Visual P2-N2 complex and arousal at the time of encoding predict the time domain characteristics of amnesia for multiple intravenous anesthetic drugs in humans

Recovery of memory retention after anesthesia with remimazolam: an exploratory, randomized, open, propofol-controlled, single-center clinical trial

PURPOSE

Remimazolam, a newly developed ultra-short-acting benzodiazepine, provides early recovery of consciousness but its effects on memory recovery are unclear. This study examined memory recovery after emergence from general anesthesia using remimazolam.

METHODS

Seventy-four patients undergoing breast surgery between October 2021 and March 2022 were enrolled and randomly assigned to receive propofol (control group) or remimazolam as general anesthetic during surgery. The primary endpoint was the number of posters patients remembered 24 h after surgery (among four posters shown after recovering from anesthesia) as an assessment of memory retention. The secondary endpoints were the recall of a numeric character patients had been shown just before anesthetic induction, as an assessment of retrograde amnesia 24 h after surgery.

RESULTS

Sixty-six patients (propofol, 32; remimazolam, 34) were assessed. Patients in the remimazolam group remembered significantly fewer posters shown to them after surgery than those in the propofol group (0 [0 - 2] vs. 2 [1 - 3], p < 0.001). In the remimazolam group, the patients who received flumazenil remembered a higher number of posters than those who did not receive flumazenil (3 [1 - 4] vs. 0 [0 - 0], p < 0.001). All patients remembered all events that occurred during the preoperative period as well as the numeric character.

CONCLUSION

Patients recovering from remimazolam anesthesia without receiving flumazenil do not remember events after regaining consciousness. IRB: Kyushu University School of Medicine Hospital Institutional Review Board (IRB) (approval number: 20212006).

TRIAL REGISTRATION

This clinical trial was registered with the University Hospital Medical Information Network (UMIN) Center on September 28, 2021 (UMIN-CTR: UMIN000045593).

IMPLICATION STATEMENT

Memory recovery is slower following emergence from remimazolam than from propofol anesthesia.

Suberoylanilide hydroxamic acid (SAHA) attenuates memory impairment in the offspring of rats exposed to sevoflurane anesthesia

BACKGROUND

SAHA was reported to enhance the expression of miR-129-5p, which was predicted to bind to 3' UTR of CASP-6, a gene playing crucial roles in the pathogenesis of memory impairment. Whether SAHA/miR-129-5p/CASP-6 is involved in the pathogenesis of prenatal exposure to sevoflurane remains to be explored.

METHODS

Morris water maze test was performed to evaluate the functional parameters of learning and memory. Quantitative real-time qPCR was carried out to analyze the expression of miRNAs and CASP-6 mRNA under different conditions.

RESULTS

Sevoflurane exposure of pregnant rats and SAHA treatment of the offspring had no effect on the blood gases, litter size, survival rate and weight. SAHA administration remarkably reversed the learning and memory impairment in prenatal rats caused by sevoflurane exposure. Mechanistically, the abnormal expression of miR-129-5p and CASP-6 in the offspring of pregnant rats exposed to sevoflurane was effectively restored by SAHA treatment. The luciferase activity of CASP-6 vector was effectively inhibited by miR-129-5p in primary neuron cells of rats. Moreover, the expression of CASP-6 mRNA and protein was significantly suppressed by miR-129-5p and SAHA treatment in a dose-dependent manner.

CONCLUSION

Our work demonstrated that the administration of SAHA suppressed the expression of CASP-6 via modulating the expression of miR-129-5p, and SAHA may rescue the apoptosis of neurons caused by exposure to sevoflurane. The underlying mechanism might be the ability of SAHA to relieve learning and memory impairment in the offspring of the pregnant rats exposed to sevoflurane.

Propofol Modulates Early Memory Consolidation in Humans

Maintenance of memory across time is crucial for adaptive behavior. Current theories posit that the underlying consolidation process depends on stabilization of synapses and reorganization of interactions between hippocampus and neocortex. However, the temporal properties of hippocampal-neocortical network reconfiguration during consolidation are still a matter of debate. Translational research on this issue is challenged by the paucity of techniques to transiently interfere with memory in the healthy human brain. Here, we report a neuro-pharmacological approach with the GABA_Aergic anesthetic propofol and a memory task sensitive to hippocampal dysfunction. Patients undergoing minor surgery learned word lists before injection of an anesthetic dose of propofol. Results show that administration of the drug shortly after learning (∼13 min) impairs recall after awakening but spares recognition. By contrast, later administration (∼105 min) has no effect. These findings suggest significant changes in memory networks very early after learning that are decisive for later recall. Propofol general anesthesia provides an experimental tool to modulate the first steps of hippocampus-mediated memory consolidation in humans.

