Search

Acute exposure to high concentrations of hydrogen sulfide (H2S) leads to sudden death and, if survived, lingering neurological disorders. Clinical signs include seizures, loss of consciousness, and dyspnea. The proximate mechanisms underlying H2S-induced acute toxicity and death have not been clearly elucidated. We investigated electrocerebral, cardiac and respiratory activity during H2S exposure using electroencephalogram (EEG), electrocardiogram (EKG) and plethysmography. H2S suppressed electrocerebral activity and disrupted breathing. Cardiac activity was comparatively less affected. To test whether Ca2+ dysregulation contributes to H2S-induced EEG suppression, we developed an in vitro real-time rapid throughput assay measuring patterns of spontaneous synchronized Ca2+ oscillations in cultured primary cortical neuronal networks loaded with the indicator Fluo-4 using the fluorescent imaging plate reader (FLIPR-Tetra®). Sulfide >5 ppm dysregulated synchronous calcium oscillation (SCO) patterns in a dose-dependent manner. Inhibitors of NMDA and AMPA receptors magnified H2S-induced SCO suppression. Inhibitors of L-type voltage gated Ca2+ channels and transient receptor potential channels prevented H2S-induced SCO suppression. Inhibitors of T-type voltage gated Ca2+ channels, ryanodine receptors, and sodium channels had no measurable influence on H2S-induced SCO suppression. Exposures to > 5 ppm sulfide also suppressed neuronal electrical activity in primary cortical neurons measured by multi-electrode array (MEA), an effect alleviated by pretreatment with the nonselective transient receptor potential channel inhibitor, 2-APB. 2-APB also reduced primary cortical neuronal cell death from sulfide exposure. These results improve our understanding of the role of different Ca2+ channels in acute H2S-induced neurotoxicity and identify transient receptor potential channel modulators as novel structures with potential therapeutic benefits.

Objective: Sudden unexpected death in epilepsy (SUDEP) results in more years of potential life lost than any neurological condition with the exception of stroke. It is generally agreed that SUDEP happens due to some form of respiratory, cardiac, and electrocerebral dysfunction following a seizure; however, the mechanistic cause of these perturbations is unclear. One possible explanation lies with adenosinergic signaling. Extracellular levels of the inhibitory neuromodulator adenosine rapidly rise during seizures, a countermeasure that is necessary for seizure termination. Previous evidence has suggested that excessive adenosinergic inhibition could increase the risk of SUDEP by silencing brain areas necessary for life, such as the respiratory nuclei of the brainstem. The goal of this investigation was to further clarify the role of adenosine in seizure‐induced respiratory and electrocerebral dysfunction. Methods: To determine the role of adenosine in postictal physiological dysregulation, we pharmacologically manipulated adenosine signaling prior to amygdala‐kindled seizures in mice while recording electroencephalogram (EEG), electromyogram, and breathing using whole body plethysmography. The adenosinergic drugs used in this study included selective and nonselective adenosine receptor antagonists and inhibitors of adenosine metabolism. Results: We found that high doses of adenosine receptor antagonists caused some seizures to result in seizure‐induced death; however, counterintuitively, animals in these conditions that did not experience seizure‐induced death had little or no postictal generalized EEG suppression. Inhibitors of adenosine metabolism had no effect on postictal breathing but did worsen some postictal electrocerebral outcomes. Significance: The unexpected effect of high doses of adenosine antagonists on seizure‐induced death observed in this study may be due to the increase in seizure severity, vasoconstriction, or phosphodiesterase inhibition caused by these drugs at high doses. These findings further clarify the role of adenosine in seizure‐induced death and may have implications for the consumption of caffeine in epilepsy patients and the prevention of SUDEP. [ABSTRACT FROM AUTHOR]

Objective: Respiratory arrest plays an important role in sudden unexpected death in epilepsy (SUDEP). Adenosine is of interest in SUDEP pathophysiology due to its influence on seizures and breathing. The objective of this investigation was to examine the role of adenosine in seizure severity, seizure‐induced respiratory disruption, and seizure‐induced death using mouse models. Understanding adenosinergic contributions to seizure cessation and seizure‐induced death may provide insights into how SUDEP can be prevented while avoiding increased seizure severity. Methods: Our approach was to examine: (1) seizure severity and seizure‐induced death after 15 mA electroshock seizures and during repeated pentylenetetrazol (PTZ) administration in wild‐type mice (Adk+/+) and transgenic mice with reduced adenosine metabolism (Adk+/−); (2) the postictal hypercapnic ventilatory response (HCVR) in wild‐type mice (the postictal HCVR could not be examined in Adk+/− mice due to their high mortality rate); and (3) the effects of adenosinergic drugs on seizure severity and seizure‐induced death following maximal electroshock (MES). Results: Adk+/− mice were more vulnerable to seizure‐induced death in the 15 mA electroshock and repeated PTZ models. Despite increased mortality, Adk+/− mice had comparable seizure severity in the PTZ model and reduced seizure severity in the 15 mA electroshock model. Breathing and HCVR were suppressed by 15 mA electroshock seizures in wild‐type mice. Pharmacological inhibition of adenosine metabolism decreased MES seizure severity but did not increase mortality. A1 selective and nonselective adenosine receptor antagonists increased seizure‐induced death following MES. Significance: Adenosine has opposing effects on seizure severity and seizure‐induced death. On the one hand, our seizure severity data highlight the importance of adenosine in seizure suppression. On the other hand, our mortality data indicate that excessive extracellular adenosine signaling can increase the risk of seizure‐induced respiratory arrest. [ABSTRACT FROM AUTHOR]

