Role of the hippocampal 5-HT1A receptor-mediated cAMP/PKA signalling pathway in sevoflurane-induced cognitivedysfunction in aged rats

Sevoflurane-induced cognitive effect on α7-nicotine receptor and M1 acetylcholine receptor expression in the hippocampus of aged rats

BACKGROUND

Sevoflurane treatment increases the incidence of postoperative cognitive dysfunction (POCD), and patients with POCD show a decline in cognitive abilities compared to preoperative levels.

OBJECTIVES

This study aimed to investigate whether the activation of α7 nicotinic acetylcholine receptor (α7nAChR) and the expression of M1 acetylcholine receptor (mAChR M1) in the hippocampus affects the cognitive function of aged rats.

METHODS

Forty-eight Sprague-Dawley (SD) rats of 1-week- and 12-months-old were divided into eight groups: four groups for α7nAChR and four groups for mAChR M1, respectively. All SD rats received 1.0-02% sevoflurane for α7nAChR and 1.0-02% sevoflurane for mAChR M1 for 2-6 h, respectively. The Y-maze test was used to assess the ability to learn and memory after receiving sevoflurane for 7 days at the same moment portion. RT-PCR was used to determine the expression of α7nAChR and mAChR M1 in the hippocampus of rats.

RESULTS

The α7nAChR mitigated the formation of sevoflurane-induced memory impairment by modulating the translocation of NR2B from the intracellular reservoir to the cell surface reservoir within the hippocampus. Next, sevoflurane-induced decline of cognitive function and significantly decreased mAChR M1 expression at mRNA levels.

CONCLUSION

α7nAChR regulates the trafficking of NR2B in the hippocampus of rats via the Src-family tyrosine kinase (SFK) pathway. This regulation is associated with cognitive deficits induced by sevoflurane in hippocampal development. Sevoflurane affects the cognitive function of rats by suppressing the mAChR M1 expression at mRNA levels in the hippocampus.

Effects of different anesthetic regimens on postoperative cognitive function of elderly patients undergoing thoracic surgery: a double-blinded randomized controlled trial

OBJECTIVE

Postoperative cognitive dysfunction (POCD) is a serious surgical complication. We assessed the different POCD incidences between anesthesia using sevoflurane and sevoflurane combined with dexmedetomidine, with propofol-based sedation in elderly patients who underwent a thoracic surgical procedure.

METHODS

A total of 90 patients aged 65 to 80 years old who underwent a thoracic surgical procedure at our hospital and 15 nonsurgical participants as controls, were enrolled in this study. Patients were divided in a randomized 1:1:1 ratio into 3 groups. All participants were randomized into a trial with three anesthesia groups (P, PS, PSD) or a control group (C) of healthy matches. All trial groups received distinct anesthetic combinations during surgery, while controls mirrored patient criteria.Group P (propofol and remifentanil were maintained during the surgery), Group PS (propofol, remifentanil, and sevoflurane were maintained during the surgery), and Group PSD (propofol, remifentanil, sevoflurane, and dexmedetomidine were maintained during the surgery).All participants were rated using a series of cognitive assessment scales before and three days after surgery. All participants were interviewed over the telephone, 7 days, 30 days, and 90 days postoperatively.

RESULTS

POCD incidences in the PSD (combined anesthetization with propofol, sevoflurane, and dexmedetomidine) group was significantly lower than that in the PS (combined anesthetization with propofol and sevoflurane) group, 1 day post-surgery (10.0% vs. 40.0%, P = 0.008), and the results were consistent at 3 days post-surgery. When the patients were assessed 7 days, 30 days, and 90 days postoperatively, there was no significant difference in POCD incidence among the three groups. Multivariate logistic regression analysis of POCD one day after surgery showed that education level was negatively correlated with incidence of POCD (P = 0.018) and single lung ventilation time was positively correlated with incidence of POCD (P = 0.001).

CONCLUSION

For elderly patients who underwent a thoracic surgical procedure, dexmedetomidine sedation shows an obvious advantage on improving short-term POCD incidence, which is caused by sevoflurane.

