Dopamine neurons in the ventral periaqueductal gray modulate isoflurane anesthesia in rats

In vivo imaging reveals a synchronized correlation among neurotransmitter dynamics during propofol and sevoflurane anesthesia

General anesthesia is widely applied in clinical practice. However, the precise mechanism of loss of consciousness induced by general anesthetics remains unknown. Here, we measured the dynamics of five neurotransmitters, including γ-aminobutyric acid, glutamate, norepinephrine, acetylcholine, and dopamine, in the medial prefrontal cortex and primary visual cortex of C57BL/6 mice through in vivo fiber photometry and genetically encoded neurotransmitter sensors under anesthesia to reveal the mechanism of general anesthesia from a neurotransmitter perspective. Results revealed that the concentrations of γ-aminobutyric acid, glutamate, norepinephrine, and acetylcholine increased in the cortex during propofol-induced loss of consciousness. Dopamine levels did not change following the hypnotic dose of propofol but increased significantly following surgical doses of propofol anesthesia. Notably, the concentrations of the five neurotransmitters generally decreased during sevoflurane-induced loss of consciousness. Furthermore, the neurotransmitter dynamic networks were not synchronized in the non-anesthesia groups but were highly synchronized in the anesthetic groups. These findings suggest that neurotransmitter dynamic network synchronization may cause anesthetic-induced loss of consciousness.

Neurobiological basis of emergence from anesthesia

The suppression of consciousness by anesthetics and the emergence of the brain from anesthesia are complex and elusive processes. Anesthetics may exert their inhibitory effects by binding to specific protein targets or through membrane-mediated targets, disrupting neural activity and the integrity and function of neural circuits responsible for signal transmission and conscious perception/subjective experience. Emergence from anesthesia was generally thought to depend on the elimination of the anesthetic from the body. Recently, studies have suggested that emergence from anesthesia is a dynamic and active process that can be partially controlled and is independent of the specific molecular targets of anesthetics. This article summarizes the fundamentals of anesthetics' actions in the brain and the mechanisms of emergence from anesthesia that have been recently revealed in animal studies.

The contribution of periaqueductal gray in the regulation of physiological and pathological behaviors

Periaqueductal gray (PAG), an integration center for neuronal signals, is located in the midbrain and regulates multiple physiological and pathological behaviors, including pain, defensive and aggressive behaviors, anxiety and depression, cardiovascular response, respiration, and sleep-wake behaviors. Due to the different neuroanatomical connections and functional characteristics of the four functional columns of PAG, different subregions of PAG synergistically regulate various instinctual behaviors. In the current review, we summarized the role and possible neurobiological mechanism of different subregions of PAG in the regulation of pain, defensive and aggressive behaviors, anxiety, and depression from the perspective of the up-down neuronal circuits of PAG. Furthermore, we proposed the potential clinical applications of PAG. Knowledge of these aspects will give us a better understanding of the key role of PAG in physiological and pathological behaviors and provide directions for future clinical treatments.

Heterogeneity of mesencephalic dopaminergic neurons: From molecular classifications, electrophysiological properties to functional connectivity

The mesencephalic dopamine (DA) system is composed of neuronal subtypes that are molecularly and functionally distinct, are responsible for specific behaviors, and are closely associated with numerous brain disorders. Existing research has made significant advances in identifying the heterogeneity of mesencephalic DA neurons, which is necessary for understanding their diverse physiological functions and disease susceptibility. Moreover, there is a conflict regarding the electrophysiological properties of the distinct subsets of midbrain DA neurons. This review aimed to elucidate recent developments in the heterogeneity of midbrain DA neurons, including subpopulation categorization, electrophysiological characteristics, and functional connectivity to provide new strategies for accurately identifying distinct subtypes of midbrain DA neurons and investigating the underlying mechanisms of these neurons in various diseases.

Dopamine D1-receptor-expressing pathway from the nucleus accumbens to ventral pallidum-mediated sevoflurane anesthesia in mice

BACKGROUND

General anesthesia has long been used in clinical practice, but its precise pharmacological effects on neural circuits are not fully understood. Recent investigations suggest that the sleep-wake system may play a role in the reversible loss of consciousness induced by general anesthetics. Studies in mice have shown that microinjection of dopamine receptor 1 (D1R) agonists into the nucleus accumbens (NAc) promotes recovery from isoflurane anesthesia, while microinjection of D1R antagonists has the opposite effect. Furthermore, during the induction and maintenance of sevoflurane anesthesia, there is a significant decrease in extracellular dopamine levels in the NAc, which subsequently increases during the recovery period. These findings suggest the involvement of the NAc in the regulation of general anesthesia. However, the specific role of D1R-expressing neurons in the NAc during general anesthesia and the downstream effect pathways are still not well understood.

