Propofol stimulates noradrenalin-inhibited neurons in the ventrolateral preoptic nucleus by reducing GABAergic inhibition

The interaction between orexin, sleep deprivation and Alzheimer's disease: Unveiling an Emerging Connection

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by progressive cognitive decline and memory loss. Sleep-wake disorders are an extremely predominant and often disabling aspect of AD. Ox is vital in maintaining the sleep-wake cycle and promoting wakefulness. Dysfunction of Ox signaling has been associated with sleep disorders such as narcolepsy. In AD patients, the increase in cerebrospinal fluid Ox levels is related to parallel sleep deterioration. The relationship between AD and sleep disturbances has gained increasing attention due to their potential bidirectional influence. Disruptions in sleep patterns are commonly observed in AD patients, leading researchers to investigate the possible involvement of Ox in sleep disturbances characteristic of the disease. This review article explores the role of the Ox system in AD, and the intricate relationship between AD and sleep, highlighting the potential mechanisms, impact on disease pathology, and therapeutic interventions to improve sleep quality in affected individuals.

Genderspezifische Unterschiede in der Anästhesie und Schmerzbehandlung – eine Übersicht

Frauen und Männer unterscheiden sich in zahlreichen anästhesierelevanten Aspekten. Hierzu zählen nicht nur die Vorerkrankungen, sondern auch geschlechtsspezifische Unterschiede in der Pharmakodynamik und -kinetik verschiedener Medikamente. Hinzu kommen die unterschiedlichen und zyklusabhängigen Einflüsse der weiblichen Sexualhormone. Diese Übersichtsarbeit soll einen Einblick in die geschlechtsspezifischen Unterschiede in der Anästhesie und Schmerzbehandlung geben.

Understanding the Neural Mechanisms of General Anesthesia from Interaction with Sleep-Wake State: A Decade of Discovery

The development of cutting-edge techniques to study specific brain regions and neural circuits that regulate sleep-wake brain states and general anesthesia (GA), has increased our understanding of these states that exhibit similar neurophysiologic traits. This review summarizes current knowledge focusing on cell subtypes and neural circuits that control wakefulness, rapid eye movement (REM) sleep, non-REM sleep, and GA. We also review novel insights into their interactions and raise unresolved questions and challenges in this field. Comparisons of the overlapping neural substrates of sleep-wake and GA regulation will help us to understand sleep-wake transitions and how anesthetics cause reversible loss of consciousness. SIGNIFICANCE STATEMENT: General anesthesia (GA), sharing numerous neurophysiologic traits with the process of natural sleep, is administered to millions of surgical patients annually. In the past decade, studies exploring the neural mechanisms underlying sleep-wake and GA have advanced our understanding of their interactions and how anesthetics cause reversible loss of consciousness. Pharmacotherapies targeting the neural substrates associated with sleep-wake and GA regulations have significance for clinical practice in GA and sleep medicine.

Orexin neurons inhibit sleep to promote arousal

Humans and animals lacking orexin neurons exhibit daytime sleepiness, sleep attacks, and state instability. While the circuit basis by which orexin neurons contribute to consolidated wakefulness remains unclear, existing models posit that orexin neurons provide their wake-stabilizing influence by exerting excitatory tone on other brain arousal nodes. Here we show using in vivo optogenetics, in vitro optogenetic-based circuit mapping, and single-cell transcriptomics that orexin neurons also contribute to arousal maintenance through indirect inhibition of sleep-promoting neurons of the ventrolateral preoptic nucleus. Activation of this subcortical circuit rapidly drives wakefulness from sleep by differentially modulating the activity of ventrolateral preoptic neurons. We further identify and characterize a feedforward circuit through which orexin (and co-released glutamate) acts to indirectly target and inhibit sleep-promoting ventrolateral preoptic neurons to produce arousal. This revealed circuitry provides an alternate framework for understanding how orexin neurons contribute to the maintenance of consolidated wakefulness and stabilize behavioral state.

Preoptic Area Modulation of Arousal in Natural and Drug Induced Unconscious States

The role of the hypothalamic preoptic area (POA) in arousal state regulation has been studied since Constantin von Economo first recognized its importance in the early twentieth century. Over the intervening decades, the POA has been shown to modulate arousal in both natural (sleep and wake) as well as drug-induced (anesthetic-induced unconsciousness) states. While the POA is well known for its role in sleep promotion, populations of wake-promoting neurons within the region have also been identified. However, the complexity and molecular heterogeneity of the POA has made distinguishing these two populations difficult. Though multiple lines of evidence demonstrate that general anesthetics modulate the activity of the POA, the region's heterogeneity has also made it challenging to determine whether the same neurons involved in sleep/wake regulation also modulate arousal in response to general anesthetics. While a number of studies show that sleep-promoting POA neurons are activated by various anesthetics, recent work suggests this is not universal to all arousal-regulating POA neurons. Technical innovations are making it increasingly possible to classify and distinguish the molecular identities of neurons involved in sleep/wake regulation as well as anesthetic-induced unconsciousness. Here, we review the current understanding of the POA's role in arousal state regulation of both natural and drug-induced forms of unconsciousness, including its molecular organization and connectivity to other known sleep and wake promoting regions. Further insights into the molecular identities and connectivity of arousal-regulating POA neurons will be critical in fully understanding how this complex region regulates arousal states.

