Molecular and neuronal substrates for general anaesthetics

GABAA receptors: structure, function, pharmacology, and related disorders

Background

γ-Aminobutyric acid sub-type A receptors (GABA_ARs) are the most prominent inhibitory neurotransmitter receptors in the CNS. They are a family of ligand-gated ion channel with significant physiological and therapeutic implications.

Main body

GABA_ARs are heteropentamers formed from a selection of 19 subunits: six α (alpha1-6), three β (beta1-3), three γ (gamma1-3), three ρ (rho1-3), and one each of the δ (delta), ε (epsilon), π (pi), and θ (theta) which result in the production of a considerable number of receptor isoforms. Each isoform exhibits distinct pharmacological and physiological properties. However, the majority of GABA_ARs are composed of two α subunits, two β subunits, and one γ subunit arranged as γ2β2α1β2α1 counterclockwise around the center. The mature receptor has a central chloride ion channel gated by GABA neurotransmitter and modulated by a variety of different drugs. Changes in GABA synthesis or release may have a significant effect on normal brain function. Furthermore, The molecular interactions and pharmacological effects caused by drugs are extremely complex. This is due to the structural heterogeneity of the receptors, and the existence of multiple allosteric binding sites as well as a wide range of ligands that can bind to them. Notably, dysfunction of the GABAergic system contributes to the development of several diseases. Therefore, understanding the relationship between GABA_A receptor deficits and CNS disorders thus has a significant impact on the discovery of disease pathogenesis and drug development.

Conclusion

To date, few reviews have discussed GABA_A receptors in detail. Accordingly, this review aims to summarize the current understanding of the structural, physiological, and pharmacological properties of GABA_ARs, as well as shedding light on the most common associated disorders.

Automatic Sensory Predictions: A Review of Predictive Mechanisms in the Brain and Their Link to Conscious Processing

The human brain has the astonishing capacity of integrating streams of sensory information from the environment and forming predictions about future events in an automatic way. Despite being initially developed for visual processing, the bulk of predictive coding research has subsequently focused on auditory processing, with the famous mismatch negativity signal as possibly the most studied signature of a surprise or prediction error (PE) signal. Auditory PEs are present during various consciousness states. Intriguingly, their presence and characteristics have been linked with residual levels of consciousness and return of awareness. In this review we first give an overview of the neural substrates of predictive processes in the auditory modality and their relation to consciousness. Then, we focus on different states of consciousness - wakefulness, sleep, anesthesia, coma, meditation, and hypnosis - and on what mysteries predictive processing has been able to disclose about brain functioning in such states. We review studies investigating how the neural signatures of auditory predictions are modulated by states of reduced or lacking consciousness. As a future outlook, we propose the combination of electrophysiological and computational techniques that will allow investigation of which facets of sensory predictive processes are maintained when consciousness fades away.

Exposure to Sevoflurane, But Not Ketamine, During Early-life Brain Development has Long-Lasting Effects on GABAA Receptor Mediated Inhibitory Neurotransmission

Understanding the different mechanisms associated with different anesthetic targeted receptors is critical towards identifying accurate long-term outcome measures as a result of early-life anesthetic exposure. We examined changes in GABA_A receptor mediated neurotransmission by a predominately GABA_A receptor targeted anesthetic, sevoflurane or a predominately NMDA receptor targeted anesthetic, ketamine. Postnatal day 7 male mice were exposed to sevoflurane or ketamine and examined as adults for changes in inhibitory neurotransmission and its associated change in induced seizure activity. Paired pulse stimulation experiment showed that early-life sevoflurane treated mice had significantly less hippocampal CA1 inhibition later in life. There was significantly increased CA1 excitatory output in the sevoflurane treated group compared to the no sevoflurane treated group after the GABA agonist muscimol. Similar to our previously established data for early-life sevoflurane, here we established early-life ketamine administration resulted in neurodevelopmental behavioral changes later in life. However, muscimol did not produce a significant difference on the excitatory CA1 output between early-life ketamine group and saline group. While sevoflurane treated mice showed significantly higher induced seizure intensities and shorter latency periods to reach seizure intensity stage 5 (Racine score) compared with no sevoflurane treated mice, this phenomenon was not observed in the ketamine vs. saline treated groups. Early-life sevoflurane, but not ketamine, exposure reduced GABAergic inhibition and enhanced seizure activity later in life. The results indicate that early-life exposure to different anesthetics lead to distinct long-term effects and their unique pathways require mechanistic studies to understand induced long-lasting changes in the brain.

Effects of general anesthetics on synaptic transmission and plasticity

General anesthetics depress excitatory and/or enhance inhibitory synaptic transmission principally by modulating the function of glutamatergic or GABAergic synapses, respectively, with relative anesthetic agent-specific mechanisms. Synaptic signaling proteins, including ligand- and voltage-gated ion channels, are targeted by general anesthetics to modulate various synaptic mechanisms, including presynaptic neurotransmitter release, postsynaptic receptor signaling, and dendritic spine dynamics to produce their characteristic acute neurophysiological effects. As synaptic structure and plasticity mediate higher-order functions such as learning and memory, long-term synaptic dysfunction following anesthesia may lead to undesirable neurocognitive consequences depending on the specific anesthetic agent and the vulnerability of the population. Here we review the cellular and molecular mechanisms of transient and persistent general anesthetic alterations of synaptic transmission and plasticity.

Genetic variation of rs12918566 affects GRIN2A expression and is associated with spontaneous movement response during sevoflurane anesthesia induction

N-methyl-D-aspartate (NMDA) receptors mediate excitatory neurotransmission in the nervous system and are preferentially inhibited by general anesthetics such as sevoflurane. Spontaneous movement is a common complication during sevoflurane anesthesia induction and seriously affects operations. In this study, we investigated the relationship between NMDA polymorphisms and spontaneous movement during sevoflurane induction. This prospective clinical study enrolled 393 patients undergoing sevoflurane anesthesia as part of their surgical routine. In the GRIN1, GRIN2A, and GRIN2B genes, 13 polymorphisms that form a heteromeric complex as part of the NMDA receptor were selected using Haploview and genotyped using matrix-assisted laser desorption ionization-time of flight mass spectrometry MassARRAY. Both RNAfold and Genotype-Tissue Expression portals were used to identify gene expression profiles. Our data showed that 35.8% of subjects exhibited spontaneous movement. The GRIN2A rs12918566 polymorphism was associated with spontaneous movement during sevoflurane induction. A logistic regression analysis of additive, dominant, and recessive models indicated a significant association (odds ratio [OR] (95% confidence limit [CI]): 0.58 (0.42-0.80), p = .00086; OR (95% CI): 0.51 (0.31-0.84), p = .0075, and OR (95% CI): 0.47 (0.27-0.81), p = .0060, respectively). After false discovery rate (FDR) correction, the additive model was still significant with a P_FDR =0.010. Bioinformatics demonstrated that the rs12918566 genomic variation affected GRIN2A expression in brain tissue. We also revealed that GRIN2A rs12918566 was significantly associated with spontaneous movement during sevoflurane induction. We believe the NMDA receptor plays an important role in regulating the anesthetic effects of sevoflurane.

Possible influence of neurosteroids in the anxiolytic effects of alpha-casozepine

Alpha-casozepine (α CZP), a tryptic hydrolysate of milk casein is a decapeptide shown to promote sleep and produce anxiolytic or anticonvulsant activity. Intriguingly, studies indicate structural similarities to benzodiazepine (BZD)-like molecules (e.g., diazepam), resulting in positive modulation of γ-aminobutyric acid A type (GABA_A) receptors. However, some unexplained anomalous behaviour of α-CZP includes 1) 1000 times less affinity for BZD site on GABA_A receptor in vitro conditions, whereas in vivo it showed 10-fold increased affinity when compared to diazepam; 2) anxiolytic effects were observed only in stressed conditions and 3) unlike diazepam, it failed to exhibit dependence or habituation. Interestingly, neurosteroids like allopregnanolone or its analogues that are synthesized de novo have both genomic and non-genomic actions. The rapid nongenomic neuronal inhibition of these compounds is mediated by GABA_A receptors through autocrine and paracrine actions. Studies have shown that changes in the levels of neurosteroids during acute (rise) and chronic stress (decreased), consequently, altering the senetivity of GABA_A receptor subunits. Neurosteroids even at low concentration (nanomolar range) potentiate the response of GABA indirectly, while at higher concentrations they directly activate the receptor-channel complex. Interestingly, coadministration of neurosteroids and BZPs has shown not only to prevent the development of tolerance of BZP and augmented recovery from BZP withdrawal anxiety and hyperactivity in mice. The combination also produced synergetic anxiolytic effects. Taken together, the evidence suggests possible implications of neurosteroids in the actions of CZP via BZD receptors. The present hypothesis brings out the possible role of neurosteroids and the various factors that might participate in CZP-induce anxiolytic effects.

