Propofol decreases the excitability of cholinergic neurons in mouse basal forebrain via GABAA receptors

The activity of cholinergic neurons in the basal forebrain interferes with anesthesia-arousal process of propofol

Previous research has demonstrated that basal forebrain (BF) regulates arousal during propofol anesthesia. However, as the BF comprises cholinergic neurons alongside two other types of neurons, the specific role of cholinergic neurons has not been definitively elucidated. In our study, calcium signal imaging was utilized to monitor the real-time activities of cholinergic neurons in the BF during propofol anesthesia. Additionally, we selectively stimulated these neurons to investigate EEG and behavioral responses during propofol anesthesia. Furthermore, we specifically lesioned cholinergic neurons in the BF to investigate the sensitivity to propofol and the induction time. The results revealed that propofol suppressed calcium signals of cholinergic neurons within the BF following intraperitoneal injection. Notably, upon recovery of the righting reflex, the calcium signals partially recovered. Spectral analysis of the EEG elucidated that optical stimulation of cholinergic neurons led to a decrease in δ power underlie propofol anesthesia. Conversely, depletion of cholinergic neurons in the BF enhanced sensitivity to propofol and shortened the induction time. These findings clarify the role of cholinergic neurons in the anesthesia-arousal process, as well as the depth and the sensitivity of propofol anesthesia.

Propofol-induced anesthesia involves the direct inhibition of glutamatergic neurons in the lateral hypothalamus

Propofol is the most widely used intravenous general anesthetic; however, the neuronal circuits that mediate its anesthetic effects are still poorly understood. Glutamatergic neurons in the lateral hypothalamus have been reported to be involved in maintenance of arousal and consciousness. Using Vglut2-Cre transgenic mice, we recorded this group of cells specifically and found that propofol can directly inhibit the glutamatergic neurons, and enhance inhibitory synaptic inputs on these cells, thereby reducing neuronal excitability. Through chemogenetic interventions, we found that inhibition of these neurons increased the duration of propofol-induced anesthesia and reduced movement in the animals after the recovery of right reflex. In contrast, activating this group of cells reduced the duration of propofol anesthesia and increased the animals' locomotor activity after the recovery of right reflex. These results suggest that propofol-induced anesthesia involves the inhibition of glutamatergic neurons in the lateral hypothalamus.

Molecular mechanisms of cholinergic neurotransmission in visceral smooth muscles with a focus on receptor-operated TRPC4 channel and impairment of gastrointestinal motility by general anaesthetics and anxiolytics

Acetylcholine is the primary excitatory neurotransmitter in visceral smooth muscles, wherein it binds to and activates two muscarinic receptors subtypes, M2 and M3, thus causing smooth muscle excitation and contraction. The first part of this review focuses on the types of cells involved in cholinergic neurotransmission and on the molecular mechanisms underlying acetylcholine-induced membrane depolarisation, which is the central event of excitation-contraction coupling causing Ca2+ entry via L-type Ca2+ channels and smooth muscle contraction. Studies of the muscarinic cation current in intestinal myocytes (mICAT) revealed its main molecular counterpart, receptor-operated TRPC4 channel, which is activated in synergy by both M2 and M3 receptors. M3 receptors activation is of permissive nature, while activation of M2 receptors via Gi/o proteins that are coupled to them plays a direct role in TRPC4 opening. Our understanding of signalling pathways underlying mICAT generation has vastly expanded in recent years through studies of TRPC4 gating in native cells and its regulation in heterologous cells. Recent studies using muscarinic receptor knockout have established that at low agonist concentration activation of both M2 receptor and the M2/M3 receptor complex elicits smooth muscle contraction, while at high agonist concentration M3 receptor function becomes dominant. Based on this knowledge, in the second part of this review we discuss the cellular and molecular mechanisms underlying the numerous anticholinergic effects on neuroactive drugs, in particular general anaesthetics and anxiolytics, which can significantly impair gastrointestinal motility. This article is part of the Special Issue on "Ukrainian Neuroscience".

Dexmedetomidine modulates neuronal activity of horizontal limbs of diagonal band via α2 adrenergic receptor in mice

BACKGROUND AND OBJECTIVES

Dexmedetomidine (DEX) is widely used in clinical sedation which has little effect on cardiopulmonary inhibition, however the mechanism remains to be elucidated. The basal forebrain (BF) is a key nucleus that controls sleep-wake cycle. The horizontal limbs of diagonal bundle (HDB) is one subregions of the BF. The purpose of this study was to examine whether the possible mechanism of DEX is through the α2 adrenergic receptor of BF (HDB).

