Enhancing the action of serotonin by three different mechanisms prevents spontaneous seizure-induced mortality in Dravet mice.

OBJECTIVE: Sudden unexpected death in epilepsy (SUDEP) is an underestimated complication of epilepsy. Previous studies have demonstrated that enhancement of serotonergic neurotransmission suppresses seizure-induced sudden death in evoked seizure models. However, it is unclear whether elevated serotonin (5-HT) function will prevent spontaneous seizure-induced mortality (SSIM), which is characteristic of human SUDEP. We examined the effects of 5-HT-enhancing agents that act by three different pharmacological mechanisms on SSIM in Dravet mice, which exhibit a high incidence of SUDEP, modeling human Dravet syndrome. METHODS: Dravet mice of both sexes were evaluated for spontaneous seizure characterization and changes in SSIM incidence induced by agents that enhance 5-HT-mediated neurotransmission. Fluoxetine (a selective 5-HT reuptake inhibitor), fenfluramine (a 5-HT releaser and agonist), SR 57227 (a specific 5-HT3 receptor agonist), or saline (vehicle) was intraperitoneally administered over an 8-day period in Dravet mice, and the effect of these treatments on SSIM was examined. RESULTS: Spontaneous seizures in Dravet mice generally progressed from wild running to tonic seizures with or without SSIM. Fluoxetine at 30 mg/kg, but not at 20 or 5 mg/kg, significantly reduced SSIM compared with the vehicle control. Fenfluramine at 1-10 mg/kg, but not .2 mg/kg, fully protected Dravet mice from SSIM, with all mice surviving. Compared with the vehicle control, SR 57227 at 20 mg/kg, but not at 10 or 5 mg/kg, significantly lowered SSIM. The effect of these drugs on SSIM was independent of sex. SIGNIFICANCE: Our data demonstrate that elevating serotonergic function by fluoxetine, fenfluramine, or SR 57227 significantly reduces or eliminates SSIM in Dravet mice in a sex-independent manner. These findings suggest that deficits in serotonergic neurotransmission likely play an important role in the pathogenesis of SSIM, and fluoxetine and fenfluramine, which are US Food and Drug Administration-approved medications, may potentially prevent SUDEP in at-risk patients.

A unified hypothesis of SUDEP: Seizure-induced respiratory depression induced by adenosine may lead to SUDEP but can be prevented by autoresuscitation and other restorative respiratory response mechanisms mediated by the action of serotonin on the periaqueductal gray.

Sudden unexpected death in epilepsy (SUDEP) is a major cause of death in people with epilepsy (PWE). Postictal apnea leading to cardiac arrest is the most common sequence of terminal events in witnessed cases of SUDEP, and postconvulsive central apnea has been proposed as a potential biomarker of SUDEP susceptibility. Research in SUDEP animal models has led to the serotonin and adenosine hypotheses of SUDEP. These neurotransmitters influence respiration, seizures, and lethality in animal models of SUDEP, and are implicated in human SUDEP cases. Adenosine released during seizures is proposed to be an important seizure termination mechanism. However, adenosine also depresses respiration, and this effect is mediated, in part, by inhibition of neuronal activity in subcortical structures that modulate respiration, including the periaqueductal gray (PAG). Drugs that enhance the action of adenosine increase postictal death in SUDEP models. Serotonin is also released during seizures, but enhances respiration in response to an elevated carbon dioxide level, which often occurs postictally. This effect of serotonin can potentially compensate, in part, for the adenosine-mediated respiratory depression, acting to facilitate autoresuscitation and other restorative respiratory response mechanisms. A number of drugs that enhance the action of serotonin prevent postictal death in several SUDEP models and reduce postictal respiratory depression in PWE. This effect of serotonergic drugs may be mediated, in part, by actions on brainstem sites that modulate respiration, including the PAG. Enhanced activity in the PAG increases respiration in response to hypoxia and other exigent conditions and can be activated by electrical stimulation. Thus, we propose the unifying hypothesis that seizure-induced adenosine release leads to respiratory depression. This can be reversed by serotonergic action on autoresuscitation and other restorative respiratory responses acting, in part, via the PAG. Therefore, we hypothesize that serotonergic or direct activation of this brainstem site may be a useful approach for SUDEP prevention.

Response to Singh et al. 2023: It is premature for a unified hypothesis of sudden unexpected death in epilepsy: A great amount of research is still needed to understand the multisystem cascade.

