Excitatory Pathways from the Lateral Habenula Enable Propofol-Induced Sedation

Parafacial GABAergic neurone ablation induces behavioural resistance to volatile anaesthetic-induced hypnosis without reducing sleep

BACKGROUND

It is hypothesised that general anaesthetics co-opt the neural circuits regulating endogenous sleep and wakefulness to produce hypnosis. To further probe this association, we focused on the GABAergic neurones of the parafacial zone (PZGABA), a brainstem site capable of promoting non-rapid eye movement sleep.

METHODS

To determine whether PZ neurones are activated by a hypnotic dose of anaesthetics, c-Fos immunohistochemistry was performed. The behavioural and physiological contributions of PZGABA neurones to anaesthetic sensitivity were assessed in mice transfected with an adeno-associated virus (AAV)-driving expression of an mCherry fluorescent control or a caspase that irreversibly eliminates PZGABA neurones. EEG-defined sleep was measured in PZGABA-ablated and mCherry control mice, as was the homeostatic drive to sleep after sleep deprivation.

RESULTS

Consistent with anaesthetic-induced depolarisation, hypnotic doses of isoflurane significantly increased c-Fos expression three-fold in PZGABA neurones compared with oxygen-exposed mice. PZGABA-ablated mice developed significant and durable behavioural resistance to both isoflurane- and sevoflurane-induced hypnosis, with roughly 50% higher likelihood of intact righting than controls. PZGABA-ablated mice emerged from isoflurane significantly faster than mCherry controls with purposeful movements. The degree of anaesthetic resistance was inversely correlated with the number of surviving PZGABA neurones. Despite confirming that PZGABA ablation reduced the potency of two distinct volatile anaesthetics behaviourally, ablation did not alter the amount of endogenous sleep or wakefulness, nor did it affect the homeostatic sleep drive after sleep deprivation, and it did not produce EEG signatures of anaesthetic resistance during isoflurane exposure.

CONCLUSIONS

There was an unexpected dissociation in which destruction of up to 70-80% of PZGABA neurones was sufficient to alter anaesthetic susceptibility behaviourally without causing insomnia or altering sleep pressure. These findings suggest that PZGABA neurones are more critical to drug-induced hypnosis than to the regulation of natural sleep and arousal.

A ventral pallidum-locus coeruleus-lateral hypothalamus pathway modulates brain arousal in freely behaving and isoflurane-anesthetized male mice

Much progress has been made in the understanding of the neural circuits associated with sleep and anesthesia. As an important component among these circuits, the forebrain nuclei have been frequently interrogated. This study demonstrates that glutamatergic (Glu) neurons in the ventral pallidum (VP) enhance activity upon salient stimuli and state-dependently modulate brain arousal and motor activity in freely behaving male mice, and bidirectionally regulate the induction of and emergence from isoflurane general anesthesia. We delineate a neural pathway, consisting of VP Glu neurons→ noradrenergic (NA) neurons in the locus coeruleus (LC)→the lateral hypothalamus (LH) in male mice, controlling the release of noradrenaline in the LH and state-dependently modulated brain arousal, motor activity, and isoflurane general anesthesia through α2a receptors in the LH. Therefore, the VPGlu-LCNA-LH pathway and α2a receptors in the LH may be promising state-dependent regulators of brain arousal in both freely behaving and anesthetized states.

Activation of CaMKII+ neurons in the paramedian raphe nucleus promotes general anesthesia in male mice

General anesthesia (GA) is an essential clinical and surgical adjunct, widely recognized as the result of coordinated networks among numerous brain regions. Anesthetic drugs with different characteristics are associated with distinct networks of brain regions involved in anesthesia. Ciprofol, a novel intravenous anesthetic derived from structural modifications of propofol, has shown promise in clinical applications. However, the specific neuronal circuits and brain regions mediating their actions may differ. Moreover, the core brain regions that mediate the common anesthetic effects of these drugs remain unclear. In this research, we identified a central ensemble of brainstem neurons within the paramedian raphe nucleus (PMnR) using c-Fos staining in mice subjected to GA induced by continuous intravenous infusion of ciprofol and propofol. This neuronal population, primarily composed of CaMKIIa and Gad1-expressing cells, demonstrated consistent activation in reaction to ciprofol. Optogenetic activation of PMnRCaMKIIa neurons induced a GA state under ciprofol pre-administration, while sole activation of PMnRCaMKIIa neurons induced a motionless state in mice. In addition, conditional inhibition of these neurons resulted in resistance to GA. In summary, we highlight the PMnR as a brain target for ciprofol and propofol. Furthermore, CaMKIIa+ neurons in the PMnR emerge as active promoters of the anesthesia process, shedding light on a previously unrecognized key player in the intricate neural network orchestrating GA.

Deficient synaptic neurotransmission results in a persistent sleep-like cortical activity across vigilance states in mice

Growing evidence suggests that brain activity during sleep, as well as sleep regulation, are tightly linked with synaptic function and network excitability at the local and global levels. We previously reported that a mutation in synaptobrevin 2 (Vamp2) in restless (rlss) mice results in a marked increase of wakefulness and suppression of sleep, in particular REM sleep (REMS), as well as increased consolidation of sleep and wakefulness. In this study, using finer-scale in vivo electrophysiology recordings, we report that spontaneous cortical activity in rlss mice during NREM sleep (NREMS) is characterized by an occurrence of abnormally prolonged periods of complete neuronal silence (OFF-periods), often lasting several seconds, similar to the burst suppression pattern typically seen under deep anesthesia. Increased incidence of prolonged network OFF-periods was not specific to NREMS but also present in REMS and wake in rlss mice. Slow-wave activity (SWA) was generally increased in rlss mice relative to controls, while higher frequencies, including theta-frequency activity, were decreased, further resulting in diminished differences between vigilance states. The relative increase in SWA after sleep deprivation was attenuated in rlss mice, suggesting either that rlss mice experience persistently elevated sleep pressure or, alternatively, that the intrusion of sleep-like patterns of activity into the wake state attenuates the accumulation of sleep drive. We propose that a deficit in global synaptic neurotransmitter release leads to "state inertia," reflected in an abnormal propensity of brain networks to enter and remain in a persistent "default state" resembling coma or deep anesthesia.

Striatal neurones expressing D1 dopamine receptors modulate consciousness in sevoflurane but not propofol anaesthesia in mice

BACKGROUND

Sevoflurane and propofol are the most widely used inhaled and i.v. general anaesthetics, respectively. The mechanisms by which sevoflurane and propofol induce loss of consciousness (LOC) remain unclear. Recent studies implicate the brain dopaminergic circuit in anaesthetic-induced LOC and the cortical-striatal-thalamic-cortical loop in decoding consciousness. We investigated the contribution of the dorsal striatum, which is a critical interface between the dopaminergic circuit and the cortical-striatal-thalamic-cortical loop, in sevoflurane and propofol anaesthesia.

METHODS

Electroencephalography and electromyography recordings and righting reflex tests were used to determine LOC and recovery of consciousness (ROC). The activity of D1 dopamine receptor (D1R)-expressing neurones in the dorsal striatum was monitored using fibre photometry, and regulated using optogenetic and chemogenetic methods in D1R-Cre mice.

RESULTS

Population activities of striatal D1R neurones began to decrease before LOC and gradually returned after ROC. During sevoflurane anaesthesia, optogenetic activation of striatal D1R neurones induced ROC at cortical and behavioural levels in steady-state anaesthesia and promoted cortical activation in deep burst suppression anaesthesia. Chemogenetic inhibition of striatal D1R neurones accelerated induction (from 242.0 [46.1] to 194.0 [26.9] s; P=0.010) and delayed emergence (from 93.5 [21.2] to 133.5 [33.9] s; P=0.005), whereas chemogenetic activation of these neurones accelerated emergence (from 107 [23.7] to 81.3 [16.1] s; P=0.011). However, neither optogenetic nor chemogenetic manipulation of striatal D1R neurones had any effects on propofol anaesthesia.

CONCLUSIONS

Striatal D1R neurones modulate the state of consciousness in sevoflurane anaesthesia, but not in propofol anaesthesia.