Sleep apnoea, gut dysbiosis and cognitive dysfunction

Sleep disorders are becoming increasingly common, and their distinct effects on physical and mental health require elaborate investigation. Gut dysbiosis (GD) has been reported in sleep-related disorders, but sleep apnoea is of particular significance because of its higher prevalence and chronicity. Cumulative evidence has suggested a link between sleep apnoea and GD. This review highlights the gut-brain communication axis that is mediated via commensal microbes and various microbiota-derived metabolites (e.g. short-chain fatty acids, lipopolysaccharide and trimethyl amine N-oxide), neurotransmitters (e.g. γ-aminobutyric acid, serotonin, glutamate and dopamine), immune cells and inflammatory mediators, as well as the vagus nerve and hypothalamic-pituitary-adrenal axis. This review also discusses the pathological role underpinning GD and altered gut bacterial populations in sleep apnoea and its related comorbid conditions, particularly cognitive dysfunction. In addition, the review examines the preclinical and clinical evidence, which suggests that prebiotics and probiotics may potentially be beneficial in sleep apnoea and its comorbidities through restoration of eubiosis or gut microbial homeostasis that regulates neural, metabolic and immune responses, as well as physiological barrier integrity via the gut-brain axis.

Scutellaria baicalensis Georgi stems and leaves flavonoids promote neuroregeneration and ameliorate memory loss in rats through cAMP-PKA-CREB signaling pathway based on network pharmacology and bioinformatics analysis

The aim of this study was to investigate the possible molecular mechanism of Scutellaria baicalensis Georgi stems and leaves flavonoids (SSF) in Alzheimer's disease (AD). The active ingredients of SSF and their targets were identified via network pharmacology and bioinformatics analysis. To test the successful establishment of a rat model of AD by Aβ25-35 combined with RHTGF-β1 and AlCl3, the Morris water maze test was used. To intervene, three different doses of SSF were administered. The model group and the control group were included among the parallel groups. A shuttle box test, immunohistochemistry, an enzyme-linked immunosorbent assay, qPCR and Western blot were performed to verify the results. Based on the intersection of genes among AD disease targets, SSF component targets, and differentially expressed genes in the single cell dataset GSE138852 and bulk-seq dataset GSE5281, nine genes related to the action of SSF on AD were identified. SSF have an important anti-AD pathway in the cAMP signaling pathway. SSF can ameliorate the conditioned memory impairment, augment Brdu protein expression and cAMP content; and differentially regulate the mRNA and protein expressions of GPCR, Gαs, AC1, PKA, and VEGF. The cAMP-PKA-CREB pathway in the SSF may mediate the ability of the SSF to ameliorate the composite-induced memory loss and nerve regeneration in rats induced by composite Aβ.

Rosemary (Rosmarinus officinalis L.) hydrosol based on serotonergic synapse for insomnia

ETHNOPHARMACOLOGICAL RELEVANCE

Rosemary (Rosmarinus officinalis L.) has been widely used as a traditional remedy for insomnia, depression and anxiety in China and Western countries. Modern pharmacological studies have shown that rosemary has important applications in neurological disorders. However, the mechanism of action of rosemary hydrosol in the treatment of insomnia is not known.

AIMS OF THE STUDY

Insomnia is closely linked to anxiety and depression, and its pathogenesis is related to biology, psychology, and sociology. Rosemary is a natural plant that has been used to treat insomnia and depression and has good biological activity, but its material basis and mechanism for the treatment of insomnia are not clear. Here, we report on the role of aqueous extracts of rosemary in the treatment of insomnia.

MATERIALS AND METHODS

The study was based on network pharmacology, using a combination of RNA-sequencing, "quantity-effect" weighting coefficients, and pharmacodynamic experiments. DL-4-chlorophenylalanine (PCPA) was intraperitoneally injected into SD rats to replicate the insomnia model with a blank, model, diazepam, and rosemary hydrosol low-, medium-, and high-dose groups were set up for the experiment. The key pathways in the treatment of insomnia with rosemary hydrosol were analyzed by molecular docking, open field assay, ELISA, western-Blot, Rt-PCR, and immunohistochemical assay.

