Effect of Repeated Exposure to Sevoflurane on Electroencephalographic Alpha Oscillation in Pediatric Patients Undergoing Radiation Therapy: A Prospective Observational Study.

BACKGROUND: Pharmacological tolerance is defined as a decrease in the effect of a drug over time, or the need to increase the dose to achieve the same effect. It has not been established whether repeated exposure to sevoflurane induces tolerance in children. METHODS: We conducted an observational study in children younger than 6 years of age scheduled for multiple radiotherapy sessions with sevoflurane anesthesia. To evaluate the development of sevoflurane tolerance, we analyzed changes in electroencephalographic spectral power at induction, across sessions. We fitted individual and group-level linear regression models to evaluate the correlation between the outcomes and sessions. In addition, a linear mixed-effect model was used to evaluate the association between radiotherapy sessions and outcomes. RESULTS: Eighteen children were included and the median number of radiotherapy sessions per child was 28 (interquartile range: 10 to 33). There was no correlation between induction time and radiotherapy sessions. At the group level, the linear mixed-effect model showed, in a subgroup of patients, that alpha relative power and spectral edge frequency 95 were inversely correlated with the number of anesthesia sessions. Nonetheless, this subgroup did not differ from the other subjects in terms of age, sex, or the total number of radiotherapy sessions. CONCLUSIONS: Our results suggest that children undergoing repeated anesthesia exposure for radiotherapy do not develop tolerance to sevoflurane. However, we found that a group of patients exhibited a reduction in the alpha relative power as a function of anesthetic exposure. These results may have implications that justify further studies.

Non-pharmacological prevention of postoperative delirium by occupational therapy teams: A randomized clinical trial.

Background: Patients who develop postoperative delirium (POD) have several clinical complications, such as increased morbidity, increased hospital stays, higher hospital costs, cognitive and functional impairment, and higher mortality. POD is a clinical condition preventable by standard non-pharmacological measures An intensive Occupational Therapy (OT) intervention has been shown to be highly effective in preventing delirium in critically ill medical patients, but it is unknown the effect in surgical patients. Thus, we designed a prospective clinical study with the aim to determine whether patients undergoing intervention by the OT team have a lower incidence of POD compared to the group treated only with standard measures. Methods: A multicenter, single-blind, randomized clinical trial was conducted between October 2018 and April 2021, in Santiago of Chile, at a university hospital and at a public hospital. Patients older than 75 years undergoing elective major surgery were eligible for the trial inclusion. Patients with cognitive impairment, severe communication disorder and cultural language limitation, delirium at admission or before surgery, and enrolled in another study were excluded. The intervention consisted of OT therapy twice a day plus standard internationally recommended non-pharmacological prevention intervention during 5 days after surgery. Our primary outcome was development of delirium and postoperative subsyndromal delirium. Results: In total 160 patients were studied. In the interventional group, treated with an intensive prevention by OT, nine patients (12.9%) developed delirium after surgery and in the control group four patients (5.5%) [p = 0.125, RR 2.34 CI 95 (0.75-7.27)]. Whereas subsyndromal POD was present in 38 patients in the control group (52.1%) and in 34 (48.6%) in the intervention group [p = 0.4, RR 0.93 CI95 (0.67-1.29)]. A post hoc analysis determined that the patient's comorbidity and cognitive status prior to hospitalization were the main risk factors to develop delirium after surgery. Discussion: Patients undergoing intervention by the OT team did not have a lower incidence of POD compared to the group treated only with standard non-pharmacological measures in adults older than 75 years who went for major surgery. Clinical trial registration: www.ClinicalTrials.gov, identifier NCT03704090.

Electroencephalography spectral edge frequency and suppression rate-guided sedation in patients with COVID-19: A randomized controlled trial.