Baseline Functional Connectivity Predicts Connectivity Changes Due to a Small Dose of Midazolam in Older Adults

BACKGROUND

In the perioperative context, benzodiazepines are widely used as anxiolytics. They affect cognition in general, but it is unclear whether the effects of a small dose of the short-acting benzodiazepine midazolam can be assessed objectively. To address this scientific question, we conducted a prospective observational study in adults 55-73 years of age. Using both validated psychometric and functional imaging techniques, we determined whether a 2-mg intravenous (IV) dose of midazolam affects cognitive function.

METHODS

We measured the effect of 2 mg IV of midazolam with both the well-established Repeatable Battery for the Assessment of Neuropsychological Status test and resting-state functional magnetic imaging (rs-fMRI) in older adults.

RESULTS

Midazolam reduces immediate and delayed memory and has a profound and robust effect on rs-fMRI. Baseline resting-state connectivity predicts memory decline after midazolam administration.

CONCLUSIONS

Observed effects of midazolam on brain networks were statistically significant even in a small group of volunteers. If validated by other investigators, resting-state brain connectivity may have utility as a measure to predict sensitivity to midazolam in older adults.

The Effects of Anesthetics on the Cortex-Lessons From Event-Related Potentials

Consciousness while under general anesthesia is a dreadful condition. Various electroencephalogram (EEG)-based technologies have been developed, on the basis of empirical evidence, in order to identify this condition. However, certain electrophysiological phenomena, which seem strongly related with depth of anesthesia in some drugs, appear less consistent with those of other anesthetic drugs. There is a gap between the complexity of the phenomenon of consciousness and its behavioral manifestations, on the one hand, and the empirical nature of the reported electrophysiological markers, which are associated with it, on the other hand. In fact, such a gap might prevent us from progressing toward unified electrophysiological markers of consciousness while under anesthesia, which are applicable to all anesthetic drugs. We believe that there is a need to bridge this conceptual gap. Therefore, in this work, we will try to present a theoretical framework for such bridging. First, we suggest focusing on neuropsychological processes, which seem to have a clear role in the behavioral manifestations of consciousness while under anesthesia but seem, nevertheless, better defined than consciousness itself-such as perception and attention. Then, we suggest analyzing the effects of anesthesia upon these neuropsychological processes, as they are manifested in the EEG signal. Specifically, we will focus on the effects of anesthesia on event-related potentials (ERPs), which seem more easily associable with neuropsychological modeling.

γ-Aminobutyric Acid Type A Receptor Potentiation Inhibits Learning in a Computational Network Model

BACKGROUND

Propofol produces memory impairment at concentrations well below those abolishing consciousness. Episodic memory, mediated by the hippocampus, is most sensitive. Two potentially overlapping scenarios may explain how γ-aminobutyric acid receptor type A (GABAA) potentiation by propofol disrupts episodic memory-the first mediated by shifting the balance from excitation to inhibition while the second involves disruption of rhythmic oscillations. We use a hippocampal network model to explore these scenarios. The basis for these experiments is the proposal that the brain represents memories as groups of anatomically dispersed strongly connected neurons.

METHODS

A neuronal network with connections modified by synaptic plasticity was exposed to patterned stimuli, after which spiking output demonstrated evidence of stimulus-related neuronal group development analogous to memory formation. The effect of GABAA potentiation on this memory model was studied in 100 unique networks.

RESULTS

GABAA potentiation consistent with moderate propofol effects reduced neuronal group size formed in response to a patterned stimulus by around 70%. Concurrently, accuracy of a Bayesian classifier in identifying learned patterns in the network output was reduced. Greater potentiation led to near total failure of group formation. Theta rhythm variations had no effect on group size or classifier accuracy.

CONCLUSIONS

Memory formation is widely thought to depend on changes in neuronal connection strengths during learning that enable neuronal groups to respond with greater facility to familiar stimuli. This experiment suggests the ability to form such groups is sensitive to alteration in the balance between excitation and inhibition such as that resulting from administration of a γ-aminobutyric acid-mediated anesthetic agent.

