Cytomorphometric changes in the dorsal raphe neurons after rapid eye movement sleep deprivation are mediated by noradrenalin in rats

REM Sleep Loss-Induced Elevated Noradrenaline Plays a Significant Role in Neurodegeneration: Synthesis of Findings to Propose a Possible Mechanism of Action from Molecule to Patho-Physiological Changes

Wear and tear are natural processes for all living and non-living bodies. All living cells and organisms are metabolically active to generate energy for their routine needs, including for survival. In the process, the cells are exposed to oxidative load, metabolic waste, and bye-products. In an organ, the living non-neuronal cells divide and replenish the lost or damaged cells; however, as neuronal cells normally do not divide, they need special feature(s) for their protection, survival, and sustenance for normal functioning of the brain. The neurons grow and branch as axons and dendrites, which contribute to the formation of synapses with near and far neurons, the basic scaffold for complex brain functions. It is necessary that one or more basic and instinct physiological process(es) (functions) is likely to contribute to the protection of the neurons and maintenance of the synapses. It is known that rapid eye movement sleep (REMS), an autonomic instinct behavior, maintains brain functioning including learning and memory and its loss causes dysfunctions. In this review we correlate the role of REMS and its loss in synaptogenesis, memory consolidation, and neuronal degeneration. Further, as a mechanism of action, we will show that REMS maintains noradrenaline (NA) at a low level, which protects neurons from oxidative damage and maintains neuronal growth and synaptogenesis. However, upon REMS loss, the level of NA increases, which withdraws protection and causes apoptosis and loss of synapses and neurons. We propose that the latter possibly causes REMS loss associated neurodegenerative diseases and associated symptoms.

Rapid eye movement sleep loss associated cytomorphometric changes and neurodegeneration

Rapid eye movement sleep (REMS) is essential for leading normal healthy living at least in higher-order mammals, including humans. In this review, we briefly survey the available literature for evidence linking cytomorphometric changes in the brain due to loss of REMS. As a mechanism of action, we add evidence that REMS loss elevates noradrenaline (NA) levels in the brain, which affects neuronal cytomorphology. These changes may be a compensatory mechanism as the changes return to normal after the subjects recover from the loss of REMS or if during REMS deprivation, the subjects are treated with NA-adrenoceptor antagonist prazosin (PRZ). We had proposed earlier that one of the fundamental functions of REMS is to maintain the level of NA in the brain. We elaborate on this idea to propose that if REMS loss continues without recovery, the sustained level of NA breaks down neurophysiologically active compensatory mechanism/s starting with changes in the neuronal cytomorphology, followed by their degeneration, leading to acute and chronic pathological conditions. Identification of neuronal cytomorphological changes could prove to be of significance for predicting future neuronal (brain) damage as well as an indicator for REMS health. Although current brain imaging techniques may not enable us to visualize changes in neuronal cytomorphology, given the rapid technological progress including use of artificial intelligence, we are optimistic that it may be a reality soon. Finally, we propose that maintenance of optimum REMS must be considered a criterion for leading a healthy life.

Mitochondria's role in sleep: Novel insights from sleep deprivation and restriction studies

OBJECTIVES/METHODS

The biology underlying sleep is not yet fully elucidated, but it is known to be complex and largely influenced by circadian rhythms. Compelling evidence supports of a link among circadian rhythms, sleep and metabolism, which suggests a role for mitochondria. These organelles play a significant role in energy metabolism via oxidative phosphorylation (OXPHOS) and several mitochondrial enzymes display circadian oscillations. However, the interplay between mitochondria and sleep is not as well-known. This review summarises human and animal studies that have examined the role of mitochondria in sleep. Literature searches were conducted using PubMed and Google Scholar.

RESULTS

Using various models of sleep deprivation, animal studies support the involvement of mitochondria in sleep via differential gene and protein expression patterns, OXPHOS enzyme activity, and morphology changes. Human studies are more limited but also show differences in OXPHOS enzyme activity and protein levels among individuals who have undergone sleep deprivation or suffer from different forms of insomnia.

CONCLUSIONS

Taken altogether, both types of study provide evidence for mitochondria's involvement in the sleep-wake cycle. We briefly discuss the potential clinical implications of these studies.