RESULTS

Rosemary hydrosol was analyzed by GC-MS to identify 19 components. 1579 differential genes were obtained by RNA-Seq analysis, 533 targets for rosemary hydrosol and 2705 targets for insomnia, and 29 key targets were obtained by intersection. The KEGG results were ranked by "quantity-effect" weighting coefficients, resulting in serotonergic synapse was the key pathway for the treatment of insomnia with rosemary hydrosol. Molecular docking results showed that 1,7,7-trimethylbicyclo[2.2.1] heptan-2-one, 3-methyl-4-isopropylphenol, caryophyllene, and citronellol of rosemary hydrosol acted synergistically to achieve a therapeutic effect on insomnia. Caryophyllene acts on the HTR1A target by upregulating 5-HT1AR, leading to increased 5-HT release, and upregulation of ADCY5, cAMP, PKA and GABAA at serotonergic synapses; citronellol upregulated ADCY5 and 1,7,7-trimethylbicyclo[2.2.1] heptan-2-one, and 3-methyl-4-isopropylphenol up-regulated GABAA to improve insomnia symptoms. In open-field experiments, ELISA kits (5-HT, GABA, and DA), Western-blotting, Rt-PCR and immunohistochemical assay experiments, insomnia rats in the low-, medium- and high-dose groups of rosemary hydrosol showed different degrees of improvement compared with the model group.

CONCLUSIONS

It was shown that rosemary hydrosol may exert its therapeutic effects on insomnia through serotonergic synapses by combining RNA-Seq, "quantity-effect" weighting coefficients network pharmacology and pharmacodynamic experiments. We have provided a preliminary theoretical study for the development of rosemary hydrosol additive into a beverage for the treatment of insomnia, but it needs to be studied in depth. This study was conducted in rats and the results have limitations and may not apply to humans.

Chronic memantine disrupts spatial memory and up-regulates Htr1a gene expression in the hippocampus of GPR39 (zinc-sensing receptor) KO male mice

GPR39 is a receptor involved in zincergic neurotransmission, and its role in regulating psychological functions is an active area of research. The purported roles of GPR39 at the cellular level include regulation of inflammatory and oxidative stress response, and modulation of GABAergic and endocannabinoid neurotransmission. GPR39 knock-out (KO) mice exhibit episodic-like and spatial memory (ELM and SM, respectively) deficits throughout their lifetime, and are similar in that respect to senescent wild-type (WT) conspecifics. Since a role for zinc has been postulated in neurodegenerative disorders, in this study we investigated the possibility of a pharmacological rescue of both types of declarative memory with memantine - a noncompetitive NMDAR antagonist used for slowing down dementia; or, a putative GPR39 agonist - TC-G 1008. First, we tested adult WT and GPR39KO male mice under acute 5 mg/kg memantine or vehicle treatment in an object recognition task designed to simultaneously probe the "what?", "where?" and "when?" components of ELM. Next, we investigated the impact of chronic memantine or TC-G 1008 on ELM and SM (Morris water maze, MWM) in both WT and GPR39KO mice. Following chronic experiments, we assessed with qRT-PCR hippocampal gene expression of targets previously associated with GPR39. We report: no effects of acute memantine on ELM; a tendency to improve the "where?" component of ELM in both WT and GPR39 KO mice following 12 days of memantine; and, a disruption of SM in GPR39KO mice after 24 days of memantine treatment. The latter result was associated with upregulation of Htr1a hippocampal expression.

Nicotinamide mononucleotide (NMN) ameliorated Nonylphenol-induced learning and memory impairment in rats via the central 5-HT system and the NAD+/SIRT1/MAO-A pathway

Nonylphenol (NP) exposure can trigger neurotoxicity and cause learning and memory impairment. Nicotinamide mononucleotide (NMN) has a therapeutic effect on neurodegenerative diseases, but the role of NMN on NP-induced learning and memory impairment is not known. Here, we examined the mitigative effect of NMN on the impaired learning and memory ability of rats exposed to NP. The NP impaired learning and memory in rats, while the low-dose intervention with NMN significantly prolonged the step-through latency of the PAT and improved the NAMPT and NMNAT1 content in brain tissue. At the same time, the NMN intervention also increased the content of 5-HTR_1A, 5-HTR₄, and 5-HTR₆ related to learning and memory in the hippocampus. In line with this, we found that the NMN intervention activated the SIRT1/MAO-A pathway in brain tissue. NMN intervention, especially at 125 mg/kg doses, may improve rats' NP-induced learning and memory impairment via the central 5-HT system and the NAD⁺/SIRT1/MAO-A pathway in the brain.