Activation of Glutamatergic Neurons in the Supramammillary Nucleus Promotes the Recovery of Consciousness under Sevoflurane Anesthesia

Volatile anesthetics have been widely applied during surgery, but the potential mechanisms by which they influence loss of consciousness (LOC), anesthesia maintenance, and recovery of consciousness (ROC) from anesthesia remain largely unknown. Recent studies have suggested that anesthesia-induced unconsciousness may be due to specific interactions between neural circuits that regulate sleep and wakefulness. Supramammillary (SuM) glutamatergic neurons are essential for sleep-wakefulness regulation. However, whether SuM glutamatergic neurons are involved in the modulation of consciousness under sevoflurane anesthesia is unclear. Here, it is shown that the activity of SuM glutamatergic neurons decreased prior to sevoflurane-induced LOC and gradually increased following ROC. Selective lesioning of SuM glutamatergic neurons promoted the induction of and delayed emergence from sevoflurane anesthesia and increased sevoflurane sensitivity. In addition, optogenetic stimulation of SuM glutamatergic neurons or the SuM-MS projection promoted behavioral arousal and cortical activation under steady-state sevoflurane anesthesia (SSSA) and reduced the depth of anesthesia and caused cortical arousal under sevoflurane-induced burst-suppression conditions. Collectively, these results provide compelling evidence that SuM glutamatergic neurons contribute to regulating states of consciousness under sevoflurane anesthesia.

The regulation of glutamatergic nervous system in sleep-wake states and general anesthesia

The sleep-wake states and general anesthesia share many neurophysiological similarities, as both involve reversible changes in consciousness and modulation of brain activity. This paper reviews the role of glutamatergic neurons, the brain's primary excitatory neurons, in regulating sleep-wake states and general anesthesia. We discuss the involvement of glutamatergic neurons across various brain regions, including the brainstem, basal forebrain, thalamus, hypothalamus, and cortex, highlighting their contributions to physiological sleep-wake and anesthesia modulation. Recent advancements in techniques such as optogenetics, chemogenetics, and neural tracing have enhanced our understanding of these neurons' functions. Understanding these mechanisms can lead to improved therapeutic strategies for sleep disorders and more precise anesthetic practices, providing new avenues for clinical intervention.

Regulation of states of consciousness by supramammillary nucleus glutamatergic neurones during sevoflurane anaesthesia in mice

BACKGROUND

The supramammillary nucleus (SuM), located in the caudal hypothalamus, includes wake-promoting glutamatergic neurones. Their potential role in regulating states of consciousness during general anaesthesia remains unknown.

METHODS

We used in vivo fibre photometry, c-Fos staining, chemogenetic and optogenetic manipulations, and electroencephalography/electromyography to explore the roles of glutamatergic SuM neurones (SuMVglut2 neurones) at different phases of sevoflurane anaesthesia. Rabies-mediated retrograde and anterograde tract tracing were used to investigate the monosynaptic glutamatergic inputs from the medial septum (MS) to SuM. Their roles in sevoflurane anaesthesia were investigated by in vivo fibre photometry and optogenetic manipulations.

RESULTS

The population activity of SuMVglut2 neurones decreased at loss of consciousness but increased during recovery of consciousness under sevoflurane anaesthesia. Their activity also decreased during suppression but increased during bursts in sevoflurane-induced burst-suppression oscillations. Activating SuMVglut2 neurones chemogenetically or optogenetically decreased sensitivity to sevoflurane, induced behavioural arousal and cortical activation during continuous steady-state anaesthesia, and stable burst-suppression oscillations under sevoflurane. In contrast, chemogenetic or optogenetic inhibition of SuMVglut2 neurones increased sensitivity to sevoflurane or intensified cortical inhibition during sevoflurane anaesthesia. Retrograde and anterograde tracing verified monosynaptic projections from MSVglut2 neurones to SuMVglut2 neurones. The activity of MSVglut2 SuM terminals increased during loss of consciousness but recovered during recovery of consciousness. Optogenetic activation or inhibition of MSVglut2 SuM terminals induced cortical activation or inhibition, respectively, during sevoflurane anaesthesia.

CONCLUSIONS

Activation of SuMVglut2 neurones or the glutamatergic septo-supramammillary circuit induces behavioural arousal and cortical activation during sevoflurane anaesthesia.

Neural Network Mechanisms Underlying General Anesthesia: Cortical and Subcortical Nuclei

General anesthesia plays a significant role in modern medicine. However, the precise mechanism of general anesthesia remains unclear, posing a key scientific challenge in anesthesiology. Advances in neuroscience techniques have enabled targeted manipulation of specific neural circuits and the capture of brain-wide neural activity at high resolution. These advances hold promise for elucidating the intricate mechanisms of action of general anesthetics. This review aims to summarize our current understanding of the role of cortical and subcortical nuclei in modulating general anesthesia, providing new evidence of cortico-cortical and thalamocortical networks in relation to anesthesia and consciousness. These insights contribute to a comprehensive understanding of the neural network mechanisms underlying general anesthesia.

Effects of propofol on the electrophysiological properties of glutamatergic neurons in the ventrolateral medulla of mice

BACKGROUND

Propofol, a commonly used intravenous anesthetic, is associated with various respiratory adverse events, most notably different degrees of respiratory depression, which pose significant concerns for patient safety. Respiration is a fundamental behavior, with the initiation of breathing in mammals dependent on neuronal activity in the lower brainstem. Previous studies have suggested that propofol-induced respiratory depression might be associated with glutamatergic neurons in the pre-Bötzinger complex (preBötC), though the precise mechanisms are not well understood. In this study, we classify glutamatergic neurons in the brainstem preBötC using whole-cell patch-clamp techniques and investigate the effects of propofol on the electrophysiological properties of these neurons. Our findings aim to shed light on the mechanisms of propofol-induced respiratory depression and provide new experimental insights.

METHODS

We first employed electrophysiological techniques to classify glutamatergic neurons within the preBötC as Type-1 or Type-2. Following this classification, we applied varying concentrations of propofol through bath application to examine its effects on the electrophysiological properties of each type of glutamatergic neuron.

RESULTS

We found that Type-1 neurons exhibited a longer latency in excitation, while Type-2 neurons did not show this delayed excitation. On this basis, we further observed that bath application of propofol at concentrations of 5 μM and 10 μM shortened the latency period of Type-1 glutamatergic neurons but did not affect the latency period of Type-2 glutamatergic neurons.

CONCLUSION

Our study focuses on the glutamatergic neurons in the preBötC of adult mice. It introduces a novel method for classifying these neurons and reveals how propofol affects the activity of the two different types of glutamatergic neurons within the preBötC. These findings contribute to understanding the cellular basis of propofol-induced respiratory depression.

A hypothalamus-lateral periaqueductal gray GABAergic neural projection facilitates arousal following sevoflurane anesthesia in mice

BACKGROUND

The lateral hypothalamus (LHA) is an evolutionarily conserved structure that regulates basic functions of an organism, particularly wakefulness. To clarify the function of LHAGABA neurons and their projections on regulating general anesthesia is crucial for understanding the excitatory and inhibitory effects of anesthetics on the brain. The aim of the present study is to investigate whether LHAGABA neurons play either an inhibitory or a facilitatory role in sevoflurane-induced anesthetic arousal regulation.

METHODS

We used fiber photometry and immunofluorescence staining to monitor changes in neuronal activity during sevoflurane anesthesia. Opto-/chemogenetic modulations were employed to study the effect of neurocircuit modulations during the anesthesia. Anterograde tracing was used to identify a GABAergic projection from the LHA to a periaqueductal gray (PAG) subregion.

RESULTS

c-Fos staining showed that LHAGABA activity was inhibited by induction of sevoflurane anesthesia. Anterograde tracing revealed that LHAGABA neurons project to multiple arousal-associated brain areas, with the lateral periaqueductal gray (LPAG) being one of the dense projection areas. Optogenetic experiments showed that activation of LHAGABA neurons and their downstream target LPAG reduced the burst suppression ratio (BSR) during continuous sevoflurane anesthesia. Chemogenetic experiments showed that activation of LHAGABA and its projection to LPAG neurons prolonged the anesthetic induction time and promoted wakefulness.

CONCLUSIONS

In summary, we show that an inhibitory projection from LHAGABA to LPAGGABA neurons promotes arousal from sevoflurane-induced loss of consciousness, suggesting a complex control of wakefulness through intimate interactions between long-range connections.