Complexities of human memory: relevance to anaesthetic practice

Mechanisms of anaesthetic actions on memory have largely focused on easily definable aspects of episodic memory, with emphasis on particular drug interactions on specific memory processes. However, the memory landscape of the perioperative experience includes many facets that lie outside these conceptualisations. These include patient recall of preoperative conversations, patient beliefs regarding allergies and unusual/uncommon anaesthetic events, memories of awareness, and particularly vivid dreams during anaesthesia. In no small part, memories are influenced by a patient's interpretations of events in light of their own belief systems. From the practitioner's point of view, relating fully to the patient's experience requires some framework of understanding. The purpose of this review is to highlight research over the previous decades on belief systems and their interactions with autobiographical memory, which organises episodic memories into a personally relevant narrative. As a result, memory is a set of continuously malleable processes, and is best described as a (re)constructive rather than photographic instantiation. Belief systems are separate but closely interacting processes with autobiographical memory. The interaction of a constantly evolving set of memories with belief systems can explain phenomena such as illusions, distortions, and (re)constructions of factitious events. How anaesthetics and our patient interactions influence these behaviours, and vice versa, will be important questions to explore and define with future research.

Feasibility of measuring memory response to increasing dexmedetomidine sedation in children

BACKGROUND

The memory effect of dexmedetomidine has not been prospectively evaluated in children. We evaluated the feasibility of measuring memory and sedation responses in children during dexmedetomidine sedation for non-painful radiological imaging studies. Secondarily, we quantified changes in memory in relation to the onset of sedation.

METHODS

A 10 min bolus of dexmedetomidine (2 mcg kg^-1) was given to children as they named simple line drawings every five s. The absence of sedation was identified as any verbal response, regardless of correctness. After recovery, recognition memory was tested with correct Yes/No recognitions (50% novel pictures) and was matched to sedation responses during the bolus period (subsequent memory paradigm).

RESULTS

Of 64 accruals, 30 children (mean [SD]6.1 (1.2) yr, eight male) received dexmedetomidine and completed all study tasks. Individual responses were able to be modelled successfully in the 30 children completing all the study tasks, demonstrating feasibility of this approach. Children had 50% probability of verbal response at five min 40 s after infusion start, whereas 50% probability of subsequent recognition memory occurred sooner at four min five s.

CONCLUSIONS

Quantifying memory and sedation effects during dexmedetomidine infusion in verbal children was possible and demonstrated that memory function was present until shortly before verbal unresponsiveness occurred. This is the first study to investigate the effect of dexmedetomidine on memory in children.

CLINICAL TRIAL REGISTRATION

NCT 02354378.

Spoken words are processed during dexmedetomidine-induced unresponsiveness

BACKGROUND

Studying the effects of anaesthetic drugs on the processing of semantic stimuli could yield insights into how brain functions change in the transition from wakefulness to unresponsiveness. Here, we explored the N400 event-related potential during dexmedetomidine- and propofol-induced unresponsiveness.

METHODS

Forty-seven healthy subjects were randomised to receive either dexmedetomidine (n=23) or propofol (n=24) in this open-label parallel-group study. Loss of responsiveness was achieved by stepwise increments of pseudo-steady-state plasma concentrations, and presumed loss of consciousness was induced using 1.5 times the concentration required for loss of responsiveness. Pre-recorded spoken sentences ending either with an expected (congruous) or an unexpected (incongruous) word were presented during unresponsiveness. The resulting electroencephalogram data were analysed for the presence of the N400 component, and for the N400 effect defined as the difference between the N400 components elicited by congruous and incongruous stimuli, in the time window 300-600 ms post-stimulus. Recognition of the presented stimuli was tested after recovery of responsiveness.

RESULTS

The N400 effect was not observed during dexmedetomidine- or propofol-induced unresponsiveness. The N400 component, however, persisted during dexmedetomidine administration. The N400 component elicited by congruous stimuli during unresponsiveness in the dexmedetomidine group resembled the large component evoked by incongruous stimuli at the awake baseline. After recovery, no recognition of the stimuli heard during unresponsiveness occurred.

CONCLUSIONS

Dexmedetomidine and propofol disrupt the discrimination of congruous and incongruous spoken sentences, and recognition memory at loss of responsiveness. However, the processing of words is partially preserved during dexmedetomidine-induced unresponsiveness.

CLINICAL TRIAL REGISTRATION

NCT01889004.

Propofol sedation in children: sleep trumps amnesia

OBJECTIVE

Detailed assessments of the effects of propofol on memory in children are lacking. We assessed the feasibility of measuring memory during propofol infusion, as commonly performed in sedation for MRI scanning. In addition, we determined the onset of memory loss in relation to the onset of sedation measured by verbal responsiveness.

