The effects of midazolam and sevoflurane on the GABA(A) receptors with alternatively spliced variants of the γ2 subunit

A comprehensive atlas of fetal splicing patterns in the brain of adult myotonic dystrophy type 1 patients

In patients with myotonic dystrophy type 1 (DM1), dysregulation of RNA-binding proteins like MBNL and CELF1 leads to alternative splicing of exons and is thought to induce a return to fetal splicing patterns in adult tissues, including the central nervous system (CNS). To comprehensively evaluate this, we created an atlas of developmentally regulated splicing patterns in the frontal cortex of healthy individuals and DM1 patients, by combining RNA-seq data from BrainSpan, GTEx and DM1 patients. Thirty-four splice events displayed an inclusion pattern in DM1 patients that is typical for the fetal situation in healthy individuals. The regulation of DM1-relevant splicing patterns could partly be explained by changes in mRNA expression of the splice regulators MBNL1, MBNL2 and CELF1. On the contrary, interindividual differences in splicing patterns between healthy adults could not be explained by differential expression of these splice regulators. Our findings lend transcriptome-wide evidence to the previously noted shift to fetal splicing patterns in the adult DM1 brain as a consequence of an imbalance in antagonistic MBNL and CELF1 activities. Our atlas serves as a solid foundation for further study and understanding of the cognitive phenotype in patients.

As part of multimodal anxiolysis oral melatonin but not midazolam decreases emergence delirium in children: A randomised, double-blind, placebo-controlled study

BACKGROUND

Pre-operative anxiety is a risk factor for emergence delirium in children and a multimodal approach including sedatives and nonpharmacological measures is the current strategy to tackle this anxiety. The efficacy of oral melatonin as a component of multimodal anxiolytic strategy to decrease emergence delirium is not well studied.

OBJECTIVE

The aim of this study was to evaluate the efficacy of a multimodal anxiolytic strategy including oral melatonin or midazolam to decrease emergence delirium after sevoflurane anaesthesia.

DESIGN

A randomised, double-blind, parallel arm, placebo-controlled trial.

SETTING

Tertiary care teaching hospital from July 2019 till January 2020.

PARTICIPANTS

Children in the age group of 3 to 8 years who received sevoflurane anaesthesia for elective ambulatory procedures.

INTERVENTIONS

Children were randomised to receive oral premedication with either melatonin 0.3 mg kg-1, midazolam 0.3 mg kg-1 or honey as placebo. All the children received standardised nonpharmacological measures involving multiple techniques to allay anxiety. The anaesthetic plan was also standardised.

MAIN OUTCOME MEASURES

The primary outcome was the incidence of emergence delirium as assessed by the Watcha scale in the postanaesthesia care unit. The secondary outcomes were pre-operative anxiety assessed using a modified Yale Preoperative Anxiety scale, patient compliance with mask induction using the Induction Compliance Checklist and postoperative sedation.

RESULTS

Data from 132 children were analysed. Melatonin significantly reduced the incidence of emergence delirium compared to placebo: 27 vs. 50%, respectively, an absolute risk reduction of 23.3 [95% confidence interval 3.7 to 42.9), P = 0.03]. Melatonin also significantly reduced the risk of emergence delirium compared with midazolam: 27 vs. 56%, respectively, an absolute risk reduction of 29.2 (95% CI 9.5 to 48.8). The midazolam group had a similar incidence of emergence delirium as placebo. Sedation scores were similar in the three groups postoperatively. The incidence and score of pre-operative anxiety as well as the compliance with mask induction were similar in the three groups.

CONCLUSIONS

A multimodal anxiolytic approach including oral melatonin, as opposed to oral midazolam, significantly reduced emergence delirium after sevoflurane anaesthesia.

TRIAL REGISTRATION

CTRI/2019/06/019850 in Clinical Trial Registry of India (www.ctri.nic.in).

Looking for Novelty in an "Old" Receptor: Recent Advances Toward Our Understanding of GABAARs and Their Implications in Receptor Pharmacology

Diverse populations of GABA_A receptors (GABA_ARs) throughout the brain mediate fast inhibitory transmission and are modulated by various endogenous ligands and therapeutic drugs. Deficits in GABA_AR signaling underlie the pathophysiology behind neurological and neuropsychiatric disorders such as epilepsy, anxiety, and depression. Pharmacological intervention for these disorders relies on several drug classes that target GABA_ARs, such as benzodiazepines and more recently neurosteroids. It has been widely demonstrated that subunit composition and receptor stoichiometry impact the biophysical and pharmacological properties of GABA_ARs. However, current GABA_AR-targeting drugs have limited subunit selectivity and produce their therapeutic effects concomitantly with undesired side effects. Therefore, there is still a need to develop more selective GABA_AR pharmaceuticals, as well as evaluate the potential for developing next-generation drugs that can target accessory proteins associated with native GABA_ARs. In this review, we briefly discuss the effects of benzodiazepines and neurosteroids on GABA_ARs, their use as therapeutics, and some of the pitfalls associated with their adverse side effects. We also discuss recent advances toward understanding the structure, function, and pharmacology of GABA_ARs with a focus on benzodiazepines and neurosteroids, as well as newly identified transmembrane proteins that modulate GABA_ARs.

