Effects of Sleep Deprivation (SD) on Rats via ERK1/2 Signaling Pathway.

BACKGROUND Sleep deprivation (SD) is common in humans, and sleep loss has a significant influence on health and produces related diseases. Orexin-A has been demonstrated to play a role in physiological processes, including feeding, sleep/wake cycle, and energy metabolism. The aim of this study was to investigate the effect of SD on rats and to define the underlying mechanism. MATERIAL AND METHODS We constructed an SD rat model. The Morris water maze test was used to assess rat learning and memory. Imaging of hippocampus and hippocampal tissue in rats were captured by magnetic resonance imaging or electron microscopy. We used the CCK-8 kit to assess cell viability. The level of protein was measured using Western blot analysis, and qRT-PCR was used to evaluate mRNA level. RESULTS SD rats had poorer learning and memory and had damage to the hippocampus. SD resulted in shrinkage of hippocampal volume and encephalocele size. SD increased the expression of Orexin-A, OX1R, OX2R, and PARP-1, and decreased the expression of ERK1/2 and p-ERK1/2. Orexin-A (0-10 µM) improved neuron viability, whereas orexin-A (10-100 µM) attenuated neuron viability. SB334867 treatment reduced the viability of neurons treated with orexin-A. NU1025 treatment increased cell viability, especially in neurons treated with orexin-A. SB334867 treatment decreased the p-ERK1/2 levels in neurons treated with orexin-A. NU1025 increased the expression of p-ERK1/2 in neurons treated with orexin-A. CONCLUSIONS SD decreases learning and memory through damage to the hippocampus. Higher concentrations of orexin-A had a major negative effect on hippocampal neurons via OX1R and PARP-1 through inhibition of the ERK1/2 signaling pathway.

Role of inducible nitric oxide synthase in myocardial ischemia-reperfusion injury in sleep-deprived rats.

INTRODUCTION: REM sleep deprivation (SD) decreases tolerance of the rat heart to ischemia-reperfusion (IR) injury; the underlying mechanisms, however, are unknown. This study aimed at determining whether changes in iNOS, Bax, and Bcl-2 gene expression are involved in this detrimental effect. METHOD: SD was induced by flowerpot technique for a period of 4 days. This method is simple and able to induce sleep fragmentation which occurs as one of the sleep disorder symptoms in clinical conditions. The hearts of control and SD rats were perfused in Langendorff apparatus and subjected to 30 min ischemia, followed by 90 min reperfusion. The hemodynamic parameters (left ventricular developed pressure (LVDP), and ± dp/dt), NOx (nitrite + nitrate) level, infarct size, and mRNA expression of iNOS, Bax, and Bcl-2 were measured after IR. RESULTS: SD rats had lower recovery of post-ischemic LVDP (32.8 ± 2.5 vs. 51.5 ± 2.1 mmHg; P < 0.05), + dp/dt (1555 ± 66 vs. 1119.5 ± 87 mmHg/s; P < 0.05) and - dp/dt (1437 ± 65 vs. 888 ± 162 mmHg/s; P < 0.05). SD rats also had higher NOx levels (41.4 ± 3.1 vs. 22.4 ± 3.6 µmol/L; P < 0.05) and infarct size (64.3 ± 2.3 vs. 38.3 ± 1.6%; P < 0.05) after IR, which along with LVDP, ± dp/dt restored to near normal status in the presence of aminoguanidine, a selective iNOS inhibitor. Following IR, expression of iNOS and Bax increased and Bcl-2 decreased (502, 372, and 54%, respectively) in SD rats; whereas in the presence of aminoguanidine, expression of iNOS and Bax significantly decreased and Bcl-2 increased (165, 168, and 19%, respectively). CONCLUSION: Higher expression of iNOS and subsequent increase in apoptosis in the hearts after IR may contribute to less tolerance to myocardial IR injury in SD rats.

One-night sleep deprivation induces changes in the DNA methylation and serum activity indices of stearoyl-CoA desaturase in young healthy men.

