Effect of sleep deprivation on multi-unit discharge activity of basal forebrain

Tired and stressed: Examining the need for sleep

A key feature of circadian rhythms is the sleep/wake cycle. Sleep causes reduced responsiveness to the environment, which puts animals in a particularly vulnerable state; yet sleep has been conserved throughout evolution, indicating that it fulfils a vital purpose. A core function of sleep across species has not been identified, but substantial advances in sleep research have been made in recent years using the genetically tractable model organism, Drosophila melanogaster. This review describes the universality of sleep, the regulation of sleep, and current theories on the function of sleep, highlighting a historical and often overlooked theory called the Free Radical Flux Theory of Sleep. Additionally, we summarize our recent work with short-sleeping Drosophila mutants and other genetic and pharmacological tools for manipulating sleep which supports an antioxidant theory of sleep and demonstrates a bi-directional relationship between sleep and oxidative stress.

Long-term effects of sleep deprivation on neuronal activity in four hypothalamic areas

Lack of adequate sleep has become increasingly common in our 24/7 society. Unfortunately diminished sleep has significant health consequences including metabolic and cardiovascular disease and mental disorders including depression. The pathways by which reduced sleep adversely affects physiology and behavior are unknown. We found that 6h of sleep deprivation in adult male rats induces changes in neuronal activity in the lateral hypothalamus, the paraventricular nucleus, the arcuate nucleus and the mammillary bodies. Surprisingly, these alterations last for up to 48h. The data show that sleep loss has prolonged effects on the activity of multiple hypothalamic areas. Our data indicate also that measuring electroencephalographic slow wave activity underestimates the amount of time that the hypothalamus requires to recover from episodes of sleep deprivation. We propose that these hypothalamic changes underlie the well-established relationship between sleep loss and several diseases such as metabolic disorders, stress and depression and that sufficient sleep is vital for autonomic functions controlled by the hypothalamus.

Sleep restriction acutely impairs glucose tolerance in rats

Chronic sleep curtailment in humans has been related to impairment of glucose metabolism. To better understand the underlying mechanisms, the purpose of the present study was to investigate the effect of acute sleep deprivation on glucose tolerance in rats. A group of rats was challenged by 4-h sleep deprivation in the early rest period, leading to prolonged (16 h) wakefulness. Another group of rats was allowed to sleep during the first 4 h of the light period and sleep deprived in the next 4 h. During treatment, food was withdrawn to avoid a postmeal rise in plasma glucose. An intravenous glucose tolerance test (IVGTT) was performed immediately after the sleep deprivation period. Sleep deprivation at both times of the day similarly impaired glucose tolerance and reduced the early-phase insulin responses to a glucose challenge. Basal concentrations of plasma glucose, insulin, and corticosterone remained unchanged after sleep deprivation. Throughout IVGTTs, plasma corticosterone concentrations were not different between the control and sleep-deprived group. Together, these results demonstrate that independent of time of day and sleep pressure, short sleep deprivation during the resting phase favors glucose intolerance in rats by attenuating the first-phase insulin response to a glucose load. In conclusion, this study highlights the acute adverse effects of only a short sleep restriction on glucose homeostasis.

Spindle Activity Orchestrates Plasticity during Development and Sleep

Spindle oscillations have been described during early brain development and in the adult brain. Besides similarities in temporal patterns and involved brain areas, neonatal spindle bursts (NSBs) and adult sleep spindles (ASSs) show differences in their occurrence, spatial distribution, and underlying mechanisms. While NSBs have been proposed to coordinate the refinement of the maturating neuronal network, ASSs are associated with the implementation of acquired information within existing networks. Along with these functional differences, separate synaptic plasticity mechanisms seem to be recruited. Here, we review the generation of spindle oscillations in the developing and adult brain and discuss possible implications of their differences for synaptic plasticity. The first part of the review is dedicated to the generation and function of ASSs with a particular focus on their role in healthy and impaired neuronal networks. The second part overviews the present knowledge of spindle activity during development and the ability of NSBs to organize immature circuits. Studies linking abnormal maturation of brain wiring with neurological and neuropsychiatric disorders highlight the importance to better elucidate neonatal plasticity rules in future research.