Increased GABAergic inhibitory function against ischemic long-term potentiation in the CA1 region of the hippocampus

Potentiation of N-methyl-D-aspartate receptor (NMDAR)-mediated excitatory synaptic plasticity around 1 h after brief exposure to anoxia/aglycemia is called ischemic long-term potentiation (iLTP), which is considered a pathological form of synaptic response during the early phase of ischemic stroke. It is known that GABAergic inhibitory transmission is also an important molecular process involved in synaptic plasticity and learning memory. However, whether GABAergic transmission is involved in iLTP and early-phase plasticity in ischemic stroke remains unknown. In this study, iLTP was found to be induced in the hippocampal Schaffer-collateral pathway by exposure to oxygen glucose deprivation (OGD). Western blot analysis was conducted to analyze excitatory synaptic receptors and inhibitory synaptic receptors following OGD. The β3 subunit of the GABA_A receptor (GABA_AR) was markedly reduced, whereas the GluN2B subunit of the NMDAR was increased in the hippocampal area in the OGD group. Using extracellular recording, we demonstrated that application of GABA_AR agonist midazolam could abolish the hippocampal iLTP. Moreover, midazolam had no significant effect on the increase in NMDAR subunit GluN2B, but ameliorated the reduction in the β3 subunit of GABA_AR after OGD. In summary, our results indicated that hippocampal GABA_AR reduction promoted synaptic potentiation after OGD. Activation of GABAergic inhibitory transmission function could inhibit iLTP; thus, modulation of GABAergic function is a protective treatment method in the acute phase of synaptic plasticity in ischemic stroke.

Sevoflurane activates hippocampal CA3 kainate receptors (Gluk2) to induce hyperactivity during induction and recovery in a mouse model

BACKGROUND

In addition to general anaesthetic effects, sevoflurane can also induce hyperactive behaviours during induction and recovery, which may contribute to neurotoxicity; however, the mechanism of such effects is unclear. Volatile anaesthetics including isoflurane have been found to activate the kainate (GluK2) receptor. We developed a novel mouse model and further explored the involvement of kainate (GluK2) receptors in sevoflurane-induced hyperactivity.

METHODS

Maximal speed, mean speed, total movement distance and resting percentage of C57BL/6 mice were quantitatively measured using behavioural tracking software before and after sevoflurane anaesthesia. Age dependence of this model was also analysed and sevoflurane-induced hyperactivity was evaluated after intracerebral injection of the GluK2 receptor blocker NS-102. Neurones from the hippocampal CA3 region were used to undertake in vitro electrophysiological measurement of kainate currents and miniature excitatory postsynaptic potential (mEPSP).

RESULTS

Sevoflurane induced significant hyperactivities in mice under sevoflurane 1% anaesthesia and during the recovery period, characterized as increased movement speed and total distance. The hyperactivity was significantly increased in young mice compared with adults (P<0.01) and pre-injection of NS-102 significantly prevented this sevoflurane-induced hyperactivity. In electrophysiological experiments, sevoflurane significantly increased the frequency of mEPSP at low concentrations and evoked kainate currents at high concentrations.

CONCLUSIONS

We developed a behavioural model in mice that enabled characterization of sevoflurane-induced hyperactivity. The kainate (GluK2) receptor antagonist attenuated these sevoflurane-induced hyperactivities in vivo, suggesting that kainate receptors might be the underlying therapeutic targets for sevoflurane-induced hyperactivities in general anaesthesia.

Role of neurosteroids in the anticonvulsant activity of midazolam

BACKGROUND AND PURPOSE

Midazolam is a short-acting benzodiazepine that is widely used as an i.v. sedative and anticonvulsant. Besides interacting with the benzodiazepine site associated with GABA(A) receptors, some benzodiazepines act as agonists of translocator protein (18 kDa) (TSPO) to enhance the synthesis of steroids, including neurosteroids with positive modulatory actions on GABA(A) receptors. We sought to determine if neurosteroidogenesis induced by midazolam contributes to its anticonvulsant action.

EXPERIMENTAL APPROACH

Mice were pretreated with neurosteroid synthesis inhibitors and potentiators followed by midazolam or clonazepam, a weak TSPO ligand. Anticonvulsant activity was assessed with the i.v. pentylenetetrazol (PTZ) threshold test.

KEY RESULTS

Midazolam (500-5000 µg·kg(-1) , i.p.) caused a dose-dependent increase in seizure threshold. Pretreatment with the neurosteroid synthesis inhibitors finasteride, a 5α-reductase inhibitor, and a functional TSPO antagonist PK 11195, reduced the anticonvulsant action of midazolam. The anticonvulsant action of midazolam was enhanced by the neurosteroidogenic drug metyrapone, an 11β-hydroxylase inhibitor. In contrast, the anticonvulsant action of clonazepam (100 µg·kg(-1) ) was reduced by finasteride but not by PK 11195, indicating a possible contribution of neurosteroids unrelated to TSPO.

CONCLUSION AND IMPLICATIONS

Enhanced endogenous neurosteroid synthesis, possibly mediated by an interaction with TSPO, contributed to the anticonvulsant action of midazolam. Enhanced neurosteroidogenesis may also be a factor in the actions of other benzodiazepines, even those that only weakly interact with TSPO.