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At this centenary of the British Journal of Anaesthesia (BJA) in 2023, six of its 12 editors/editors-in-chief detail developments over the decades that have led to the BJA becoming a high-impact international scientific journal. As a charity, the BJA supports academic research and training in anaesthesia, critical care, and pain medicine including funding of research grants and postgraduate education. Building on this foundation, the BJA continues to innovate as it aims to become fully electronic, expand into open access publishing, and increase the diversity of its editorial board.

Background The cellular and molecular mechanisms by which general anaesthesia occurs is poorly understood. Hippocampal interneurone subpopulations, which are critical regulators of cognitive function, have diverse neurophysiological and synaptic properties, but their responses to anaesthetics are unclear. Methods We used live-cell imaging of fluorescent biosensors expressed in mouse hippocampal neurones to delineate interneurone subtype-specific effects of isoflurane on synaptic vesicle exocytosis. The role of voltage-gated sodium channel (Nav) subtype expression in determining isoflurane sensitivity was probed by overexpression or knockdown of specific Nav subtypes in identified interneurones. Results Clinically relevant concentrations of isoflurane differentially inhibited synaptic vesicle exocytosis: to 83.1% (11.7%) of control in parvalbumin-expressing interneurones, and to 58.6% (13.3%) and 64.5% (8.5%) of control in somatostatin-expressing interneurones and glutamatergic neurones, respectively. The relative expression of Nav1.1 (associated with lower sensitivity) and Nav1.6 (associated with higher sensitivity) determined the sensitivity of exocytosis to isoflurane. Conclusions Isoflurane inhibits synaptic vesicle exocytosis from hippocampal glutamatergic neurones and GABAergic interneurones in a cell-type-specific manner depending on their expression of voltage-gated sodium channel subtypes.

In 2023, the British Journal of Anaesthesia commemorates its first century of publishing innovations in anaesthesia, pain, critical care and perioperative medicine. In honour of this special anniversary we outline a number of exciting initiatives to occur over the course of the year to commemorate this important milestone, and to highlight the many contributions that the British Journal of Anaesthesia has made to patient care, medical research, and medical education in our first 100 years.

BACKGROUND: General anaesthetics have marked effects on synaptic transmission, but their neuronal and circuit-level effects remain unclear. The volatile anaesthetic isoflurane differentially inhibits synaptic vesicle exocytosis in specific neuronal subtypes, but whether other common anaesthetics also have neurone-subtype-specific actions is unknown. METHODS: We used the genetically encoded fluorescent Ca(2+) sensor GCaMP6f to compare the pharmacological effects of isoflurane, sevoflurane, propofol, and ketamine on presynaptic excitability in hippocampal glutamatergic neurones and in hippocampal parvalbumin-, somatostatin-, and vasoactive intestinal peptide-expressing (PV(+), SST(+), and VIP(+), respectively) GABAergic interneurones. RESULTS: Isoflurane and sevoflurane depressed activity-driven presynaptic Ca(2+) transients in a neurone-type-specific manner, with greater potency for inhibition of glutamate and SST(+) compared with PV(+) and VIP(+) neurone presynaptic activation. In contrast, clinical concentrations of propofol (1 μM) or ketamine (15 μM) had no significant effects on presynaptic activation. Propofol potentiated evoked Ca(2+) entry in PV(+) interneurones but only at a supraclinical concentration (3 μM). CONCLUSIONS: Anaesthetic-agent-selective effects on presynaptic Ca(2+) entry have functional implications for hippocampal circuit function during i.v. or volatile anaesthetic-mediated anaesthesia. Hippocampal interneurones have distinct subtype-specific sensitivities to volatile anaesthetic actions on presynaptic Ca(2+), which are similar between isoflurane and sevoflurane.

Volatile anesthetics alter presynaptic function including effects on Ca2+ influx and neurotransmitter release. These actions are proposed to play important roles in their pleiotropic neurophysiological effects including unconsciousness and amnesia. The nitric oxide and cyclic guanosine monophosphate (NO/cGMP) signaling pathway has been implicated in presynaptic mechanisms, and disruption of NO/cGMP signaling has been shown to alter sensitivity to volatile anesthetics in vivo. We investigated NO/cGMP signaling in relation to volatile anesthetic actions in cultured rat hippocampal neurons using pharmacological tools and genetically encoded biosensors of cGMP levels. Using the fluorescent biosensor cGull we found that electrical stmulation-evoked NMDA-type glutamate receptor-independent presynaptic cGMP transients were inhibited −33.2% by isoflurane (0.51 mM) and −23.8% by sevoflurane (0.57 mM) (p2+ concentration, measured with synaptophysin-GCaMP6f, and synaptic vesicle exocytosis, measured with synaptophysin-pHlourin, were reduced by in neurons expressing the cGMP scavenger sponGee. This reduction in anesthetic effect was recapitulated by inhibiting HCN channels, a cGMP-modulated effector that can facilitate glutamate release. We propose that volatile anesthetics depress presynaptic cGMP signaling and downstream effectors like HCN channels that are essential to presynaptic function and excitability. These findings identify a novel mechanism by which volatile anesthetics depress synaptic transmission via second messenger signaling involving the NO/cGMP pathway.

General anesthetics disrupt brain processes involved in consciousness by altering synaptic patterns of excitation and inhibition. In the cerebral cortex and hippocampus, GABAergic inhibition is largely mediated by inhibitory interneurons, a heterogeneous group of specialized neuronal subtypes that form characteristic microcircuits with excitatory neurons. Distinct interneuron subtypes regulate specific excitatory neuron networks during normal behavior, but how these interneuron subtypes are affected by general anesthetics is unclear. This narrative review summarizes current principles of the synaptic architecture of cortical and interneuron subtypes, their contributions to different forms of inhibition, and their roles in distinct neuronal microcircuits. The molecular and cellular targets in these circuits that are sensitive to anesthetics are reviewed in the context of how anesthetics impact interneuron function in a subtype-specific manner. The implications of this functional interneuron diversity for mechanisms of anesthesia are discussed, as are their implications for anesthetic-induced changes in neural plasticity and overall brain function.