Objective: For an antiseizure medication (ASM) to be effective in status epilepticus (SE), the drug should be administered intravenously (i.v.) to provide quick access to the brain. However, poor aqueous solubility is a major problem in the development of parenteral drug solutions. Given its multiple mechanisms of action, topiramate (TPM) is a promising candidate for the treatment of established or refractory SE, as supported by clinical studies using nasogastric tube TPM administration. However, TPM is not clinically available as a solution for i.v. administration, which hampers its use in the treatment of SE. Here, we describe a novel easy‐to‐use and easy‐to‐prepare i.v. TPM formulation using the U.S. Food and Drug Administration (FDA)–approved excipient meglumine. Methods: During formulation development, we compared the solubility of TPM in bi‐distilled water with vs without a range of meglumine concentrations. Furthermore, the solubility of combinations of TPM and levetiracetam and TPM, levetiracetam, and atorvastatin in aqueous meglumine concentrations was determined. Subsequently, the pharmacokinetics and tolerability of meglumine‐based solutions of TPM and TPM combinations were evaluated in rats, including animals following fluid percussion injury or pilocarpine‐induced SE. Results: The amino sugar meglumine markedly enhances the aqueous solubility of TPM. A comparison with data on dissolving TPM using sulfobutylether‐β‐cyclodextrin (Captisol) demonstrates that meglumine is much more effective for dissolving TPM. Furthermore, meglumine can be used to prepare drug cocktails where TPM is co‐administered with another ASM for SE treatment. The tolerability studies of the meglumine‐based TPM solution and meglumine‐based TPM combinations in normal rats and the rat fluid percussion injury and pilocarpine‐induced SE models demonstrate excellent tolerability of the novel drug solutions. Preclinical studies on antiseizure efficacy in the SE model are underway. Significance: In conclusion, the novel meglumine‐based solution of TPM presented here may be well suited for clinical development. [ABSTRACT FROM AUTHOR]

Adenosine is an inhibitory modulator of neuronal excitability. Neuronal activity results in increased adenosine release, thereby constraining excessive excitation. The exceptionally high neuronal activity of a seizure results in a surge in extracellular adenosine to concentrations many-fold higher than would be observed under normal conditions. In this review, we discuss the multifarious effects of adenosine signaling in the context of epilepsy, with emphasis on sudden unexpected death in epilepsy (SUDEP). We describe and categorize the beneficial, detrimental, and potentially deadly aspects of adenosine signaling. The good or beneficial characteristics of adenosine signaling in the context of seizures include: (1) its direct effect on seizure termination and the prevention of status epilepticus; (2) the vasodilatory effect of adenosine, potentially counteracting postictal vasoconstriction; (3) its neuroprotective effects under hypoxic conditions; and (4) its disease modifying antiepileptogenic effect. The bad or detrimental effects of adenosine signaling include: (1) its capacity to suppress breathing and contribute to peri-ictal respiratory dysfunction; (2) its contribution to postictal generalized EEG suppression (PGES); (3) the prolonged increase in extracellular adenosine following spreading depolarization waves may contribute to postictal neuronal dysfunction; (4) the excitatory effects of A2A receptor activation is thought to exacerbate seizures in some instances; and (5) its potential contributions to sleep alterations in epilepsy. Finally, the adverse effects of adenosine signaling may potentiate a deadly outcome in the form of SUDEP by suppressing breathing and arousal in the postictal period. Evidence from animal models suggests that excessive postictal adenosine signaling contributes to the pathophysiology of SUDEP. The goal of this review is to discuss the beneficial, harmful, and potentially deadly roles that adenosine plays in the context of epilepsy and to identify crucial gaps in knowledge where further investigation is necessary. By better understanding adenosine dynamics, we may gain insights into the treatment of epilepsy and the prevention of SUDEP. [ABSTRACT FROM AUTHOR]