Isoflurane Suppresses Hippocampal High-frequency Ripples by Differentially Modulating Pyramidal Neurons and Interneurons in Mice

BACKGROUND

Isoflurane can induce anterograde amnesia. Hippocampal ripples are high-frequency oscillatory events occurring in the local field potentials of cornu ammonis 1 involved in memory processes. The authors hypothesized that isoflurane suppresses hippocampal ripples at a subanesthetic concentration by modulating the excitability of cornu ammonis 1 neurons.

METHODS

The potencies of isoflurane for memory impairment and anesthesia were measured in mice. Hippocampal ripples were measured by placing recording electrodes in the cornu ammonis 1. Effects of isoflurane on the excitability of hippocampal pyramidal neurons and interneurons were measured. A simulation model of ripples based on the firing frequency of hippocampal cornu ammonis 1 neurons was used to validate the effects of isoflurane on neuronal excitability in vitro and on ripples in vivo.

RESULTS

Isoflurane at 0.5%, which did not induce loss of righting reflex, impaired hippocampus-dependent fear memory by 97.4 ± 3.1% (mean ± SD; n = 14; P < 0.001). Isoflurane at 0.5% reduced ripple amplitude (38 ± 13 vs. 42 ± 13 μV; n = 9; P = 0.003), rate (462 ± 66 vs. 538 ± 81 spikes/min; n = 9; P = 0.002) and duration (36 ± 5 vs. 48 ± 9 ms; n = 9; P < 0.001) and increased the interarrival time (78 ± 7 vs. 69 ± 6 ms; n = 9; P < 0.001) and frequency (148.2 ± 3.9 vs. 145.0 ± 2.9 Hz; n = 9; P = 0.001). Isoflurane at the same concentration depressed action potential frequency in fast-spiking interneurons while slightly enhancing action potential frequency in cornu ammonis 1 pyramidal neurons. The simulated effects of isoflurane on hippocampal ripples were comparable to recordings in vivo.

CONCLUSIONS

The authors' results suggest that a subanesthetic concentration of isoflurane can suppress hippocampal ripples by differentially modulating the excitability of pyramidal neurons and interneurons, which may contribute to its amnestic action.

EDITOR’S PERSPECTIVE

Glycine substitution of α1F64 residue at the loop D of GABAA receptor impairs gating - Implications for importance of binding site-channel gate linker rigidity

GABA_A receptors (GABA_ARs) play a crucial role in mediating inhibition in adult mammalian brains. In the recent years, an impressive progress in revealing the static structure of GABA_ARs was achieved but the molecular mechanisms underlying their conformational transitions remain elusive. Phenylalanine 64 (α1F64) is located at the loop D of the orthosteric binding site of GABA_AR and was found to directly interact with GABA molecule. Mutations of α1F64 were demonstrated to affect not only binding but also some gating properties. Loop D is a rigid β strand which seems to be particularly suitable to convey activatory signaling from the ligand binding site (LBS) to the gate at the channel pore. To test this scenario, we have investigated the substitution of α1F64 with glycine, the smallest amino acid, widely recognized as a rigidity "reducer" of protein structures. To this end, we assessed the impact of the α1F64G mutation in the α1β2γ2L type of GABA_ARs on gating properties by analyzing both macroscopic responses to rapid agonist applications and single-channel currents. We found that this substitution dramatically altered all gating features of the receptor (opening/closing, preactivation and desensitization) which contrasts with markedly weaker effects of previously considered substitutions (α1F64L and α1F64A). In particular, α1F64G mutation practically abolished the desensitization process. At the same time, the α1F64G mutant maintained gating integrity manifested as single-channel activity in the form of clusters. We conclude that rigidity of the loop D plays a crucial role in conveying the activation signal from the LBS to the channel gate.

Neonatal administration of a subanaesthetic dose of JM-1232(-) in mice results in no behavioural deficits in adulthood

In animal models, neonatal exposure of general anaesthetics significantly increases apoptosis in the brain, resulting in persistent behavioural deficits later in adulthood. Consequently, there is growing concern about the use of general anaesthetics in obstetric and paediatric practice. JM-1232(−) has been developed as a novel intravenous anaesthetic, but the effects of JM-1232(−) on the developing brain are not understood. Here we show that neonatal administration of JM-1232(−) does not lead to detectable behavioural deficits in adulthood, contrarily to other widely-used intravenous anaesthetics. At postnatal day 6 (P6), mice were injected intraperitoneally with a sedative-equivalent dose of JM-1232(−), propofol, or midazolam. Western blot analysis of forebrain extracts using cleaved poly-(adenosine diphosphate-ribose) polymerase antibody showed that JM-1232(−) is accompanied by slight but measurable apoptosis 6 h after administration, but it was relatively small compared to those of propofol and midazolam. Behavioural studies were performed in adulthood, long after the neonatal anaesthesia, to evaluate the long-term effects on cognitive, social, and affective functions. P6 administration to JM-1232(−) was not accompanied by detectable long-term behavioural deficits in adulthood. However, animals receiving propofol or midazolam had impaired social and/or cognitive functions. These data suggest that JM-1232(−) has prospects for use in obstetric and paediatric practice.

Optimized Propofol Anesthesia Increases Power of Subthalamic Neuronal Activity in Patients with Parkinson's Disease Undergoing Deep Brain Stimulation

Introduction

Propofol is a general anesthetic option for deep brain stimulation (DBS) of the subthalamic nucleus (STN) of patients with Parkinson's disease (PD). However, its effects on STN activity and neuropsychological outcomes are controversial. The optimal propofol anesthesia for asleep DBS is unknown. This study investigated the safety and effectiveness of an optimized propofol anesthesia regimen in asleep DBS.

Methods

This retrospective study enrolled 68 PD patients undergoing bilateral STN-DBS surgery. All patients received local scalp anesthesia, with (asleep group, n = 35) or without (awake group, n = 33) propofol-remifentanil general anesthesia by target-controlled infusion under electroencephalogram monitoring. The primary outcome was subthalamic neuronal spiking characterization during microelectrode recording. The secondary outcomes were clinical outcomes including motor, cognition, mind, sleep, and quality of life at 6 months.

Results

Significantly increased delta and theta power were obtained under propofol anesthesia (awake vs. asleep group, mean ± standard deviation; delta: 31.97 ± 9.87 vs. 39.77 ± 10.56, p < 0.01; theta: 21.09 ± 5.55 vs. 24.82 ± 6.63, p = 0.01). After excluding the influence of confounding factors of age and preoperative motor scores, there was a statistically significant influence on the delta, theta, and alpha power of STN neuronal activity under different anesthesia regimens (delta: β = 2.64, p < 0.01; theta: β = 2.11, p < 0.01; alpha: β = 1.42, p = 0.01). There were no differences in modified burst index, firing rate, tract numbers of microelectrode recording, and other clinical outcomes between the two groups.

Conclusion

Optimized propofol anesthesia enhanced the delta, theta, and alpha power in STN compared with the awake technique and likely contributed to target recognition under propofol anesthesia. These results demonstrate that propofol is suitable, but needs to be optimized, for asleep STN-DBS.

Trial Registration

Chinese Clinical Trial Registry Identification number: ChiCTR2100045942. Registered 29 April 2021–Retrospectively registered

Supplementary Information

The online version contains supplementary material available at 10.1007/s40120-021-00259-y.

Dissociative and analgesic properties of ketamine are independent and unaltered by sevoflurane general anesthesia

Ketamine-induced dissociation and analgesia are independent and robust to general anesthesia neural circuit alterations, suggesting that ketamine can be refined into a targeted pain therapeutic.