METHODS

In this study, we investigated the effects of DEX on the BF (HDB) by using whole cell patch clamp recordings. The threshold stimulus intensity, the inter-spike-intervals (ISIs) and the frequency of action potential firing in the BF (HDB) neurons were recorded by application of DEX (2 µM) and co-application of a α2 adrenergic receptor antagonist phentolamine (PHEN) (10 µM).

RESULTS

DEX (2 µM) increased the threshold stimulus intensity, inhibited the frequency of action potential firing and enlarged the inter-spike-interval (ISI) in the BF (HDB) neurons. These effects were reversed by co-application of PHEN (10 µM).

CONCLUSION

Taken together, our findings revealed DEX decreased the discharge activity of BF (HDB) neuron via α2 adrenergic receptors.

The Efficacy and Safety of Remimazolam Besylate Combined with Esketamine for Outpatient Colonoscopy: A Prospective, Randomized, Controlled Clinical Trial

Purpose

Evaluate the efficacy and safety of remimazolam besylate combined with esketamine for outpatient colonoscopy.

Patients and methods

A total of 150 outpatients undergoing colonoscopy were randomized into two groups. A MOAA/S score ≤3 was maintained. The primary outcome was the rate of successful colonoscopy completion. Time indicators, hemodynamic parameters, the consumption of lidocaine, esketamine, propofol and remimazolam besylate, MOAA/S scores and bispectral index (BIS) values, the lowest SpO2, body movement, the use of rescue medication, endoscopist and patient satisfaction, recall of the procedure, mini-mental state examination (MMSE), fatigue level and adverse events were recorded.

Results

Procedure completion was equivalent between groups (P > 0.05). Both induction and awakening times were significantly shorter in the P group (P < 0.05). There were no significant differences in colonoscopy time and discharge time (P > 0.05). The lowest SpO2 was significantly lower in the P group, while the level of fatigue was higher (P < 0.05). Patient satisfaction was significantly higher in the R group (P < 0.05). Endoscopist satisfaction was significantly higher in the P group (P < 0.05). There were no significant differences in both systolic and diastolic blood pressure between groups except at T5 and T6 (P > 0.05). Both HR and RR were significantly lower in the P group from T3 to T5 (P < 0.05). BIS values were significantly lower in the P group from T3 to T5, while MOAA/S was significantly lower in the P group at T3 and T4 (P < 0.05). Pain on injection was significantly higher in the P group (P < 0.05).

Conclusion

Remimazolam besylate has a similar efficacy to propofol when combined with subanesthetic doses of esketamine during outpatient colonoscopy. Remimazolam besylate combined with esketamine resulted in less injection pain and more stable hemodynamics, although it prolonged induction and awakening time.

Understanding the Neural Mechanisms of General Anesthesia from Interaction with Sleep-Wake State: A Decade of Discovery

The development of cutting-edge techniques to study specific brain regions and neural circuits that regulate sleep-wake brain states and general anesthesia (GA), has increased our understanding of these states that exhibit similar neurophysiologic traits. This review summarizes current knowledge focusing on cell subtypes and neural circuits that control wakefulness, rapid eye movement (REM) sleep, non-REM sleep, and GA. We also review novel insights into their interactions and raise unresolved questions and challenges in this field. Comparisons of the overlapping neural substrates of sleep-wake and GA regulation will help us to understand sleep-wake transitions and how anesthetics cause reversible loss of consciousness. SIGNIFICANCE STATEMENT: General anesthesia (GA), sharing numerous neurophysiologic traits with the process of natural sleep, is administered to millions of surgical patients annually. In the past decade, studies exploring the neural mechanisms underlying sleep-wake and GA have advanced our understanding of their interactions and how anesthetics cause reversible loss of consciousness. Pharmacotherapies targeting the neural substrates associated with sleep-wake and GA regulations have significance for clinical practice in GA and sleep medicine.

