus for post-extinction LFS. Sleep was recorded before (two sessions, 1 day apart) and after conditioning (five tone and eyelid-shock pairings), and following extinction training (25 tone-alone presentations) for 6 h per session. Fear conditioning reduced time spent in REM sleep, which was restored with fear extinction. Hippocampal LFS, applied immediately following extinction training, abolished the restorative effect of fear extinction on REM sleep and impaired extinction retrieval. These data extend previous findings and suggest bidirectional interactions between hippocampal functioning and REM sleep for successful extinction retrieval.

Acute nicotine treatment prevents REM sleep deprivation-induced learning and memory impairment in rat

Rapid eye movement (REM) sleep deprivation (SD) is implicated in impairment of spatial learning and memory and hippocampal long-term potentiation (LTP). An increase in nicotine consumption among habitual smokers and initiation of tobacco use by nonsmokers was observed during SD. Although nicotine treatment was reported to attenuate the impairment of learning and memory and LTP associated with several mental disorders, the effect of nicotine on SD-induced learning and memory impairment has not been studied. Modified multiple platform paradigm was used to induce SD for 24 or 48 h during which rats were injected with saline or nicotine (1 mg kg(-1) s.c.) twice a day. In the radial arm water maze (RAWM) task, 24- or 48-h SD significantly impaired learning and short-term memory. In addition, extracellular recordings from CA1 and dentate gyrus (DG) regions of the hippocampus in urethane anesthetized rats showed a significant impairment of LTP after 24- and 48-h SD. Treatment of normal rats with nicotine for 24 or 48 h did not enhance spatial learning and memory or affect magnitude of LTP in the CA1 and DG regions. However, concurrent, acute treatment of rats with nicotine significantly attenuated SD-induced impairment of learning and STM and prevented SD-induced impairment of LTP in the CA1 and DG regions. These results show that acute nicotine treatment prevented the deleterious effect of sleep loss on cognitive abilities and synaptic plasticity.