RESUMO
Cannabis has been used as an herbal remedy for thousands of years, and recent research indicates promising new uses in medicine. So far, some studies have shown cannabinoids to be safe in helping mitigate some cancer-associated complications, including chemotherapy-induced nausea and vomiting, cancer-associated pain, and tumor growth. Researchers have been particularly interested in the potential uses of cannabinoids in treating cancer due to their ability to regulate cancer-related cell cycle pathways, prompting many beneficial effects, such as tumor growth prevention, cell cycle obstruction, and cell death. Cannabinoids have been found to affect tumors of the brain, prostate, colon and rectum, breast, uterus, cervix, thyroid, skin, pancreas, and lymph. However, the full potential of cannabinoids is yet to be understood. This review discusses current knowledge on the promising applications of cannabinoids in treating three different side effects of cancer-chemotherapy-induced nausea and vomiting, cancer-associated pain, and tumor development. The findings suggest that cannabinoids can be used to address some side effects of cancer and to limit the growth of tumors, though a lack of supporting clinical trials presents a challenge for use on actual patients. An additional challenge will be examining whether any of the over one hundred naturally occurring cannabinoids or dozens of synthetic compounds also exhibit useful clinical properties. Currently, clinical trials are underway; however, no regulatory agencies have approved cannabinoid use for any cancer symptoms beyond antinausea.
Assuntos
Antineoplásicos , Dor do Câncer , Canabinoides , Neoplasias , Feminino , Masculino , Humanos , Canabinoides/uso terapêutico , Náusea/tratamento farmacológico , Náusea/etiologia , Vômito/induzido quimicamente , Vômito/tratamento farmacológico , Neoplasias/complicações , Neoplasias/tratamento farmacológicoRESUMO
Intravenous anesthetic agents are associated with cardiovascular instability and poorly tolerated in patients with cardiovascular disease, trauma, or acute systemic illness. We hypothesized that a new class of intravenous (IV) anesthetic molecules that is highly selective for the slow type of γ-aminobutyric acid type A receptor (GABAAR) could have potent anesthetic efficacy with limited cardiovascular effects. Through in silico screening using our GABAAR model, we identified a class of lead compounds that are N-arylpyrrole derivatives. Electrophysiological analyses using both an in vitro expression system and intact rodent hippocampal brain slice recordings demonstrate a GABAAR-mediated mechanism. In vivo experiments also demonstrate overt anesthetic activity in both tadpoles and rats with a potency slightly greater than that of propofol. Unlike the clinically approved GABAergic anesthetic etomidate, the chemical structure of our N-arylpyrrole derivative is devoid of the chemical moieties producing adrenal suppression. Our class of compounds also shows minimal to no suppression of blood pressure, in marked contrast to the hemodynamic effects of propofol. These compounds are derived from chemical structures not previously associated with anesthesia and demonstrate that selective targeting of GABAAR-slow subtypes may eliminate the hemodynamic side effects associated with conventional IV anesthetics.
Assuntos
Anestésicos , Agonistas de Receptores de GABA-A , Pirróis , Receptores de GABA-A/metabolismo , Anestésicos/química , Anestésicos/farmacologia , Animais , Avaliação Pré-Clínica de Medicamentos , Etomidato/química , Etomidato/farmacologia , Agonistas de Receptores de GABA-A/química , Agonistas de Receptores de GABA-A/farmacologia , Humanos , Camundongos , Pirróis/química , Pirróis/farmacologia , Ratos , Receptores de GABA-A/genética , Xenopus laevisRESUMO
BACKGROUND: Several devices record and interpret patient brain activity via electroencephalogram (EEG) to aid physician assessment of anaesthetic effect. Few studies have compared EEG monitors on data from the same patient. Here, we describe a set-up to simultaneously compare the performance of three processed EEG monitors using pre-recorded EEG signals from older surgical patients. METHODS: A playback system was designed to replay EEG signals into three different commercially available EEG monitors. We could then simultaneously calculate indices from the SedLine® Root (Masimo Inc., Irvine, CA, USA; patient state index [PSI]), bilateral BIS VISTA™ (Medtronic Inc., Minneapolis, MN, USA; bispectral index [BIS]), and Datex Ohmeda S/5 monitor with the Entropy™ Module (GE Healthcare, Chicago, IL, USA; E-entropy index [Entropy]). We tested the ability of each system to distinguish activity before anaesthesia administration (pre-med) and before/after loss of responsiveness (LOR), and to detect suppression incidences in EEG recorded from older surgical patients receiving beta-adrenergic blockers. We show examples of processed EEG monitor output tested on 29 EEG recordings from older surgical patients. RESULTS: All monitors showed significantly different indices and high effect sizes between comparisons pre-med to after LOR and before/after LOR. Both PSI and BIS showed the highest percentage of deeply anaesthetised indices during periods with suppression ratios (SRs) > 25%. We observed significant negative correlations between percentage of suppression and indices for all monitors (at SR >5%). CONCLUSIONS: All monitors distinguished EEG changes occurring before anaesthesia administration and during LOR. The PSI and BIS best detected suppressed periods. Our results suggest that the PSI and BIS monitors might be preferable for older patients with risk factors for intraoperative awareness or increased sensitivity to anaesthesia.