A potentiation of REM sleep-active neurons in the lateral habenula may be responsible for the sleep disturbance in depression

Psychiatric disorders with dysfunction of the lateral habenula (LHb) show sleep disturbance, especially a disinhibition of rapid eye movement (REM) sleep in major depression. However, the role of LHb in physiological sleep control and how LHb contributes to sleep disturbance in major depression remain elusive. Here, we found that functional manipulations of LHb glutamatergic neurons bidirectionally modulated both non-REM (NREM) sleep and REM sleep. Activity recording revealed heterogeneous activity patterns of LHb neurons across sleep/wakefulness cycles, but LHb neurons were preferentially active during REM sleep. Using an activity-dependent tagging method, we selectively labeled a population of REM sleep-active LHb neurons and demonstrated that these neurons specifically promoted REM sleep. Neural circuit studies showed that LHb neurons regulated REM sleep via projections to the ventral tegmental area but not to the rostromedial tegmental nucleus. Furthermore, we found that the increased REM sleep in a depression mouse model was associated with a potentiation of REM sleep-active LHb neurons, including an increased proportion, elevated spike firing, and altered activity mode. Importantly, inhibition of REM sleep-active LHb neurons not only attenuated the increased REM sleep but also alleviated depressive-like behaviors in a depression mouse model. Thus, our results demonstrated that REM sleep-active LHb neurons selectively promoted REM sleep, and a potentiation of these neurons contributed to depression-associated sleep disturbance.

A REM-active basal ganglia circuit that regulates anxiety

Rapid eye movement (REM) sleep has been hypothesized to promote emotional resilience, but any neuronal circuits mediating this have not been identified. We find that in mice, somatostatin (Som) neurons in the entopeduncular nucleus (EPSom)/internal globus pallidus are predominantly active during REM sleep. This unique REM activity is both necessary and sufficient for maintaining normal REM sleep. Inhibiting or exciting EPSom neurons reduced or increased REM sleep duration, respectively. Activation of the sole downstream target of EPSom neurons, Vglut2 cells in the lateral habenula (LHb), increased sleep via the ventral tegmental area (VTA). A simple chemogenetic scheme to periodically inhibit the LHb over 4 days selectively removed a significant amount of cumulative REM sleep. Chronic, but not acute, REM reduction correlated with mice becoming anxious and more sensitive to aversive stimuli. Therefore, we suggest that cumulative REM sleep, in part generated by the EP → LHb → VTA circuit identified here, could contribute to stabilizing reactions to habitual aversive stimuli.

Myelin modulates the process of isoflurane anesthesia through the regulation of neural activity

AIMS

The mechanism underlying the reversible unconsciousness induced by general anesthetics (GA) remains unclear. Recent studies revealed the critical roles of myelin and oligodendrocytes (OLs) in higher functions of the brain. However, it is unknown whether myelin actively participates in the regulation of GA. The aim of this study is to investigate the roles and possible mechanisms of myelin in the regulation of consciousness alterations induced by isoflurane anesthesia.

METHODS

First, demyelination models for the entire brain and specific neural nuclei were established to investigate the potential role of myelination in the regulation of GA, as well as its possible regional specificity. c-Fos staining was then performed on the demyelinated nuclei to verify the impact of myelin loss on neuronal activity. Finally, the activity of neurons during isoflurane anesthesia in demyelinated mice was recorded by optical fiber photometric calcium signal. The related behavioral indicators and EEG were recorded and analyzed.

RESULTS

A prolonged emergence time was observed from isoflurane anesthesia in demyelinated mice, which suggested the involvement of myelin in regulating GA. The demyelination in distinct nuclei by LPC further clarified the region-specific roles of isoflurane anesthesia regulation by myelin. The effect of demyelination on isoflurane anesthesia in the certain nucleus was consistent with that in neurons towards isoflurane anesthesia. Finally, we found that the mechanism of myelin in the modulation of isoflurane anesthesia is possibly through the regulation of neuronal activity.

CONCLUSIONS

In brief, myelin in the distinct neural nucleus plays an essential role in regulating the process of isoflurane anesthesia. The possible mechanism of myelin in the regulation of isoflurane anesthesia is neuronal activity modification by myelin integrity during GA. Our findings enhanced the comprehension of myelin function, and offered a fresh perspective for investigating the neural mechanisms of GA.

Glutamatergic neurons of piriform cortex delay induction of inhalational general anesthesia

Since their clinical application in the 1840s, the greatest mystery surrounding general anesthesia (GA) is how different kinds of general anesthetics cause reversible unconsciousness, and the precise neural mechanisms underlying the processes. Over past years, although many studies revealed the roles of cortex, thalamus, brainstem, especially the sleep-wake circuits in GA-induced loss of consciousness (LOC),the full picture of the neural circuit mechanism of GA is still largely unknown. Recent studies have focused on the importance of other brain regions. Here, we report that the activity of glutamatergic (Glu) neurons in the piriform cortex (PC), a critical brain region for odor encoding, began to increase during the LOC of GA and gradually recovered after recovery of consciousness. Chemical lesions of the anterior PC (APC) neurons accelerated the induction time of isoflurane anesthesia. Chemogenetic and optogenetic activation of APCGlu neurons prolonged isoflurane and sevoflurane anesthesia induction, whereas APCGlu neuron inhibition displayed the opposite effects. Moreover, the modification of APCGlu neurons did not affect the induction or emergence time of propofol GA. In addition, odor processing may be partially involved in the induction of isoflurane and sevoflurane GA regulated by APCGlu neurons. In conclusion, our findings reveal a critical role of APCGlu neurons in inhalational GA induction.

Anesthetized animal experiments for neuroscience research

Brain research has progressed with anesthetized animal experiments for a long time. Recent progress in research techniques allows us to measure neuronal activity in awake animals combined with behavioral tasks. The trends became more prominent in the last decade. This new research style triggers the paradigm shift in the research of brain science, and new insights into brain function have been revealed. It is reasonable to consider that awake animal experiments are more ideal for understanding naturalistic brain function than anesthetized ones. However, the anesthetized animal experiment still has advantages in some experiments. To take advantage of the anesthetized animal experiments, it is important to understand the mechanism of anesthesia and carefully handle the obtained data. In this minireview, we will shortly summarize the molecular mechanism of anesthesia in animal experiments, a recent understanding of the neuronal activities in a sensory system in the anesthetized animal brain, and consider the advantages and disadvantages of the anesthetized and awake animal experiments. This discussion will help us to use both research conditions in the proper manner.

Effect of propofol and ciprofol on the euphoric reaction in patients with painless gastroscopy: A prospective randomized controlled trial

Objective

To explore the effects of propofol and ciprofol on patient euphoric reactions during sedation in patients undergoing gastroscopy and to investigate potential factors that may influence euphoric reactions in patients.

Methods

A total of 217 patients were randomly divided into two groups: the propofol group (P group, n = 109) and the ciprofol group (C group, n = 108). The patients in the P group were given 2 mg/kg propofol, and those in the C group were given 0.5 mg/kg ciprofol. The patients were assessed using the Addiction Research Center Inventory-Chinese Version (ARCI-CV) to measure euphoric reactions at three time points: preexamination, 30 min after awakening, and 1 week after examination. Anxiety, depression, and sleep status were evaluated using appropriate scales at admission and 1 week after the examination. The dream rate, sedative effects, vital sign dynamics, and adverse reactions were documented during the sedation process.

Results

After 30 min of awakening, the P group and C group showed no statistically significant differences in the mean morphine-benzedrine group (MBG) score (8.84 vs. 9.09, P > 0.05), dream rate (42.2 % vs. 40.7 %, P > 0.05), or MBG score one week after the examination (7.04 vs. 7.05, P > 0.05). The regression analysis revealed that sex, dream status, Alcohol Use Disorders Identification Test (AUDIT) score, and examination time had notable impacts on the MBG-30 min score. No statistically significant differences were observed in sedative effects, anxiety, depression, or sleep status between the two groups (P > 0.05). The incidence of injection pain and severe hypotension was significantly lower in the C group (P < 0.05), and hemodynamics and SpO2 were more stable during sedation (P < 0.05).

Conclusion

There was no significant difference between propofol and ciprofol in terms of euphoria experienced by patients after sedation in patients undergoing gastroscopy. Ciprofol has demonstrated addictive potential similar to that of propofol, warranting careful attention to its addictive potential during clinical application.

Comparative brain-wide mapping of ketamine- and isoflurane-activated nuclei and functional networks in the mouse brain

Ketamine (KET) and isoflurane (ISO) are two widely used general anesthetics, yet their distinct and shared neurophysiological mechanisms remain elusive. In this study, we conducted a comparative analysis of the effects of KET and ISO on c-Fos expression across the mouse brain, utilizing hierarchical clustering and c-Fos-based functional network analysis to evaluate the responses of individual brain regions to each anesthetic. Our findings reveal that KET activates a wide range of brain regions, notably in the cortical and subcortical nuclei involved in sensory, motor, emotional, and reward processing, with the temporal association areas (TEa) as a strong hub, suggesting a top-down mechanism affecting consciousness by primarily targeting higher order cortical networks. In contrast, ISO predominantly influences brain regions in the hypothalamus, impacting neuroendocrine control, autonomic function, and homeostasis, with the locus coeruleus (LC) as a connector hub, indicating a bottom-up mechanism in anesthetic-induced unconsciousness. KET and ISO both activate brain areas involved in sensory processing, memory and cognition, reward and motivation, as well as autonomic and homeostatic control, highlighting their shared effects on various neural pathways. In conclusion, our results highlight the distinct but overlapping effects of KET and ISO, enriching our understanding of the mechanisms underlying general anesthesia.