MATERIALS AND METHODS

Children scheduled for sedation for MRI received a 10-min infusion of propofol (3 mg/kg) as they viewed and named 100 simple line drawings, one shown every five seconds, until they were no longer responsive (encoding). A control group receiving no sedation for MRI underwent similar tasks. Sedation was measured as any verbal response, regardless of correctness. After recovery from sedation, recognition memory was tested, with correct yes/no recognitions matched to sedation responses during encoding (subsequent memory paradigm).

RESULTS

Of the 48 children who received propofol, 30 could complete all study tasks (6.2 ± 1.6 years, 16 males). Individual responses could be modeled in all 30 children. On average, there was a 50% probability of no verbal response 3.1 min after the start of infusion, with 50% memory loss at 2.7 min. Children receiving propofol recognized 65 ± 16% of the pictures seen, whereas the control group recognized 93 ± 5%.

CONCLUSION

Measurement of memory and sedation is possible in verbal children receiving propofol by infusion in a clinical setting. Despite propofol being an amnestic agent, there was little or no amnestic effect of propofol while the child was verbally responsive. It is important for sedation providers to realize that propofol sedation does not always produce amnesia while the child is responsive. CLINICALTRIALS.

GOV NUMBER

NCT02278003.

Anaesthetic interventions for prevention of awareness during surgery

BACKGROUND

General anaesthesia is usually associated with unconsciousness. 'Awareness' is when patients have postoperative recall of events or experiences during surgery. 'Wakefulness' is when patients become conscious during surgery, but have no postoperative recollection of the period of consciousness.

OBJECTIVES

To evaluate the efficacy of two types of anaesthetic interventions in reducing clinically significant awareness:- anaesthetic drug regimens; and- intraoperative anaesthetic depth monitors.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, ISSUE 4 2016); PubMed from 1950 to April 2016; MEDLINE from 1950 to April 2016; and Embase from 1980 to April 2016. We contacted experts to identify additional studies. We performed a handsearch of the citations in the review. We did not search trial registries.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of either anaesthetic regimens or anaesthetic depth monitors. We excluded volunteer studies, studies of patients prior to skin incision, intensive care unit studies, and studies that only randomized different word presentations for memory tests (not anaesthetic interventions).Anaesthetic drug regimens included studies of induction or maintenance, or both. Anaesthetic depth monitors included the Bispectral Index monitor, M-Entropy, Narcotrend monitor, cerebral function monitor, cerebral state monitor, patient state index, and lower oesophageal contractility monitor. The use of anaesthetic depth monitors allows the titration of anaesthetic drugs to maintain unconsciousness.

DATA COLLECTION AND ANALYSIS

At least two authors independently scanned abstracts, extracted data from the studies, and evaluated studies for risk of bias. We made attempts to contact all authors for additional clarification. We performed meta-analysis statistics in packages of the R language.

MAIN RESULTS

We included 160 studies with 54,109 enrolled participants; 53,713 participants started the studies and 50,034 completed the studies or data analysis (or both). We could not use 115 RCTs in meta-analytic comparisons because they had zero awareness events. We did not merge 27 of the remaining 45 studies because they had excessive clinical and methodological heterogeneity. We pooled the remaining 18 eligible RCTs in meta-analysis. There are 10 studies awaiting classification which we will process when we update the review.The meta-analyses included 18 trials with 36,034 participants. In the analysis of anaesthetic depth monitoring (either Bispectral Index or M-entropy) versus standard clinical and electronic monitoring, there were nine trials with 34,744 participants. The overall event rate was 0.5%. The effect favoured neither anaesthetic depth monitoring nor standard clinical and electronic monitoring, with little precision in the odds ratio (OR) estimate (OR 0.98, 95% confidence interval (CI) 0.59 to 1.62).In a five-study subset of Bispectral Index monitoring versus standard clinical and electronic monitoring, with 34,181 participants, 503 participants gave awareness reports to a blinded, expert panel who adjudicated or judged the outcome for each patient after reviewing the questionnaires: no awareness, possible awareness, or definite awareness. Experts judged 351 patient awareness reports to have no awareness, 87 to have possible awareness, and 65 to have definite awareness. The effect size favoured neither Bispectral Index monitoring nor standard clinical and electronic monitoring, with little precision in the OR estimate for the combination of definite and possible awareness (OR 0.96, 95% CI 0.35 to 2.65). The effect size favoured Bispectral Index monitoring for definite awareness, but with little precision in the OR estimate (OR 0.60, 95% CI 0.13 to 2.75).We performed three smaller meta-analyses of anaesthetic drugs. There were nine studies with 1290 participants. Wakefulness was reduced by ketamine and etomidate compared to thiopental. Wakefulness was more frequent than awareness. Benzodiazepines reduces awareness compared to thiopental, ketamine, and placebo., Also, higher doses of inhaled anaesthetics versus lower doses reduced the risk of awareness.We graded the quality of the evidence as low or very low in the 'Summary of findings' tables for the five comparisons.Most of the secondary outcomes in this review were not reported in the included RCTs.