BACKGROUND: Sleep deprivation has been associated with obesity among adults, and accumulating data suggests that stearoyl-CoA desaturase 1 (SCD1) expression has a relevant impact on fatty acid (FA) composition of lipid pools and obesity. The aim of this study was to investigate the effect of one-night total sleep deprivation (TSD) on DNA methylation in the 5'-prime region of SCD1, and whether detected changes in DNA methylation are associated with SCD activity indices (product to precursor FA ratios; 16:1n-7/16:0 and 18:1n-9/18:0) derived from serum phospholipids (PL). METHODS: Sixteen young, normal-weight, healthy men completed two study sessions, one with one-night TSD and one with one-night normal sleep (NS). Sleep quality and length was assessed by polysomnography, and consisted of electroencephalography, electrooculography, and electromyography. Fasting whole blood samples were collected on the subsequent morning for analysis of DNA methylation and FAs in serum PL. Linear regression analyses were performed to assess the association between changes in DNA methylation and SCD activity indices. RESULTS: Three CpG sites close to the transcription start site (TSS) of SCD1 (cg00954566, cg24503796, cg14089512) were significantly differentially methylated in dependency of sleep duration (-log10 P-value > 1.3). Both SCD-16 and SCD-18 activity indices were significantly elevated (P < 0.05) following one-night TSD, and significantly associated with DNA methylation changes of the three mentioned probes in the 5' region of SCD1. CONCLUSION: Our results suggest a relevant link between TSD, hepatic SCD1 expression and de-novo fatty acid synthesis via epigenetically driven regulatory mechanisms.

Rapid Eye Movement Sleep Deprivation Associated Increase in Na-K ATPase Activity in the Rat Brain is Due to Noradrenaline Induced α1-Adrenoceptor Mediated Increased α-Subunit of the Enzyme.

Rapid eye movement sleep (REMS) modulates Na-K ATPase activity and maintains brain excitability. REMS deprivation (REMSD)-associated increased Na-K ATPase activity is mediated by noradrenaline (NA) acting on α1-adrenoceptor (AR) in the brain. It was shown that NA-induced increased Na-K ATPase activity was due to allosteric modulation as well as increased turnover of the enzyme. Although the former has been studied in detail, our understanding on the latter was lacking, which we have studied. Male Wistar rats were REMS deprived for 4-days by classical flower-pot method; suitable control experiments were conducted. In another set, α1-AR antagonist prazosin (PRZ) was i.p. injected 48 h REMSD onward. At the end of experiments rats were sacrificed by cervical dislocation and brains were removed. Synaptosomes prepared from the brains were used to estimate Na-K ATPase activity as well as protein expressions of different isoforms of the enzyme subunits using western blot. REMSD significantly increased synaptosomal Na-K ATPase activity and that was due to differential increase in the expressions of α1-, α2- and α3-isoforms, but not that of ß1- and ß2-isoforms. PRZ reduced the REMSD-induced increased Na-K ATPase activity and protein expressions. We also observed that the increased Na-K ATPase subunit expression was not due to enhanced mRNA synthesis, which suggests the possibility of post-transcriptional regulation. Thus, the findings suggest that REMSD-associated increased Na-K ATPase activity is due to elevated level of α-subunit of the enzyme and that is induced by NA acting on α1-AR mediated mRNA-stabilization.

Protein kinase A in the pedunculopontine tegmental nucleus of rat contributes to regulation of rapid eye movement sleep.

Intracellular signaling mechanisms within the pedunculopontine tegmental (PPT) nucleus for the regulation of recovery rapid eye movement (REM) sleep following REM sleep deprivation remain unknown. This study was designed to determine the role of PPT intracellular cAMP-dependent protein kinase A (cAMP-PKA) in the regulation of recovery REM sleep in freely moving rats. The results show that a brief period (3 h) of selective REM sleep deprivation caused REM sleep rebound associated with increased PKA activity and expression of the PKA catalytic subunit protein (PKA-CU) in the PPT. Local application of a cAMP-PKA-activation-selective inhibitor, RpCAMPS (0.55, 1.1, and 2.2 nmol/100 nl; n = 8 rats/group), bilaterally into the PPT, reduced PKA activity and PKA-CU expression in the PPT, and suppressed the recovery REM sleep, in a dose-dependent manner. Regression analyses revealed significant positive relationships between: PPT levels of PKA activity and the total percentages of REM sleep recovery (Rsqr = 0.944; n = 40 rats); PPT levels of PKA-CU expression and the total percentages of REM sleep recovery (Rsqr = 0.937; n = 40 rats); PPT levels of PKA-CU expression and PKA activity (Rsqr = 0.945; n = 40 rats). Collectively, these results provide evidence that activation of intracellular PKA in the PPT contributes to REM sleep recovery following REM sleep deprivation.

