Sevoflurane prevents stroke-induced depressive and anxiety behaviors by promoting cannabinoid receptor subtype I-dependent interaction between β-arrestin 2 and extracellular signal-regulated kinases 1/2 in the rat hippocampus

Sevoflurane acts as an antidepressant by suppression of GluN2D-containing NMDA receptors on interneurons

BACKGROUND AND PURPOSE

Sevoflurane, a commonly used inhaled anaesthetic known for its favourable safety profile and rapid onset and offset, has not been thoroughly investigated as a potential treatment for depression. In this study, we reveal the mechanism through which sevoflurane delivers enduring antidepressant effects.

EXPERIMENTAL APPROACH

To assess the antidepressant effects of sevoflurane, behavioural tests were conducted, along with in vitro and ex vivo whole-cell patch-clamp recordings, to examine the effects on GluN1-GluN2 incorporated N-methyl-d-aspartate (NMDA) receptors (NMDARs) and neuronal circuitry in the medial prefrontal cortex (mPFC). Multiple-channel electrophysiology in freely moving mice was performed to evaluate sevoflurane's effects on neuronal activity, and GluN2D knockout (grin2d-/-) mice were used to confirm the requirement of GluN2D for the antidepressant effects.

KEY RESULTS

Repeated exposure to subanaesthetic doses of sevoflurane produced sustained antidepressant effects lasting up to 2 weeks. Sevoflurane preferentially inhibited GluN2C- and GluN2D-containing NMDARs, causing a reduction in interneuron activity. In contrast, sevoflurane increased action potentials (AP) firing and decreased spontaneous inhibitory postsynaptic current (sIPSC) in mPFC pyramidal neurons, demonstrating a disinhibitory effect. These effects were absent in grin2d-/- mice, and both pharmacological blockade and genetic knockout of GluN2D abolished sevoflurane's antidepressant actions, suggesting that GluN2D is essential for its antidepressant effect.

CONCLUSION AND IMPLICATIONS

Sevoflurane directly targets GluN2D, leading to a specific decrease in interneuron activity and subsequent disinhibition of pyramidal neurons, which may underpin its antidepressant effects. Targeting the GluN2D subunit could hold promise as a potential therapeutic strategy for treating depression.

Activation of GPR55 Ameliorates Maternal Separation-Induced Learning and Memory Deficits by Augmenting 5-HT Synthesis in the Dorsal Raphe Nucleus of Juvenile Mice

Maternal separation (MS) represents a profound early life stressor with enduring impacts on neuronal development and adult cognitive function in both humans and rodents. MS is associated with persistent dysregulations in neurotransmitter systems, including the serotonin (5-HT) pathway, which is pivotal for mood stabilization and stress-coping mechanisms. Although the novel cannabinoid receptor, GPR55, is recognized for its influence on learning and memory, its implications on the function and synaptic dynamics of 5-HT neurons within the dorsal raphe nucleus (DRN) remain to be elucidated. In this study, we sought to discern the repercussions of GPR55 activation on 5-HT synthesis within the DRN of adult C57BL/6J mice that experienced MS. Concurrently, we analyzed potential alterations in excitatory synaptic transmission, long-term synaptic plasticity, and relevant learning and memory outcomes. Our behavioral assessments indicated a marked amelioration in MS-induced learning and memory deficits following GPR55 activation. In conjunction with this, we noted a substantial decrease in 5-HT levels in the MS model, while GPR55 activation stimulated tryptophan hydroxylase 2 synthesis and fostered the release of 5-HT. Electrophysiological patch-clamp analyses highlighted the ability of GPR55 activation to alleviate MS-induced cognitive deficits by modulating the frequency and magnitude of miniature excitatory postsynaptic currents within the DRN. Notably, this cognitive enhancement was underpinned by the phosphorylation of both NMDA and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. In summary, our findings underscore the capacity of GPR55 to elevate 5-HT synthesis and modify synaptic transmissions within the DRN of juvenile mice, positing GPR55 as a promising therapeutic avenue for ameliorating MS-induced cognitive impairment.

