Sleep deficits in rats after NMDA receptor blockade

Effects of Transient Administration of the NMDA Receptor Antagonist MK-801 in Drosophila melanogaster Activity, Sleep, and Negative Geotaxis

MK-801, also called dizocilpine, is an N-methyl-D-aspartate (NMDA) receptor antagonist widely used in animal research to model schizophrenia-like phenotypes. Although its effects in rodents are well characterised, little is known about the outcomes of this drug in other organisms. In this study, we characterise the effects of MK-801 on the locomotion, sleep, and negative geotaxis of the fruit fly Drosophila melanogaster. We observed that acute (24 h) and chronic (7 days) administration of MK-801 enhanced negative geotaxis activity in the forced climbing assay for all tested concentrations (0.15 mM, 0.3 mM, and 0.6 mM). Moreover, acute administration, but not chronic, increased the flies' locomotion in a dose-dependent matter. Finally, average sleep duration was not affected by any concentration or administration protocol. Our results indicate that acute MK-801 could be used to model hyperactivity phenotypes in Drosophila melanogaster. Overall, this study provides further evidence that the NMDA receptor system is functionally conserved in flies, suggesting the usefulness of this model to investigate several phenotypes as a complement and replacement of the rodent models within drug discovery.

Sleep as a predictor of tDCS and language therapy outcomes

STUDY OBJECTIVES

To determine whether sleep at baseline (before therapy) predicted improvements in language following either language therapy alone or coupled with transcranial direct current stimulation (tDCS) in individuals with primary progressive aphasia (PPA).

METHODS

Twenty-three participants with PPA (mean age 68.13 ± 6.21) received written naming/spelling therapy coupled with either anodal tDCS over the left inferior frontal gyrus (IFG) or sham condition in a crossover, sham-controlled, double-blind design (ClinicalTrials.gov identifier: NCT02606422). The outcome measure was percent of letters spelled correctly for trained and untrained words retrieved in a naming/spelling task. Given its particular importance as a sleep parameter in older adults, we calculated sleep efficiency (total sleep time/time in bed x100) based on subjective responses on the Pittsburgh Sleep Quality Index (PSQI). We grouped individuals based on a median split: high versus low sleep efficiency.

RESULTS

Participants with high sleep efficiency benefited more from written naming/spelling therapy than participants with low sleep efficiency in learning therapy materials (trained words). There was no effect of sleep efficiency in generalization of therapy materials to untrained words. Among participants with high sleep efficiency, those who received tDCS benefitted more from therapy than those who received sham condition. There was no additional benefit from tDCS in participants with low sleep efficiency.

CONCLUSION

Sleep efficiency modified the effects of language therapy and tDCS on language in participants with PPA. These results suggest sleep is a determinant of neuromodulation effects.Clinical Trial: tDCS Intervention in Primary Progressive Aphasia https://clinicaltrials.gov/ct2/show/NCT02606422.

Application of Transcranial Direct Current Stimulation in Neurorehabilitation: The Modulatory Effect of Sleep

The relationship between sleep disorders and neurological disorders is often reciprocal, such that sleep disorders are worsened by neurological symptoms and that neurological disorders are aggravated by poor sleep. Animal and human studies further suggest that sleep disruption not only worsens single neurological symptoms but may also lead to long-term negative outcomes. This suggests that sleep may play a fundamental role in neurorehabilitation and recovery. We further propose that sleep may not only alter the efficacy of behavioral treatments but also plasticity-enhancing adjunctive neurostimulation methods, such as transcranial direct current stimulation (tDCS). At present, sleep receives little attention in the fields of neurorehabilitation and neurostimulation. In this review, we draw together the strands of evidence from both fields of research to highlight the proposition that sleep is an important parameter to consider in the application of tDCS as a primary or adjunct rehabilitation intervention.