Key points: Sudden unexpected death in epilepsy (SUDEP) is the leading cause of premature death in patients with refractory epilepsy.SUDEP typically occurs during the night, although the reason for this is unclear.We found that, in normally entrained mice, time‐of‐day alters vulnerability to seizure‐induced death.We found that, in free‐running mice, circadian phase alters the vulnerability to seizure‐induced death.These findings suggest that circadian rhythmicity may be responsible for the increased night‐time prevalence of SUDEP Sudden unexpected death in epilepsy (SUDEP) is the leading cause of epilepsy‐related death. SUDEP typically occurs during the night following a seizure. Many aspects of mammalian physiology are regulated by circadian rhythms in ways that might make seizures occuring during the night more dangerous. Using two mouse models of seizure‐induced death, we demonstrate that time‐of‐day and circadian rhythms alter vulnerability to seizure‐induced death. We exposed normally entrained DBA/1 mice to a potentially seizure‐inducing acoustic stimulus at different times of day and compared the characteristics and outcomes of the seizures. Time‐of‐day did not alter the probability of a seizure but it did alter the probability of seizure‐induced death. To determine whether circadian rhythms alter vulnerability to seizure‐induced death, we induced maximal electroshock seizures in free‐running C57BL/6J mice at different circadian time points at the same time as measuring breathing via whole body plethysmography. Circadian phase did not affect seizure severity but it did alter postictal respiratory outcomes and the probability of seizure‐induced death. By contrast to our expectations, in entrained and free‐running mice, vulnerability to seizure‐induced death was greatest during the night and subjective night, respectively. These findings suggest that circadian rhythmicity may be responsible for the increased night‐time prevalence of SUDEP and that the underlying mechanism is phase conserved between nocturnal and diurnal mammals. All of the seizures in the present study were induced during wakefulness, indicating that the effect of time point on vulnerability to seizure‐induced death was not the result of sleep. Understanding why SUDEP occurs more frequently during the night may inform future preventative countermeasures. Key points: Sudden unexpected death in epilepsy (SUDEP) is the leading cause of premature death in patients with refractory epilepsy.SUDEP typically occurs during the night, although the reason for this is unclear.We found that, in normally entrained mice, time‐of‐day alters vulnerability to seizure‐induced death.We found that, in free‐running mice, circadian phase alters the vulnerability to seizure‐induced death.These findings suggest that circadian rhythmicity may be responsible for the increased night‐time prevalence of SUDEP [ABSTRACT FROM AUTHOR]

It is widely agreed that breathing is subject to circadian regulation. Circadian differences in respiratory physiology significantly impact a number of diseases including sleep apnea, asthma, and seizure-induced death. The effect of time of day on breathing has been previously characterized; however, an endogenous free-running respiratory rhythm in mammals has not previously been described. Furthermore, it is assumed that circadian rhythms in breathing are dependent on the hypothalamic suprachiasmatic nucleus (SCN), the home of the mammalian central circadian oscillator, but this has not been shown experimentally. The breathing of mice was monitored during wakefulness using whole body plethysmography at six times of day while housed under light-dark conditions and at six circadian phases while housed under constant darkness. Respiratory frequency and minute ventilation, but not tidal volume, were significantly higher during the active phase in both entrained and free-running conditions. To determine whether circadian regulation of breathing requires the SCN, in separate sets of animals this structure was electrolytically lesioned bilaterally or a sham surgery was performed, and breathing was measured at six different time points. Time-dependent oscillations in breathing were lost in SCN-lesioned animals, but not those subjected to sham surgery. These results suggest that breathing is subject to circadian regulation via the SCN. Mechanistic insights into the circadian regulation of breathing may lead to targeted interventions to reduce the morbidity and mortality associated with diseases with respiratory pathophysiology. [ABSTRACT FROM AUTHOR]

Summary: Objective: Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in patients with refractory epilepsy. Although the mechanisms for SUDEP are incompletely understood, seizure‐induced respiratory arrest (S‐IRA) has been strongly and consistently implicated. A body of evidence indicates that serotonin (5‐HT), a modulator of breathing, plays a critical role in SUDEP. Because the 5‐HT and norepinephrine (NE) systems interact in many biologic processes and NE is known to modulate breathing and seizures, we hypothesized that NE may play a role in S‐IRA and SUDEP. Methods: We examined the effects of pharmacologic manipulation of 5‐HT and NE on S‐IRA and death following maximal electroshock (MES)–induced seizures in adult wild‐type (WT) mice, genetically 5‐HT neuron–deficient (Lmx1bf/f/p) mice, and chemically NE neuron–deficient mice. Mice were treated with pharmacologic agents targeting the serotonergic and noradrenergic systems and subjected to seizure induction via MES while breathing was measured via whole‐body plethysmography. Results: S‐IRA and death was reduced in WT mice with NE reuptake inhibitors (NRIs), reboxetine and atomoxetine, selective serotonin reuptake inhibitors (SSRIs), fluoxetine and citalopram, and the dual 5‐HT/NE reuptake inhibitor (SNRI), duloxetine. S‐IRA and death was also reduced in Lmx1bf/f/p mice with reboxetine and fluoxetine. The protective effects of the reuptake inhibitors were prevented by the α1 antagonist, prazosin. Citalopram did not reduce S‐IRA and death in NE neuron–deficient mice. Significance: These data suggest that 5‐HT and NE critically interact in the modulation of breathing following a seizure and potentially inform preventive strategies for SUDEP. [ABSTRACT FROM AUTHOR]

