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Goense JBM, Logothetis NK. Neurophysiology of the BOLD fMRI signal in awake monkeys. Curr Biol 2008; 18:631-40. [PMID: 18439825 DOI: 10.1016/j.cub.2008.03.054] [Citation(s) in RCA: 455] [Impact Index Per Article: 28.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2007] [Revised: 03/19/2008] [Accepted: 03/20/2008] [Indexed: 11/17/2022]
Abstract
BACKGROUND Simultaneous intracortical recordings of neural activity and blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) in primary visual cortex of anesthetized monkeys demonstrated varying degrees of correlation between fMRI signals and the different types of neural activity, such as local field potentials (LFPs), multiple-unit activity (MUA), and single-unit activity (SUA). One important question raised by the aforementioned investigation is whether the reported correlations also apply to alert subjects. RESULTS Monkeys were trained to perform a fixation task while stimuli within the receptive field of each recording site were used to elicit neural responses followed by a BOLD response. We show -- also in alert behaving monkeys -- that although both LFP and MUA make significant contributions to the BOLD response, LFPs are better and more reliable predictors of the BOLD signal. Moreover, when MUA responses adapt but LFP remains unaffected, the BOLD signal remains unaltered. CONCLUSIONS The persistent coupling of the BOLD signal to the field potential when LFP and MUA have different time evolutions suggests that BOLD is primarily determined by the local processing of inputs in a given cortical area. In the alert animal the largest portion of the BOLD signal's variance is explained by an LFP range (20-60 Hz) that is most likely related to neuromodulation. Finally, the similarity of the results in alert and anesthetized subjects indicates that at least in V1 anesthesia is not a confounding factor. This enables the comparison of human fMRI results with a plethora of electrophysiological results obtained in alert or anesthetized animals.
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Affiliation(s)
- Jozien B M Goense
- Department of Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Tuebingen, Germany
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Heightened aggression after chronic flunitrazepam in male rats: potential links to cortical and caudate-putamen-binding sites. Psychopharmacology (Berl) 2008; 197:309-18. [PMID: 18080114 DOI: 10.1007/s00213-007-1031-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/03/2007] [Accepted: 11/22/2007] [Indexed: 10/22/2022]
Abstract
RATIONALE Higher doses of benzodiazepines induce sedation. However, in low to moderate doses, benzodiazepines can increase aggressive behavior both after acute and chronic administration. The determinants for increasing aggression after chronic intake of flunitrazepam, a so-called date rape drug, in violence-prone individuals are incompletely understood. OBJECTIVES The aim of this study is to assess the effects of acute and chronic treatment with flunitrazepam on male aggression in resident rats. We also examined possible changes in binding to benzodiazepine receptors throughout the brain of rats that display aggressive behavior after repeated flunitrazepam treatment using quantitative receptor autoradiography. MATERIALS AND METHODS The behaviors of the male Wistar resident rats (n = 35) toward a male intruder were recorded for 10 min twice a week. The salient aggressive and non-aggressive elements in the resident rat's behavior were analyzed. Initially, the dose-dependent effects of flunitrazepam (0.01, 0.03, 0.1, 0.18, and 0.3 mg/kg) or vehicle were determined in all rats; subsequently, 0.3 mg/kg per day flunitrazepam was administered for 42 days (n = 15), and a parallel group was treated with vehicle (n = 20). After the chronic treatment, the flunitrazepam (0, 0.01, 0.03, 0.1, 0.18, and 0.3 mg/kg) effects were again assessed. RESULTS The most significant finding is the escalation of aggression after chronic treatment with flunitrazepam. A previously sedative 0.3 mg/kg dose of flunitrazepam engendered very high levels of attack bites, sideways threats, and aggressive postures (total aggression) after 6 weeks of daily administration. Individual differences emerged, and these were associated with decreased binding to benzodiazepine receptors, mainly in the limbic structures such as the cingulate cortex (cingulate areas 1 and 2) and caudate-putamen (posterior part) of aggressive animals, suggesting that these areas are pivotal in the control of emotional and aggressive behavior. CONCLUSIONS Chronic flunitrazepam produces changes in receptor binding in discrete areas of the cingulate cortex and caudate-putamen that are proposed to be part of the mechanisms for increased expression of aggressive behavior.
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Eriksson O, Josephsson R, Långstrom B, Bergström M. Positron emission tomography and target-controlled infusion for precise modulation of brain drug concentration. Nucl Med Biol 2008; 35:299-303. [PMID: 18355685 DOI: 10.1016/j.nucmedbio.2007.12.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2007] [Revised: 12/07/2007] [Accepted: 12/11/2007] [Indexed: 11/29/2022]
Abstract
INTRODUCTION There are several instances when it is desirable to control brain concentration of pharmaceuticals, e.g., to modulate the concentration of anesthetic agents to different desired levels fitting to different needs during the course of surgery. This has so far only been possible using indirect estimates of drug concentration such as assuming constant relation between tissue and blood including extrapolations from animals. METHODS A system for controlling target tissue concentration (UIPump) was used to regulate whole-brain concentrations of a central benzodiazepine receptor antagonist at therapeutic levels with input from brain kinetics as determined with PET. The system was tested by using pharmacological doses of flumazenil mixed with tracer amounts of [11C]flumazenil. Flumazenil was used as a model compound for anesthesia. An infusion scheme to produce three different steady-state levels in sequence was designed based on kinetic curves obtained after bolus injection. The subjects (Sprague-Dawley rats, n=6) were monitored in a microPET scanner during the whole experiment to verify resulting brain kinetic curves. RESULTS A steady-state brain concentration was rapidly achieved corresponding to a whole-brain concentration of 118+/-6 ng/ml. As the infusion rate decreased to lower the exposure by a factor of 2, the brain concentration decreased to 56+/-4 ng/ml. A third increased steady-state level of anesthesia corresponding to a whole-brain concentration of 107+/-7 ng/ml was rapidly achieved. CONCLUSION The experimental setup with computerized pump infusion and PET supervision enables accurate setting of target tissue drug concentration.
