Basal forebrain parvalbumin neurons modulate vigilant attention and rescue deficits produced by sleep deprivation

Attention is impaired in many neuropsychiatric disorders, as well as by sleep disruption, leading to decreased workplace productivity and increased risk of accidents. Thus, understanding the neural substrates is important. Here we test the hypothesis that basal forebrain neurons that contain the calcium-binding protein parvalbumin modulate vigilant attention in mice. Furthermore, we test whether increasing the activity of basal forebrain parvalbumin neurons can rescue the deleterious effects of sleep deprivation on vigilance. A lever release version of the rodent psychomotor vigilance test was used to assess vigilant attention. Brief and continuous low-power optogenetic excitation (1 s, 473 nm @ 5 mW) or inhibition (1 s, 530 nm @ 10 mW) of basal forebrain parvalbumin neurons was used to test the effect on attention, as measured by reaction time, under control conditions and following 8 hr of sleep deprivation by gentle handling. Optogenetic excitation of basal forebrain parvalbumin neurons that preceded the cue light signal by 0.5 s improved vigilant attention as indicated by quicker reaction times. By contrast, both sleep deprivation and optogenetic inhibition slowed reaction times. Importantly, basal forebrain parvalbumin excitation rescued the reaction time deficits in sleep-deprived mice. Control experiments using a progressive ratio operant task confirmed that optogenetic manipulation of basal forebrain parvalbumin neurons did not alter motivation. These findings reveal for the first time a role for basal forebrain parvalbumin neurons in attention, and show that increasing their activity can compensate for disruptive effects of sleep deprivation.

Role of the locus coeruleus and basal forebrain in arousal and attention

Experimental evidence has implicated multiple neurotransmitter systems in either the direct or indirect modulation of cortical arousal and attention circuitry. In this review, we selectively focus on three such systems: 1) norepinephrine (NE)-containing neurons of the locus coeruleus (LC), 2) acetylcholine (ACh)-containing neurons of the basal forebrain (BF), and 3) parvalbumin (PV)-containing gamma-aminobutyric acid neurons of the BF. Whereas BF-PV neurons serve as a rapid and transient arousal system, LC-NE and BF-ACh neuromodulation are typically activated on slower but longer-lasting timescales. Recent findings suggest that the BF-PV system serves to rapidly respond to even subtle sensory stimuli with a microarousal. We posit that salient sensory stimuli, such as those that are threatening or predict the need for a response, will quickly activate the BF-PV system and subsequently activate both the BF-ACh and LC-NE systems if the circumstances require longer periods of arousal and vigilance. We suggest that NE and ACh have overlapping psychological functions with the main difference being the precise internal/environmental sensory situations/contexts that recruit each neurotransmitter system - a goal for future research to determine. Implications of dysfunction of each of these three attentional systems for our understanding of neuropsychiatric conditions are considered. Finally, the contemporary availability of research tools to selectively manipulate and measure the activity of these distinctive neuronal populations promises to answer longstanding questions, such as how various arousal systems influence downstream decision-making and motor responding.

Optogenetic manipulation of an ascending arousal system tunes cortical broadband gamma power and reveals functional deficits relevant to schizophrenia

Increases in broadband cortical electroencephalogram (EEG) power in the gamma band (30-80 Hz) range have been observed in schizophrenia patients and in mouse models of schizophrenia. They are also seen in humans and animals treated with the psychotomimetic agent ketamine. However, the mechanisms which can result in increased broadband gamma power and the pathophysiological implications for cognition and behavior are poorly understood. Here we report that tonic optogenetic manipulation of an ascending arousal system bidirectionally tunes cortical broadband gamma power, allowing on-demand tests of the effect on cortical processing and behavior. Constant, low wattage optogenetic stimulation of basal forebrain (BF) neurons containing the calcium-binding protein parvalbumin (PV) increased broadband gamma frequency power, increased locomotor activity, and impaired novel object recognition. Concomitantly, task-associated gamma band oscillations induced by trains of auditory stimuli, or exposure to novel objects, were impaired, reminiscent of findings in schizophrenia patients. Conversely, tonic optogenetic inhibition of BF-PV neurons partially rescued the elevated broadband gamma power elicited by subanesthetic doses of ketamine. These results support the idea that increased cortical broadband gamma activity leads to impairments in cognition and behavior, and identify BF-PV activity as a modulator of this activity. As such, BF-PV neurons may represent a novel target for pharmacotherapy in disorders such as schizophrenia which involve aberrant increases in cortical broadband gamma activity.

Basal Forebrain Parvalbumin Neurons Mediate Arousals from Sleep Induced by Hypercarbia or Auditory Stimuli

The ability to rapidly arouse from sleep is important for survival. However, increased arousals in patients with sleep apnea and other disorders prevent restful sleep and contribute to cognitive, metabolic, and physiologic dysfunction [1, 2]. Little is currently known about which neural systems mediate these brief arousals, hindering the development of treatments that restore normal sleep. The basal forebrain (BF) receives inputs from many nuclei of the ascending arousal system, including the brainstem parabrachial neurons, which promote arousal in response to elevated blood carbon dioxide levels, as seen in sleep apnea [3]. Optical inhibition of the terminals of parabrachial neurons in the BF impairs cortical arousals to hypercarbia [4], but which BF cell types mediate cortical arousals in response to hypercarbia or other sensory stimuli is unknown. Here, we tested the role of BF parvalbumin (PV) neurons in arousal using optogenetic techniques in mice. Optical stimulation of BF-PV neurons produced rapid transitions to wakefulness from non-rapid eye movement (NREM) sleep but did not affect REM-wakefulness transitions. Unlike previous studies of BF glutamatergic and cholinergic neurons, arousals induced by stimulation of BF-PV neurons were brief and only slightly increased total wake time, reminiscent of clinical findings in sleep apnea [5, 6]. Bilateral optical inhibition of BF-PV neurons increased the latency to arousal produced by exposure to hypercarbia or auditory stimuli. Thus, BF-PV neurons are an important component of the brain circuitry that generates brief arousals from sleep in response to stimuli, which may indicate physiological dysfunction or danger to the organism.