AUTHORS' CONCLUSIONS

Anaesthetic depth monitors may have similar effects to standard clinical and electrical monitoring on the risk of awareness during surgery. In older studies comparing anaesthetics in a smaller portion of the patient sample, wakefulness occurred more frequently than awareness. Use of etomidate and ketamine lowered the risk of wakefulness compared to thiopental. Benzodiazepines compared to thiopental and ketamine, or higher doses of inhaled anaesthetics versus lower doses, reduced the risk of awareness.

α2-Adrenergic Receptor and Isoflurane Modulation of Presynaptic Ca2+ Influx and Exocytosis in Hippocampal Neurons

BACKGROUND

Evidence indicates that the anesthetic-sparing effects of α2-adrenergic receptor (AR) agonists involve α2A-AR heteroreceptors on nonadrenergic neurons. Since volatile anesthetics inhibit neurotransmitter release by reducing synaptic vesicle (SV) exocytosis, the authors hypothesized that α2-AR agonists inhibit nonadrenergic SV exocytosis and thereby potentiate presynaptic inhibition of exocytosis by isoflurane.

METHODS

Quantitative imaging of fluorescent biosensors of action potential-evoked SV exocytosis (synaptophysin-pHluorin) and Ca influx (GCaMP6) were used to characterize presynaptic actions of the clinically used α2-AR agonists dexmedetomidine and clonidine, and their interaction with isoflurane, in cultured rat hippocampal neurons.

RESULTS

Dexmedetomidine (0.1 μM, n = 10) or clonidine (0.5 μM, n = 8) inhibited action potential-evoked exocytosis (54 ± 5% and 59 ± 8% of control, respectively; P < 0.001). Effects on exocytosis were blocked by the subtype-nonselective α2-AR antagonist atipamezole or the α2A-AR-selective antagonist BRL 44408 but not by the α2C-AR-selective antagonist JP 1302. Dexmedetomidine inhibited exocytosis and presynaptic Ca influx without affecting Ca coupling to exocytosis, consistent with an effect upstream of Ca-exocytosis coupling. Exocytosis coupled to both N-type and P/Q-type Ca channels was inhibited by dexmedetomidine or clonidine. Dexmedetomidine potentiated inhibition of exocytosis by 0.7 mM isoflurane (to 42 ± 5%, compared to 63 ± 8% for isoflurane alone; P < 0.05).

CONCLUSIONS

Hippocampal SV exocytosis is inhibited by α2A-AR activation in proportion to reduced Ca entry. These effects are additive with those of isoflurane, consistent with a role for α2A-AR presynaptic heteroreceptor inhibition of nonadrenergic synaptic transmission in the anesthetic-sparing effects of α2A-AR agonists.

Dexmedetomidine promotes the recovery of the field excitatory postsynaptic potentials (fEPSPs) in rat hippocampal slices exposed to oxygen-glucose deprivation

Dexmedetomidine (DEX), a selective α2 adrenergic agonist, is an anesthetic and sedative agent, and is reported to exert neuroprotective effects after hypoxic ischemia. However, there are few studies on the electrophysiological effect of DEX in hippocampal slices under ischemic conditions. The effects of DEX on field potential in hippocampal slices exposed to oxygen-glucose deprivation (OGD) were evaluated. Hippocampal slices were prepared from rats, and the evoked field excitatory postsynaptic potentials (fEPSPs) were recorded using the MED 64 system. Hypoxic-ischemia was induced by perfusion with glucose-free artificial cerebrospinal fluid (aCSF) bubbled with 95% N2 and 5% CO2, and hippocampal slices were perfused with DEX-added aCSF before, during, and after OGD induction. In the normal hippocampal slices, perfusion with 1 and 10μM DEX did not significantly decrease the normalized fEPSP amplitude, but 100μM DEX significantly reduced the fEPSP amplitude compared with its baseline control. The induction of OGD remarkably decreased the fEPSP amplitude, whereas the pre-, co-, and post-treatment of 10μM DEX gradually promoted recovery after washing out, and consequently the amplitude of fEPSP in DEX pre-, co-, and post-treated OGD slices were significantly higher than that in the untreated OGD slices at 10min and 60min after washing out. In particular, co-treatment with DEX conspicuously promoted the recovery of the fEPSP amplitude at the beginning of washing out. These results suggest the possibility of DEX as a therapeutic agent to prevent hypoxic-ischemic brain damage and promote functional recovery after ischemia.