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Electrophysiologic effects of systemic and locally infused epibatidine on locus coeruleus neurons. Eur J Pharmacol 2008; 584:93-9. [PMID: 18304527 DOI: 10.1016/j.ejphar.2008.01.034] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2007] [Revised: 01/10/2008] [Accepted: 01/24/2008] [Indexed: 11/22/2022]
Abstract
We evaluated the electrophysiologic response of locus coeruleus neurons to the systemic and local infusion of epibatidine. Rats were anesthetized with 2% halothane and single-unit locus coeruleus discharge was recorded after administration of systemic (2.5, 5 and 10 microg/kg subcutaneously) and intracoerulear (0.03-0.01-0.001 microg) epibatidine. The subcutaneous epibatidine activated locus coeruleus neurons only at the highest dose (10 microg/kg). The 2.5-5 microg/kg doses, previously shown to induce analgesia, did not activate locus coeruleus neurons. The intracoerulear infusion of epibatidine induced excitement of locus coeruleus neurons at every tested dose. Higher doses (0.03 and 0.01 microg) excited 100% of the recorded neurons. A significantly lower number of neurons (50% and 43% respectively) were excited when lower doses (0.005-0.001 microg) were used (P=0.035). The intracoerulear infusion of mecamylamine (1 microg) significantly reduced neuronal discharge rate (45%) and blocked the effects of epibatidine. The intra-dorsal raphe infusion of 0.03 microg epibatidine induced significant excitation of locus coeruleus neurons. These data show that the administration of epibatidine induces excitation of locus coeruleus neurons, which is mediated by nicotinic receptors. This activation occurs after systemic and selective local administration of epibatidine. The response of locus coeruleus neurons to systemic and locally administered epibatidine is dose-related.
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105
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Bonin RP, Orser BA. GABA(A) receptor subtypes underlying general anesthesia. Pharmacol Biochem Behav 2008; 90:105-12. [PMID: 18201756 DOI: 10.1016/j.pbb.2007.12.011] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Revised: 11/20/2007] [Accepted: 12/03/2007] [Indexed: 02/05/2023]
Abstract
General anesthetics produce a constellation of behavioral responses and widespread neurodepression. Recent studies have implicated the gamma-aminobutyric acid (GABA) subtype A receptor as a primary anesthetic target. During the past decade, considerable progress has been made in dissecting the behavioral effects of anesthetics according to the subunit composition of GABA(A) receptors. In this review, we describe how particular GABA(A) receptor subtypes expressed in different brain regions are critical for the expression of behavioral endpoints, such as amnesia, sedation, and hypnosis.
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Affiliation(s)
- Robert P Bonin
- Department of Physiology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
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Zeller A, Crestani F, Camenisch I, Iwasato T, Itohara S, Fritschy JM, Rudolph U. Cortical glutamatergic neurons mediate the motor sedative action of diazepam. Mol Pharmacol 2007; 73:282-91. [PMID: 17965197 DOI: 10.1124/mol.107.038828] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The neuronal circuits mediating the sedative action of diazepam are unknown. Although the motor-depressant action of diazepam is suppressed in alpha1(H101R) homozygous knockin mice expressing diazepam-insensitive alpha1-GABA(A) receptors, global alpha1-knockout mice show greater motor sedation with diazepam. To clarify this paradox, attributed to compensatory up-regulation of the alpha2 and alpha3 subunits, and to further identify the neuronal circuits supporting diazepam-induced sedation, we generated Emx1-cre-recombinase-mediated conditional mutant mice, selectively lacking the alpha1 subunit (forebrain-specific alpha1(-/-)) or expressing either a single wild-type (H) or a single point-mutated (R) alpha1 allele (forebrain-specific alpha1(-/H) and alpha1(-/R) mice, respectively) in forebrain glutamatergic neurons. In the rest of the brain, alpha1(-/R) mutants are heterozygous alpha1(H101R) mice. Forebrain-specific alpha1(-/-) mice showed enhanced diazepam-induced motor depression and increased expression of the alpha2 and alpha3 subunits in the neocortex and hippocampus, in comparison with their pseudo-wild-type littermates. Forebrain-specific alpha1(-/R) mice were less sensitive than alpha1(-/H) mice to the motor-depressing action of diazepam, but each of these conditional mutants had a similar behavioral response as their corresponding control littermates. Unexpectedly, expression of the alpha1 subunit was reduced in forebrain, notably in alpha1(-/R) mice, and the alpha3 subunit was up-regulated in neocortex, indicating that proper alpha1 subunit expression requires both alleles. In conclusion, conditional manipulation of GABA(A) receptor alpha1 subunit expression can induce compensatory changes in the affected areas. Specifically, alterations in GABA(A) receptor expression restricted to forebrain glutamatergic neurons reproduce the behavioral effects seen after a global alteration, thereby implicating these neurons in the motor-sedative effect of diazepam.
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Affiliation(s)
- A Zeller
- Laboratory of Genetic Neuropharmacology, McLean Hospital, Department of Psychiatry, Harvard Medical School, 115 Mill St., Belmont, MA 02478, USA
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Baldauf K, Henrich-Noack P, Reymann KG. Detrimental effects of halothane narcosis on damage after endothelin-1-induced MCAO. J Neurosci Methods 2007; 162:14-8. [PMID: 17197033 DOI: 10.1016/j.jneumeth.2006.11.019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2006] [Revised: 11/29/2006] [Accepted: 11/30/2006] [Indexed: 12/01/2022]
Abstract
The influence of anaesthesia in experimental stroke research is controversial. We addressed this problem using the model of endothelin-1-induced occlusion of the middle cerebral artery (eMCAO). This model provided the opportunity to compare the infarct volumes of rats which were under halothane anaesthesia during eMCAO induction with the lesions of rats which were without anaesthesia during eMCAO. All animals were implanted with guide cannulae which allowed the induction of ischaemia in freely moving animals. For comparison, one group of animals was exposed to halothane during the induction of ischaemia. Seven days after eMCAO, the average infarct volume of halothane-anaesthetised rats was significantly larger than the lesion in freely moving animals. This difference was mainly due to increased cortical damage, whereas the striatum was much less influenced. The cortical infarct volume 21 days after induction of eMCAO under anaesthesia was significantly reduced compared to the infarct volume 7 days after eMCAO under anaesthesia. Our results indicate that halothane anaesthesia during eMCAO can cause a transient cortical increase in ischaemic infarct volume. The influence of volatile anaesthetics on ischaemic pathophysiology should be taken into consideration when preclinically testing potential neuroprotective drugs for clinical applications.