One node among many: sevoflurane-induced hypnosis and the challenge of an integrative network-level view of anaesthetic action

Building on their known ability to influence sleep and arousal, Li and colleagues show that modulating the activity of glutamatergic pedunculopontine tegmental neurones also alters sevoflurane-induced hypnosis. This finding adds support for the shared sleep-anaesthesia circuit hypothesis. However, the expanding recognition of many neuronal clusters capable of modulating anaesthetic hypnosis raises the question of how disparate and anatomically distant sites ultimately interact to coordinate global changes in the state of the brain. Understanding how these individual sites work in concert to disrupt cognition and behaviour is the next challenge for anaesthetic mechanisms research.

Microglia facilitate and stabilize the response to general anesthesia via modulating the neuronal network in a brain region-specific manner

General anesthesia leads to a loss of consciousness and an unrousable state in patients. Although general anesthetics are widely used in clinical practice, their underlying mechanisms remain elusive. The potential involvement of nonneuronal cells is unknown. Microglia are important immune cells in the central nervous system (CNS) that play critical roles in CNS function and dysfunction. We unintentionally observed delayed anesthesia induction and early anesthesia emergence in microglia-depleted mice. We found that microglial depletion differentially regulates neuronal activities by suppressing the neuronal network of anesthesia-activated brain regions and activating emergence-activated brain regions. Thus, microglia facilitate and stabilize the anesthesia status. This influence is not mediated by dendritic spine plasticity. Instead, it relies on the activation of microglial P2Y12 and subsequent calcium influx, which facilitates the general anesthesia response. Together, we elucidate the regulatory role of microglia in general anesthesia, extending our knowledge of how nonneuronal cells modulate neuronal activities.

Entorhinal cortical delta oscillations drive memory consolidation

Long-term memories are formed by creating stable memory representations via memory consolidation, which mainly occurs during sleep following the encoding of labile memories in the hippocampus during waking. The entorhinal cortex (EC) has intricate connections with the hippocampus, but its role in memory consolidation is largely unknown. Using cell-type- and input-specific in vivo neural activity recordings, here we show that the temporoammonic pathway neurons in the EC, which directly innervate the output area of the hippocampus, exhibit potent oscillatory activities during anesthesia and sleep. Using in vivo individual and populational neuronal activity recordings, we demonstrate that a subpopulation of the temporoammonic pathway neurons, which we termed sleep cells, generate delta oscillations via hyperpolarization-activated cyclic-nucleotide-gated channels during sleep. The blockade of these oscillations significantly impaired the consolidation of hippocampus-dependent memory. Together, our findings uncover a key driver of delta oscillations and memory consolidation that are found in the EC.

A clock-dependent brake for rhythmic arousal in the dorsomedial hypothalamus

Circadian clocks generate rhythms of arousal, but the underlying molecular and cellular mechanisms remain unclear. In Drosophila, the clock output molecule WIDE AWAKE (WAKE) labels rhythmic neural networks and cyclically regulates sleep and arousal. Here, we show, in a male mouse model, that mWAKE/ANKFN1 labels a subpopulation of dorsomedial hypothalamus (DMH) neurons involved in rhythmic arousal and acts in the DMH to reduce arousal at night. In vivo Ca2+ imaging reveals elevated DMHmWAKE activity during wakefulness and rapid eye movement (REM) sleep, while patch-clamp recordings show that DMHmWAKE neurons fire more frequently at night. Chemogenetic manipulations demonstrate that DMHmWAKE neurons are necessary and sufficient for arousal. Single-cell profiling coupled with optogenetic activation experiments suggest that GABAergic DMHmWAKE neurons promote arousal. Surprisingly, our data suggest that mWAKE acts as a clock-dependent brake on arousal during the night, when mice are normally active. mWAKE levels peak at night under clock control, and loss of mWAKE leads to hyperarousal and greater DMHmWAKE neuronal excitability specifically at night. These results suggest that the clock does not solely promote arousal during an animal's active period, but instead uses opposing processes to produce appropriate levels of arousal in a time-dependent manner.

Somatostatin neurons in prefrontal cortex initiate sleep-preparatory behavior and sleep via the preoptic and lateral hypothalamus

The prefrontal cortex (PFC) enables mammals to respond to situations, including internal states, with appropriate actions. One such internal state could be 'tiredness'. Here, using activity tagging in the mouse PFC, we identified particularly excitable, fast-spiking, somatostatin-expressing, γ-aminobutyric acid (GABA) (PFCSst-GABA) cells that responded to sleep deprivation. These cells projected to the lateral preoptic (LPO) hypothalamus and the lateral hypothalamus (LH). Stimulating PFCSst-GABA terminals in the LPO hypothalamus caused sleep-preparatory behavior (nesting, elevated theta power and elevated temperature), and stimulating PFCSst-GABA terminals in the LH mimicked recovery sleep (non-rapid eye-movement sleep with higher delta power and lower body temperature). PFCSst-GABA terminals had enhanced activity during nesting and sleep, inducing inhibitory postsynaptic currents on diverse cells in the LPO hypothalamus and the LH. The PFC also might feature in deciding sleep location in the absence of excessive fatigue. These findings suggest that the PFC instructs the hypothalamus to ensure that optimal sleep takes place in a suitable place.

Effects of propofol and sevoflurane on social and anxiety-related behaviours in sleep-deprived rats

BACKGROUND

Sleep disorders can profoundly affect neurological function. We investigated changes in social and anxiety-related brain functional connectivity induced by sleep deprivation, and the potential therapeutic effects of the general anaesthetics propofol and sevoflurane in rats.

METHODS

Twelve-week-old male Sprague-Dawley rats were subjected to sleep deprivation for 20 h per day (from 14:00 to 10:00 the next day) for 4 consecutive weeks. They were free from sleep deprivation for the remaining 4 h during which they received propofol (40 mg kg-1 i.p.) or sevoflurane (2% for 2 h) per day or no treatment. These cohorts were instrumented for EEG/EMG recordings on days 2, 14, and 28. Different cohorts were used for open field and three-chambered social behavioural tests, functional MRI, nuclear magnetic resonance spectroscopy, and positron emission tomography imaging 48 h after 4 weeks of sleep deprivation.

RESULTS

Propofol protected against sleep deprivation-induced anxiety behaviours with more time (44.7 [8.9] s vs 24.2 [4.1] s for the sleep-deprivation controls; P<0.001) spent in the central area of the open field test and improved social preference index by 30% (all P<0.01). Compared with the sleep-deprived rats, propofol treatment enhanced overall functional connectivity by 74% (P<0.05) and overall glucose metabolism by 30% (P<0.01), and improved glutamate kinetics by 20% (P<0.05). In contrast, these effects were not found after sevoflurane treatment.

CONCLUSIONS

Unlike sevoflurane, propofol reduced sleep deprivation-induced social and anxiety-related behaviours. Propofol might be superior to sevoflurane for patients with sleep disorders who receive anaesthesia, which should be studied in clinical studies.

Bright light treatment counteracts stress-induced sleep alterations in mice, via a visual circuit related to the rostromedial tegmental nucleus

Light in the environment greatly impacts a variety of brain functions, including sleep. Clinical evidence suggests that bright light treatment has a beneficial effect on stress-related diseases. Although stress can alter sleep patterns, the effect of bright light treatment on stress-induced sleep alterations and the underlying mechanism are poorly understood. Here, we show that bright light treatment reduces the increase in nonrapid eye movement (NREM) sleep induced by chronic stress through a di-synaptic visual circuit consisting of the thalamic ventral lateral geniculate nucleus and intergeniculate leaflet (vLGN/IGL), lateral habenula (LHb), and rostromedial tegmental nucleus (RMTg). Specifically, chronic stress causes a marked increase in NREM sleep duration and a complementary decrease in wakefulness time in mice. Specific activation of RMTg-projecting LHb neurons or activation of RMTg neurons receiving direct LHb inputs mimics the effects of chronic stress on sleep patterns, while inhibition of RMTg-projecting LHb neurons or RMTg neurons receiving direct LHb inputs reduces the NREM sleep-promoting effects of chronic stress. Importantly, we demonstrate that bright light treatment reduces the NREM sleep-promoting effects of chronic stress through the vLGN/IGL-LHb-RMTg pathway. Together, our results provide a circuit mechanism underlying the effects of bright light treatment on sleep alterations induced by chronic stress.