Summary The British Journal of Anaesthesia (BJA) had an eventful 2021, following what was a cataclysmic 2020 for the whole world. Despite the tragic challenges of multiple waves of the COVID-19 pandemic and the unparalleled burdens this created for everyone working in anaesthesia and critical care, the BJA underwent a major transformation during 2021. The BJA strongly supported research and education relevant to the pandemic, and to the broader missions of anaesthesia, critical, and pain medicine. Innovations to the BJA in 2021 included a special section on COVID-19 and the Anaesthetist; a new open access journal in the BJA stable; creation of a new social media editor position; new webinar and author interview series; transition to a new manuscript management system; and a move away from paper to electronic publication.

Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New Background Volatile anesthetics inhibit presynaptic voltage-gated sodium channels to reduce neurotransmitter release, but their effects on excitatory neuron excitability by sodium current inhibition are unclear. The authors hypothesized that inhibition of transient and persistent neuronal sodium currents by the volatile anesthetic isoflurane contributes to reduced hippocampal pyramidal neuron excitability. Methods Whole-cell patch-clamp recordings of sodium currents of hippocampal cornu ammonis pyramidal neurons were performed in acute mouse brain slices. The actions of isoflurane on both transient and persistent sodium currents were analyzed at clinically relevant concentrations of isoflurane. Results The median inhibitory concentration of isoflurane for inhibition of transient sodium currents was 1.0 ± 0.3 mM (~3.7 minimum alveolar concentration [MAC]) from a physiologic holding potential of −70 mV. Currents from a hyperpolarized holding potential of −120 mV were minimally inhibited (median inhibitory concentration = 3.6 ± 0.7 mM, ~13.3 MAC). Isoflurane (0.55 mM; ~2 MAC) shifted the voltage-dependence of steady-state inactivation by −6.5 ± 1.0 mV (n = 11, P < 0.0001), but did not affect the voltage-dependence of activation. Isoflurane increased the time constant for sodium channel recovery from 7.5 ± 0.6 to 12.7 ± 1.3 ms (n = 13, P < 0.001). Isoflurane also reduced persistent sodium current density (median inhibitory concentration = 0.4 ± 0.1 mM, ~1.5 MAC) and resurgent currents. Isoflurane (0.55 mM; ~2 MAC) reduced action potential amplitude, and hyperpolarized resting membrane potential from −54.6 ± 2.3 to −58.7 ± 2.1 mV (n = 16, P = 0.001). Conclusions Isoflurane at clinically relevant concentrations inhibits both transient and persistent sodium currents in hippocampal cornu ammonis pyramidal neurons. These mechanisms may contribute to reductions in both hippocampal neuron excitability and synaptic neurotransmission.

Volatile anesthetics depress neurotransmitter release in a brain region- and neurotransmitter-selective manner by unclear mechanisms. Voltage-gated sodium channels (Na(v)s), which are coupled to synaptic vesicle exocytosis, are inhibited by volatile anesthetics through reduction of peak current and modulation of gating. Subtype-selective effects of anesthetics on Na(v) might contribute to observed neurotransmitter-selective anesthetic effects on release. We analyzed anesthetic effects on Na(+) currents mediated by the principal neuronal Na(v) subtypes Na(v)1.1, Na(v)1.2, and Na(v)1.6 heterologously expressed in ND7/23 neuroblastoma cells using whole-cell patch-clamp electrophysiology. Isoflurane at clinically relevant concentrations induced a hyperpolarizing shift in the voltage dependence of steady-state inactivation and slowed recovery from fast inactivation in all three Na(v) subtypes, with the voltage of half-maximal steady-state inactivation significantly more positive for Na(v)1.1 (−49.7 ± 3.9 mV) than for Na(v)1.2 (−57.5 ± 1.2 mV) or Na(v)1.6 (−58.0 ± 3.8 mV). Isoflurane significantly inhibited peak Na(+) current (I(Na)) in a voltage-dependent manner: at a physiologically relevant holding potential of −70 mV, isoflurane inhibited peak I(Na) of Na(v)1.2 (16.5% ± 5.5%) and Na(v)1.6 (18.0% ± 7.8%), but not of Na(v)1.1 (1.2% ± 0.8%). Since Na(v) subtypes are differentially expressed both between neuronal types and within neurons, greater inhibition of Na(v)1.2 and Na(v)1.6 compared with Na(v)1.1 could contribute to neurotransmitter-selective effects of isoflurane on synaptic transmission.

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 specific anesthetic agent and the vulnerability of population. Here we review the cellular and molecular mechanisms of transient and persistent general anesthetic alterations of synaptic transmission and plasticity.

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 What We Already Know about This Topic What This Article Tells Us That Is New

Protein phosphatase-1 (PP-1), a highly conserved multifunctional serine/threonine phosphatase, is enriched in dendritic spines where it plays a major role in modulating excitatory synaptic activity. In addition to established functions in spine maturation and development, multi-subunit holoenzyme forms of PP-1 modulate higher-order cognitive functions such learning and memory. Mechanisms involved in regulating PP-1 activity and localization in spines include interactions with neurabin and spinophilin, structurally related synaptic scaffolding proteins associated with the actin cytoskeleton. Since PP-1 is a critical element in synaptic development, signaling, and plasticity, alterations in PP-1 signaling in dendritic spines are implicated in various neurological and psychiatric disorders. The effects of PP-1 depend on its isoform-specific association with regulatory proteins and activation of downstream signaling pathways. Here we review the role of PP-1 and its binding proteins neurabin and spinophilin in both developing and established dendritic spines, as well as some of the disorders that result from its dysregulation.