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Affiliation(s)
- Kathrin Baldauf
- Leibniz Institute for Neurobiology, Brenneckestrasse 6, D-39118 Magdeburg, Germany.
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Berger T, Borgdorff A, Crochet S, Neubauer FB, Lefort S, Fauvet B, Ferezou I, Carleton A, Lüscher HR, Petersen CCH. Combined Voltage and Calcium Epifluorescence Imaging In Vitro and In Vivo Reveals Subthreshold and Suprathreshold Dynamics of Mouse Barrel Cortex. J Neurophysiol 2007; 97:3751-62. [PMID: 17360827 DOI: 10.1152/jn.01178.2006] [Citation(s) in RCA: 148] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cortical dynamics can be imaged at high spatiotemporal resolution with voltage-sensitive dyes (VSDs) and calcium-sensitive dyes (CaSDs). We combined these two imaging techniques using epifluorescence optics together with whole cell recordings to measure the spatiotemporal dynamics of activity in the mouse somatosensory barrel cortex in vitro and in the supragranular layers in vivo. The two optical signals reported distinct aspects of cortical function. VSD fluorescence varied linearly with membrane potential and was dominated by subthreshold postsynaptic potentials, whereas the CaSD signal predominantly reflected local action potential firing. Combining VSDs and CaSDs allowed us to monitor the synaptic drive and the spiking activity of a given area at the same time in the same preparation. The spatial extent of the two dye signals was different, with VSD signals spreading further than CaSD signals, reflecting broad subthreshold and narrow suprathreshold receptive fields. Importantly, the signals from the dyes were differentially affected by pharmacological manipulations, stimulation strength, and depth of isoflurane anesthesia. Combined VSD and CaSD measurements can therefore be used to specify the temporal and spatial relationships between subthreshold and suprathreshold activity of the neocortex.
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Affiliation(s)
- Thomas Berger
- Laboratory of Sensory Processing, Brain Mind Institute, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne, Switzerland
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Sukhotinsky I, Zalkind V, Lu J, Hopkins DA, Saper CB, Devor M. Neural pathways associated with loss of consciousness caused by intracerebral microinjection of GABAA-active anesthetics. Eur J Neurosci 2007; 25:1417-36. [PMID: 17425568 DOI: 10.1111/j.1460-9568.2007.05399.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Anesthesia, slow-wave sleep, syncope, concussion and reversible coma are behavioral states characterized by loss of consciousness, slow-wave cortical electroencephalogram, and motor and sensory suppression. We identified a focal area in the rat brainstem, the mesopontine tegmental anesthesia area (MPTA), at which microinjection of pentobarbital and other GABA(A) receptor (GABA(A)-R) agonists reversibly induced an anesthesia-like state. This effect was attenuated by local pre-treatment with the GABA(A)-R antagonist bicuculline. Using neuroanatomical tracing we identified four pathways ascending from the MPTA that are positioned to mediate electroencephalographic synchronization and loss of consciousness: (i) projections to the intralaminar thalamic nuclei that, in turn, project to the cortex; (ii) projections to several pontomesencephalic, diencephalic and basal forebrain nuclei that project cortically and are considered parts of an ascending "arousal system"; (iii) a projection to other parts of the subcortical forebrain, including the septal area, hypothalamus, zona incerta and striato-pallidal system, that may indirectly affect cortical arousal and hippocampal theta rhythm; and (iv) modest projections directly to the frontal cortex. Several of these areas have prominent reciprocal projections back to the MPTA, notably the zona incerta, lateral hypothalamus and frontal cortex. We hypothesize that barbiturate anesthetics and related agents microinjected into the MPTA enhance the inhibitory response of local GABA(A)-R-bearing neurons to endogenous GABA released at baseline during wakefulness. This modulates activity in one or more of the identified ascending neural pathways, ultimately leading to loss of consciousness.
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Affiliation(s)
- I Sukhotinsky
- Department of Cell and Animal Biology, Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel
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Tsuda N, Hayashi K, Hagihira S, Sawa T. Ketamine, an NMDA-antagonist, increases the oscillatory frequencies of alpha-peaks on the electroencephalographic power spectrum. Acta Anaesthesiol Scand 2007; 51:472-81. [PMID: 17378787 DOI: 10.1111/j.1399-6576.2006.01246.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
BACKGROUND Ketamine, an N-methyl-D-aspartate (NMDA) antagonist, is known to activate the electroencephalogram (EEG), despite its sedative effects. Spindle oscillations are known to be related to the sedative actions of the reticular thalamic nucleus with links to thalamocortical neurons. This study was designed to examine the effect of ketamine on the spindle oscillations to understand the simultaneous sedative effect and EEG activation that occurs with ketamine, by comparing the EEG in emergence. METHODS Anesthesia was induced with propofol using a target-controlled infusion (TCI) system (3.5 microg/ml). Seventeen patients, scheduled for non-cranial surgery under general anesthesia combined with epidural anesthesia, were randomly divided into two groups: (i) anesthesia was maintained with TCI-propofol alone (n= 8) and (ii) anesthesia was maintained with TCI-propofol and intravenously administered ketamine (n= 9). The EEG was continuously monitored and EEG indices and power spectra were determined. RESULTS Propofol alone caused the alpha-peaks of the power spectra to occur at an average frequency of 10.4 +/- 0.9 Hz; the addition of ketamine shifted the peaks to higher frequencies of 15.1 +/- 1.4 Hz (P < 0.05). On the other hand, when the EEG was activated by discontinuation of propofol, the corresponding alpha-peaks disappeared. CONCLUSIONS Ketamine increased the frequencies of alpha-spindle waves induced by propofol, but did not block their formations. The phenomena have the possibility to underlie the cooperative effect between propofol and ketamine concerning sedation and anesthesia.