Assuntos
Antagonistas Adrenérgicos beta/farmacologia , Anestésicos/farmacologia , Eletroencefalografia/instrumentação , Monitorização Intraoperatória/métodos , Idoso , Idoso de 80 Anos ou mais , Monitores de Consciência , Feminino , Humanos , Masculino , Monitorização Intraoperatória/instrumentação , Fatores de RiscoRESUMO
Ketamine is a clinical anesthetic and antidepressant. Although ketamine is a known NMDA receptor antagonist, the mechanisms contributing to antidepression are unclear. This present study examined the loci and duration of ketamine's actions, and the involvement of NMDA receptors. Local field potentials were recorded from the CA1 region of mouse hippocampal slices. Ketamine was tested at antidepressant and anesthetic concentrations. Effects of NMDA receptor antagonists APV and MK-801, GABA receptor antagonist bicuculline, and a potassium channel blocker TEA were also studied. Ketamine decreased population spike amplitudes during application, but a long-lasting increase in amplitudes was seen during washout. Bicuculline reversed the acute effects of ketamine, but the washout increase was not altered. This long-term increase was statistically significant, sustained for >2 h, and involved postsynaptic mechanisms. A similar effect was produced by MK-801, but was only partially evident with APV, demonstrating the importance of the NMDA receptor ion channel block. TEA also produced a lasting excitability increase, indicating a possible involvement of potassium channel block. This is this first report of a long-lasting increase in excitability following ketamine exposure. These results support a growing literature that increased GABA inhibition contributes to ketamine anesthesia, while increased excitatory transmission contributes to its antidepressant effects.
Assuntos
Anestésicos/farmacologia , Antidepressivos/farmacologia , Hipocampo/efeitos dos fármacos , Ketamina/farmacologia , Neurônios/efeitos dos fármacos , Transmissão Sináptica/efeitos dos fármacos , Animais , Hipocampo/citologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Neurônios/citologia , Receptores de N-Metil-D-Aspartato/metabolismoRESUMO
Anesthetic agents cause unique electroencephalogram (EEG) activity resulting from actions on their diverse molecular targets. Typically to produce balanced anesthesia in the clinical setting, several anesthetic and adjuvant agents are combined. This creates challenges for the clinical use of intraoperative EEG monitoring, because computational approaches are mostly limited to spectral analyses and different agents and combinations produce different EEG responses. Thus, testing of many combinations of agents is needed to generate accurate, protocol independent analyses. Additionally, most studies to develop new computational approaches take place in young, healthy adults and electrophysiological responses to anesthetics vary widely at the extremes of age, due to physiological brain differences. Below, we discuss the challenges associated with EEG biomarker identification for anesthetic depth based on the diversity of molecular targets. We suggest that by focusing on the generalized effects of anesthetic agents on network activity, we can create paths for improved universal analyses.
