Sevoflurane depresses neurons in the medial parabrachial nucleus by potentiating postsynaptic GABAA receptors and background potassium channels

Anesthetic Mechanisms: Synergistic Interactions With Lipid Rafts and Voltage-Gated Sodium Channels

Despite successfully utilizing anesthetics for over 150 years, the mechanism of action remains relatively unknown. Recent studies have shown promising results, but due to the complex interactions between anesthetics and their targets, there remains a clear need for further mechanistic research. We know that lipophilicity is directly connected to anesthetic potency since lipid solubility relates to anesthetic partition into the membrane. However, clinically relevant concentrations of anesthetics do not significantly affect lipid bilayers but continue to influence various molecular targets. Lipid rafts are derived from liquid-ordered phases of the plasma membrane that contain increased concentrations of cholesterol and sphingomyelin and act as staging platforms for membrane proteins, including ion channels. Although anesthetics do not perturb membranes at clinically relevant concentrations, they have recently been shown to target lipid rafts. In this review, we summarize current research on how different types of anesthetics-local, inhalational, and intravenous-bind and affect both lipid rafts and voltage-gated sodium channels, one of their major targets, and how those effects synergize to cause anesthesia and analgesia. Local anesthetics block voltage-gated sodium channel pores while also disrupting lipid packing in ordered membranes. Inhalational anesthetics bind to the channel pore and the voltage-sensing domain while causing an increase in the number, size, and diameter of lipid rafts. Intravenous anesthetics bind to the channel primarily at the voltage-sensing domain and the selectivity filter, while causing lipid raft perturbation. These changes in lipid nanodomain structure possibly give proteins access to substrates that have translocated as a result of these structural alterations, resulting in lipid-driven anesthesia. Overall, anesthetics can impact channel activity either through direct interaction with the channel, indirectly through the lipid raft, or both. Together, these result in decreased sodium ion flux into the cell, disrupting action potentials and producing anesthetic effects. However, more research is needed to elucidate the indirect mechanisms associated with channel disruption through the lipid raft, as not much is known about anionic lipid products and their influence over voltage-gated sodium channels. Anesthetics' effect on S-palmitoylation, a promising mechanism for direct and indirect influence over voltage-gated sodium channels, is another auspicious avenue of research. Understanding the mechanisms of different types of anesthetics will allow anesthesiologists greater flexibility and more specificity when treating patients.

Propofol-induced anesthesia involves the direct inhibition of glutamatergic neurons in the lateral hypothalamus

Propofol is the most widely used intravenous general anesthetic; however, the neuronal circuits that mediate its anesthetic effects are still poorly understood. Glutamatergic neurons in the lateral hypothalamus have been reported to be involved in maintenance of arousal and consciousness. Using Vglut2-Cre transgenic mice, we recorded this group of cells specifically and found that propofol can directly inhibit the glutamatergic neurons, and enhance inhibitory synaptic inputs on these cells, thereby reducing neuronal excitability. Through chemogenetic interventions, we found that inhibition of these neurons increased the duration of propofol-induced anesthesia and reduced movement in the animals after the recovery of right reflex. In contrast, activating this group of cells reduced the duration of propofol anesthesia and increased the animals' locomotor activity after the recovery of right reflex. These results suggest that propofol-induced anesthesia involves the inhibition of glutamatergic neurons in the lateral hypothalamus.

Sevoflurane-induced high-frequency oscillations, effective connectivity and intraoperative classification of epileptic brain areas

OBJECTIVE

To determine how sevoflurane anesthesia modulates intraoperative epilepsy biomarkers on electrocorticography, including high-frequency oscillation (HFO) effective connectivity (EC), and to investigate their relation to epileptogenicity and anatomical white matter.

METHODS

We studied eight pediatric drug-resistant focal epilepsy patients who achieved seizure control after invasive monitoring and resective surgery. We visualized spatial distributions of the electrocorticography biomarkers at an oxygen baseline, three time-points while sevoflurane was increasing, and at a plateau of 2 minimum alveolar concentration (MAC) sevoflurane. HFO EC was combined with diffusion-weighted imaging, in dynamic tractography.

RESULTS

Intraoperative HFO EC diffusely increased as a function of sevoflurane concentration, although most in epileptogenic sites (defined as those included in the resection); their ability to classify epileptogenicity was optimized at sevoflurane 2 MAC. HFO EC could be visualized on major white matter tracts, as a function of sevoflurane level.