Sleep and the price of plasticity: from synaptic and cellular homeostasis to memory consolidation and integration

Sleep is universal, tightly regulated, and its loss impairs cognition. But why does the brain need to disconnect from the environment for hours every day? The synaptic homeostasis hypothesis (SHY) proposes that sleep is the price the brain pays for plasticity. During a waking episode, learning statistical regularities about the current environment requires strengthening connections throughout the brain. This increases cellular needs for energy and supplies, decreases signal-to-noise ratios, and saturates learning. During sleep, spontaneous activity renormalizes net synaptic strength and restores cellular homeostasis. Activity-dependent down-selection of synapses can also explain the benefits of sleep on memory acquisition, consolidation, and integration. This happens through the offline, comprehensive sampling of statistical regularities incorporated in neuronal circuits over a lifetime. This Perspective considers the rationale and evidence for SHY and points to open issues related to sleep and plasticity.

Social and environmental contexts modulate sleep deprivation-induced c-Fos activation in rats

People often sleep deprive themselves voluntarily for social and lifestyle reasons. Animals also appear to stay awake longer as a result of their natural curiosity to explore novel environments and interact socially with conspecifics. Although multiple arousal systems in the brain are known to act jointly to promote and maintain wakefulness, it remains unclear whether these systems are similarly engaged during voluntary vs. forced wakefulness. Using c-Fos immunohistochemistry, we compared neuronal responses in rats deprived of sleep for 2 h by gentle sensory stimulation, exploration under social isolation, or exploration with social interaction, and rats under undisturbed control conditions. In many arousal, limbic, and autonomic nuclei examined (e.g., anterior cingulate cortex and locus coeruleus), the two sleep deprivation procedures involving exploration were similarly effective, and both were more effective than sleep deprivation with sensory stimulation, in increasing the number of c-Fos immunoreactive neurons. However, some nuclei (e.g., paraventricular hypothalamic nucleus and select amygdala nuclei) were more responsive to exploration with social interaction, while others (e.g., histaminergic tuberomammillary nucleus) responded more strongly to exploration in social isolation. In the rostral basal forebrain, cholinergic and GABAergic neurons responded preferentially to exploration with social interaction, whereas resident neurons in general responded most strongly to exploration without social interaction. These results indicate that voluntary exploration with/without social interaction is more effective than forced sleep deprivation with gentle sensory stimulation for inducing c-Fos in arousal and limbic/autonomic brain regions, and suggest that these nuclei participate in different aspects of arousal during sustained voluntary wakefulness.

Sleep homeostasis

Research on sleep homeostasis aims to answer the question: how does the brain measure the duration and intensity of previous wakefulness in order to increase the duration and intensity of subsequent sleep? The search of regulatory factors has identified a number of potential molecules that increase their concentration in waking and decrease it during sleep. These factors regulate many physiological functions, including energy metabolism, neural plasticity and immune functions and one molecule may participate in the regulation of all these functions. The method to study regulation of sleep homeostasis is experimental prolongation of waking, which is used also to address the question of physiological purpose of sleep: prolonging wakefulness provokes symptoms that tell us what goes wrong during lack of sleep. The interpretation of the role of each identified factor in the regulation of sleep/sleep homeostasis reflects the theoretical background concept of the research. Presently three main concepts are being actively studied: the energy (depletion) hypothesis, the neural plasticity hypothesis and the (immune) defense hypothesis.

Histamine release in the basal forebrain mediates cortical activation through cholinergic neurons

The basal forebrain (BF) is a key structure in regulating both cortical activity and sleep homeostasis. It receives input from all ascending arousal systems and is particularly highly innervated by histaminergic neurons. Previous studies clearly point to a role for histamine as a wake-promoting substance in the BF. We used in vivo microdialysis and pharmacological treatments in rats to study which electroencephalogram (EEG) spectral properties are associated with histamine-induced wakefulness and whether this wakefulness is followed by increased sleep and increased EEG delta power during sleep. We also investigated which BF neurons mediate histamine-induced cortical activation. Extracellular BF histamine levels rose immediately and remained constant throughout a 6 h period of sleep deprivation, returning to baseline levels immediately afterward. During the spontaneous sleep-wake cycle, we observed a strong correlation between wakefulness and extracellular histamine concentrations in the BF, which was unaffected by the time of day. The perfusion of histamine into the BF increased wakefulness and cortical activity without inducing recovery sleep. The perfusion of a histamine receptor 1 antagonist into the BF decreased both wakefulness and cortical activity. Lesioning the BF cholinergic neurons abolished these effects. Together, these results show that activation of the cholinergic BF by histamine is important in sustaining a high level of cortical activation, and that a lack of activation of the cholinergic BF by histamine may be important in initiating and maintaining nonrapid eye movement sleep. The level of histamine release is tightly connected to behavioral state, but conveys no information about sleep pressure.