The role of the basal forebrain in general anesthesia

The basal forebrain is a group of nerve nuclei on the ventral side of the ventral ganglion, composed of γ-aminobutyric acid neurons, glutamatergic neurons, cholinergic neurons, and orexigenic neurons. Previous studies have focused on the involvement of the basal forebrain in regulating reward, learning, movement, sleep-awakening, and other neurobiological behaviors, but its role in the regulation of general anesthesia has not been systematically elucidated. Therefore, the different neuronal subtypes in the basal forebrain and projection pathways in general anesthesia will be discussed in this paper. In this paper, we aim to determine and elaborate on the role of the basal forebrain in general anesthesia and the development of theoretical research and provide a new theory.

An Integrative Bioinformatics Analysis of the Potential Mechanisms Involved in Propofol Affecting Hippocampal Neuronal Cells

The aim of this study is to probe the possible molecular mechanisms underlying the effects of propofol on HT22 cells. HT22 cells treated with different concentrations were sequenced, and then the results of the sequencing were analyzed for dynamic trends. Expression pattern clustering analysis was performed to demonstrate the expression of genes in the significant trend modules in each group of samples. We first chose the genes related to the trend module for WGCNA analysis, then constructed the PPI network of module genes related to propofol treatment group, and screened the key genes. Finally, GSEA analysis was performed on the key genes. Overall, 2,506 genes showed a decreasing trend with increasing propofol concentration, and 1,871 genes showed an increasing trend with increasing propofol concentration. WGCNA analysis showed that among them, turquoise panel genes were negatively correlated with propofol treatment, and genes with Cor R >0.9 in the turquoise panel were selected for PPI network construction. The MCC algorithm screened a total of five key genes (CD86, IL10RA, PTPRC, SPI1, and ITGAM). GSEA analysis showed that CD86, IL10RA, PTPRC, SPI1, and ITGAM are involved in the PRION_DISEASES pathway. Our study showed that propofol sedation can affect mRNA expression in the hippocampus, providing new ideas to identify treatment of nerve injury induced by propofol anesthesia.

Neural Substrates for Regulation of Sleep and General Anesthesia

General anesthesia has been successfully used in clinics for over 170 years, but its mechanisms of effect remain unclear. Behaviorally, general anesthesia is similar to sleep as it produces a reversible transition between wakefulness and the state of being unaware of one’s surroundings. A discussion regarding the common circuits of sleep and general anesthesia has been ongoing as an increasing number of sleep-arousal regulatory nuclei are reported to participate in the consciousness shift occurring during general anesthesia. Recently, with progress in research technology, both positive and negative evidence for overlapping neural circuits between sleep and general anesthesia has emerged. This article provides a review of the latest evidence on the neural substrates for sleep and general anesthesia regulation by comparing the roles of pivotal nuclei in sleep and anesthesia.

Effect of basal forebrain somatostatin and parvalbumin neurons in propofol and isoflurane anesthesia

Aims

The basal forebrain (BF) plays an essential role in wakefulness and cognition. Two subtypes of BF gamma‐aminobutyric acid (GABA) neurons, including somatostatin‐expressing (GABA^SOM) and parvalbumin‐positive (GABA^Parv) neurons, function differently in mediating the natural sleep–wake cycle. Since the loss of consciousness induced by general anesthesia and the natural sleep–wake cycle probably share similar mechanisms, it is important to clarify the accurate roles of these neurons in general anesthesia procedure.

Methods

Based on two transgenic mouse lines expressing SOM‐IRES‐Cre and PV‐IRES‐Cre, we used a combination of genetic activation, inactivation, and chronic ablation approaches to further explore the behavioral and electroencephalography (EEG) roles of BF^SOM and BF^Parv neurons in general anesthesia. After a single intravenous injection of propofol and the induction and recovery times of isoflurane anesthesia, the anesthesia time was compared. The changes in cortical EEG under different conditions were also compared.

Results

Activation of BF GABA^SOM neurons facilitates both the propofol and isoflurane anesthesia, manifesting as a longer anesthesia duration time with propofol anesthesia and a fast induction time and longer recovery time with isoflurane anesthesia. Moreover, BF GABA^SOM‐activated mice displayed a greater suppression of cortical electrical activity during anesthesia, showing an increase in δ power bands or a simultaneous decrease in high‐frequency power bands. However, only a limited and nuanced effect on propofol and isoflurane anesthesia was observed with the manipulated BF GABA^Parv neurons.

Conclusions

Our results suggested that BF GABA^SOM neurons play a critical role in propofol and isoflurane general anesthesia, while BF GABA^Parv neurons appeared to have little effect.

