REM sleep loss increases brain excitability: role of noradrenaline and its mechanism of action. Sleep Med Rev. 2011;15:165-178. [PMID: 21482157 DOI: 10.1016/j.smrv.2010.11.001]

Protective role of noradrenaline in benzo[a]pyrene-induced learning impairment in developing rat

Benzo[a]pyrene (B[a]P), a carcinogen, affects brain development, learning, and memory. Isolated studies have reported that B[a]P elevates noradrenaline (NA) level that may modulate neuronal growth, learning, and memory. Therefore, we investigated in vivo and in vitro the effects of B[a]P on learning and memory and its possible mechanism of action. Intracisternal administration of B[a]P on postnatal day 5 significantly reduced learning and memory in adolescent rats as observed by probe test using the Morris water maze. The density of both the subunits of the N-methyl-D-aspartate (NMDA) receptor, NMDAR1 and NMDAR2B, significantly increased in the hippocampus. In vitro, B[a]P significantly increased NMDAR1 in both C6 and Neuro2a cell lines, whereas NMDAR2B was significantly increased in C6 but was significantly decreased in Neuro2a. Pretreatment with NA prevented the B[a]P-induced effect on NMDAR1 expression in both cell lines. However, although NA prevented the B[a]P-mediated increase in NMDAR2B expression in C6, it further potentiated the decrease of NMDAR2B in Neuro2a cells. Also, NA prevented the B[a]P-induced increase in intracellular Ca(2+) both in C6 and in Neuro2a. Our findings show that postnatal exposure of developing rats to B[a]P impairs learning and memory even when the rats became adolescent. We also observed that the effects were mediated by elevated intracellular Ca(2+) levels and increased expression of NMDAR; furthermore, NA exerted a protective effect by modulating those factors. NA differentially affects neurons and glia, which may have a compensatory role during toxic insults, especially from B[a]P.

One night of total sleep deprivation promotes a state of generalized hyperalgesia: a surrogate pain model to study the relationship of insomnia and pain

Sleep disturbances are highly prevalent in chronic pain patients. Understanding their relationship has become an important research topic since poor sleep and pain are assumed to closely interact. To date, human experimental studies exploring the impact of sleep disruption/deprivation on pain perception have yielded conflicting results. This inconsistency may be due to the large heterogeneity of study populations and study protocols previously used. In addition, none of the previous studies investigated the entire spectrum of nociceptive modalities. To address these shortcomings, a standardized comprehensive quantitative sensory protocol was used in order to compare the somatosensory profile of 14 healthy subjects (6 female, 8 male, 23.5 ± 4.1 year; mean ± SD) after a night of total sleep deprivation (TSD) and a night of habitual sleep in a cross-over design. One night of TSD significantly increased the level of sleepiness (P<0.001) and resulted in higher scores of the State Anxiety Inventory (P<0.01). In addition to previously reported hyperalgesia to heat (P<0.05) and blunt pressure (P<0.05), study participants developed hyperalgesia to cold (P<0.01) and increased mechanical pain sensitivity to pinprick stimuli (P<0.05) but no changes in temporal summation. Paradoxical heat sensations or dynamic mechanical allodynia were absent. TSD selectively modulated nociception, since detection thresholds of non-nociceptive modalities remained unchanged. Our findings show that a single night of TSD is able to induce generalized hyperalgesia and to increase State Anxiety scores. In the future, TSD may serve as a translational pain model to elucidate the pathomechanisms underlying the hyperalgesic effect of sleep disturbances.

Involvement of the α1-adrenoceptor in sleep-waking and sleep loss-induced anxiety behavior in zebrafish

Sleep is a universal phenomenon in vertebrates, and its loss affects various behaviors. Independent studies have reported that sleep loss increases anxiety; however, the detailed mechanism is unknown. Because sleep deprivation increases noradrenalin (NA), which modulates many behaviors and induces patho-physiological changes, this study utilized zebrafish as a model to investigate whether sleep loss-induced increased anxiety is modulated by NA. Continuous behavioral quiescence for at least 6s was considered to represent sleep in zebrafish; although some authors termed it as a sleep-like state, in this study we have termed it as sleep. The activity of fish that signified sleep-waking was recorded in light-dark, during continuous dark and light; the latter induced sleep loss in fish. The latency, number of entries, time spent and distance travelled in the light chamber were assessed in a light-dark box test to estimate the anxiety behavior of normal, sleep-deprived and prazosin (PRZ)-treated fish. Zebrafish showed increased waking during light and complete loss of sleep upon continuous exposure to light for 24h. PRZ significantly increased sleep in normal fish. Sleep-deprived fish showed an increased preference for dark (expression of increased anxiety), and this effect was prevented by PRZ, which increased sleep as well. Our findings suggest that sleep loss-induced anxiety-like behavior in zebrafish is likely to be mediated by NA's action on the α1-adrenoceptor.