In response to the comments by Singh and colleagues about our recent paper proposing a unified hypothesis of SUDEP, we definitely agree that more research is needed. This research should include studies in other models, including Dravet mice, emphasized by Singh et al. However, we strongly believe the hypothesis is timely, because it is based on the continuing progress on SUDEP-related research on serotonin (5-HT) and adenosine as well as neuroanatomical findings.We propose testing of 5-HT enhancing drugs, neurotoxicity blocking drugs, such as N-methyl-D-aspartate (NMDA) antagonists and periaqueductal gray (PAG) electrical stimulation for SUDEP prevention. There are FDA-approved drugs that enhance the action of 5-HT, including fluoxetine and fenfluramine, which is approved for Dravet syndrome. NMDA antagonists, including memantine and ketamine, are also approved for other disorders. PAG electrical stimulation, which is proposed to activate a suffocation alarm, is also approved to treat other conditions and is known to enhance respiration. Experiments using these methods are currently being carried out in animal studies. If these approaches are validated in SUDEP models, treatments could be evaluated relatively quickly in patients with epilepsy (PWE) who exhibit a biomarker for high SUDEP risk, such as peri-ictal respiratory abnormalities. An example of such a study is the ongoing clinical trial of a selective serotonin reuptake inhibitor in PWE. Although, gene-based therapies may ultimately become treatments of choice to prevent SUDEP, as Singh et al suggested, one or more of the approaches we proposed could become temporizing treatments before gene-based therapies can be available. Establishing genetic treatments would require extensive time for each of the genetic abnormalities associated with SUDEP, and too many PWE are likely to die in the meantime.The temporizing treatments may help to reduce the incidence of SUDEP sooner, which is urgently needed.

The impact of powdered activated carbon types on membrane anti-fouling mechanism in membrane bioreactors.

Dosing powdered activated carbon (PAC) has been proven to be an economical and effective method to mitigate membrane fouling. However, the effects of pretreated PAC with different redox properties on membrane fouling still need to be further investigated. Here, the impact of commercial PAC, oxidized-PAC, and reduced-PAC on membrane fouling was investigated in membrane bioreactors (MBRs). Surprisingly, the filtration cycles were extended from 12-36 h to 132-156 h only by dosing reduced-PAC and commercial PAC with a finial dosage of 3 g/L, which were provided with reductive properties. However, few improvements of filtration cycle (less than 50 h) were achieved by dosing oxidized-PAC in the same dosage, which had the same adsorption performance as reduced-PAC and commercial PAC. The biomass and foulant concentration suggested that the enhanced anti-fouling performances by PAC with reductive properties were mainly attributed to the reduction of extracellular polymer substances (EPS) and soluble microbial products (SMP) content in the bulk solutions after 14 days of continuous operation. The model foulant degradation tests and the confocal laser scanning microscope (CLSM) images of activated sludge further demonstrated that PAC with reductive properties directly affected the microbial activities by controlling the EPS and SMP concentrations in the bulk solution, thereby suppressing membrane fouling. Such a finding provides new insights into anti-fouling mechanisms that the redox properties of PAC played a decisive role in membrane fouling mitigation, and also provides a strategy to prolong the anti-fouling effects by restoring the reductive properties of PAC. KEY POINTS: • The anti-fouling mechanisms of PAC with reductive property were investigated. • Reductive property was the main reason for fouling control instead of adsorption. • PAC with reductive property hindered the sludge activity to produce fewer foulants.

Acylglycerol kinase promotes paclitaxel resistance in nasopharyngeal carcinoma cells by regulating FOXM1 via the JAK2/STAT3 pathway.

OBJECTIVE: Drug resistance is an important factor that impedes the treatment of nasopharyngeal cancer (NPC). Acylglycerol kinase (AGK) has been found to be overexpressed in NPC and correlates with poor prognosis. Our objective was to demonstrate the effect of AGK on paclitaxel resistance in NPC and determine the underlying mechanisms. METHODS: MTT assay was employed to determine the IC50 of paclitaxel in NPC cells after different treatments. Flow cytometry assays were employed to evaluate cell apoptosis. RT-qPCR and Western blot assays were used to detect alterations in mRNA and protein expression, respectively. Luciferase assays and chromatin immunoprecipitation (ChIP) assays were used to determine the relationship between and the regulatory effect of STAT3 on the promoter of FOXM1. RESULTS: AGK was elevated in paclitaxel-resistant NPC cells, and knockdown of AGK suppressed the resistance of CNE1-TR and CNE2-TR cells to paclitaxel. Moreover, upregulation of FOXM1 rescued the effects of AGK knockdown. Furthermore, the JAK2/STAT3 signalling pathway was overactivated in CNE1-TR and CNE2-TR cells, and knockdown of AGK suppressed JAK2/STAT3 signalling. STAT3 was verified to bind to and activate the promoter region of FOXM1. An in vivo tumour xenograft assay also verified that AGK knockdown inhibited tumour growth and mitigated paclitaxel resistance by regulating the JAK2/STAT3/FOXM1 axis. CONCLUSION: AGK levels were increased in paclitaxel-resistant NPC cells. AGK activates JAK2/STAT3 signalling, thus promoting FOXM1 transcription and eventually enhancing the drug resistance of NPC cells.