The relationship between exposure to general anesthetic agents and the risk of developing an impulse control disorder

Most studies examining the effect of extended exposure to general anesthetic agents (GAAs) have demonstrated that extended exposure induces both structural and functional changes in the central nervous system. These changes are frequently accompanied by neurobehavioral changes that include impulse control disorders that are generally characterized by deficits in behavioral inhibition and executive function. In this review, we will.

GABAA receptors in the basal forebrain mediates emergence from propofol anaesthesia in rats

PURPOSE

The aim of the current study was to explore the role of the basal forebrain (BF) in propofol anaesthesia.

METHODS

In the present study, we observed the neural activities of the BF during propofol anaesthesia using calcium fibre photometry recording. Subsequently, ibotenic acid was injected into the BF to verify the role of the BF in propofol anaesthesia. Finally, to test whether GABA_A receptors in the BF were involved in modulating propofol anaesthesia, muscimol (GABA_A receptor agonist) and gabazine (GABA_A receptor antagonist) were microinjected into the BF. Cortical electroencephalogram (EEG), time to loss of righting reflex (LORR), and recovery of righting reflex (RORR) under propofol anaesthesia were recorded and analysed.

RESULTS

The activity of BF neurons was inhibited during induction of propofol anaesthesia and activated during emergence from propofol anaesthesia. In addition, non-specifical lesion of BF neurons significantly prolonged the time to RORR and increased delta power in the frontal cortex under propofol anaesthesia. Next, microinjection of muscimol into the BF delayed emergence from propofol anaesthesia, increased delta power of the frontal cortex, and decreased gamma power under propofol anaesthesia. Conversely, infusion of gabazine accelerated emergence times and decreased EEG delta power.

CONCLUSIONS

The basal forebrain is involved in modulating frontal cortex delta activity and emergence from propofol anaesthesia. Additionally, the GABA_A receptors in the basal forebrain are involved in regulating emergence propofol anaesthesia.

Basal Forebrain Cholinergic Activity Modulates Isoflurane and Propofol Anesthesia

Cholinergic neurons in the basal forebrain (BF) have long been considered to be the key neurons in the regulation of cortical and behavioral arousal, and cholinergic activation in the downstream region of the BF can arouse anesthetized rats. However, whether the activation of BF cholinergic neurons can induce behavior and electroencephalogram (EEG) recovery from anesthesia is unclear. In this study, based on a transgenic mouse line expressing ChAT-IRES-Cre, we applied a fiber photometry system combined with GCaMPs expression in the BF and found that both isoflurane and propofol inhibit the activity of BF cholinergic neurons, which is closely related to the consciousness transition. We further revealed that genetic lesion of BF cholinergic neurons was associated with a markedly increased potency of anesthetics, while designer receptor exclusively activated by designer drugs (DREADD)-activated BF cholinergic neurons was responsible for slower induction and faster recovery of anesthesia. We also documented a significant increase in δ power bands (1-4 Hz) and a decrease in β (12-25 Hz) power bands in BF cholinergic lesioned mice, while there was a clearly noticeable decline in EEG δ power of activated BF cholinergic neurons. Moreover, sensitivity to anesthetics was reduced after optical stimulation of BF cholinergic cells, yet it failed to restore wake-like behavior in constantly anesthetized mice. Our results indicate a functional role of BF cholinergic neurons in the regulation of general anesthesia. Inhibition of BF cholinergic neurons mediates the formation of unconsciousness induced by general anesthetics, and their activation promotes recovery from the anesthesia state.

Effect of sleep deprivation on general anesthesia in rats

OBJECTIVE

To explore the effects of sleep deprivation on perioperative general anesthesia in rats.

METHODS

45 healthy male Sprague-Dawley (SD) rats were randomly divided into 3 groups, the control group (Group A), the anesthesia group (Group B) and the sleep deprivation anesthesia group (Group C), 15 in each group. The sleep deprivation model was established by improving multi-platform water environment method. The group B and C were received propofol 80 mg/kg by intraperitoneally, the group A was given the same dose of normal saline. The EEG in each group was measured. The GABAa R-β3 protein in cerebral cortex was detected by Western Blot. The rats were treated with Brennan incision, and the changes of thermal pain sensitive (PWL) and open field behavior were measured in each group.