P2X7 Receptor in microglia contributes to propofol-induced unconsciousness by regulating synaptic plasticity in mice

Propofol infusion is processed through the wake-sleep cycle in neural connections, and the ionotropic purine type 2X7 receptor (P2X7R) is a nonspecific cation channel implicated in sleep regulation and synaptic plasticity through its regulation of electric activity in the brain. Here, we explored the potential roles of P2X7R of microglia in propofol-induced unconsciousness. Propofol induced loss of the righting reflex in male C57BL/6 wild-type mice and increased spectral power of the slow wave and delta wave of the medial prefrontal cortex (mPFC), all of which were reversed with P2X7R antagonist A-740003 and strengthened with P2X7R agonist Bz-ATP. Propofol increased the P2X7R expression level and P2X7R immunoreactivity with microglia in the mPFC, induced mild synaptic injury and increased GABA release in the mPFC, and these changes were less severe when treated with A-740003 and were more obvious when treated with Bz-ATP. Electrophysiological approaches showed that propofol induced a decreased frequency of sEPSCs and an increased frequency of sIPSCs, A-740003 decrease frequency of sEPSCs and sIPSCs and Bz-ATP increase frequency of sEPSCs and sIPSCs under propofol anesthesia. These findings indicated that P2X7R in microglia regulates synaptic plasticity and may contribute to propofol-mediated unconsciousness.

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.

Corticotropin-releasing factor neurones in the paraventricular nucleus of the hypothalamus modulate isoflurane anaesthesia and its responses to acute stress in mice

BACKGROUND

Corticotropin-releasing factor (CRF) neurones in the paraventricular nucleus (PVN) of the hypothalamus (PVN^CRF neurones) can promote wakefulness and are activated under anaesthesia. However, whether these neurones contribute to anaesthetic effects is unknown.

METHODS

With a combination of chemogenetic and molecular approaches, we examined the roles of PVN^CRF neurones in isoflurane anaesthesia in mice and further explored the underlying cellular and molecular mechanisms.

RESULTS

PVN neurones exhibited increased Fos expression during isoflurane anaesthesia (mean [standard deviation], 218 [69.3] vs 21.3 [7.3]; P<0.001), and ∼75% were PVN^CRF neurones. Chemogenetic inhibition of PVN^CRF neurones facilitated emergence from isoflurane anaesthesia (11.7 [1.1] vs 13.9 [1.2] min; P=0.001), whereas chemogenetic activation of these neurones delayed emergence from isoflurane anaesthesia (16.9 [1.2] vs 13.9 [1.3] min; P=0.002). Isoflurane exposure increased CRF protein expression in PVN (4.0 [0.1] vs 2.2 [0.3], respectively; P<0.001). Knockdown of CRF in PVN^CRF neurones mimicked the effects of chemogenetic inhibition of PVN^CRF neurones in facilitating emergence (9.6 [1.1] vs 13.0 [1.4] min; P=0.003) and also abolished the effects of chemogenetic activation of PVN^CRF neurones on delaying emergence from isoflurane anaesthesia (10.3 [1.3] vs 16.0 [2.6] min; P<0.001). Acute, but not chronic, stress delayed emergence from isoflurane anaesthesia (15.5 [1.5] vs 13.0 [1.4] min; P=0.004). This effect was reversed by chemogenetic inhibition of PVN^CRF neurones (11.7 [1.6] vs 14.7 [1.4] min; P=0.001) or knockdown of CRF in PVN^CRF neurones (12.3 [1.5] vs 15.3 [1.6] min; P=0.002).

CONCLUSIONS

CRF neurones in the PVN of the hypothalamus neurones modulate isoflurane anaesthesia and acute stress effects on anaesthesia through CRF signalling.

In Vivo Photoadduction of Anesthetic Ligands in Mouse Brain Markedly Extends Sedation and Hypnosis

Photoaffinity ligands are best known as tools used to identify the specific binding sites of drugs to their molecular targets. However, photoaffinity ligands have the potential to further define critical neuroanatomic targets of drug action. In the brains of WT male mice, we demonstrate the feasibility of using photoaffinity ligands in vivo to prolong anesthesia via targeted yet spatially restricted photoadduction of azi-m-propofol (aziPm), a photoreactive analog of the general anesthetic propofol. Systemic administration of aziPm with bilateral near-ultraviolet photoadduction in the rostral pons, at the border of the parabrachial nucleus and locus coeruleus, produced a 20-fold increase in the duration of sedative and hypnotic effects compared with control mice without UV illumination. Photoadduction that missed the parabrachial-coerulean complex also failed to extend the sedative or hypnotic actions of aziPm and was indistinguishable from nonadducted controls. Paralleling the prolonged behavioral and EEG consequences of on target in vivo photoadduction, we conducted electrophysiologic recordings in rostral pontine brain slices. Using neurons within the locus coeruleus to further highlight the cellular consequences of irreversible aziPm binding, we demonstrate transient slowing of spontaneous action potentials with a brief bath application of aziPm that becomes irreversible on photoadduction. Together, these findings suggest that photochemistry-based strategies are a viable new approach for probing CNS physiology and pathophysiology.SIGNIFICANCE STATEMENT Photoaffinity ligands are drugs capable of light-induced irreversible binding, which have unexploited potential to identify the neuroanatomic sites of drug action. We systemically administer a centrally acting anesthetic photoaffinity ligand in mice, conduct localized photoillumination within the brain to covalently adduct the drug at its in vivo sites of action, and successfully enrich irreversible drug binding within a restricted 250 µm radius. When photoadduction encompassed the pontine parabrachial-coerulean complex, anesthetic sedation and hypnosis was prolonged 20-fold, thus illustrating the power of in vivo photochemistry to help unravel neuronal mechanisms of drug action.

Paraventricular thalamus controls consciousness transitions during propofol anaesthesia in mice

BACKGROUND

The neuronal mechanisms underlying propofol-induced modulation of consciousness are poorly understood. Neuroimaging studies suggest a potential role for non-specific thalamic nuclei in propofol-induced loss of consciousness. We investigated the contribution of the paraventricular thalamus (PVT), a midline thalamic nucleus that has been implicated in arousal control and general anaesthesia with inhaled anaesthetics, to loss and recovery of consciousness during propofol anaesthesia.

METHODS

Polysomnographic recordings and righting reflex test were used to determine the transitions of loss and recovery of righting reflex, used as a measure of consciousness in mice, during propofol anaesthesia in mice under conditions mimicking clinical propofol administration. PVT neuronal activities were monitored using fibre photometry and regulated using optogenetic and chemogenetic methods.

RESULTS

Population activities of PVT glutamatergic neurones began to decrease before propofol-induced loss of consciousness and rapidly increased to a peak at the onset of recovery of consciousness. Chemogenetic inhibition of PVT calretinin-expressing (PVT^CR) neurones shortened onset (from 176 [35] to 127 [26] s; P=0.001) and prolonged return (from 1568 [611] to 3126 [1616] s; P=0.002) of righting reflex. Conversely, chemogenetic activation of PVT^CR neurones exerted opposite effects. Furthermore, optogenetic silencing of PVT^CR neurones accelerated transitions to loss of consciousness (from 205 [35] to 158 [44] s; P=0.027) and slowed transitions to recovery of consciousness (from 230 [78] to 370 [99] s; P=0.041). During a steady period of unconsciousness maintained with continuous propofol infusion, brief optical activation of PVT^CR neurones restored cortical activity and arousal with a latency of about 5 s.

CONCLUSIONS

The paraventricular thalamus contributes to the control of consciousness transitions in propofol anaesthesia in mice. This provides a potential neuroanatomical target for controlling consciousness to reduce anaesthetic dose requirements and side effects.

Orexinergic innervations at GABAergic neurons of the lateral habenula mediates the anesthetic potency of sevoflurane

AIMS

The circuitry mechanism associated with anesthesia-induced unconsciousness is still largely unknown. It has been reported that orexinergic neurons of the lateral hypothalamus (LHA) facilitate the emergence from anesthesia through their neuronal projections to the arousal-promoting brain areas. However, the lateral habenula (LHb), as one of the orexin downstream targets, is known for its anesthesia-promoting effect. Therefore, the current study aimed to explore whether and how the orexinergic projections from the LHA to the LHb have a regulatory effect on unconsciousness induced by general anesthesia.