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Affiliation(s)
- N Tsuda
- Department of Anesthesiology, Kyoto Prefectural University of Medicine, Kyoto, Japan
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Grasshoff C, Thiermann H, Antkowiak B. Anaesthesia in patients suffering from organophosphorus intoxication—interactions between general anaesthetics and acetylcholine in cortical networks in vitro. Toxicology 2007; 233:214-22. [PMID: 17030394 DOI: 10.1016/j.tox.2006.09.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2006] [Revised: 08/31/2006] [Accepted: 09/01/2006] [Indexed: 10/24/2022]
Abstract
In scenarios of mass destruction it is likely that victims are intoxicated by organophosphates and, at the same time, physically injured. Organophosphate compounds produce excessive cholinergic overstimulation in the CNS via blocking acetylcholinesterase activity. The specifics of acute care and anaesthesia in physically traumatized and intoxicated patients are largely unknown. Recent studies in animals and human subjects demonstrated that acetylcholinesterase inhibitors reverse anaesthesia. Two distinct mechanisms are potentially involved. First, acetylcholine produces an excitatory drive onto neurons, thereby counterbalancing the inhibitory actions of anaesthetics. Anaesthesia is reversed because it critically depends on a distinctive depression of several central nervous functions. Second, cholinergic stimulation may affect the mechanisms by which anaesthetics mediate their depressant actions on central neurons. In this case acetylcholine reverses anaesthesia by decreasing the potency of anaesthetic agents. In order to identify potential mechanisms involved in cholinergic reversal of anaesthesia we have investigated interactions between acetylcholine and the volatile anaesthetic sevoflurane in isolated cortical brain slices. Our results provide evidence that cholinergic stimulation counterbalances the effects of general anaesthetics by increasing neuronal excitability, and, in addition, by decreasing anaesthetic potency. These findings imply that in patients suffering from organophosphorus intoxication dose requirements for general anaesthetics are considerably increased.
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Affiliation(s)
- Christian Grasshoff
- Department of Anesthesiology, Experimental Anesthesiology Section, University of Tuebingen, Schaffhausenstr. 113, D-72072 Tuebingen, Germany
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Time-dependent effects of hyperoxia on the BOLD fMRI signal in primate visual cortex and LGN. Neuroimage 2007; 35:1044-63. [PMID: 17321759 DOI: 10.1016/j.neuroimage.2006.12.039] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2005] [Revised: 08/24/2006] [Accepted: 12/12/2006] [Indexed: 11/28/2022] Open
Abstract
Hyperoxia is present in many anaesthesia protocols used in animal blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) studies. However, little data exist on the influence of hyperoxia on the magnitude of stimulus-induced relative changes in BOLD fMRI signal (DeltaBOLD%). No study to date has investigated these effects in a time-resolved manner, although cerebral vasoregulation offers sites for a time-dependent interaction of hyperoxia and DeltaBOLD%. Here we investigated time-dependent effects of an inspiratory oxygen fraction of 90%. We tightly clamped end tidal CO(2) and body temperature and recorded physiological parameters relevant to rCBF in (fentanyl/isoflurane) anaesthetized monkeys while using visual stimulation to elicit DeltaBOLD%. To clarify whether changes in DeltaBOLD% arose from changes in baseline blood oxygenation or rather altered neuronal or vascular reactivity, we directly measured changes in rCBV using monocrystalline ion oxide nanoparticles (MION) as contrast agent. In visual cortex we found a biphasic modulation of stimulus-induced DeltaBOLD% under hyperoxia: We observed first a significant decrease in DeltaBOLD% by -24% for data averaged over the time interval of 0-180 min post onset of hyperoxia followed by a subsequent recovery to baseline. rCBV response amplitudes were decreased by 21% in the same time interval (0-180 min). In the LGN, we neither found a significant modulation of DeltaBOLD% nor of MION response amplitude. The cerebrovascular effects of hyperoxia may, therefore, be regionally specific and cannot be explained by a deoxyhemoglobin dilution model accounting for plasma oxygenation without assuming altered neuronal activity or altered neurovascular coupling.
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Stevenson CW, Halliday DM, Marsden CA, Mason R. Systemic administration of the benzodiazepine receptor partial inverse agonist FG-7142 disrupts corticolimbic network interactions. Synapse 2007; 61:646-63. [PMID: 17503486 DOI: 10.1002/syn.20414] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The medial prefrontal cortex (mPFC) and basolateral amygdala (BLA) coordinate various stress responses. Although the effects of stressors on mPFC and BLA activity have been previously examined, it remains unclear to what extent stressors affect functional interactions between these regions. In vivo electrophysiology in the anesthetized rat was used to examine mPFC and BLA activity simultaneously in response to FG-7142, a benzodiazepine receptor partial inverse agonist that mimics various stress responses, in an attempt to model the effects of stressors on corticolimbic functional connectivity. Extracellular unit and local field potential (LFP) recordings, using multielectrode arrays positioned in mPFC and BLA, were conducted under basal conditions and in response to systemic FG-7142 administration. This drug increased mPFC and BLA unit firing at the lowest dose tested, whereas higher doses of FG-7142 decreased various burst firing parameters in both regions. Moreover, LFP power was attenuated at lower (<1 Hz) and potentiated at higher frequencies in mPFC (1-12 Hz) and BLA (4-8 Hz). Interestingly, FG-7142 diminished synchronized unit firing, both within and between mPFC and BLA. Finally, FG-7142 decreased LFP synchronization between these regions. In a separate group of animals, pretreatment with the selective benzodiazepine receptor antagonist flumazenil blocked the changes in burst firing, LFP power and synchronized activity induced by FG-7142, confirming direct benzodiazepine receptor-mediated effects. These results indicate that FG-7142 disrupts corticolimbic network interactions via benzodiazepine receptor partial inverse agonism. Perturbation of mPFC-BLA functional connectivity induced by FG-7142 may provide a useful model of corticolimbic dysfunction induced by stressors.