β-adrenergic signaling regulates evolutionarily derived sleep loss in the Mexican cavefish

Sleep is a fundamental behavior exhibited almost universally throughout the animal kingdom. The required amount and circadian timing of sleep differs greatly between species in accordance with habitats and evolutionary history. The Mexican blind cavefish, Astyanax mexicanus, is a model organism for the study of adaptive morphological and behavioral traits. In addition to loss of eyes and pigmentation, cave populations of A. mexicanus exhibit evolutionarily derived sleep loss and increased vibration attraction behavior, presumably to cope with a nutrient-poor environment. Understanding the neural mechanisms of evolutionarily derived sleep loss in this system may reveal critical insights into the regulation of sleep in vertebrates. Here we report that blockade of β-adrenergic receptors with propranolol rescues the decreased-sleep phenotype of cavefish. This effect was not seen with α-adrenergic antagonists. Treatment with selective β1-, β2-, and β3-antagonists revealed that the increased sleep observed with propranolol could partially be explained via the β1-adrenergic system. Morphological analysis of catecholamine circuitry revealed conservation of gross catecholaminergic neuroanatomy between surface and cave morphs. Taken together, these findings suggest that evolutionarily derived changes in adrenergic signaling underlie the reduced sleep of cave populations.

Pharmacokinetics and cerebral distribution of glycine administered to rats

High doses of glycine have been reported to improve negative schizophrenic symptoms, suggesting that ingested glycine activates glutamatergic transmission via N-methyl-D-aspartate (NMDA) receptors. However, the pharmacokinetics of administered glycine in the brain has not been evaluated. In the present study, the time- and dose-dependent distributions of administered glycine were investigated from a pharmacokinetic viewpoint. Whole-body autoradiography of radiolabeled glycine was performed, and time-concentration curves for glycine and serine in plasma, cerebrospinal fluid (CSF), and brain tissues were obtained. Furthermore, pharmacokinetic parameters were calculated. For a more detailed analysis, the amount of glycine uptake in the brain was evaluated using the brain uptake index method. Radiolabeled glycine was distributed among periventricular organs in the brain. Oral administration of 2 g/kg of glycine significantly elevated the CSF glycine concentration above the ED50 value for NMDA receptors. The glycine levels in CSF were 100 times lower than those in plasma. Glycine levels were elevated in brain tissue, but with a slower time-course than in CSF. Serine, a major metabolite of glycine, was elevated in plasma, CSF, and brain tissue. Glycine uptake in brain tissue increased in a dose-dependent manner. Time-concentration curves revealed that glycine was most likely transported via the blood-CSF barrier and activated NMDA receptors adjacent to the ventricles. The pharmacokinetic analysis and the brain uptake index for glycine suggested that glycine was transported into brain tissue by passive diffusion. These results provide further insight into the potential therapeutic applications of glycine.

Interaction between orexinergic neurons and NMDA receptors in the control of locus coeruleus-cerebrocortical noradrenergic activity of the rat

Several studies suggest that NMDA glutamate receptors may play an important role in the activation of a number of brain regions by orexin (OX). We hypothesized that OX and NMDA receptors may interact with cerebrocortical noradrenergic neuron originating from the locus coeruleus (LC). To test this hypothesis, using rats as experimental animals, we examined (i) in vitro effects of MK801 on OXA-evoked norepinephrine release from rat cerebrocortical slices, (ii) in vivo interaction between OXA and the NMDA receptor antagonist, MK801 on norepinephrine release from the prefrontal cortex assessed using microdialysis and (iii) MK801 and OXA-modulation of the electroencephalogram (EEG). We have found that MK801 produced a concentration-dependent inhibition of OXA-evoked norepinephrine release from rat cerebrocortical slices with the IC(50) of 0.9 microM. Moreover, we have also found that icv OXA dose-dependently stimulated norepinephrine release from the rat prefrontal cortex saturating at 213% of baseline. In addition, ip MK801 0.1 mg/kg also significantly increased norepinephrine release in prefrontal cortex to 213%. However, these increases in norepinephrine release were significantly reduced by approximately 70% by simultaneous administration of icv OXA 1 nmol and ip MK801 0.1 mg/kg. Both OXA and MK801 decreased sleep and increased wakefulness, but co-administration caused a return to base-line sleep state. These findings strongly indicate that there is a significant interaction between orexinergic neurons and NMDA receptors in the control of LC-cerebrocortical noradrenergic activity.