0224 Optogenetic Manipulation of Basal Forebrain Parvalbumin Neurons Modulates Vigilant Attention and Rescues Sleep Deprivation Induced Impairments

Introduction

Sleep disruption leads to attention impairments, excessive daytime sleepiness, and is a major contributor to accident rates and decreased workplace productivity. The basal forebrain (BF) region has long been associated with promoting cortical arousal and wakefulness. Recently, selective excitation of BF parvalbumin (PV) GABAergic neurons has been shown to produce high frequency cortical activation and brief periods of wakefulness. Here we test the hypothesis that BF PV neurons are involved in vigilant attention using bidirectional optogenetic manipulations in a signaled reaction time task.

Methods

Brief optogenetic excitation (ChR2) and inhibition (ArchT) of BF PV neurons was applied during a lever release version of the rodent psychomotor vigilance task (rPVT). Mice were trained to hold a lever down to initiate a trial and after a random delay, a 200ms cue light signaled the mouse to quickly release the lever within 1s to receive a sucrose pellet reward. The reaction time between cue light onset and lever release was the primary measure of attentional performance. Sleep deprivation (8h) produced by gentle handling was also investigated. Laser parameters: brief (1s) of continuous (non-pulsatile) laser stimulation was delivered beginning 500ms prior to cue light onset (5mW 473nm blue light for ChR2-mediated excitation; 10mW 530nm green light for ArchT-mediated inhibition).

Results

BF PV excitation led to faster reactions times (N=6, 14% faster, p<.001), interpreted as an enhancement of attention. Sleep deprivation slowed reaction times (20% slower, p<.01) and BF PV excitation rescued the sleep deprivation induced impairments. BF PV inhibition significantly slowed reaction times (25% slower, p<.02), an effect that resembled the effects of sleep deprivation.

Conclusion

This is the first demonstration of a role for BF PV neurons in attention and in the attention deficits produced by sleep deprivation.

Support

T32 HL007901, I01 BX002774, P01 HL095491, R01 MH039683, I01 BX004500, IK2 BX002130, Stonehill College SURE program, I01 BX001356

Validation of an automated sleep spindle detection method for mouse electroencephalography

Study Objectives

Sleep spindles are abnormal in several neuropsychiatric conditions and have been implicated in associated cognitive symptoms. Accordingly, there is growing interest in elucidating the pathophysiology behind spindle abnormalities using rodent models of such disorders. However, whether sleep spindles can reliably be detected in mouse electroencephalography (EEG) is controversial necessitating careful validation of spindle detection and analysis techniques.

Methods

Manual spindle detection procedures were developed and optimized to generate an algorithm for automated detection of events from mouse cortical EEG. Accuracy and external validity of this algorithm were then assayed via comparison to sigma band (10-15 Hz) power analysis, a proxy for sleep spindles, and pharmacological manipulations.

Results

We found manual spindle identification in raw mouse EEG unreliable, leading to low agreement between human scorers as determined by F1-score (0.26 ± 0.07). Thus, we concluded it is not possible to reliably score mouse spindles manually using unprocessed EEG data. Manual scoring from processed EEG data (filtered, cubed root-mean-squared), enabled reliable detection between human scorers, and between human scorers and algorithm (F1-score > 0.95). Algorithmically detected spindles correlated with changes in sigma-power and were altered by the following conditions: sleep-wake state changes, transitions between NREM and REM sleep, and application of the hypnotic drug zolpidem (10 mg/kg, intraperitoneal).

Conclusions

Here we describe and validate an automated paradigm for rapid and reliable detection of spindles from mouse EEG recordings. This technique provides a powerful tool to facilitate investigations of the mechanisms of spindle generation, as well as spindle alterations evident in mouse models of neuropsychiatric disorders.

Effects of a patient-derived de novo coding alteration of CACNA1I in mice connect a schizophrenia risk gene with sleep spindle deficits

CACNA1I, a schizophrenia risk gene, encodes a subtype of voltage-gated T-type calcium channel CaV3.3. We previously reported that a patient-derived missense de novo mutation (R1346H) of CACNA1I impaired CaV3.3 channel function. Here, we generated CaV3.3-RH knock-in animals, along with mice lacking CaV3.3, to investigate the biological impact of R1346H (RH) variation. We found that RH mutation altered cellular excitability in the thalamic reticular nucleus (TRN), where CaV3.3 is abundantly expressed. Moreover, RH mutation produced marked deficits in sleep spindle occurrence and morphology throughout non-rapid eye movement (NREM) sleep, while CaV3.3 haploinsufficiency gave rise to largely normal spindles. Therefore, mice harboring the RH mutation provide a patient derived genetic model not only to dissect the spindle biology but also to evaluate the effects of pharmacological reagents in normalizing sleep spindle deficits. Importantly, our analyses highlighted the significance of characterizing individual spindles and strengthen the inferences we can make across species over sleep spindles. In conclusion, this study established a translational link between a genetic allele and spindle deficits during NREM observed in schizophrenia patients, representing a key step toward testing the hypothesis that normalizing spindles may be beneficial for schizophrenia patients.

Alterations in sleep, sleep spindle, and EEG power in mGluR5 knockout mice

The type 5 metabotropic glutamate receptor (mGluR5) represents a novel therapeutic target for schizophrenia and other disorders. Schizophrenia is associated with progressive abnormalities in cortical oscillatory processes including reduced spindles (8-15 Hz) during sleep and increased delta (0.5-4 Hz)- and gamma-band activity (30-80 Hz) during wakefulness. mGluR5 knockout (KO) mice demonstrate many schizophrenia-like behaviors, including abnormal sleep. To examine the effects of mGluR5 on the maintenance of the neocortical circuitry responsible for such neural oscillations, we analyzed sleep/wake electroencephalographic (EEG) activity of mGluR5 KO mice at baseline, after 6 h of sleep deprivation, and during a visual method of cortical entrainment (visual steady state response). We hypothesized mGluR5-KO mice would exhibit translationally relevant abnormalities in sleep and neural oscillations that mimic schizophrenia. Power spectral and spindle density analyses were performed across 24-h EEG recordings in mGluR5-KO mice and wild-type (WT) controls. Novel findings in mGluR5 KO mice include deficits in sleep spindle density, wake alpha power, and 40-Hz visual task-evoked gamma power and phase locking. Sigma power (10-15 Hz), an approximation of spindle activity, was also reduced during non-rapid eye movement sleep transitions. Our observations on abnormal sleep/wake are generally in agreement with previous reports, although we did not replicate changes in rapid eye movement sleep. The timing of these phenotypes may suggest an impaired circadian process in mGluR5 KO mice. In conclusion, EEG phenotypes in mGluR5 KO mice resemble deficits observed in patients with schizophrenia. These findings implicate mGluR5-mediated pathways in several translationally relevant phenotypes associated with schizophrenia, and suggest that agents targeting this receptor may have harmful consequences on sleep health and daily patterns of EEG power.NEW & NOTEWORTHY Metabotropic glutamate receptor type 5 (mGluR5) knockout (KO) mice show several translationally relevant abnormalities in neural oscillatory activity associated with schizophrenia. These include deficits in sleep spindle density, sigma and alpha power, and 40-Hz task-evoked gamma power. The timing of these phenotypes suggests an impaired circadian process in these mice. Previously reported rapid eye movement sleep deficits in this model were not observed. These findings suggest mGluR5-enhancing drugs may improve sleep stability and sleep spindle density, which could impact memory and cognition.