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Affiliation(s)
- Carl W Stevenson
- School of Biomedical Sciences, University of Nottingham, Nottingham, United Kingdom.
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Grasshoff C, Drexler B, Antkowiak B. Effects of cholinergic overstimulation on isoflurane potency and efficacy in cortical and spinal networks. Toxicology 2007; 229:206-13. [PMID: 17141935 DOI: 10.1016/j.tox.2006.10.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2006] [Revised: 10/23/2006] [Accepted: 10/24/2006] [Indexed: 11/19/2022]
Abstract
In scenarios of terrorist attacks with organophosphorus compounds it appears likely that medical aid is required by victims not only suffering from the intoxication but also from physical trauma. These subjects may have to undergo surgical interventions, raising the need for anaesthesia. This prompts the question of how anaesthetic agents work in intoxicated patients. Organophosphates block acetylcholinesterase activity, thereby inducing excessive cholinergic overstimulation in the central nervous system. As the neocortex and spinal cord are important substrates for general anaesthetics, we investigated to what extent cholinergic overstimulation affects the potency and efficacy of the commonly used volatile anaesthetic isoflurane in depressing action potential activity of cortical and spinal neurons. We first quantified the effects of isoflurane in the absence of acetylcholine by performing extracellular voltage recordings in cultured tissue slices. Isoflurane induced a concentration-dependent decrease of neuronal activity in neocortical (EC(50)=0.43+/-0.08 MAC) and spinal slices (EC(50)=0.41+/-0.03 MAC). At concentrations above 1.5 MAC, the anaesthetic almost completely depressed action potential firing in both preparations. Next, we studied the effects of acetylcholine (10microM) in the absence of isoflurane. Acetylcholine approximately doubled spontaneous activity in neocortical and spinal slices. When applying isoflurane together with acetylcholine, different interactions between these agents were observed in neocortical and spinal networks. Acetylcholine significantly reduced both the potency and efficacy of the anaesthetic in neocortical (efficacy 83%; EC(50)=1.16+/-0.02 MAC) but not in spinal (efficacy 100%; EC(50)=0.41+/-0.04 MAC) slices. Our results indicate that cholinergic overstimulation increases the requirement for anaesthetic agents in patients suffering from organophosphorus poisoning via enhancing neuronal background activity of neocortical and spinal neurons and in addition via decreasing drug potency and efficacy in the cortex. Raising anaesthetic concentrations into a high-dose range may not be an appropriate alternative to compensate the increased excitability, since high concentrations of anaesthetics may worsen cardiac abnormalities and hemodynamic instability frequently observed in these patients.
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Affiliation(s)
- Christian Grasshoff
- Department of Anesthesiology, Experimental Anesthesiology Section, Eberhard-Karls-University, Schaffhausenstrasse 113, D-72072 Tuebingen, Germany.
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Sukhotinsky I, Reiner K, Govrin-Lippmann R, Belenky M, Lu J, Hopkins DA, Saper CB, Devor M. Projections from the mesopontine tegmental anesthesia area to regions involved in pain modulation. J Chem Neuroanat 2006; 32:159-78. [PMID: 17049433 DOI: 10.1016/j.jchemneu.2006.08.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2006] [Revised: 08/25/2006] [Accepted: 08/30/2006] [Indexed: 11/19/2022]
Abstract
Pentobarbital microinjected into a restricted locus in the upper brainstem induces a general anesthesia-like state characterized by atonia, loss of consciousness, and pain suppression as assessed by loss of nocifensive response to noxious stimuli. This locus is the mesopontine tegmental anesthesia area (MPTA). Although anesthetic agents directly influence spinal cord nociceptive processing, antinociception during intracerebral microinjection indicates that they can also act supraspinally. Using neuroanatomical tracing methods we show that the MPTA has multiple descending projections to brainstem and spinal areas associated with pain modulation. Most prominent is a massive projection to the rostromedial medulla, a nodal region for descending pain modulation. Together with the periaqueductal gray (PAG), the MPTA is the major mesopontine input to this region. Less dense projections target the PAG, the locus coeruleus and pericoerulear areas, and dorsal and ventral reticular nuclei of the caudal medulla. The MPTA also has modest direct projections to the trigeminal nuclear complex and to superficial layers of the dorsal horn. Double anterograde and retrograde labeling at the light and electron microscopic levels shows that MPTA neurons with descending projections synapse directly on spinally projecting cells of rostromedial medulla. The prominence of the MPTA's projection to the rostromedial medulla suggests that, like the PAG, it may exert antinociceptive actions via this bulbospinal relay.
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Affiliation(s)
- I Sukhotinsky
- Department of Cell and Animal Biology, Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel.
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119
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Butovas S, Hormuzdi SG, Monyer H, Schwarz C. Effects of electrically coupled inhibitory networks on local neuronal responses to intracortical microstimulation. J Neurophysiol 2006; 96:1227-36. [PMID: 16837655 DOI: 10.1152/jn.01170.2005] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Using in vivo multielectrode electrophysiology in mice, we investigated the underpinnings of a local, long-lasting firing rate suppression evoked by intracortical microstimulation. Synaptic inhibition contributes to this suppression as it was reduced by pharmacological blockade of gamma-aminobutyric acid type B (GABAB) receptors. Blockade of GABAB receptors also abolished the known sublinear addition of inhibitory response duration after repetitive electrical stimulation. Furthermore, evoked inhibition was weaker and longer in connexin 36 knockout (KO) mice that feature decoupled cortical inhibitory networks. In supragranular layers of KO mice even an unusually long excitatory response (< or = 50 ms) appeared that was never observed in wild-type (WT) mice. Furthermore, the spread and duration of very fast oscillations (> 200 Hz) evoked by microstimulation at a short latency were strongly enhanced in KO mice. In the spatial domain, lack of connexin 36 unmasked a strong anisotropy of inhibitory spread. Although its reach along layers was almost the same as that in WT mice, the spread across cortical depth was severely hampered. In summary, the present data suggest that connexin 36-coupled networks significantly shape the electrically evoked cortical inhibitory response. Electrical coupling renders evoked cortical inhibition more precise and strong and ensures a uniform spread along the two cardinal axes of neocortical geometry.