Testosterone attenuates sevoflurane-induced tau phosphorylation and cognitive impairment in neonatal male mice.

BACKGROUND: Sevoflurane anaesthesia induces phosphorylation of the microtubule-associated protein tau and cognitive impairment in neonatal, but not adult, mice. The underlying mechanisms remain largely to be determined. Sex hormones can be neuroprotective, but little is known about the influence of testosterone on age-dependent anaesthesia effects. METHODS: Six- and 60-day-old male mice received anaesthesia with sevoflurane 3% for 2 h daily for 3 days. Morris water maze, immunoassay, immunoblotting, co-immunoprecipitation, nanobeam technology, and electrophysiology were used to assess cognition; testosterone concentrations; tau phosphorylation; glycogen synthase kinase-3ß (GSK3ß) activation; binding or interaction between tau and GSK3ß; and neuronal activation in mice, cells, and neurones. RESULTS: Compared with 60-day-old male mice, 6-day-old male mice had lower testosterone concentrations (3.03 [0.29] vs 0.44 [0.12] ng ml-1; P<0.01), higher sevoflurane-induced tau phosphorylation in brain (133 [20]% vs 100 [6]% in 6-day-old mice, P<0.01; 103 [8]% vs 100 [13]% in 60-day-old mice, P=0.77), and sevoflurane-induced cognitive impairment. Testosterone treatment increased brain testosterone concentrations (1.76 [0.10] vs 0.39 [0.05] ng ml-1; P<0.01) and attenuated the sevoflurane-induced tau phosphorylation and cognitive impairment in neonatal male mice. Testosterone inhibited the interaction between tau and GSK3ß, and attenuated sevoflurane-induced inhibition of excitatory postsynaptic currents in hippocampal neurones. CONCLUSIONS: Lower brain testosterone concentrations in neonatal compared with adult male mice contributed to age-dependent tau phosphorylation and cognitive impairment after sevoflurane anaesthesia. Testosterone might attenuate the sevoflurane-induced tau phosphorylation and cognitive impairment by inhibiting the interaction between tau and GSK3ß.

Numerical study of hydrodynamic characteristics in a moving bed biofilm reactor.

The moving bed biofilm reactor (MBBR) has certain advantages, such as high wastewater treatment efficiency, low maintenance and operating costs, and simple operation. It has emerged as a valuable option for small decentralized facilities. The filling ratio, aeration mode and aeration intensity are the main factors that affect the performance of MBBRs in wastewater treatment. However, the information that concerns the used criteria that pertain to the process design for the MBBR is not adequate. In this study, a three dimensional computational fluid dynamics (CFD) model was constructed and the maximum error was only 1.98%, which was much smaller than the traditional 2D-CFD model. The filling ratio, aeration mode and aeration intensity of MBBR were optimized by CFD model from the point of view of fluid mechanics. The results show that the fluidization performance of the filling is the best under the one-side aeration mode with 30% filling ratio. The cost-performance ratio of the reactor with 30% filling ratio was 1.53, 25% and 35% filling ratio were only 1.17 and 1.14 respectively. Increasing the aeration intensity could improve the fluidization performance. However, the effect of high aeration intensity on the fluidization performance of the carrier was limited and the energy consumption increased greatly. The results revealed that when the aeration intensity increased from 0.07 min-1 to 0.13 min-1, the proportion of the carrier area increased by 16.56%. The proportion of the carrier area with an aeration rate of 0.20 min-1 was only 4.23%, which is higher than 0.13 min-1. The main factors that control the fluidization of the carrier were the range of the flow zone and the flow velocity of the liquid. Increasing the range of the flow zone could facilitate the flow of the carriers. The critical value of the flow velocity of the liquid in the flow zone was 0.04 m/s. These results could guide the optimization design of the filling ratio and the aeration conditions and provide a theoretical basis for the application of MBBR.