Introduction:

Ketamine, an anesthetic adjunct, is routinely administered as part of a balanced general anesthetic technique. We recently showed that the acute analgesic and dissociation properties of ketamine are separable to suggest that distinct neural circuits underlie these states.

Objective:

We aimed to study whether this finding is robust to the substantial neural circuit alterations associated with general anesthesia.

Methods:

We conducted a single-site, open-label, randomized controlled, cross-over study of sevoflurane and sevoflurane-plus-ketamine (SK) general anesthesia in healthy subjects (n = 12). Before and after general anesthesia, we assessed precalibrated cuff pain intensity and nociceptive pain quality as well as dissociation using the Clinician-Administered Dissociative States Scale (CADSS). For statistical inference, we ran a variation of backward elimination repeated-measures analysis of covariance. Models with CADSS as a covariate term were used to assess whether dissociation mediated the effect of ketamine on pain intensity and quality.

Results:

Sevoflurane-plus-ketamine general anesthesia was associated with a significant (P = 0.0002) pain intensity decline of 3 (SE, 0.44). There was an order effect for dissociation such that SK was associated with a significant (P = 0.0043) CADSS increase of 17.8 (3.2) when the SK treatment came first. When the pain intensity model was reanalyzed with CADSS as an additional covariate, the effect of CADSS was not significant. These results were also conserved for pain quality.

Conclusions:

Our findings suggest that the analgesic and dissociation properties of ketamine remain separable despite general anesthesia. Thus, ketamine may be used as a probe to advance our knowledge of dissociation independent pain circuits.

Monitoring anesthesia using simultaneous functional Near Infrared Spectroscopy and Electroencephalography

OBJECTIVE

This study aims to understand the neural and hemodynamic responses during general anesthesia in order to develop a comprehensive multimodal anesthesia depth monitor using simultaneous functional Near Infrared Spectroscopy (fNIRS) and Electroencephalogram (EEG).

METHODS

37 adults and 17 children were monitored with simultaneous fNIRS and EEG, during the complete general anesthesia process. The coupling of fNIRS signals with neuronal signals (EEG) was calculated. Measures of complexity (sample entropy) and phase difference were also quantified from fNIRS signals to identify unique fNIRS based biomarkers of general anesthesia.

RESULTS

A significant decrease in the complexity and power of fNIRS signals characterize the anesthesia maintenance phase. Furthermore, responses to anesthesia vary between adults and children in terms of neurovascular coupling and frontal EEG alpha power.

CONCLUSIONS

This study shows that fNIRS signals could reliably quantify the underlying neuronal activity under general anesthesia and clearly distinguish the different phases throughout the procedure in adults and children (with less accuracy).

SIGNIFICANCE

A multimodal approach incorporating the specific differences between age groups, provides a reliable measure of anesthesia depth.

Deciphering the scopolamine challenge rat model by preclinical functional MRI

During preclinical drug testing, the systemic administration of scopolamine (SCO), a cholinergic antagonist, is widely used. However, it suffers important limitations, like non-specific behavioural effects partly due to its peripheral side-effects. Therefore, neuroimaging measures would enhance its translational value. To this end, in Wistar rats, we measured whisker-stimulation induced functional MRI activation after SCO, peripherally acting butylscopolamine (BSCO), or saline administration in a cross-over design. Besides the commonly used gradient-echo echo-planar imaging (GE EPI), we also used an arterial spin labeling method in isoflurane anesthesia. With the GE EPI measurement, SCO decreased the evoked BOLD response in the barrel cortex (BC), while BSCO increased it in the anterior cingulate cortex. In a second experiment, we used GE EPI and spin-echo (SE) EPI sequences in a combined (isoflurane + i.p. dexmedetomidine) anesthesia to account for anesthesia-effects. Here, we also examined the effect of donepezil. In the combined anesthesia, with the GE EPI, SCO decreased the activation in the BC and the inferior colliculus (IC). BSCO reduced the response merely in the IC. Our results revealed that SCO attenuated the evoked BOLD activation in the BC as a probable central effect in both experiments. The likely peripheral vascular actions of SCO with the given fMRI sequences depended on the type of anesthesia or its dose.

Sevoflurane excites nociceptive sensory neurons by inhibiting K+ conductances in rats

Sevoflurane, which is preferentially used as a day-case anesthetic based on its low blood solubility, acts on the central nervous system and exerts analgesic effects. However, it still remains unknown whether sevoflurane affects the excitability of nociceptive sensory neurons. Therefore, we conducted this study to examine the effects of sevoflurane on the excitability of small-sized dorsal root ganglion (DRG) neurons of rats using the whole-cell patch-clamp technique. In a voltage-clamp condition, sevoflurane elicited the membrane current in a concentration-dependent manner, in which the reversal potential was similar to the equilibrium potential of K⁺. In a current-clamp condition, sevoflurane directly depolarized the membrane potentials in a concentration-dependent manner. Moreover, at a clinically relevant concentration, sevoflurane decreased the threshold for action potential generation. These findings suggest that sevoflurane acts on the leak K⁺ channels to increase the excitability of DRG neurons. Sevoflurane increased the half-width of single action potentials, which resulted from the inhibition of voltage-gated K⁺ currents, including the fast inactivating A-type and non-inactivating delayed rectifier K⁺ currents. Our study indicates that sevoflurane could exhibit pronociceptive effects on nociceptive sensory neurons by inhibiting K⁺ conductances.

Elevation of propofol sensitivity of cardiac IKs channel by KCNE1 polymorphism D85N

BACKGROUND AND PURPOSE

The slowly activating delayed rectifier K⁺ channel (I_Ks ), composed of pore-forming KCNQ1 α-subunits and ancillary KCNE1 β-subunits, regulates ventricular repolarization in human heart. Propofol, at clinically used concentrations, modestly inhibits the intact (wild-type) I_Ks channels and is therefore unlikely to appreciably prolong QT interval in ECG during anaesthesia. However, little information is available concerning the inhibitory effect of propofol on I_Ks channel associated with its gene variants implicated in QT prolongation. The KCNE1 single nucleotide polymorphism leading to D85N is associated with drug-induced QT prolongation and therefore regarded as a clinically important genetic variant. This study examined whether KCNE1-D85N affects the sensitivity of I_Ks to inhibition by propofol.

EXPERIMENTAL APPROACH

Whole-cell patch-clamp and immunostaining experiments were conducted in HEK293 cells and/or mouse cardiomyocyte-derived HL-1 cells, transfected with wild-type KCNQ1, wild-type or variant KCNE1 cDNAs.

KEY RESULTS

Propofol inhibited KCNQ1/KCNE1-D85N current more potently than KCNQ1/KCNE1 current in HEK293 cells and HL-1 cells. Immunostaining experiments in HEK293 cells revealed that pretreatment with propofol (10 μM) did not appreciably affect cell membrane expression of KCNQ1 and KCNE1 proteins in KCNQ1/KCNE1 and KCNQ1/KCNE1-D85N channels.

CONCLUSION AND IMPLICATIONS

The KCNE1 polymorphism D85N significantly elevates the sensitivity of I_Ks to inhibition by propofol. This study detects a functionally important role of KCNE1-D85N polymorphism in conferring genetic susceptibility to propofol-induced QT prolongation and further suggests the possibility that the inhibitory action of anaesthetics on ionic currents becomes exaggerated in patients carrying variants in genes encoding ion channels.

Real-Time EEG Signal Classification for Monitoring and Predicting the Transition Between Different Anaesthetic States

Quantitative identification of the transitions between anaesthetic states is very essential for optimizing patient safety and quality care during surgery but poses a very challenging task. The state-of-the-art monitors are still not capable of providing their manifest variables, so the practitioners must diagnose them based on their own experience. The present paper proposes a novel real-time method to identify these transitions. Firstly, the Hurst method is used to pre-process the de-noised electro-encephalograph (EEG) signals. The maximum of Hurst's ranges is then accepted as the EEG real-time response, which induces a new real-time feature under moving average framework. Its maximum power spectral density is found to be very differentiated into the distinct transitions of anaesthetic states and thus can be used as the quantitative index for their identification.

