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

Activity of the Sodium Leak Channel Maintains the Excitability of Paraventricular Thalamus Glutamatergic Neurons to Resist Anesthetic Effects of Sevoflurane in Mice

BACKGROUND

Stimulation of the paraventricular thalamus has been found to enhance anesthesia recovery; however, the underlying molecular mechanism by which general anesthetics modulate paraventricular thalamus is unclear. This study aimed to test the hypothesis that the sodium leak channel (NALCN) maintains neuronal activity in the paraventricular thalamus to resist anesthetic effects of sevoflurane in mice.

METHODS

Chemogenetic and optogenetic manipulations, in vivo multiple-channel recordings, and electroencephalogram recordings were used to investigate the role of paraventricular thalamus neuronal activity in sevoflurane anesthesia. Virus-mediated knockdown and/or overexpression was applied to determine how NALCN influenced excitability of paraventricular thalamus glutamatergic neurons under sevoflurane. Viral tracers and local field potentials were used to explore the downstream pathway.

RESULTS

Single neuronal spikes in the paraventricular thalamus were suppressed by sevoflurane anesthesia and recovered during emergence. Optogenetic activation of paraventricular thalamus glutamatergic neurons shortened the emergence period from sevoflurane anesthesia, while chemogenetic inhibition had the opposite effect. Knockdown of the NALCN in the paraventricular thalamus delayed the emergence from sevoflurane anesthesia (recovery time: from 24 ± 14 to 64 ± 19 s, P < 0.001; concentration for recovery of the righting reflex: from 1.13% ± 0.10% to 0.97% ± 0.13%, P < 0.01). As expected, the overexpression of the NALCN in the paraventricular thalamus produced the opposite effects. At the circuit level, knockdown of the NALCN in the paraventricular thalamus decreased the neuronal activity of the nucleus accumbens, as indicated by the local field potential and decreased single neuronal spikes in the nucleus accumbens. Additionally, the effects of NALCN knockdown in the paraventricular thalamus on sevoflurane actions were reversed by optical stimulation of the nucleus accumbens.

CONCLUSIONS

Activity of the NALCN maintains the excitability of paraventricular thalamus glutamatergic neurons to resist the anesthetic effects of sevoflurane in mice.

EDITOR’S PERSPECTIVE

Distinct Neural Mechanisms Between Anesthesia Induction and Emergence: A Narrative Review

Anesthesia induction and emergence are critical periods for perioperative safety in the clinic. Traditionally, the emergence from general anesthesia has been recognized as a simple inverse process of induction resulting from the elimination of general anesthetics from the central nervous system. However, accumulated evidence has indicated that anesthesia induction and emergence are not mirror-image processes because of the occurrence of hysteresis/neural inertia in both animals and humans. An increasing number of studies have highlighted the critical role of orexinergic neurons and their involved circuits in the selective regulation of emergence but not the induction of general anesthesia. Moreover, additional brain regions have also been implicated in distinct neural mechanisms for anesthesia induction and emergence, which extends the concept that anesthetic induction and emergence are not antiparallel processes. Here, we reviewed the current literature and summarized the evidence regarding the differential mechanism of neural modulation in anesthesia induction and emergence, which will facilitate the understanding of the underlying neural mechanism for emergence from general anesthesia.

GABAergic neurons of anterior thalamic reticular nucleus regulate states of consciousness in propofol- and isoflurane-mediated general anesthesia

BACKGROUND

The thalamus system plays critical roles in the regulation of reversible unconsciousness induced by general anesthetics, especially the arousal stage of general anesthesia (GA). But the function of thalamus in GA-induced loss of consciousness (LOC) is little known. The thalamic reticular nucleus (TRN) is the only GABAergic neurons-composed nucleus in the thalamus, which is composed of parvalbumin (PV) and somatostatin (SST)-expressing GABAergic neurons. The anterior sector of TRN (aTRN) is indicated to participate in the induction of anesthesia, but the roles remain unclear. This study aimed to reveal the role of the aTRN in propofol and isoflurane anesthesia.