Quantifying the electron-donating and -accepting capacities of wastewater for evaluating and optimizing biological wastewater treatment processes.

Biological processes have been widely used for the treatment of both domestic and industrial wastewaters. In such biological processes, pollutants are converted into pollution-free substances by microorganisms through oxidation-reduction reactions. Thus, how to quantify the internal oxidation-reduction properties wastewaters and seek out targeted countermeasures is essential to understand, operate, and optimize biological wastewater treatment systems. So far, no such approach is available yet. In this work, a novel concept of electron neutralization-based evaluation is proposed to describe the internal oxidation-reduction properties of wastewater. Pollutants in wastewater are defined as electron donor substances (EDSs) or electron acceptor substances (EASs), which could give or accept electrons, respectively. With such an electron neutralization concept, several parameters, i.e., electron residual concentration (R), economy-related index (E and Er), and economical evaluation index (Y and Yr), are defined. Then, these parameters are used to evaluate the performance and economic aspects of currently applied wastewater treatment processes and even optimize systems. Three case studies demonstrate that the proposed concept could be effectively used to reduce wastewater treatment costs, assess energy recovery, and evaluate process performance. Therefore, a new, simple, and reliable methodology is established to describe the oxidation-reduction properties of wastewater and assess the biological wastewater treatment processes.

Etomidate Effects on Desensitization and Deactivation of α4ß3δ GABAA Receptors Inducibly Expressed in HEK293 TetR Cells.

Central α4ßδ receptors are the most abundant isoform of δ subunit-containing extrasynaptic GABAA receptors that mediate tonic inhibition. Although the amplitude of GABA-activated currents through α4ßδ receptors is modulated by multiple general anesthetics, the effects of general anesthetics on desensitization and deactivation of α4ßδ receptors remain unknown. In the current study, we investigated the effect of etomidate, a potent general anesthetic, on the kinetics and the pseudo steady-state current amplitude of α4ß3δ receptors inducibly expressed in human embryonic kidney 293 TetR cells. Etomidate directly activates α4ß3δ receptors in a concentration-dependent manner. Etomidate at a clinically relevant concentration (3.2 µM) enhances maximal response without altering the EC50 of GABA concentration response. Etomidate also increases the extent of desensitization and prolongs the deactivation of α4ß3δ receptors in the presence of maximally activating concentrations of GABA (1 mM). To mimic the modulatory effect of etomidate on tonic currents, long pulses (30-60 seconds) of a low GABA concentration (1 µM) were applied to activate α4ß3δ receptors in the absence and presence of etomidate. Although etomidate increases the desensitization of α4ß3δ receptors, the pseudo steady-state current amplitude at 1 µM GABA is augmented by etomidate. Our data demonstrate that etomidate enhances the pseudo steady-state current of α4ß3δ receptors evoked by a GABA concentration comparable to an ambient GABA level, suggesting that α4ß3δ receptors may mediate etomidate's anesthetic effect in the brain.

Repeated generalized seizures can produce calcified cardiac lesions in DBA/1 mice.

Studies suggest that cardiorespiratory dysfunction likely contributes to sudden unexpected death in epilepsy (SUDEP). Seizures result in autonomic and respiratory dysfunction, leading to sympathetic hyperactivity and respiratory distress, including apnea. While the heart is vulnerable to catecholamine surges and hypoxia, it remains unknown if repetitive generalized seizures lead to cardiac damage. DBA/1 mice exhibit seizure-induced respiratory arrest (S-IRA) following generalized audiogenic seizures (AGS), which can be resuscitated using a rodent ventilator. In the current study, we induced different numbers of S-IRA episodes in DBA/1 mice and determined the association of repeated S-IRA induction with cardiac damage using histology. After repetitive induction of 18 S-IRA, calcified lesions, as revealed by calcium (Ca2+)-specific alizarin red staining, were observed in the ventricular myocardium in 61.5% of DBA/1 mice, which was higher compared to mice with 5 S-IRA and 1 S-IRA as well as age-matched untested control mice. The incidence of lesions in mice with 9 S-IRA was only higher than that of control mice. Only 1-2, small lesions were observed in mice with 5 S-IRA and 1 S-IRA and in control mice. Larger lesions (>2500 µm2) were observed in mice with 9 and 18 S-IRA. The incidence of larger lesions was higher in mice with 18 S-IRA (53.8%) as compared to mice with 5 S-IRA and 1 S-IRA as well as with control mice, and the incidence of larger lesions in mice with 9 S-IRA was only higher than that of control mice. Repeated induction of S-IRA in DBA/1 mice can result in calcified necrotic lesions in the ventricles of the heart, and their incidence and size are dependent on the total number of S-IRA.

