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

A computational approach to evaluate how molecular mechanisms impact large-scale brain activity

Assessing the impact of pharmaceutical compounds on brain activity is a critical issue in contemporary neuroscience. Currently, no systematic approach exists for evaluating these effects in whole-brain models, which typically focus on macroscopic phenomena, while pharmaceutical interventions operate at the molecular scale. Here we address this issue by presenting a computational approach for brain simulations using biophysically grounded mean-field models that integrate membrane conductances and synaptic receptors, showcased in the example of anesthesia. We show that anesthetics targeting GABAA and NMDA receptors can switch brain activity to generalized slow-wave patterns, as observed experimentally in deep anesthesia. To validate our models, we demonstrate that these slow-wave states exhibit reduced responsiveness to external stimuli and functional connectivity constrained by anatomical connectivity, mirroring experimental findings in anesthetized states across species. Our approach, founded on mean-field models that incorporate molecular realism, provides a robust framework for understanding how molecular-level drug actions impact whole-brain dynamics.

Ventral pallidum GABAergic and glutamatergic neurons modulate arousal during sevoflurane general anaesthesia in male mice

BACKGROUND AND PURPOSE

The induction and emergence of general anaesthesia involve an altered process of states of consciousness, yet the central nervous system mechanisms remain inadequately understood. The ventral pallidum (VP) within the basal ganglia is crucial in sleep-wake modulation. However, its involvement in general anaesthesia and the underlying neuronal mechanisms are not well elucidated.

EXPERIMENTAL APPROACH

In vivo electrophysiological recordings were conducted to examine changes in the activity of different types of VP neurons before and after sevoflurane exposure. Fibre photometry, combined with electroencephalogram and electromyography recordings, was employed to analyse neuronal activity during both the induction and recovery phases of sevoflurane anaesthesia. Chemogenetics was implemented to investigate the impact of modulated neuronal activity on anaesthesia induction and emergence, whereas optogenetics was used for real time activation of neurons at different depths of anaesthesia.

KEY RESULTS

Sevoflurane exposure reduced the firing activity of both VP GABAergic (VPGABA) and VP glutamatergic (VPglu) neurons, without affecting cholinergic neurons. VPGABA and VPglu neuronal activity decreased during sevoflurane anaesthesia induction and increased during emergence. Manipulation of VPGABA neurons bidirectionally influenced the duration of induction and emergence. Inhibiting VPglu neurons accelerated induction. Real time activation of VPGABA neurons triggered cortical activation and behavioural emergence during steady-state sevoflurane anaesthesia and reduced the burst suppression ratio during deep anaesthesia.

CONCLUSION AND IMPLICATIONS

These findings highlight the role of VPGABA and VPglu neurons in modulating transitions between anaesthesia stages, providing valuable insights into the neuronal mechanisms underlying sevoflurane-induced anaesthesia.

The Neurochemical Signature of Cardiac Arrest: A Multianalyte Online Microdialysis Study

This work describes the use of high resolution online microdialysis coupled with a wireless microfluidic electrochemical sensing platform for continuous monitoring of the effect of cardiac arrest and resuscitation methods on brain glucose and other key neurochemicals in a porcine model. The integrated portable device incorporates low-volume three-dimensional (3D) printed microfluidic flow cells containing enzyme-based biosensors for glucose, lactate and glutamate measurement and a complementary metal-oxide semiconductor (CMOS)-based ion-sensitive field effect transistor (ISFET) for potassium measurement. Both analysis systems incorporate wireless electronics forming a complete compact system that is ideal for use in a crowded clinical environment. Using this integrated system we were able to build a signature of the neurochemical impact of cardiac arrest and resuscitation. Our results demonstrate the almost complete depletion of brain glucose following cardiac arrest and the subsequent increase in lactate, highlighting the vulnerability of the brain while the blood flow is compromised. Following a return of spontaneous circulation, glucose levels increased again and remained higher than baseline levels. These trends were correlated with simultaneous blood measurements to provide further explanation of the metabolic changes occurring in the brain. In addition, the onset of cardiac arrest corresponded to a transient increase in potassium. In most cases glutamate levels remained unchanged after cardiac arrest, while in some cases a transient increase was detected. We were also able to validate the trends seen using online microdialysis with traditional discontinuous methods; the two methods showed good agreement although online microdialysis was able to capture dynamic changes that were not seen in the discontinuous data.