Antidepressant effects of dexmedetomidine compared with ECT in patients with treatment-resistant depression

OBJECTIVE

This pilot study was designed to investigate the antidepressant effects of dexmedetomidine (DEX), a selective α2-adrenergic receptor agonist, in patients with treatment-resistant depression (TRD). The antidepressant effects of dexmedetomidine was compared with ECT, which is widely used in clinical practice for treatment of patients with TRD.

METHODS

Seventy six patients with TRD were randomly assigned to receive 10 sessions of DEX infusions or electroconvulsive therapy (ECT) treatment. The primary outcome was the changes of depression severity determined by the improvement of 24-item Hamilton Depression Rating Scale (HDRS-24). The second outcomes were the rates of therapeutic response (reduction in HDRS-24 ≥ 50 %) and remission (HDRS-24 ≤ 10 and reduction in HDRS-24 ≥ 60 %) at posttreatment and after 3 months of follow-up visits.

RESULTS

We found that 10 sessions of DEX infusions or ECT treatments significantly improved HDRS-24 scores at posttreatment and after 3 months of follow-up visits compared with the baseline. In addition, there was no significant difference between DEX infusions and ECT treatments regarding HDRS-24 at these evaluating points. Furthermore, the depression severity dropped to mild after 2 sessions of DEX infusion. In contrast, at least 6 sessions of ECT treatment were needed to achieve a same level. Finally, the rates of therapeutic response and remission were comparable between the two groups. No serious adverse events were observed.

CONCLUSIONS

Based on current published evidence, we conclude that DEX exhibits rapid and durable antidepressant properties similar to ECT but with fewer side effects.

Synthetic surprise as the foundation of the psychedelic experience

Psychedelic agents, such as LSD and psilocybin, induce marked alterations in consciousness via activation of the 5-HT2A receptor (5-HT2ARs). We hypothesize that psychedelics enforce a state of synthetic surprise through the biased activation of the 5-HTRs system. This idea is informed by recent insights into the role of 5-HT in signaling surprise. The effects on consciousness, explained by the cognitive penetrability of perception, can be described within the predictive coding framework where surprise corresponds to prediction error, the mismatch between predictions and actual sensory input. Crucially, the precision afforded to the prediction error determines its effect on priors, enabling a dynamic interaction between top-down expectations and incoming sensory data. By integrating recent findings on predictive coding circuitry and 5-HT2ARs transcriptomic data, we propose a biological implementation with emphasis on the role of inhibitory interneurons. Implications arise for the clinical use of psychedelics, which may rely primarily on their inherent capacity to induce surprise in order to disrupt maladaptive patterns.

Extremely Low-Frequency Electromagnetic Stimulation (ELF-EMS) Improves Neurological Outcome and Reduces Microglial Reactivity in a Rodent Model of Global Transient Stroke

Extremely low-frequency electromagnetic stimulation (ELF-EMS) was demonstrated to be significantly beneficial in rodent models of permanent stroke. The mechanism involved enhanced cerebrovascular perfusion and endothelial cell nitric oxide production. However, the possible effect on the neuroinflammatory response and its efficacy in reperfusion stroke models remains unclear. To evaluate ELF-EMS effectiveness and possible immunomodulatory response, we studied neurological outcome, behavior, neuronal survival, and glial reactivity in a rodent model of global transient stroke treated with 13.5 mT/60 Hz. Next, we studied microglial cells migration and, in organotypic hippocampal brain slices, we assessed neuronal survival and microglia reactivity. ELF-EMS improved the neurological score and behavior in the ischemia-reperfusion model. It also improved neuronal survival and decreased glia reactivity in the hippocampus, with microglia showing the first signs of treatment effect. In vitro ELF-EMS decreased (Lipopolysaccharide) LPS and ATP-induced microglia migration in both scratch and transwell assay. Additionally, in hippocampal brain slices, reduced microglial reactivity, improved neuronal survival, and modulation of inflammation-related markers was observed. Our study is the first to show that an EMF treatment has a direct impact on microglial migration. Furthermore, ELF-EMS has beneficial effects in an ischemia/reperfusion model, which indicates that this treatment has clinical potential as a new treatment against ischemic stroke.