METHODS

In order to analyze the impact of sevoflurane anesthesia on NAcD1R  neurons and the NAcD1R -VP pathway, this study employed calcium fiber photometry to investigate alterations in the fluorescence intensity of calcium signals in dopamine D1-receptor-expressing neurons located in the nucleus accumbens (NAcD1R  neurons) and the NAcD1R -VP pathway during sevoflurane anesthesia. Subsequently, optogenetic techniques were utilized to activate or inhibit NAcD1R  neurons and their synaptic terminals in the ventral pallidum (VP), aiming to elucidate the role of NAcD1R  neurons and the NAcD1R -VP pathway in sevoflurane anesthesia. These experiments were supplemented with electroencephalogram (EEG) recordings and behavioral tests. Lastly, a genetically-encoded fluorescent sensor was employed to observe changes in extracellular GABA neurotransmitters in the VP during sevoflurane anesthesia.

RESULTS

Our findings revealed that sevoflurane administration led to the inhibition of NAcD1R neuron population activity, as well as their connections within the ventral pallidum (VP). We also observed a reversible reduction in extracellular GABA levels in the VP during both the induction and emergence phases of sevoflurane anesthesia. Additionally, the optogenetic activation of NAcD1R  neurons and their synaptic terminals in the VP resulted in a promotion of wakefulness during sevoflurane anesthesia, accompanied by a decrease in EEG slow wave activity and burst suppression rate. Conversely, the optogenetic inhibition of the NAcD1R -VP pathway exerted opposite effects.

CONCLUSION

The NAcD1R -VP pathway serves as a crucial downstream pathway of NAcD1R neurons, playing a significant role in regulating arousal during sevoflurane anesthesia. Importantly, this pathway appears to be associated with the release of GABA neurotransmitters from VP cells.

Dopaminergic System in Promoting Recovery from General Anesthesia

Dopamine is an important neurotransmitter that plays a biological role by binding to dopamine receptors. The dopaminergic system regulates neural activities, such as reward and punishment, memory, motor control, emotion, and sleep-wake. Numerous studies have confirmed that the dopaminergic system has the function of maintaining wakefulness in the body. In recent years, there has been increasing evidence that the sleep-wake cycle in the brain has similar neurobrain network mechanisms to those associated with the loss and recovery of consciousness induced by general anesthesia. With the continuous development and innovation of neurobiological techniques, the dopaminergic system has now been proved to be involved in the emergence from general anesthesia through the modulation of neuronal activity. This article is an overview of the dopaminergic system and the research progress into its role in wakefulness and general anesthesia recovery. It provides a theoretical basis for interpreting the mechanisms regulating consciousness during general anesthesia.

Glutamatergic neurons in the paraventricular hypothalamic nucleus regulate isoflurane anesthesia in mice

The glutamatergic-mediated excitatory system in the brain is vital for the regulation of sleep-wake and general anesthesia. Specifically, the paraventricular hypothalamic nucleus (PVH), which contains mainly glutamatergic neurons, has been shown to play a critical role in sleep-wake. Here, we sought to explore whether the PVH glutamatergic neurons have an important effect on the process of general anesthesia. We used c-fos staining and in vivo calcium signal recording to observe the activity changes of the PVH glutamatergic neurons during isoflurane anesthesia and found that both c-fos expression in the PVH and the calcium activity of PVH glutamatergic neurons decreased in isoflurane anesthesia and significantly increased during the recovery process. Chemogenetic activation of PVH glutamatergic neurons prolonged induction time and shortened emergence time from anesthesia by decreasing the depth of anesthesia. Using chemogenetic inhibition of PVH glutamatergic neurons under isoflurane anesthesia, we found that inhibition of PVH glutamatergic neurons facilitated the induction process and delayed the emergence accompanied by deepening the depth of anesthesia. Together, these results identify a crucial role for PVH glutamatergic neurons in modulating isoflurane anesthesia.