Assuntos
Anestesia/métodos , Anestésicos/administração & dosagem , Eletroencefalografia/efeitos dos fármacos , Monitorização Intraoperatória/métodos , Anestésicos/classificação , Animais , Humanos , Ketamina/administração & dosagem , Propofol/administração & dosagem , Remifentanil/administração & dosagem , Sevoflurano/administração & dosagemRESUMO
Theta oscillations generated in hippocampal (HPC) and cortical neuronal networks are involved in various aspects of brain function, including sensorimotor integration, movement planning, memory formation and attention. Disruptions of theta rhythms are present in individuals with brain disorders, including epilepsy and Alzheimer's disease. Theta rhythm generation involves a specific interplay between cellular (ion channel) and network (synaptic) mechanisms. HCN channels are theta modulators, and several medications are known to enhance their activity. We investigated how different doses of lamotrigine (LTG), an HCN channel modulator, and antiepileptic and neuroprotective agent, would affect HPC theta rhythms in acute HPC slices (in vitro) and anaesthetized rats (in vivo). Whole-cell patch clamp recordings revealed that LTG decreased GABAA-fast transmission in CA3 cells, in vitro. In addition, LTG directly depressed CA3 and CA1 pyramidal neuron excitability. These effects were partially blocked by ZD 7288, a selective HCN blocker, and are consistent with decreased excitability associated with antiepileptic actions. Lamotrigine depressed HPC theta oscillations in vitro, also consistent with its neuronal depressant effects. In contrast, it exerted an opposite, enhancing effect, on theta recorded in vivo. The contradictory in vivo and in vitro results indicate that LTG increases ascending theta activating medial septum/entorhinal synaptic inputs that over-power the depressant effects seen in HPC neurons. These results provide new insights into LTG actions and indicate an opportunity to develop more precise therapeutics for the treatment of dementias, memory disorders and epilepsy.
Assuntos
Potenciais de Ação/efeitos dos fármacos , Anticonvulsivantes/farmacologia , Hipocampo/efeitos dos fármacos , Lamotrigina/farmacologia , Ritmo Teta/efeitos dos fármacos , Animais , Região CA3 Hipocampal/citologia , Região CA3 Hipocampal/efeitos dos fármacos , Região CA3 Hipocampal/fisiologia , Hipocampo/citologia , Hipocampo/fisiologia , Masculino , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Ratos , Ratos Wistar , Sinapses/efeitos dos fármacos , Sinapses/fisiologia , Ácido gama-Aminobutírico/metabolismoRESUMO
This study investigated behavioral, anatomical and electrophysiological effects produced by electrical stimulation of posterior hypothalamic (PH) or median raphe (MR) nuclei, independently and during combined stimulation of both PH and MR. These three stimulation conditions were applied during spontaneous behavior in an open field and during PH stimulation-induced wheel running, while simultaneously recording hippocampal (HPC) field activity. An additional objective was to determine the effects of MR stimulation on Type 1 movement related theta and Type 2 sensory processing related theta. To achieve the latter, when behavioral studies were completed we studied the same rats under urethane anesthesia and then during urethane anesthesia with the addition of atropine sulfate (ATSO4). Here we demonstrated that electrical stimulation of a localized region of the MR nucleus resulted in a profound inhibition of both spontaneously occurring theta related motor behaviors and the theta related motor behaviors induced by electrical stimulation of the PH nucleus. Furthermore, this motor inhibition occurred concurrently with strong suppression of hippocampal theta field oscillations in the freely moving rat, a condition where the theta recorded is Type 2 sensory processing theta occurring coincidently with Type 1 movement related theta (Bland, 1986). Our results indicate that motor inhibition resulted from stimulation of neurons located in the mid central region of the MR, while stimulation in adjacent regions produced variable responses, including movements and theta activity. The present study provided evidence that the pharmacological basis of the suppression of Type 2 sensory processing HPC theta was cholinergic. However, MR inhibition of PH-induced wheel running was not affected by cholinergic blockade, which blocks Type 2 theta, indicating that MR stimulation-induced motor inhibition also requires the suppression of Type 1 theta.