Histopathological study on neuroapoptotic alterations induced by etomidate in rat hippocampus

In human, there is substantial neurogenesis in the hippocampus that is implicated in memory formation and learning. These new-born neurons can be affected by neuropathological conditions. Anesthesia and surgical procedures are associated with postoperative cognitive changes particularly, impaired memory and learning. Therefore, the aim of this study was to evaluate the possible neurodegenerative effects of etomidate in rat hippocampus. Thirty male Wistar rats weighing 250 ± 30 g were randomly divided into 3 groups: 1) Etomidate group; four times 20 mg intraperitoneal injection with 1-h intervals, 2) Control group; the equal volume of normal saline, and 3) Normal group; without any intervention. 6 h after the last injection, the brains were removed and processed according to routine histological methods. TUNEL assay and toluidine blue staining were performed to evaluate neuro-histopathological changes in different regions of hippocampus. Our results showed that the number of TUNEL positive cells and dark neurons (DNs) in etomidate group were significantly higher in the CA1, CA2, CA3, and dentate gyrus (DG) of hippocampus compared with the control and normal groups (p < 0.05). While, there was no significant difference between the various regions of hippocampus in control and normal groups. Our findings showed that etomidate can increase apoptotic cells and dark neurons induction in different regions of hippocampus mainly in DG.

Anesthetics fragment hippocampal network activity, alter spine dynamics, and affect memory consolidation

General anesthesia is characterized by reversible loss of consciousness accompanied by transient amnesia. Yet, long-term memory impairment is an undesirable side effect. How different types of general anesthetics (GAs) affect the hippocampus, a brain region central to memory formation and consolidation, is poorly understood. Using extracellular recordings, chronic 2-photon imaging, and behavioral analysis, we monitor the effects of isoflurane (Iso), medetomidine/midazolam/fentanyl (MMF), and ketamine/xylazine (Keta/Xyl) on network activity and structural spine dynamics in the hippocampal CA1 area of adult mice. GAs robustly reduced spiking activity, decorrelated cellular ensembles, albeit with distinct activity signatures, and altered spine dynamics. CA1 network activity under all 3 anesthetics was different to natural sleep. Iso anesthesia most closely resembled unperturbed activity during wakefulness and sleep, and network alterations recovered more readily than with Keta/Xyl and MMF. Correspondingly, memory consolidation was impaired after exposure to Keta/Xyl and MMF, but not Iso. Thus, different anesthetics distinctly alter hippocampal network dynamics, synaptic connectivity, and memory consolidation, with implications for GA strategy appraisal in animal research and clinical settings.

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.

Cell-type-specific imaging of neurotransmission reveals a disrupted excitatory-inhibitory cortical network in isoflurane anaesthesia

BACKGROUND

Despite the fundamental clinical significance of general anaesthesia, the cortical mechanism underlying anaesthetic-induced loss of consciousness (aLOC) remains elusive.

METHODS

Here, we measured the dynamics of two major cortical neurotransmitters, gamma-aminobutyric acid (GABA) and glutamate, through in vivo two-photon imaging and genetically encoded neurotransmitter sensors in a cell type-specific manner in the primary visual (V1) cortex.

FINDINGS

We found a general decrease in cortical GABA transmission during aLOC. However, the glutamate transmission varies among different cortical cell types, where in it is almost preserved on pyramidal cells and is significantly reduced on inhibitory interneurons. Cortical interneurons expressing vasoactive intestinal peptide (VIP) and parvalbumin (PV) specialize in disinhibitory and inhibitory effects, respectively. During aLOC, VIP neuronal activity was delayed, and PV neuronal activity was dramatically inhibited and highly synchronized.

INTERPRETATION

These data reveal that aLOC resembles a cortical state with a disrupted excitatory-inhibitory network and suggest that a functional inhibitory network is indispensable in the maintenance of consciousness.

FUNDING

This work was supported by the grants of the National Natural Science Foundation of China (grant nos. 81620108012 and 82030038 to H.D. and grant nos. 31922029, 61890951, and 61890950 to J.H.).

Behavioural impairments after exposure of neonatal mice to propofol are accompanied by reductions in neuronal activity in cortical circuitry

BACKGROUND

Both animal and retrospective human studies have linked extended and repeated general anaesthesia during early development with cognitive and behavioural deficits later in life. However, the neuronal circuit mechanisms underlying this anaesthesia-induced behavioural impairment are poorly understood.

METHODS

Neonatal mice were administered one or three doses of propofol, a commonly used i.v. general anaesthetic, over Postnatal days 7-11. Control mice received Intralipid® vehicle injections. At 4 months of age, the mice were subjected to a series of behavioural tests, including motor learning. During the process of motor learning, calcium activity of pyramidal neurones and three classes of inhibitory interneurones in the primary motor cortex were examined in vivo using two-photon microscopy.

RESULTS

Repeated, but not a single, exposure of neonatal mice to propofol i.p. caused motor learning impairment in adulthood, which was accompanied by a reduction of pyramidal neurone number and activity in the motor cortex. The activity of local inhibitory interneurone networks was also altered: somatostatin-expressing and parvalbumin-expressing interneurones were hypoactive, whereas vasoactive intestinal peptide-expressing interneurones were hyperactive when the mice were performing a motor learning task. Administration of low-dose pentylenetetrazol to attenuate γ-aminobutyric acid A receptor-mediated inhibition or CX546 to potentiate α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-subtype glutamate receptor function during emergence from anaesthesia ameliorated neuronal dysfunction in the cortex and prevented long-term behavioural deficits.

CONCLUSIONS

Repeated exposure of neonatal mice to propofol anaesthesia during early development causes cortical circuit dysfunction and behavioural impairments in later life. Potentiation of neuronal activity during recovery from anaesthesia reduces these adverse effects of early-life anaesthesia.

Effects of sevoflurane and desflurane on the nociceptive responses of substantia gelatinosa neurons in the rat spinal cord dorsal horn: An in vivo patch-clamp analysis

Background

Volatile anesthetics suppress noxiously evoked activity in the spinal dorsal horn, which could contribute in part to analgesia, immobility. Modulation of excitatory and inhibitory synaptic transmission in substantia gelatinosa neurons could lead to the suppression of dorsal horn activity; however, this phenomenon has not yet been investigated fully.

Methods

In urethane-anesthetized rats, extracellular activity of dorsal horn neurons (action potentials) and excitatory/inhibitory postsynaptic currents in substantia gelatinosa neurons were recorded using extracellular and in vivo patch-clamp techniques, respectively, to assess the spontaneous and the noxious-evoked activity. Sevoflurane or desflurane at concentrations ranging from 0.1 to 2 minimum alveolar concentration was administered by inhalation. Hot- and cold-plate tests were performed to assess nociceptive responses during the inhalation of volatile anesthetics at lower anesthetic doses (0.1–0.5 minimum alveolar concentration).

Results

At anesthetic doses (1 and 2 minimum alveolar concentration), both sevoflurane and desflurane decreased the frequency of action potentials in the dorsal horn and the activities of excitatory postsynaptic currents in substantia gelatinosa neurons during pinch stimulation and decreased the activities of spontaneous and miniature excitatory postsynaptic currents. Inhibition of the frequencies was more prominent than that of amplitudes in spontaneous and miniature excitatory postsynaptic currents at these anesthetic doses. However, at subanesthetic doses (0.1 and 0.2 minimum alveolar concentration), desflurane facilitated action potentials and excitatory postsynaptic currents. Inhibitory postsynaptic currents were inhibited by both anesthetics at anesthetic doses (1 and 2 minimum alveolar concentration). Hot- or cold-plate tests showed hyperalgesic effects of desflurane at subanesthetic doses (0.1 and 0.2 minimum alveolar concentration) and a dose-dependent analgesic effect of sevoflurane.

Conclusions

Sevoflurane and desflurane at anesthetic doses suppressed dorsal horn activity mainly via inhibition of excitatory postsynaptic currents in substantia gelatinosa neurons, which would contribute to their analgesic properties. Presynaptic mechanisms were likely in excitatory postsynaptic currents inhibition. Desflurane but not sevoflurane may have a hyperalgesic effect at subanesthetic doses.

