Spontaneous electrodermal activity during sleep and waking in cats.

Preoptic/anterior hypothalamic neurons: thermosensitivity in wakefulness and non rapid eye movement sleep

Thermosensitive neurons of the preoptic/anterior hypothalamic area (POAH) have been implicated in the regulation of non-rapid eye movement (NREM) sleep. We attempted to identify those medial POAH thermosensitive neurons that may be involved in NREM sleep regulation. The thermosensitivity of medial POAH neurons was studied in five freely moving adult cats by local cooling or warming of the medial POAH with a water-perfused thermode. Of 308 neurons, 65 (21%) were classified as thermosensitive, including 31 (10%) warm-sensitive and 34 (11%) cold-sensitive neurons. The spontaneous discharge rates of 28 warm-sensitive, 34 cold-sensitive, and 115 randomly selected thermoinsensitive neurons were recorded through one to three sleep-waking cycles. Patterns of spontaneous activity for warm- and cold-sensitive neurons were different. Of 28 warm-sensitive neurons, 18 (64%) exhibited increased discharge rate during NREM sleep compared with waking (NREM/wake, > or = 1.2). This subpopulation of warm-sensitive neurons also exhibited significantly increased thermosensitivity when tested during NREM sleep. Of 34 cold-sensitive neurons, 25 (74%) discharged more slowly during NREM sleep compared with waking (NREM/wake, < or = 0.8). This subpopulation of cold-sensitive neurons exhibited decreased thermosensitivity during NREM sleep. These results are consistent with a hypothesis that the activation of sleep-related warm-sensitive neurons and the deactivation of wake-related cold-sensitive neurons may play a key role in the onset and regulation of NREM sleep.

Sleep spindles are distinctive transient patterns of brain activity that typically occur during non-rapid eye movement (NREM) sleep in humans and other mammals. Thought to be important for the consolidation of learning, they may also be useful for indicating the progression of aging and neurodegenerative diseases. The aim of this study was to characterize sleep spindles in sheep (Ovis aries). We recorded electroencephalographs wirelessly from six sheep over a continuous period containing 2 nights and a day. We detected and characterized spindles using an automated algorithm. We found that sheep sleep spindles fell within the classical range seen in humans (10–16 Hz), but we did not see a further separation into fast and slow bands. Spindles were detected predominantly during NREM sleep. Spindle characteristics (frequency, duration, density, topography) varied between individuals, but were similar within individuals between nights. Spindles that occurred during NREM sleep in daytime were indistinguishable from those found during NREM sleep at night. Surprisingly, we also detected numerous spindle-like events during unequivocal periods of wake during the day. These events were mainly local (detected at single sites), and their characteristics differed from spindles detected during sleep. These “wake spindles” are likely to be events that are commonly categorized as “spontaneous alpha activity” during wake. We speculate that wake and sleep spindles are generated via different mechanisms, and that wake spindles play a role in cognitive processes that occur during the daytime.

<h3>Abstract</h3> There is increasing evidence that level of consciousness can be captured by neural informational complexity: for instance, complexity, as measured by the Lempel Ziv (LZ) compression algorithm, decreases during anesthesia and non-rapid eye movement (NREM) sleep in humans and rats, when compared to LZ in awake and REM sleep. In contrast, LZ is higher in humans under the effect of psychedelics, including subanesthetic doses of ketamine. However, it is both unclear how this result would be modulated by varying ketamine doses, and whether it would extend to other species. Here we studied LZ with and without auditory stimulation during wakefulness and different sleep stages in 5 cats implanted with intracranial electrodes, as well as under subanesthetic doses of ketamine (5, 10, and 15 mg/kg i.m.). In line with previous results, LZ was lowest in NREM sleep, but similar in REM and wakefulness. Furthermore, we found an inverted U-shaped curve following different levels of ketamine doses in a subset of electrodes, primarily in prefrontal cortex. However, it is worth noting that the variability in the ketamine dose-response curve across cats and cortices was larger than that in the sleep-stage data, highlighting the differential local dynamics created by two different ways of modulating conscious state. These results replicate previous findings, both in humans and other species, demonstrating that neural complexity is highly sensitive to capture state changes between wake and sleep stages while adding a local cortical description. Finally, this study describes the differential effects of ketamine doses, replicating a rise in complexity for low doses, and further fall as doses approach anesthetic levels in a differential manner depending on the cortex. <h3>In brief</h3> Previous studies have shown that Lempel Ziv complexity (LZ) decreases during anesthesia and non-rapid eyes movement (NREM) sleep in humans and rats whereas it increases in REM sleep and under the effect of psychedelics. In this work we show that in the cat, LZ is lowest in NREM sleep, but similar in REM and wakefulness. We also found a ketamine inverted U-shape dose-response curve only in the auditory and prefrontal cortex, with a much larger variability in the ketamine across cats and cortices when compared to the sleep cycle.