Sleep deprivation triggers inducible nitric oxide-dependent nitric oxide production in wake-active basal forebrain neurons.

Sleep loss negatively impacts performance, mood, memory, and immune function, but the homeostatic factors that impel sleep after sleep loss are imperfectly understood. Pharmacological studies had implicated the basal forebrain (BF) inducible nitric oxide (NO) synthase (iNOS)-dependent NO as a key homeostatic factor, but its cellular source was obscure. To obtain direct evidence about the cellular source of iNOS-generated NO during sleep deprivation (SD), we used intracerebroventricular perfusion in rats of the cell membrane-permeable dye diaminofluorescein-2/diacetate (DAF-2/DA) that, once intracellular, bound NO and fluoresced. To circumvent the effects of neuronal NOS (nNOS), DAF-2/DA was perfused in the presence of an nNOS inhibitor. SD led to DAF-positive fluorescence only in the BF neurons, not glia. SD increased expression of iNOS, which colocalized with NO in neurons and, more specifically, in prolonged wakefulness-active neurons labeled by Fos. SD-induced iNOS expression in wakefulness-active neurons positively correlated with sleep pressure, as measured by the number of attempts to enter sleep. Importantly, SD did not induce Fos or iNOS in stress-responsive central amygdala and paraventricular hypothalamic neurons, nor did SD elevate corticosterone, suggesting that the SD protocol did not provoke iNOS expression through stress. We conclude that iNOS-produced neuronal NO is an important homeostatic factor promoting recovery sleep after SD.

Angiotensin I-converting enzyme (ACE) activity and expression in rat central nervous system after sleep deprivation.

Proteases are essential either for the release of neuropeptides from active or inactive proteins or for their inactivation. Neuropeptides have a fundamental role in sleep-wake cycle regulation and their actions are also likely to be regulated by proteolytic processing. Using fluorescence resonance energy transfer substrates, specific protease inhibitors and real-time PCR we demonstrate changes in angiotensin I-converting enzyme (ACE) expression and proteolytic activity in the central nervous system in an animal model of paradoxical sleep deprivation during 96 h (PSD). Male rats were distributed into five groups (PSD, 24 h, 48 h and 96 h of sleep recovery after PSD and control). ACE activity and mRNA levels were measured in hypothalamus, hippocampus, brainstem, cerebral cortex and striatum tissue extracts. In the hypothalamus, the significant decrease in activity and mRNA levels, after PSD, was only totally reversed after 96 h of sleep recovery. In the brainstem and hippocampus, although significant, changes in mRNA do not parallel changes in ACE specific activity. Changes in ACE activity could affect angiotensin II generation, angiotensin 1-7, bradykinin and opioid peptides metabolism. ACE expression and activity modifications are likely related to some of the physiological changes (cardiovascular, stress, cognition, metabolism function, water and energy balance) observed during and after sleep deprivation.

The impact of sleep deprivation on sexual behaviors and FAAH expression in the prefrontal cortex of male rats.

Sleep deprivation (SD) causes alterations in the function of the endocannabinoid (EC) system and also results in alteration in many behaviors such as increased anxiety, deteriorated alertness, memory deficits, as well as sexual behaviors. Controversial data about the effects of SD on sexual response are provided. Fatty acid amide hydrolase (FAAH), the enzymes involved in the degradation of the EC system play an important role in the function of the EC system. This study aimed to investigate the effect of REM SD (RSD) and total SD (TSD) on the sexual behaviors and FAAH expression in the prefrontal cortex (PFC) of male rats. RSD was carried out through the flower pot technique for 24 h and 48 h, and TSD also was induced by keeping awake the rats by gentle handling for 6 h. Immediately after RSD and TSD, sexual behaviors were recorded for 45 min. Sexual behaviors were reduced by both types of RSD and TSD. The deleterious effects of 24 h RSD were more severe compared with 6 h of TSD. Serum testosterone concentration was significantly higher after TSD but not RSD compared to the normal sleep (NS) group. FAAH expression in the PFC was significantly reduced after both RSD and TSD compared to the NS group. Given that the function of the EC system has been previously shown to change different behaviors such as sexual activity, our results could suggest that behavioral effects of both types of SD on sexual behavior may partially result from activation of this signaling pathway by the reduction of FAAH in the PFC.