Background: Sedation in coronavirus disease 2019 (COVID-19) patients has been identified as a major challenge. We aimed to investigate whether the use of a multiparameter electroencephalogram (EEG) protocol to guide sedation in COVID-19 patients would increase the 30-day mechanical ventilation-free days (VFD). Methods: We conducted a double-blind randomized clinical trial. We included patients with severe pneumonia due to COVID-19 who required mechanical ventilation (MV) and deep sedation. We randomized to the control (n = 25) or multiparameter group (n = 25). Sedation in the intervention group was administered following the standard institutional protocols together with a flow chart designed to reduce the propofol administration dose if the EEG suppression rate was over 2% or the spectral edge frequency 95 (SEF95) was below 10 Hz. We performed an intention-to-treat analysis to evaluate our primary outcome (30-day VFD). Results: There was no difference in VFD at day 30 (median: 11 [IQR 0-20] days in the control group vs. 0 [IQR 0-21] days in the BIS multiparameter group, p = 0.87). Among secondary outcomes, we documented a 17% reduction in the total adjusted propofol administered during the first 5 days of the protocol [median: 2.3 (IQR 1.9-2.8) mg/k/h in the control group vs. 1.9(IQR 1.5-2.2) mg/k/h in the MP group, p = 0.005]. This was accompanied by a higher average BIS value in the intervention group throughout the treatment period. Conclusion: A sedation protocol guided by multivariate EEG-derived parameters did not increase the 30-day VFD. However, the intervention led to a reduction in total propofol administration.

Electroencephalographic Alpha and Delta Oscillation Dynamics in Response to Increasing Doses of Propofol.

BACKGROUND: The electroencephalogram (EEG) may be useful for monitoring anesthetic depth and avoiding overdose. We aimed to characterize EEG-recorded brain oscillations during increasing depth of anesthesia in a real-life surgical scenario. We hypothesized that alpha power and coherency will diminish as propofol dose increases between loss of consciousness (LOC) and an EEG burst suppression (BS) pattern. METHODS: This nonrandomized dose-response clinical trial with concurrent control included EEG monitoring in 16 patients receiving slowly increasing doses of propofol. We assessed 3 intraoperative EEG segments (LOC, middle-dose, and BS) with spectral analysis. RESULTS: Alpha band power diminished with each step increase in propofol dose. Average alpha power and average delta power during the BS step (-1.4±3.8 and 6.2±3.1 dB, respectively) were significantly lower than during the LOC step (2.8±2.6; P=0.004 and 10.1±5.2 dB; P=0.03, respectively). Peak alpha power was significantly higher during the LOC (5.4±2.6 dB) compared with middle-dose (2.6±3.6; P=0.04) and BS (0.7±3.2; P=0.0002) steps. In addition, as propofol dose increased, alpha band coherence between the F7 and F8 electrodes decreased, whereas delta band coherence exhibited a biphasic response (initial increase between LOC and middle-dose steps and decrease between middle-dose and BS steps). CONCLUSION: We report compelling data regarding EEG patterns associated with increases in propofol dose. This information may more accurately define "therapeutic windows" for anesthesia and provide insights into brain dynamics that are sequentially affected by increased anesthetic doses.

Association Between Lower Preoperative Cognition With Intraoperative Electroencephalographic Features Consistent With Deep States of Anesthesia in Older Patients: An Observational Cohort Study.

BACKGROUND: Patients with low cognitive performance are thought to have a higher risk of postoperative neurocognitive disorders. Here we analyzed the relationship between preoperative cognition and anesthesia-induced brain dynamics. We hypothesized that patients with low cognitive performance would be more sensitive to anesthetics and would show differences in electroencephalogram (EEG) activity consistent with a brain anesthesia overdose. METHODS: This is a retrospective analysis from a previously reported observational study. We evaluated cognitive performance using the Montreal cognitive assessment (MoCA) test. All patients received general anesthesia maintained with sevoflurane or desflurane during elective major abdominal surgery. We analyzed the EEG using spectral, coherence, and phase-amplitude modulation analyses. RESULTS: Patients were separated into a low MoCA group (<26 points, n = 12) and a high MoCA group (n = 23). There were no differences in baseline EEG, nor end-tidal age-corrected minimum alveolar concentration (MACage). However, under anesthesia, the low MoCA group had lower α-ß power (high MoCA: 2.9 [interquartile range {IQR}: 0.6-5.8 dB] versus low MoCA: -1.2 [IQR: -2.1 to 0.6 dB], difference 4.1 [1.0-5.7]) and a lower α peak frequency (high MoCA: 9.0 [IQR: 8.3-9.8 Hz] versus low MoCA: 7.5 [IQR: 6.3-9.0 Hz], difference 1.5 [0-2.3]) compared to the high MoCA group. The low MoCA group also had a lower α band coherence and a stronger peak-max phase-amplitude coupling (PAC). Finally, patients in the low MoCA group had longer emergence times (high MoCA 663 ± 345 seconds versus low MoCA: 960 ± 352 seconds, difference 297 [15-578]). Multiple linear regression shows up that both age and MoCA scores are independently associated with intraoperative α-ß power. CONCLUSIONS: All these EEG features, together with a prolonged emergence time, are consistent with the possibility that older patients with low cognitive performance are receiving a brain anesthesia overdose compare to cognitive normal patients.