The effects of the general anesthetic sevoflurane on neurotransmission: an experimental and computational study

The brain functions can be reversibly modulated by the action of general anesthetics. Despite a wide number of pharmacological studies, an extensive analysis of the cellular determinants of anesthesia at the microcircuits level is still missing. Here, by combining patch-clamp recordings and mathematical modeling, we examined the impact of sevoflurane, a general anesthetic widely employed in the clinical practice, on neuronal communication. The cerebellar microcircuit was used as a benchmark to analyze the action mechanisms of sevoflurane while a biologically realistic mathematical model was employed to explore at fine grain the molecular targets of anesthetic analyzing its impact on neuronal activity. The sevoflurane altered neurotransmission by strongly increasing GABAergic inhibition while decreasing glutamatergic NMDA activity. These changes caused a notable reduction of spike discharge in cerebellar granule cells (GrCs) following repetitive activation by excitatory mossy fibers (mfs). Unexpectedly, sevoflurane altered GrCs intrinsic excitability promoting action potential generation. Computational modelling revealed that this effect was triggered by an acceleration of persistent sodium current kinetics and by an increase in voltage dependent potassium current conductance. The overall effect was a reduced variability of GrCs responses elicited by mfs supporting the idea that sevoflurane shapes neuronal communication without silencing neural circuits.

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

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

CHARMM-GUI supports the Amber force fields

As part of our ongoing efforts to support diverse force fields and simulation programs in CHARMM-GUI, this work presents the development of FF-Converter to prepare Amber simulation inputs with various Amber force fields within the current CHARMM-GUI workflow. The currently supported Amber force fields are ff14SB/ff19SB (protein), Bsc1 (DNA), OL3 (RNA), GLYCAM06 (carbohydrate), Lipid17 (lipid), GAFF/GAFF2 (small molecule), TIP3P/TIP4P-EW/OPC (water), and 12-6-4 ions, and more will be added if necessary. The robustness and usefulness of this new CHARMM-GUI extension are demonstrated by two exemplary systems: a protein/N-glycan/ligand/membrane system and a protein/DNA/RNA system. Currently, CHARMM-GUI supports the Amber force fields only for the Amber program, but we will expand the FF-Converter functionality to support other simulation programs that support the Amber force fields.

Regulation of GABAARs by Transmembrane Accessory Proteins

The vast majority of fast inhibitory transmission in the brain is mediated by GABA acting on GABAA receptors (GABAARs), which provides inhibitory balance to excitatory drive and controls neuronal output. GABAARs are also effectively targeted by clinically important drugs for treatment in a number of neurological disorders. It has long been hypothesized that function and pharmacology of GABAARs are determined by the channel pore-forming subunits. However, recent studies have provided new dimensions in studying GABAARs due to several transmembrane proteins that interact with GABAARs and modulate their trafficking and function. In this review, we summarize recent findings on these novel GABAAR transmembrane regulators and highlight a potential avenue to develop new GABAAR psychopharmacology by targeting these receptor-associated membrane proteins.

Understanding the Effects of Anesthesia on Cortical Electrophysiological Recordings: A Scoping Review

General anesthesia in animal experiments is an ethical must and is required for all the procedures that are likely to cause more than slight or momentary pain. As anesthetics are known to deeply affect experimental findings, including electrophysiological recordings of brain activity, understanding their mechanism of action is of paramount importance. It is widely recognized that the depth and type of anesthesia introduce significant bias in electrophysiological measurements by affecting the shape of both spontaneous and evoked signals, e.g., modifying their latency and relative amplitude. Therefore, for a given experimental protocol, it is relevant to identify the appropriate anesthetic, to minimize the impact on neuronal circuits and related signals under investigation. This review focuses on the effect of different anesthetics on cortical electrical recordings, examining their molecular mechanisms of action, their influence on neuronal microcircuits and, consequently, their impact on cortical measurements.

General Anaesthesia Shifts the Murine Circadian Clock in a Time-Dependant Fashion

Following general anaesthesia (GA), patients frequently experience sleep disruption and fatigue, which has been hypothesized to result at least in part by GA affecting the circadian clock. Here, we provide the first comprehensive time-dependent analysis of the effects of the commonly administered inhalational anaesthetic, isoflurane, on the murine circadian clock, by analysing its effects on (a) behavioural locomotor rhythms and (b) PER2::LUC expression in the suprachiasmatic nuclei (SCN) of the mouse brain. Behavioural phase shifts elicited by exposure of mice (n = 80) to six hours of GA (2% isoflurane) were determined by recording wheel-running rhythms in constant conditions (DD). Phase shifts in PER2::LUC expression were determined by recording bioluminescence in organotypic SCN slices (n = 38) prior to and following GA exposure (2% isoflurane). Full phase response curves for the effects of GA on behaviour and PER2::LUC rhythms were constructed, which show that the effects of GA are highly time-dependent. Shifts in SCN PER2 expression were much larger than those of behaviour (c. 0.7 h behaviour vs. 7.5 h PER2::LUC). We discuss the implications of this work for understanding how GA affects the clock, and how it may inform the development of chronotherapeutic strategies to reduce GA-induced phase-shifting in patients.

Attenuation of Native Hyperpolarization-Activated, Cyclic Nucleotide-Gated Channel Function by the Volatile Anesthetic Sevoflurane in Mouse Thalamocortical Relay Neurons

As thalamocortical relay neurons are ascribed a crucial role in signal propagation and information processing, they have attracted considerable attention as potential targets for anesthetic modulation. In this study, we analyzed the effects of different concentrations of sevoflurane on the excitability of thalamocortical relay neurons and hyperpolarization-activated, cyclic-nucleotide gated (HCN) channels, which play a decisive role in regulating membrane properties and rhythmic oscillatory activity. The effects of sevoflurane on single-cell excitability and native HCN channels were investigated in acutely prepared brain slices from adult wild-type mice with the whole-cell patch-clamp technique, using voltage-clamp and current-clamp protocols. Sevoflurane dose-dependently depressed membrane biophysics and HCN-mediated parameters of neuronal excitability. Respective half-maximal inhibitory and effective concentrations ranged between 0.30 (95% CI, 0.18–0.50) mM and 0.88 (95% CI, 0.40–2.20) mM. We witnessed a pronounced reduction of HCN dependent I_h current amplitude starting at a concentration of 0.45 mM [relative change at −133 mV; 0.45 mM sevoflurane: 0.85 (interquartile range, 0.79–0.92), n = 12, p = 0.011; 1.47 mM sevoflurane: 0.37 (interquartile range, 0.34–0.62), n = 5, p < 0.001] with a half-maximal inhibitory concentration of 0.88 (95% CI, 0.40–2.20) mM. In contrast, effects on voltage-dependent channel gating were modest with significant changes only occurring at 1.47 mM [absolute change of half-maximal activation potential; 1.47 mM: −7.2 (interquartile range, −10.3 to −5.8) mV, n = 5, p = 0.020]. In this study, we demonstrate that sevoflurane inhibits the excitability of thalamocortical relay neurons in a concentration-dependent manner within a clinically relevant range. Especially concerning its effects on native HCN channel function, our findings indicate substance-specific differences in comparison to other anesthetic agents. Considering the importance of HCN channels, the observed effects might mechanistically contribute to the hypnotic properties of sevoflurane.

General Anesthesia Versus Conscious Sedation in Endovascular Thrombectomy for Stroke: A Meta-analysis of 4 Randomized Controlled Trials

BACKGROUND

In ischemic stroke patients, studies have suggested that clinical outcomes following endovascular thrombectomy are worse after general anesthesia (GA) compared with conscious sedation (CS). Most data are from observational trials, which are prone to measure and unmeasure confounding. We performed a systematic review and meta-analysis of thrombectomy trials where patients were randomized to GA or CS, and compared efficacy and safety outcomes.

METHODS

The Medline, Embase, and Cochrane databases were searched for randomized controlled trials comparing GA to CS in endovascular thrombectomy. Efficacy outcomes included successful recanalization (Thrombolysis in Cerebral Infarction score of 2b to 3), and good functional outcome, defined as a modified Rankin Scale score of 0 to 2 at 3 months. Safety outcomes included intracerebral hemorrhage and 3-month mortality.