The Effects of Different Concentrations of the α2-Adrenoceptor Agonist Medetomidine on Basal Excitatory Synaptic Transmission and Synaptic Plasticity in Hippocampal Slices of Adult Mice

BACKGROUND

α2-Adrenoceptor agonists are used frequently in human and veterinary anesthesia as sedative/analgesic drugs. However, they can impair cognition. Little is known about the concentration-dependent effects of α2-adrenoceptor agonists on synaptic plasticity, the neurophysiological basis of learning and memory. Therefore, we investigated the effects of different concentrations of medetomidine, an α2-adrenoceptor agonist, on basal excitatory synaptic transmission and on 2 forms of synaptic plasticity: paired-pulse facilitation (PPF) and long-term potentiation (LTP).

METHODS

Evoked field excitatory postsynaptic potentials were recorded in Schaffer fibers-CA1 pyramidal cell synapses of mouse hippocampal slices, and the initial field excitatory postsynaptic potentials slope was measured. For basal synaptic transmission and PPF, increasing concentrations of medetomidine (1-200 μM) were applied to each slice. For LTP experiments, individual slices were used for each tested concentration of medetomidine (0.1-0.4 μM), where LTP induction and LTP maintenance were measured.

RESULTS

The lower tested concentrations of medetomidine decreased LTP in a concentration-dependent manner, whereas greater concentrations were required to decrease fiber volley amplitude and basal excitatory synaptic transmission. PPF was only affected by the greatest concentration (200 μM).

CONCLUSIONS

Medetomidine decreased LTP in the mouse hippocampus, in accordance with the ability of medetomidine to induce memory deficits.

Effect of propofol on the medial temporal lobe emotional memory system: a functional magnetic resonance imaging study in human subjects

BACKGROUND

Subclinical doses of propofol produce anterograde amnesia, characterized by an early failure of memory consolidation. It is unknown how propofol affects the amygdala-dependent emotional memory system, which modulates consolidation in the hippocampus in response to emotional arousal and neurohumoral stress. We present an event-related functional magnetic resonance imaging study of the effects of propofol on the emotional memory system in human subjects.

METHODS

Thirty-five healthy subjects were randomized to receive propofol, at an estimated brain concentration of 0.90 μg ml(-1), or placebo. During drug infusion, emotionally arousing and neutral images were presented in a continuous recognition task, while blood-oxygen-level-dependent activation responses were acquired. After a drug-free interval of 2 h, subsequent memory for successfully encoded items was assessed. Imaging analysis was performed using statistical parametric mapping and behavioural analysis using signal detection models.

RESULTS

Propofol had no effect on the stereotypical amygdalar response to emotional arousal, but caused marked suppression of the hippocampal response. Propofol caused memory performance to become uncoupled from amygdalar activation, but it remained correlated with activation in the posterior hippocampus, which decreased in proportion to amnesia.

CONCLUSIONS

Propofol is relatively ineffective at suppressing amygdalar activation at sedative doses, but abolishes emotional modulation and causes amnesia via mechanisms that commonly involve hyporesponsiveness of the hippocampus. These findings raise the possibility that amygdala-dependent fear systems may remain intact even when a patient has diminished memory of events. This may be of clinical importance in the perioperative development of fear-based psychopathologies, such as post-traumatic stress disorder.

CLINICAL TRIAL REGISTRATION

NCT00504894.

Dexmedetomidine suppresses long-term potentiation in the hippocampal CA1 field of anesthetized rats

PURPOSE

The aim of this study was to evaluate the effect of dexmedetomidine (DEX) on hippocampal synaptic activity in vivo.

METHODS

The adult rats used for this study received a intraperitoneal bolus injection of 3, 10, 30, or 100 μg/kg of DEX or an equivalent volume of saline. Electrophysiological recording of the hippocampal CA1 region was initiated 20 min after drug administration. The results are expressed as the percentages of the population spike amplitude measured just before high-frequency stimulation (HFS). The electrophysiological data were analyzed with an area under the curve (AUC) of 10-60 min after HFS. Moreover, to investigate the sedative dose of DEX in rats, we recorded the duration of loss of spontaneous movement after the administration of each dose of DEX.