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Affiliation(s)
- Sergejus Butovas
- Hertie-Institute for Clinical Brain Research, Department of Cognitive Neurology, University Tübingen, Otfried Müller Str. 27, 72076 Tübingen, Germany
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120
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Antognini JF, Bravo E, Atherley R, Carstens E. Propofol, more than halothane, depresses electroencephalographic activation resulting from electrical stimulation in reticular formation. Acta Anaesthesiol Scand 2006; 50:993-8. [PMID: 16923096 DOI: 10.1111/j.1399-6576.2006.01114.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
BACKGROUND Halothane and propofol depress the central nervous system, and this is partly manifested by a decrease in electroencephalographic (EEG) activity. Little work has been performed to determine the differences between these anesthetics with regard to their effects on evoked EEG activity. We examined the effects of halothane and propofol on EEG responses to electrical stimulation of the reticular formation. METHODS Rats (n= 12) were anesthetized with either halothane or propofol, and EEG responses were recorded before and after electrical stimulation of the reticular formation. Two anesthetic concentrations were used (0.8 and 1.2 times the amount needed to prevent gross, purposeful movement in response to supramaximal noxious stimulation), and both anesthetics were studied in each rat using a cross-over design. RESULTS Electrical stimulation in the reticular formation increased the spectral edge (SEF) and median edge (MEF) frequencies by approximately 1-2 Hz during halothane anesthesia at low and high concentrations. During propofol anesthesia, MEF increased at the low propofol infusion rate, but SEF was unaffected. At the high propofol infusion rate, SEF and MEF decreased following electrical stimulation in the reticular formation. CONCLUSIONS At immobilizing concentrations, propofol produces a larger decrease than halothane in EEG responses to reticular formation stimulation, consistent with propofol having a more profound depressant effect on cortical and subcortical structures.
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Affiliation(s)
- J F Antognini
- Department of Anesthesiology and Pain Medicine, University of California, Davis, CA 95616, USA.
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121
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Abstract
PURPOSE OF REVIEW The concept of minimum alveolar concentration is central to the study of inhalational anesthetics. The minimum alveolar concentration curve is a population concentration-response curve that describes the relationship between anesthetic concentration and oblation of the movement response to painful stimuli. Two features of the minimum alveolar concentration curve, the anesthetic concentration that immobilizes 50% of patients and the steep slope of the curve, may contain useful mechanistic information. There is some dispute, however, about the interpretation of this information. This review examines hypotheses about the shape of the minimum alveolar concentration curve, and recent theoretical and experimental approaches to the question. RECENT FINDINGS The major determining factor for the slope of a quantal, population concentration-response curve is individual variability. The slope of the underlying in-vitro concentration-response curves contributes as well. At the molecular level, in-vitro curves are not steep. The integration of molecular signals that occurs in cells and neuronal circuits can result in steep in-vitro curves, due to multiple molecular targets, amplification and co-operativity. SUMMARY The shape of the minimum alveolar concentration curve has not provided any unambiguous clues about the sites or mechanisms of general anesthesia; however, the universality of anesthetic-induced immobility suggests some future research directions.
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Affiliation(s)
- James P Dilger
- Department of Anesthesiology, Stony Brook University, Stony Brook, New York 11794-8480, USA.
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Orth M, Bravo E, Barter L, Carstens E, Antognini JF. The differential effects of halothane and isoflurane on electroencephalographic responses to electrical microstimulation of the reticular formation. Anesth Analg 2006; 102:1709-14. [PMID: 16717314 DOI: 10.1213/01.ane.0000205752.00303.94] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Isoflurane and halothane cause electroencephalographic (EEG) depression and neuronal depression in the reticular formation, a site critical to consciousness. We hypothesized that isoflurane, more than halothane, would depress EEG activation elicited by electrical microstimulation of the reticular formation. Rats were anesthetized with either halothane or isoflurane and stimulating electrodes were positioned in the reticular formation. In a crossover design, anesthetic concentration was adjusted to 0.8 and 1.2 minimum alveolar concentration (MAC) of halothane or isoflurane and electrical microstimulation was performed and the EEG responses were recorded. Microstimulation increased the spectral edge and median edge frequencies 2-2.5 Hz at 0.8 MAC for halothane and isoflurane and 1.2 MAC halothane. At 1.2 MAC isoflurane, burst suppression occurred and microstimulation decreased the period of isoelectricity (24% +/- 19% to 8% +/- 7%; P < 0.05), whereas the spectral edge and median edge frequencies were unchanged. At anesthetic concentrations required to produce immobility, the cortex remains responsive to electrical microstimulation of the reticular formation, although the EEG response is depressed in the transition from 0.8 to 1.2 MAC. These data indicate that cortical neurons remain responsive to synaptic input during isoflurane and halothane anesthesia.
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Affiliation(s)
- Mashawn Orth
- Department of Anesthesiology and Pain Medicine, Section of Neurobiology, Physiology and Behavior, University of California, Davis, Davis, California 95616, USA
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Wentlandt K, Samoilova M, Carlen PL, El Beheiry H. General anesthetics inhibit gap junction communication in cultured organotypic hippocampal slices. Anesth Analg 2006; 102:1692-8. [PMID: 16717311 DOI: 10.1213/01.ane.0000202472.41103.78] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Gap junctions are protein channels that directly connect the cytosol of neighboring cells, thus forming electrical synapses and promoting synchronous neuronal activities. Such activities lead to the initiation and propagation of electroencephalogram oscillations implicated in cognition and consciousness. In this study, we investigated the effects of propofol, thiopental, and halothane on gap junction communication in cultured organotypic hippocampal slices by recovery of fluorescence after photo bleaching (FRAP) technique and electrophysiological recordings. Propofol 15 microM and thiopental 10 microM attenuated gap junction communication in slice cultures by 46.7% +/- 4.5% and 48.8% +/- 5.5%, respectively, as measured by FRAP. Smaller concentrations of propofol 5 microM and thiopental 2 microM did not change gap junction coupling. Accompanying the decreased gap junction communication, hippocampus slice cultures exposed to propofol 15 microM and thiopental 10 microM were found to have reduced electrophysiologic spontaneous discharges and primary after discharges evoked by a tetanic train of 50 Hz for 2 s. On the other hand, halothane 0.64 mM, a concentration slightly larger than twice its minimum alveolar concentration had no effect on gap junction coupling while halothane 2.8 mM blocked FRAP by 70%. The current study illustrates that anesthetic concentrations of propofol and thiopental, but not halothane, attenuate gap junction communication in cultured hippocampal slices. Suppression of gap junction function could compound the mechanisms of anesthetic actions.