Na+/K+-ATPase and lipid peroxidation in forebrain cortex and hippocampus of sleep-deprived rats treated with therapeutic lithium concentration for different periods of time.

Lithium (Li) is a typical mood stabilizer and the first choice for treatment of bipolar disorder (BD). Despite an extensive clinical use of Li, its mechanisms of action remain widely different and debated. In this work, we studied the time-course of the therapeutic Li effects on ouabain-sensitive Na+/K+-ATPase in forebrain cortex and hippocampus of rats exposed to 3-day sleep deprivation (SD). We also monitored lipid peroxidation as malondialdehyde (MDA) production. In samples of plasma collected from all experimental groups of animals, Li concentrations were followed by ICP-MS. The acute (1 day), short-term (7 days) and chronic (28 days) treatment of rats with Li resulted in large decrease of Na+/K+-ATPase activity in both brain parts. At the same time, SD of control, Li-untreated rats increased Na+/K+-ATPase along with increased production of MDA. The SD-induced increase of Na+/K+-ATPase and MDA was attenuated in Li-treated rats. While SD results in a positive change of Na+/K+-ATPase, the inhibitory effect of Li treatment may be interpreted as a pharmacological mechanism causing a normalization of the stress-induced shift and return the Na+/K+-ATPase back to control level. We conclude that SD alone up-regulates Na+/K+-ATPase together with increased peroxidative damage of lipids. Chronic treatment of rats with Li before SD, protects the brain tissue against this type of damage and decreases Na+/K+-ATPase level back to control level.

Cholinergic augmentation modulates visual task performance in sleep-deprived young adults.

Using 24 h of total sleep deprivation to perturb normal cognitive function, we conducted a double-blind, placebo-controlled crossover study to evaluate the effect of the acetylcholinesterase inhibitor, donepezil, on behavioral performance and task-related brain activation in 28 healthy, young, adult volunteers. The behavioral tasks involved the parametric manipulation of visual short-term memory load and perceptual load in separate experiments indirectly evaluating attention. Sleep deprivation significantly reduced posterior cortical activation (intraparietal sulcus and extrastriate cortex) at all levels of visual memory as well as perceptual load. Donepezil modulated an individual's performance in both tasks in accordance to whether accuracy declined after sleep deprivation without treatment. Critically, there were significant correlations between donepezil-induced increases in neural activation in the posterior cortical areas and improvement in accuracy. Reduced visual short-term memory after sleep deprivation may thus originate from a decline in visual attention and/or visual processing. Cholinergic augmentation can alleviate these deficits in individuals vulnerable to the effects of sleep deprivation, but it may have neutral or negative effects on those resistant to sleep deprivation.

Polysomnographic abnormalities in succinic semialdehyde dehydrogenase (SSADH) deficiency.

OBJECTIVES: Patients with SSADH deficiency, a disorder of chronically elevated endogenous GABA and GHB, were studied for sleep symptoms and polysomnography. We hypothesized that patients would have excessive daytime somnolence and decreased REM sleep. DESIGN: Polysomnography and MSLT were performed on patients enrolled for comprehensive clinical studies of SSADH deficiency. SETTING: Sleep studies were obtained in the sleep laboratories at CNMC and NIH. PATIENTS: Sleep recordings were obtained in 10 patients with confirmed SSADH deficiency. INTERVENTIONS: Thirteen overnight polysomnograms were obtained in 10 patients (7 male, 3 female, ages 11-27 y). Eleven MSLT studies were completed in 8 patients. MEASUREMENTS AND RESULTS: Polysomnograms showed prolongation of REM stage latency (mean 272 +/- 89 min) and decreased percent stage REM (mean 8.9%, range 0.3% to 13.8%). Decreased mean sleep latency was present in 6 of 11 MSLTs. CONCLUSIONS: SSADH deficiency is associated with prolonged latency to stage REM and decreased percent stage REM. This disorder represents a model of chronic GABA and GHB accumulation associated with suppression of REM sleep.