The effects of zimeldine and alaproclate combined with a small dose of 5-HTP on waking and sleep stages in cats

Sleep is one of the fundamental requirements of all animals from nematodes to humans. It appears in different formats with shared features such as reduced muscle activities and reduced responsiveness to the environment. Despite the long history of sleep research, why a brain must be taken offline for a large portion of each day remains unknown. Moreover, sleep research focused on mammals and birds reveals two stages, rapid-eye-movement (REM) and slow-wave (SW) sleep, alternating during sleep. Whether these two stages of sleep exist in other vertebrates, particularly reptiles, is debated, as is the evolution of sleep in general. Recordings from the brain of a lizard, the Australian bearded dragon Pogona vitticeps, indicate the presence of two electrophysiological states and provides a better picture of their sleep. Local field potential (LFP) signals, head velocity, eye movements, and heart rate during sleep match the pattern of REM and SW sleep in mammals. The SW and REM sleep patterns that we observed in lizards oscillated continuously for 6 to 10 hours with a period of 80-100 seconds when the ambient temperature was ~27°C. Lizard SW dynamics closely resemble those observed in rodent hippocampal CA1, yet originated from a brain area, the dorsal ventricular ridge (DVR), that does not correspond anatomically or transcriptomically to the mammalian hippocampus. This finding pushes back the probable evolution of these dynamics to the emergence of amniotes, at least 300 million years ago. Unlike mammals and birds, REM and SW sleep in lizards occupy an almost equal amount of time during sleep. The clock-like alternation between these two sleep states was found initially by measuring the power modulation of two frequency bands, delta and beta. I recorded the full-band LFP and found an infra-slow oscillation (ISO) in the frequency range between 5 and 20 milli-Hz during sleep. The magnitude of ISO increased during sleep and decreased during both wakefulness and arousal during sleep. The up- and down-states of ISO were synchronized with the sleep state alternating rhythm but with a significant time lag dependent on the locations of the recording electrodes. Multi-site LFP recordings indicated that this ISO is a putative propagation wave sweeping extremely slowly, 30-67 µm/sec, from the posterior-dorsal pole to the anterior-ventral pole of the DVR. Previous studies in other animals showed that brainstem areas such as the locus coeruleus, laterodorsal tegmentum, and periaqueductal gray are involved in sleep states regulation. It is sadly impossible to carry out in vivo recordings in the lizard brainstem without severely affecting them and their quality of life. I thus carried out ex vivo recordings in both DVR and brainstem. Pharmacological stimulation of the brainstem could reversibly silence one distinct EEG pattern characteristic of SW sleep, the sharp-wave and ripple complex, in DVR. An ISO could be recorded simultaneously in both DVR and brainstem. From data collected in both intact and split ex vivo brains, I concluded that there are independent ISO generators in at least two areas, the brainstem and the telencephalon. Their signals may normally be synchronized by long-range connections. The DVR ISO leads the brainstem ISO by ~29 sec. Optogenetic stimulation of brainstem neurons was able to disrupt the ISO in DVR reversibly. In conclusion, the lizard brain offers a relatively simple model system to study sleep. Despite a diversity of results in different lizard species, my results revealed a number of new findings. Relevant for sleep research in general: 1) REM and SW sleep exist in a reptile. Since they also exist in birds and mammals, they probably existed in their common amniote ancestor, if not earlier. 2) REM and SW occupy equal amounts of time during sleep (50% duty cycle), a unique feature among all described sleep electrophysiological patterns, suggesting the possible existence of a simple central pattern generator of sleep, possibly ancestral. 3) I discovered the existence, in the local field potential, of an infra slow oscillation with extremely slow propagation, locked to the SW-REM alternating rhythm. The causes and mechanisms of this ISO remain to be understood. To my knowledge, the correlation between sleep states and a slow rhythm has only been reported in human scalp EEG recordings so far.