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Affiliation(s)
- Kirsten Wentlandt
- Division of Cellular and Molecular Biology, Toronto Western Research Institute, Department of Anesthesia & Pain Management, Physiology, University of Toronto, University Health Network, Toronto, Ontario, Canada
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Vahle-Hinz C, Detsch O, Siemers M, Kochs E. Contributions of GABAergic and glutamatergic mechanisms to isoflurane-induced suppression of thalamic somatosensory information transfer. Exp Brain Res 2006; 176:159-72. [PMID: 16847609 DOI: 10.1007/s00221-006-0604-6] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2005] [Accepted: 06/14/2006] [Indexed: 12/01/2022]
Abstract
Indications for a pivotal role of the thalamocortical network in producing the state of anesthesia have come from in vivo animal studies as well as imaging studies in humans. We studied possible synaptic mechanisms of anesthesia-induced suppression of touch perception in the rat's thalamus. Thalamocortical relay neurons (TCNs) receive ascending and descending glutamatergic excitatory inputs via NMDA and non-NMDA receptors (AMPAR) and are subjected to GABA(A)ergic inhibitory input which shapes the sensory information conveyed to the cortex. The involvement of these synaptic receptors in the suppressive effects of the prototypic volatile anesthetic isoflurane was assessed by local iontophoretic administration of receptor agonists/antagonists during extracellular recordings of TCNs of the ventral posteromedial nucleus responding to whisker vibration in rats anesthetized with isoflurane concentrations of approximately 0.9 vol.% (baseline) and approximately 1.9 vol.% (ISO high). ISO high induced a profound suppression of response activity reflected by a conversion of the sustained vibratory responses to ON responses. Administration of NMDA, AMPA, or GABA(A)R antagonists caused a reversal to sustained responses in 88, 94 and 88% of the neurons, respectively, with a recovery to baseline levels of response activity. The data show that the block of thalamocortical transfer of tactile information under ISO high may result from an enhancement of GABA(A)ergic inhibition and/or a reduction of glutamatergic excitation. Furthermore, they show that the ascending vibratory signals still reach the thalamic neurons under the high isoflurane concentration, indicating that this input is resistant to isoflurane while the attenuation of excitation may be brought about at the corticothalamic glutamatergic facilitatory input.
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Affiliation(s)
- Christiane Vahle-Hinz
- Institut für Neurophysiologie und Pathophysiologie, Zentrum für Experimentelle Medizin, Universitätsklinikum Hamburg-Eppendorf, Martinistr. 52, 20246, Hamburg, Germany.
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125
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Kopjas NN, Jones RT, Bany B, Patrylo PR. Reeler mutant mice exhibit seizures during recovery from isoflurane-induced anesthesia. Epilepsy Res 2006; 69:87-91. [PMID: 16466907 DOI: 10.1016/j.eplepsyres.2005.12.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2005] [Revised: 12/13/2005] [Accepted: 12/13/2005] [Indexed: 11/28/2022]
Abstract
Reeler mice are a model of cortical malformation with enhanced seizure susceptibility. Data suggest that the propensity to anesthesia-induced seizures may be enhanced in animal models with developmental anomalies. Consequently, reeler mice were monitored behaviorally before, during and after isoflurane anesthesia. During recovery, 12% of reeler homozygotes had class I/II seizures while the remaining 88% exhibited convulsive seizures entailing opisthotonus and forepaw drumming. Similar behavior was not observed in controls. These data reveal that reeler mice display isoflurane-induced seizures and provide support for the hypothesis that developmental anomalies may predispose the central nervous system to anesthesia-induced seizures.
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Affiliation(s)
- Nicholas N Kopjas
- Department of Physiology, Southern Illinois University School of Medicine, Carbondale, IL 62901, USA
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Abstract
Advances in electroencephalogram (EEG) processing have produced new interest in measuring anesthesia using the EEG. There are a number of EEG-based anesthesia 'depth' monitors now available and their use in pediatric anesthesia is increasing. Although these monitors have been extensively studied in adults, there are relatively few studies examining their validity or use in children. To some extent we must rely on adult data. However, extrapolation of data from adults to children requires an in depth understanding of the physiology behind the data. The first question is what is being measured. What is anesthesia? A model of anesthesia has several components with arousal as a core component. Arousal can be linked to clinical observations, and correlates with anatomical and physiological studies. The EEG has characteristics that fairly consistently change with arousal during anesthesia, but the relationship between arousal and the EEG is imprecise and drug dependent. This relationship is the basis for using the EEG to measure anesthesia and provides only an indirect measure of consciousness and memory formation. A good understanding of how the EEG is related to anesthesia is essential when interpreting the EEG during anesthesia, and especially when extending the use of the EEG to measure anesthesia in children. Physiological studies in adults and children indicate that EEG-derived anesthesia depth monitors can provide an imprecise and drug-dependent measure of arousal. Although the outputs from these monitors do not closely represent any true physiological entity, they can be used as guides for anesthesia and in so doing have improved outcomes in adults. In older children the physiology, anatomy and clinical observations indicate the performance of the monitors may be similar to that in adults, although the clinical relevance of outcomes may be different. In infants their use cannot yet be supported in theory or in practice.
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Affiliation(s)
- Andrew J Davidson
- Department of Anaesthesia and Pain Management, Royal Children's Hospital, Parkville, Vic., Australia.