General anesthesia is critical to modern medicine and animal research, but the cellular and molecular actions of general anesthetics on the central nervous system remain poorly understood. Volatile anesthetics such as isoflurane disrupt synaptic transmission and inhibit synaptic vesicle release in a neurotransmitter-selective manner. For example, GABA release from interneurons is less sensitive to isoflurane inhibition than are glutamate or dopamine release. Hippocampal and cortical interneuron subpopulations have diverse neurophysiological and synaptic properties, and their individual subtype-specific responses to isoflurane are unknown. We used live-cell optical imaging of exocytosis using fluorescent biosensors expressed in transgenic mouse hippocampal neuron cultures to delineate interneuron subtype-specific effects of isoflurane on synaptic vesicle exocytosis. We found that a clinically relevant concentration of isoflurane (0.5 mM) differentially modulated action potential-mediated exocytosis from GABAergic interneurons: parvalbumin-expressing interneurons were inhibited to 83.1±11.7% of control, whereas somatostatin-expressing and interneurons glutamatergic neurons were inhibited to 58.6±13.3% and 64.5±8.5% of control, respectively. The role of presynaptic voltage-gated sodium channel (Nav) subtype expression in determining isoflurane sensitivity was probed by overexpression or knockdown of specific Nav subtypes, which have distinct sensitivities to isoflurane and are differentially expressed between glutamatergic and GABAergic neurons. We found that the sensitivity of exocytosis to isoflurane was determined by the relative expression of Nav1.1 (associated with lower sensitivity) and Nav1.6 (associated with higher sensitivity). Thus the selective effects of isoflurane on synaptic vesicle exocytosis from hippocampal interneuron subtypes is determined by synaptic diversity in the relative expression of Nav1.1 and Nav1.6.Significance statementThe volatile anesthetic isoflurane inhibits hippocampal GABAergic interneuron synaptic vesicle exocytosis with differences in potency between interneuron subtypes. This neuron subtype-specific pharmacology derives in part from synaptic diversity in the expression of presynaptic voltage-gated sodium channels that have different sensitivities to anesthetic modulation of channel function. GABAergic interneurons are generally more resistant to the presynaptic effects of isoflurane owing to predominant Nav1.1 expression, whereas glutamatergic neurons are more sensitive owing to predominant Nav1.6 expression, which supports heterogenous pharmacologic effects on specific neural circuits.

Summary Delirium and postoperative neurocognitive disorder are the commonest perioperative complications in patients more than 65 yr of age. However, data suggest that we often fail to screen patients for preoperative cognitive impairment, to warn patients and families of risk, and to take preventive measures to reduce the incidence of perioperative neurocognitive disorders. As part of the American Society of Anesthesiologists (ASA) Perioperative Brain Health Initiative, an international group of experts was invited to review published best practice statements and guidelines. The expert group aimed to achieve consensus on a small number of practical recommendations that could be implemented by anaesthetists and their partners to reduce the incidence of perioperative neurocognitive disorders. Six statements were selected based not only on the strength of the evidence, but also on the potential for impact and the feasibility of widespread implementation. The actions focus on education, cognitive and delirium screening, non-pharmacologic interventions, pain control, and avoidance of antipsychotics. Strategies for effective implementation are discussed. Anaesthetists should be key members of multidisciplinary perioperative care teams to implement these recommendations.

Background An estimated 87% of torture survivors experience chronic pain such as brachial plexopathy from upper extremity suspension or lumbosacral plexus injury from leg hyperextension. However, a vast majority of pain is undetected by evaluators due to a lack of diagnostic tools and confounding psychiatric illness. This diagnostic gap results in exclusive psychological treatment rather than multimodal therapies, substantially limiting rehabilitation. We hypothesized that the United Nations Istanbul Protocol (UNIP) would have a sensitivity of approximately 15% for pain detection, and that the use of a validated pain screen would improve its sensitivity by at least 29%, as compared to the reference standard (pain specialist evaluation). Methods and findings This prospective blind-comparison-to-gold-standard study of survivors of torture, as defined by the World Medical Association, took place at Weill Cornell Medicine between February 1, 2017, and June 21, 2019. 11 women and 9 men, for a total of 20 participants, were included in the analysis. Five participants received 2 UNIP evaluations, for a total of 25 unique evaluations included in the analysis. Participants were representative of a global population, with home countries in Africa, Central America, South Asia, the Caribbean, and the Middle East. Methods of torture experienced were homogeneous, following the predictable pattern of systematic torture. Participants first received the standard evaluation protocol for torture survivors (UNIP) by a trained evaluator, and subsequently received a validated pain screen (Brief Pain Inventory–Short Form [BPISF]) followed by a noninvasive examination by a pain specialist physician (reference standard). The primary outcome was the diagnostic and treatment capability of the standard protocol (index test) versus the validated pain screen (BPISF), as compared to the reference standard. Trained evaluators performing the initial assessment with the UNIP (index test) were blinded to the study, and the pain specialist physician (reference standard) was blinded to the outcome of the initial UNIP evaluation and the BPISF; data from the initial UNIP assessment were not gathered by the principal investigator until all other study procedures were completed. Providers using only the UNIP captured pain in a maximum of 16% of evaluations, as compared to 85% of participants being diagnosed with pain by the reference standard. When employed, the validated pain screen had a sensitivity of 100% (95% CI 72%–100%) and a negative predictive value of 100%, as compared to a sensitivity of 24% (95% CI 8%–50%) and a negative predictive value of 19% (95% CI 5%–46%) for the index test. The difference in the sensitivity of the UNIP as compared to the BPISF was significant, with p < 0.001. No adverse events owing to participation in the study were reported by participants. Limitations of the study include small sample size, its single-site nature, and the exclusion of individuals who did not speak 1 of the 5 study languages. Conclusions These data indicate that a validated pain screen can supplement the current global standard assessment of torture survivors, the UNIP, to increase the accuracy of pain diagnosis. Trial registration ClinicalTrials.gov NCT03018782., Gunisha Kaur and co-workers investigate diagnosis of chronic pain in people who have survived torture., Author summary Why was this study done? The number of refugee torture survivors worldwide is increasing as violent global conflict accelerates. Refugee torture survivors often experience chronic, debilitating pain that is underdiagnosed due to complex, confounding psychiatric illness, which impacts treatment and rehabilitation. General evaluators do not have diagnostic tools to assist them in the diagnosis of pain in this complex population. What did the researchers do and find? We conducted a prospective blind-comparison-to-gold-standard study of diagnostic accuracy in torture survivors that took place at Weill Cornell Medicine in New York City between February 1, 2017, and June 21, 2019. Following a standard medical, psychiatric, and/or gynecological evaluation according to the guidelines of the United Nations Istanbul Protocol (UNIP), study participants received a validated pain screen and noninvasive physical examination by a pain specialist physician. We found that providers using only the UNIP diagnosed pain significantly less frequently than was indicated necessary by the reference standard (pain specialist evaluation), and that the validated pain screen accurately identified pain when utilized. What do these findings mean? The global standard assessment of torture survivors, the UNIP, should be supplemented by the use of a validated pain screen to increase the accuracy of chronic pain diagnosis. This would potentially shift the standard medical evaluation of 31 million displaced torture survivors globally. Accurately diagnosing pain after torture enhances the ability of providers to treat pain and rehabilitate individuals. Further studies are warranted to investigate outcomes of treatment of pain after torture.