Derivatives of 3, 4, 5-Trimethoxycinnamic Acid Ameliorate Stress-Induced Anxiety in Mice and Rats

Stress is an overwhelming problem associated with neuronal damage leading to anxiety and depression. The compound 3, 4, 5-trimethoxycinnamic acid (TMCA) has shown anti-stress effects; however, its derivatives remained unknown for their anxiolytic properties. Here, therefore, we investigated derivatives of TMCA (dTMCA) for their anxiolytic effects using immobilization and electric shock-induced stress in rats. Derivatives of TMCA ameliorated anxiety in mice and rats revealed by extended period of time spent in the open arms of elevated plus maze. Stress-mediated repression of tyrosine hydroxylase (TH) protein expression in the amygdala regions of rat brain and dopamine levels in the PC12 cells was restored by two selected derivatives (TMCA#5 and TMCA#9). Unlike TH expression, stress-induced protein expression of phospho-extracellular signal-regulated kinase (pERK) was unaffected by both derivatives in rats. Given the preferential inhibitory activity of dTMCA on dopamine and serotonin receptors, serotonergic road map of cellular signaling could be their target for anxiolytic effects. Thus, dTMCA would be promising agents to prevent neuronal damage associated with rampant stressful conditions.

Cross state-dependent memory retrieval between cannabinoid CB1 and serotonergic 5-HT1A receptor agonists in the mouse dorsal hippocampus

Understanding the neurobiological mechanisms of drug-related learning and memory formation may help the treatment of cognitive disorders. Dysfunction of the cannabinoid and serotonergic systems has been demonstrated in learning and memory disorders. The present paper investigates the phenomenon called state-dependent memory (SDM) induced by ACPA (a selective cannabinoid CB1 receptor agonist) and 8-OH-DPAT (a nonselective 5-HT1A receptor agonist) with special focus on the role of the 5-HT1A receptor in the effects of both ACPA and 8-OH-DPAT SDM and cross state-dependent memory retrieval between ACPA and 8-OH-DPAT in a step-down inhibitory avoidance task. The dorsal hippocampal CA1 regions of adult male NMRI mice were bilaterally cannulated, and all drugs were microinjected into the intended injection sites. A single-trial step-down inhibitory avoidance task was used to assess memory retrieval and state-dependence. Post-training and/or pre-test microinjections of ACPA (1 and 2 ng/mouse) and 8-OH-DPAT (0.5 and 1 μg/mouse) dose-dependently induced amnesia. Pre-test administration of the same doses of ACPA and 8-OH-DPAT reversed the post-training ACPA- and 8-OH-DPAT-induced amnesia, respectively. This phenomenon has been named SDM. 8-OH-DPAT (1 μg/mouse) reversed the amnesia induced by ACPA (0.5, 1, and 2 ng/mouse) and induced ACPA SDM. ACPA (2 ng/mouse) reversed the amnesia induced by 8-OH-DPAT (0.25, 0.5, and 1 μg/mouse) and induced 8-OH-DPAT SDM. Pre-test administration of a 5-HT1A receptor antagonist, (S)-WAY 100135 (0.25 and 0.5 μg/mouse), 5 min before ACPA and 8-OH-DPAT dose-dependently inhibited ACPA- and 8-OH-DPAT-induced SDM, respectively. The present study results demonstrated ACPA- and 8-OH-DPAT- induced SDM. Overall, the data revealed that dorsal hippocampal 5-HT1A receptor mechanisms play a pivotal role in modulating cross state-dependent memory retrieval between ACPA and 8-OH-DPAT.