METHODS

We applied optogenetic, chemogenetic, or pharmacological approaches to regulate the orexinergic^LHA-LHb pathway. Fiber photometry was used to assess neuronal activity. Loss or recovery of the righting reflex was used to evaluate the induction or emergence time of general anesthesia. The burst-suppression ratio and electroencephalography spectra were used to measure the anesthetic depth.

RESULTS

We found that activation of the orexinergic^LHA-LHb pathway promoted emergence and reduced anesthetic depth during sevoflurane anesthesia. Surprisingly, the arousal-promoting effect of the orexinergic^LHA-LHb pathway was mediated by excitation of glutamate decarboxylase (GAD2)-expressing neurons, but not glutamatergic neurons in the LHb.

CONCLUSION

The orexinergic^LHA-LHb pathway facilitates emergence from sevoflurane anesthesia, and this effect was mediated by OxR2 in GAD2-expressing GABA neurons.

Divergent Neural Activity in the VLPO During Anesthesia and Sleep

The invention of general anesthesia (GA) represents a significant advance in modern clinical practices. However, the exact mechanisms of GA are not entirely understood. Because of the multitude of similarities between GA and sleep, one intriguing hypothesis is that anesthesia may engage the sleep-wake regulation circuits. Here, using fiber photometry and micro-endoscopic imaging of Ca²⁺ signals at both population and single-cell levels, it investigates how various anesthetics modulate the neural activity in the ventrolateral preoptic nucleus (vLPO), a brain region essential for the initiation of sleep. It is found that different anesthetics primarily induced suppression of neural activity and tended to recruit a similar group of vLPO neurons; however, each anesthetic caused comparable modulations of both wake-active and sleep-active neurons. These results demonstrate that anesthesia creates a different state of neural activity in the vLPO than during natural sleep, suggesting that anesthesia may not engage the same vLPO circuits for sleep generation.

A Role for Thalamic Projection GABAergic Neurons in Circadian Responses to Light

The thalamus is an important hub for sensory information and participates in sensory perception, regulation of attention, arousal and sleep. These functions are executed primarily by glutamatergic thalamocortical neurons that extend axons to the cortex and initiate cortico-thalamocortical connectional loops. However, the thalamus also contains projection GABAergic neurons that do not extend axons toward the cortex. Here, we have harnessed recent insight into the development of the intergeniculate leaflet (IGL) and the ventral lateral geniculate nucleus (LGv) to specifically target and manipulate thalamic projection GABAergic neurons in female and male mice. Our results show that thalamic GABAergic neurons of the IGL and LGv receive retinal input from diverse classes of retinal ganglion cells (RGCs) but not from the M1 intrinsically photosensitive retinal ganglion cell (ipRGC) type. We describe the synergistic role of the photoreceptor melanopsin and the thalamic neurons of the IGL/LGv in circadian entrainment to dim light. We identify a requirement for the thalamic IGL/LGv neurons in the rapid changes in vigilance states associated with circadian light transitions.SIGNIFICANCE STATEMENT The intergeniculate leaflet (IGL) and ventral lateral geniculate nucleus (LGv) are part of the extended circadian system and mediate some nonimage-forming visual functions. Here, we show that each of these structures has a thalamic (dorsal) as well as prethalamic (ventral) developmental origin. We map the retinal input to thalamus-derived cells in the IGL/LGv complex and discover that while RGC input is dominant, this is not likely to originate from M1ipRGCs. We implicate thalamic cells in the IGL/LGv in vigilance state transitions at circadian light changes and in overt behavioral entrainment to dim light, the latter exacerbated by concomitant loss of melanopsin expression.

Remimazolam Tosylate Combined with Low-Dose Propofol Improves Sedation and Safety in Hysteroscopy

Background

Propofol is widely used for sedation of hysteroscopy. It can cause injection pain, respiratory depression, and hypotension. Remimazolam is a novel ultra-short-acting benzodiazepine. Clinical practice has found that the use of remimazolam alone often leads to body movement during hysteroscopy, which decreases the safety and comfort. Here this study is to investigate whether remimazolam combined with low-dose propofol can improve the sedation effect and safety of hysteroscopy.

Patients and Methods

In this prospective, randomized, parallel-controlled trial, women (18 to 60 years) undergoing hysteroscopy were randomly assigned to receive propofol (Group P), remimazolam tosylate (Group R), or remimazolam tosylate plus propofol (Group RP). Intraoperative sedation depth was kept at the bispectral index (BIS) value of 40-60. 6 μg/kg alfentanil was used for analgesic before sedation. Intraoperative low pulse oxygen saturation (SpO2), body movement, injection pain, mean arterial pressure (MAP), heart rate (HR), and postoperative recovery time, dizziness, nausea and vomiting were recorded and compared.

Results

From February to July 2022, 193 patients were recruited and randomly assigned to group P (n=64), group R (n=64), or group RP (n=65). There was no significant inter-group difference of the intraoperative BIS values. The incidence of low SpO2, injection pain, hypotension, and postoperative dizziness in group RP were less than that in group P, and had no significant difference from group R. The incidence of body movement in group RP was less than that in group R, and had no significant difference from group P. Postoperative recovery time of group RP was shorter than that of the other two groups. No significant inter-group difference in bradycardia, nausea and vomiting was observed.

Conclusion

Remimazolam tosylate combined with low dose of propofol improved sedation and safety in hysteroscopy, and may be a more ideal sedative method for hysteroscopy.

Claustrum modulates behavioral sensitivity and EEG activity of propofol anesthesia

AIMS

The claustrum has long been regarded as a vital center for conscious control. Electrical stimulation or damage to the claustrum can result in decreased awareness or loss of consciousness, suggesting that the claustrum may be a target for the action of general anesthetics. This study aimed to determine the role of the claustrum in propofol anesthesia.

METHODS

We first applied a fiber photometry calcium signal recording system to record the claustral neuronal activity during the entire process of propofol anesthesia. Chemogenetic activation of claustral neurones was then performed to verify their role in anesthesia. Finally, muscimol (GABAa receptor agonist) and gabazine (GABAa receptor antagonist) were microinjected into the claustrum to determine whether their GABAa receptors were involved in modulating propofol anesthesia. EEG and behavioral indicators, such as anesthetic sensitivity and efficacy, were recorded and analyzed.

RESULTS

An evident anesthesia-related change in claustrum neuronal activity was suppressed during propofol-induced unconsciousness and restored following recovery from anesthesia. Chemogenetic activation of claustrum neurons results in attenuated propofol sensitivity, a shorter anesthesia duration, and an EEG shift toward wakefulness. Manipulation of GABAa receptors in the claustrum showed bidirectional control of propofol sensitivity, as activation decreases anesthesia efficiency while inactivation augments it. Additionally, inhibiting claustrum GABAa receptors increases cortical EEG slow waves.

CONCLUSIONS

Claustrum neurones and their GABAa receptors are implicated in the modulation of propofol anesthesia in both behavioral and EEG assessments. Our findings create scope to reveal the brain targets of anesthetic action further and add to the existing evidence on the consciousness-modulating role of the claustrum.

Hypoxia-triggered O-GlcNAcylation in the brain drives the glutamate-glutamine cycle and reduces sensitivity to sevoflurane in mice

BACKGROUND

Hypersensitivity to general anaesthetics predicts adverse postoperative outcomes in patients. Hypoxia exerts extensive pathophysiological effects on the brain; however, whether hypoxia influences sevoflurane sensitivity and its underlying mechanisms remain poorly understood.

METHODS

Mice were acclimated to hypoxia (oxygen 10% for 8 h day^-1) for 28 days and anaesthetised with sevoflurane; the effective concentrations for 50% of the animals (EC₅₀) showing loss of righting reflex (LORR) and loss of tail-pinch withdrawal response (LTWR) were determined. Positron emission tomography-computed tomography, O-glycoproteomics, seahorse analysis, carbon-13 tracing, site-specific mutagenesis, and electrophysiological techniques were performed to explore the underlying mechanisms.

RESULTS

Compared with the control group, the hypoxia-acclimated mice required higher concentrations of sevoflurane to present LORR and LTWR (EC50_LORR: 1.61 [0.03]% vs 1.46 [0.04]%, P<0.01; EC50_LTWR: 2.46 [0.14]% vs 2.22 [0.06]%, P<0.01). Hypoxia-induced reduction in sevoflurane sensitivity was correlated with elevation of protein O-linked N-acetylglucosamine (O-GlcNAc) modification in brain, especially in the thalamus, and could be abolished by 6-diazo-5-oxo-l-norleucine, a glutamine fructose-6-phosphate amidotransferase inhibitor, and mimicked by thiamet-G, a selective O-GlcNAcase inhibitor. Mechanistically, O-GlcNAcylation drives de novo synthesis of glutamine from glucose in astrocytes and promotes the glutamate-glutamine cycle, partially via glycolytic flux and activation of glutamine synthetase.