Maternal sevoflurane exposure induces neurotoxicity in offspring rats via the CB1R/CDK5/p-tau pathway

Sevoflurane is widely used for maternal anesthesia during pregnancy. Sevoflurane exposure of rats at mid-gestation can cause abnormal development of the central nervous system in their offspring. Sevoflurane is known to increase the expression of cannabinoid 1 receptor (CB1R) in the hippocampus. However, the effect of cannabinoid 1 receptor on fetal and offspring rats after maternal anesthesia is still unclear. At gestational day 14, pregnant rats were subjected to 2-h exposure to 3.5% sevoflurane or air. Rats underwent intraperitoneal injection with saline or rimonabant (1 mg/kg) 30 min prior to sevoflurane or air exposure. cannabinoid 1 receptor, cyclin-dependent kinase 5 (CDK5), p35, p25, tau, and p-tau expression in fetal brains was measured at 6, 12, and 24 h post-sevoflurane/air exposure. Neurobehavioral and Morris water maze tests were performed postnatal days 3-33. The expression of cannabinoid 1 receptor/cyclin-dependent kinase 5/p-tau and histopathological staining of brain tissues in offspring rats was observed. We found that a single exposure to sevoflurane upregulated the activity of cyclin-dependent kinase 5 and the level of p-tau via cannabinoid 1 receptor. This was accompanied by the diminished number of neurons and dendritic spines in hippocampal CA1 regions. Finally, these effects induced lower scores and platform crossing times in behavioral tests. The present study suggests that a single exposure to 3.5% sevoflurane of rats at mid-gestation impairs neurobehavioral abilities and cognitive memory in offspring. cannabinoid 1 receptor is a possible target for the amelioration of postnatal neurobehavioral ability and cognitive memory impairments induced by maternal anesthesia.

Sevoflurane up-regulates miR-7a to protect against ischemic brain injury in rats by down-regulating ATG7 and reducing neuronal autophagy

The current study aimed to elucidate the effects of Sevoflurane on neuronal autophagy and ischemic brain injury by regulating miR-7a/ATG7 axis. The rat model of middle cerebral artery occlusion (MCAO) was established by thread embolization. The expression pattern of microRNA-7a (miR-7a) and autophagy-related gene 7 (ATG7) was subsequently determined in Sevoflurane-treated MCAO rats with their relation and effects on neuronal autophagy and ischemic brain injury further analyzed. Bioinformatics analysis confirmed that miR-7a could target to inhibit ATG7 in ischemic brain injury samples. Sevoflurane could alleviate ischemic brain injury in rats by reducing the level of neuronal autophagy-related factors. The expression of miR-7a was up-regulated and ATG7 was down-regulated in the brain tissues of MCAO rats after Sevoflurane treatment. ATG7 was found to induce neuronal autophagy during autophagy in the brain tissues of MCAO rats. In summary, Sevoflurane exerts protective effects on ischemic brain injury via inhibiting autophagy of neurons and microglia through the miR-7a-mediated downregulation of ATG7.

Arrb2 promotes endothelial progenitor cell-mediated postischemic neovascularization

Background and aim: Modulating biological functions of endothelial progenitor cells (EPCs) is essential for therapeutic angiogenesis in ischemic vascular diseases. This study aimed to explore the role and molecular mechanisms of β-arrestin 2 (Arrb2) in EPCs biology and angiogenic therapy. Methods: The influence of Arrb2 on postischemic neovascularization was evaluated in Arrb2-deficient mice. The proliferation, apoptosis, and various functions of EPCs were analyzed in vitro by manipulating the expression of Arrb2. Finally, the in vivo effect of Arrb2 on EPC-mediated neovascularization was investigated in a mouse model of hind-limb ischemia (HLI). Results: Arrb2-deficient mice exhibited impaired blood flow recovery based on laser Doppler measurements and reduced capillary density in the adductor muscle after unilateral HLI. Arrb2-deficient mice also showed restricted intraplug angiogenesis in subcutaneously implanted Matrigel plugs. In vitro, lentivirus-mediated Arrb2 overexpression promoted EPC proliferation, migration, adhesion, and tube formation, whereas Arrb2 knockdown had opposite effects. In addition, the overexpression of Arrb2 in EPCs protected them from hypoxia-induced apoptosis and improved intraplug angiogenesis ex vivo. Mechanistically, Arrb2 interacted with and activated extracellular signal-regulated kinase (ERK)1/2 and protein kinase B (Akt) signaling pathways. Finally, the transplantation of EPCs overexpressing Arrb2 resulted in a significantly higher blood flow restoration in ischemic hind limb and higher capillary density during histological analysis compared with control or Arrb2-knockdown EPC-treated nude mice. Conclusions: The data indicated that Arrb2 augmented EPC-mediated neovascularization through the activation of ERK and Akt signaling pathways. This novel biological function of Arrb2 might provide a potential therapeutic option to promote EPCs in the treatment of ischemic vascular diseases.