Mortalidad posoperatoria después de un año del evento quirúrgico en una cohorte de pacientes adultos mayores / One-year postoperative mortality in a cohort of older patients

AIM: To determine one-year postoperative mortality in patients older than 65 years at the Hospital Clínico de la Universidad de Chile. MATERIAL AND METHODS: After approval by the ethics committee, a random sample of 235 patients was obtained from 2,832 patients ≥ 65 years who underwent surgery that required general or regional anesthesia. This sample size was calculated to detect a mortality incidence of 10% ± 5%, with a power of 80%, an  error of 0.05, and a loss of 10%. We recorded the demographic variables together with the Charlson Comorbidity Index (CCI) score from the electronic medical records. While the date of mortality was obtained from the Civil Registry. RESULTS: We studied 233 patients with an age of 73.1 ± 6.3 years, 52.4% were women, and a mean CCI score of 4 (2-11) points. In total 65.7% underwent general anesthesia, 34.3% underwent regional anesthesia, and 24% underwent major surgery. Mortality at 30 days was 1.3% and at one year it was 6%. The patients who died were older and had a higher CCI, especially due to a higher incidence of dementia and solid tumors with metastases. CONCLUSIONS: In our study, postoperative mortality at one year was lower than those reported in older adult patients, and deceased patients were older with more comorbidities, especially with solid tumors with metastases and dementia.

OBJETIVO: Determinar la mortalidad al primer año postoperatorio de pacientes mayores de 65 años en el Hospital Clínico de la Universidad de Chile.MATERIALES Y MÉTODOS: Tras la aprobación del comité de ética, se obtuvo una muestra aleatoria de 235 pacientes de un total de 2.832 pacientes ≥ 65 años sometidos a una cirugía que requirió de anestesia general o regional. Este tamaño muestral fue calculado para detectar una incidencia de mortalidad de 10% ± 4%, con un poder de 80%, un error  de 0,05 y una pérdida de 10%. Se registraron los antecedentes demográficos, se calculó el puntaje de Charlson Comorbidity Index (CCI) y se consignó la mortalidad desde el Registro Civil. RESULTADOS: Se estudiaron 233 pacientes con una edad de 73,1 ± 6,3 años, un 52,4% fueron mujeres y una mediana del puntaje CCI de 4 (2-11) puntos. En total 65,7% fue intervenido bajo anestesia general y 34,3% bajo anestesia regional, y 24% fue sometido a una cirugía de alta complejidad. La mortalidad a los 30 días fue de 1,3% y al año fue de 6%. El grupo de pacientes fallecidos se caracterizó por ser más añoso y tener un CCI mayor, especialmente por una mayor incidencia de demencia y tumores con metástasis. CONCLUSIONES: En nuestro estudio se observó una mortalidad postoperatoria al año menor a lo reportado internacionalmente en pacientes adultos mayores. La mortalidad fue mayor en pacientes de mayor edad, con un mayor número de comorbilidades, con tumores sólidos con metástasis y demencia.

Intraoperative Ketamine and Magnesium Therapy to Control Postoperative Pain After Abdominoplasty and/or Liposuction: A Clinical Randomized Trial.