Associations Between a Polymorphism in the Rat 5-HT1A Receptor Gene Promoter Region (rs198585630) and Cognitive Alterations Induced by Microwave Exposure

The nervous system is a sensitive target of electromagnetic radiation (EMR). Chronic microwave exposure can induce cognitive deficits, and 5-HT system is involved in this effect. Genetic polymorphisms lead to individual differences. In this study, we evaluated whether the single-nucleotide polymorphism (SNP) rs198585630 of 5-HT_1A receptor is associated with cognitive alterations in rats after microwave exposure with a frequency of 2.856 GHz and an average power density of 30 mW/cm². Rats were exposed to microwaves for 6 min three times a week for up to 6 weeks. PC12 cells and 293T cells were exposed to microwaves for 5 min up to 3 times at 2 intervals of 5 min. Transcriptional activity of 5-HT_1A receptor promoter containing rs198585630 C/T allele was determined in vitro. Electroencephalograms (EEGs), spatial learning and memory, and mRNA and protein expression of 5-HT_1A receptor were evaluated in vivo. We demonstrated that transcriptional activity of 5-HT_1A receptor promoter containing rs198585630 C allele was higher than that of 5-HT_1A receptor promoter containing T allele. The transcriptional activity of 5-HT_1A receptor promoter was stimulated by 30 mW/cm² microwave exposure, and rs198585630 C allele was more sensitive to microwave exposure, as it showed stronger transcriptional activation. Rats carrying rs198585630 C allele exhibited increased mRNA and protein expression of 5-HT_1A receptor and were more susceptible to 30 mW/cm² microwave exposure, showing cognitive deficits and inhibition of brain electrical activity. These findings suggest SNP rs198585630 of the 5-HT_1A receptor is an important target for further research exploring the mechanisms of hypersensitivity to microwave exposure.

Update on the Mechanism and Treatment of Sevoflurane-Induced Postoperative Cognitive Dysfunction

Sevoflurane is one of the most widely used anesthetics for the induction and maintenance of general anesthesia in surgical patients. Sevoflurane treatment may increase the incidence of postoperative cognitive dysfunction (POCD), and patients with POCD exhibit lower cognitive abilities than before the operation. POCD affects the lives of patients and places an additional burden on patients and their families. Understanding the mechanism of sevoflurane-induced POCD may improve prevention and treatment of POCD. In this paper, we review the diagnosis of POCD, introduce animal models of POCD in clinical research, analyze the possible mechanisms of sevoflurane-induced POCD, and summarize advances in treatment for this condition.

Sevoflurane protects against ischemia-reperfusion injury in mice after total knee arthroplasty via facilitating RASD1-mediated protein kinase A pathway activation

This study aimed to explore effects of Sevoflurane on ischemia-reperfusion (I/R) injury after total knee arthroplasty (TKA). To explore potential molecular mechanism, Ras related dexamethasone induced 1 (RASD1), a Protein kinase A (PKA) activator, frequently associated with various models of I/R injury, was also investigated. In vivo mouse models with I/R injury after TKA and in vitro cell models with I/R injury were induced. Contents of creatinine kinase (CK), lactic dehydrogenase (LDH), superoxide dismutase (SOD), and malondialdehyde (MDA), serum levels of inflammatory factors, expression of PKA pathway-related genes and cell proliferation and apoptosis were measured. RASD1 was altered and PKA pathway was inhibited in mice and cells to elucidate the involvement of RASD1 and PKA pathway in Sevoflurane treatment on I/R injury. RASD1 was upregulated in I/R injury after TKA. Sevoflurane treatment or silencing RASD1 reduced RASD1 expression, CK, LDH and MDA contents, inflammation, apoptosis, but increased proliferation, SOD content, cAMP expression, and extents of PKA and cAMP responsive element binding protein (CREB) phosphorylation in skeletal muscle cells of I/R injury. Additionally, PKA pathway activation potentiated the therapeutic effect of Sevoflurane on I/R injury after TKA. Altogether, Sevoflurane treatment confines I/R injury after TKA via RASD1-mediated PKA pathway activation.

Biased agonism in drug discovery: Is there a future for biased 5-HT1A receptor agonists in the treatment of neuropsychiatric diseases?