Sex and gender differences in anesthesia: Relevant also for perioperative safety?

Sex (a biological determination) and gender (a social construct) are not interchangeable terms and both impact perioperative management and patient safety. Sex and gender differences in clinical phenotypes of chronic illnesses and risk factors for perioperative morbidity and mortality are relevant for preoperative evaluation and optimization. Sex-related differences in physiology, as well as in pharmacokinetics and pharmacodynamics of anesthetic drugs may influence the anesthesia plan, the management of pain, postoperative recovery, adverse effects, patient satisfaction, and outcomes. Further studies are needed to characterize outcome differences between men and women in non-cardiac, cardiac, and transplantation surgery in order to individualize perioperative management and improve patient safety. Transgender patients represent a vulnerable population who need special perioperative care. Gender balance increases team performance and may improve perioperative outcomes.

Activation of Preoptic Tachykinin 1 Neurons Promotes Wakefulness over Sleep and Volatile Anesthetic-Induced Unconsciousness

Endogenous sleep and general anesthesia are distinct states that share similar traits. Of particular interest to neuroscience is the loss of consciousness that accompanies both states. Multiple lines of evidence demonstrate that general anesthetics can co-opt the neural circuits regulating arousal to produce unconsciousness. However, controversy remains as to whether the neural circuits and, more specifically, the same neurons shaping sleep and wakefulness actually do influence the anesthetic state in vivo. Hypothalamic preoptic area (POA) neurons are intimately involved in modulating spontaneous and anesthetic-induced changes in arousal. Nevertheless, recent work suggests that POA GABAergic or glutamatergic neurons capable of regulating endogenous sleep fail to influence the onset or dissipation of anesthesia. We hypothesized that the POA's broad neuronal diversity could mask convergent roles of a subset of neurons in regulating both arousal and anesthesia. Contrary to a previously published report, we show that chemogenetic activation of POA Tac1 neurons obliterates both non-rapid eye movement (NREM) and rapid eye movement (REM) sleep, strongly consolidating the waking state for hours, even during a period of elevated sleep drive. Moreover, chemogenetic activation of Tac1 POA neurons stabilizes the wake state against both isoflurane- and sevoflurane-induced unconsciousness. Tac1-activated mice display a partial resistance to entering isoflurane anesthesia and a more pronounced ability to exit both isoflurane- and sevoflurane-induced unconscious states. We conclude that POA Tac1 neurons can potently reinforce arousal both against endogenous and drug-induced unconscious states. POA Tac1 neurons thus add causal support for the involvement of arousal-regulating systems in the state of general anesthesia.

Neuropeptide S promotes wakefulness through the inhibition of sleep-promoting ventrolateral preoptic nucleus neurons

STUDY OBJECTIVES

The regulation of sleep-wake cycles is crucial for the brain's health and cognitive skills. Among the various substances known to control behavioral states, intraventricular injection of neuropeptide S (NPS) has already been shown to promote wakefulness. However, the NPS signaling pathway remains elusive. In this study, we characterized the effects of NPS in the ventrolateral preoptic nucleus (VLPO) of the hypothalamus, one of the major brain structures regulating non-rapid eye movement (NREM) sleep.

METHODS

We combined polysomnographic recordings, vascular reactivity, and patch-clamp recordings in mice VLPO to determine the NPS mode of action.

RESULTS

We demonstrated that a local infusion of NPS bilaterally into the anterior hypothalamus (which includes the VLPO) significantly increases awakening and specifically decreases NREM sleep. Furthermore, we established that NPS application on acute brain slices induces strong and reversible tetrodotoxin (TTX)-sensitive constriction of blood vessels in the VLPO. This effect strongly suggests that the local neuronal network is downregulated in the presence of NPS. At the cellular level, we revealed by electrophysiological recordings and in situ hybridization that NPSR mRNAs are only expressed by non-Gal local GABAergic neurons, which are depolarized by the application of NPS. Simultaneously, we showed that NPS hyperpolarizes sleep-promoting neurons, which is associated with an increased frequency in their spontaneous IPSC inputs.