PURPOSE: This study aimed to compare the effects of ketamine and ketamine associated with magnesium on opioid consumption and pain scores in patients undergoing abdominoplasty and/or liposuction compared to standard treatment. PATIENTS AND METHODS: A total of 63 patients were included and randomized as follows: 21 patients in the Control group, 20 patients in the Ketamine group (Ket), and 22 patients in the Ketamine-magnesium group (KetMag). The KetMag group received an IV bolus of 0.3 mg/kg of ketamine and 50 mg/kg magnesium, followed by continuous infusion of ketamine (0.15 mg/kg/h) and magnesium (10 mg/kg/h) until extubation. The Ket group received the same bolus and infusion of ketamine, together with a bolus and continuous infusion of placebo instead of magnesium. The Control group received saline instead of ketamine and magnesium. The groups were compared in morphine consumption during the first 12h, body-postoperative pain and disability scale until the 90th day, the time until the first morphine request on the PCA pump, pain scores, and the adverse effects related to the use of study drugs. RESULTS: The KetMag group had a lower morphine consumption by almost 50% during the first 12h than the Control and the Ket groups. In addition, the KetMag group required the first dose of morphine later than the other two groups. There were no differences in the adverse effects of the proposed treatments. Finally, multiple linear regression and a nonlinear approach analysis indicated that the Control group experienced a higher degree of pain and increased morphine consumption per hour than Ket and KetMag groups. CONCLUSION: Co-administration of intraoperative ketamine plus magnesium and ketamine alone are an effective and easy regime for reducing pain and opioid consumption in the postoperative period.

Sensibilidad aumentada a lidocaína: estudio genético de un caso / Increased sensitivity to lidocaine: Genetic study of a case

Systemic toxicity by local anesthetics (LAs) is a severe and feared complication in anesthetic practice that generally results from the administration of an inappropriately high dose of LAs or an injection at an inappropriate place, either intravascular or a site with high absorption[1]. However, it is known that the susceptibility to these drugs may vary within the population, which may occur due to genetic changes in the LA binding site, located in the potential-dependent Na+ channels (Nav), thus increasing or decreasing its affinity and, therefore, its clinical consequences. We present a case of a 61 years-old female patient with a medical history of increased sensitivity to LAs. In this scenario, a genetic study was performed to exclude a Nav channel dysfunction.

La toxicidad sistémica por anestésicos locales (ALs) es una grave y temida complicación en la práctica anestésica que generalmente resulta de la administración de una dosis inapropiadamente alta de ALs o a una inyección en un lugar inadecuado, llámese intravascular o un sitio al alta absorción[1]. A pesar de lo anterior, es conocido que la susceptibilidad al efecto de estos fármacos puede variar dentro de la población, lo cual puede ocurrir debido a cambios genéticos en el sitio de unión de los AL, localizado en los canales de Na+ dependientes de potencial (Nav), incrementando o disminuyendo así su afinidad y, por ende, sus consecuencias clínicas. Presentamos el caso de una paciente de 61 años con historia de sensibilidad aumentada a Als. En este escenario, se le ofreció un estudio genético para excluir una disfunción específica a nivel de canal Nav

Remifentanil-Induced Secondary Hyperalgesia Is Not Prevented By Preoperative Acetazolamide Administration In Patients Undergoing Total Thyroidectomy: A Randomized Controlled Trial.