Serotonin (5-HT) is one of the fundamental neurotransmitters that contribute to the information essential for an organism's normal, physiological function. Serotonin acts centrally and systemically. The 5-HT_1A receptor is the most widespread serotonin receptor, and participates in many brain-related disorders, including anxiety, depression, and cognitive impairments. The 5-HT_1A receptor can activate several different biochemical pathways and signals through both G protein-dependent and G protein-independent pathways. Preclinical experiments indicate that distinct signaling pathways in specific brain regions may be crucial for antidepressant-like, anxiolytic-like, and procognitive responses. Therefore, the development of new ligands that selectively target a particular signaling pathway(s) could open new possibilities for more effective and safer pharmacotherapy. This review discusses the current state of preclinical studies focusing on the concept of functional selectivity (biased agonism) regarding the 5-HT_1A receptor and its role in antidepressant-like, anxiolytic-like, and procognitive regulation. Such work highlights not only the differential effects of targeted autoreceptors, vs. heteroreceptors, but also the importance of targeting specific downstream intracellular signaling processes, thereby enhancing favorable over unfavorable signaling activation.

Leite L, da S. Tavares-Henriques M, Lopes LAF, Oliveira LGR, Silva-Filho SE, da Silveira APS, Cuman RKN, de S. Silva-Comar FM, Comar JF, do A. Brasileiro L, dos Santos JN, de Freitas WR, Leão KV, da Silva JG, Klein RC, Klein MHF, da S. Ramos BH, Fernandes CKC, de L. Ribas DG, Oesterreich SA. Modulation of the Serotonergic Receptosome in the Treatment of Anxiety and Depression: A Narrative Review of the Experimental Evidence

Serotonin (5-HT) receptors are found throughout central and peripheral nervous systems, mainly in brain regions involved in the neurobiology of anxiety and depression. 5-HT receptors are currently promising targets for discovering new drugs for treating disorders ranging from migraine to neuropsychiatric upsets, such as anxiety and depression. It is well described in the current literature that the brain expresses seven types of 5-HT receptors comprising eighteen distinct subtypes. In this article, we comprehensively reviewed 5-HT1-7 receptors. Of the eighteen 5-HT receptors known today, thirteen are G protein-coupled receptors (GPCRs) and represent targets for approximately 40% of drugs used in humans. Signaling pathways related to these receptors play a crucial role in neurodevelopment and can be modulated to develop effective therapies to treat anxiety and depression. This review presents the experimental evidence of the modulation of the “serotonergic receptosome” in the treatment of anxiety and depression, as well as demonstrating state-of-the-art research related to phytochemicals and these disorders. In addition, detailed aspects of the pharmacological mechanism of action of all currently known 5-HT receptor families were reviewed. From this review, it will be possible to direct the rational design of drugs towards new therapies that involve signaling via 5-HT receptors.

Sub-Acute Treatment of Curcumin Derivative J147 Ameliorates Depression-Like Behavior Through 5-HT1A-Mediated cAMP Signaling

Background

Major depressive disorder (MDD) is a severe mental disorder related to the deficiency of monoamine neurotransmitters, particularly to abnormalities of 5-HT (5-hydroxytryptamine, serotonin) and its receptors. Our previous study suggested that acute treatment with a novel curcumin derivative J147 exhibited antidepressant-like effects by increasing brain derived neurotrophic factor (BDNF) level in the hippocampus of mice. The present study expanded upon our previous findings and investigated the antidepressant-like effects of sub-acute treatment of J147 for 3 days in male ICR mice and its possible relevancy to 5-HT_1A and 5-HT_1B receptors and downstream cAMP-BDNF signaling.

Methods

J147 at doses of 1, 3, and 9 mg/kg (via gavage) was administered for 3 days, and the anti-immobility time in the forced swimming and tail suspension tests (FST and TST) was recorded. The radioligand binding assay was used to determine the affinity of J147 to 5-HT_1A and 5-HT_1B receptor. Moreover, 5-HT_1A or 5-HT_1B agonist or its antagonist was used to determine which 5-HT receptor subtype is involved in the antidepressant-like effects of J147. The downstream signaling molecules such as cAMP, PKA, pCREB, and BDNF were also measured to determine the mechanism of action.