Neurogenesis in the rat neonate's hippocampus with maternal short-term REM sleep deprivation restores by royal jelly treatment

BACKGROUND

Numerous studies have shown the effects of rapid eye movement sleep deprivation (REM-SD) on behavior and brain structures. The impact of REM-SD on learning and memory, thus neurogenesis, has been reported in previous studies. Royal jelly (RJ) is known as the wealthiest biological nutrient with various physiological properties. This study aimed to study the possible effect of RJ on neurogenesis of the rat hippocampus neonates following exposure of mother to REM-SD during pregnancy.

METHODS

Thirty neonate rats from 15 pregnant Wistar rats were used. To induce REM-SD, the flowerpot method was used. The pregnant rats were divided into five groups (n = 3): group 1, no treatment; group 2, REM-SD; groups 3, 4, and 5, REM-SD +RJ. The former group received 72 h REM-SD during pregnancy (days 7, 14, 21), and the latter group received REM-SD + RJ (three trial groups). At week 4, the rat neonates of all groups were sacrificed (n = 6 each group). Their brains were fixed, removed, and prepared for Nissl and Hoechst 33342 staining. By using real time polymerase chain reaction methode the brain-derived neurotrophic factor BDNF gene expression was studied (RT-PCR), brain-derived neurotrophic factor (BDNF) gene expression was studied. The results were analyzed statistically, and the Pv  < .05 was considered significant.

RESULTS

The results showed a significant decrease in the number of neurons in the hippocampus of neonatal rats of REM-SD mothers compared to the neonates of the mother with REM-SD + RJ. REM-SD also led to an increase in apoptosis reaching the neonates from the REM-SD + RJ animals. High expression of BDNF was observed in the hippocampus of the neonates from REM-SD + RJ treated mothers.

CONCLUSION

RJ acts as a neuroprotective agent that could compensate for the effects of REM-SD on learning and memory via restoring neurogenesis.

Rapid eye movement sleep deprivation impairs neuronal plasticity and reduces hippocampal neuronal arborization in male albino rats: Noradrenaline is involved in the process

Rapid eye movement sleep (REMS) favors brain development and memory, while it is decreased in neurodegenerative diseases. REMS deprivation (REMSD) affects several physiological processes including memory consolidation; however, its detailed mechanism(s) of action was unknown. REMS reduces, while REMSD elevates noradrenaline (NA) level in the brain; the latter induces several deficiencies and disorders, including changes in neuronal cytomorphology and apoptosis. Therefore, we proposed that REMS- and REMSD-associated modulation of NA level might affect neuronal plasticity and affect brain functions. Male albino rats were REMS deprived by flower-pot method for 6 days, and its effects were compared with home cage and large platform controls as well as post-REMSD recovered and REMS-deprived prazosin (α1-adrenoceptor antagonist)-treated rats. We observed that REMSD reduced CA1 and CA3 neuronal dendritic length, branching, arborization, and spine density, while length of active zone and expressions of pre- as well as post-synaptic proteins were increased as compared to controls; interestingly, prazosin prevented most of the effects in vivo. Studies on primary culture of neurons from chick embryo brain confirmed that NA at lower concentration(s) induced neuronal branching and arborization, while higher doses were destructive. The findings support our contention that REMSD adversely affects neuronal plasticity, branching, and synaptic scaffold, which explain the underlying cytoarchitectural basis of REMSD-associated patho-physio-behavioral changes. Consolidation of findings of this study along with that of our previous reports suggest that the neuronal disintegration could be due to either withdrawal of direct protective and proliferative role of low dose of NA or indirect effect of high dose of NA or both.

Effects of Sleep Deprivation on the Tryptophan Metabolism

Sleep has a regulatory role in maintaining metabolic homeostasis and cellular functions. Inadequate sleep time and sleep disorders have become more prevalent in the modern lifestyle. Fragmentation of sleep pattern alters critical intracellular second messengers and neurotransmitters which have key functions in brain development and behavioral functions. Tryptophan metabolism has also been found to get altered in SD and it is linked to various neurodegenerative diseases. The kynurenine pathway is a major regulator of the immune response. Adequate sleep alleviates neuroinflammation and facilitates the cellular clearance of metabolic toxins produced within the brain, while sleep deprivation activates the enzymatic degradation of tryptophan via the kynurenine pathway, which results in an increased accumulation of neurotoxic metabolites. SD causes increased production and accumulation of kynurenic acid in various regions of the brain. Higher levels of kynurenic acid have been found to trigger apoptosis, leads to cognitive decline, and inhibit neurogenesis. This review aims to link the impact of sleep deprivation on tryptophan metabolism and associated complication in the brain.