RESULTS

Intraperitoneal administration of DEX at doses of 30 and 100 μg/kg induced a range of sedative effects. The AUC measurements were significantly lower in the 30 and 100 μg/kg groups than in those injected with vehicle (vehicle: 8.81 ± 0.49, n = 7; DEX 30 µg/kg: 6.02 ± 0.99, n = 6; DEX 100 µg/kg: 5.10 ± 0.43, n = 5; P < 0.05).

CONCLUSION

The results of our in vivo study reveal that sedative doses of DEX impaired the induction of hippocampal long-term potentiation (LTP). These findings may signify a causal link between DEX-induced sedative action and hippocampal LTP suppression, providing a better understanding of the mechanisms underlying the DEX-induced sedative and/or amnestic effect.

Cognitive unbinding: a neuroscientific paradigm of general anesthesia and related states of unconsciousness

"Cognitive unbinding" refers to the impaired synthesis of specialized cognitive activities in the brain and has been proposed as a mechanistic paradigm of unconsciousness. This article draws on recent neuroscientific data to revisit the tenets and predictions of cognitive unbinding, using general anesthesia as a representative state of unconsciousness. Current evidence from neuroimaging and neurophysiology supports the proposition that cognitive unbinding is a parsimonious explanation for the direct mechanism (or "proximate cause") of anesthetic-induced unconsciousness across multiple drug classes. The relevance of cognitive unbinding to sleep, disorders of consciousness, and psychological processes is also explored. It is concluded that cognitive unbinding is a viable neuroscientific framework for unconscious processes across the fields of anesthesiology, sleep neurobiology, neurology and psychoanalysis.

Event-related functional magnetic resonance imaging of a low dose of dexmedetomidine that impairs long-term memory

BACKGROUND

Work suggests the amnesia from dexmedetomidine (an α2-adrenergic agonist) is caused by a failure of information to be encoded into long-term memory and that dexmedetomidine might differentially affect memory for emotionally arousing material. We investigated these issues in humans using event-related neuroimaging to reveal alterations in brain activity and subsequent memory effects associated with drug exposure.

METHODS

Forty-eight healthy volunteers received a computer-controlled infusion of either placebo or low-dose dexmedetomidine (target = 0.15 ng/ml plasma) during neuroimaging while they viewed and rated 80 emotionally arousing (e.g., graphic war wound) and 80 nonarousing neutral (e.g., cup) pictures for emotional arousal content. Long-term picture memory was tested 4 days later without neuroimaging. Imaging data were analyzed for drug effects, emotional processing differences, and memory-related changes with statistical parametric mapping-8.

RESULTS

Dexmedetomidine impaired overall (mean ± SEM) picture memory (placebo: 0.58 ± 0.03 vs. dexmedetomidine: 0.45 ± 0.03, P = 0.001), but did not differentially modulate memory as a function of item arousal. Arousing pictures were better remembered for both groups. Dexmedetomidine had regionally heterogeneous effects on brain activity, primarily decreasing it in the cortex and increasing it in thalamic and posterior hippocampal regions. Nevertheless, a single subsequent memory effect for item memory common to both groups was identified only in the left hippocampus/amygdala. Much of this effect was found to be larger for the placebo than dexmedetomidine group.

CONCLUSION

Dexmedetomidine impaired long-term picture memory, but did not disproportionately block memory for emotionally arousing items. The memory impairment on dexmedetomidine corresponds with a weakened hippocampal subsequent memory effect.

Rescue of cAMP response element-binding protein signaling reversed spatial memory retention impairments induced by subanesthetic dose of propofol

AIMS

The intravenous anesthetic propofol caused episodic memory impairments in human. We hypothesized propofol caused episodic-like spatial memory retention but not acquisition impairments in rats and rescuing cAMP response element-binding protein (CREB) signaling using selective type IV phosphodiesterase (PDEIV) inhibitor rolipram reversed these effects.

METHODS

Male Sprague-Dawley rats were randomized into four groups: control; propofol (25 mg/kg, intraperitoneal); rolipram; and rolipram + propofol (pretreatment of rolipram 25 min before propofol, 0.3 mg/kg, intraperitoneal). Sedation and motor coordination were evaluated 5, 15, and 25 min after propofol injection. Invisible Morris water maze (MWM) acquisition and probe test (memory retention) were performed 5 min and 24 h after propofol injection. Visible MWM training was simultaneously performed to resist nonspatial effects. Hippocampal CREB signaling was detected 5 min, 50 min, and 24 h after propofol administration.