Neural Subtype-dependent Cholinergic Modulation of Neural Activities by Activation of Muscarinic 2 Receptors and G Protein-activated Inwardly Rectifying Potassium Channel in Rat Periaqueductal Gray Neurons

Acetylcholine plays a pivotal role in the regulation of functions such as pain and the sleep and wake cycle by modulating neural activities of the ventrolateral periaqueductal gray (vlPAG). Electrophysiological studies have shown that cholinergic effects are inconsistent among recorded neurons, particularly in the depolarization and hyperpolarization of the resting membrane potential (RMP). This discrepancy may be due to the neural subtype-dependent cholinergic modulation of the RMP. To examine this possibility, we performed whole-cell patch-clamp recordings from subtype-identified neurons using vesicular GABA transporter (VGAT)-Venus × ChAT-TdTomato rats and elucidated cellular mechanisms of cholinergic effects on the RMP. The application of carbachol hyperpolarized the RMP of cholinergic neurons in a dose-dependent manner but had much less of an effect on other neural subtypes, including GABAergic/glycinergic and glutamatergic neurons. Cholinergic hyperpolarization was accompanied by a decrease in input resistance. These cholinergic effects were blocked by AF-DX384 or gallamine and were mimicked by arecaidine but-2-ynyl ester tosylate, suggesting that the carbachol-induced hyperpolarization of the RMP in cholinergic neurons is mediated via M₂ receptors. Tertiapin suppressed the carbachol-induced G protein-activated inwardly rectifying potassium channel (GIRK) currents and hyperpolarization of the RMP in cholinergic neurons. Intracellular application of GDP-β-S blocked the carbachol-induced hyperpolarization of the RMP. Neostigmine slowly hyperpolarized the RMP in cholinergic neurons. These results suggest that neural firing of vlPAG cholinergic neurons is suppressed by GIRK currents induced via M₂ receptor activation, and this negative feedback regulation of cholinergic neuronal activities can be induced by acetylcholine, which is intrinsically released in the vlPAG.

Claustrum modulates behavioral sensitivity and EEG activity of propofol anesthesia

AIMS

The claustrum has long been regarded as a vital center for conscious control. Electrical stimulation or damage to the claustrum can result in decreased awareness or loss of consciousness, suggesting that the claustrum may be a target for the action of general anesthetics. This study aimed to determine the role of the claustrum in propofol anesthesia.

METHODS

We first applied a fiber photometry calcium signal recording system to record the claustral neuronal activity during the entire process of propofol anesthesia. Chemogenetic activation of claustral neurones was then performed to verify their role in anesthesia. Finally, muscimol (GABAa receptor agonist) and gabazine (GABAa receptor antagonist) were microinjected into the claustrum to determine whether their GABAa receptors were involved in modulating propofol anesthesia. EEG and behavioral indicators, such as anesthetic sensitivity and efficacy, were recorded and analyzed.

RESULTS

An evident anesthesia-related change in claustrum neuronal activity was suppressed during propofol-induced unconsciousness and restored following recovery from anesthesia. Chemogenetic activation of claustrum neurons results in attenuated propofol sensitivity, a shorter anesthesia duration, and an EEG shift toward wakefulness. Manipulation of GABAa receptors in the claustrum showed bidirectional control of propofol sensitivity, as activation decreases anesthesia efficiency while inactivation augments it. Additionally, inhibiting claustrum GABAa receptors increases cortical EEG slow waves.

CONCLUSIONS

Claustrum neurones and their GABAa receptors are implicated in the modulation of propofol anesthesia in both behavioral and EEG assessments. Our findings create scope to reveal the brain targets of anesthetic action further and add to the existing evidence on the consciousness-modulating role of the claustrum.

Glutamatergic neurons in paraventricular nucleus of the thalamus regulate the recovery from isoflurane anesthesia

Objectives

Previous studies have demonstrated that the paraventricular nucleus of the thalamus (PVT) is a key wakefulness-controlling nucleus in the thalamus. Therefore, PVT may also be involved in the process of general anesthesia. This study intends to explore the role of PVT in isoflurane anesthesia.

Methods

In the present study, we used the expression of c-Fos to observe the neuronal activity of PVT neurons under isoflurane anesthesia. We further recorded the effect of isoflurane anesthesia on the calcium signal of PVT glutamatergic neurons in real time with the help of calcium fiber photometry. We finally used chemogenetic technology to specifically regulate PVT glutamatergic neurons, and observed its effect on isoflurane anesthesia and cortical electroencephalography (EEG) in mice.