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Soteropoulos DS, Baker SN. Cortico-cerebellar coherence during a precision grip task in the monkey. J Neurophysiol 2006; 95:1194-206. [PMID: 16424458 DOI: 10.1152/jn.00935.2005] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We studied the synchronization of single units in macaque deep cerebellar nuclei (DCN) with local field potentials (LFPs) in primary motor cortex (M1) bilaterally during performance of a precision grip task. Analysis was restricted to periods of steady holding, during which M1 oscillations are known to be strongest. Significant coherence between DCN units and M1 LFP oscillations bilaterally was seen at approximately 10-40 Hz (contralateral M1: 25/87 units; ipsilateral: 9/87 units). Averaged coherence between DCN units and contralateral M1 LFP showed a prominent approximately 17-Hz coherence peak and an average phase of approximately -pi/2 radians, implying that the DCN units fired around the time of maximal depolarization of M1 cells. The lack of a time delay between DCN and M1 activity suggests that the cerebellum and cortex may form a pair of phase coupled oscillators. Although coherence values were low (mean peak coherence, 0.018), we used a computational model to show that this probably resulted from the nonlinearity of spike generating mechanisms within the DCN. DCN unit discharge and DCN LFPs also showed significant coherence at approximately 10-40 Hz, with similarly low magnitude (mean peak coherence, 0.012). The average coherence phase was -2.5 radians for the 6- to 14-Hz range and -1.1 radians for the 17- to 41-Hz range, suggesting different frequency-specific underlying mechanisms. Finally, 4/40 pairs of simultaneously recorded DCN units showed a significant cross-correlation peak, and 16/40 pairs showed significant unit-unit coherence. The extensive oscillatory synchronization observed between cerebellum and motor cortex may have functional importance in sensorimotor processing.
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Affiliation(s)
- Demetris S Soteropoulos
- University of Newcastle, Sir James Spence Institute, Royal Victoria Infirmary, Newcastle upon Tyne, United Kingdom
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Grasshoff C, Rudolph U, Antkowiak B. Molecular and systemic mechanisms of general anaesthesia: the ‘multi-site and multiple mechanisms’ concept. Curr Opin Anaesthesiol 2005; 18:386-91. [PMID: 16534263 DOI: 10.1097/01.aco.0000174961.90135.dc] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PURPOSE OF REVIEW Amnesia, hypnosis and immobility are essential components of general anaesthesia. This review highlights recent advances in our understanding of how these components are achieved at a molecular level. RECENT FINDINGS Commonly used volatile anaesthetic agents such as isoflurane or sevoflurane cause immobility by modulating multiple molecular targets predominantly in the spinal cord, including gamma-aminobutyric acidA receptors, glycine receptors, glutamate receptors and TREK-1 potassium channels. In contrast, intravenously applied drugs such as propofol or etomidate depress spinal motor reflexes almost exclusively via enhancing gamma-aminobutyric acidA receptor function. Studies on knock-in animals showed that etomidate and propofol act via gamma-aminobutyric acidA receptors containing beta3 subunits, whereas gamma-aminobutyric acidA receptors including alpha2 and gamma subunits mediate the myorelaxant properties of diazepam. These findings suggest that a large fraction of gamma-aminobutyric acidA receptors in the spinal cord assemble from alpha2, beta3 and most probably gamma2 subunits. The hypnotic actions of etomidate are mediated by beta3-containing gamma-aminobutyric acidA receptors expressed in the brain. In contrast, gamma-aminobutyric acidA receptors harbouring beta2 subunits produce sedation, but not hypnosis. Furthermore, there is growing evidence that extrasynaptic gamma-aminobutyric acidA receptors in the hippocampus containing alpha5 subunits contribute to amnesia. SUMMARY Clinical anaesthesia is based on drug actions at multiple anatomical sites in the brain. The finding that amnesia, hypnosis and immobility involve distinct molecular targets opens new avenues for developing improved therapeutic strategies in anaesthesia.
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Moliadze V, Giannikopoulos D, Eysel UT, Funke K. Paired-pulse transcranial magnetic stimulation protocol applied to visual cortex of anaesthetized cat: effects on visually evoked single-unit activity. J Physiol 2005; 566:955-65. [PMID: 15919717 PMCID: PMC1464771 DOI: 10.1113/jphysiol.2005.086090] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
In this study, we tested the paired-pulse transcranial magnetic stimulation (ppTMS) protocol - a conditioning stimulus (CS) given at variable intervals prior to a test stimulus (TS) - for visually evoked single-unit activity in cat primary visual cortex. We defined the TS as being supra-threshold when it caused a significant increase or decrease in the visually evoked activity. By systematically varying the interstimulus interval (ISI) between 2 and 30 ms and the strength of CS within the range 15-130% of TS, we found a clear dependence of the ppTMS effect on CS strength but little relation to ISI. The CS effect was strongest with an ISI of 3 ms and steadily declined for longer ISIs. A switch from enhancement of intracortical inhibition at short ISIs (2-5 ms, SICI) to intracortical facilitation (ICF) at longer ISIs (7-30 ms), as demonstrated for human motor cortex, was not evident. Whether the CS caused facilitation or suppression of the TS effect mainly depended on the strength of CS and the polarity of the TS effect: within a range of 60-130% a positive correlation between ppTMS and TS effect was evident, resulting in a stronger facilitation if the TS caused facilitation of visual activity, and more suppression if the TS was suppressive by itself. The correlation inverted when CS was reduced to 15-30%. The ppTMS effect was not simply the sum of the CS and TS effect, it was much smaller at weak CS strength (15-50%) but stronger than the sum of CS and TS effects at CS strength 60-100%. Differences in the physiological state between sensory and motor cortices and the interactions of paired synaptic inputs are discussed as possible reasons for the partly different effects of ppTMS in cat visual cortex and human motor cortex.
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Affiliation(s)
- Vera Moliadze
- Department of Neurophysiology, Medical Faculty, Ruhr-University Bochum, 44780 Bochum, Germany
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