Voltage-gated Na+ channels (Nav ) modulate neuronal excitability, but the roles of the various Nav subtypes in specific neuronal functions such as synaptic transmission are unclear. We investigated expression of the three major brain Nav subtypes (Nav 1.1, Nav 1.2, Nav 1.6) in area CA1 and dentate gyrus of rat hippocampus. Using light and electron microscopy, we found labeling for all three Nav subtypes on dendrites, dendritic spines, and axon terminals, but the proportion of pre- and post-synaptic labeling for each subtype varied within and between subregions of CA1 and dentate gyrus. In the central hilus (CH) of the dentate gyrus, Nav 1.1 immunoreactivity was selectively expressed in presynaptic profiles, while Nav 1.2 and Nav 1.6 were expressed both pre- and post-synaptically. In contrast, in the stratum radiatum (SR) of CA1, Nav 1.1, Nav 1.2, and Nav 1.6 were selectively expressed in postsynaptic profiles. We next compared differences in Nav subtype expression between CH and SR axon terminals and between CH and SR dendrites and spines. Nav 1.1 and Nav 1.2 immunoreactivity was preferentially localized to CH axon terminals compared to SR, and in SR dendrites and spines compared to CH. No differences in Nav 1.6 immunoreactivity were found between axon terminals of CH and SR or between dendrites and spines of CH and SR. All Nav subtypes in both CH and SR were preferentially associated with asymmetric synapses rather than symmetric synapses. These findings indicate selective presynaptic and postsynaptic Nav expression in glutamatergic synapses of CH and SR supporting neurotransmitter release and synaptic plasticity.

General anesthetics revolutionized medicine by allowing surgeons to perform more complex and much longer procedures. This widely used class of drugs is essential to patient care, yet their exact molecular mechanism(s) are incompletely understood. One early hypothesis over a century ago proposed that nonspecific interactions of anesthetics with the lipid bilayer lead to changes in neuronal function via effects on membrane properties. This model was supported by the Meyer-Overton correlation between anesthetic potency and lipid solubility and despite more recent evidence for specific protein targets, in particular ion-channels, lipid bilayer-mediated effects of anesthetics is still under debate. We therefore tested a wide range of chemically diverse general anesthetics on lipid bilayer properties using a sensitive and functional gramicidin-based assay. None of the tested anesthetics altered lipid bilayer properties at clinically relevant concentrations. Some anesthetics did affect the bilayer, though only at high supratherapeutic concentrations, which are unlikely relevant for clinical anesthesia. These results suggest that anesthetics directly interact with membrane proteins without altering lipid bilayer properties at clinically relevant concentrations. Voltage-gated Na+ channels are potential anesthetic targets and various isoforms are inhibited by a wide range of volatile anesthetics. They inhibit channel function by reducing peak Na+ current and shifting steady-state inactivation toward more hyperpolarized potentials. Recent advances in crystallography of prokaryotic Na+ channels, which are sensitive to volatile anesthetics, together with molecular dynamics simulations and electrophysiological studies will help identify potential anesthetic interaction sites within the channel protein itself.

Voltage-gated Na + channels (Na v ) have emerged as important presynaptic targets for volatile anesthetic (VA) effects on synaptic transmission. However, the detailed biophysical mechanisms by which VAs modulate Na v function remain unclear. VAs alter macroscopic activation and inactivation of the prokaryotic Na + channel, NaChBac, which provides a useful structural and functional model of mammalian Na v . Here, we study the effects of the common general anesthetic isoflurane on NaChBac function by analyzing macroscopic Na + currents ( I Na ) in wild-type (WT) channels and mutants with impaired (G229A) or enhanced (G219A) inactivation. We use a previously described six-state Markov model to analyze empirical WT and mutant NaChBac channel gating data. The model reproduces the mean empirical gating manifest in I Na time courses and optimally estimates microscopic rate constants, valences ( z ), and fractional electrical distances ( x ) of forward and backward transitions. The model also reproduces gating observed for all three channels in the absence or presence of isoflurane, providing further validation. We show using this model that isoflurane increases forward activation and inactivation rate constants at 0 mV, which are associated with estimated chemical free energy changes of approximately −0.2 and −0.7 kcal/mol, respectively. Activation is voltage dependent ( z ≈ 2 e 0 , x ≈ 0.3), inactivation shows little voltage dependence, and isoflurane has no significant effect on either. Forward inactivation rate constants are more than 20-fold greater than backward rate constants in the absence or presence of isoflurane. These results indicate that isoflurane modulates NaChBac gating primarily by increasing forward activation and inactivation rate constants. These findings support accumulating evidence for multiple sites of anesthetic interaction with the channel.