Curcumin prevents neuronal loss and structural changes in the superior cervical (sympathetic) ganglion induced by chronic sleep deprivation, in the rat model

Background

In modern societies, sleep deprivation is a serious health problem. This problem could be induced by a variety of reasons, including lifestyle habits or neurological disorders. Chronic sleep deprivation (CSD) could have complex biological consequences, such as changes in neural autonomic control, increased oxidative stress, and inflammatory responses. The superior cervical ganglion (SCG) is an important sympathetic component of the autonomic nervous system. CSD can lead to a wide range of neurological consequences in SCG, which mainly supply innervations to circadian system and other structures. As the active component of Curcuma longa, curcumin possesses many therapeutic properties; including neuroprotective. This study aimed to evaluate the effect of CSD on the SCG histomorphometrical changes and the protective effect of curcumin in preventing these changes.

Methods

Thirty-six male rats were randomly assigned to the control, curcumin, CSD, CSD + curcumin, grid floor control, and grid floor + curcumin groups. The CSD was induced by a modified multiple platform apparatus for 21 days and animals were sacrificed at the end of CSD or treatment, and their SCGs removed for stereological and TUNEL evaluations and also spatial arrangement of neurons in this structure.

Results

Concerning stereological findings, CSD significantly reduced the volume of SCG and its total number of neurons and satellite glial cells in comparison with the control animals (P < 0.05). Treatment of CSD with curcumin prevented these decreases. Furthermore, TUNEL evaluation showed significant apoptosis in the SCG cells in the CSD group, and treatment with curcumin significantly decreased this apoptosis (P < 0.01). This decrease in apoptosis was observed in all control groups that received curcumin. CSD also changed the spatial arrangement of ganglionic neurons into a random pattern, whereas treatment with curcumin preserved its regular pattern.

Conclusions

CSD could potentially induce neuronal loss and structural changes including random spatial distribution in the SCG neurons. Deleterious effects of sleep deprivation could be prevented by the oral administration of curcumin. Furthermore, the consumption of curcumin in a healthy person might lead to a reduction of cell death.

Noradrenaline Acting on Alpha1 Adrenoceptor as well as by Chelating Iron Reduces Oxidative Burden on the Brain: Implications With Rapid Eye Movement Sleep

The noradrenaline (NA) level in the brain is reduced during rapid eye movement sleep (REMS). However, upon REMS deprivation (REMSD) its level is elevated, which induces apoptosis and the degeneration of neurons in the brain. In contrast, isolated studies have reported that NA possesses an anti-oxidant property, while REMSD reduces lipid peroxidation (LP) and reactive oxygen species (ROS). We argued that an optimum level of NA is likely to play a physiologically beneficial role. To resolve the contradiction and for a better understanding of the role of NA in the brain, we estimated LP and ROS levels in synaptosomes prepared from the brains of control and REMS deprived rats with or without in vivo treatment with either α1-adrenoceptor (AR) antagonist, prazosin (PRZ) or α2-AR agonist, clonidine (CLN). REMSD significantly reduced LP and ROS in synaptosomes; while the effect on LP was ameliorated by both PRZ and CLN; ROS was prevented by CLN only. Thereafter, we evaluated in vitro the effects of NA, vitamin E (Vit E), vitamin C (Vit C), and desferrioxamine (DFX, iron chelator) in modulating hydrogen peroxide (H₂O₂)-induced LP and ROS in rat brain synaptosomes, Neuro2a, and C6 cells. We observed that NA prevented ROS generation by chelating iron (inhibiting a Fenton reaction). Also, interestingly, a lower dose of NA protected the neurons and glia, while a higher dose damaged the neurons and glia. These in vitro and in vivo results are complementary and support our contention. Based on the findings, we propose that REMS maintains an optimum level of NA in the brain (an antioxidant compromised organ) to protect the latter from continuous oxidative onslaught.