Activation of Glutamatergic Neurons in the Supramammillary Nucleus Promotes the Recovery of Consciousness under Sevoflurane Anesthesia

Volatile anesthetics have been widely applied during surgery, but the potential mechanisms by which they influence loss of consciousness (LOC), anesthesia maintenance, and recovery of consciousness (ROC) from anesthesia remain largely unknown. Recent studies have suggested that anesthesia-induced unconsciousness may be due to specific interactions between neural circuits that regulate sleep and wakefulness. Supramammillary (SuM) glutamatergic neurons are essential for sleep-wakefulness regulation. However, whether SuM glutamatergic neurons are involved in the modulation of consciousness under sevoflurane anesthesia is unclear. Here, it is shown that the activity of SuM glutamatergic neurons decreased prior to sevoflurane-induced LOC and gradually increased following ROC. Selective lesioning of SuM glutamatergic neurons promoted the induction of and delayed emergence from sevoflurane anesthesia and increased sevoflurane sensitivity. In addition, optogenetic stimulation of SuM glutamatergic neurons or the SuM-MS projection promoted behavioral arousal and cortical activation under steady-state sevoflurane anesthesia (SSSA) and reduced the depth of anesthesia and caused cortical arousal under sevoflurane-induced burst-suppression conditions. Collectively, these results provide compelling evidence that SuM glutamatergic neurons contribute to regulating states of consciousness under sevoflurane anesthesia.

Effects of propofol on the electrophysiological properties of glutamatergic neurons in the ventrolateral medulla of mice

BACKGROUND

Propofol, a commonly used intravenous anesthetic, is associated with various respiratory adverse events, most notably different degrees of respiratory depression, which pose significant concerns for patient safety. Respiration is a fundamental behavior, with the initiation of breathing in mammals dependent on neuronal activity in the lower brainstem. Previous studies have suggested that propofol-induced respiratory depression might be associated with glutamatergic neurons in the pre-Bötzinger complex (preBötC), though the precise mechanisms are not well understood. In this study, we classify glutamatergic neurons in the brainstem preBötC using whole-cell patch-clamp techniques and investigate the effects of propofol on the electrophysiological properties of these neurons. Our findings aim to shed light on the mechanisms of propofol-induced respiratory depression and provide new experimental insights.

METHODS

We first employed electrophysiological techniques to classify glutamatergic neurons within the preBötC as Type-1 or Type-2. Following this classification, we applied varying concentrations of propofol through bath application to examine its effects on the electrophysiological properties of each type of glutamatergic neuron.

RESULTS

We found that Type-1 neurons exhibited a longer latency in excitation, while Type-2 neurons did not show this delayed excitation. On this basis, we further observed that bath application of propofol at concentrations of 5 μM and 10 μM shortened the latency period of Type-1 glutamatergic neurons but did not affect the latency period of Type-2 glutamatergic neurons.

CONCLUSION

Our study focuses on the glutamatergic neurons in the preBötC of adult mice. It introduces a novel method for classifying these neurons and reveals how propofol affects the activity of the two different types of glutamatergic neurons within the preBötC. These findings contribute to understanding the cellular basis of propofol-induced respiratory depression.

Recent advances in neural mechanism of general anesthesia induced unconsciousness: insights from optogenetics and chemogenetics

For over 170 years, general anesthesia has played a crucial role in clinical practice, yet a comprehensive understanding of the neural mechanisms underlying the induction of unconsciousness by general anesthetics remains elusive. Ongoing research into these mechanisms primarily centers around the brain nuclei and neural circuits associated with sleep-wake. In this context, two sophisticated methodologies, optogenetics and chemogenetics, have emerged as vital tools for recording and modulating the activity of specific neuronal populations or circuits within distinct brain regions. Recent advancements have successfully employed these techniques to investigate the impact of general anesthesia on various brain nuclei and neural pathways. This paper provides an in-depth examination of the use of optogenetic and chemogenetic methodologies in studying the effects of general anesthesia on specific brain nuclei and pathways. Additionally, it discusses in depth the advantages and limitations of these two methodologies, as well as the issues that must be considered for scientific research applications. By shedding light on these facets, this paper serves as a valuable reference for furthering the accurate exploration of the neural mechanisms underlying general anesthesia. It aids researchers and clinicians in effectively evaluating the applicability of these techniques in advancing scientific research and clinical practice.