Stimulatory role of calcium in rapid eye movement sleep deprivation-induced noradrenaline-mediated increase in Na-K-ATPase activity in rat brain.

Rapid eye movement (REM) sleep deprivation elevates noradrenaline level, which upon acting on alpha1-adrenoceptors increases Na-K-ATPase activity; however, the detailed intracellular mechanism of action was unknown. Since membrane integrity is crucial for maintaining Na-K-ATPase activity as well as ionic exchange and noradrenaline affects membrane lipid-peroxidation, we proposed that the deprivation might modulate membrane lipid-peroxidation, which would modulate intracellular ionic concentration and thereby increase Na-K-ATPase activity. Hence, in this in vivo and in vitro study, rats were deprived of REM sleep for 4 days by the flowerpot method and suitable control experiments were conducted. The deprivation simultaneously decreased membrane lipid-peroxidation as well as increased Na-K-ATPase activity by its dephosphorylation and all the effects were induced by noradrenaline. Further, in vitro experiments showed that hydrogen peroxide (H(2)O(2))-induced enhanced lipid-peroxidation increased synaptosomal calcium (Ca(2+))-influx, which was also prevented by noradrenaline and nifidipine, an L-type Ca(2+)-channel blocker. Additionally, both nifidipine and cyclopiazonic acid, which have opposite effects on intracellular Ca(2+)-concentration, prevented deprivation induced increased Na-K-ATPase activity. We propose that REM sleep deprivation elevates noradrenaline level in the brain that acting on alpha1-adrenoceptor simultaneously reduces membrane lipid-peroxidation but activates phospholipase-C, resulting in closure of L-type Ca(2+)-channel and releasing membrane bound Ca(2+); the latter then dephosphorylates Na-K-ATPase, the active form, causing its increased activity.

[Diencephalo-telencephalic changes of tyrosine hydroxylase in rats and common frogs (Rana temporaria) after sleep deprivation].

Based on sleep deprivation-produced changes of electrographic parameters of the wakefulness--sleep cycle (WSC) in rats and common frogs, dynamics of activity of tyrosine hydroxylase, the key enzyme of dopamine synthesis, was studied immunohistochemically in substantia nigra and nigrostriatal pathway in rats and in striatum, paraventricular organ, and extrahypothalamic pathways in frogs. There are revealed changes in dynamics of tyrosine hydroxylase in rats and in common frogs after the 6-h sleep deprivation and after 2 h of postdeprivation sleep. This allows determining the degree of participation of corticostriatal neuroregulatory and hypothalamo-pituitary neurosecretory systems and their role in regulation of WSC. Possible evolutionary peculiarities of morphofunctional differences in homoiothermal and poikilothermal animals are discussed.

Protein-Tyrosine Phosphatase-1B Mediates Sleep Fragmentation-Induced Insulin Resistance and Visceral Adipose Tissue Inflammation in Mice.

Study Objectives: Sleep fragmentation (SF) is highly prevalent and has emerged as an important contributing factor to obesity and metabolic syndrome. We hypothesized that SF-induced increases in protein tyrosine phosphatase-1B (PTP-1B) expression and activity underlie increased food intake, inflammation, and leptin and insulin resistance. Methods: Wild-type (WT) and ObR-PTP-1b-/- mice (Tg) were exposed to SF and control sleep (SC), and food intake was monitored. WT mice received a PTP-1B inhibitor (RO-7d; Tx) or vehicle (Veh). Upon completion of exposures, systemic insulin and leptin sensitivity tests were performed as well as assessment of visceral white adipose tissue (vWAT) insulin receptor sensitivity and macrophages (ATM) polarity. Results: SF increased food intake in either untreated or Veh-treated WT mice. Leptin-induced hypothalamic STAT3 phosphorylation was decreased, PTP-1B activity was increased, and reduced insulin sensitivity emerged both systemic and in vWAT, with the latter displaying proinflammatory ATM polarity changes. All of the SF-induced effects were abrogated following PTP-1B inhibitor treatment and in Tg mice. Conclusions: SF induces increased food intake, reduced leptin signaling in hypothalamus, systemic insulin resistance, and reduced vWAT insulin sensitivity and inflammation that are mediated by increased PTP-1B activity. Thus, PTP-1B may represent a viable therapeutic target in the context of SF-induced weight gain and metabolic dysfunction.