Optogenetic activation of 5-HT neurons in the dorsal raphe suppresses seizure-induced respiratory arrest and produces anticonvulsant effect in the DBA/1 mouse SUDEP model.

Sudden unexpected death in epilepsy (SUDEP) is a devastating epilepsy complication. Seizure-induced respiratory arrest (S-IRA) occurs in many witnessed SUDEP patients and animal models as an initiating event leading to death. Thus, understanding the mechanisms underlying S-IRA will advance the development of preventive strategies against SUDEP. Serotonin (5-HT) is an important modulator for many vital functions, including respiration and arousal, and a deficiency of 5-HT signaling is strongly implicated in S-IRA in animal models, including the DBA/1 mouse. However, the brain structures that contribute to S-IRA remain elusive. We hypothesized that the dorsal raphe (DR), which sends 5-HT projections to the forebrain, is implicated in S-IRA. The present study used optogenetics in the DBA/1 mouse model of SUDEP to selectively activate 5-HT neurons in the DR. Photostimulation of DR 5-HT neurons significantly and reversibly reduced the incidence of S-IRA evoked by acoustic stimulation. Activation of 5-HT neurons in the DR suppressed tonic seizures in most DBA/1 mice without altering the seizure latency and duration of wild running and clonic seizures evoked by acoustic stimulation. This suppressant effect of photostimulation on S-IRA is independent of seizure models, as optogenetic stimulation of DR also reduced S-IRA induced by pentylenetetrazole, a proconvulsant widely used to model human generalized seizures. The S-IRA-suppressing effect of photostimulation was increased by 5-hydroxytryptophan, a chemical precursor for 5-HT synthesis, and was reversed by ondansetron, a specific 5-HT3 receptor antagonist, indicating that reduction of S-IRA by photostimulation of the DR is specifically mediated by enhanced 5-HT neurotransmission. Our findings suggest that deficits in 5-HT neurotransmission in the DR are implicated in S-IRA in DBA/1 mice, and that targeted intervention in the DR is potentially useful for prevention of SUDEP.

Comparison of αßδ and αßγ GABAA receptors: Allosteric modulation and identification of subunit arrangement by site-selective general anesthetics.

GABAA receptors play a dominant role in mediating inhibition in the mature mammalian brain, and defects of GABAergic neurotransmission contribute to the pathogenesis of a variety of neurological and psychiatric disorders. Two types of GABAergic inhibition have been described: αßγ receptors mediate phasic inhibition in response to transient high-concentrations of synaptic GABA release, and αßδ receptors produce tonic inhibitory currents activated by low-concentration extrasynaptic GABA. Both αßδ and αßγ receptors are important targets for general anesthetics, which induce apparently different changes both in GABA-dependent receptor activation and in desensitization in currents mediated by αßγ vs. αßδ receptors. Many of these differences are explained by correcting for the high agonist efficacy of GABA at most αßγ receptors vs. much lower efficacy at αßδ receptors. The stoichiometry and subunit arrangement of recombinant αßγ receptors are well established as ß-α-γ-ß-α, while those of αßδ receptors remain controversial. Importantly, some potent general anesthetics selectively bind in transmembrane inter-subunit pockets of αßγ receptors: etomidate acts at ß+/α- interfaces, and the barbiturate R-5-allyl-1-methyl-5-(m-trifluoromethyl-diazirynylphenyl) barbituric acid (R-mTFD-MPAB) acts at α+/ß- and γ+/ß- interfaces. Thus, these drugs are useful as structural probes in αßδ receptors formed from free subunits or concatenated subunit assemblies designed to constrain subunit arrangement. Although a definite conclusion cannot be drawn, studies using etomidate and R-mTFD-MPAB support the idea that recombinant α1ß3δ receptors may share stoichiometry and subunit arrangement with α1ß3γ2 receptors.

Comparison of γ-Aminobutyric Acid, Type A (GABAA), Receptor αßγ and αßδ Expression Using Flow Cytometry and Electrophysiology: EVIDENCE FOR ALTERNATIVE SUBUNIT STOICHIOMETRIES AND ARRANGEMENTS.