The dual orexinergic receptor antagonist DORA-22 improves the sleep disruption and memory impairment produced by a rodent insomnia model

Insomnia-related sleep disruption can contribute to impaired learning and memory. Treatment of insomnia should ideally improve the sleep profile while minimally affecting mnemonic function, yet many hypnotic drugs (e.g. benzodiazepines) are known to impair memory. Here, we used a rat model of insomnia to determine whether the novel hypnotic drug DORA-22, a dual orexin receptor antagonist, improves mild stress-induced insomnia with minimal effect on memory. Animals were first trained to remember the location of a hidden platform (acquisition) in the Morris Water Maze and then administered DORA-22 (10, 30, or 100 mg/kg doses) or vehicle control. Animals were then subjected to a rodent insomnia model involving two exposures to dirty cages over a 6-hr time period (at time points 0 and 3 hr), followed immediately by a probe trial in which memory of the water maze platform location was evaluated. DORA-22 treatment improved the insomnia-related sleep disruption—wake was attenuated and NREM sleep was normalized. REM sleep amounts were enhanced compared with vehicle treatment for one dose (30 mg/kg). In the first hour of insomnia model exposure, DORA-22 promoted the number and average duration of NREM sleep spindles, which have been previously proposed to play a role in memory consolidation (all doses). Water maze measures revealed probe trial performance improvement for select doses of DORA-22, including increased time spent in the platform quadrant (10 and 30 mg/kg) and time spent in platform location and number of platform crossings (10 mg/kg only). In conclusion, DORA-22 treatment improved insomnia-related sleep disruption and memory consolidation deficits.

Somatostatin+/nNOS+ neurons are involved in delta electroencephalogram activity and cortical-dependent recognition memory

Slow-wave activity (SWA) is an oscillatory neocortical activity occurring in the electroencephalogram delta (δ) frequency range (~0.5-4 Hz) during nonrapid eye movement sleep. SWA is a reliable indicator of sleep homeostasis after acute sleep loss and is involved in memory processes. Evidence suggests that cortical neuronal nitric oxide synthase (nNOS) expressing neurons that coexpress somatostatin (SST) play a key role in regulating SWA. However, previous studies lacked selectivity in targeting specific types of neurons that coexpress nNOS-cells which are activated in the cortex after sleep loss. We produced a mouse model that knocks out nNOS expression in neurons that coexpress SST throughout the cortex. Mice lacking nNOS expression in SST positive neurons exhibited significant impairments in both homeostatic low-δ frequency range SWA production and a recognition memory task that relies on cortical input. These results highlight that SST+/nNOS+ neurons are involved in the SWA homeostatic response and cortex-dependent recognition memory.

Thalamic Reticular Nucleus Parvalbumin Neurons Regulate Sleep Spindles and Electrophysiological Aspects of Schizophrenia in Mice

The thalamic reticular nucleus (TRN) is implicated in schizophrenia pathology. However, it remains unclear whether alterations of TRN activity can account for abnormal electroencephalographic activity observed in patients, namely reduced spindles (10-15 Hz) during sleep and increased delta (0.5-4 Hz) and gamma-band activity (30-80 Hz) during wakefulness. Here, we utilized optogenetic and reverse-microdialysis approaches to modulate activity of the major subpopulation of TRN GABAergic neurons, which express the calcium-binding protein parvalbumin (PV), and are implicated in schizophrenia dysfunction. An automated algorithm with enhanced efficiency and reproducibility compared to manual detection was used for sleep spindle assessment. A novel, low power, waxing-and-waning optogenetic stimulation paradigm preferentially induced spindles that were indistinguishable from spontaneously occurring sleep spindles without altering the behavioral state, when compared to a single pulse laser stimulation used by us and others. Direct optogenetic inhibition of TRN-PV neurons was ineffective in blocking spindles but increased both wakefulness and cortical delta/gamma activity, as well as impaired the 40 Hz auditory steady-state response. For the first time we demonstrate that spindle density is markedly reduced by (i) optogenetic stimulation of a major GABA/PV inhibitory input to TRN arising from basal forebrain parvalbumin neurons (BF-PV) and; (ii) localized pharmacological inhibition of low-threshold calcium channels, implicated as a genetic risk factor for schizophrenia. Together with clinical findings, our results support impaired TRN-PV neuron activity as a potential cause of schizophrenia-linked abnormalities in cortical delta, gamma, and spindle activity. Modulation of the BF-PV input to TRN may improve these neural abnormalities.

Partnerships in Neuroscience Research Between Small Colleges and Large Institutions: A Case Study

There are advantages and limitations associated with a science, technology, engineering and math (STEM) education at small, liberal arts colleges relative to larger universities. While there may be increased opportunity for personal attention and access to faculty, students at liberal arts colleges may not always have the opportunity to gain experience with state-of-the-art equipment and technology. Herein, we describe a case study of an inter-institutional partnership between Stonehill College and two neuroscience research laboratories which are part of the Veterans Affairs Boston Healthcare System (VABHS). Both laboratories are affiliated with Harvard Medical School (HMS). We discuss the benefits as well as the challenges associated with the development and maintenance of this partnership. The experience with the use of sophisticated instrumentation and technology available in these laboratories may give students a competitive edge when applying to graduate school programs. However, we contend that the most important advantage of this research experience is the development of a sense of self-esteem and professional competence that will allow students to meet the many challenges that lie ahead in graduate school and beyond.