PURPOSE: Acute administration of remifentanil may lead to opioid-induced hyperalgesia (OIH). Studies in mice suggest that OIH is mediated by impaired anionic homeostasis in spinal lamina I neurons due to a down-regulation of the K+-Cl- co-transporter KCC2, which was reverted using acetazolamide (ACTZ), a carbonic anhydrase inhibitor. We propose that ACTZ prevents remifentanil-mediated OIH in humans. PATIENTS AND METHODS: We conducted a randomized, double-blind, placebo-controlled clinical trial between December 2016 and September 2018. Patients were randomly allocated to receive ACTZ (250 mg of ACTZ 2 h before surgery) or placebo. To detect hyperalgesia, mechanical pain threshold (MPT) were measured before and after surgery using hand-held von Frey filaments in the forearm. Anesthesia was maintained with remifentanil at a target effect site of 4.5 ± 0.5 ng/mL, and sevoflurane at an end-tidal concentration of 0.8 MAC corrected for age. RESULTS: In total, 47 patients completed the study. Both groups were comparable in the baseline characteristics and intraoperative variables. Baseline MPT were similar in both groups. However, MPT in the forearm significantly diminished in the time in both groups. Finally, postoperative pain and morphine consumption were similar between groups. CONCLUSION: Both groups developed remifentanil-mediated OIH at 12-18 h after surgery. However, ACTZ did not prevent the MPT reduction in patients undergoing total thyroidectomy.

Intraoperative Low Alpha Power in the Electroencephalogram Is Associated With Postoperative Subsyndromal Delirium.

BACKGROUND: Postoperative delirium (PD) and subsyndromal delirium (PSSD) are frequent complications in older patients associated with poor long-term outcome. It has been suggested that certain electroencephalogram features may be capable of identifying patients at risk during surgery. Thus, the goal of this study was to characterize intraoperative electroencephalographic markers to identify patients prone to develop PD or PSSD. METHODS: We conducted an exploratory observational study in older patients scheduled for elective major abdominal surgery. Intraoperative 16 channels electroencephalogram was recorded, and PD/PSSD were diagnosed after surgery with the confusion assessment method (CAM). The total power spectra and relative power of alpha band were calculated. RESULTS: PD was diagnosed in 2 patients (6.7%), and 11 patients (36.7%) developed PSSD. All of them (13 patients, PD/PSSD group) were compared with patients without any alterations in CAM (17 patients, control group). There were no detectable power spectrum differences before anesthesia between both groups of patients. However, PD/PSSD group in comparison with control group had a lower intraoperative absolute alpha power during anesthesia (4.4 ± 3.8 dB vs. 9.6 ± 3.2 dB, p = 0.0004) and a lower relative alpha power (0.09 ± 0.06 vs. 0.21 ± 0.08, p < 0.0001). These differences were independent of the anesthetic dose. Finally, relative alpha power had a good ability to identify patients with CAM alterations in the ROC analysis (area under the curve 0.90 (CI 0.78-1), p < 0.001). DISCUSSION: In conclusion, a low intraoperative alpha power is a novel electroencephalogram marker to identify patients who will develop alterations in CAM - i.e., with PD or PSSD - after surgery.

Gabapentin increases expression of δ subunit-containing GABAA receptors.

BACKGROUND: Gabapentin is a structural analog of the inhibitory neurotransmitter γ-aminobutyric acid (GABA). Its anticonvulsant, analgesic and anxiolytic properties suggest that it increases GABAergic inhibition; however, the molecular basis for these effects is unknown as gabapentin does not directly modify GABA type A (GABAA) receptor function, nor does it modify synaptic inhibition. Here, we postulated that gabapentin increases expression of δ subunit-containing GABAA (δGABAA) receptors that generate a tonic inhibitory conductance in multiple brain regions including the cerebellum and hippocampus. METHODS: Cell-surface biotinylation, Western blotting, electrophysiologic recordings, behavioral assays, high-performance liquid chromatography and gas chromatography-mass spectrometry studies were performed using mouse models. FINDINGS: Gabapentin enhanced expression of δGABAA receptors and increased a tonic inhibitory conductance in neurons. This increased expression likely contributes to GABAergic effects as gabapentin caused ataxia and anxiolysis in wild-type mice but not δ subunit null-mutant mice. In contrast, the antinociceptive properties of gabapentin were observed in both genotypes. Levels of GABAA receptor agonists and neurosteroids in the brain were not altered by gabapentin. INTERPRETATION: These results provide compelling evidence to account for the GABAergic properties of gabapentin. Since reduced expression of δGABAA receptor occurs in several disorders, gabapentin may have much broader therapeutic applications than is currently recognized. FUND: Supported by a Foundation Grant (FDN-154312) from the Canadian Institutes of Health Research (to B.A.O.); a NSERC Discovery Grant (RGPIN-2016-05538), a Canada Research Chair in Sensory Plasticity and Reconsolidation, and funding from the University of Toronto Centre for the Study of Pain (to R.P.B.).