CONCLUSIONS

Intermittent hypoxia exposure decreased mouse sensitivity to sevoflurane anaesthesia through enhanced O-GlcNAc-dependent modulation of the glutamate-glutamine cycle in the brain.

NMDA Receptors in the Lateral Preoptic Hypothalamus Are Essential for Sustaining NREM and REM Sleep

The lateral preoptic (LPO) hypothalamus is a center for NREM and REM sleep induction and NREM sleep homeostasis. Although LPO is needed for NREM sleep, we found that calcium signals were, surprisingly, highest in REM sleep. Furthermore, and equally surprising, NMDA receptors in LPO were the main drivers of excitation. Deleting the NMDA receptor GluN1 subunit from LPO abolished calcium signals in all cells and produced insomnia. Mice of both sexes had highly fragmented NREM sleep-wake patterns and could not generate conventionally classified REM sleep. The sleep phenotype produced by deleting NMDA receptors depended on where in the hypothalamus the receptors were deleted. Deleting receptors from the anterior hypothalamic area (AHA) did not influence sleep-wake states. The sleep fragmentation originated from NMDA receptors on GABA neurons in LPO. Sleep fragmentation could be transiently overcome with sleeping medication (zolpidem) or sedatives (dexmedetomidine; Dex). By contrast, fragmentation persisted under high sleep pressure produced by sleep deprivation (SD), mice had a high propensity to sleep but woke up. By analyzing changes in δ power, sleep homeostasis (also referred to as "sleep drive") remained intact after NMDA receptor ablation. We suggest NMDA glutamate receptor activation stabilizes firing of sleep-on neurons and that mechanisms of sleep maintenance differ from that of the sleep drive itself.SIGNIFICANCE STATEMENT Insomnia is a common affliction. Most insomniacs feel that they do not get enough sleep, but in fact, often have good amounts of sleep. Their sleep, however, is fragmented, and sufferers wake up feeling unrefreshed. It is unknown how sleep is maintained once initiated. We find that in mice, NMDA-type glutamate receptors in the hypothalamus are the main drivers of excitation and are required for a range of sleep properties: they are, in fact, needed for both sustained NREM sleep periods, and REM sleep generation. When NMDA receptors are selectively reduced from inhibitory preoptic (PO) neurons, mice have normal total amounts of sleep but high sleep-wake fragmentation, providing a model for studying intractable insomnia.

Relevance of sleep and associated structural changes in GBA1 mouse to human rapid eye movement behavior disorder

Rapid eye movement (REM) sleep behaviour disorder (RBD) is a REM parasomnia that often predicts the later occurrence of alpha-synucleinopathies. Variants in the gene encoding for the lysosomal enzyme glucocerebrosidase, GBA, strongly increase the risk of RBD. In a GBA1-mouse model recently shown to mimic prodromal stages of α-synucleinopathy, we now demonstrate striking REM and NREM electroencephalographic sleep abnormalities accompanied by distinct structural changes in the more widespread sleep neurocircuitry.

A Neural Circuit from the Paraventricular Thalamus to the Bed Nucleus of the Stria Terminalis for the Regulation of States of Consciousness during Sevoflurane Anesthesia in Mice

BACKGROUND

The neural circuitry underlying sevoflurane-induced modulation of consciousness is poorly understood. This study hypothesized that the paraventricular thalamus bed nucleus of the stria terminalis pathway plays an important role in regulating states of consciousness during sevoflurane anesthesia.

METHODS

Rabies virus-based transsynaptic tracing techniques were employed to reveal the neural pathway from the paraventricular thalamus to the bed nucleus of the stria terminalis. This study investigated the role of this pathway in sevoflurane anesthesia induction, maintenance, and emergence using chemogenetic and optogenetic methods combined with cortical electroencephalogram recordings. Both male and female mice were used in this study.

RESULTS

Both γ-aminobutyric acid-mediated and glutamatergic neurons in the bed nucleus of the stria terminalis receive paraventricular thalamus glutamatergic projections. Chemogenetic inhibition of paraventricular thalamus glutamatergic neurons prolonged the sevoflurane anesthesia emergence time (mean ± SD, hM4D-clozapine N-oxide vs. mCherry-clozapine N-oxide, 281 ± 88 vs. 172 ± 48 s, P < 0.001, n = 24) and decreased the induction time (101 ± 32 vs. 136 ± 34 s, P = 0.002, n = 24), as well as the EC5 0 for the loss or recovery of the righting reflex under sevoflurane anesthesia (mean [95% CI] for the concentration at which 50% of the mice lost their righting reflex, 1.16 [1.12 to 1.20] vs. 1.49 [1.46 to 1.53] vol%, P < 0.001, n = 20; and for the concentration at which 50% of the mice recovered their righting reflex, 0.95 [0.86 to 1.03] vs. 1.34 [1.29 to 1.40] vol%, P < 0.001, n = 20). Similar results were observed during suppression of the paraventricular thalamus bed nucleus-stria terminalis pathway. Optogenetic activation of this pathway produced the opposite effects. Additionally, transient stimulation of this pathway efficiently induced behavioral arousal during continuous steady-state general anesthesia with sevoflurane and reduced the depth of anesthesia during sevoflurane-induced burst suppression.

CONCLUSIONS

In mice, axonal projections from the paraventricular thalamic neurons to the bed nucleus of the stria terminalis contribute to regulating states of consciousness during sevoflurane anesthesia.

A Comparison of Brain-State Dynamics across Common Anesthetic Agents in Male Sprague-Dawley Rats

Anesthesia is a powerful tool in neuroscientific research, especially in sleep research where it has the experimental advantage of allowing surgical interventions that are ethically problematic in natural sleep. Yet, while it is well documented that different anesthetic agents produce a variety of brain states, and consequently have differential effects on a multitude of neurophysiological factors, these outcomes vary based on dosages, the animal species used, and the pharmacological mechanisms specific to each anesthetic agent. Thus, our aim was to conduct a controlled comparison of spontaneous electrophysiological dynamics at a surgical plane of anesthesia under six common research anesthetics using a ubiquitous animal model, the Sprague-Dawley rat. From this direct comparison, we also evaluated which anesthetic agents may serve as pharmacological proxies for the electrophysiological features and dynamics of unconscious states such as sleep and coma. We found that at a surgical plane, pentobarbital, isoflurane and propofol all produced a continuous pattern of burst-suppression activity, which is a neurophysiological state characteristically observed during coma. In contrast, ketamine-xylazine produced synchronized, slow-oscillatory activity, similar to that observed during slow-wave sleep. Notably, both urethane and chloral hydrate produced the spontaneous, cyclical alternations between forebrain activation (REM-like) and deactivation (non-REM-like) that are similar to those observed during natural sleep. Thus, choice of anesthesia, in conjunction with continuous brain state monitoring, are critical considerations in order to avoid brain-state confounds when conducting neurophysiological experiments.

Identification of Brain Regions Activated by Sevoflurane and Propofol and Regional Changes in Gene Expression

General anesthetics have different efficacies and side effect incidences based on their mechanism of action. However, detailed comparative studies of anesthetics are incomplete. In this study, target brain regions and gene expression changes in these brain regions were determined for sevoflurane and propofol to understand the mechanisms that cause differences among anesthetics. Rats were anesthetized with sevoflurane or propofol for 1 hr, and brain regions with anesthesia-induced changes in neuronal activity were examined by immunohistochemistry and in situ hybridization for c-Fos. Among the identified target brain regions, gene expression analysis was performed in the habenula, the solitary nucleus and the medial vestibular nucleus from laser microdissected samples. Genes altered by sevoflurane and propofol were different and included genes involved in the incidence of postoperative nausea and vomiting and emergence agitation, such as Egr1 and Gad2. GO enrichment analysis showed that the altered genes tended to be evenly distributed in all functional category. The detailed profiles of target brain regions and induced gene expression changes of sevoflurane and propofol in this study will provide a basis for analyzing the effects of each anesthetic agent and the risk of adverse events.

Clinical effects of low-dose esketamine for anaesthesia induction in the elderly: A randomized controlled trial

WHAT IS KNOWN AND OBJECTIVE

Esketamine is an N-methyl-D-aspartic acid (NMDA) receptor antagonist, which has stronger sedative and analgesic effects and fewer adverse events than ketamine. The effects of low-dose esketamine on haemodynamics and postoperative quality of recovery in elderly patients have not been evaluated. To evaluate whether low-dose esketamine can be safely used for anaesthesia induction in the elderly.