The subunit stoichiometry and arrangement of synaptic αßγ GABAA receptors are generally accepted as 2α:2ß:1γ with a ß-α-γ-ß-α counterclockwise configuration, respectively. Whether extrasynaptic αßδ receptors adopt the analogous ß-α-δ-ß-α subunit configuration remains controversial. Using flow cytometry, we evaluated expression levels of human recombinant γ2 and δ subunits when co-transfected with α1 and/or ß2 subunits in HEK293T cells. Nearly identical patterns of γ2 and δ subunit expression were observed as follows: both required co-transfection with α1 and ß2 subunits for maximal expression; both were incorporated into receptors primarily at the expense of ß2 subunits; and both yielded similar FRET profiles when probed for subunit adjacency, suggesting similar underlying subunit arrangements. However, because of a slower rate of δ subunit degradation, 10-fold less δ subunit cDNA was required to recapitulate γ2 subunit expression patterns and to eliminate the functional signature of α1ß2 receptors. Interestingly, titrating γ2 or δ subunit cDNA levels progressively altered GABA-evoked currents, revealing more than one kinetic profile for both αßγ and αßδ receptors. This raised the possibility of alternative receptor isoforms, a hypothesis confirmed using concatameric constructs for αßγ receptors. Taken together, our results suggest a limited cohort of alternative subunit arrangements in addition to canonical ß-α-γ/δ-ß-α receptors, including ß-α-γ/δ-α-α receptors at lower levels of γ2/δ expression and ß-α-γ/δ-α-γ/δ receptors at higher levels of expression. These findings provide important insight into the role of GABAA receptor subunit under- or overexpression in disease states such as genetic epilepsies.

Atomoxetine, a norepinephrine reuptake inhibitor, reduces seizure-induced respiratory arrest.

Sudden unexpected death in epilepsy (SUDEP) is a devastating epilepsy complication, and no effective preventive strategies are currently available for this fatal disorder. Clinical and animal studies of SUDEP demonstrate that seizure-induced respiratory arrest (S-IRA) is the primary event leading to death after generalized seizures in many cases. Enhancing brain levels of serotonin reduces S-IRA in animal models relevant to SUDEP, including the DBA/1 mouse. Given that serotonin in the brain plays an important role in modulating respiration and arousal, these findings suggest that deficits in respiration and/or arousal may contribute to S-IRA. It is well known that norepinephrine is an important neurotransmitter that modulates respiration and arousal in the brain as well. Therefore, we hypothesized that enhancing noradrenergic neurotransmission suppresses S-IRA. To test this hypothesis, we examined the effect of atomoxetine, a norepinephrine reuptake inhibitor (NRI), on S-IRA evoked by either acoustic stimulation or pentylenetetrazole in DBA/1 mice. We report the original observation that atomoxetine specifically suppresses S-IRA without altering the susceptibility to seizures evoked by acoustic stimulation, and atomoxetine also reduces S-IRA evoked by pentylenetetrazole in DBA/1 mice. Our data suggest that the noradrenergic signaling is importantly involved in S-IRA, and that atomoxetine, a medication widely used to treat attention deficit hyperactivity disorder (ADHD), is potentially useful to prevent SUDEP.

Abnormalities of serotonergic neurotransmission in animal models of SUDEP.

Sudden unexpected death in epilepsy (SUDEP) is a devastating event, and both DBA/1 and DBA/2 mice have been shown to be relevant animal models for studying SUDEP. DBA mice exhibit seizure-induced respiratory arrest (S-IRA), leading to cardiac arrest and subsequent sudden death after generalized audiogenic seizures (AGSs). This sequence of terminal events is also observed in the majority of witnessed human SUDEP cases. Several pathophysiological mechanisms, including respiratory/cardiac dysfunction, have been proposed to contribute to human SUDEP. Several (but not all) selective serotonin (5-HT) reuptake inhibitors (SSRIs), including fluoxetine, can reversibly block S-IRA, and abnormal expression of 5-HT receptors is found in the brainstem of DBA mice. DBA mice, which do not initially show S-IRA, exhibit S-IRA after treatment with a nonselective 5-HT antagonist. These studies suggest that abnormalities of 5-HT neurotransmission are involved in the pathogenesis of S-IRA in DBA mice. Serotonergic (5-HT) transmission plays an important role in normal respiration, and DBA mice exhibiting S-IRA can be resuscitated using a rodent ventilator. It is important and interesting to know if fluoxetine blocks S-IRA in DBA mice by enhancing respiratory ventilation. To test this, the effects of breathing stimulants, doxapram, and 5,6,7,8-tetrahydropyrido[4,3-d]pyrimidine (PK-THPP) were compared with the effects of fluoxetine on S-IRA in DBA/1 mice. Although fluoxetine reduces the incidence of S-IRA in DBA/1 mice, as reported previously, the same dose of fluoxetine fails to enhance baseline respiratory ventilation in the absence of AGSs. Doxapram and PK-THPP augment the baseline ventilation in DBA/1 mice. However, these breathing stimulants are ineffective in preventing S-IRA in DBA/1 mice. These data suggest that fluoxetine blocks S-IRA in DBA/1 mice by cellular/molecular mechanisms other than enhancement of basal ventilation. Future research directions are also discussed. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

5-Hydroxytryptophan, a precursor for serotonin synthesis, reduces seizure-induced respiratory arrest.