CONCLUSIONS

The results strengthened the hypothesis that sevoflurane-activated HFO biomarkers may help intraoperatively localize the epileptogenic zone.

SIGNIFICANCE

Our results help characterize how HFOs at non-epileptogenic and epileptogenic networks respond to sevoflurane. It may be warranted to establish a normative HFO atlas incorporating the modifying effects of sevoflurane and major white matter pathways, as critical reference in epilepsy presurgical evaluation.

A Sleep-Specific Midbrain Target for Sevoflurane Anesthesia

Sevoflurane has been the most widely used inhaled anesthetics with a favorable recovery profile; however, the precise mechanisms underlying its anesthetic action are still not completely understood. Here the authors show that sevoflurane activates a cluster of urocortin 1 (UCN1+ )/cocaine- and amphetamine-regulated transcript (CART+ ) neurons in the midbrain involved in its anesthesia. Furthermore, growth hormone secretagogue receptor (GHSR) is highly enriched in sevoflurane-activated UCN1+ /CART+ cells and is necessary for sleep induction. Blockade of GHSR abolishes the excitatory effect of sevoflurane on UCN1+ /CART+ neurons and attenuates its anesthetic effect. Collectively, their data suggest that anesthetic action of sevoflurane necessitates the GHSR activation in midbrain UCN1+ /CART+ neurons, which provides a novel target including the nucleus and receptor in the field of anesthesia.

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.

Glutamatergic neurons in the paraventricular hypothalamic nucleus regulate isoflurane anesthesia in mice

The glutamatergic-mediated excitatory system in the brain is vital for the regulation of sleep-wake and general anesthesia. Specifically, the paraventricular hypothalamic nucleus (PVH), which contains mainly glutamatergic neurons, has been shown to play a critical role in sleep-wake. Here, we sought to explore whether the PVH glutamatergic neurons have an important effect on the process of general anesthesia. We used c-fos staining and in vivo calcium signal recording to observe the activity changes of the PVH glutamatergic neurons during isoflurane anesthesia and found that both c-fos expression in the PVH and the calcium activity of PVH glutamatergic neurons decreased in isoflurane anesthesia and significantly increased during the recovery process. Chemogenetic activation of PVH glutamatergic neurons prolonged induction time and shortened emergence time from anesthesia by decreasing the depth of anesthesia. Using chemogenetic inhibition of PVH glutamatergic neurons under isoflurane anesthesia, we found that inhibition of PVH glutamatergic neurons facilitated the induction process and delayed the emergence accompanied by deepening the depth of anesthesia. Together, these results identify a crucial role for PVH glutamatergic neurons in modulating isoflurane anesthesia.

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.

Study of the Association of Single Nucleotide Polymorphisms in Candidate Genes With Sevoflurane

The susceptibility of different individuals to anesthetics varies widely, and sevoflurane is no exception. We hypothesized that polymorphisms in genes involved in pharmacokinetics and pharmacodynamics may explain this variation. A total of 151 individuals undergoing otorhinolaryngology surgery were included. The influence of genetic polymorphisms on sevoflurane sensitivity were investigated through SNaPshot technology. Individuals carrying KCNK2 rs6686529 G > C, MTRR rs3733784 TT, rs2307116 GG, or rs1801394 AA polymorphisms had a higher sensitivity to the sedative effect of sevoflurane than those without those polymorphisms. The univariate linear regression analysis indicated that MTRR rs3733784 TT, rs2307116 GG, and rs1801394 AA were potentially significant predictors of higher sensitivity to the sedative effect of sevoflurane. Moreover, CYP2E1 rs3813867 G > C and rs2031920 C > T, GABRG1 rs279858 T > C, KCNK3 rs1275988 CC, GRIN2B rs1806201 GG, MTRR rs2307116 G > A, and rs1801394 A > G were associated with a higher sensitivity to the cardiovascular effect of sevoflurane. Our results suggested that 9 single nucleotide polymorphisms in genes involved in metabolizing enzymes, transport proteins, target proteins of sevoflurane and folate metabolism may help to explain individual differences in the susceptibility to the sedative or cardiovascular effect of sevoflurane.