Inhaled anesthetics, beginning with diethyl ether, were first introduced into clinical practice in the 1840s. Since then a wide variety of inhaled agents, including ethers, alkanes, nitrous oxide, cyclopropane, and xenon, have been used to induce unconsciousness, amnesia, and immobility. The pharmacokinetics of these drugs depends on their physical properties. The rate of inhaled anesthetic uptake and elimination from the alveoli is driven largely by blood solubility; both are faster with less soluble agents. The effects of inhaled anesthetics depend on the anesthetic concentration at their effect sites, which parallels the alveolar anesthetic concentration and not the total amount of absorbed anesthetic. The potency of different agents can be compared using the minimum alveolar concentration of anesthetic required to prevent movement in 50% of subjects in response to a standardized surgical stimulus. Physiologic factors that govern inhaled anesthetic uptake and elimination include alveolar ventilation and cardiac output. Extrinsic factors that affect inhaled anesthetic uptake and elimination, by determining changes in the alveolar concentration, include minute ventilation, fresh gas flow, and inspired concentration. Inhaled anesthetic tissue distribution depends on relative perfusion, the gradient between arterial and venous anesthetic concentration, and intertissue distribution. Inhaled anesthetics differ dramatically in their degree of metabolism, mostly by the cytochrome P450 system; the volatile anesthetics in use today are minimally metabolized. Emerging developments in inhaled anesthetics include alternative delivery methods and anesthetic applications outside of the operating room.

Understanding the basic principles of pharmacology is fundamental to the practice of medicine in general, but it is perhaps most relevant to the practice of anesthesiology. It is now widely accepted that cells contain a host of specific receptors that mediate the medicinal properties of drugs. Although the use of plant-derived medicinal compounds dates back to antiquity, the mechanisms by which these drugs act to modify disease processes remained mysterious until relatively recently. As late as 1964, de Jong wrote, “To most of the modern pharmacologists the receptor is like a beautiful but remote lady. He has written her many a letter and quite often she has answered the letters. From these answers the pharmacologist has built himself an image of this fair lady. He cannot, however, truly, claim ever to have seen her, although one day he may do so.”1 This chapter briefly reviews the history of the receptor concept from the abstract notion alluded to by de Jong to the modern view of receptors as specific, identifiable cellular macromolecules to which drugs must bind to initiate their effects. Also introduced and defined are basic concepts that describe drug-receptor interactions such as affinity, efficacy, specificity, agonism, antagonism, and the dose-response curve. Finally, the evolving discipline of molecular pharmacology is discussed as it relates to modern drug development. Mathematic representations of the concepts are included in the form of equations for the reader seeking quantitative understanding, although the explanations of key concepts in the text are intended to be understood without reliance on mathematics.

Significant progress has been made in the 21st century towards a comprehensive understanding of the mechanisms of action of general anesthetics, coincident with progress in structural biology and molecular, cellular, and systems neuroscience. This review summarizes important new findings that include target identification through structural determination of anesthetic binding sites, details of receptors and ion channels involved in neurotransmission, and the critical roles of neuronal networks in anesthetic effects on memory and consciousness. These recent developments provide a comprehensive basis for conceptualizing pharmacological control of amnesia, unconsciousness, and immobility.

The mechanisms by which volatile anaesthetics such as isoflurane alter neuronal function are poorly understood, in particular their presynaptic mechanisms. Presynaptic voltage-gated sodium channels (Na(v)) have been implicated as a target for anaesthetic inhibition of neurotransmitter release. We hypothesize that state-dependent interactions of isoflurane with Na(v) lead to increased inhibition of Na(+) current (I(Na)) during periods of high-frequency neuronal activity.The electrophysiological effects of isoflurane, at concentrations equivalent to those used clinically, were measured on recombinant brain-type Na(v)1.2 expressed in ND7/23 neuroblastoma cells and on endogenous Na(v) in isolated rat neurohypophysial nerve terminals. Rate constants determined from experiments on the recombinant channel were used in a simple model of Na(v) gating.At resting membrane potentials, isoflurane depressed peak I(Na) and shifted steady-state inactivation in a hyperpolarizing direction. After membrane depolarization, isoflurane accelerated entry (τ(control)=0.36 [0.03] ms compared with τ(isoflurane)=0.33 [0.05] ms, P0.05) and slowed recovery (τ(control)=6.9 [1.1] ms compared with τ(isoflurane)=9.0 [1.9] ms, P0.005) from apparent fast inactivation, resulting in enhanced depression of I(Na), during high-frequency stimulation of both recombinant and endogenous nerve terminal Na(v). A simple model of Na(v) gating involving stabilisation of fast inactivation, accounts for this novel form of activity-dependent block.Isoflurane stabilises the fast-inactivated state of neuronal Na(v) leading to greater depression of I(Na) during high-frequency stimulation, consistent with enhanced inhibition of fast firing neurones.

General anesthetics have revolutionized medicine by facilitating invasive procedures, and have thus become essential drugs. However, detailed understanding of their molecular mechanisms remains elusive. A mechanism proposed over a century ago involving unspecified interactions with the lipid bilayer known as the unitary lipid-based hypothesis of anesthetic action, has been challenged by evidence for direct anesthetic interactions with a range of proteins, including transmembrane ion channels. Anesthetic concentrations in the membrane are high (10-100 mM), however, and there is no experimental evidence ruling out a role for the lipid bilayer in their ion channel effects. A recent hypothesis proposes that anesthetic-induced changes in ion channel function result from changes in bilayer lateral pressure that arise from partitioning of anesthetics into the bilayer. We examined the effects of a broad range of chemically diverse general anesthetics and related nonanesthetics on lipid bilayer properties using an established fluorescence assay that senses drug-induced changes in lipid bilayer properties. None of the compounds tested altered bilayer properties sufficiently to produce meaningful changes in ion channel function at clinically relevant concentrations. Even supra-anesthetic concentrations caused minimal bilayer effects, although much higher (toxic) concentrations of certain anesthetic agents did alter lipid bilayer properties. We conclude that general anesthetics have minimal effects on bilayer properties at clinically relevant concentrations, indicating that anesthetic effects on ion channel function are not bilayer-mediated but rather involve direct protein interactions.