OBJECTIVE: The DBA/1 mouse is a relevant animal model of sudden unexpected death in epilepsy (SUDEP), as it exhibits seizure-induced respiratory arrest (S-IRA) evoked by acoustic stimulation, followed by cardiac arrhythmia and death. Defects in serotonergic neurotransmission may contribute to S-IRA. The tryptophan hydroxylase-2 (TPH2) enzyme converts L-tryptophan to 5-hydroxytryptophan (5-HTP), a precursor for central nervous system (CNS) serotonin (5-HT) synthesis; and DBA/1 mice have a polymorphism that decreases TPH2 activity. We, therefore, hypothesized that supplementation with 5-HTP may bypass TPH2 and suppress S-IRA in DBA/1 mice. METHODS: TPH2 expression was examined by Western blot in the brainstem of DBA/1 and C57BL/6J mice both with and without acoustic stimulation. Changes in breathing and cardiac electrical activity in DBA/1 and C57BL/6J mice that incurred sudden death during generalized seizures evoked by pentylenetetrazole (PTZ) were studied by plethysmography and electrocardiography. The effect of 5-HTP administration on seizure-induced mortality evoked by acoustic stimulation or by PTZ was investigated in DBA/1 mice. RESULTS: Repetitive acoustic stimulation resulted in reduced TPH2 protein in the brainstem of DBA/1 mice as compared with C57BL/6J mice. S-IRA evoked by acoustic stimulation in DBA/1 mice was significantly reduced by 5-HTP. Following S-IRA, cardiac electrical activity could be detected for minutes before terminal asystole and death in both DBA/1 and C57BL/6J mice after PTZ treatment. The incidence of S-IRA by PTZ administration was greater in DBA/1 than in C57BL/6J mice, and administration of 5-HTP also significantly reduced S-IRA by PTZ in DBA/1 mice. SIGNIFICANCE: Our data suggest that S-IRA is the primary event leading to death incurred in most DBA/1 and some C57BL/6J mice during PTZ-evoked seizures. Suppression of S-IRA by 5-HTP suggests that 5-HT transmission contributes to the pathophysiology of S-IRA, and that 5-HTP, an over-the-counter supplement available for human consumption, may be clinically useful in preventing SUDEP.

Serotonergic agents act on 5-HT3 receptors in the brain to block seizure-induced respiratory arrest in the DBA/1 mouse model of SUDEP.

Drugs that enhance the action of serotonin (5-hydroxytrypamine, 5-HT), including several selective serotonin reuptake inhibitors (SSRIs), reduce susceptibility to seizure-induced respiratory arrest (S-IRA) that leads to death in the DBA/1 mouse model of sudden unexpected death in epilepsy (SUDEP). However, it is not clear if specific 5-HT receptors are important in the action of these drugs and whether the brain is the major site of action of these agents in this SUDEP model. The current study examined the actions of agents that affect the 5-HT3 receptor subtype on S-IRA and whether intracerebroventricular (ICV) microinjection of an SSRI would reduce S-IRA susceptibility in DBA/1 mice. The data indicate that systemic administration of SR 57227, a 5-HT3 agonist, was effective in blocking S-IRA in doses that did not block seizures, and the S-IRA blocking effect of the SSRI, fluoxetine, was abolished by coadministration of a 5-HT3 antagonist, ondansetron. Intracerebroventricular administration of fluoxetine in the present study was also able to block S-IRA without blocking seizures. These findings suggest that 5-HT3 receptors play an important role in the block of S-IRA by serotonergic agents, such as SSRIs, which is consistent with the abnormal expression of 5-HT3 receptors in the brainstem of DBA mice observed previously. Taken together, these data indicate that systemically administered serotonergic agents act, at least, in part, in the brain, to reduce S-IRA susceptibility in DBA/1 mice and that 5-HT3 receptors may be important to this effect.

Fluoxetine prevents respiratory arrest without enhancing ventilation in DBA/1 mice.