Effects of REM deprivation and an NMDA agonist on the extinction of conditioned fear

Rapid eye movement sleep (REM) has been implicated in a number of learning and memory tasks. Previous research has demonstrated that REM deprivation impairs the development of extinction of conditioned fear responses. However, the neurobiological mechanisms of this effect remain unclear. The present study investigated the effects of systemic administration of d-cycloserine (DCS), an NMDA agonist, on the extinction of a conditioned fear response following 6 h of REM deprivation. In experiment 1, rats were administered DCS between fear training and REM deprivation. In experiment 2, rats were administered DCS prior to extinction training. The results of experiment 1 indicated that both DCS alone and REM deprivation alone impaired extinction learning. Administration of DCS to REM deprived animals partially, but not completely, reversed the deficit in extinction. The results of experiment 2 indicated that regardless of prior REM deprivation history, DCS facilitated extinction learning. The results provide further evidence for a role of REM in the extinction of cued fear learning and indicate that this effect appears to be partially mediated by NMDA-dependent mechanisms.

Effects of AP5 infusion into the lateral ventricle on the activities and hippocampal electrical patterns of sleep episodes in rats

Although N-methyl-D-aspartate (NMDA) receptors of the hippocampus are mainly associated with learning and memory that might occur "on-line" during sharp waves (SPWs) and theta-rhythm, the participation of hippocampal NMDA receptors in sleep-related processes has not been well studied. In this study, the activity of sleep episodes, hippocampal SPWs and theta-rhythm were recorded in rats received a repeated infusion of NMDA receptor antagonist, D,L-2-amino-5-phosphonopentanoic acid (AP5), into the lateral ventricle in a 5-h daytime sleep. The first trial AP5 infusion (30 mM/2 microl) did not change measures of the activity of slow wave sleep (SWS), paradoxical sleep (PS) and awake episodes, but induced a delay in the latency of the first onset of PS; in the hippocampal EEG, it increased the amplitude of SPWs within SWS and shifted the amplitude/spectral power of theta-rhythm from high to low frequency within PS. The repeated AP5 infusion augmented the activity of SWS, and impaired PS and awake episodes; in the EEG-sleep picture, it maintained high scores of SPWs with the complete blockade of theta-rhythm generation. When AP5 rat was woken, the theta-rhythm was seen during exploratory behavior. These findings provide evidence that hippocampal NMDA receptors via SPWs or directly associated with the synaptic events of theta-rhythm generation are critical for the PS activities.

Changes of [3H]Muscimol, [3H]Flunitrazepam and [3H]MK-801 Binding in Rat Brain by Prolonged Ventricular Infusion of 7-Nitroindazole

In the present study, we have investigated the effects of prolonged inhibition of nitric oxide synthase (NOS) by infusion of neuronal NOS (nNOS) inhibitor, 7-nitroindazole (7-NI), to examine modulation of NMDA and GABAA receptor binding in rat brain. The duration of sleeping time was significantly increased by the pre-treatment with 7-NI (100 mg/kg) 30 min before pentobarbital (40 mg/kg) treatment in rats. However, the duration of pentobarbital-induced sleep was shortened by the prolonged infusion of 7-NI into cerebroventricle for 7 days. We have investigated the effect of NOS inhibitor on NMDA and GABAA receptor binding characteristics in discrete areas of brain regions by using autoradiographic techniques. The GABAA receptors were analyzed by quantitative autoradiography using [3H]muscimol and [3H]flunitrazepam binding, and NMDA receptor binding was analyzed by using [3H]MK-801 binding in rat brain slices. Rats were infused with 7-NI (500 pmol/10 microl/h, i.c.v.) for 7 days, through pre-implanted cannula by osmotic minipumps. The levels of [3H]muscimol were markedly elevated in cortex, caudate putamen, and thalamus while the levels of [3H]flunitrazepam binding were only elevated in cerebellum by NOS inhibitor. However, there was no change in the level of [3H]MK-801 binding except decreasing in the thalamus. These results show that the prolonged inhibition of NOS by 7-NI-infusion highly elevates [3H]muscimol binding in a region-specific manner and decreases the pentobarbital-induced sleep.