Volatile anesthetics act directly on neuronal sodium channels, independently of effects on the lipid bilayer., Although general anesthetics are clinically important and widely used, their molecular mechanisms of action remain poorly understood. Volatile anesthetics such as isoflurane (ISO) are thought to alter neuronal function by depressing excitatory and facilitating inhibitory neurotransmission through direct interactions with specific protein targets, including voltage-gated sodium channels (Nav). Many anesthetics alter lipid bilayer properties, suggesting that ion channel function might also be altered indirectly through effects on the lipid bilayer. We compared the effects of ISO and of a series of fluorobenzene (FB) model volatile anesthetics on Nav function and lipid bilayer properties. We examined the effects of these agents on Nav in neuronal cells using whole-cell electrophysiology, and on lipid bilayer properties using a gramicidin-based fluorescence assay, which is a functional assay for detecting changes in lipid bilayer properties sensed by a bilayer-spanning ion channel. At clinically relevant concentrations (defined by the minimum alveolar concentration), both the FBs and ISO produced prepulse-dependent inhibition of Nav and shifted the voltage dependence of inactivation toward more hyperpolarized potentials without affecting lipid bilayer properties, as sensed by gramicidin channels. Only at supra-anesthetic (toxic) concentrations did ISO alter lipid bilayer properties. These results suggest that clinically relevant concentrations of volatile anesthetics alter Nav function through direct interactions with the channel protein with little, if any, contribution from changes in bulk lipid bilayer properties. Our findings further suggest that changes in lipid bilayer properties are not involved in clinical anesthesia.

Dopaminergic activity is both associated with sociosexual exposure and modulated by sexual experience and hormonal state across vertebrate taxa. Mature leopard geckos, a reptile with temperature-dependent sex determination, have dopaminoceptive nuclei that are influenced by their embryonic environment and sensitive to adult hormonal manipulation. In this study, we exposed hormonally manipulated male leopard geckos from different incubation temperatures to conspecifics and measured their sociosexual investigation, as well as phosphorylated DARPP-32 at Threonine 34 (pDARPP-32) immunoreactivity as a marker for D1 dopamine receptor activity in the nucleus accumbens, striatum, and preoptic area. Social investigation time by males of different incubation temperatures was modulated in opposite directions by exogenous androgen treatment. Males exposed to novel stimuli spent a greater proportion of time investigating females of different incubation temperatures. The time spent investigating females was positively correlated to pDARPP-32 immunoreactivity in the preoptic area. This is the first study quantifying pDARPP-32 in a lizard species, and suggests the protein as a potential marker to measure differences in the dopaminergic pathway in a social setting with consideration of embryonic environment and hormonal state.

A wide variety of phytochemicals are consumed for their perceived health benefits. Many of these phytochemicals have been found to alter numerous cell functions, but the mechanisms underlying their biological activity tend to be poorly understood. Phenolic phytochemicals are particularly promiscuous modifiers of membrane protein function, suggesting that some of their actions may be due to a common, membrane bilayer-mediated mechanism. To test whether bilayer perturbation may underlie this diversity of actions, we examined five bioactive phenols reported to have medicinal value: capsaicin from chili peppers, curcumin from turmeric, EGCG from green tea, genistein from soybeans, and resveratrol from grapes. We find that each of these widely consumed phytochemicals alters lipid bilayer properties and the function of diverse membrane proteins. Molecular dynamics simulations show that these phytochemicals modify bilayer properties by localizing to the bilayer/solution interface. Bilayer-modifying propensity was verified using a gramicidin-based assay, and indiscriminate modulation of membrane protein function was demonstrated using four proteins: membrane-anchored metalloproteases, mechanosensitive ion channels, and voltage-dependent potassium and sodium channels. Each protein exhibited similar responses to multiple phytochemicals, consistent with a common, bilayer-mediated mechanism. Our results suggest that many effects of amphiphilic phytochemicals are due to cell membrane perturbations, rather than specific protein binding.

Protein phosphatase 1I (PP-1I) is a major endogenous form of protein phosphatase 1 (PP-1) that consists of the core catalytic subunit PP-1c and the regulatory subunit inhibitor 2 (I-2). Phosphorylation of the Thr-72 residue of I-2 is required for activation of PP-1I. We studied the effects of two protein kinases identified previously in purified brain PP-1I by mass spectrometry, Cdc25C-associated kinase 1 (C-TAK1) and PFTAIRE (PFTK1) kinase, for their ability to regulate PP-1I. Purified C-TAK1 phosphorylated I-2 in reconstituted PP-1I (PP-1c. I-2) on Ser-71, which resulted in partial inhibition of its ATP-dependent phosphatase activity and inhibited subsequent phosphorylation of Thr-72 by the exogenous activating kinase GSK-3. In contrast, purified PFTK1 phosphorylated I-2 at Ser-86, a site known to potentiate Thr-72 phosphorylation and activation of PP-1I phosphatase activity by GSK-3. These findings indicate that brain PP-1I associates with and is regulated by the associated protein kinases C-TAK1 and PFTK1. Multisite phosphorylation of the I-2 regulatory subunit of PP-1I leads to activation or inactivation of PP-1I through bidirectional modulation of Thr-72 phosphorylation, the critical activating residue of I-2.