Sex differences in susceptibility to oxidative injury and sleepiness from intermittent hypoxia.

STUDY OBJECTIVES: Adult male mice exposed to long-term intermittent hypoxia (LTIH), modeling sleep apnea oxygenation patterns, develop nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-dependent residual hypersomnolence and oxidative injury in select brain regions, including wake-active regions. Premenopausal females are less susceptible to selective oxidative brain injuries. We sought to determine whether female mice exposed to LTIH would confer resistance to LTIH-induced wake impairments and oxidative injuries. SUBJECTS AND SETTING: Young adult male and female C57BI/6J mice were studied in a university laboratory. INTERVENTIONS: Mice were randomly assigned to either LTIH or sham LTIH for 8 weeks. Total (24-h) wake time and mean sleep latency were measured under 2 conditions: rested and following 6 hours of enforced wakefulness. NADPH oxidase activation, carbonylation, and lipid peroxidation assays were also performed to assess sex differences in oxidative responses to LTIH. RESULTS: In contrast with the significant LTIH-induced wake impairments observed in male mice, females following LTIH showed normal wake times and sleep latencies. Female mice revealed less baseline carbonylation and less carbonylation following LTIH but showed robust NADPH oxidase activation and lipid peroxidation. In contrast with the female relative resistance to LTIH sleepiness, female mice showed more-pronounced sleepiness and delta response after enforced wakefulness. CONCLUSIONS: Despite a robust oxidative response to LTIH, age-matched female mice may be protected, at least temporarily, from LTIH wake impairments by lower basal carbonylation. In contrast, females show greater wake impairments after sleep deprivation. We hypothesize sex differences in polysomnographic predictors of sleepiness and residual sleepiness in humans with sleep apnea.

Hypothalamic L-Histidine Decarboxylase Is Up-Regulated During Chronic REM Sleep Deprivation of Rats.

A competition of neurobehavioral drives of sleep and wakefulness occurs during sleep deprivation. When enforced chronically, subjects must remain awake. This study examines histaminergic neurons of the tuberomammillary nucleus of the posterior hypothalamus in response to enforced wakefulness in rats. We tested the hypothesis that the rate-limiting enzyme for histamine biosynthesis, L-histidine decarboxylase (HDC), would be up-regulated during chronic rapid eye movement sleep deprivation (REM-SD) because histamine plays a major role in maintaining wakefulness. Archived brain tissues of male Sprague Dawley rats from a previous study were used. Rats had been subjected to REM-SD by the flowerpot paradigm for 5, 10, or 15 days. For immunocytochemistry, rats were transcardially perfused with acrolein-paraformaldehyde for immunodetection of L-HDC; separate controls used carbodiimide-paraformaldehyde for immunodetection of histamine. Immunolocalization of histamine within the tuberomammillary nucleus was validated using carbodiimide. Because HDC antiserum has cross-reactivity with other decarboxylases at high antibody concentrations, titrations localized L-HDC to only tuberomammillary nucleus at a dilution of ≥ 1:300,000. REM-SD increased immunoreactive HDC by day 5 and it remained elevated in both dorsal and ventral aspects of the tuberomammillary complex. Our results suggest that up-regulation of L-HDC within the tuberomammillary complex during chronic REM-SD may be responsible for maintaining wakefulness.

Sleep deprivation decreases superoxide dismutase activity in rat hippocampus and brainstem.

Sleep deprivation by the disk-over-water technique results in a predictable syndrome of physiological changes in rats. It has been proposed that reactive oxygen species (ROS) may be responsible for some of these effects. A variety of antioxidative enzymes such as superoxide dismutase (SOD) and glutathione peroxidase (GPx) help to regulate the level of ROS. In this study we investigated the effects of prolonged (5-11 days) sleep deprivation on the activities of SOD and GPx as well as the metabolic activity of the mitochondria (using alamar blue) in several brain regions (cortex, hippocampus, hypothalamus, brainstem and cerebellum). We show that prolonged sleep deprivation significantly decreased Cu/Zn-SOD activity in the hippocampus and brainstem, suggesting an alteration in the metabolism of ROS resulting in oxidative stress.