Changes of GABA(A) receptor binding and subunit mRNA level in rat brain by infusion of NOS inhibitor

In the present study, we have investigated the effects of prolonged inhibition of nitric oxide synthase (NOS) by infusion of NOS inhibitor, L-nitroarginine, to examine the pentobarbital-induced sleep, modulation of GABA(A) receptor binding, and GABA(A) receptor subunit mRNA level in rat brain. Pre-treatment with L-nitroarginine 30 min before pentobarbital treatment (60 mg/kg, i.p.) significantly increased the duration of sleep in rats. However, the duration of pentobarbital-induced sleep was shortened by the prolonged infusion of L-nitroarginine into ventricle. We have investigated the effect of NOS inhibitor on GABA(A) receptor binding characteristics in discrete areas of brain regions by using autoradiographic and in situ hybridization techniques. Rats were infused with L-nitroarginine (10, 100 pmol/10 microl/h, i.c.v.) for 7 days, through pre-implanted cannula by osmotic minipumps. The levels of [(3)H]muscimol and [(3)H]flunitrazepam binding were markedly elevated in almost all of brain regions including cortex, caudate putamen, thalamus, hippocampus, and cerebellum. However, there was no change in the level of [(35)S]TBPS binding. The levels of beta2-subunit were elevated in the cortex, brainstem, and cerebellar granule layers. By contrast, the levels of beta3-subunit were significantly decreased in the cortex, hippocampus, and cerebellar granule layers in L-nitroarginine-infused rats. Following L-nitroarginine treatment, the levels of alpha6- and delta-subunits which were strictly localized to the cerebellum, were not changed in the cerebellar granule layer. These results show that the prolonged inhibition of NOS by L-nitroarginine-infusion markedly elevates [(3)H]muscimol and [(3)H]flunitrazepam binding throughout the brain, and alters GABA(A) receptor subunit mRNA levels in different directions. Chronic inhibition of NO generation has differential effects on the various expressions of GABA(A) receptor subunits. These suggest the involvement of different regulatory mechanisms for the NO-induced expression of GABA(A) receptor.

Inhibition of the ERK pathway prevents HIVgp120-induced REM sleep increase

Approximately 35% of HIV-infected subjects, both children and adults, exhibit alterations in the sleep-waking cycle. HIV surface glycoprotein gp120 has been postulated to contribute to this abnormality. For example, it has been reported that HIVgp120 modifies sleep in freely-moving rats and that it also activates the ERK pathway in brain slices. The goal of this work was to determine if sleep changes induced by HIVgp120 in normal rats are mediated by the MAPK pathway. Our results show that a single intraventricular administration of HIVgp120 selectively increases REMS and that such an increase can be prevented by U0126, an inhibitor of ERK activating enzyme, MEK. In contrast, SB202190, a MAPK-p38 inhibitor, had no effect on HIVgp120-induced increase in REMS. These results suggest that HIVgp120 increases REMS in the rat by specifically affecting the ERK signal transduction pathway.