Results

We found that glutamatergic neurons of PVT exhibited high activity during wakefulness and low activity during isoflurane anesthesia. Activation of PVT glutamatergic neuronal caused an acceleration in emergence from isoflurane anesthesia accompanied with a decrease in EEG delta power (1–4 Hz). Whereas suppression of PVT glutamatergic neurons induced a delay recovery of isoflurane anesthesia, without affecting anesthesia induction.

Conclusions

Assuming a pharmacokinetic explanation for results can be excluded, these results demonstrate that the PVT is involved in regulating anesthesia emergence.

Regulation of Neural Circuitry under General Anesthesia: New Methods and Findings

General anesthesia has been widely utilized since the 1840s, but its underlying neural circuits remain to be completely understood. Since both general anesthesia and sleep are reversible losses of consciousness, studies on the neural-circuit mechanisms affected by general anesthesia have mainly focused on the neural nuclei or the pathways known to regulate sleep. Three advanced technologies commonly used in neuroscience, in vivo calcium imaging, chemogenetics, and optogenetics, are used to record and modulate the activity of specific neurons or neural circuits in the brain areas of interest. Recently, they have successfully been used to study the neural nuclei and pathways of general anesthesia. This article reviews these three techniques and their applications in the brain nuclei or pathways affected by general anesthesia, to serve as a reference for further and more accurate exploration of other neural circuits under general anesthesia and to contribute to other research fields in the future.

The Aged Striatum: Evidence of Molecular and Structural Changes Using a Longitudinal Multimodal Approach in Mice

To study the aging human brain requires significant resources and time. Thus, mice models of aging can provide insight into changes in brain biological functions at a fraction of the time when compared to humans. This study aims to explore changes in dopamine D₁ and D₂ receptor availability and of gray matter density in striatum during aging in mice and to evaluate whether longitudinal imaging in mice may serve as a model for normal brain aging to complement cross-sectional research in humans. Mice underwent repeated structural magnetic resonance imaging (sMRI), and [¹¹C]Raclopride and [¹¹C]SCH23390 positron emission tomography (PET) was performed on a subset of aging mice. PET and sMRI data were analyzed by binding potential (BP_ND), voxel- and tensor-based morphometry (VBM and TBM, respectively). Longitudinal PET revealed a significant reduction in striatal BP_ND for D₂ receptors over time, whereas no significant change was found for D₁ receptors. sMRI indicated a significant increase in modulated gray matter density (mGMD) over time in striatum, with limited clusters showing decreased mGMD. Mouse [¹¹C]Raclopride data is compatible with previous reports in human cross-sectional studies, suggesting that a natural loss of dopaminergic D₂ receptors in striatum can be assessed in mice, reflecting estimates from humans. No changes in D₁ were found, which may be attributed to altered [¹¹C]SCH23390 kinetics in anesthetized mice, suggesting that this tracer is not yet able to replicate human findings. sMRI revealed a significant increase in mGMD. Although contrary to expectations, this increase in modulated GM density may be attributed to an age-related increase in non-neuronal cells.

Dorsal raphe serotonergic neurons promote arousal from isoflurane anesthesia

Aims

General anesthesia has been widely applied in surgical or nonsurgical medical procedures, but the mechanism behind remains elusive. Because of shared neural circuits of sleep and anesthesia, whether serotonergic system, which is highly implicated in modulation of sleep and wakefulness, regulates general anesthesia as well is worth investigating.

Methods

Immunostaining and fiber photometry were used to assess the neuronal activities. Electroencephalography spectra and burst‐suppression ratio (BSR) were used to measure anesthetic depth and loss or recovery of righting reflex to indicate the induction or emergence time of general anesthesia. Regulation of serotonergic system was achieved through optogenetic, chemogenetic, or pharmacological methods.

Results

We found that both Fos expression and calcium activity were significantly decreased during general anesthesia. Activation of 5‐HT neurons in the dorsal raphe nucleus (DRN) decreased the depth of anesthesia and facilitated the emergence from anesthesia, and inhibition deepened the anesthesia and prolonged the emergence time. Furthermore, agonism or antagonism of 5‐HT 1A or 2C receptors mimicked the effect of manipulating DRN serotonergic neurons.

Conclusion

Our results demonstrate that 5‐HT neurons in the DRN play a regulative role of general anesthesia, and activation of serotonergic neurons could facilitate emergence from general anesthesia partly through 5‐HT 1A and 2C receptors.