The 9th International Symposium on Memory and Awareness in Anesthesia (MAA9) was held in Tokyo, Japan on June 20–23, 2014, attracting over 70 delegates from around the world. It was chaired by Jiro Kurata, from the Tokyo Medical and Dental University, and was jointly sponsored by the British Journal of Anaesthesia to support research activities in the fields of awareness during anaesthesia, neurobiological mechanisms of general anaesthesia, consciousness, and memory. This topic complements the recently published National Audit Project NAP5 survey of accidental awareness under general anaesthesia conducted in the UK in 2012 and published in the British Journal of Anaesthesia last year.1–3 The present British Journal of Anaesthesia special issue on Memory and Awareness in Anaesthesia was planned by Hugh Hemmings, a co-organizer of MAA9, to present the most current findings and views on topics from selected presentations during the meeting, in addition to submissions in response to an open call for papers. All the MAA9 abstracts are also included in this special on-line-only issue. Details of the MAA9 programme can be found at the conference website (http://maa9.umin.jp/). The scope of previous MAA symposia has ranged from the neuroscience of anaesthetic action, memory, and consciousness to the clinical aspects of awareness during anaesthesia. The MAA9 followed this tradition, while emphasizing the clinical aspects: epidemiology, diagnosis, prevention, and treatment of intraoperative awareness, with a conference slogan of ‘Minding the Mind of Subconscious Self’. Although anaesthesiology has devoted tremendous efforts to studies of anaesthetic pharmacology and the mechanisms of anaesthetic-induced unconsciousness, which can be approached in a relatively direct manner through behavioural analyses, it has paid much less attention to subconscious processes of mind. At least part of memory is formed in the subconscious domain of mind,4 and for this reason could be resistant to clinical ranges of general anaesthetics aimed to produce elimination of conscious behaviour. The MAA9 was programmed to propose that anaesthesiology should now approach the next stage, the care for the subconscious mind. Detection of intraoperative awareness during anaesthesia has historically been a major focus of research and technology development in anaesthesiology. Currently, there are several kinds of anaesthetic depth monitors, in addition to real-time or simulated monitors of anaesthetic concentrations, available in most operating theatres. Behaviour-based standardization of mathematically processed EEG, cortical evoked potentials, or both has attempted to turn ‘probability of awareness’ into an anaesthetic depth index, or a ‘vital sign for consciousness’. In recent years, such indices for anaesthetic depth have been tested for efficacy in detecting intraoperative awareness compared with anaesthetic concentration monitors, which is summarized in the review by Mashour,5 along with some of the controversial and established aspects of intraoperative awareness. Despite such efforts, titrated administration of anaesthetics, using either an anaesthetic depth or a concentration monitor, has not been successful in decreasing the incidence of intraoperative awareness with recall. No single reliable anaesthetic technique or monitor is yet available to eliminate awareness with recall during general anaesthesia. A significant concern is the increasing reliance on EEG-based monitors of anaesthetic depth to titrate administration of anaesthetic agents. Some of the issues with using processed indices of the EEG rather than the raw waveform are addressed in the review by Hagihira,6 along with editorial commentary by Veselis.7 Purdon and colleagues8 report profound age-dependent changes in the EEG that also have important implications for depth-of-anaesthesia monitors relying on processed EEG signals. Greater sensitivity to anaesthetics evident in the increased susceptibility to burst suppression in the elderly7 is supported by animal studies that demonstrate delayed emergence and increased sensitivity to anaesthetics in old rats.9 This is highlighted in an editorial by Hudson and Proekt.10 Age-dependent changes in the EEG response to anaesthesia also occur in children, as demonstrated for sevoflurane by Akeju and colleagues;11 this phenomenon has implications for EEG-based monitors of anaesthetic depth in both the young and the elderly. The impact of the unique pharmacological profile of ketamine on its EEG signature is described in a study by Pal and colleagues,12 who show that ketamine, like other general anaesthetics, suppresses high-frequency γ activity and promotes a breakdown in cortical coherence. Reasons for failure of general anaesthesia in suppressing memory and awareness could include technical problems or mishaps, such as an inadvertent discontinuation or a low concentration of general anaesthetic agent. Neuromuscular blocking agents, which are non-hypnotics, could also conceal conscious behaviour and affect reliability of EEG-based depth-of-anaesthesia monitors. These issues are highlighted in two studies by Thomsen and colleagues13,14 from a Danish registry of patients with documented butyrylcholinesterase (plasma cholinesterase) deficiency, showing that prolonged paralysis due to impaired elimination of esterase-dependent neuromuscular blockers (succinylcholine or mivacurium) markedly increased the likelihood of awareness during emergence from anaesthesia, particularly when neuromuscular function monitoring was not used. The importance of not withholding neuromuscular function monitoring when paralytic drugs are used during anaesthesia is highlighted in the editorial by Avidan and Stevens.15 An important limitation of EEG-based depth-of-anaesthesia monitors is described by Schuller and colleagues16 in a fascinating study of volunteer anaesthetists who underwent intentional awake paralysis using the isolated forearm technique to show that the bispectral index monitor itself cannot always distinguish ‘anaesthesia’ from paralysis, the implications of which are highlighted in an editorial by Schneider and Pilge.17 Use of the isolated forearm technique as a monitor of depth of anaesthesia and as a research tool into mechanisms of anaesthesia is presented in a thought-provoking debate and review by Pandit and colleagues.18 Not all known cases of intraoperative awareness with recall, however, can be explained by such ‘logical’ causes. Should we now question the ability of general anaesthetics to produce unconsciousness and amnesia reliably? Targeting only conscious behaviour might not necessarily provide reliable protection of patients from traumatic memory of physical or psychological injuries during surgery and anaesthesia. The mechanisms of memory formation are reviewed by Veselis,4 while Pryor and colleagues19 used functional magnetic resonance imaging to show that propofol suppresses emotional memory formation through a hippocampal mechanism. Implicit memory formation during anaesthesia remains understudied and poses a significant problem that could be relevant to post-traumatic stress disorder, and possibly, postoperative delirium and cognitive dysfunction. A report from the Anesthesia Awareness Registry of the American Society of Anesthesiologists indicates that explicit recall of intraoperative awareness can have significant negative psychological impact on patients, which suggests that a more systematic response and follow-up care are necessary.20 Amongst the irreplaceable roles of the MAA conferences has been, and hopefully will continue to be, an investigation into subconscious processing of information during anaesthesia. Now that we have abundant, if not sufficient, evidence for anaesthetic-induced unconsciousness, we should investigate further the science of subconsciousness. The next meeting, MAA10, will continue this conversation around the clinical and basic science of memory and awareness in anaesthesia, to be chaired by Professor Sinikka Munte in Helsinki, Finland in 2017. Until the details of MAA10 are officially announced, the MAA9 facebook page (http://www.facebook.com/maa9.jp/) will remain a source of information on the development of MAA10. Please leave a comment on this page if you have suggestions or would like to be included in the mailing list for MAA10. We sincerely hope that this special issue, marking the up-to-date knowledge and insights on memory and awareness in anaesthesia, will help to promote further scientific inquiries and technological development to eliminate the most dreadful complication of general anaesthesia: intraoperative awareness. Caring for the whole human existence, conscious and subconscious, should continue to be the core mission of anaesthesiology. Finally, we would like to thank all the authors of these excellent articles, all the attendees, support staff, and sponsors of the MAA9, and Oxford University Press for realizing this special issue.