Tau Pathology of Alzheimer Disease: Possible Role of Sleep Deprivation

Sleep deprivation is a common complaint in modern societies. Insufficient sleep has increased the risk of catching neurodegenerative diseases such as Alzheimer’s. Several studies have indicated that restricted sleep increases the level of deposition of β-amyloid and formation of neurofibrillary tangles, the major brain microstructural hallmarks for Alzheimer disease. The mechanisms by which sleep deprivation affects the pathology of Alzheimer disease has not yet been fully and definitively identified. However, risk factors like apolipoprotein E risk alleles, kinases and phosphatases dysregulation, reactive oxygen species, endoplasmic reticulum damages, glymphatic system dysfunctions and orexinergic system inefficacy have been identified as the most important factors which mediates between the two conditions. In this review, these factors are briefly discussed.

Relevance of deprivation studies in understanding rapid eye movement sleep

Rapid eye movement sleep (REMS) is a unique phenomenon essential for maintaining normal physiological processes and is expressed at least in species higher in the evolution. The basic scaffold of the neuronal network responsible for REMS regulation is present in the brainstem, which may be directly or indirectly influenced by most other physiological processes. It is regulated by the neurons in the brainstem. Various manipulations including chemical, elec-trophysiological, lesion, stimulation, behavioral, ontogenic and deprivation studies have been designed to understand REMS genesis, maintenance, physiology and functional significance. Although each of these methods has its significance and limitations, deprivation studies have contributed significantly to the overall understanding of REMS. In this review, we discuss the advantages and limitations of various methods used for REMS deprivation (REMSD) to understand neural regulation and physiological significance of REMS. Among the deprivation strategies, the flowerpot method is by far the method of choice because it is simple and convenient, exploits physiological parameter (muscle atonia) for REMSD and allows conducting adequate controls to overcome experimental limitations as well as to rule out nonspecific effects. Notwithstanding, a major criticism that the flowerpot method faces is that of perceived stress experienced by the experimental animals. Nevertheless, we conclude that like most methods, particularly for in vivo behavioral studies, in spite of a few limitations, given the advantages described above, the flowerpot method is the best method of choice for REMSD studies.

Noradrenaline from Locus Coeruleus Neurons Acts on Pedunculo-Pontine Neurons to Prevent REM Sleep and Induces Its Loss-Associated Effects in Rats

Normally, rapid eye movement sleep (REMS) does not appear during waking or non-REMS. Isolated, independent studies showed that elevated noradrenaline (NA) levels inhibit REMS and induce REMS loss-associated cytomolecular, cytomorphological, psychosomatic changes and associated symptoms. However, the source of NA and its target in the brain for REMS regulation and function in health and diseases remained to be confirmed in vivo. Using tyrosine hydroxylase (TH)-siRNA and virus-coated TH-shRNA in normal freely moving rats, we downregulated NA synthesis in locus coeruleus (LC) REM-OFF neurons in vivo. These TH-downregulated rats showed increased REMS, which was prevented by infusing NA into the pedunculo-pontine tegmentum (PPT), the site of REM-ON neurons, normal REMS returned after recovery. Moreover, unlike normal or control-siRNA- or shRNA-injected rats, upon REMS deprivation (REMSD) TH-downregulated rat brains did not show elevated Na-K ATPase (molecular changes) expression and activity. To the best of our knowledge, these are the first in vivo findings in an animal model confirming that NA from the LC REM-OFF neurons (1) acts on the PPT REM-ON neurons to prevent appearance of REMS, and (2) are responsible for inducing REMSD-associated molecular changes and symptoms. These observations clearly show neuro-physio-chemical mechanism of why normally REMS does not appear during waking. Also, that LC neurons are the primary source of NA, which in turn causes some, if not many, REMSD-associated symptoms and behavioral changes. The findings are proof-of-principle for the first time and hold potential to be exploited for confirmation toward treating REMS disorder and amelioration of REMS loss-associated symptoms in patients.