Learning and memory are impaired in the object recognition task during metestrus/diestrus and after sleep deprivation

Females are an under-represented research model and the mechanisms through which sleep loss impairs cognition are not clear. Since levels of reproductive hormones and the estrous cycle are sensitive to sleep loss and necessary for learning and memory, we hypothesized that sleep deprivation impacts learning and memory in female mice by interfering with the estrous cycle. We used the object recognition task to assess learning and memory in female mice during separate phases of the estrous cycle and after sleep loss. Mice in metestrus/diestrus attended to sample objects less than mice in proestrus/estrus during object acquisition, the first phase of the object recognition task. Subsequently, during the recognition phase of the task, only mice in proestrus/estrus displayed a preference for the novel object. Sleep deprivation for 12h immediately before the object recognition task reduced time attending to sample objects and novel object preference for mice in proestrus/estrus, without changing length of the estrous cycle. These results show that sleep deprived mice in proestrus/estrus had learning deficits and memory impairments, like mice in metestrus/diestrus. Since sleep deprivation did not disrupt the estrous cycle, however, results did not support the hypothesis. Cognitive impairments due to acute sleep loss were not due to alterations to the estrous cycle.

GENETICALLY MODIFIED PRIMARY ASTROCYTES AS CELLULAR VEHICLES FOR GENE THERAPY IN THE BRAIN

Combining genetic engineering and cell transplantation has been proposed as one way to overcome the limited availability of donor tissue that may restrict the application of graft therapy to neurological diseases. Important issues in this approach concern the choice of a suitable cellular vehicle, and the method of gene insertion. In this regard, we have investigated the use of brain-derived primary astrocytes as cellular vehicles for gene therapy, because they can be transfected, divide in culture, are brain-region specific, possess a secretory mechanism, and may migrate several mm from the transplant site. To address the issue of gene insertion, we have generated stably transfected primary rat astrocytes using the nonviral calcium phosphate method to co-transfect a reporter construct (RSV-chloramphenicol acetyltransferase (CAT), or human enkephalin promoter CAT, plus a neomycin resistance plasmid (pRSVNeo). Modified astrocytes were then propagated by transfer to selective media containing G418 (300 μg/mL) for 3 wk. The presence of the reporter gene product (CAT) was demonstrated by immunocytochemistry, and by biochemical assay of CAT enzyme catalytic activity. These genetically modified astrocytes were followed for up to 3 wk after transplantation into the rat striatum. Criteria used to distinguish transplanted astrocytes included histological evidence of abundant nuclei interrupting the normal cytoarchitecture of the striatum, astrocyte morphology, and the presence of CAT enzyme activity. Our data indicates that genetically modified astrocytes are an important candidate vehicle for use in transplantation therapy in neurological diseases. We suggest that genetically modified astrocytes can also be used for studying the human enkephalin promoter, other promoters, and expressed proteins using this paradigm.

The NLRP3 inflammasome modulates sleep and NREM sleep delta power induced by spontaneous wakefulness, sleep deprivation and lipopolysaccharide

Both sleep loss and pathogens can enhance brain inflammation, sleep, and sleep intensity as indicated by electroencephalogram delta (δ) power. The pro-inflammatory cytokine interleukin-1 beta (IL-1β) is increased in the cortex after sleep deprivation (SD) and in response to the Gram-negative bacterial cell-wall component lipopolysaccharide (LPS), although the exact mechanisms governing these effects are unknown. The nucleotide-binding domain and leucine-rich repeat protein-3 (NLRP3) inflammasome protein complex forms in response to changes in the local environment and, in turn, activates caspase-1 to convert IL-1β into its active form. SD enhances the cortical expression of the somnogenic cytokine IL-1β, although the underlying mechanism is, as yet, unidentified. Using NLRP3-gene knockout (KO) mice, we provide evidence that NLRP3 inflammasome activation is a crucial mechanism for the downstream pathway leading to increased IL-1β-enhanced sleep. NLRP3 KO mice exhibited reduced non-rapid eye movement (NREM) sleep during the light period. We also found that sleep amount and intensity (δ activity) were drastically attenuated in NLRP3 KO mice following SD (homeostatic sleep response), as well as after LPS administration, although they were enhanced by central administration of IL-1β. NLRP3, ASC, and IL1β mRNA, IL-1β protein, and caspase-1 activity were greater in the somatosensory cortex at the end of the wake-active period when sleep propensity was high and after SD in wild-type but not NLRP3 KO mice. Thus, our novel and converging findings suggest that the activation of the NLRP3 inflammasome can modulate sleep induced by both increased wakefulness and a bacterial component in the brain.

Chronic sleep restriction induces long-lasting changes in adenosine and noradrenaline receptor density in the rat brain

Although chronic sleep restriction frequently produces long-lasting behavioural and physiological impairments in humans, the underlying neural mechanisms are unknown. Here we used a rat model of chronic sleep restriction to investigate the role of brain adenosine and noradrenaline systems, known to regulate sleep and wakefulness, respectively. The density of adenosine A1 and A2a receptors and β-adrenergic receptors before, during and following 5 days of sleep restriction was assessed with autoradiography. Rats (n = 48) were sleep-deprived for 18 h day(-1) for 5 consecutive days (SR1-SR5), followed by 3 unrestricted recovery sleep days (R1-R3). Brains were collected at the beginning of the light period, which was immediately after the end of sleep deprivation on sleep restriction days. Chronic sleep restriction increased adenosine A1 receptor density significantly in nine of the 13 brain areas analysed with elevations also observed on R3 (+18 to +32%). In contrast, chronic sleep restriction reduced adenosine A2a receptor density significantly in one of the three brain areas analysed (olfactory tubercle which declined 26-31% from SR1 to R1). A decrease in β-adrenergic receptors density was seen in substantia innominata and ventral pallidum which remained reduced on R3, but no changes were found in the anterior cingulate cortex. These data suggest that chronic sleep restriction can induce long-term changes in the brain adenosine and noradrenaline receptors, which may underlie the long-lasting neurocognitive impairments observed in chronic sleep restriction.