Short or moderate-time exposure to the inhalational anesthetics isoflurane and sevoflurane does not alter the marble-burying behavior in mice

Several studies suggest the involvement of glutamatergic neurotransmission in obsessive-compulsive disorder (OCD). Some NMDA glutamatergic receptor antagonists, such as the general anesthetic ketamine, have shown anti-OCD effects in preclinical and clinical studies. Therefore, we investigated whether the inhalational anesthetics isoflurane and sevoflurane, which are general anesthetics acting as NMDA receptor antagonists, would induce the same effects. To test our hypothesis, adult male Swiss mice were exposed to different concentrations of isoflurane (0.5, 1.5 or 3 %) or sevoflurane (0.8, 2.5 or 4 %) for 20 min (short-time exposure) or 1 h (moderate-time exposure) and submitted to the open field test (OFT) and the marble-burying test (MBT) in the same day (acute effect) or 7 days (long-lasting effect) after anesthetics administration. We found that single short or moderate-time exposure to isoflurane or sevoflurane, at sub-anesthetic or anesthetic concentrations, did not affect marble-burying behavior acutely or even 7 days after their administration. The same treatment schedules with isoflurane or sevoflurane did not impair total distance travelled in the OFT. A single moderate-time exposure to isoflurane (3 %) reduced, acutely, the central exploration of the open field, suggesting an anxiogenic-like effect of isoflurane in mice. Our results suggest that isoflurane and sevoflurane may not be promising anti-compulsive drugs.

The endocannabinoid system and stroke: A focused review

Stroke is an important cause of morbidity and mortality worldwide. Development of novel neuroprotectants is of paramount importance. This review seeks to summarize the recent evidence for the role of the endocannabinoid signaling system in stroke pathophysiology, as well as the evidence from preclinical studies regarding the efficacy of cannabinoids as neuroprotective therapies in the treatment of stroke. Recent evidence from rodent models implicating cannabinoid 1 receptor (CB1R), cannabinoid 2 receptor (CB2R), and CB1R and CB2R co-antagonism as neuroprotective strategies in stroke are reviewed. Rodent evidence for the therapeutic role of the endocannabinoid system in treating poststroke depression is reviewed. Finally, evidence for the role of cannabidiol, a publicly available cannabinoid that does not bind directly to known endocannabinoid receptors, as a stroke neuroprotectant is also reviewed. The review closes with a consideration of the role of human cannabinoid abuse in stroke and considers future directions for research on endocannabinoid-based stroke therapeutics.

Cdh1 overexpression improves emotion and cognitive-related behaviors via regulating hippocampal neuroplasticity in global cerebral ischemia rats

Post-stroke survivors exhibited cognitive deficits and performed emotional impairment. However, the effect of global cerebral ischemia on standard behavioral measures of emotionality and underlying mechanism remain largely unknown. Our previous work identified that down-regulation of Cdh1 contributed to ischemic neuronal death in rat, thus we hypothesized that Cdh1 exerts a role in emotionality after cerebral ischemia, and we investigated the effect of Cdh1 overexpression on neurogenic behaviors and possible mechanisms in transient global cerebral ischemia reperfusion (tGCI/R) rats. A series of behavioral tests were used to evaluate emotion and cognitive related behaviors, and molecular biological techniques were employed to investigate hippocampal neuroplasticity. The results showed that tGCI/R rats displayed anxiety- and depression-like behaviors and a certain degree of cognitive impairment, and these abnormal behaviors accompanied with a loss of hippocampal synapses and dendritic spines, disruption of dendrite arborization and decline in the level of GAP-43, synaptophysin, synapsin and PSD-95. However, Cdh1 overexpression improved negative emotionality, ameliorated cognitive deficits, rescued hippocampal synapses loss, prevented dendritic network disorganization, and increased the level of synaptic-associated proteins after tGCI/R. Taken together, these findings suggest that Cdh1 overexpression exerts a neuroprotective effect by regulating hippocampal neuroplasticity thus improving negative emotionality and cognitive deficits after tGCI/R.

