The general anesthetic propofol induces ictal-like seizure activity in hippocampal mouse brain slices

The general anaesthetic propofol prevents cerebrocortical potentiation in neocortical mouse brain slices

Propofol is well known to cause amnesia independent of its sedative effect. Memory consolidation processes in the hippocampus have been proposed as a target - however the neural substrates for propofol's amnesic actions remain understudied and poorly described. In particular, the potential role of the cerebral cortex has not been investigated. As an in vitro experimental model of cortical memory consolidation, potentiated cerebral cortex evoked responses were generated in mouse neocortical slices using high frequency (20 Hz) stimulation to layer IV cortical grey matter or subcortical white matter. In separate experiments, slices were pretreated with propofol at two concentrations, 2 µg/mL and 4 µg/mL, to determine the effect of clinically relevant propofol levels on the potentiation response. Only grey matter stimulation induced a significant and lasting increase in cortical evoked potential amplitude in the drug-free condition. Propofol at 2 µg/mL completely inhibited cortical evoked response potentiation, while the 4 µg/mL concentration caused a small but significant depressant effect consequent to the high frequency stimulation. These findings support the hypothesis that propofol disrupts memory consolidation and actively facilitates memory decay in the cerebral cortex. The results further highlight the importance of the cerebral cortex in the early phase of long term memory consolidation.

A Metabolic Mechanism for Anaesthetic Suppression of Cortical Synaptic Function in Mouse Brain Slices-A Pilot Investigation

Regulation of synaptically located ionotropic receptors is thought to be the main mechanism by which anaesthetics cause unconsciousness. An alternative explanation, which has received much less attention, is that of primary anaesthetic disruption of brain metabolism via suppression of mitochondrial proteins. In this pilot study in mouse cortical slices, we investigated the effect of disrupting cellular metabolism on tissue oxygen handling and cortical population seizure-like event (SLE) activity, using the mitochondrial complex I inhibitor rotenone, and compared this to the effects of the general anaesthetics sevoflurane, propofol and ketamine. Rotenone caused an increase in tissue oxygen (98 mmHg to 157 mmHg (p < 0.01)) before any measurable change in SLE activity. Thereafter, tissue oxygen continued to increase and was accompanied by a significant and prolonged reduction in SLE root mean square (RMS) activity (baseline RMS of 1.7 to 0.7 µV, p < 0.001) and SLE frequency (baseline 4.2 to 0.4 events/min, p = 0.001). This temporal sequence of effects was replicated by all three anaesthetic drugs. In conclusion, anaesthetics with differing synaptic receptor mechanisms all effect changes in tissue oxygen handling and cortical network activity, consistent with a common inhibitory effect on mitochondrial function. The temporal sequence suggests that the observed synaptic depression—as seen in anaesthesia—may be secondary to a reduction in cellular metabolic capacity.

Role of estradiol in mediation of etomidate-caused seizure-like activity in neonatal rats

BACKGROUND

The goal of this study was to investigate the effect of estradiol in mediation of electroencephalogram (EEG) abnormality induced by etomidate in neonatal rats.

METHODS

Sprague-Dawley rats were anesthetized using intraperitoneal etomidate for 2 h on postnatal days (P) 4, 5, or 6 and recorded electroencephalogram in two ways. First, pups were recorded EEG two and a half hours under etomidate anesthesia, in subgroups, estradiol receptor antagonist ICI182780 and estradiol synthase inhibitor formestane were given subcutaneously in male rats 15 min prior to etomidate. Second, pups were anesthetized with etomidate for 2 h on P4,5 or 6 and then recovered from anesthesia, EEG were recorded for one hour in two postnatal periods of P9-P11 and P14-P16. Subgroup rats that received bumetanide, NKCC1 inhibitor, to test the NKCC1-GABAAR signaling effect on neonatal brain development, negative control groups and maternally separated for 2 h on P4, 5, or 6 were studied in 16 groups. Each group's n was = 8.

RESULTS

Male pups showed more severe seizure-like activities than female pups in P4-P6 under etomidate anesthesia. Pups pretreated with ICI182780 and formestane showed a less abnormalities of EEG in male rats. Etomidate caused seizure-like activity in P4-P6 could extend to P9-P11, but not seen in P14-P16, Pretreated with bumetanide only alleviated abnormalities in male pups other than female in P9-P11.

CONCLUSIONS

Estradiol involves in the NKCC1-GABA_AR mediated seizure-like activity caused by etomidte in neonatal rats and these the abnormality lasts near two weeks.

Understanding the Effects of General Anesthetics on Cortical Network Activity Using Ex Vivo Preparations

General anesthetics have been used to ablate consciousness during surgery for more than 150 yr. Despite significant advances in our understanding of their molecular-level pharmacologic effects, comparatively little is known about how anesthetics alter brain dynamics to cause unconsciousness. Consequently, while anesthesia practice is now routine and safe, there are many vagaries that remain unexplained. In this paper, the authors review the evidence that cortical network activity is particularly sensitive to general anesthetics, and suggest that disruption to communication in, and/or among, cortical brain regions is a common mechanism of anesthesia that ultimately produces loss of consciousness. The authors review data from acute brain slices and organotypic cultures showing that anesthetics with differing molecular mechanisms of action share in common the ability to impair neurophysiologic communication. While many questions remain, together, ex vivo and in vivo investigations suggest that a unified understanding of both clinical anesthesia and the neural basis of consciousness is attainable.

Dl-3n-butylphthalide reduces epileptiform activity through GluA2-lacking calcium-permeable AMPARs in epilepsy models

Epilepsy is the most prevalent chronic neurological disorder, and its pathological mechanism indicates that an imbalance between excitatory and inhibitory neurotransmission leads to neuronal hyperexcitability. Previous studies have suggested that dl-3n-butylphthalide (NBP) regulates the excitatory neurotransmitter glutamate in the brains of epileptic mice, however, the mechanisms are unknown. We investigated behavioral and electrophysiological factors in rats using NBP. In an in vivo pentylenetetrazole (PTZ)-induced epileptic seizure animal model, NBP decreased the generalized tonic-clonic seizure (GTCS) severity. In an acute hippocampal slice 4-aminopyridine (4-AP) epilepsy model in vitro, NBP decreased the epileptiform activity and miniature excitatory postsynaptic current (mEPSC) amplitude; there was no change in the miniature inhibitory postsynaptic current (mIPSC) amplitude or frequency. This effect suggested changes in excitatory synaptic transmission, which was altered through postsynaptic GluA2-lacking calcium-permeable AMPA receptors (CP-AMPARs). These findings showed that NBP suppressed epileptiform activity in these epilepsy models and provided the first detailed electrophysiological analysis of the impact of NBP in epilepsy models, which may be employed in future experimental or clinical therapies for patients with epilepsy.