Reduced expression of α5GABAA receptors elicits autism-like alterations in EEG patterns and sleep-wake behavior.

A reduction in the activity of GABAA receptors, particularly α5 subunit-containing GABAA receptors (α5GABAARs), has been implicated in the etiology of Autism Spectrum Disorders (ASD). Genetically modified mice that lack α5GABAARs (Gabra5-/-) exhibit autism-like behaviors and both enhanced and impaired learning and memory, depending on the behavioral task. The aim of this study was to examine the electroencephalogram (EEG) activity and sleep-wake behaviors in Gabra5-/- mice and wild-type mice. In addition, since some individuals with ASD can exhibit elevated innate immune response, mice were treated with lipopolysaccharide (LPS; 125mg/kg intraperitoneal injection) or vehicle and EEG and sleep-wake patterns were assessed. The results showed that Gabra5-/- mice (n=3) exhibited elevated 0-2Hz EEG activity during all sleep-wake states (all p<0.04), decreased 8-12Hz EEG activity during REM sleep (p=0.04), and decreased sleep spindles under baseline conditions compared to wild-type controls (n=4) (all p≤0.03). Alterations in EEG activity and sleep-wake behavior were identified in Gabra5-/- mice following treatment with LPS, however these changes were similar to those in wild-type mice. Our findings support the hypothesis that reduced α5GABAAR activity contributes to an ASD phenotype. The results also suggest that Gabra5-/- mice may serve as an animal model for ASD, as assessed through EEG activity and sleep-wake behaviors.

Ketamine Increases the Function of γ-Aminobutyric Acid Type A Receptors in Hippocampal and Cortical Neurons.

BACKGROUND: The "dissociative " general anesthetic ketamine is a well-known N-methyl-D-aspartate receptor antagonist. However, whether ketamine, at clinically relevant concentrations, increases the activity of inhibitory γ-aminobutyric acid (GABA) receptor type A (GABAA) receptors in different brain regions remains controversial. Here, the authors studied the effects of ketamine on synaptic and extrasynaptic GABAA receptors in hippocampal neurons. Ketamine modulation of extrasynaptic GABAA receptors in cortical neurons was also examined. METHODS: Whole cell currents were recorded from cultured murine neurons. Current evoked by exogenous GABA, miniature inhibitory postsynaptic currents, and currents directly activated by ketamine were studied. RESULTS: Ketamine did not alter the amplitude, frequency, or kinetics of postsynaptic currents but increased a tonic inhibitory current generated by extrasynaptic GABAA receptors in hippocampal neurons. For example, ketamine (100 µM) increased the tonic current by 33.6 ± 6.5% (mean ± SEM; 95% CI, 18.2 to 48.9; n = 8, P < 0.001). Ketamine shifted the GABA concentration-response curve to the left, but only when GABAA receptors were activated by low concentrations of GABA (n = 6). The selective increase in tonic current was attributed to ketamine increasing the apparent potency of GABA at high-affinity extrasynaptic GABAA receptors. Ketamine also increased a tonic current in cortical neurons (n = 11). Ketamine directly gated the opening of GABAA receptors, but only at high concentrations that are unlikely to occur during clinical use. CONCLUSIONS: Clinically relevant concentrations of ketamine increased the activity of high-affinity extrasynaptic GABAA receptors in the hippocampus and cortex, an effect that likely contributes to ketamine's neurodepressive properties.

Inflammation Increases Neuronal Sensitivity to General Anesthetics.