Dopaminergic Projections From the Ventral Tegmental Area to the Nucleus Accumbens Modulate Sevoflurane Anesthesia in Mice

The role of the dopaminergic pathway in general anesthesia and its potential mechanisms are still unknown. In this study, we usedc-Fos staining combined with calcium fiber photometry recording to explore the activity of ventral tegmental area (VTA) dopaminergic neurons(VTA-DA) and nucleus accumbens (NAc) neurons during sevoflurane anesthesia. A genetically encoded dopamine (DA) sensor was used to investigate thefunction of the NAc in sevoflurane anesthesia. Chemogenetics and optogenetics were used to explore the role of the VTA-DA in sevofluraneanesthesia. Electroencephalogram (EEG) spectra, time of loss of righting reflex (LORR) and recovery of righting reflex (RORR) were recorded asassessment indicators. We found that VTA-DA and NAc neurons were inhibited during the induction period and were activated during the recoveryperiod of sevoflurane anesthesia. The fluorescence signals of dopamine decreased in the induction of and increased in the emergence from sevoflurane anesthesia.Activation of VTA-DA and the VTA^DA-NAc pathway delayed the induction and facilitated the emergence accompanying with thereduction of delta band and the augmentation of the gamma band. These data demonstrate that VTA-DA neurons play a critical role in modulating sevofluraneanesthesia via the VTA^DA-NAc pathway.

Lateral Habenula Glutamatergic Neurons Modulate Isoflurane Anesthesia in Mice

Since their introduction in the 1840s, one of the largest mysteries of modern anesthesia are how general anesthetics create the state of reversible loss of consciousness. Increasing researchers have shown that neural pathways that regulate endogenous sleep–wake systems are also involved in general anesthesia. Recently, the Lateral Habenula (LHb) was considered as a hot spot for both natural sleep–wake and propofol-induced sedation; however, the role of the LHb and related pathways in the isoflurane-induced unconsciousness has yet to be identified. Here, using real-time calcium fiber photometry recordings in vivo, we found that isoflurane reversibly increased the activity of LHb glutamatergic neurons. Then, we selectively ablated LHb glutamatergic neurons in Vglut2-cre mice, which caused a longer induction time and less recovery time along with a decrease in delta-band power in mice under isoflurane anesthesia. Furthermore, using a chemogenetic approach to specifically activate LHb glutamatergic neurons shortened the induction time and prolonged the recovery time in mice under isoflurane anesthesia with an increase in delta-band power. In contrast, chemogenetic inhibition of LHb glutamatergic neurons was very similar to the effects of selective lesions of LHb glutamatergic neurons. Finally, optogenetic activation of LHb glutamatergic neurons or the synaptic terminals of LHb glutamatergic neurons in the rostromedial tegmental nucleus (RMTg) produced a hypnosis-promoting effect in isoflurane anesthesia with an increase in slow wave activity. Our results suggest that LHb glutamatergic neurons and pathway are vital in modulating isoflurane anesthesia.

The Inert Brain: Explaining Neural Inertia as Post-anaesthetic Sleep Inertia

"Neural inertia" is the brain's tendency to resist changes in its arousal state: it is manifested as emergence from anaesthesia occurring at lower drug doses than those required for anaesthetic induction, a phenomenon observed across very different species, from invertebrates to mammals. However, the brain is also subject to another form of inertia, familiar to most people: sleep inertia, the feeling of grogginess, confusion and impaired performance that typically follows awakening. Here, we propose a novel account of neural inertia, as the result of sleep inertia taking place after the artificial sleep induced by anaesthetics. We argue that the orexinergic and noradrenergic systems may be key mechanisms for the control of these transition states, with the orexinergic system exerting a stabilising effect through the noradrenergic system. This effect may be reflected at the macroscale in terms of altered functional anticorrelations between default mode and executive control networks of the human brain. The hypothesised link between neural inertia and sleep inertia could explain why different anaesthetic drugs induce different levels of neural inertia, and why elderly individuals and narcoleptic patients are more susceptible to neural inertia. This novel hypothesis also enables us to generate several empirically testable predictions at both the behavioural and neural levels, with potential implications for clinical practice.

Cell-type-specific imaging of neurotransmission reveals a disrupted excitatory-inhibitory cortical network in isoflurane anaesthesia

BACKGROUND

Despite the fundamental clinical significance of general anaesthesia, the cortical mechanism underlying anaesthetic-induced loss of consciousness (aLOC) remains elusive.