Brain areas modulation in consciousness during sevoflurane anesthesia

Sevoflurane is presently one of the most used inhaled anesthetics worldwide. However, the mechanisms through which sevoflurane acts and the areas of the brain associated with changes in consciousness during anesthesia remain important and complex research questions. Sevoflurane is generally regarded as a volatile anesthetic that blindly targets neuronal (and sometimes astrocyte) GABAA receptors. This review focuses on the brain areas of sevoflurane action and their relation to changes in consciousness during anesthesia. We cover 20 years of history, from the bench to the bedside, and include perspectives on functional magnetic resonance, electroencephalogram, and pharmacological experiments. We review the interactions and neurotransmitters involved in brain circuits during sevoflurane anesthesia, improving the effectiveness and accuracy of sevoflurane's future application and shedding light on the mechanisms behind human consciousness.

Role of the paraventricular nucleus of the hypothalamus in sleep–wake regulation

The paraventricular nucleus of the hypothalamus (PVH) acts as a cohesive functional unit that regulates neuroendocrine and autonomic function, complex behavior, and negative emotions after stress. However, how the PVH integrates arousal with these biological functions has only recently been explored. Clinical reports, combined with neurotoxic lesioning, immunochemistry, neuronal activity recordings, and the polysomnographic analyses of genetically modified animals, have revealed that the PVH is important for the control of wakefulness. Here, we review emerging anatomical and neural mechanisms for sleep–wake regulation in the PVH to support its essential role in the promotion and maintenance of wakefulness.

Bone Marrow-Derived Mesenchymal Stem Cells (BMSCs)-Exosome Carrying MiRNA-312 Inhibits Sevoflurane-Induced Cardiomyocyte Apoptosis Through Activation of Phosphatidylinositol 3-Kinase/Protein Kinase B (PI3K/AKT) Pathway

This study was to explore the mechanism by how exosomes (exo) derived from BMSCs affects cardiomyocyte apoptosis. BMSCs were isolated and incubated with cardiomyocytes while the cardiomyocytes were exposed to sevoflurane or DMSO treatment. Apoptotic cells were calculated and level of apoptosis related proteins was detected by Western blot. Through transfection with microRNA-(miRNA)-312 inhibitor, we evaluated the effect of BMSC-exo on the sevoflurane-induced apoptosis. Sevoflurane significantly inhibited the viability of cardiomyocytes and induced cardiomyocyte apoptosis. Besides, sevoflurane decreased the expression of miR-312 and enhanced Bax expression in cardiomyocytes through restraining the phosphorylation of MAPK/ERK. Treatment with BMSC-exo, however, activated MAPK/ERK signaling by up-regulating miR-312, thereby inhibiting cardiomyocyte apoptosis, promoting cardiomyocyte proliferation, and elevating the level of Bcl-2. In conclusion, BMSC-exo-derived miR-312 inhibits sevoflurane-induced cardiomyocyte apoptosis by activating PI3K/AKT signaling pathway.

Update on the Mechanism and Treatment of Sevoflurane-Induced Postoperative Cognitive Dysfunction

Sevoflurane is one of the most widely used anesthetics for the induction and maintenance of general anesthesia in surgical patients. Sevoflurane treatment may increase the incidence of postoperative cognitive dysfunction (POCD), and patients with POCD exhibit lower cognitive abilities than before the operation. POCD affects the lives of patients and places an additional burden on patients and their families. Understanding the mechanism of sevoflurane-induced POCD may improve prevention and treatment of POCD. In this paper, we review the diagnosis of POCD, introduce animal models of POCD in clinical research, analyze the possible mechanisms of sevoflurane-induced POCD, and summarize advances in treatment for this condition.

Dopaminergic Projections From the Ventral Tegmental Area to the Nucleus Accumbens Modulate Sevoflurane Anesthesia in Mice

The role of the dopaminergic pathway in general anesthesia and its potential mechanisms are still unknown. In this study, we usedc-Fos staining combined with calcium fiber photometry recording to explore the activity of ventral tegmental area (VTA) dopaminergic neurons(VTA-DA) and nucleus accumbens (NAc) neurons during sevoflurane anesthesia. A genetically encoded dopamine (DA) sensor was used to investigate thefunction of the NAc in sevoflurane anesthesia. Chemogenetics and optogenetics were used to explore the role of the VTA-DA in sevofluraneanesthesia. Electroencephalogram (EEG) spectra, time of loss of righting reflex (LORR) and recovery of righting reflex (RORR) were recorded asassessment indicators. We found that VTA-DA and NAc neurons were inhibited during the induction period and were activated during the recoveryperiod of sevoflurane anesthesia. The fluorescence signals of dopamine decreased in the induction of and increased in the emergence from sevoflurane anesthesia.Activation of VTA-DA and the VTA^DA-NAc pathway delayed the induction and facilitated the emergence accompanying with thereduction of delta band and the augmentation of the gamma band. These data demonstrate that VTA-DA neurons play a critical role in modulating sevofluraneanesthesia via the VTA^DA-NAc pathway.