8-OH-DPAT and MK-801 affect epileptic activity independently of vigilance

Vigilance and parallel occurrence of epileptic activity after administration of the 5-HT(1A) agonist 8-OH-DPAT and the NMDA receptor antagonist MK-801 were studied in the genetic absence epilepsy model WAG/Rij rats. Spike-wave discharges (SWD) were present predominantly in passive awake and light slow wave sleep (SWS1) either in control animals or after treatments. Injection of 8-OH-DPAT (20.0 microg/rat i.c.v.) caused marked increase and MK-801 (10.0 microg/rat i.c.v.) decrease in SWD densities, thus the ratios of SWD in passive awake and in SWS1. SWD densities of MK-801 plus 8-OH-DPAT in combination were similar to those of CSF+CSF treated control rats. Both 8-OH-DPAT and MK-801 transiently increased the duration of active awake, increased latency and decreased duration of rapid eye movement (REM) sleep. 8-OH-DPAT increased the amount of SWD despite the decrease in the duration of SWS1. MK-801 decreased the amount of SWD despite the lack of significant change in duration of passive awake or SWS1. Pre-treatment with MK-801 reversed 8-OH-DPAT- induced increase in duration of SWD without any effect on 8-OH-DPAT-induced changes in sleep parameters. Our studies provide evidence that 8-OH-DPAT-induced epileptic activity is independent of its effect on sleep, and that interaction of serotonergic and glutamatergic systems plays a role in the generation of SWD, but not in the regulation of vigilance and sleep.

The promnesic neurosteroid pregnenolone sulfate increases paradoxical sleep in rats

The effect of systemic administration of the neurosteroid pregnenolone sulfate (PREG-S) on sleep-wakefulness cycle and on spatial memory performances was investigated in male Sprague-Dawley rats. In the first experiment, the effect of PREG-S administration (saline, 4.75, 47.5 mg/kg, i.p.) on 24 h EEG recording was evaluated. In the second experiment, spatial memory performance in a two-trial memory task was evaluated after post-acquisition administration of similar doses of PREG-S as in the first experiment. Results show that PREG-S increases paradoxical sleep and improves the performance on the memory task yielding similar dose response curves. Starting 4 h after administration of 47.5 mg/kg PREG-S, paradoxical sleep is increased for 10 h. The PREG-S effect on spatial memory lasts for at least 24 h after injection. These results suggest that an enhancement of paradoxical sleep may be involved in the promnesic effects of this neurosteroid.

Oxidized glutathione promotes sleep in rabbits

Glutatione is implicated in sleep regulation. There are circadian changes in brain glutathione levels, and nocturnal intracerebroventricular (i.c.v.) slow infusion of oxidized glutathione (GSSG) or reduced glutathione (GSH) promotes rapid-eye-movement sleep (REMS) and non-REMS (NREMS) in rats. In the present experiments, we tested the effects of GSSG on duration of sleep, NREMS intensity, and brain temperature in another species, rabbits. Male New Zealand rabbits were injected with isotonic NaCl on a baseline day and one dose of GSSG on the test day [0.15, 1.5, 15, and 150 microg/rabbit, i.c.v., or 1.5 or 15 mg/kg intravenously (i.v.)]. Electroencephalogram (EEG), motor activity, and brain temperature were recorded for 6 h. Injection of 15 microg GSSG i.c.v. significantly increased the time spent in NREMS in the first 3 h after the injection. Injection of 0.15, 1.5, and 150 microg i.s.v. GSSG, as well as systemic injections of GSSG did not affect NREMS. Intensity of NREMS as measured by EEG slow-wave activity during NREMS, and brain temperature were not affected by any of the treatments. These results are consistent with the hypothesis that glutathione may be a sleep-inducing factor in the brain.

Effects of a vigilance-enhancing drug, modafinil, on rat brain metabolism: a 2D COSY 1H-NMR study

The effects of modafinil, a vigilance-enhancing drug, on brain metabolism were investigated directly in situ by the 2D COSY 1H-NMR spectroscopy in anesthetized rats. Modafinil (600 mg/kg, i.p.) induced significant increases in both aspartate (72% +/- 15%) and glutamate-glutamine pool (28% +/- 8%) simultaneously with increases in inositol (51% +/- 19%) and creatine-phosphocreatine pool (47% +/- 14%) in comparison with control values (P < 0.05; n = 5). These results suggest that the awakening properties of modafinil could be mediated by metabolic activation.