Assuntos
Núcleo Dorsal da Rafe/fisiologia , Hipocampo/fisiologia , Atividade Motora/fisiologia , Corrida/fisiologia , Ritmo Teta/fisiologia , Analgésicos Opioides/farmacologia , Animais , Atropina/farmacologia , Difenoxilato/farmacologia , Núcleo Dorsal da Rafe/efeitos dos fármacos , Relação Dose-Resposta a Droga , Combinação de Medicamentos , Estimulação Elétrica , Comportamento Exploratório/efeitos dos fármacos , Comportamento Exploratório/fisiologia , Hipotálamo Posterior/fisiologia , Masculino , Atividade Motora/efeitos dos fármacos , Antagonistas Muscarínicos/farmacologia , Vias Neurais/fisiologia , Ratos , Ratos Long-Evans , Ritmo Teta/efeitos dos fármacos , Uretana/farmacologiaRESUMO
BACKGROUND: Anesthetics enhance γ-aminobutyric acid (GABA)-mediated inhibition in the central nervous system. Different agents have been shown to act on tonic versus synaptic GABA receptors to different degrees, but it remains unknown whether different forms of synaptic inhibition are also differentially engaged. With this in mind, we tested the hypothesis that different types of GABA-mediated synapses exhibit different anesthetic sensitivities. The present study compared effects produced by isoflurane, halothane, pentobarbital, thiopental, and propofol on paired-pulse GABAA receptor-mediated synaptic inhibition. Effects on glutamate-mediated facilitation were also studied. METHODS: Synaptic responses were measured in rat hippocampal brain slices. Orthodromic paired-pulse stimulation was used to assess anesthetic effects on either glutamate-mediated excitatory inputs or GABA-mediated inhibitory inputs to CA1 neurons. Antidromic stimulation was used to assess anesthetic effects on CA1 background excitability. Agents were studied at equieffective concentrations for population spike depression to compare their relative degree of effect on synaptic inhibition. RESULTS: Differing degrees of anesthetic effect on paired-pulse facilitation at excitatory glutamate synapses were evident, and blocking GABA inhibition revealed a previously unseen presynaptic action for pentobarbital. Although all 5 anesthetics depressed synaptically evoked excitation of CA1 neurons, the involvement of enhanced GABA-mediated inhibition differed considerably among agents. Single-pulse inhibition was enhanced by propofol, thiopental, and pentobarbital, but only marginally by halothane and isoflurane. In contrast, isoflurane enhanced paired-pulse inhibition strongly, as did thiopental, but propofol, pentobarbital, and halothane were less effective. CONCLUSIONS: These observations support the idea that different GABA synapses use receptors with differing subunit compositions and that anesthetics exhibit differing degrees of selectivity for these receptors. The differing anesthetic sensitivities seen in the present study, at glutamate and GABA synapses, help explain the unique behavioral/clinical profiles produced by different classes of anesthetics and indicate that there are selective targets for new agent development.
Assuntos
Anestésicos/farmacologia , Antagonistas GABAérgicos/farmacologia , Inibição Neural/efeitos dos fármacos , Sinapses/efeitos dos fármacos , Anestesiologia , Animais , Barbitúricos/farmacologia , Bicuculina/farmacologia , Região CA1 Hipocampal/efeitos dos fármacos , Interpretação Estatística de Dados , Dendritos/efeitos dos fármacos , Relação Dose-Resposta a Droga , Potenciais Evocados/efeitos dos fármacos , Técnicas In Vitro , Cinética , Masculino , Técnicas de Patch-Clamp , Soluções Farmacêuticas , Picrotoxina/farmacologia , Ratos , Ratos Sprague-Dawley , Receptores de GABA-A/efeitos dos fármacosRESUMO
Increasing evidence indicates a role of hyperpolarization activated cation (HCN) channels in controlling the resting membrane potential, pacemaker activity, memory formation, sleep, and arousal. Their disfunction may be associated with the development of epilepsy and age-related memory decline. Neuronal hyperexcitability involved in epileptogenesis and EEG desynchronization occur in the course of dementia in human Alzheimer's Disease (AD) and animal models, nevertheless the underlying ionic and cellular mechanisms of these effects are not well understood. Some suggest that theta rhythms involved in memory formation could be used as a marker of memory disturbances in the course of neurogenerative diseases, including AD. This review focusses on the interplay between hyperpolarization HCN channels, theta oscillations, memory formation and their role(s) in dementias, including AD. While individually, each of these factors have been linked to each other with strong supportive evidence, we hope here to expand this linkage to a more inclusive picture. Thus, HCN channels could provide a molecular target for developing new therapeutic agents for preventing and/or treating dementia.