The cholinesterase inhibitor DFP facilitates the expression of paradoxical sleep (PS) propensity in rats subjected to short-term PS deprivation.

Short-term paradoxical sleep (PS) deprivation was used to examine the effects of chronic exposure to subtoxic doses of the cholinesterase inhibitor diisopropylfluorophosphate (DFP) on PS regulation. Rats were injected once daily with DFP (0.2 mg/kg per day; s.c.) for 11 consecutive days; control rats received a daily injection of oil vehicle. The experiment was conducted on the 10th and 11th days of treatment, when brain cholinesterase inhibition induced by DFP exposure was maximal. On the 10th day, an 8-h baseline recording was carried out. On the 11th day, a 6-h PS deprivation was carried out by manually awaking rats each time they showed polygraphic signs of PS; recordings were then continued for another 2 h to examine recovery sleep. During deprivation, though they slept less than controls, DFP-treated rats made more attempts to enter PS. After deprivation, their PS rebound had an overall amount comparable to that of the controls, but its time course was shortened: whereas PS elevation was manifested through the 2 h of recovery in the control group, it occurred only during the first hour in the DFP group. These results demonstrate that chronic, low-level DFP exposure facilitated the expression of the PS propensity that accumulated as a result of PS deprivation: it enhanced the tendency for PS during deprivation; it accelerated the rate of compensatory PS expression after deprivation. They support the hypothesis that DFP promotes PS initiation by increasing cholinergic transmission.

Sleep deprivation impairs spatial memory and decreases extracellular signal-regulated kinase phosphorylation in the hippocampus.

Loss of sleep may result in memory impairment. However, little is known about the biochemical basis for memory deficits induced by sleep deprivation. Extracellular signal-regulated kinase (ERK) is involved in memory consolidation in different tasks. Phosphorylation of ERK is necessary for its activation and is an important step in mediating neuronal responses to synaptic activities. The aim of the present study was to determine the effects of total sleep deprivation (TSD) on memory and ERK phosphorylation in the brain. Rats were trained in Morris water maze to find a hidden platform (a spatial task) or a visible platform (a nonspatial task) after 6 h TSD or spontaneous sleep. TSD had no effect on spatial learning, but significantly impaired spatial memory tested 24 h after training. Nonspatial learning and memory were not impaired by TSD. Phospho-ERK levels in the hippocampus were significantly reduced after 6 h TSD compared to the controls and returned to the control levels after 2 h recovery sleep. Total ERK1 and ERK2 were slightly increased after 6 h TSD and returned to the control levels after 2 h recovery sleep. These alterations were not observed in the cortex after TSD. Protein phosphotase-1 and mitogen-activated protein kinase phosphatase-2, which dephosphorylates phospho-ERK, were also measured, but they were not altered by TSD. The impairments of both spatial memory and ERK phosphorylation indicate that the hippocampus is vulnerable to sleep loss. These results are consistent with the idea that decreased ERK activation in the hippocampus is involved in sleep deprivation-induced spatial memory impairment.

Increased levels of tyrosine hydroxylase and glutamic acid decarboxylase in locus coeruleus neurons after rapid eye movement sleep deprivation in rats.

Norepinephrine, acetylcholine and GABA levels alter during rapid eye movement (REM) sleep and its deprivation. Increased synthesis of those neurotransmitters is necessary for their sustained release. Hence, in this study, the concentrations of tyrosine hydroxylase (TH), choline acetyl transferase (ChAT) and glutamic acid decarboxylase (GAD), the enzymes responsible for their synthesis, were immunohistochemically estimated within the neurons in locus coeruleus, laterodorsal tegmentum and pedunculopontine tegmentum and medial preoptic area in REM sleep deprived and control rats. It was observed that as compared to controls, deprivation increased TH and GAD significantly in the locus coeruleus only, while in other areas, they remained unchanged. The findings help explaining the mechanism of increase in neurotransmitter levels in the brain after REM sleep deprivation and their significance has been discussed.