Chronic sleep restriction elevates brain interleukin-1 beta and tumor necrosis factor-alpha and attenuates brain-derived neurotrophic factor expression

Acute sleep loss increases pro-inflammatory and synaptic plasticity-related molecules in the brain, including interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), and brain-derived neurotrophic factor (BDNF). These molecules enhance non-rapid eye movement sleep slow wave activity (SWA), also known as electroencephalogram delta power, and modulate neurocognitive performance. Evidence suggests that chronic sleep restriction (CSR), a condition prevalent in today's society, does not elicit the enhanced SWA that is seen after acute sleep loss, although it cumulatively impairs neurocognitive functioning. Rats were continuously sleep deprived for 18h per day and allowed 6h of ad libitum sleep opportunity for 1 (SR1), 3 (SR3), or 5 (SR5) successive days (i.e., CSR). IL-1β, TNF-α, and BDNF mRNA levels were determined in the somatosensory cortex, frontal cortex, hippocampus, and basal forebrain. Largely, brain IL-1β and TNF-α expression were significantly enhanced throughout CSR. In contrast, BDNF mRNA levels were similar to baseline values in the cortex after 1 day of SR and significantly lower than baseline values in the hippocampus after 5 days of SR. In the basal forebrain, BDNF expression remained elevated throughout the 5 days of CSR, although IL-1β expression was significantly reduced. The chronic elevations of IL-1β and TNF-α and inhibition of BDNF might contribute to the reported lack of SWA responses reported after CSR. Further, the CSR-induced enhancements in brain inflammatory molecules and attenuations in hippocampal BDNF might contribute to neurocognitive and vigilance detriments that occur from CSR.

Sleep allostasis in chronic sleep restriction: the role of the norepinephrine system

Sleep responses to chronic sleep restriction may be very different from those observed after acute total sleep deprivation. Specifically, when sleep restriction is repeated for several consecutive days, animals express attenuated compensatory increases in sleep time and intensity during daily sleep opportunities. The neurobiological mechanisms underlying these adaptive, or more specifically, allostatic, changes in sleep homeostasis are unknown. Several lines of evidence indicate that norepinephrine may play a key role in modulating arousal states and NREM EEG delta power, which is widely recognized as a marker for sleep intensity. Therefore, we investigated time course changes in brain adrenergic receptor mRNA levels in response to chronic sleep restriction using a rat model. Here, we observed that significantly altered mRNA levels of the α1- adrenergic receptor in the basal forebrain as well as α2- and β1-adrenergic receptor in the anterior cingulate cortex only on the first sleep restriction day. On the other hand, the frontal cortex α1-, α2-, and β1-adrenergic receptor mRNA levels were reduced throughout the period of sleep restriction. Combined with our earlier findings on EEG that sleep time and intensity significantly increased only on the first sleep restriction days, these results suggest that alterations in the brain norepinephrine system in the basal forebrain and cingulate cortex may mediate allostatic changes in sleep time and intensity observed during chronic sleep restriction.

Recent developments in home sleep-monitoring devices

Improving our understanding of sleep physiology and pathophysiology is an important goal for both medical and general wellness reasons. Although the gold standard for assessing sleep remains the laboratory polysomnogram, there is an increasing interest in portable monitoring devices that provide the opportunity for assessing sleep in real-world environments such as the home. Portable devices allow repeated measurements, evaluation of temporal patterns, and self-experimentation. We review recent developments in devices designed to monitor sleep-wake activity, as well as monitors designed for other purposes that could in principle be applied in the field of sleep (such as cardiac or respiratory sensing). As the body of supporting validation data grows, these devices hold promise for a variety of health and wellness goals. From a clinical and research standpoint, the capacity to obtain longitudinal sleep-wake data may improve disease phenotyping, individualized treatment decisions, and individualized health optimization. From a wellness standpoint, commercially available devices may allow individuals to track their own sleep with the goal of finding patterns and correlations with modifiable behaviors such as exercise, diet, and sleep aids.

Control of sleep and wakefulness

This review summarizes the brain mechanisms controlling sleep and wakefulness. Wakefulness promoting systems cause low-voltage, fast activity in the electroencephalogram (EEG). Multiple interacting neurotransmitter systems in the brain stem, hypothalamus, and basal forebrain converge onto common effector systems in the thalamus and cortex. Sleep results from the inhibition of wake-promoting systems by homeostatic sleep factors such as adenosine and nitric oxide and GABAergic neurons in the preoptic area of the hypothalamus, resulting in large-amplitude, slow EEG oscillations. Local, activity-dependent factors modulate the amplitude and frequency of cortical slow oscillations. Non-rapid-eye-movement (NREM) sleep results in conservation of brain energy and facilitates memory consolidation through the modulation of synaptic weights. Rapid-eye-movement (REM) sleep results from the interaction of brain stem cholinergic, aminergic, and GABAergic neurons which control the activity of glutamatergic reticular formation neurons leading to REM sleep phenomena such as muscle atonia, REMs, dreaming, and cortical activation. Strong activation of limbic regions during REM sleep suggests a role in regulation of emotion. Genetic studies suggest that brain mechanisms controlling waking and NREM sleep are strongly conserved throughout evolution, underscoring their enormous importance for brain function. Sleep disruption interferes with the normal restorative functions of NREM and REM sleep, resulting in disruptions of breathing and cardiovascular function, changes in emotional reactivity, and cognitive impairments in attention, memory, and decision making.

Decoupling of sleepiness from sleep time and intensity during chronic sleep restriction: evidence for a role of the adenosine system

STUDY OBJECTIVE

Sleep responses to chronic sleep restriction (CSR) might be very different from those observed after short-term total sleep deprivation. For example, after sleep restriction continues for several consecutive days, animals no longer express compensatory increases in daily sleep time and sleep intensity. However, it is unknown if these allostatic, or adaptive, sleep responses to CSR are paralleled by behavioral and neurochemical measures of sleepiness.

DESIGN

This study was designed to investigate CSR-induced changes in (1) sleep time and intensity as a measure of electrophysiological sleepiness, (2) sleep latency as a measure of behavioral sleepiness, and (3) brain adenosine A1 (A1R) and A2a receptor (A2aR) mRNA levels as a putative neurochemical correlate of sleepiness.