Assuntos
Demência , Epilepsia , Fenômenos Fisiológicos do Sistema Nervoso , Animais , Humanos , Potenciais da Membrana/fisiologiaRESUMO
The repeating arrangement of tubulin dimers confers great mechanical strength to microtubules, which are used as scaffolds for intracellular macromolecular transport in cells and exploited in biohybrid devices. The crystalline order in a microtubule, with lattice constants short enough to allow energy transfer between amino acid chromophores, is similar to synthetic structures designed for light harvesting. After photoexcitation, can these amino acid chromophores transfer excitation energy along the microtubule like a natural or artificial light-harvesting system? Here, we use tryptophan autofluorescence lifetimes to probe energy hopping between aromatic residues in tubulin and microtubules. By studying how the quencher concentration alters tryptophan autofluorescence lifetimes, we demonstrate that electronic energy can diffuse over 6.6 nm in microtubules. We discover that while diffusion lengths are influenced by tubulin polymerization state (free tubulin versus tubulin in the microtubule lattice), they are not significantly altered by the average number of protofilaments (13 versus 14). We also demonstrate that the presence of the anesthetics etomidate and isoflurane reduce exciton diffusion. Energy transport as explained by conventional Förster theory (accommodating for interactions between tryptophan and tyrosine residues) does not sufficiently explain our observations. Our studies indicate that microtubules are, unexpectedly, effective light harvesters.
RESUMO
The accompanying articles in this issue of the journal's special collection describe attempts to improve on the dynamics of distribution and reduce side effects of analogs of etomidate and benzodiazepines. Both classes of drugs have their principal sites of action on γ-aminobutyric acid type A receptors, although at very different binding sites and by different mechanisms of action. Herein, we review the structure of γ-aminobutyric acid type A receptors and describe the location of the 2 likely binding sites. In addition, we describe how these drugs can interact with the nervous system at a systems level. We leave it to other reviewers to discuss whether these new drugs offer true clinical improvements.
Assuntos
Anestésicos Intravenosos/farmacologia , Benzodiazepinas/farmacologia , Etomidato/farmacologia , Agonistas de Receptores de GABA-A/farmacologia , Hipnóticos e Sedativos/farmacologia , Receptores de GABA-A/efeitos dos fármacos , Sinapses/efeitos dos fármacos , Anestésicos Intravenosos/efeitos adversos , Animais , Benzodiazepinas/efeitos adversos , Sítios de Ligação , Etomidato/efeitos adversos , Etomidato/análogos & derivados , Agonistas de Receptores de GABA-A/efeitos adversos , Humanos , Hipnóticos e Sedativos/efeitos adversos , Modelos Moleculares , Conformação Proteica , Receptores de GABA-A/química , Receptores de GABA-A/metabolismo , Sinapses/metabolismoRESUMO
Electromagnetic field (EMF) theories of mind/brain integration have been proposed to explain brain function for over seventy years. Interest in this theory continues to this day because it explains mind-brain integration and it offers a simple solution to the "binding problem" of our unified conscious experience. Thus, it addresses at least in part the "hard problem" of consciousness. EMFs are easily measured and many corelates have been noted for field activity; associated with loss and recovery of consciousness, sensory perceptions, and behavior. Unfortunately, the theory was challenged early on by experiments that were thought to have ruled out a role of EMFs in brain activity, and the field of neuroscience has since marginalized EMF theories. Here I explain why early evidence against EMFs contributing to consciousness was misinterpreted and offer an alternative view to help direct future research.