Reliability of spontaneous electrodermal activity in the cat as a function of waking and sleep stages

Chapter 2 NREM–REM sleep

ASSOCIATIONS BETWEEN SLEEP ARCHITECTURE AND INDICES OF OBSTRUCTIVE SLEEP APNEA

Effect of sleep stage on somatosensory evoked potentials by median nerve stimulation

Chapter 2 - Normal Human Sleep: An Overview

Regulation of REM sleep in mice: The role of dopamine and serotonin function in the basolateral amygdala

Visual declarative memory is associated with non-rapid eye movement sleep and sleep cycles in patients with chronic non-restorative sleep

Sleep disturbances are found in the course of most dementing syndromes. We report a longitudinal polysomnographic and 18FDG-PET study in a 38-year-old male with FTDP17 carrying the Tau gene mutation G389R. All-night sleep EEG and wake cerebral glucose metabolism at rest (eyes/ears covered) of the preceding day were studied twice, eight months (Night 1; PET 1) and sixteen months (Night 2; PET 2) after the initial neurological evaluation. The Night 1 study showed sleep fragmentation associated to a short REM latency and a severe reduction of slow wave sleep, with relatively preserved NREM-REM sleep cycles; daytime PET 1 revealed severe cerebral glucose metabolic reductions in frontal and temporal areas, with relative preservation of remaining cortical regions and subcortical structures. On Night 2, the total sleep time was less than 5 hours, delta sleep and REM latency remained shortened and only two sleep cycles could be identified; daytime PET 2 exam revealed a greater cortical metabolic impairment and an involvement of subcortical brain regions as compared to PET 1. Post-mortem neuropathological data showed severe neuronal loss, spongiosis and gliosis that were mostly marked in cortical layers I, II, V and VI. In vivo, neurometabolic and post-mortem neuropathological data are consistent with and indicative of a severe dysfunction of intra- and trans-hemispheric regional connectivity and of cortico-thalamic circuits. These findings suggest that the decreased cortical and subcortical connectivity may have been the main pathophysiological mechanism responsible for delta sleep reduction and the cognitive decline.

Objective The poor sleep quality of epileptic patients may be partly due to the occurrence epileptiform discharges (EDs). We observed the number of interictal discharges in each sleep stage and explored the associations between EDs and sleep phases in epilepsy patients. Methods Two hundred and forty epileptic patients and 213 healthy volunteers were enrolled in the current study. For all subjects, video-electroencephalogram monitoring and 24 h-night polysomnography were conducted to detect EDs and analyze the sleep structures. Results EDs were detected in 88.7%（213/240） of epilepsy patients with the most frequent cases from the temporal lobe. The EDs detected during waking, sleeping, or both waking and non-rapid eye movement (NREM) sleep stage accounted for 20.6%（44/213）, 40.4%（86/213）, and 38.9%（83/213） of the total patients, respectively. The total sleep time and time spent in REM were similar between the epileptic patients and healthy volunteers. However, epileptic patients spent a significantly longer mean sleep time in NREMⅠ—Ⅱ（(304±39） min versus （225±29） min, t= 3.51, P=0.000） and less in NREM Ⅲ—Ⅳ（(49±7) min versus（133±17） min, t=2.30, P=0.000） than healthy volunteers. Furthermore, asymmetric sleep spindles and fragmentary sleep structure as well as high inversion frequency were found in epilepsy patients, respectively. Conclusion Combination of long-term video electroencephalogram with polysomnography is a useful method to analyze associations between EDs and the sleep-wake cycle. This strategy can also help identify the nature of sleep disorders in epileptic patients, which may improve the treatment efficacy. Key words: Epilepsy; Sleep stages; Polysomnography; Sleep disorders