RESULTS

Four studies were identified and included in the random effects meta-analysis. Patients treated with GA achieved a higher proportion of successful recanalization (odds ratio [OR]: 2.14, 95% confidence interval [CI]: 1.26-3.62; P=0.005) and good functional outcome (OR: 1.71, 95% CI: 1.13-2.59; P=0.01). For every 7.9 patients receiving GA, one more achieved good functional outcome compared with those receiving CS. There were no significant differences in intracerebral hemorrhage (OR: 0.61, 95% CI: 0.20-1.85; P=0.38) or 3-month mortality (OR: 0.62, 95% CI: 0.33-1.17; P=0.14) between GA and CS patients.

CONCLUSIONS

In centers with high quality, specialized neuroanesthesia care, GA treated thrombectomy patients had superior recanalization rates and better functional outcome at 3 months than patients receiving CS.

Propofol sedation-induced alterations in brain connectivity reflect parvalbumin interneurone distribution in human cerebral cortex

BACKGROUND

Propofol, a commonly used intravenous anaesthetic, binds to type A gamma aminobutyric acid (GABA) receptors in mammalian brain. Previous work on its anaesthetic action has characterised either the biochemistry underlying propofol binding or the associated changes in brain network dynamics during sedation. Despite these advances, no study has focused on understanding how propofol action at the cellular level results in changes in brain network connectivity.

METHODS

We used human whole-brain microarray data to generate distribution maps for genes that mark the primary GABAergic cortical interneurone subtypes (somatostatin, parvalbumin [PV], and 5-hydroxytryptamine 3A. Next, 25 healthy participants underwent propofol-induced sedation during resting state functional MRI scanning. We used partial least squares analysis to identify the brain regions in which connectivity patterns were most impacted by propofol sedation. We then correlated these multimodal cortical patterns to determine if a specific interneurone subtype was disproportionately expressed in brain regions in which connectivity patterns were altered during sedation.

RESULTS

Brain networks that were significantly altered by propofol sedation had a high density of PV-expressing GABAergic interneurones. Brain networks that anticorrelated during normal wakefulness, namely the default mode network and attentional and frontoparietal control networks, increased in correlation during sedation.

CONCLUSIONS

PV-expressing interneurones are highly expressed in brain regions with altered connectivity profiles during propofol-induced sedation. This study also demonstrates the utility of leveraging multiple datasets to address multiscale neurobiological problems.

Isoflurane Potentiation of GABAA Receptors Is Reduced but Not Eliminated by the β3(N265M) Mutation

Background: Mice carrying the GABA_A receptor β3(N265M) point mutation, which renders receptors incorporating β3-subunits insensitive to many general anesthetics, have been used experimentally to link modulation of different receptor subtypes to distinct behavioral endpoints. Remarkably, however, the effect of the mutation on the susceptibility to modulation by isoflurane (a standard reference agent for inhalational vapors) has never been tested directly. Therefore, we compared the modulation by isoflurane of expressed α5β3(N265M)γ2L receptors with their wild type counterparts. Methods: Using whole-cell electrophysiological recording and rapid solution exchange techniques, we tested the effects of isoflurane at concentrations ranging from 80 μM to 320 μM on currents activated by 1 μM GABA. We measured drug modulation of wild-type α5β3γ2L GABA_A receptors and their counterparts harboring the β3(N265M) mutation. Results: Currents elicited by GABA were enhanced two- to four-fold by isoflurane, in a concentration-dependent manner. Under the same conditions, receptors incorporating the β3(N265M) mutation were enhanced by approximately 1.5- to two-fold; i.e., modulation by isoflurane was attenuated by approximately one-half. Direct activation by isoflurane was also present in mutant receptors but also attenuated. Conclusions: In contrast to the complete insensitivity of β3(N265M) mutant receptors to etomidate and propofol, the mutation has only a partial effect on receptor modulation by isoflurane. Therefore, the persistence of isoflurane effects in mutant mice does not exclude a possible contribution of β3-GABA_A receptors.

Global genetic deletion of CaV3.3 channels facilitates anaesthetic induction and enhances isoflurane-sparing effects of T-type calcium channel blockers

We previously documented that the Ca_V3.3 isoform of T-type calcium channels (T-channels) is inhibited by clinically relevant concentrations of volatile anaesthetics, including isoflurane. However, little is understood about the functional role of Ca_V3.3 channels in anaesthetic-induced hypnosis and underlying neuronal oscillations. To address this issue, we used Ca_V3.3 knock-out (KO) mice and a panselective T-channel blocker 3,5-dichloro-N-[1-(2,2-dimethyltetrahydro-pyran-4-ylmethyl)-4-fluoro-piperidin-4-ylmethyl]-benzamide (TTA-P2). We found that mutant mice injected with the vehicle showed faster induction of hypnosis than wild-type (WT) mice, while the percent isoflurane at which hypnosis and immobility occurred was not different between two genotypes. Furthermore, we found that TTA-P2 facilitated isoflurane induction of hypnosis in the Ca_V3.3 KO mice more robustly than in the WT mice. Isoflurane-induced hypnosis following injections of TTA-P2 was accompanied with more prominent delta and theta EEG oscillations in the mutant mice, and reached burst-suppression pattern earlier when compared to the WT mice. Our findings point to a relatively specific value of Ca_V3.3 channels in anaesthetic induced hypnosis. Furthermore, we propose that T-channel blockers may be further explored as a valuable adjunct to reducing the usage of potent volatile anaesthetics, thereby improving their safety.

Validation of a new approach for distinguishing anesthetized from awake state in patients using directed transfer function applied to raw EEG

We test whether a measure based on the directed transfer function (DTF) calculated from short segments of electroencephalography (EEG) time-series can be used to monitor the state of the patients also during sevoflurane anesthesia as it can for patients undergoing propofol anesthesia. We collected and analyzed 25-channel EEG from 7 patients (3 females, ages 41–56 years) undergoing surgical anesthesia with sevoflurane, and quantified the sensor space directed connectivity for every 1-s epoch using DTF. The resulting connectivity parameters were compared to corresponding parameters from our previous study (n = 8, patients anesthetized with propofol and remifentanil, but otherwise using a similar protocol). Statistical comparisons between and within studies were done using permutation statistics, a data driven algorithm based on the DTF-parameters was employed to classify the epochs as coming from awake or anesthetized state. According to results of the permutation tests, DTF-parameter topographies were significantly different between the awake and anesthesia state at the group level. However, the topographies were not significantly different when comparing results computed from sevoflurane and propofol data, neither in the awake nor in anesthetized state. Optimizing the algorithm for simultaneously having high sensitivity and specificity in classification yielded an accuracy of 95.1% (SE = 0.96%), with sensitivity of 98.4% (SE = 0.80%) and specificity of 94.8% (SE = 0.10%). These findings indicate that the DTF changes in a similar manner when humans undergo general anesthesia caused by two distinct anesthetic agents with different molecular mechanisms of action.

Allopregnanolone Enhances GABAergic Inhibition in Spinal Motor Networks

The neurosteroid allopregnanolone (ALLO) causes unconsciousness by allosteric modulation of γ-aminobutyric acid type A (GABA_A) receptors, but its actions on the spinal motor networks are unknown. We are therefore testing the hypothesis that ALLO attenuates the action potential firing of spinal interneurons and motoneurons predominantly via enhancing tonic, but not synaptic GABAergic inhibition. We used video microscopy to assess motoneuron-evoked muscle activity in organotypic slice cultures prepared from the spinal cord and muscle tissue. Furthermore, we monitored GABA_A receptor-mediated currents by performing whole-cell voltage-clamp recordings. We found that ALLO (100 nM) reduced the action potential firing of spinal interneurons by 27% and that of α-motoneurons by 33%. The inhibitory effects of the combination of propofol (1 µM) and ALLO on motoneuron-induced muscle contractions were additive. Moreover, ALLO evoked a tonic, GABA_A receptor-mediated current (amplitude: 41 pA), without increasing phasic GABAergic transmission. Since we previously showed that at a clinically relevant concentration of 1 µM propofol enhanced phasic, but not tonic GABAergic inhibition, we conclude that ALLO and propofol target distinct subpopulations of GABA_A receptors. These findings provide first evidence that the combined application of ALLO and propofol may help to reduce intraoperative movements and undesired side effects that are frequently observed under total intravenous anesthesia.