RESULTS

Rolipram did not change propofol-induced anesthetic/sedative states or impair motor skills. No difference was found on the latency to the platform during the visible MWM. Propofol impaired spatial memory retention but not acquisition. Rolipram reversed propofol-induced spatial memory impairments and suppression on cAMP levels, CaMKIIα and CREB phosphorylation, brain-derived neurotropic factor (BDNF) and Arc protein expression.

CONCLUSIONS

Propofol caused spatial memory retention impairments but not acquisition inability possibly by inhibiting CREB signaling.

Dexmedetomidine versus Midazolam for Conscious Sedation in Postoperative Patients Undergoing Flexible Bronchoscopy: A Randomized Study

OBJECTIVE: This prospective randomized study evaluated the efficacy and patient tolerance of dexmedetomidine compared with midazolam for sedation in postoperative patients undergoing flexible bronchoscopy. METHODS: A total of 198 postoperative patients were randomized to receive dexmedetomidine ( n = 99) or midazolam ( n = 99) to produce conscious sedation for bronchoscopy. Peripheral oxygen saturation, heart rate and systolic and diastolic arterial pressures were recorded before, during and after the procedure. Patient tolerance was recorded using various visual analogue scales. RESULTS: The mean lowest peripheral oxygen saturation was significantly lower in the midazolam group than in the dexmedetomidine group. Heart rate and systolic arterial pressure were both significantly higher during bronchoscopy in the midazolam group than in the dexmedetomidine group. Bronchoscopy was well tolerated in both groups; there was no between-group difference in patient discomfort scores or in the percentage of patients who would accept repeat bronchoscopy. CONCLUSIONS: Compared with midazolam, dexmedetomidine provided better oxygen saturation and was equally well tolerated for conscious sedation in postoperative patients undergoing bronchoscopy.

Isoflurane impairs odour discrimination learning in rats: differential effects on short- and long-term memory

BACKGROUND

Anaesthetics suppress the formation of lasting memories at concentrations that do not suppress perception, but it is unclear which elements of the complex cascade leading from a conscious experience to a lasting memory trace are disrupted. Experiments in conscious humans suggest that subhypnotic concentrations of anaesthetics impair consolidation or maintenance rather than acquisition of a representation (long-term more than short-term memory). We sought to test whether these agents similarly impair learning in rats.

METHODS

We used operant conditioning in rats to examine the effect of isoflurane on acquisition compared with long-term (24 h) memory of non-aversive olfactory memories using two different odour discrimination tasks. Rats learned the 'valences' of odour pairs presented either separately (task A) or simultaneously (task B), under control conditions and under isoflurane inhalation. In a separate set of experiments, we tested the ability of the animals to recall a learning set that had been acquired 24 h previously.

RESULTS

Under 0.4% isoflurane inhalation, the average number of trials required to reach criterion performance (18 correct responses in 20 successive trials) increased from 21.9 to 43.5 (P<0.05) and 24.2 to 54.4 (P<0.05) for tasks A and B, respectively. Under 0.3% isoflurane inhalation, only task B was impaired (from 24.2 to 31.5 trials, P<0.05). Recall at 24 h was dose-dependently impaired or prevented by isoflurane for both tasks.

CONCLUSIONS

Isoflurane interfered with long-term memory of odour valence without preventing its acquisition. This paradigm may serve as a non-aversive animal model of conscious amnesia.

How we recall (or don't): the hippocampal memory machine and anesthetic amnesia

PURPOSE

The hippocampal formation occupies a central position for the processing of sensory input into learned, remembered, and consciously retrievable information. The mechanisms by which anesthetic drugs interfere with these processes are now emerging. We review the current understanding of the role of the hippocampal formation in the generation of memory traces and how anesthetics might interfere with its function.

CLINICAL FEATURES

Intraoperative amnesia is a desired endpoint of general anesthesia from the perspective of both the patient and the practitioner. "Intraoperative awareness with recall" can result when learning and memory do occur. In addition, anesthetics are capable of inducing a state of "conscious amnesia" that can provide insight into the workings of the brain and might be useful clinically.

CONCLUSIONS

Anesthesiologists routinely induce the most fascinating pharmacologic effects in existence, the reversible interference of anesthetics with higher cognitive functions. Understanding how the drugs in our custody exert their effects should be our contribution to mankind's universal knowledge base.