METHODS

Here, we measured the dynamics of two major cortical neurotransmitters, gamma-aminobutyric acid (GABA) and glutamate, through in vivo two-photon imaging and genetically encoded neurotransmitter sensors in a cell type-specific manner in the primary visual (V1) cortex.

FINDINGS

We found a general decrease in cortical GABA transmission during aLOC. However, the glutamate transmission varies among different cortical cell types, where in it is almost preserved on pyramidal cells and is significantly reduced on inhibitory interneurons. Cortical interneurons expressing vasoactive intestinal peptide (VIP) and parvalbumin (PV) specialize in disinhibitory and inhibitory effects, respectively. During aLOC, VIP neuronal activity was delayed, and PV neuronal activity was dramatically inhibited and highly synchronized.

INTERPRETATION

These data reveal that aLOC resembles a cortical state with a disrupted excitatory-inhibitory network and suggest that a functional inhibitory network is indispensable in the maintenance of consciousness.

FUNDING

This work was supported by the grants of the National Natural Science Foundation of China (grant nos. 81620108012 and 82030038 to H.D. and grant nos. 31922029, 61890951, and 61890950 to J.H.).

The Inert Brain: Explaining Neural Inertia as Post-anaesthetic Sleep Inertia

"Neural inertia" is the brain's tendency to resist changes in its arousal state: it is manifested as emergence from anaesthesia occurring at lower drug doses than those required for anaesthetic induction, a phenomenon observed across very different species, from invertebrates to mammals. However, the brain is also subject to another form of inertia, familiar to most people: sleep inertia, the feeling of grogginess, confusion and impaired performance that typically follows awakening. Here, we propose a novel account of neural inertia, as the result of sleep inertia taking place after the artificial sleep induced by anaesthetics. We argue that the orexinergic and noradrenergic systems may be key mechanisms for the control of these transition states, with the orexinergic system exerting a stabilising effect through the noradrenergic system. This effect may be reflected at the macroscale in terms of altered functional anticorrelations between default mode and executive control networks of the human brain. The hypothesised link between neural inertia and sleep inertia could explain why different anaesthetic drugs induce different levels of neural inertia, and why elderly individuals and narcoleptic patients are more susceptible to neural inertia. This novel hypothesis also enables us to generate several empirically testable predictions at both the behavioural and neural levels, with potential implications for clinical practice.

Dopamine neurons in the ventral periaqueductal gray modulate isoflurane anesthesia in rats

Aims

General anesthesia has been applied in surgery for more than 170 years, and there is little doubt that GABA_A receptors have an important role as anesthetic molecular targets, but its neural mechanisms remain unclear. Increasing researchers have shown that dopaminergic pathways in the brain are crucial for sleep and wake. General anesthesia‐induced unconsciousness and natural sleep share some neural correlates. However, the role of GABA_A receptors in ventral periaqueductal gray (vPAG) dopamine (DA) neurons in the isoflurane‐induced unconsciousness has yet to be identified.

Methods

In the present study, we used calcium fiber photometry recording to explore that the activity of ventral periaqueductal gray (vPAG) neurons. Then, rats were unilaterally microinjected with 6‐hydroxydopamine into the vPAG area to determine the role of vPAG‐DA neurons in isoflurane‐induced‐anesthesia. Furthermore, thirty SD rats were divided into three groups: a GABA_AR agonist‐muscimol group, a GABA_AR antagonist‐gabazine group, and a control group. Finally, whole‐cell patch clamp was used to examine the effects of isoflurane and GABA_A receptor agonist/antagonist on vPAG‐DA neurons.

Results

The vPAG neurons were markedly inhibited during isoflurane anesthesia induction and that these neurons were activated during emergence from isoflurane anesthesia. Lesion to the vPAG‐DA neurons shortened the induction time and prolonged the emergence time while increasing δ power in isoflurane anesthesia. Intracerebral injection of the GABA_A receptor agonist (muscimol) into the vPAG accelerated the induction of anesthesia and delayed recovery from isoflurane anesthesia, with a decrease of δ power and an augment of β power. Injection of GABA_A receptor antagonist gabazine generated the opposite effects. Isoflurane enhanced GABAergic transmission, and GABA_A receptor agonist partly increased isoflurane‐induced inhibition of vPAG‐DA neurons, while GABA_A receptor antagonist evidently attenuated GABAergic transmission.

Conclusion

Our results suggest that vPAG‐DA neurons are involved in isoflurane anesthesia through activation of the GABA_A receptor.