RESUMO
BACKGROUND: During deep brain stimulation implant surgery, microelectrode recordings are used to map the location of targeted neurons. The effects produced by propofol or remifentanil on discharge activity of subthalamic neurons were studied intraoperatively to determine whether they alter neuronal activity. METHODS: Microelectrode recordings from 11 neurons, each from individual patients, were discriminated and analyzed before and after administration of either propofol or remifentanil. Subthalamic neurons in rat brain slices were recorded in patch-clamp to investigate cellular level effects. RESULTS: Neurons discharged at 42 ± 9 spikes/s (mean ± SD) and showed a common pattern of inhibition that lasted 4.3 ms. Unique discharge profiles were evident for each neuron, seen using joint-interval analysis. Propofol (intravenous bolus 0.3 mg/kg) produced sedation, with minor effects on discharge activity (less than 2.0% change in frequency). A prolongation of recurrent inhibition was evident from joint-interval analysis, and propofol's effect peaked within 2 min, with recovery evident at 10 min. Subthalamic neurons recorded in rat brain slices exhibited inhibitory synaptic currents that were prolonged by propofol (155%) but appeared to lack tonic inhibitory currents. Propofol did not alter membrane potential, membrane resistance, current-evoked discharge, or holding current during voltage clamp. Remifentanil (0.05 mg/kg) had little effect on overall subthalamic neuron discharge activity and did not prolong recurrent inhibition. CONCLUSIONS: These results help to characterize the circuit properties and feedback inhibition of subthalamic neurons and demonstrate that both propofol and remifentanil produce only minor alterations of subthalamic neuron discharge activity that should not interfere with deep brain stimulation implant surgery.
Assuntos
Hipnóticos e Sedativos/farmacologia , Núcleo Subtalâmico/efeitos dos fármacos , Animais , Feminino , Humanos , Masculino , Piperidinas/farmacologia , Propofol/farmacologia , Ratos , Ratos Sprague-Dawley , Remifentanil , Núcleo Subtalâmico/fisiologia , Sinapses/efeitos dos fármacos , Sinapses/fisiologia , Ácido gama-Aminobutírico/fisiologiaRESUMO
BACKGROUND: Anesthesia is produced by a depression of neuronal signaling in the central nervous system (CNS); however, the mechanism(s) of action underlying this depression remain unclear. Recent studies have indicated that anesthetics can enhance inhibition of CNS neurons by increasing current flow through tonic gamma-aminobutyric acid (GABA(A)) receptor gated chloride channels in their membranes. Enhanced tonic inhibition would contribute to CNS depression produced by anesthetics, but it remains to be determined to what extent anesthetic actions at these receptors contribute to CNS depression. In the present study, we compared and contrasted the involvement of tonic versus synaptic GABA(A) receptors in the functional depression of CNS neurons produced by isoflurane and thiopental. METHODS: In rat hippocampal slices, whole cell patch clamp recordings were used to study anesthetic effects on CA1 neuron intrinsic excitability, and population spike recordings were used to investigate effects on synaptically evoked discharge. These responses were chosen to test whether anesthetic effects on GABA receptors alter single neuron discharge and/or circuit level synaptic functioning. Phasic (synaptic) GABA receptors were selectively blocked using the GABA(A) antagonist gabazine and tonic responses were blocked using the chloride channel blocker picrotoxin. RESULTS: Clinically relevant and equi-effective concentrations of thiopental and isoflurane depressed CA1 neuron synaptically evoked discharge. This depression was partially reversed by blocking synaptic GABA(A) receptors with gabazine (20 microM). The thiopental-induced depression was reversed by approximately 60%, but the isoflurane-induced depression was reversed by only approximately 20%. Blocking tonic GABA(A) receptors with the addition of 100 microM picrotoxin produced an additional 40% reversal of the thiopental-induced depression, but no additional reversal was seen for isoflurane-depressed responses. In response to direct DC current injection, CA1 neuron discharge was depressed by thiopental and membrane conductance was increased. Both of these effects were reversed by picrotoxin, but not by gabazine. Isoflurane, in contrast, neither depressed current-evoked discharge, nor altered the membrane conductance of CA1 neurons. CONCLUSIONS: These results indicate that general anesthetics discriminate between synaptic and tonic GABA(A) receptors. Effects on both phasic and tonic receptors combined to depress circuit responses produced by thiopental, whereas only effects on synaptic GABA receptors appeared to play an important role for isoflurane. Together with the other known sites of action for these two anesthetics, our results support a multisite, agent-specific mechanism for anesthetic actions.