RESULTS

In group C, the δ band of brainwave of EEG increased significantly, the disappearance time of righting reflex shortened significantly, the recovery time prolonged significantly, the GABAa R-β3 protein was significantly increased, and the time of passing through the central area before operation was significantly decreased.

CONCLUSION

Sleep deprivation can significantly inhibit the electrical activity of rat cerebral cortex induced by propofol, up-regulating the GABAa R-β3 protein in cortex.

[Etomidate reduces excitability of the neurons and suppresses the function of nAChR ventral horn in the spinal cord of neonatal rats]

OBJECTIVE

To investigate the effects of etomidate on electrophysiological properties and nicotinic acetylcholine receptors (nAChRs) of ventral horn neurons in the spinal cord.

METHODS

The spinal cord containing lumbosacral enlargement was isolated from 19 neonatal SD rats aged 7-12 days. The spinal cord were sliced and digested with papain (0.18 g/30 mL artificial cerebrospinal fluid) and incubated for 40 min. At the ventral horn, acute mechanical separation of neurons was performed with fire-polished Pasteur pipettes, and perforated patch-clamp recordings combined with pharmacological methods were employed on the adherent healthy neurons. In current-clamp mode, the spontaneous action potential (AP) of the ventral horn neurons in the spinal cord was recorded. The effects of pretreatment with different concentrations of etomidate on AP recorded in the ventral horn neurons were examined. In the voltage-clamp mode, nicotine was applied to induce inward currents in the ventral horn neurons, and the effect of pretreatment with etomidate on the inward currents induced by nicotine were examined with different etomidate concentrations, different holding potentials and different use time.

RESULTS

The isolated ventral horn neurons were in good condition with large diverse somata and intact processes. The isolated spinal ventral horn neurons (n=21) had spontaneous action potentials, and were continuously perfused for 2 min with 0.3, 3.0 and 30.0 μmol/L etomidate. Compared with those before administration, the AP amplitude, spike potential amplitude and overshoot were concentration-dependently suppressed (P < 0.01), and spontaneous discharge frequency was obviously reduced (P < 0.01, n=12). The APs of the other 9 neurons were completely abolished by etomidate at 3.0 or 30 μmol/L. At the same holding potential (VH=-70 mV), pretreatment with 0.3, 3.0 or 30.0 μmol/L etomidate for 2 min concentration-dependently suppressed the current amplitude induced by 0.4 mmol/L nicotine (P < 0.01, n=7). At the holding potentials of - 30, - 50, and - 70 mV, pretreatment with 30.0 μmol/L etomidate for 2 min voltage-dependently suppressed the current amplitude induced by 0.4 mmol/L nicotine (P < 0.01, n=6 for each holding potential). During the 6 min of 30.0 μmol/L etomidate pretreatment, the clamped cells were exposed to 0.4 mmol/L nicotine for 4 times at 0, 2, 4, and 6 min (each exposure time was 2 s), and the nicotinic current amplitude decreased gradually as the number of exposures increased. But at the same concentration, two nicotine exposures (one at the beginning and the other at the end of the 6 min pretreatment) resulted in a significantly lower inhibition rate compared with 4 nicotine exposures (P < 0.01, n=6).

CONCLUSIONS

etomidate reduces the excitability of the spinal ventral neurons in a concentration-dependent manner and suppresses the function of nAChR in a concentration-, voltage-, and use-dependent manner.

The hypnotic effect of propofol involves inhibition of GABAergic neurons in the lateral hypothalamus

Propofol is widely used for induction and maintenance of anaesthesia, which causes a rapid loss of consciousness. So far the mechanisms underlying the effect of propofol are still largely unknown. Here, we found that microinjection of propofol in the lateral hypothalamus caused a significant decrease in wakefulness and an increase in the amount of non-rapid eye movement sleep and rapid eye movement sleep. Application of propofol in the lateral hypothalamus affected the electroencephalogram power spectra with a decrease in theta oscillations and an increase in the delta oscillations. Additionally, using whole-cell patch clamp recording, we found propofol inhibited the excitability of the GABAergic neurons in the lateral hypothalamus, which plays a critical role in controlling wakefulness. Altogether, these findings indicate that propofol targets lateral hypothalamus and generates a hypnotic state, which might involve the inhibition of GABAergic neurons. These results provide a novel mechanism to explain propofol-elicited anaesthesia.