BACKGROUND: Critically ill patients with severe inflammation often exhibit heightened sensitivity to general anesthetics; however, the underlying mechanisms remain poorly understood. Inflammation increases the number of γ-aminobutyric acid type A (GABAA) receptors expressed on the surface of neurons, which supports the hypothesis that inflammation increases up-regulation of GABAA receptor activity by anesthetics, thereby enhancing the behavioral sensitivity to these drugs. METHODS: To mimic inflammation in vitro, cultured hippocampal and cortical neurons were pretreated with interleukin (IL)-1ß. Whole cell patch clamp methods were used to record currents evoked by γ-aminobutyric acid (GABA) (0.5 µM) in the absence and presence of etomidate or isoflurane. To mimic inflammation in vivo, mice were treated with lipopolysaccharide, and several anesthetic-related behavioral endpoints were examined. RESULTS: IL-1ß increased the amplitude of current evoked by GABA in combination with clinically relevant concentrations of either etomidate (3 µM) or isoflurane (250 µM) (n = 5 to 17, P < 0.05). Concentration-response plots for etomidate and isoflurane showed that IL-1ß increased the maximal current 3.3-fold (n = 5 to 9) and 1.5-fold (n = 8 to 11), respectively (P < 0.05 for both), whereas the half-maximal effective concentrations were unchanged. Lipopolysaccharide enhanced the hypnotic properties of both etomidate and isoflurane. The immobilizing properties of etomidate, but not isoflurane, were also increased by lipopolysaccharide. Both lipopolysaccharide and etomidate impaired contextual fear memory. CONCLUSIONS: These results provide proof-of-concept evidence that inflammation increases the sensitivity of neurons to general anesthetics. This increase in anesthetic up-regulation of GABAA receptor activity in vitro correlates with enhanced sensitivity for GABAA receptor-dependent behavioral endpoints in vivo.

KCa3.1-Dependent Hyperpolarization Enhances Intracellular Ca2+ Signaling Induced by fMLF in Differentiated U937 Cells.

Formylated peptides are chemotactic agents generated by pathogens. The most relevant peptide is fMLF (formyl-Met-Leu-Phe) which participates in several immune functions, such as chemotaxis, phagocytosis, cytokine release and generation of reactive oxygen species. In macrophages fMLF-dependent responses are dependent on both, an increase in intracellular calcium concentration and on a hyperpolarization of the membrane potential. However, the molecular entity underlying this hyperpolarization remains unknown and it is not clear whether changes in membrane potential are linked to the increase in intracellular Ca2+. In this study, differentiated U937 cells, as a macrophage-like cell model, was used to characterize the fMLF response using electrophysiological and Ca2+ imaging techniques. We demonstrate by means of pharmacological and molecular biology tools that fMLF induces a Ca2+-dependent hyperpolarization via activation of the K+ channel KCa3.1 and thus, enhancing fMLF-induced intracellular Ca2+ increase through an amplification of the driving force for Ca2+ entry. Consequently, enhanced Ca2+ influx would in turn lengthen the hyperpolarization, operating as a positive feedback mechanism for fMLF-induced Ca2+ signaling.

Sustained increase in α5GABAA receptor function impairs memory after anesthesia.

Many patients who undergo general anesthesia and surgery experience cognitive dysfunction, particularly memory deficits that can persist for days to months. The mechanisms underlying this postoperative cognitive dysfunction in the adult brain remain poorly understood. Depression of brain function during anesthesia is attributed primarily to increased activity of γ-aminobutyric acid type A receptors (GABA(A)Rs), and it is assumed that once the anesthetic drug is eliminated, the activity of GABA(A)Rs rapidly returns to baseline and these receptors no longer impair memory. Here, using a murine model, we found that a single in vivo treatment with the injectable anesthetic etomidate increased a tonic inhibitory current generated by α5 subunit-containing GABA(A)Rs (α5GABA(A)Rs) and cell-surface expression of α5GABA(A)Rs for at least 1 week. The sustained increase in α5GABA(A)R activity impaired memory performance and synaptic plasticity in the hippocampus. Inhibition of α5GABA(A)Rs completely reversed the memory deficits after anesthesia. Similarly, the inhaled anesthetic isoflurane triggered a persistent increase in tonic current and cell-surface expression of α5GABA(A)Rs. Thus, α5GABA(A)R function does not return to baseline after the anesthetic is eliminated, suggesting a mechanism to account for persistent memory deficits after general anesthesia.