Assuntos
Anestésicos/farmacologia , Hipocampo/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Receptores de GABA/efeitos dos fármacos , Potenciais de Ação/efeitos dos fármacos , Anestésicos Inalatórios/farmacologia , Anestésicos Intravenosos/farmacologia , Animais , Antagonistas GABAérgicos/farmacologia , Moduladores GABAérgicos/farmacologia , Hipocampo/citologia , Isoflurano/farmacologia , Células Piramidais/efeitos dos fármacos , Piridazinas/farmacologia , Ratos , Ratos Sprague-Dawley , Sinapses/efeitos dos fármacos , Tiopental/farmacologiaRESUMO
The information processing capability of the brain decreases during unconscious states. Capturing this decrease during anesthesia-induced unconsciousness has been attempted using standard spectral analyses as these correlate relatively well with breakdowns in corticothalamic networks. Much of this work has involved the use of propofol to perturb brain activity, as it is one of the most widely used anesthetics for routine surgical anesthesia. Propofol administration alone produces EEG spectral characteristics similar to most hypnotics; however, inter-individual and drug variation render spectral measures inconsistent. Complexity measures of EEG signals could offer better measures to distinguish brain states, because brain activity exhibits nonlinear behavior at several scales during transitions of consciousness. We tested the potential of complexity analyses from nonlinear dynamics to identify loss and recovery of consciousness at clinically relevant timepoints. Patients undergoing propofol general anesthesia for various surgical procedures were identified as having changes in states of consciousness by the loss and recovery of response to verbal stimuli after induction and upon cessation of anesthesia, respectively. We demonstrate that nonlinear dynamics analyses showed more significant differences between consciousness states than spectral measures. Notably, attractors in conscious and anesthesia-induced unconscious states exhibited significantly different shapes. These shapes have implications for network connectivity, information processing, and the total number of states available to the brain at these different levels. They also reflect some of our general understanding of the network effects of consciousness in a way that spectral measures cannot. Thus, complexity measures could provide a universal means for reliably capturing depth of consciousness based on EEG changes at the beginning and end of anesthesia administration.
Assuntos
Anestésicos/farmacologia , Encéfalo/efeitos dos fármacos , Encéfalo/fisiologia , Estado de Consciência/efeitos dos fármacos , Estado de Consciência/fisiologia , Dinâmica não Linear , Propofol/farmacologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Ondas Encefálicas/efeitos dos fármacos , Eletroencefalografia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Processamento de Sinais Assistido por Computador , Adulto JovemRESUMO
BACKGROUND: Previous reports of inhibition in the neocortex suggest that inhibition is mediated predominantly through GABA(A) receptors exhibiting fast kinetics. Within the hippocampus, it has been shown that GABA(A) responses can take the form of either fast or slow response kinetics. Our findings indicate, for the first time, that the neocortex displays synaptic responses with slow GABA(A) receptor mediated inhibitory postsynaptic currents (IPSCs). These IPSCs are kinetically and pharmacologically similar to responses found in the hippocampus, although the anatomical specificity of evoked responses is unique from hippocampus. Spontaneous slow GABA(A) IPSCs were recorded from both pyramidal and inhibitory neurons in rat visual cortex. RESULTS: GABA(A) slow IPSCs were significantly different from fast responses with respect to rise times and decay time constants, but not amplitudes. Spontaneously occurring GABA(A) slow IPSCs were nearly 100 times less frequent than fast sIPSCs and both were completely abolished by the chloride channel blocker, picrotoxin. The GABA(A) subunit-specific antagonist, furosemide, depressed spontaneous and evoked GABA(A) fast IPSCs, but not slow GABA(A)-mediated IPSCs. Anatomical specificity was evident using minimal stimulation: IPSCs with slow kinetics were evoked predominantly through stimulation of layer 1/2 apical dendritic zones of layer 4 pyramidal neurons and across their basal dendrites, while GABA(A) fast IPSCs were evoked through stimulation throughout the dendritic arborization. Many evoked IPSCs were also composed of a combination of fast and slow IPSC components. CONCLUSION: GABA(A) slow IPSCs displayed durations that were approximately 4 fold longer than typical GABA(A)fast IPSCs, but shorter than GABA(B)-mediated inhibition. The anatomical and pharmacological specificity of evoked slow IPSCs suggests a unique origin of synaptic input. Incorporating GABA(A) slow IPSCs into computational models of cortical function will help improve our understanding of cortical information processing.