Sleep effects following intrathecal administration of the 5-HT1A agonist 8-OH-DPAT and the NMDA antagonist AP-5 in rats

The modulating effect of an intrathecally (i.t.) administered 5-HT1A agonist and an NMDA antagonist on sleep, waking and EEG power spectra was investigated in rats. The 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (38 nmol) increased total slow wave sleep (TSWS) and decreased waking over the 8 h recording period. The TSWS increase was mostly due to an increase in SWS1. Sleep latency to SWS1 was also reduced. The NMDA antagonist dl-2-amino 5-phosphonovaleric acid (AP-5) (31.5 nmol) reduced waking. SWS1 was increased, but TSWS was not changed. An increase in REM sleep was seen during the last part of the recording. Combined treatment with 8-OH-DPAT and AP-5 reduced waking and increased TSWS. No change in REM sleep was seen. There were no systematic changes in either waking, TSWS or REM fronto-frontal or fronto-parietal EEG power spectrum after any of the treatments. The results suggest that in the spinal cord stimulation of 5-HT1A receptors have a dampening effect on transmission of sensory information, leading to deactivation and thereby increased possibilities for sleep induction. Blockade of the NMDA receptors may also lead to a small dampening of sensory transmission with similar consequences.

Inhibition of nitric oxide synthesis inhibits rat sleep

Previous findings indicate that nitric oxide (NO) may play a role in the regulation of sleep-wake activity. In rabbits, blocking the production of endogenous NO by a nitric oxide synthase inhibitor, N omega-nitro-L-arginine (L-NAME) suppresses spontaneous sleep and interferes the somnogenic actions of interleukin 1. In the present experiments we extended our earlier work by studying the long-term effects of L-NAME treatment on sleep-wake activity including power spectra analyses of the electroencephalogram (EEG) in rats. Rats implanted with EEG electrodes, brain thermistor, and intracerebroventricular (i.c.v.) guide cannula were injected i.c.v. with vehicle or 0.2, 1, or 5 mg L-NAME at light onset. In separate experiments, rats were injected intraperitoneally (i.p.) with L-NAME three times (50, 50, 100 mg/kg), 12-12 h apart. Both i.c.v. and i.p. injections of L-NAME elicited decreases in time spent in NREMS and REMS. After i.c.v. injection of 5 mg L-NAME the sleep responses were long-lasting; NREMS did not return to baseline even 72 h after injection. EEG delta-wave activity during NREMS (slow wave activity) was also suppressed after 0.2 and 5 mg L-NAME. Brain temperature was slightly increased after the two lower doses of L-NAME, whereas there was a transient decrease in Tbr after 5 mg L-NAME. Acute i.p. injection of 50 mg/kg L-NAME elicited an immediate decrease in NREMS which lasted for approximately 2 h. The second injection of 50 mg/kg L-NAME and the following injection of 100 mg/kg L-NAME induced biphasic decreases in NREMS but not REMS.

Pharmacology of ethanol and glutamate antagonists on rodent sleep: a comparative study

Twenty-five Sprague-Dawley rats were implanted with electrodes for standard sleep-wake cycle recordings. A guide cannula was stereotaxically implanted into the lateral ventricle. Rats were divided into five groups (n = 5) and challenged with an intraventricular administration of 10 microliters of a 5 nM solution of either: ethanol (EtOH), MK-801, AP5 (noncompetitive and competitive NMDA receptor antagonists, respectively), CNQX (AMPA receptor antagonist), or saline. Rats were recorded polygraphically for the following 4 h. Results showed that, at comparable doses, all tested drugs reduced REM sleep. No significant changes were detected in slow-wave sleep or wakefulness. This selective effect of glutamatergic antagonists suggests that glutamate may be a selective modulator of REM sleep. These findings also show that EtOH shares similar pharmacological effects on the sleep-wake cycle of the rat. Ultimately, glutamatergic mechanisms could contribute to the EtOH-mediated reduction of REM sleep.