SUBJECTS

Male Sprague-Dawley rats

INTERVENTIONS

A 5-day sleep restriction (SR) protocol consisting of 18-h sleep deprivation and 6-h sleep opportunity each day.

MEASUREMENT AND RESULTS

Unlike the first SR day, rats did not sleep longer or deeper on days 2 through 5, even though they exhibited significant elevations of behavioral sleepiness throughout all 5 SR days. For all SR days and recovery day 1, A1R mRNA in the basal forebrain was maintained at elevated levels, whereas A2aR mRNA in the frontal cortex was maintained at reduced levels.

CONCLUSION

CSR LEADS TO A DECOUPLING OF SLEEPINESS FROM SLEEP TIME AND SLEEP INTENSITY, SUGGESTING THAT THERE ARE AT LEAST TWO DIFFERENT SLEEP REGULATORY SYSTEMS: one mediating sleepiness (homeostatic) and the other mediating sleep time/intensity (allostatic). The time course of changes observed in adenosine receptor mRNA levels suggests that the basal forebrain and cortical adenosine system might mediate sleepiness rather than sleep time or intensity.

Chronic ramelteon treatment in a mouse model of Alzheimer's disease

Prior research has reported beneficial effects of melatonin in rodent models of Alzheimer's disease (AD). This study evaluated the effect of ramelteon (Rozerem, a melatonin receptor agonist) on spatial learning & memory and neuropathological markers in a transgenic murine model of AD (the B6C3-Tg(APPswe,PSEN1dE9)85Dbo/J transgenic mouse strain; hereafter 'AD mice'). Three months of daily ramelteon treatment (~3mg/kg/day), starting at 3 months of age, did not produce an improvement in the cognitive performance of AD mice (water maze). In contrast to wild-type control mice, AD mice did not show any evidence of having learned the location of the escape platform. The cortex and hippocampus of AD mice contained significant quantities of beta-amyloid plaques and PARP-positive (poly ADP ribose polymerase) cells, indicating apoptosis. Six months of ramelteon treatment, starting at 3 months of age, did not produce any change in these neuropathological markers. The ability of long term melatonin treatment to improve cognition and attenuate neuropathology in AD mice did not generalize to this dosage of ramelteon.

The cognitive cost of sleep lost

A substantial body of literature supports the intuitive notion that a good night's sleep can facilitate human cognitive performance the next day. Deficits in attention, learning & memory, emotional reactivity, and higher-order cognitive processes, such as executive function and decision making, have all been documented following sleep disruption in humans. Thus, whilst numerous clinical and experimental studies link human sleep disturbance to cognitive deficits, attempts to develop valid and reliable rodent models of these phenomena are fewer, and relatively more recent. This review focuses primarily on the cognitive impairments produced by sleep disruption in rodent models of several human patterns of sleep loss/sleep disturbance. Though not an exclusive list, this review will focus on four specific types of sleep disturbance: total sleep deprivation, experimental sleep fragmentation, selective REM sleep deprivation, and chronic sleep restriction. The use of rodent models can provide greater opportunities to understand the neurobiological changes underlying sleep loss induced cognitive impairments. Thus, this review concludes with a description of recent neurobiological findings concerning the neuroplastic changes and putative brain mechanisms that may underlie the cognitive deficits produced by sleep disturbances.

Twenty-four hours, or five days, of continuous sleep deprivation or experimental sleep fragmentation do not alter thirst or motivation for water reward in rats

Sleep disruption results in an increased demand for energy, which typically causes hyperphagia in an attempt to redress the energy metabolism imbalance. Therefore, experiments combining food reward and sleep disruption may underestimate the effect of sleep disruption due to their contradictory influences on behavior (for example on operant measures of attention). In contrast, water is not a central component of energy metabolism and thus thirst may not be affected by sleep disruption. However, little work has been done examining the effect of sleep disruption on thirst and motivation for water. The effect of total sleep deprivation (SD) and experimental sleep fragmentation (SF) on thirst and motivation for water was assessed. In experiment 1 (using 22 month old male Fisher-Norway rats) the amount of water consumed during a 15 min period immediately following a period of 24h SD or SF (in which water was not available) was measured, and, in a separate session, the amount of water consumed during the 24h of SD or SF was measured. Thereafter, the effect of 5 days SD or SF on motivation for water was assessed with the progressive ratio task (using water reward), which is widely used to assess motivation. Experiment 2 (using 6 month, and 22 month, old male Sprague- Dawley rats) followed an identical design except that the SF condition was dropped (due to a lack of any difference between the SD and SF conditions in experiment 1), and only the 6 month old rats experienced the full 5 day SD condition. Daily measurements of body weight and food consumption were recorded in experiment 2 in order to confirm previously published findings that food consumption goes up and body weight declines in sleep deprived rats. In both experiments the quantity of water rats consumed during a 15 min period immediately following the 24h period of sleep disruption, or consumed during the 24h period of SD or SF, did not change compared to control rats. Furthermore, 5 days of SD or SF had no effect on breakpoint in the progressive ratio task indicating that 5 days of SD or SF did not alter motivation for water reward. As previously reported, food consumption increased and body weight decreased during the 5 days of SD. in experiment 2. The findings indicate that although sleep disruption increases food consumption and decreases body weight, it does not alter thirst or motivation for water reward. Thus, water restriction is well suited for experiments examining the effect of sleep disruption on reward motivated behavioral tests in rats.

Sleep fragmentation reduces hippocampal CA1 pyramidal cell excitability and response to adenosine

Sleep fragmentation (SF) impairs the restorative/cognitive benefits of sleep via as yet unidentified alterations in neural physiology. Previously, we found that hippocampal synaptic plasticity and spatial learning are impaired in a rat model of SF which utilizes a treadmill to awaken the animals every 2 min, mimicking the frequency of awakenings observed in human sleep apnea patients. Here, we investigated the cellular mechanisms responsible for these effects, using whole-cell patch-clamp recordings. 24h of SF decreased the excitability of hippocampal CA1 pyramidal neurons via decreased input resistance, without alterations in other intrinsic membrane or action potential properties (when compared to cage controls, or to exercise controls that experienced the same total amount of treadmill movement as SF rats). Contrary to our initial prediction, the hyperpolarizing response to bath applied adenosine (30 microM) was reduced in the CA1 neurons of SF treated rats. Our initial prediction was based on the evidence that sleep loss upregulates cortical adenosine A1 receptors; however, the present findings are consistent with a very recent report that hippocampal A1 receptors are not elevated by sleep loss. Thus, increased adenosinergic inhibition is unlikely to be responsible for reduced hippocampal long-term potentiation in SF rats. Instead, the reduced excitability of CA1 pyramidal neurons observed here may contribute to the loss of hippocampal long-term potentiation and hippocampus-dependent cognitive impairments associated with sleep disruption.