METHODS

Eighty elderly patients were selected for unilateral total knee replacement under general anaesthesia from February 2021 to August 2021. Patients were randomly divided into two groups (n = 40): control group (C group) and esketamine group (K group). During induction of anaesthesia, the control group was intravenously injected with normal saline of equal volume, and the esketamine group was intravenously injected with 0.2-mg/kg esketamine. Both groups were induced by etomidate, sufentanil and rocuronium and maintained by combined intravenous and inhaled anaesthesia during operation.

MAIN OUTCOME MEASURES

HR, SBP, DBP, MAP and BIS values were recorded before induction of anaesthesia (T₀ ), immediately before endotracheal intubation (T₁ ), 1min(T₂ ) and 5min(T₃ ) after endotracheal intubation, surgical skin incision (T₄ ), 1min(T₅ ) and 5min(T₆ ) after surgical skin incision.

RESULTS

Compared with the C group, SBP, DBP, MAP, HR and BIS of the K group were significantly higher at T₁ -T₃ (p < 0.05). There were no significant differences in SBP, DBP, MAP, HR and BIS between the two groups at T₄ -T₆ (p > 0.05). Compared with T₀ , SBP, MAP and BIS values of the two groups at T₁ -T₆ were decreased (p < 0.05). DBP of the K group at T₂ was not significantly different from DBP at T₀ (p < 0.05), but DBP of the C group decreased from T₁ to T₆ (p < 0.05). Compared with T₀ , HR in both groups decreased at T₁ , T₃ , T₄ , T₅ and T₆ (p < 0.05). Compared with the C group, the incidence of cough in the K group was significantly lower (p < 0.05); There was no significant difference in the number of myoclonus during induction between the two groups (p > 0.05). Compared with the C group, the number of hypotension episodes in the K group during induction was much smaller (p < 0.05). There were no significant differences in the incidence of hypertension, bradycardia and tachycardia (p > 0.05). There were no significant differences in postoperative recovery quality and incidence of adverse events between the two groups (p > 0.05).

WHAT IS NEW AND CONCLUSION

Low-dose esketamine for anaesthesia induction in the elderly undergoing knee arthroplasty may better maintain the stability of haemodynamics and has no adverse effect on the quality of early recovery after operation.

Central Neural Circuits Orchestrating Thermogenesis, Sleep-Wakefulness States and General Anesthesia States

Great progress has been made in specifically identifying the central neural circuits (CNCs) of the core body temperature (Tcore), sleep-wakefulness states (SWs), and general anesthesia states (GAs), mainly utilizing optogenetic or chemogenetic manipulations. We summarize the neuronal populations and neural pathways of these three CNCs, which gives evidence for the orchestration within these three CNCs, and the integrative regulation of these three CNCs by different environmental light signals. We also outline some transient receptor potential (TRP) channels that function in the CNCs-Tcore and are modulated by some general anesthetics, which makes TRP channels possible targets for addressing the general-anestheticsinduced- hypothermia (GAIH). We suggest this review will provide new orientations for further consummating these CNCs and elucidating the central mechanisms of GAIH.

The role of ventral tegmental area orexinergic afferents in depressive-like behavior in a chronic unpredictable mild stress (CUMS) mouse model

Orexin has been implicated in comorbid diseases of depression, making it a promising target for anti-depression treatment. Although orexin neurons exhibit abnormal activity in depression, the neurocircuit mechanism of orexin remains unclear. As one of the important downstream factors of orexin neurons, the ventral tegmental area (VTA) is considered crucial to the mechanism of depression. However, the role of VTA orexinergic afferents in depression remains unclear. In this study, we applied a combination of opto/chemogenetic and neuropharmacology methods to investigate whether the VTA orexinergic afferents participate in the pathogenesis of depression in a chronic unpredictable mild stress (CUMS) mouse model. We found that c-Fos expression in these VTA-projecting orexin neurons specifically decreased in CUMS-treated mice. Optogenetic and chemogenetic activation of orexin terminals in the VTA significantly reversed depressive behavior. Microinjection of orexin-A, but not orexin-B, into the VTA significantly improved depressive-like behavior. Our study provided direct evidence that the VTA orexinergic afferents participate in the mechanism of depression, and the orexin-1 receptor plays a major role.

Brain Clocks, Sleep, and Mood

The suprachiasmatic nucleus houses the master clock, but the genes which encode the circadian clock components are also expressed throughout the brain. Here, we review how circadian clock transcription factors regulate neuromodulator systems such as histamine, dopamine, and orexin that promote arousal. These circadian transcription factors all lead to repression of the histamine, dopamine, and orexin systems during the sleep period, so ensuring integration with the ecology of the animal. If these transcription factors are deleted or mutated, in addition to the global disturbances in circadian rhythms, this causes a chronic up-regulation of neuromodulators leading to hyperactivity, elevated mood, and reduced sleep, which have been suggested to be states resembling mania.

The inescapable drive to sleep: Overlapping mechanisms of sleep and sedation

[Figure: see text].

Anesthesia in mice activates discrete populations of neurons throughout the brain

The brain undergoes rapid, dramatic, and reversible transitioning between states of wakefulness and unconsciousness during natural sleep and in pathological conditions such as hypoxia, hypotension, and concussion. Transitioning can also be induced pharmacologically using general anesthetic agents. The effect is selective. Mobility, sensory perception, memory formation, and awareness are lost while numerous housekeeping functions persist. How is selective transitioning accomplished? Classically a handful of brainstem and diencephalic "arousal nuclei" have been implicated in driving brain-state transitions on the grounds that their net activity systematically varies with brain state. Here we used transgenic targeted recombination in active populations mice to label neurons active during wakefulness with one reporter and neurons active during pentobarbital-induced general anesthesia with a second, contrasting reporter. We found 'wake-on' and 'anesthesia-on' neurons in widely distributed regions-of-interest, but rarely encountered neurons labeled with both reporters. Nearly all labeled neurons were either wake-on or anesthesia-on. Thus, anesthesia-on neurons are not unique to the few nuclei discovered to date whose activity appears to increase during anesthesia. Rather neuronal populations selectively active during anesthesia are located throughout the brain where they likely play a causative role in transitioning between wakefulness and anesthesia. The widespread neuronal suppression reported in prior comparisons of the awake and anesthetized brain in animal models and noninvasive imaging in humans reflects only net differences. It misses the ubiquitous presence of neurons whose activity increases during anesthesia. The balance in recruitment of anesthesia-on versus wake-on neuronal populations throughout the brain may be a key driver of regional and global vigilance states. [Correction added on September 22, 2021, after first online publication: Due to a typesetting error, the abstract text was cut off. This has been corrected now.].

Identifying c-fos Expression as a Strategy to Investigate the Actions of General Anesthetics on the Central Nervous System

Although general anesthetics have been used in the clinic for more than 170 years, the ways in which they induce amnesia, unconsciousness, analgesia, and immobility remain elusive. Modulations of various neural nuclei and circuits are involved in the actions of general anesthetics. The expression of the immediate-early gene c-fos and its nuclear product, c-fos protein, can be induced by neuronal depolarization; therefore, c-fos staining is commonly used to identify the activated neurons during sleep and/or wakefulness, as well as in various physiological conditions in the central nervous system. Identifying c-fos expression is also a direct and convenient method to explore the effects of general anesthetics on the activity of neural nuclei and circuits. Using c-fos staining, general anesthetics have been found to interact with sleep- and wakefulness-promoting systems throughout the brain, which may explain their ability to induce unconsciousness and emergence from general anesthesia. This review summarizes the actions of general anesthetics on neural nuclei and circuits based on a c-fos expression.

Activation of anterior thalamic reticular nucleus GABAergic neurons promotes arousal from propofol anesthesia in mice

Propofol is widely used for the induction and maintenance of anesthesia, which causes a rapid loss of consciousness. However, the mechanisms underlying the hypnosis effect of propofol are still not fully understood. The thalamic reticular nucleus (TRN) is crucial for regulating wakefulness, sleep rhythm generation, and sleep stability, while the role of TRN in the process of propofol-induced anesthesia is still unknown. Here, we investigated the function of the anterior TRN in propofol general anesthesia. Our results demonstrated that the neural activity of anterior TRN is suppressed during propofol anesthesia, whereas it is robustly activated from anesthesia by recording the calcium signals using fiber photometry technology. The results showed that the activation of anterior TRN neurons by chemogenetic and optogenetic methods shortens the emergency time without changing the induction time. Conversely, chemogenetic or optogenetic inhibition of the TRN neurons leads to a delay in the recovery time. Our study showed that anterior TRN is crucial for behavioral arousal without affecting the induction time of propofol anesthesia.