Grooming analysis algorithm: use in the relationship between sleep deprivation and anxiety-like behavior

Increased anxiety is a classic effect of sleep deprivation. However, results regarding sleep deprivation-induced anxiety-like behavior are contradictory in rodent models. The grooming analysis algorithm is a method developed to examine anxiety-like behavior and stress in rodents, based on grooming characteristics and microstructure. This study evaluated the applicability of the grooming analysis algorithm to distinguish sleep-deprived and control rats in comparison to traditional grooming analysis. Forty-six animals were distributed into three groups: control (n=22), paradoxical sleep-deprived (96 h, n=10) and total sleep deprived (6 h, n=14). Immediately after the sleep deprivation protocol, grooming was evaluated using both the grooming analysis algorithm and traditional measures (grooming latency, frequency and duration). Results showed that both paradoxical sleep-deprived and total sleep-deprived groups displayed grooming in a fragmented framework when compared to control animals. Variables from the grooming analysis algorithm were successful in distinguishing sleep-deprived and normal sleep animals regarding anxiety-like behavior. The grooming analysis algorithm and traditional measures were strongly correlated. In conclusion, the grooming analysis algorithm is a reliable method to assess the relationship between anxiety-like behavior and sleep deprivation.

Increased cortical excitability after selective REM sleep deprivation in healthy humans: a transcranial magnetic stimulation study

BACKGROUND

REM sleep has antiepileptogenic properties whereas, its loss is known to have a proconvulsive role. However, the mechanisms underlying the proepileptogenic effects of REM sleep deprivation are yet not fully understood. The aim of our study was to evaluate the effects of selective REM sleep deprivation (SRD) on cortical excitability in healthy subjects by means of transcranial magnetic stimulation (TMS).

METHODS

Ten normal subjects underwent three TMS sessions: (1) in baseline condition (BL), (2) after SRD by awakening them at each REM sleep onset and (3) after non-rapid eye movement sleep awakenings (NREM-A) as control for potential non-specific effects of interruptions. The TMS investigation included two protocols: (a) the evaluation of motor evoked potentials (MEPs) and silent period (SP) parameters, recorded in response to single pulse magnetic stimulation; (b) the evaluation of the time course of intracortical motor activity tested with paired-pulse TMS applied at inter-stimulus intervals of 1-10 ms.

RESULTS

After SRD the principal finding observed using single pulse TMS was a significant reduction in the duration of SP whereas, a reduction of intracortical inhibition was found, using the paired-pulse TMS. TMS parameters did not show significant changes after NREM-A with respect to BL.

CONCLUSIONS

SRD may influence cortical excitability with a reduction of inhibitory intracortical mechanisms, thus supporting the proconvulsant role of REM loss.

Paradoxical sleep deprivation potentiates epilepsy induced by homocysteine thiolactone in adult rats

There is an intriguing and still poorly understood relationship between sleep deprivation and epilepsy. It has recently been shown that paradoxical sleep deprivation decreases levels of homocysteine, an amino acid involved together with its thiolactone metabolite in epileptogenesis. The aim of the present study was to investigate the effects of paradoxical sleep deprivation on homocysteine thiolactone (H)-induced seizures in rats, a model of generalized seizures. Selective deprivation of paradoxical sleep in adult male Wistar rats was achieved by the platform method. Animals with implanted electrodes for electroencephalogram (EEG) registration were assigned to appropriate experimental conditions (dry cage for control, large platform for stress control and small platform for paradoxical sleep deprivation) and 72 h later were intraperitoneally treated with either H (5.5 mmol/kg) or saline (0.9% NaCl). This study showed that paradoxical sleep deprivation increased the incidence and number of H-induced seizure episodes, shortened latency time to seizures and led to significant rates of lethality after H administration, but without effect on the seizure severity. Paradoxical sleep deprivation increased the number and duration of spikes-and-wave discharges, while decreased latency to its appearance in EEG. Judging by the behavioral and EEG findings, it could be concluded that paradoxical sleep deprivation can provoke the expression of factors that can potentiate H-induced seizures in adult rats.