Experimental sleep fragmentation impairs spatial reference but not working memory in Fischer/Brown Norway rats

Sleep fragmentation is a common symptom in sleep disorders and other medical complaints resulting in excessive daytime sleepiness. The present study seeks to explore the effects of sleep fragmentation on learning and memory in a spatial reference memory task and a spatial working memory (WM) task. Fischer/Brown Norway rats lived in custom treadmills designed to induce locomotor activity every 2 min throughout a 24-h period. Separate rats were either on a treadmill schedule that allowed for consolidated sleep or experienced no locomotor activation. Rats were tested in one of two water maze-based tests of learning and memory immediately following 24 h of sleep interruption. Rats tested in a spatial reference memory task (eight massed acquisition trials) with a 24-h follow-up probe trial to assess memory retention showed no differences in acquisition performance but were impaired on the 24 h retention of the platform location. In contrast, the performance of rats tested in a spatial WM task (delayed matching to position task) was not impaired. Therefore, sleep fragmentation prior to testing impairs the ability to retain spatial reference memories but does not impair spatial reference memory acquisition or spatial WM in Fischer-Norway rats.

24 hours of sleep deprivation in the rat increases sleepiness and decreases vigilance: introduction of the rat-psychomotor vigilance task

A novel animal-analog of the human psychomotor vigilance task (PVT) was validated by subjecting rats to 24 h of sleep deprivation (SD) and examining the effect on performance in the rat-PVT (rPVT), and a rat multiple sleep latency test (rMSLT). During a three-phase (separate cohorts) crossover design, vigilance performance in the rPVT was compared with 24 h SD-induced changes in sleepiness assessed by polysomnographic evaluation and the rMSLT. Twenty-four hours of SD was produced by brief rotation of activity wheels at regular intervals in which the animals resided throughout the experiment. In the rPVT experiment, exercise controls (EC) experienced the same overall amount of locomotor activity as during SD, but allowed long periods of undisturbed sleep. After 24 h SD response latencies slowed, and lapses increased significantly during rPVT performance when compared with baseline and EC conditions. During the first 3 h of the recovery period following 24 h SD, polysomnographic measures indicated sleepiness. Latency to fall asleep after 24 h SD was assessed six times during the first 3 h after SD. Rats fell asleep significantly faster immediately after SD, than after non-SD baseline sessions. In conclusion, 24 h of SD in rats increased sleepiness, as indicated by polysomnography and the rMSLT, and impaired vigilance as measured by the rPVT. The rPVT closely resembles the human PVT test widely used in human sleep research and will assist investigation of the neurobiologic mechanisms that produce vigilance impairments after sleep disruption.

Microdialysis elevation of adenosine in the basal forebrain produces vigilance impairments in the rat psychomotor vigilance task

STUDY OBJECTIVE

The inhibitory neuromodulator adenosine has been proposed as a homeostatic sleep factor that acts potently in the basal forebrain (BF) to increase sleepiness. Here 300 microM of adenosine was dialyzed in the BF of rats, and the effect on vigilance was determined in the rat Psychomotor Vigilance Task (rPVT).

DESIGN

Rats experienced all experimental conditions in a repeated-measures, cross-over design.

PATIENTS OR PARTICIPANTS

Twelve young adult male Fischer-Norway rats.

INTERVENTIONS

Sustained attention performance in the rPVT was evaluated following 2 hours of bilateral microdialysis perfusion of vehicle, adenosine (300 microM), or codialysis of 300 microM of adenosine with the A1 receptor antagonist 8-cyclopentyltheophylline.

MEASUREMENTS AND RESULTS

During rPVT performance, response latencies and performance lapses increased significantly after adenosine dialysis when compared with baseline (no dialysis) or vehicle dialysis sessions. The codialysis of 8-cyclopentyltheophylline with adenosine completely blocked the effects produced by adenosine alone, resulting in performance equivalent to that of the vehicle sessions.

CONCLUSIONS

Pharmacologic elevation of BF adenosine in rats produced vigilance impairments resembling the effect of sleep deprivation on vigilance performance in both man and rats. This effect of exogenous adenosine was completely blocked by codialysis with an adenosine A1 receptor antagonist. The results are consistent with the hypothesis that sleep loss induces elevations of BF adenosine that, acting via A1 receptors, lead to increased sleepiness and impaired vigilance.

Assessing sleepiness in the rat: a multiple sleep latencies test compared to polysomnographic measures of sleepiness

Sleepiness following 6 h of sleep deprivation (SD) was evaluated with a rat multiple sleep latencies test (rMSLT), and the findings were compared to conventional polysomnographic measures of sleepiness. The 6 h of SD was produced by automated activity wheels, and was terminated at either the end of the light period or at the beginning of the dark period. The rMSLT consisted of 5 min wakefulness induced by sensory stimulation followed by 25 min of freedom to sleep. This procedure was repeated every 30 min for 3 h and was designed to minimize the amount of sleep lost due to the testing procedure. In separate rats, 6 h SD was followed by undisturbed recovery, allowing evaluation of conventional polysomnographic measures of sleepiness. Sleep onset latencies were reduced following SD, with recovery in the light (baseline = 8 min, 3 s versus post-SD = 1 min, 17 s) and dark period (baseline = 14 min, 17 s versus 7 min, 7 s). Sleep onset latencies were not altered by varying the duration criterion for the first sleep bout (i.e., sleep bout length criteria of 10, 20, 30, or 60 s were compared). Polysomnographic variables (non-rapid eye movement sleep episode duration, delta power, and number of awakenings) also provided reliable indirect measures of sleepiness, regardless of whether the recovery sleep occurred in the light or dark period. Evaluation of effect size indicated that the rMSLT was a strong measure of sleepiness, and was influenced by homeostatic, circadian, and illumination factors. The rMSLT provided a simple, objective, robust and direct measure of sleepiness that was as effective as conventional polysomnographic measures of sleepiness.