Assuntos
Potenciais Pós-Sinápticos Inibidores/fisiologia , Inibição Neural/fisiologia , Receptores de GABA-A/metabolismo , Transmissão Sináptica/fisiologia , Córtex Visual/metabolismo , Animais , Canais de Cloreto/antagonistas & inibidores , Canais de Cloreto/metabolismo , Dendritos/efeitos dos fármacos , Dendritos/metabolismo , Dendritos/ultraestrutura , Furosemida/farmacologia , Antagonistas GABAérgicos/farmacologia , Masculino , Técnicas de Cultura de Órgãos , Técnicas de Patch-Clamp , Picrotoxina/farmacologia , Células Piramidais/citologia , Células Piramidais/efeitos dos fármacos , Células Piramidais/metabolismo , Ratos , Ratos Long-Evans , Tempo de Reação/fisiologia , Sinapses/metabolismo , Fatores de Tempo , Córtex Visual/citologia , Córtex Visual/efeitos dos fármacos , Vias Visuais/citologia , Vias Visuais/efeitos dos fármacos , Vias Visuais/metabolismoRESUMO
Nitrous oxide (N2O) and remifentanil (remi) are used along with other anesthetic and adjuvant agents for routine surgical anesthesia, yet the electroencephalogram (EEG) changes produced by this combination are poorly described. N2O administered alone produces EEG spectral characteristics that are distinct from most hypnotics. Furthermore, EEG frequency-derived trends before and after clinically relevant time points vary depending on N2O concentration. Remifentanil typically increases low frequency and decreases high frequency activity in the EEG, but how it influences N2O's EEG effect is not known. Previous attempts to characterize EEG signals of patients anesthetized with N2O using frequency-derived measures have shown conflicts and inconsistencies. Thus, in addition to determining the spectral characteristics of this unique combination, we also test whether a newly proposed characterization of time-delayed embeddings of the EEG signal tracks loss and recovery of consciousness significantly at clinically relevant time points. We retrospectively investigated the effects of remi and N2O on EEG signals recorded from 32 surgical patients receiving anesthesia for elective abdominal surgeries. Remifentanil and N2O (66%) were co-administered during the procedures. Patients were tested for loss and recovery of response (ROR) to verbal stimuli after induction and upon cessation of anesthesia, respectively. We found that the addition of remifentanil to N2O anesthesia improves the ability of traditional frequency-derived measures, including the Bispectral Index (BIS), to discriminate between loss and ROR. Finally, we found that a novel analysis of EEG using nonlinear dynamics showed more significant differences between states than most spectral measures.
RESUMO
While geriatric patients have a high likelihood of requiring anesthesia, they carry an increased risk for adverse cognitive outcomes from its use. Previous work suggests this could be mitigated by better intraoperative monitoring using indexes defined by several processed electroencephalogram (EEG) measures. Unfortunately, inconsistencies between patients and anesthetic agents in current analysis techniques have limited the adoption of EEG as standard of care. In attempts to identify new analyses that discriminate clinically-relevant anesthesia timepoints, we tested 1/f frequency scaling as well as measures of complexity from nonlinear dynamics. Specifically, we tested whether analyses that characterize time-delayed embeddings, correlation dimension (CD), phase-space geometric analysis, and multiscale entropy (MSE) capture loss-of-consciousness changes in EEG activity. We performed these analyses on EEG activity collected from a traditionally hard-to-monitor patient population: geriatric patients on beta-adrenergic blockade who were anesthetized using a combination of fentanyl and propofol. We compared these analyses to traditional frequency-derived measures to test how well they discriminated EEG states before and after loss of response to verbal stimuli. We found spectral changes similar to those reported previously during loss of response. We also found significant changes in 1/f frequency scaling. Additionally, we found that our phase-space geometric characterization of time-delayed embeddings showed significant differences before and after loss of response, as did measures of MSE. Our results suggest that our new spectral and complexity measures are capable of capturing subtle differences in EEG activity with anesthesia administration-differences which future work may reveal to improve geriatric patient monitoring.