Results

The results demonstrated that sub-acute treatment of J147 remarkably decreased the immobility time in both the FST and TST in a dose-dependent manner. J147 displayed high affinity in vitro to 5-HT_1A receptor prepared from mice cortical tissue and was less potent at 5-HT_1B receptor. These effects of J147 were blocked by pretreatment with a 5-HT_1A antagonist NAD-299 and enhanced by a 5-HT_1A agonist 8-OH-DPAT. However, 5-HT_1B receptor antagonist NAS-181 did not appreciably alter the effects of J147 on depression-like behaviors. Moreover, pretreatment with NAD-299 blocked J147-induced increases in cAMP, PKA, pCREB, and BDNF expression in the hippocampus, while 8-OH-DPAT enhanced the effects of J147 on these proteins’ expression.

Conclusion

The results suggest that J147 induces rapid antidepressant-like effects during a 3-day treatment period without inducing drug tolerance. These effects might be mediated by 5-HT_1A-dependent cAMP/PKA/pCREB/BDNF signaling.

A New Rat Model of Chronic Cerebral Hypoperfusion Resulting in Early-Stage Vascular Cognitive Impairment

Objective

Currently, most models of vascular cognitive impairment are established by occluding the carotid arteries uni- or bilaterally to reduce the cerebral blood flow mimicking chronic cerebral hypoxia. Due to the sudden blood flow interruption, a gradual narrowing of the carotid artery cannot be completely imitated. This paper aims to establish a bilateral carotid stenosis model with mild cognitive dysfunction and mild white matter changes to simulate patients with vascular predementia.

Methods

Aged Wistar rats (18 months old) underwent either bilateral common carotid artery stenosis (BCAS) or occlusion (BCAO) surgery or a sham operation (control group). The cerebral blood flow in the frontal cortex was measured using Doppler flowmetry. Thirty days after surgery, cognitive function impairments were determined with the Morris water maze; cerebral magnetic resonance imaging was performed to detect changes in fractional anisotropy to assess white matter injuries, and histological studies were performed.

Results

The aged rats in the BCAS group showed a more gradual cerebral blood flow reduction and a lower mortality rate (11%) compared to rats in the BCAO group. The water maze test revealed a more marginal impairment affecting spatial learning and memory in rats with BCAS than in rats with BCAO. Diffusion tensor imaging detected white matter injuries in the hippocampus and cerebral cortex of BCAS rats. Particularly, a small portion of nerve fibers of the lateral somatosensory cortex was significantly different between rats of the BCAO and BCAS groups. In the BCAS group, the microscopic structure of the hippocampal CA1 region changed slightly after 30 days and sustained a slight mitochondrial crista crack. Fluorescence staining indicated that the number of GFAP-positive cells was increased in rat brains of the BCAS group, and this phenomenon was even more pronounced in the BCAO group. The hnRNPA2/B1 and GABA_AR-α1 expression levels were significantly decreased in the hippocampus of rats with BCAS compared to those of controls.

Conclusion

Severe bilateral carotid stenosis induced mild cognitive dysfunction and slight structural changes in the brains of aged rats. Thus, a chronic cerebral hypoperfusion model was successfully established.

Forkhead Box O1-p21 Mediates Macrophage Polarization in Postoperative Cognitive Dysfunction Induced by Sevoflurane

PURPOSE

The current study was conducted in order to investigate the role of Forkhead box O1 and p21-mediated macrophage polarization in postoperative cognitive dysfunction induced by sevoflurane.

METHODS

There involved a total of 30 healthy mice that were randomly divided into two groups: control group (without any treatment) and anaesthesia group (treated with sevoflurane inhalation). The effects of sevoflurane on cognitive function (memory) in mice were studied by trace fear conditioned reflex, and the effects of systemic inflammation and behavior after operation were measured by enzyme-linked immunosorbent assay (ELISA), the concentrations of CD163 and tumor necrosis factor-α (TNF-α) were measured. The expression of macrophage phenotype was observed by immunofluorescence staining, the expression levels of M1 and M2 markers mRNA were detected by real-time fluorescence quantitative PCR (RT-PCR), and the expression levels of FoxO1 and p21 were analyzed by immunoblotting (Western blot).