Effects of sevoflurane anaesthesia on radioligand binding to monoamine oxidase-B in vivo

Background

The molecular actions underlying the clinical effects of inhaled anaesthetics such as sevoflurane and isoflurane are not fully understood. Unexpected observations in positron emission tomography (PET) studies with [¹¹C]AZD9272, a metabotropic glutamate receptor 5 (mGluR5) radioligand with possible affinity for monoamine oxidase-B (MAO-B), suggest that its binding is sensitive to anaesthesia with sevoflurane. The objective of the present study was to assess the effects of sevoflurane anaesthesia on the binding of [¹¹C]AZD9272 and of [¹¹C]L-deprenyl-D₂, a radioligand selective for MAO-B in non-human primates (NHPs).

Methods

Altogether, 12 PET measurements were conducted with a high-resolution research tomograph using the ligands [¹¹C]AZD9272 or [¹¹C]L-deprenyl-D₂ in six cynomolgus monkeys anaesthetised with sevoflurane or ketamine/xylazine.

Results

The specific binding of [¹¹C]AZD9272 and [¹¹C]L-deprenyl-D₂ was markedly reduced during anaesthesia with sevoflurane compared with ketamine/xylazine. The reduction was 80–90% (n=3) for [¹¹C]AZD9272 and 77–80% (n=3) for [¹¹C]L-deprenyl-D₂.

Conclusions

Sevoflurane anaesthesia inhibited radioligand binding to MAO-B in the primate brain. The observation of lower MAO-B binding at clinically relevant concentrations of sevoflurane warrants further exploration of the potential role of MAO-B related mechanisms in regulation of systemic blood pressure during anaesthesia.

Cryo-EM: The Resolution Revolution and Drug Discovery

Single-particle cryogenic electron microscopy (cryo-EM) has been elevated to the mainstream of structural biology propelled by technological advancements in numerous fronts, including imaging analysis and the development of direct electron detectors. The drug discovery field has watched with (initial) skepticism and wonder at the progression of the technique and how it revolutionized the molecular understanding of previously intractable targets. This article critically assesses how cryo-EM has impacted drug discovery in diverse therapeutic areas. Targets that have been brought into the realm of structure-based drug design by cryo-EM and are thus reviewed here include membrane proteins like the GABA_A receptor, several TRP channels, and G protein-coupled receptors, and multiprotein complexes like the ribosomes, the proteasome, and eIF2B. We will describe these studies highlighting the achievements, challenges, and caveats.

Prenatal sevoflurane exposure causes neuronal excitatory/inhibitory imbalance in the prefrontal cortex and neurofunctional abnormality in rats

The balance of excitatory and inhibitory neurons in the central nervous system is critical for maintaining brain function and sevoflurane, a general anesthetic and an GABA receptor modulator, may change the balance of excitatory and inhibitory neurons in the cortex during early brain development. Herein, we investigated whether prenatal sevoflurane exposure (PSE) disturbs cortical neuronal development and brain function. Pregnant rats at the gestational day 14.5 were subjected to sevoflurane exposure at 3.0% for 3 h and their offspring were studied thereafter. We found a significant increase of parvalbumin-positive neurons, vesicular GABA transporter (VGAT) and GAD67 expression, and GABA neurotransmitter, and a significant decrease of vesicular glutamate transporter 1 (VGLUT1) expression and glutamate in the medial prefrontal cortex (mPFC) of offspring. Pyramidal neurons showed atrophy with shorter dendrites, less branches and lower spine density visualized by Golgi stain and a decrease of excitability with the increased miniature inhibitory postsynaptic current (mIPSC) frequency and amplitude, the decreased miniature excitatory postsynaptic current (mEPSC) frequency and excitation/inhibition (E/I) ratio using whole-cell recording in offspring. There was a significant increase of inhibitory synapse in the mPFC detected by electron microscopy. Furthermore, PSE animals showed hypo-excitatory phenotype including depression-like behaviors and learning deficits. Thus, our studies provide novel evidence that PSE causes the persisted imbalance of excitatory and inhibitory neurons in the mPFC, and this is very likely the mechanisms of the sevoflurane-induced brain functional abnormalities.

The Biology of General Anesthesia from Paramecium to Primate

General anesthesia serves a critically important function in the clinical care of human patients. However, the anesthetized state has foundational implications for biology because anesthetic drugs are effective in organisms ranging from paramecia, to plants, to primates. Although unconsciousness is typically considered the cardinal feature of general anesthesia, this endpoint is only strictly applicable to a select subset of organisms that are susceptible to being anesthetized. We review the behavioral endpoints of general anesthetics across species and propose the isolation of an organism from its environment - both in terms of the afferent arm of sensation and the efferent arm of action - as a generalizable definition. We also consider the various targets and putative mechanisms of general anesthetics across biology and identify key substrates that are conserved, including cytoskeletal elements, ion channels, mitochondria, and functionally coupled electrical or neural activity. We conclude with a unifying framework related to network function and suggest that general anesthetics - from single cells to complex brains - create inefficiency and enhance modularity, leading to the dissociation of functions both within an organism and between the organism and its surroundings. Collectively, we demonstrate that general anesthesia is not restricted to the domain of modern medicine but has broad biological relevance with wide-ranging implications for a diverse array of species.

Propofol Affects Cortico-Hippocampal Interactions via β3 Subunit-Containing GABAA Receptors

BACKGROUND

General anesthetics depress neuronal activity. The depression and uncoupling of cortico-hippocampal activity may contribute to anesthetic-induced amnesia. However, the molecular targets involved in this process are not fully characterized. GABA_A receptors, especially the type with β3 subunits, represent a main molecular target of propofol. We therefore hypothesized that GABA_A receptors with β3 subunits mediate the propofol-induced disturbance of cortico-hippocampal interactions.

METHODS

We used local field potential (LFP) recordings from chronically implanted cortical and hippocampal electrodes in wild-type and β3(N265M) knock-in mice. In the β3(N265M) mice, the action of propofol via β3subunit containing GABA_A receptors is strongly attenuated. The analytical approach contained spectral power, phase locking, and mutual information analyses in the 2-16 Hz range to investigate propofol-induced effects on cortico-hippocampal interactions.

RESULTS

Propofol caused a significant increase in spectral power between 14 and 16 Hz in the cortex and hippocampus of wild-type mice. This increase was absent in the β3(N265M) mutant. Propofol strongly decreased phase locking of 6-12 Hz oscillations in wild-type mice. This decrease was attenuated in the β3(N265M) mutant. Finally, propofol reduced the mutual information between 6-16 Hz in wild-type mice, but only between 6 and 8 Hz in the β3(N265M) mutant.

CONCLUSIONS

GABA_A receptors containing β3 subunits contribute to frequency-specific perturbation of cortico-hippocampal interactions. This likely explains some of the amnestic actions of propofol.

Apremilast regulates acute effects of ethanol and other GABAergic drugs via protein kinase A-dependent signaling

Phosphodiesterase type 4 (PDE4) inhibitors prevent hydrolysis of cyclic adenosine monophosphate and increase protein kinase A (PKA)-mediated phosphorylation. PDE4 inhibitors also regulate responses to ethanol and GABAergic drugs. We investigated mechanisms by which the PDE4 inhibitor, apremilast, regulates acute effects of ethanol and GABAergic drugs in male and female mice. Apremilast prolonged the sedative-hypnotic effects of gaboxadol, zolpidem, and propofol but did not alter etomidate effects, and unexpectedly shortened the sedative-hypnotic effects of diazepam. Apremilast prolonged rotarod ataxia induced by zolpidem, propofol, and loreclezole, shortened recovery from diazepam, but had no effect on ataxia induced by gaboxadol or etomidate. The PKA inhibitor H-89 blocked apremilast's ability to prolong the sedative-hypnotic effects of ethanol, gaboxadol, and propofol and to prolong ethanol- and propofol-induced ataxia. H-89 also blocked apremilast's ability to shorten the sedative-hypnotic and ataxic effects of diazepam. The β1-specific antagonist, salicylidene salicylhydrazide (SCS), produced faster recovery from ethanol- and diazepam-induced ataxia, but did not alter propofol- or etomidate-induced ataxia. SCS shortened the sedative-hypnotic effects of ethanol and diazepam but not of propofol. In Xenopus oocytes, a phosphomimetic (aspartate) mutation at the PKA phosphorylation site in β1 subunits decreased the maximal GABA current in receptors containing α1 or α3, but not α2 subunits. In contrast, phosphomimetic mutations at PKA sites in β3 subunits increased the maximal GABA current in receptors containing α1 or α2, but not α3 subunits. The GABA potency and allosteric modulation by ethanol, propofol, etomidate, zolpidem, flunitrazepam, or diazepam were not altered by these mutations. We propose a model whereby apremilast increases PKA-mediated phosphorylation of β1-and β3-containing GABA_A receptors and selectively alters acute tolerance to ethanol and GABAergic drugs.