MicroRNA-150 contributes to ischemic stroke through its effect on cerebral cortical neuron survival and function by inhibiting ERK1/2 axis via Mal

Ischemic stroke, caused by the blockage of blood supply, is a major cause of death worldwide. For identifying potential candidates, we explored the effects microRNA-150 (miR-150) has on ischemic stroke and its underlying mechanism by developing a stable middle cerebral artery occlusion (MCAO) rat model. Gene expression microarray analysis was performed to screen differentially expressed genes associated with MCAO. We evaluated the expression of miR-150 and Mal and the status of ERK1/2 axis in the brain tissues of MCAO rats. Then the cerebral cortical neurons (CCNs) were obtained and introduced with elevated or suppressed miR-150 or silenced Mal to validate regulatory mechanisms for miR-150 governing Mal in vitro. The relationship between miR-150 and Mal was verified by dual luciferase reporter gene assay. Besides, cell growth and apoptosis of CCNs were detected by means of MTT assay and flow cytometry analyses. We identified Mal as a downregulated gene in MCAO, based on the microarray data of GSE16561. MiR-150 was over-expressed and negatively targeted Mal in the brain tissues obtained from MCAO rats and their CCNs. Increasing miR-150 blocked the ERK1/2 axis, resulting in an inhibited cell growth of CNNs but an enhanced apoptosis. Furthermore, MiR-150 inhibition was observed to have effects on CNNs as opposed to those inhibited by miR-150 promotion. The key findings of this study support the notion that miR-150 under-expression-mediated direct promotion of Mal protects CNN functions through the activation of the ERK1/2 axis, and underscore the concept that miR-150 may represent a novel pharmacological target for ischemic stroke intervention.

Effects of sevoflurane on rats with ischemic brain injury and the role of the TREK-1 channel

The purpose of this investigation was to determine the effects of sevoflurane on rats with ischemic brain injury and to determine the potential role of the TREK-1 channel in this process. Normal rats were randomly divided into three groups: Sham operation, sevoflurane anesthesia or chloral hydrate anesthesia group, an additional group of TREK-1 knockout rats were also studied. Semi-quantitative PCR and western blot analysis confirmed the lack of TREK-1 expression in the brain of TREK-1 knockout rats. The thread-tie method was used to establish middle cerebral artery occlusion (MCAO) model to induce cerebral ischemic brain injury. All rates were treated for 4 days prior to ischemia (for 2 h) followed by a 24 h reperfusion period. Physiological indexes of rats in each group both prior to and after surgery showed no statistical difference (P>0.05). Neurological function was scored both before (no statistical difference) and after surgery where it was found to be significantly better (lower score) in the sevoflurane anesthesia group than in chloral hydrate anesthesia and TREK-1 knockout groups (P<0.01). The area of cerebral infarction was measured by triphenyl tetrazolium chloride staining and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay to detect the apoptosis of brain cells. TTC staining showed different degrees of cerebral infarction in the various groups; the area of cerebral infarction in sevoflurane anesthesia group was significantly lower than that in chloral hydrate anesthesia and TREK-1 knockout groups (P<0.01). TUNEL assay showed that the number of TUNEL-positive cells was significantly lower in sevoflurane anesthesia group than in TREK-1 knockout and chloral hydrate anesthesia groups (P<0.01). In conclusion, results from this investigation showed that sevoflurane can protect the nerve function of rats with cerebral ischemic brain injury possibly by affecting the expression of proteins involved in the TREK-1 signaling pathway.