CONCLUSION

Altogether, our data reveal that NPS controls local neuronal activity in the VLPO. Following the depolarization of local GABAergic neurons, NPS indirectly provokes feed-forward inhibition onto sleep-promoting neurons, which translates into a decrease in NREM sleep to favor arousal.

Propofol decreases the excitability of cholinergic neurons in mouse basal forebrain via GABAA receptors

Propofol is an intravenous anesthetic that can active γ-aminobutyric acid A (GABAA) receptors and generate sedative-hypnotic effects. Propofol has been widely applied clinically to achieve sedation comparable to sleep in humans. The basal forebrain (BF) is a brain region that plays an important role in sleep-wake regulation. Previous studies suggest that propofol affects the sleep-wake circuit via the BF; however, the mechanism remains elusive. In the current study we investigated the effects of propofol on the inherent properties of cholinergic neurons and their ability to convert excitatory inputs into spikes in mouse BF slices using whole-cell patch clamp recordings. Bath application of propofol (10 μM) significantly elevated the threshold potentials (Vts), decreased the number of spikes in response to a depolarizing current injection, and augmented the inter-spike intervals (ISIs), energy barrier (Vts-Vrs), and absolute refractory periods (ARPs). These effects were eliminated by co-application of a GABAA receptor antagonist picrotoxin (50 μM). Altogether, our results reveal that propofol decreases the excitability of cholinergic neurons in mouse BF via GABAA receptors.

Propofol-sparing effect of different concentrations of dexmedetomidine : Comparison of gender differences

Background

The pharmacodynamics of propofol are closely linked to gender. Dexmedetomidine can decrease propofol needs during propofol anesthesia. The aim of this study was to compare the gender differences on the calculated effect site median effective concentration (EC₅₀) of propofol for loss of consciousness (LOC) after pretreatment with different concentrations of dexmedetomidine.

Methods

In this study 60 male and 60 female patients were randomly allocated to receive dexmedetomidine at target plasma concentrations of 0.0 ng/ml (0.0 group), 0.4 ng/ml (0.4 group), 0.6 ng/ml (0.6 group) and 0.8 ng/ml (0.8 group). Propofol was administered after dexmedetomidine had been intravenously infused for 15 min. The propofol infusion was targeted to provide an initial effect-site concentration of 1.0 μg/ml, followed by increments by 0.2 μg/ml when the effect-site concentration and target concentration of propofol were in equilibrium until LOC was established, where LOC was defined by the observer’s assessment of alertness/sedation scale (OAA/S) score < 2.

Results

The calculated effect-site EC₅₀ of propofol LOC was higher in males than in females in the 0.0, 0.4, 0.6, and 0.8 groups (2.43 vs. 2.17, 1.99 vs. 1.82, 1.72 vs. 1.56 and 1.50 vs. 1.32 μg/ml, respectively, all p < 0.05). The hypnotic interaction between dexmedetomidine and propofol could be described with an additive model of pharmacodynamic interaction.

Conclusion

Gender significantly influenced the calculated effect-site EC₅₀ of propofol for LOC after pretreatment with different concentrations of intravenous dexmedetomidine. It was concluded that an additive interaction could describe the results seen. Thus, gender has to be considered when these drugs are co-administered.

GABAergic ventrolateral pre‑optic nucleus neurons are involved in the mediation of the anesthetic hypnosis induced by propofol

Intravenous anesthetics have been used clinically to induce unconsciousness for seventeen decades, however the mechanism of anesthetic-induced unconsciousness remains to be fully elucidated. It has previously been demonstrated that anesthetics exert sedative effects by acting on endogenous sleep-arousal circuits. However, few studies focus on the ventrolateral pre-optic (VLPO) to locus coeruleus (LC) sleep-arousal pathway. The present study aimed to investigate if VLPO is involved in unconsciousness induced by propofol. The present study additionally investigated if the inhibitory effect of propofol on LC neurons was mediated by activating VLPO neurons. Microinjection, target lesion and extracellular single-unit recordings were used to study the role of the VLPO-LC pathway in propofol anesthesia. The results demonstrated that GABAA agonist (THIP) or GABAA antagonist (gabazine) microinjections into VLPO altered the time of loss of righting reflex and the time of recovery of righting reflex. Furthermore, propofol suppressed the spontaneous firing activity of LC noradrenergic neurons. There was no significant difference observed in firing activity between VLPO sham lesion and VLPO lesion rats. The findings indicate that VLPO neurons are important in propofol-induced unconsciousness, however are unlikely to contribute to the inhibitory effect of propofol on LC spontaneous firing activity.