METHODS

We first set up c-Fos straining to monitor the activity variation of aTRNPV and aTRNSST neurons during propofol and isoflurane anesthesia. Subsequently, optogenetic tools were utilized to activate aTRNPV and aTRNSST neurons to elucidate the roles of aTRNPV and aTRNSST neurons in propofol and isoflurane anesthesia. Electroencephalogram (EEG) recordings and behavioral tests were recorded and analyzed. Lastly, chemogenetic activation of the aTRNPV neurons was applied to confirm the function of the aTRN neurons in propofol and isoflurane anesthesia.

RESULTS

c-Fos straining showed that both aTRNPV and aTRNSST neurons are activated during the LOC period of propofol and isoflurane anesthesia. Optogenetic activation of aTRNPV and aTRNSST neurons promoted isoflurane induction and delayed the recovery of consciousness (ROC) after propofol and isoflurane anesthesia, meanwhile chemogenetic activation of the aTRNPV neurons displayed the similar effects. Moreover, optogenetic and chemogenetic activation of the aTRN neurons resulted in the accumulated burst suppression ratio (BSR) during propofol and isoflurane GA, although they represented different effects on the power distribution of EEG frequency.

CONCLUSION

Our findings reveal that the aTRN GABAergic neurons play a critical role in promoting the induction of propofol- and isoflurane-mediated GA.

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.

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.

Ketamine and the paradox of anaesthetic state transitions

Administration of subanaesthetic doses of ketamine during isoflurane anaesthesia has been shown in animals to deepen the anaesthetised state, while accelerating emergence. Duan and colleagues have now shown that the addition of subanaesthetic doses of esketamine to isoflurane has a similar effect of increasing the burst suppression ratio, while accelerating emergence. Using c-Fos expression and fibre photometry, they show that esketamine activates glutamatergic neurones in the paraventricular nucleus of the thalamus, a structure that regulates wakefulness. Chemogenetic inhibition of these neurones attenuates the arousal-promoting effects, suggesting a causal role of the paraventricular nucleus of the thalamus in esketamine-mediated acceleration of recovery from anaesthesia.

Esketamine accelerates emergence from isoflurane general anaesthesia by activating the paraventricular thalamus glutamatergic neurones in mice

BACKGROUND

Delayed emergence from general anaesthesia poses a significant perioperative safety hazard. Subanaesthetic doses of ketamine not only deepen anaesthesia but also accelerate recovery from isoflurane anaesthesia; however, the mechanisms underlying this phenomenon remain elusive. Esketamine exhibits a more potent receptor affinity and fewer adverse effects than ketamine and exhibits shorter recovery times after brief periods of anaesthesia. As the paraventricular thalamus (PVT) plays a pivotal role in regulating wakefulness, we studied its role in the emergence process during combined esketamine and isoflurane anaesthesia.

METHODS

The righting reflex and cortical electroencephalography were used as measures of consciousness in mice during isoflurane anaesthesia with coadministration of esketamine. The expression of c-Fos was used to determine neuronal activity changes in PVT neurones after esketamine administration. The effect of esketamine combined with isoflurane anaesthesia on PVT glutamatergic (PVTGlu) neuronal activity was monitored by fibre photometry, and chemogenetic technology was used to manipulate PVTGlu neuronal activity.

RESULTS

A low dose of esketamine (5 mg kg-1) accelerated emergence from isoflurane general anaesthesia (474 [30] s vs 544 [39] s, P=0.001). Esketamine (5 mg kg-1) increased PVT c-Fos expression (508 [198] vs 258 [87], P=0.009) and enhanced the population activity of PVTGlu neurones (0.03 [1.7]% vs 6.9 [3.4]%, P=0.002) during isoflurane anaesthesia (1.9 [5.7]% vs -5.1 [5.3]%, P=0.016) and emergence (6.1 [6.2]% vs -1.1 [5.0]%, P=0.022). Chemogenetic suppression of PVTGlu neurones abolished the arousal-promoting effects of esketamine (459 [33] s vs 596 [33] s, P<0.001).

CONCLUSIONS

Our results suggest that esketamine promotes recovery from isoflurane anaesthesia by activating PVTGlu neurones. This mechanism could explain the rapid arousability exhibited upon treatment with a low dose of esketamine.