Medial Parabrachial Nucleus Is Essential in Controlling Wakefulness in Rats

Activation of the parabrachial nucleus (PB) in the brainstem induced wakefulness in rats, suggesting which is an important nucleus that controls arousal. However, the sub-regions of PB in regulating sleep-wake cycle is still unclear. Here, we employ chemogenetics and optogenetics strategies and find that activation of the medial part of PB (MPB), but not the lateral part, induces continuous wakefulness for 10 h without sleep rebound in neither sleep amount nor the power spectra. Optogenetic activation of glutamatergic MPB neurons in sleeping rats immediately wake rats mediated by the basal forebrain (BF) and lateral hypothalamus (LH), but not the ventral medial thalamus. Most importantly, chemogenetic inhibition of PB neurons decreases wakefulness for 10 h. Conclusively, these findings indicate that the glutamatergic MPB neurons are essential in controlling wakefulness, and that MPB-BF and MPB-LH pathways are the major neuronal circuits.

Nucleus accumbens neurons expressing dopamine D1 receptors modulate states of consciousness in sevoflurane anesthesia

Although general anesthesia (GA) enables patients to undergo surgery without consciousness, the precise neural mechanisms underlying this phenomenon have yet to be identified. In addition to many studies over the past two decades implicating the thalamus, cortex, brainstem, and conventional sleep-wake circuits in GA-induced loss of consciousness (LOC), some recent studies have begun to highlight the importance of other brain areas as well. Here, we found that population activities of neurons expressing dopamine D1 receptor (D1R) in the nucleus accumbens (NAc), a critical interface between the basal ganglia and limbic system, began to decrease before sevoflurane-induced LOC and gradually returned after recovery of consciousness (ROC). Chemogenetic activation of NAc^D1R neurons delayed induction of and accelerated emergence from sevoflurane GA, whereas chemogenetic inhibition of NAc^D1R neurons exerted opposite effects. Moreover, transient activation of NAc^D1R neurons induced significant cortical activation and behavioral emergence during continuous steady-state GA with sevoflurane or deep anesthesia state with constant and stable burst-suppression oscillations. Taken together, our findings uncover that NAc^D1R neurons modulated states of consciousness associated with sevoflurane GA and may represent an area for targeting GA-induced changes in consciousness and ameliorating related adverse effects.

Lateral Habenula Glutamatergic Neurons Modulate Isoflurane Anesthesia in Mice

Since their introduction in the 1840s, one of the largest mysteries of modern anesthesia are how general anesthetics create the state of reversible loss of consciousness. Increasing researchers have shown that neural pathways that regulate endogenous sleep–wake systems are also involved in general anesthesia. Recently, the Lateral Habenula (LHb) was considered as a hot spot for both natural sleep–wake and propofol-induced sedation; however, the role of the LHb and related pathways in the isoflurane-induced unconsciousness has yet to be identified. Here, using real-time calcium fiber photometry recordings in vivo, we found that isoflurane reversibly increased the activity of LHb glutamatergic neurons. Then, we selectively ablated LHb glutamatergic neurons in Vglut2-cre mice, which caused a longer induction time and less recovery time along with a decrease in delta-band power in mice under isoflurane anesthesia. Furthermore, using a chemogenetic approach to specifically activate LHb glutamatergic neurons shortened the induction time and prolonged the recovery time in mice under isoflurane anesthesia with an increase in delta-band power. In contrast, chemogenetic inhibition of LHb glutamatergic neurons was very similar to the effects of selective lesions of LHb glutamatergic neurons. Finally, optogenetic activation of LHb glutamatergic neurons or the synaptic terminals of LHb glutamatergic neurons in the rostromedial tegmental nucleus (RMTg) produced a hypnosis-promoting effect in isoflurane anesthesia with an increase in slow wave activity. Our results suggest that LHb glutamatergic neurons and pathway are vital in modulating isoflurane anesthesia.