Histaminergic H1 and H2 Receptors Mediate the Effects of Propofol on the Noradrenalin-Inhibited Neurons in Rat Ventrolateral Preoptic Nucleus

The ventrolateral preoptic nucleus is a sleep-promoting nucleus located in the basal forebrain. A commonly used intravenous anesthetic, propofol, had been reported to induce sleep spindles and augment the firing rate of neurons in ventrolateral preoptic nucleus, but the underlining mechanism is yet to be known. By using patch clamp recording on neuron in acute brain slice, present study tested if histaminergic H1 and H2 receptors play a role in the effect of propofol on the noradrenalin-inhibited neurons in ventrolateral preoptic nucleus. We found that the firing rate of noradrenalin-inhibited neurons were significantly augmented by propofol; the frequency of inhibitory postsynaptic currents of noradrenalin-inhibited neuron were evidently attenuated by propofol; such inhibition effect was suppressed by histamine; and both triprolidine (antagonist for H1 histamine receptor) and ranitidine (antagonist for H2 histamine receptor) were able to increase the inhibition rate of propofol in presence of histamine. Present study demonstrated that propofol-induced inhibition of inhibitory postsynaptic currents on noradrenalin-inhibited neurons were mediated by histaminergic H1 and H2 receptors.

Cellular and neurochemical basis of sleep stages in the thalamocortical network

The link between the combined action of neuromodulators in the brain and global brain states remains a mystery. In this study, using biophysically realistic models of the thalamocortical network, we identified the critical intrinsic and synaptic mechanisms, associated with the putative action of acetylcholine (ACh), GABA and monoamines, which lead to transitions between primary brain vigilance states (waking, non-rapid eye movement sleep [NREM] and REM sleep) within an ultradian cycle. Using ECoG recordings from humans and LFP recordings from cats and mice, we found that during NREM sleep the power of spindle and delta oscillations is negatively correlated in humans and positively correlated in animal recordings. We explained this discrepancy by the differences in the relative level of ACh. Overall, our study revealed the critical intrinsic and synaptic mechanisms through which different neuromodulators acting in combination result in characteristic brain EEG rhythms and transitions between sleep stages.

Serotonin differentially modulates excitatory and inhibitory synaptic inputs to putative sleep-promoting neurons of the ventrolateral preoptic nucleus

The role of serotonin (5-HT) in sleep-wake regulation has been a subject of intense debate and remains incompletely understood. In the ventrolateral preoptic nucleus (VLPO), the main structure that triggers non-rapid eye movement (NREM) sleep, putative sleep-promoting (PSP) neurons were shown ex vivo to be either inhibited (Type-1) or excited (Type-2) by 5-HT application. To determine the complex action of this neurotransmitter on PSP neurons, we recorded spontaneous and miniature excitatory and inhibitory postsynaptic currents (sEPSCs, sIPSCs, mEPSCs and mIPSCs) in response to bath application of 5-HT. We established in mouse acute VLPO slices that 5-HT reduces spontaneous and miniature EPSC and IPSC frequencies to Type-1 neurons, whereas 5-HT selectively increases sIPSC and mIPSC frequencies to Type-2 VLPO neurons. We further determined that Type-1 neurons display a lower action potential threshold and a smaller soma size than Type-2 neurons. Finally, single-cell RT-PCR designed to identify the 13 serotonergic receptor subtypes revealed the specific mRNA expression of the 5-HT1A,B,D,F receptors by Type-1 neurons. Furthermore, the 5-HT2A-C,4,7 receptors were found to be equivalently expressed by both neuronal types. Altogether, our results establish that the excitatory and inhibitory inputs to Type-1 and Type-2 VLPO PSP neurons are differentially regulated by 5-HT. Electrophysiological, morphological and molecular differences were also identified between these two neuronal types. Our results provide new insights regarding the orchestration of sleep regulation by 5-HT release, and strongly suggest that Type-2 neurons could play a permissive role, whereas Type-1 neurons could have an executive role in sleep induction and maintenance.

Astrocyte-derived adenosine is central to the hypnogenic effect of glucose

Sleep has been hypothesised to maintain a close relationship with metabolism. Here we focus on the brain structure that triggers slow-wave sleep, the ventrolateral preoptic nucleus (VLPO), to explore the cellular and molecular signalling pathways recruited by an increase in glucose concentration. We used infrared videomicroscopy on ex vivo brain slices to establish that glucose induces vasodilations specifically in the VLPO via the astrocytic release of adenosine. Real-time detection by in situ purine biosensors further revealed that the adenosine level doubles in response to glucose, and triples during the wakefulness period. Finally, patch-clamp recordings uncovered the depolarizing effect of adenosine and its A2A receptor agonist, CGS-21680, on sleep-promoting VLPO neurons. Altogether, our results provide new insights into the metabolically driven release of adenosine. We hypothesise that adenosine adjusts the local energy supply to local neuronal activity in response to glucose. This pathway could contribute to sleep-wake transition and sleep intensity.