A mathematical model towards understanding the mechanism of neuronal regulation of wake-NREMS-REMS states

In this study we have constructed a mathematical model of a recently proposed functional model known to be responsible for inducing waking, NREMS and REMS. Simulation studies using this model reproduced sleep-wake patterns as reported in normal animals. The model helps to explain neural mechanism(s) that underlie the transitions between wake, NREMS and REMS as well as how both the homeostatic sleep-drive and the circadian rhythm shape the duration of each of these episodes. In particular, this mathematical model demonstrates and confirms that an underlying mechanism for REMS generation is pre-synaptic inhibition from substantia nigra onto the REM-off terminals that project on REM-on neurons, as has been recently proposed. The importance of orexinergic neurons in stabilizing the wake-sleep cycle is demonstrated by showing how even small changes in inputs to or from those neurons can have a large impact on the ensuing dynamics. The results from this model allow us to make predictions of the neural mechanisms of regulation and patho-physiology of REMS.

Rapid eye movement sleep deprivation modulates synapsinI expression in rat brain

Rapid eye movement sleep (REMS) deprivation (REMSD) has been reported to elevate neurotransmitter level in the brain; however, intracellular mechanism of its increased release was not studied. Phosphorylation of synapsinI, a synaptic vesicle-associated protein, is involved in the regulation of neurotransmitter release. In this study, rats were REMS deprived by classical flowerpot method; free moving control (FMC), large platform control (LPC) and recovery control (REC) was carried out. In another set REMS deprived rats were intraperitoneally (i.p.) injected with α1-adrenoceptor antagonist, prazosin (PRZ). Effects of REMSD on Na-K ATPase activity and on the total synapsinI as well as phosphorylated synapsinI levels were estimated in synaptosomes prepared from whole brain. It was observed that REMSD significantly increased synaptosomal Na-K ATPase activity, which was prevented by PRZ. Western blotting of the same samples by anti-synapsinI and anti-synapsinI-phosphoSer603 showed that REMSD increased both the total as well as phospho-form of synapsinI as compared to respective levels in FMC and LPC samples. These findings suggest a functional link between REMSD and synaptic vesicular mobilization at the presynaptic terminal, a process that is essential for neurotransmitter release. The findings help explaining the intracellular mechanism of elevated neurotransmitter release associated to REMSD.

Activation of inactivation process initiates rapid eye movement sleep

Interactions among REM-ON and REM-OFF neurons form the basic scaffold for rapid eye movement sleep (REMS) regulation; however, precise mechanism of their activation and cessation, respectively, was unclear. Locus coeruleus (LC) noradrenalin (NA)-ergic neurons are REM-OFF type and receive GABA-ergic inputs among others. GABA acts postsynaptically on the NA-ergic REM-OFF neurons in the LC and presynaptically on the latter's projection terminals and modulates NA-release on the REM-ON neurons. Normally during wakefulness and non-REMS continuous release of NA from the REM-OFF neurons, which however, is reduced during the latter phase, inhibits the REM-ON neurons and prevents REMS. At this stage GABA from substantia nigra pars reticulate acting presynaptically on NA-ergic terminals on REM-ON neurons withdraws NA-release causing the REM-ON neurons to escape inhibition and being active, may be even momentarily. A working-model showing neurochemical-map explaining activation of inactivation process, showing contribution of GABA-ergic presynaptic inhibition in withdrawing NA-release and dis-inhibition induced activation of REM-ON neurons, which in turn activates other GABA-ergic neurons and shutting-off REM-OFF neurons for the initiation of REMS-generation has been explained. Our model satisfactorily explains yet unexplained puzzles (i) why normally REMS does not appear during waking, rather, appears following non-REMS; (ii) why cessation of LC-NA-ergic-REM-OFF neurons is essential for REMS-generation; (iii) factor(s) which does not allow cessation of REM-OFF neurons causes REMS-loss; (iv) the association of changes in levels of GABA and NA in the brain during REMS and its deprivation and associated symptoms; v) why often dreams are associated with REMS.