Sleep fragmentation impairs ventilatory long-term facilitation via adenosine A1 receptors

Sleep fragmentation (SF), a primary feature of obstructive sleep apnoea (OSA), impairs hippocampal long-term potentiation and causes cognitive/attention deficits. However, its influence upon respiratory control has hardly been studied. This study examined the effect of SF on ventilatory long-term facilitation (LTF, a persistent augmentation of respiratory activity after episodic hypoxia) and the hypoxic ventilatory response (HVR), and investigated the role of adenosine A1 receptors in these SF effects in conscious adult male Sprague-Dawley rats. SF, confirmed by sleep architecture recordings, was achieved by periodic, forced locomotion in a rotating drum (30 s rotation/90 s stop for 24 h). LTF, elicited by five episodes of 5 min poikilocapnic hypoxia (10% O2) with 5 min intervals, was measured by plethysmography. Resting ventilation and metabolic rate were unchanged, HVR was reduced (150.6 +/- 3.5% versus 110.4 +/- 12.3%) and LTF was eliminated (22.6 +/- 0.5% versus -0.1 +/- 1.3%) shortly after 24 h SF. The SF-induced impairments were SF duration dependent, and completely reversible as HVR (< 24 h) and LTF (< 48 h) returned spontaneously to their pre-SF values. The SF-impaired HVR was improved (130.3 +/- 4.2%) and SF-eliminated LTF was restored (19.6 +/- 0.9%) by systemic injection of the adenosine A1 receptor antagonist 8-CPT (2.5 mg kg(-1)) approximately 30 min before LTF elicitation. Both HVR and LTF were also similarly impaired by 24 h total sleep deprivation or 24 h repeated cage tapping-induced SF, but not by a 24 h locomotion control protocol for SF. Collectively, these data suggest that: (1) 24 h SF impairs LTF and poikilocapnic HVR; (2) these impairments require A1 receptors; and (3) SF of OSA may exacerbate OSA via impaired ventilatory control mechanisms.

Experimental sleep fragmentation and sleep deprivation in rats increases exploration in an open field test of anxiety while increasing plasma corticosterone levels

Sleep deprivation alters mood and anxiety in man. In rats, 24 h of treadmill-induced total sleep deprivation or sleep fragmentation increased exploratory behavior in an open field test of anxiety compared to cage or exercise controls. Plasma corticosterone (CORT) levels of sleep disturbed and exercise control rats were elevated compared to cage controls, suggesting that the increased exploration observed in the sleep disturbed rats was not due to a hypothalamic-pituitary-adrenal (HPA) stress response.

Sleep fragmentation elevates behavioral, electrographic and neurochemical measures of sleepiness

Sleep fragmentation, a feature of sleep apnea as well as other sleep and medical/psychiatric disorders, is thought to lead to excessive daytime sleepiness. A rodent model of sleep fragmentation was developed (termed sleep interruption, SI), where rats were awakened every 2 min by the movement of an automated treadmill for either 6 or 24 h of exposure. The sleep pattern of rats exposed to 24 h of SI resembled sleep of the apneic patient in the following ways: sleep was fragmented (up to 30 awakening/h), total rapid eye movement (REM) sleep time was greatly reduced, non-rapid eye movement (NREM) sleep episode duration was reduced (from 2 min, 5 s baseline to 58 s during SI), whereas the total amount of NREM sleep time per 24 h approached basal levels. Both 6 and 24 h of SI made rats more sleepy, as indicated by a reduced latency to fall asleep upon SI termination. Electrographic measures in the recovery sleep period following either 6 or 24 h of SI also indicated an elevation of homeostatic sleep drive; specifically, the average NREM episode duration increased (e.g. for 24 h SI, from 2 min, 5 s baseline to 3 min, 19 s following SI), as did the NREM delta power during recovery sleep. Basal forebrain (BF) levels of extracellular adenosine (AD) were also measured with microdialysis sample collection and high performance liquid chromatography detection, as previous work suggests that increasing concentrations of BF AD are related to sleepiness. BF AD levels were significantly elevated during SI, peaking at 220% of baseline during 30 h of SI exposure. These combined findings imply an elevation of the homeostatic sleep drive following either 6 or 24 h of SI, and BF AD levels appear to correlate more with sleepiness than with the cumulative amount of prior wakefulness, since total NREM sleep time declined only slightly. SI may be partially responsible for the symptom of daytime sleepiness observed in a number of clinical disorders, and this may be mediated by mechanisms involving BF AD.

Experimental Sleep Fragmentation Impairs Attentional Set-Shifting in Rats

STUDY OBJECTIVE

To evaluate the effect of experimental sleep fragmentation (sleep interruption; SI) on complex learning in an intradimensional-extradimensional (ID/ED) set-shifting task in rats.

DESIGN

A sleep fragmentation paradigm of intermittent forced locomotion was validated in adult rats by examining electrographic effects. Discrimination task performances were assessed in rats following sleep fragmentation or 2 control conditions.

PARTICIPANTS

41 young adult male Fischer-Norway rats.

INTERVENTION

A treadmill was used to produce 30 awakenings/h for the 24-h period prior to testing. Exercise control rats received an equivalent amount of treadmill-induced locomotion that permitted 30-minute pauses to allow consolidated sleep.

MEASUREMENT AND RESULTS

SI rats were selectively impaired on the extradimensional-shift phase of the task, taking significantly more trials to achieve criterion performance (15.4 +/- 2.0) than either control group (cage control = 10.4 +/- 0.9; exercise control = 6.3 +/- 0.2). The SI schedule reduced the average duration of nonREM sleep (NREMS) episodes to 56 s (baseline = 182 s), while the exercise control group increased average NREMS episode duration to 223 s. Total (24-h) NREMS time declined from 50% during baseline to 33% during SI, whereas rapid eye movement sleep (REMS) was absent in SI animals (7% during baseline and 0% during SI), and time spent awake increased proportionally (from 43% during baseline to 67% during SI).

CONCLUSION

24-hour SI produced impairment in an attentional set-shifting that is comparable to the executive function and cognitive deficits observed in humans with sleep apnea or after a night of experimental sleep fragmentation.