RESULTS

Compared with the control group, the freezing time in the anesthesia group was lower than that in the control group (P<0.01), indicating that sevoflurane anesthesia led to the decrease of cognitive ability. The blood concentrations of CD163 and TNF-α increased significantly at 24 h after the operation with sevoflurane anesthesia (P<0.05). Fluorescence microscopic observation showed that M2 was the main type of macrophages in normal tissues, while M1 and M2 phenotypes were highly expressed in sevoflurane anesthetized tissues at the same time, especially in M1 phenotypes (P<0.01). The polarization of macrophages in the anesthetic group showed the high level of M1 mRNA, and the expression levels of TNF-α, monocyte chemotactic protein 1(MCP-1) and Interleukin-6 (IL-6)mRNA in the anesthetic group were significantly higher than those in the control group (P<0.05). The expression levels of M2 mRNA such as transforming growth factor-β (TGF-β) and IL-10 were significantly lower than those in the control group (P<0.05). Compared with the control group, the expression of FoxO1 and p21 protein in the anesthesia group was significantly lower than that in the control group with a significant statistical difference (P<0.01).

CONCLUSION

This study offers a theoretical basis and insight for further understanding of the prevention and treatment of cognitive dysfunction induced by anesthetic drugs.

Activation of 5-HT1A Receptors Promotes Retinal Ganglion Cell Function by Inhibiting the cAMP-PKA Pathway to Modulate Presynaptic GABA Release in Chronic Glaucoma

Serotonin (5-hydroxytryptamine, 5-HT) receptor agonists are neuroprotective in CNS injury models. However, the neuroprotective functional implications and synaptic mechanism of 8-hydroxy-2- (di-n-propylamino) tetralin (8-OH-DPAT), a serotonin receptor (5-HT1A) agonist, in an adult male Wistar rat model of chronic glaucoma model remain unknown. We found that ocular hypertension decreased 5-HT1A receptor expression in rat retinas because the number of retinal ganglion cells (RGCs) was significantly reduced in rats with induced ocular hypertension relative to that in control retinas and 8-OH-DPAT enhanced the RGC viability. The protective effects of 8-OH-DPAT were blocked by intravitreal administration of the selective 5-HT1A antagonist WAY-100635 or the selective GABA_A receptor antagonist SR95531. Using patch-clamp techniques, spontaneous and miniature GABAergic IPSCs (sIPSCs and mIPSCs, respectively) of RGCs in rat retinal slices were recorded. 8-OH-DPAT significantly increased the frequency and amplitude of GABAergic sIPSCs and mIPSCs in ON- and OFF-type RGCs. Among the signaling cascades mediated by the 5-HT1A receptor, the role of cAMP-protein kinase A (PKA) signaling was investigated. The 8-OH-DPAT-induced changes at the synaptic level were enhanced by PKA inhibition by H-89 and blocked by PKA activation with bucladesine. Furthermore, the density of phosphorylated PKA (p-PKA)/PKA was significantly increased in glaucomatous retinas and 8-OH-DPAT significantly decreased p-PKA/PKA expression, which led to the inhibition of PKA phosphorylation upon relieving neurotransmitter GABA release. These results showed that the activation of 5-HT1A receptors in retinas facilitated presynaptic GABA release functions by suppressing cAMP-PKA signaling and decreasing PKA phosphorylation, which could lead to the de-excitation of RGC circuits and suppress excitotoxic processes in glaucoma.SIGNIFICANCE STATEMENT We found that serotonin (5-HT) receptors in the retina (5-HT1A receptors) were downregulated after intraocular pressure elevation. Patch-clamp recordings demonstrated differences in the frequencies of miniature GABAergic IPSCs (mIPSCs) in ON- and OFF-type retinal ganglion cells (RGCs) and RGCs in normal and glaucomatous retinal slices. Therefore, phosphorylated protein kinase A (PKA) inhibition upon release of the neurotransmitter GABA was eliminated by 8-hydroxy-2- (di-n-propylamino) tetralin (8-OH-DPAT), which led to increased levels of GABAergic mIPSCs in ON- and OFF-type RGCs, thus enhancing RGC viability and function. These protective effects were blocked by the GABA_A receptor antagonist SR95531 or the 5-HT1A antagonist WAY-100635. This study identified a novel mechanism by which activation of 5-HT1A receptors protects damaged RGCs via the cAMP-PKA signaling pathway that modulates GABAergic presynaptic activity.