Sudden unexpected death in epilepsy (SUDEP) is a fatal epileptic event. DBA/1 mice are a relevant animal model for the study of SUDEP, as these mice exhibit seizure-induced respiratory arrest (S-IRA) leading to death, which has been observed in patients with witnessed SUDEP. Fluoxetine, a selective serotonin (5-hydroxytryptamine or 5-HT) reuptake inhibitor (SSRI), reduces S-IRA in DBA/1 mice. Given that DBA/1 mice with S-IRA can be resuscitated using a ventilator, we hypothesized that breathing stimulants can prevent S-IRA and that fluoxetine prevents S-IRA by enhancing ventilation in these mice. Spontaneous respiratory function in anesthetized or awake DBA/1 mice was examined using noninvasive plethysmography before and after administering fluoxetine or breathing stimulants, doxapram, and 5,6,7,8-tetrahydropyrido[4,3-d]pyrimidine (PK-THPP). The effects of these drugs on S-IRA in DBA/1 mice were tested. As reported previously, systemic administration of fluoxetine reduced S-IRA in awake DBA/1 mice, but fluoxetine in anesthetized and awake DBA/1 mice did not increase basal ventilation or the ventilatory response to 7% CO2. Both doxapram and PK-THPP increased ventilation in room air and in air+7% CO2 in anesthetized DBA/1 mice. However, neither of the breathing stimulants reduced the incidence of S-IRA. Our studies confirm that fluoxetine reduces S-IRA in DBA/1 mice without enhancing basal ventilation in the absence of seizures. Although breathing stimulants increased ventilation in the absence of seizures, they were ineffective in reducing S-IRA, indicating that drug-induced increases in ventilation are insufficient to compensate for S-IRA in DBA/1 mice.

5-HT receptors exert differential effects on seizure-induced respiratory arrest in DBA/1 mice.

Both clinical and animal studies demonstrated that seizure-induced respiratory arrest (S-IRA) contributes importantly to sudden unexpected death in epilepsy (SUDEP). It has been shown that enhancing serotonin (5-HT) function relieves S-IRA in animal models of SUDEP, including DBA/1 mice. Direct activation of 5-HT3 and 5-HT4 receptors suppresses S-IRA in DBA/1 mice, indicating that these receptors are involved in S-IRA. However, it remains unknown if other subtypes of 5-HT receptors are implicated in S-IRA in DBA/1 mice. In this study, we investigated the action of an agonist of the 5-HT1A (8-OH-DPAT), 5-HT2A (TCB-2), 5-HT2B (BW723C86), 5-HT2C (MK-212), 5-HT6 (WAY-208466) and 5-HT7 (LP-211) receptor on S-IRA in DBA/1 mice. An agonist of the 5-HT receptor or a vehicle was intraperitoneally administered 30 min prior to acoustic simulation, and the effect of each drug/vehicle on the incidence of S-IRA was videotaped for offline analysis. We found that the incidence of S-IRA was significantly reduced by TCB-2 at 10 mg/kg (30%, n = 10; p < 0.01, Fisher's exact test) but was not altered by other agonists compared with the corresponding vehicle controls in DBA/1 mice. Our data demonstrate that 5-HT2A receptors are implicated in S-IRA, and 5-HT1A, 5-HT2B, 5-HT2C, 5-HT6 and 5-HT7 receptors are not involved in S-IRA in DBA/1 mice.

Review on mechanism and remediation strategies of dissolved oxygen abnormal in surface water.

Dissolved oxygen (DO) is an important index to evaluate the quality of surface water environments. In recent years, anomalies in DO level have emerged as a major contributor to the decline of surface water quality. These anomalies have triggered several ecological and environmental challenges such as biodiversity loss, the degradation of water environmental quality, intensification of eutrophication, and an exacerbation of the greenhouse effect. Understanding the mechanisms underlying DO anomalies and devising targeted remediation strategies holds paramount importance in the scientific pursuit of water pollution control and aquatic ecosystem restoration. We explored and summarized the fluctuations and abnormal mechanism of DO concentration in surface water, focusing on factors like oxygen solubility, reoxygenation rates, and oxygen consumption by water bodies. We compiled a range of approaches for addressing DO anomalies, including pollution source management, artificial oxygenation, and the reconfiguration of aquatic ecosystems. Ultimately, we underscored the emerging significance of monitoring and regulating DO level in surface waters. Future research in this realm should encompass the establishment of distinct quality standards for surface water, the development of a comprehensive real-time spatial monitoring system for DO levels across watersheds, and the formulation of standardized procedures and technical norms.