PLD2-PI(4,5)P2 interactions in fluid phase membranes: Structural modeling and molecular dynamics simulations

Interaction of phospholipase D2 (PLD2) with phosphatidylinositol (4,5)-bisphosphate (PIP2) is regarded as the critical step of numerous physiological processes. Here we build a full-length model of human PLD2 (hPLD2) combining template-based and ab initio modeling techniques and use microsecond all-atom molecular dynamics (MD) simulations of the protein in contact with a complex membrane to determine hPLD2-PIP2 interactions. MD simulations reveal that the intermolecular interactions preferentially occur between specific PIP2 phosphate groups and hPLD2 residues; the most strongly interacting residues are arginine at the pbox consensus sequence (PX) and pleckstrin homology (PH) domain. Interaction networks indicate formation of clusters at the protein-membrane interface consisting of amino acids, PIP2, and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidic acid (POPA); the largest cluster was in the PH domain.

Open-channel blocking action of volatile anaesthetics desflurane and sevoflurane on human voltage-gated Kv 1.5 channel

BACKGROUND AND PURPOSE

Volatile anaesthetics have been shown to differentially modulate mammalian Shaker-related voltage-gated potassium (K_v 1.x) channels. This study was designed to investigate molecular and cellular mechanisms underlying the modulatory effects of desflurane or sevoflurane on human K_v 1.5 (hK_v 1.5) channels.

EXPERIMENTAL APPROACH

Thirteen single-point mutations were constructed within pore domain of hK_v 1.5 channel using site-directed mutagenesis. The effects of desflurane or sevoflurane on heterologously expressed wild-type and mutant hK_v 1.5 channels were examined by whole-cell patch-clamp technique. A computer simulation was conducted to predict the docking pose of desflurane or sevoflurane within hK_v 1.5 channel.

KEY RESULTS

Both desflurane and sevoflurane increased hK_v 1.5 current at mild depolarizations but decreased it at strong depolarizations, indicating that these anaesthetics produce both stimulatory and inhibitory actions on hK_v 1.5 channels. The inhibitory effect of desflurane or sevoflurane on hK_v 1.5 channels arose primarily from its open-channel blocking action. The inhibitory action of desflurane or sevoflurane on hK_v 1.5 channels was significantly attenuated in T480A, V505A, and I508A mutant channels, compared with wild-type channel. Computational docking simulation predicted that desflurane or sevoflurane resides within the inner cavity of channel pore and has contact with Thr479, Thr480, Val505, and Ile508.

CONCLUSION AND IMPLICATIONS

Desflurane and sevoflurane exert an open-channel blocking action on hK_v 1.5 channels by functionally interacting with specific amino acids located within the channel pore. This study thus identifies a novel molecular basis mediating inhibitory modulation of hK_v 1.5 channels by desflurane and sevoflurane.

Exploratory analyses of postanesthetic effects of desflurane using behavioral test battery of mice

Halogenated ethers, such as desflurane, sevoflurane, and isoflurane, are known to exert an array of effects besides sedation. However, the postanesthetic effects of desflurane remain undiscovered as no study has explored these effects systematically. Phenotypic screening using behavioral test batteries is a powerful method to identify such effects. In the present study, we behaviorally phenotyped desflurane-treated mice to investigate postanesthetic effects. We applied comprehensive behavioral test batteries measuring sensorimotor functions, anxiety, depression, sociability, attention, and learning abilities, starting 7 days after anesthesia performed with 8.0% desflurane for 6 h. Although our previous study revealed postanesthetic effects of isoflurane in adult mice, in the current study, desflurane-treated mice exhibited no such effects in any behavioral test. To further examine whether desflurane affect behavior in more early time point, we built up a new additional test battery, which carried out 1 day or 3 days after exposure to desflurane. Mice treated with desflurane 1 day before testing showed more slips than other two groups in the first trial, suggesting mild acute side effects of desflurane on motor coordination. These results suggest the safety of desflurane in clinical settings and imply that postanesthetic effects are unique to each halogenated ether.

Anesthesia-induced loss of consciousness disrupts auditory responses beyond primary cortex

Despite its ubiquitous use in medicine, and extensive knowledge of its molecular and cellular effects, how anesthesia induces loss of consciousness (LOC) and affects sensory processing remains poorly understood. Specifically, it is unclear whether anesthesia primarily disrupts thalamocortical relay or intercortical signaling. Here we recorded intracranial electroencephalogram (iEEG), local field potentials (LFPs), and single-unit activity in patients during wakefulness and light anesthesia. Propofol infusion was gradually increased while auditory stimuli were presented and patients responded to a target stimulus until they became unresponsive. We found widespread iEEG responses in association cortices during wakefulness, which were attenuated and restricted to auditory regions upon LOC. Neuronal spiking and LFP responses in primary auditory cortex (PAC) persisted after LOC, while responses in higher-order auditory regions were variable, with neuronal spiking largely attenuated. Gamma power induced by word stimuli increased after LOC while its frequency profile slowed, thus differing from local spiking activity. In summary, anesthesia-induced LOC disrupts auditory processing in association cortices while relatively sparing responses in PAC, opening new avenues for future research into mechanisms of LOC and the design of anesthetic monitoring devices.

The Efficacy and Safety of Concomitant Psychotropic Medication and Electroconvulsive Therapy (ECT)

Electroconvulsive therapy (ECT) is an effective treatment for severe psychiatric disorders. Patients referred to ECT are often taking multiple medications, many of which can potentially affect the safety and efficacy of their course of ECT. This review evaluates the impact of a variety of psychotropic medications often used in conjunction with ECT and examines strategies to optimize their management. The review encompasses mood stabilizers, antidepressants, benzodiazepines, antiepileptics, antipsychotics, and other commonly used psychotropics.

Shisa7 is a GABAA receptor auxiliary subunit controlling benzodiazepine actions

The function and pharmacology of γ-aminobutyric acid type A receptors (GABA_ARs) are of great physiological and clinical importance and have long been thought to be determined by the channel pore-forming subunits. We discovered that Shisa7, a single-passing transmembrane protein, localizes at GABAergic inhibitory synapses and interacts with GABA_ARs. Shisa7 controls receptor abundance at synapses and speeds up the channel deactivation kinetics. Shisa7 also potently enhances the action of diazepam, a classic benzodiazepine, on GABA_ARs. Genetic deletion of Shisa7 selectively impairs GABAergic transmission and diminishes the effects of diazepam in mice. Our data indicate that Shisa7 regulates GABA_AR trafficking, function, and pharmacology and reveal a previously unknown molecular interaction that modulates benzodiazepine action in the brain.

Impact of soman and acetylcholine on the effects of propofol in cultured cortical networks

Patients intoxicated with organophosphorous compounds may need general anaesthesia to enable mechanical ventilation or for control of epileptiform seizures. It is well known that cholinergic overstimulation attenuates the efficacy of general anaesthetics to reduce spontaneous network activity in the cortex. However, it is not clear how propofol, the most frequently used intravenous anaesthetic today, is affected. Here, we investigated the effects of cholinergic overstimulation induced by soman and acetylcholine on the ability of propofol to depress spontaneous action potential activity in organotypic cortical slices measured by extracellular voltage recordings. Cholinergic overstimulation by co-application of soman and acetylcholine (10 μM each) did not reduce the relative inhibition of propofol (1.0 μM; mean normalized action potential firing rate 0.49 ± 0.06 of control condition, p < 0.001, Wilcoxon signed rank test) but clearly reduced its efficacy. Co-application of atropine (10 nM) did not improve the efficacy. Propofol preserved its relative inhibitory potential but did not produce a degree of neuronal depression which can be expected to assure hypnosis in humans. Since a combination with atropine did not improve its efficacy, an increase in dosage will probably be necessary when propofol is used in victims suffering from organophosphorous intoxication.