Rapid Eye Movement Sleep Deprivation Induces Neuronal Apoptosis by Noradrenaline Acting on Alpha1 Adrenoceptor and by Triggering Mitochondrial Intrinsic Pathway

Many neurodegenerative disorders are associated with rapid eye movement sleep (REMS) loss; however, the mechanism was unknown. As REMS loss elevates noradrenaline (NA) level in the brain as well as induces neuronal apoptosis and degeneration, in this study, we have delineated the intracellular molecular pathway involved in REMS deprivation (REMSD)-associated NA-induced neuronal apoptosis. Rats were REMS deprived for 6 days by the classical flower pot method; suitable controls were conducted and the effects on apoptosis markers evaluated. Further, the role of NA was studied by one, intraperitoneal (i.p.) injection of NA-ergic alpha1 adrenoceptor antagonist prazosin (PRZ) and two, by downregulation of NA synthesis in locus coeruleus (LC) neurons by local microinjection of tyrosine hydroxylase siRNA (TH-siRNA). Immunoblot estimates showed that the expressions of proapoptotic proteins viz. Bcl2-associated death promoter protein, apoptotic protease activating factor-1 (Apaf-1), cytochrome c, caspase9, caspase3 were elevated in the REMS-deprived rat brains, while caspase8 level remained unaffected; PRZ treatment did not allow elevation of these proapoptotic factors. Further, REMSD increased cytochrome c expression, which was prevented if the NA synthesis from the LC neurons was blocked by microinjection of TH-siRNA in vivo into the LC during REMSD in freely moving normal rats. Mitochondrial damage was re-confirmed by transmission electron microscopy, which showed distinctly swollen mitochondria with disintegrated cristae, chromosomal condensation, and clumping along the nuclear membrane, and all these changes were prevented in PRZ-treated rats. Combining findings of this study along with earlier reports, we propose that upon REMSD NA level increases in the brain as the LC, NA-ergic REM-OFF neurons do not cease firing and TH is upregulated in those neurons. This elevated NA acting on alpha1 adrenoceptors damages mitochondria causing release of cytochrome c to activate intrinsic pathway for inducing neuronal apoptosis in REMS-deprived rat brain.

Targeting modulation of noradrenalin release in the brain for amelioration of REMS loss-associated effects

Rapid eye movement sleep (REMS) loss affects most of the physiological processes, and it has been proposed that REMS maintains normal physiological processes. Changes in cultural, social, personal traits and life-style severely affect the amount and pattern of sleep, including REMS, which then manifests symptoms in animals, including humans. The effects may vary from simple fatigue and irritability to severe patho-physiological and behavioral deficits such as cognitive and behavioral dysfunctions. It has been a challenge to identify a molecule(s) that may have a potential for treating REMS loss-associated symptoms, which are very diverse. For decades, the critical role of locus coeruleus neurons in regulating REMS has been known, which has further been supported by the fact that the noradrenalin (NA) level is elevated in the brain after REMS loss. In this review, we have collected evidence from the published literature, including those from this laboratory, and argue that factors that affect REMS and vice versa modulate the level of a common molecule, the NA. Further, NA is known to affect the physiological processes affected by REMS loss. Therefore, we propose that modulation of the level of NA in the brain may be targeted for treating REMS loss-related symptoms. Further, we also argue that among the various ways to affect the release of NA-level, targeting α₂ adrenoceptor autoreceptor on the pre-synaptic terminal may be the better option for ameliorating REMS loss-associated symptoms.

Wake-active neurons across aging and neurodegeneration: a potential role for sleep disturbances in promoting disease

Sleep/wake disturbance is a feature of almost all common age-related neurodegenerative diseases. Although the reason for this is unknown, it is likely that this inability to maintain sleep and wake states is in large part due to declines in the number and function of wake-active neurons, populations of cells that fire only during waking and are silent during sleep. Consistent with this, many of the brain regions that are most susceptible to neurodegeneration are those that are necessary for wake maintenance and alertness. In the present review, these wake-active populations are systematically assessed in terms of their observed pathology across aging and several neurodegenerative diseases, with implications for future research relating sleep and wake disturbances to aging and age-related neurodegeneration.

Effect of REM sleep deprivation on the antioxidant status in the brain of Wistar rats

Background

Rapid eye movement [REM] sleep deprivation is a stressor. It results in a predictable syndrome of physiological changes in rats. It has been proposed that reactive oxygen species and the resulting oxidative stress may be responsible for some of the effects of sleep deprivation.

