Uncompetitive stimulation of rat brain Na-K ATPase activity by rapid eye movement sleep deprivation

Noradrenergic β-Adrenoceptor-Mediated Intracellular Molecular Mechanism of Na-K ATPase Subunit Expression in C6 Cells

Rapid eye movement sleep deprivation-associated elevated noradrenaline increases and decreases neuronal and glial Na-K ATPase activity, respectively. In this study, using C6 cell-line as a model, we investigated the possible intracellular molecular mechanism of noradrenaline-induced decreased glial Na-K ATPase activity. The cells were treated with noradrenaline in the presence or absence of adrenoceptor antagonists, modulators of extra- and intracellular Ca⁺⁺ and modulators of intracellular signalling pathways. We observed that noradrenaline acting on β-adrenoceptor decreased Na-K ATPase activity and mRNA expression of the catalytic α2-Na-K ATPase subunit in the C6 cells. Further, cAMP and protein kinase-A mediated release of intracellular Ca⁺⁺ played a critical role in such decreased α2-Na-K ATPase expression. In contrast, noradrenaline acting on β-adrenoceptor up-regulated the expression of regulatory β2-Na-K ATPase subunit, which although was cAMP and Ca⁺⁺ dependent, was independent of protein kinase-A and protein kinase-C. Combining these with previous findings (including ours) we have proposed a working model for noradrenaline-induced suppression of glial Na-K ATPase activity and alteration in its subunit expression. The findings help understanding noradrenaline-associated maintenance of brain excitability during health and altered states, particularly in relation to rapid eye movement sleep and its deprivation when the noradrenaline level is naturally altered.

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.

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.

Endogenous ouabain-like compounds in locus coeruleus modulate rapid eye movement sleep in rats

Although the detailed mechanism of spontaneous generation and regulation of rapid eye movement sleep (REMS) is yet unknown, it has been reported that noradrenergic REM-OFF neurons in the locus coeruleus (LC) cease firing during REMS and, if they are kept active, REMS is significantly reduced. On the other hand, the activity as well as expression of Na-K ATPase has been shown to increase in the LC following REMS deprivation. Ouabain is a specific inhibitor of Na-K ATPase, and endogenous ouabain-like compounds are present in the brain. These findings led us to propose that a decrease in the level of ouabain-like compounds spontaneously available in and around the LC would stimulate and increase the REM-OFF neuronal activities in this region and thus would reduce REMS. To test this hypothesis, we generated anti-ouabain antibodies and then microinjected it bilaterally into the LC in freely moving chronically prepared rats and recorded electrophysiological signals for evaluation of sleep-wakefulness states; suitable control experiments were also conducted. Injection of anti-ouabain antibodies into the LC, but not into adjacent brain areas, significantly reduced percent REMS (mean +/- SEM) from 7.12 (+/-0.74) to 3.63 (+/-0.65). The decrease in REMS was due to reduction in the mean frequency of REMS episode, which is likely due to increased excitation of the LC REM-OFF neurons. Control microinjections of normal IgG did not elicit this effect. These results support our hypothesis that interactions of naturally available endogenous ouabain-like compounds with the Na-K ATPase in the LC modulate spontaneous REMS.

Prazosin modulates rapid eye movement sleep deprivation-induced changes in body temperature in rats

Prolonged rapid eye movement sleep deprivation (REMSD) causes hypothermia and death; however, the effect of deprivation within 24 h and its mechanism(s) of action were unknown. Based on existing reports we argued that REMSD should, at least initially, induce hyperthermia and the death upon prolonged deprivation could be due to persistent hypothermia. We proposed that noradrenaline (NA), which modulates body temperature and is increased upon REMSD, may be involved in REMSD- associated body temperature changes. Adult male Wistar rats were REM sleep deprived for 6-9 days by the classical flower pot method; suitable free moving, large platform and recovery controls were carried out. The rectal temperature (Trec) was recorded every minute for 1 h, or once daily, or before and after i.p. injection of prazosin, an alpha-1 adrenergic antagonist. The Trec was indeed elevated within 24 h of REMSD which decreased steadily, despite continuation of deprivation. Prazosin injection into the deprived rats reduced the Trec within 30 min, and the duration of effect was comparable to its pharmacological half life. The findings have been explained on the basis of REMSD-induced elevated NA level, which has opposite actions on the peripheral and the central nervous systems. We propose that REMSD-associated immediate increase in Trec is due to increased Na-K ATPase as well as metabolic activities and peripheral vasoconstriction. However, upon prolonged deprivation, probably the persistent effect of NA on the central thermoregulatory sites induced sustained hypothermia, which if remained uncontrolled, results in death. Thus, our findings suggest that peripheral prazosin injection in REMSD would not bring the body temperature to normal, rather might become counterproductive.

Increased turnover of Na-K ATPase molecules in rat brain after rapid eye movement sleep deprivation

It has been shown that rapid eye movement (REM) sleep deprivation increases Na-K ATPase activity. Based on kinetic study, it was proposed that increased activity was due to enhanced turnover of enzyme molecules. To test this, anti-alpha1 Na-K ATPase monoclonal antibody (mAb 9A7) was used to label Na-K ATPase molecules. These labeled enzymes were quantified on neuronal membrane by two methods: histochemically on neurons in tissue sections from different brain areas, and by Western blot analysis in control and REM sleep-deprived rat brains. The specific enzyme activity was also estimated and found to be increased, as in previous studies. The results confirmed our hypothesis that after REM sleep deprivation, increased Na-K ATPase activity was at least partly due to increased turnover of Na-K ATPase molecules in the rat brain.

Role of norepinephrine in the regulation of rapid eye movement sleep

Sleep and wakefulness are instinctive behaviours that are present across the animal species. Rapid eye movement (REM) sleep is a unique biological phenomenon expressed during sleep. It evolved about 300 million years ago and is noticed in the more evolved animal species. Although it has been objectively identified in its present characteristic form about half a century ago, the mechanics of how REM is generated, and what happens upon its loss are not known. Nevertheless, extensive research has shown that norepinephrine plays a crucial role in its regulation. The present knowledge that has been reviewed in this manuscript suggests that neurons in the brain stem are responsible for controlling this state and presence of excess norepinephrine in the brain does not allow its generation. Furthermore, REM sleep loss increases levels of norepinephrine in the brain that affects several factors including an increase in Na-K ATPase activity. It has been argued that such increased norepinephrine is ultimately responsible for REM sleep deprivation, associated disturbances in at least some of the physiological conditions leading to alteration in behavioural expression and settling into pathological conditions.