General anesthesia consists of key separable and independent neurobiological end points. Each of these involves distinct but possibly overlapping neuroanatomical and molecular mechanisms that converge to produce the characteristic behavioral end points of anesthesia: amnesia, unconsciousness, and immobility. The potency of various structurally dissimilar general anesthetics correlates with their solubilities in oil (lipophilicity), consistent with critical interactions with hydrophobic molecular targets. The pharmacologically relevant binding sites of general anesthetics are lipophilic cavities in proteins identified by a combination of site-directed mutagenesis and high-resolution structural analysis of anesthetic binding. Specific point mutations render putative target proteins insensitive to certain general anesthetics. Expression of these mutations in mice reduces anesthetic potency for specific end points.

Background Evidence indicates that the anesthetic-sparing effects of α2-adrenergic receptor (AR) agonists involve α2A-AR heteroreceptors on nonadrenergic neurons. Since volatile anesthetics inhibit neurotransmitter release by reducing synaptic vesicle (SV) exocytosis, the authors hypothesized that α2-AR agonists inhibit nonadrenergic SV exocytosis and thereby potentiate presynaptic inhibition of exocytosis by isoflurane. Methods Quantitative imaging of fluorescent biosensors of action potential–evoked SV exocytosis (synaptophysin-pHluorin) and Ca2+ influx (GCaMP6) were used to characterize presynaptic actions of the clinically used α2-AR agonists dexmedetomidine and clonidine, and their interaction with isoflurane, in cultured rat hippocampal neurons. Results Dexmedetomidine (0.1 μM, n = 10) or clonidine (0.5 μM, n = 8) inhibited action potential–evoked exocytosis (54 ± 5% and 59 ± 8% of control, respectively; P < 0.001). Effects on exocytosis were blocked by the subtype-nonselective α2-AR antagonist atipamezole or the α2A-AR–selective antagonist BRL 44408 but not by the α2C-AR–selective antagonist JP 1302. Dexmedetomidine inhibited exocytosis and presynaptic Ca2+ influx without affecting Ca2+ coupling to exocytosis, consistent with an effect upstream of Ca2+–exocytosis coupling. Exocytosis coupled to both N-type and P/Q-type Ca2+ channels was inhibited by dexmedetomidine or clonidine. Dexmedetomidine potentiated inhibition of exocytosis by 0.7 mM isoflurane (to 42 ± 5%, compared to 63 ± 8% for isoflurane alone; P < 0.05). Conclusions Hippocampal SV exocytosis is inhibited by α2A-AR activation in proportion to reduced Ca2+ entry. These effects are additive with those of isoflurane, consistent with a role for α2A-AR presynaptic heteroreceptor inhibition of nonadrenergic synaptic transmission in the anesthetic-sparing effects of α2A-AR agonists.

The pharmacological effects of inhaled anesthetics on ion channel function are poorly understood. Sand et al. analyze macroscopic gating of the prokaryotic voltage-gated sodium channel, NaChBac, using a six-state kinetic scheme and demonstrate that isoflurane modulates microscopic gating properties., Voltage-gated Na+ channels (Nav) have emerged as important presynaptic targets for volatile anesthetic (VA) effects on synaptic transmission. However, the detailed biophysical mechanisms by which VAs modulate Nav function remain unclear. VAs alter macroscopic activation and inactivation of the prokaryotic Na+ channel, NaChBac, which provides a useful structural and functional model of mammalian Nav. Here, we study the effects of the common general anesthetic isoflurane on NaChBac function by analyzing macroscopic Na+ currents (INa) in wild-type (WT) channels and mutants with impaired (G229A) or enhanced (G219A) inactivation. We use a previously described six-state Markov model to analyze empirical WT and mutant NaChBac channel gating data. The model reproduces the mean empirical gating manifest in INa time courses and optimally estimates microscopic rate constants, valences (z), and fractional electrical distances (x) of forward and backward transitions. The model also reproduces gating observed for all three channels in the absence or presence of isoflurane, providing further validation. We show using this model that isoflurane increases forward activation and inactivation rate constants at 0 mV, which are associated with estimated chemical free energy changes of approximately −0.2 and −0.7 kcal/mol, respectively. Activation is voltage dependent (z ≈ 2e0, x ≈ 0.3), inactivation shows little voltage dependence, and isoflurane has no significant effect on either. Forward inactivation rate constants are more than 20-fold greater than backward rate constants in the absence or presence of isoflurane. These results indicate that isoflurane modulates NaChBac gating primarily by increasing forward activation and inactivation rate constants. These findings support accumulating evidence for multiple sites of anesthetic interaction with the channel.