Purpose

The present study was undertaken to investigate the reversible nature of the effects of 96 hours of REM sleep deprivation on lipid peroxidation and total reduced glutathione level in the hypothalamus, midbrain and hindbrain of Wistar strain rats.

Methods

The rats were deprived of REM sleep using the inverted flowerpot technique. All the animals were maintained in standard animal house condition with 12-h light and 12-h dark cycles. At the end of the stipulated time Jugular venous blood sample of 2 ml was collected under mild ether anesthesia for the assay of stress index, plasma corticosterone. Lipid peroxidation using thiobarbituric acid, total reduced glutathione using DTNB (GSH) were assayed in the brain regions dissected out.

Results

This study showed that 96 hours of REM sleep deprivation results in increased lipid peroxidation and reduction in total reduced glutathione level in the discrete regions of brain studied. However following restorative sleep for 24 hours all the changes reverts back to base line value. This study shows that oxidative stress produced by 96 hours of REM sleep deprivation is reversible.

Conclusion

From this study it is clear that, REM sleep deprivation is a potent oxidative stressor. This could probably play a role in the behavioral and performance alteration seen in both experimental animals as well as humans following REM sleep deprivation. Further investigations in this line are needed to highlight the importance of REM sleep.

Cytomorphometric Changes in Hippocampal CA1 Neurons Exposed to Simulated Microgravity Using Rats as Model

Microgravity and sleep loss lead to cognitive and learning deficits. These behavioral alterations are likely to be associated with cytomorphological changes and loss of neurons. To understand the phenomenon, we exposed rats (225–275 g) to 14 days simulated microgravity (SMg) and compared its effects on CA1 hippocampal neuronal plasticity, with that of normal cage control rats. We observed that the mean area, perimeter, synaptic cleft, and length of active zone of CA1 hippocampal neurons significantly decreased while dendritic arborization and number of spines significantly increased in SMg group as compared with controls. The mean thickness of the postsynaptic density and total dendritic length remained unaltered. The changes may be a compensatory effect induced by exposure to microgravity; however, the effects may be transient or permanent, which need further study. These findings may be useful for designing effective prevention for those, including the astronauts, exposed to microgravity. Further, subject to confirmation, we propose that SMg exposure might be useful for recovery of stroke patients.

A hypnic hypothesis of Alzheimer's disease

BACKGROUND

Understanding the pathophysiology of Alzheimer's disease (AD) is of fundamental importance for improved diagnosis, monitoring and ultimately, treatment.

OBJECTIVE

A role for the sleep-wake cycle in the pathogenesis of AD has been proposed, but remains to be worked out in detail.

METHODS

Here we draw together several lines of previous work to outline a 'hypnic hypothesis' of AD.

RESULTS

We propose that altered function of brainstem neurotransmitter pathways associated with sleep, promotes regionally specific disintegration of a cortico-subcortical 'default mode' brain network that is selectively vulnerable in AD.

CONCLUSION

The formation of a dynamic toxic state within this vulnerable network linked to sleep-wake disruption, would in turn lead to failure of synaptic repair, increased transmission of pathogenic misfolded proteins and a self-amplifying neurodegenerative process. We consider the evidence for this hypnic hypothesis and the implications that follow on from it.

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.

REM sleep loss increases brain excitability: role of noradrenaline and its mechanism of action

Ever since the discovery of rapid eye movement sleep (REMS), studies have been undertaken to understand its necessity, function and mechanism of action on normal physiological processes as well as in pathological conditions. In this review, first, we briefly surveyed the literature which led us to hypothesise REMS maintains brain excitability. Thereafter, we present evidence from in vivo and in vitro studies tracing behavioural to cellular to molecular pathways showing REMS deprivation (REMSD) increases noradrenaline level in the brain, which stimulates neuronal Na-K ATPase, the key factor for maintaining neuronal excitability, the fundamental property of a neuron for executing brain functions; we also show for the first time the role of glia in maintaining ionic homeostasis in the brain. As REMSD exerts a global effect on most of the physiological processes regulated by the brain, we propose that REMS possibly serves a housekeeping function in the brain. Finally, subject to confirmation from clinical studies, based on the results reviewed here, it is being proposed that the subjects suffering from REMS loss may be effectively treated by reducing either noradrenaline level or Na-K ATPase activity in the brain.