Arousal from sleep in response to CO2is a critical protective phenomenon. Dysregulation of CO2-induced arousal contributes to morbidity and mortality from prevalent diseases, such as obstructive sleep apnea and sudden infant death syndrome. Despite the critical nature of this protective reflex, the precise mechanism for CO2-induced arousal is unknown. Because CO2is a major regulator of breathing, prevailing theories suggest that activation of respiratory chemo- and mechano-sensors is required for CO2-induced arousal. However, populations of neurons that are not involved in the regulation of breathing are also chemosensitive. Among these are serotonin (5-HT) neurons in the dorsal raphe nucleus (DRN) that comprise a component of the ascending arousal system. We hypothesized that direct stimulation of these neurons with CO2could cause arousal from sleep independently of enhancing breathing. Dialysis of CO2-rich acidified solution into DRN, but not medullary raphe responsible for modulating breathing, caused arousal from sleep. Arousal was lost in mice with a genetic absence of 5-HT neurons, and with acute pharmacological or optogenetic inactivation of DRN 5-HT neurons. Here we demonstrate that CO2can cause arousal from sleep directly, without requiring enhancement of breathing, and that chemosensitive 5-HT neurons in the DRN critically mediate this arousal. Better understanding mechanisms underlying this protective reflex may lead to interventions to reduce disease-associated morbidity and mortality. [ABSTRACT FROM AUTHOR]

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in refractory epilepsy patients. Although specific mechanisms underlying SUDEP are not well understood, evidence suggests most SUDEP occurs due to seizure-induced respiratory arrest. SUDEP also tends to happen at night. Although this may be due to circumstances in which humans find themselves at night, such as being alone without supervision or sleeping prone, or to independent influences of sleep state, there are a number of reasons why the night (i.e., circadian influences) could be an independent risk factor for SUDEP. We explored this possibility. Adult male WT mice were instrumented for EEG, EMG, and EKG recording and subjected to maximal electroshock (MES) seizures during wakefulness, non-rapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep during the nighttime/dark phase. These data were compared with data collected following seizures induced during the daytime/light phase. Seizures induced during the nighttime were similar in severity and duration to those induced during the daytime; however, seizures induced during the nighttime were associated with a lesser degree of respiratory dysregulation and postictal EEG suppression. Seizures induced during REM sleep during the nighttime were universally fatal, as is seen when seizures are induced during REM during the daytime. Taken together, these data implicate a role for time of day in influencing the physiological consequences of seizures that may contribute to seizure-induced death. NEW & NOTEWORTHY Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in patients with refractory epilepsy. SUDEP frequently occurs during the night, which has been attributed to an effect of sleep. We have shown that sleep state does indeed influence survival following a seizure. That SUDEP occurs during the night could also implicate a circadian influence. In this study we found that time of day independently affects the physiological consequences of seizures. [ABSTRACT FROM AUTHOR]

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of epilepsy-related death in patients with refractory epilepsy. Convergent lines of evidence suggest that SUDEP occurs due to seizure induced perturbation of respiratory, cardiac, and electrocerebral function as well as potential predisposing factors. It is consistently observed that SUDEP happens more during the night and the early hours of the morning. The aim of this review is to discuss evidence from patient cases, clinical studies, and animal research which is pertinent to the nocturnality of SUDEP. There are a number of factors which might contribute to the nighttime predilection of SUDEP. These factors fall into four categories: influences of (1) being unwitnessed, (2) lying prone in bed, (3) sleep-wake state, and (4) circadian rhythms. During the night, seizures are more likely to be unwitnessed; therefore, it is less likely that another person would be able to administer a lifesaving intervention. Patients are more likely to be prone on a bed following a nocturnal seizure. Being prone in the accouterments of a bed during the postictal period might impair breathing and increase SUDEP risk. Sleep typically happens at night and seizures which emerge from sleep might be more dangerous. Lastly, there are circadian changes to physiology during the night which might facilitate SUDEP. These possible explanations for the nocturnality of SUDEP are not mutually exclusive. The increased rate of SUDEP during the night is likely multifactorial involving both situational factors, such as being without a witness and prone, and physiological changes due to the influence of sleep and circadian rhythms. Understanding the causal elements in the nocturnality of SUDEP may be critical to the development of effective preventive countermeasures.