Low doses of ethanol markedly potentiate the anti-seizure effect of diazepam in a mouse model of difficult-to-treat focal seizures

Bumetanide potentiates the anti-seizure and disease-modifying effects of midazolam in a noninvasive rat model of term birth asphyxia

Birth asphyxia and the resulting hypoxic-ischemic encephalopathy (HIE) are highly associated with perinatal and neonatal death, neonatal seizures, and an adverse later-life outcome. Currently used drugs, including phenobarbital and midazolam, have limited efficacy to suppress neonatal seizures. There is a medical need to develop new therapies that not only suppress neonatal seizures but also prevent later-life consequences. We have previously shown that the loop diuretic bumetanide does not potentiate the effects of phenobarbital in a rat model of birth asphyxia. Here we compared the effects of bumetanide (0.3 or 10 mg/kg i.p.), midazolam (1 mg/kg i.p.), and a combination of bumetanide and midazolam on neonatal seizures and later-life outcomes in this model. While bumetanide at either dose was ineffective when administered alone, the higher dose of bumetanide markedly potentiated midazolam's effect on neonatal seizures. Median bumetanide brain levels (0.47-0.53 µM) obtained with the higher dose were in the range known to inhibit the Na-K-Cl-cotransporter NKCC1 but it remains to be determined whether brain NKCC1 inhibition was underlying the potentiation of midazolam. When behavioral and cognitive alterations were examined over three months after asphyxia, treatment with the bumetanide/midazolam combination, but not with bumetanide or midazolam alone, prevented impairment of learning and memory. Furthermore, the combination prevented the loss of neurons in the dentate hilus and aberrant mossy fiber sprouting in the CA3a area of the hippocampus. The molecular mechanisms that explain that bumetanide potentiates midazolam but not phenobarbital in the rat model of birth asphyxia remain to be determined.

Simulating dynamic interaction between diazepam and ethanol targeting the GABAA receptor via in silico model

Combined diazepam-ethanol poisoning is common in forensic toxicology. Both diazepam and ethanol can inhibit the central nervous system via the γ-aminobutyric acid (GABA) ligand gated chloride ion channel, GABA_A Receptor (GABA_AR). As the common target of diazepam and ethanol, whether GABA_AR is the key target of their combined action remains unclear. This study aimed to explore their interaction based on the synergistic mechanisms between diazepam and ethanol targeting the GABA_AR. Four models were built in silico based on the crystal structure of GABA_AR. Molecular dynamic processes of the four models were simulated by the GPU-accelerated pmemd.cuda program in the Amber18 package. Results showed that ethanol inclined to combine the adjacent GABA or diazepam sites, minimized fluctuations of the root-mean-square deviation (RMSD) in the molecular dynamic process of GABA or diazepam binding the GABA_AR, and increased the release of binding energy of GABA or diazepam binding the GABA_AR. Results also showed that diazepam had less effect on the RMSD fluctuation or the binding energy release of GABA binding GABA_AR. The formation of complex of diazepam and GABA_AR could minimize the RMSD fluctuation and increase binding energy release of ethanol binding GABA_AR. Thus, ethanol, bridging GABA and diazepam, could strengthen the complex of GABA binding the GABA_AR, as well as the complex of diazepam binding the GABA_AR. However, whether diazepam binds GABA_AR or not, it cannot affect GABA binding the GABA_AR; and yet the complex of diazepam and GABA_AR can stabilize the complex of ethanol and GABA_AR.

Phenobarbital and midazolam suppress neonatal seizures in a noninvasive rat model of birth asphyxia, whereas bumetanide is ineffective

OBJECTIVE

Neonatal seizures are the most frequent type of neurological emergency in newborn infants, often being a consequence of prolonged perinatal asphyxia. Phenobarbital is currently the most widely used antiseizure drug for treatment of neonatal seizures, but fails to stop them in ~50% of cases. In a neonatal hypoxia-only model based on 11-day-old (P11) rats, the NKCC1 inhibitor bumetanide was reported to potentiate the antiseizure activity of phenobarbital, whereas it was ineffective in a human trial in neonates. The aim of this study was to evaluate the effect of clinically relevant doses of bumetanide as add-on to phenobarbital on neonatal seizures in a noninvasive model of birth asphyxia in P11 rats, designed for better translation to the human term neonate.

METHODS

Intermittent asphyxia was induced for 30 minutes by exposing the rat pups to three 7 + 3-minute cycles of 9% and 5% O₂ at constant 20% CO₂ . Drug treatments were administered intraperitoneally either before or immediately after asphyxia.

RESULTS

All untreated rat pups had seizures within 10 minutes after termination of asphyxia. Phenobarbital significantly blocked seizures when applied before asphyxia at 30 mg/kg but not 15 mg/kg. Administration of phenobarbital after asphyxia was ineffective, whereas midazolam (0.3 or 1 mg/kg) exerted significant antiseizure effects when administered before or after asphyxia. In general, focal seizures were more resistant to treatment than generalized convulsive seizures. Bumetanide (0.3 mg/kg) alone or in combination with phenobarbital (15 or 30 mg/kg) exerted no significant effect on seizure occurrence.

SIGNIFICANCE

The data demonstrate that bumetanide does not increase the efficacy of phenobarbital in a model of birth asphyxia, which is consistent with the negative data of the recent human trial. The translational data obtained with the novel rat model of birth asphyxia indicate that it is a useful tool to evaluate novel treatments for neonatal seizures.

Time-dependent interacting effects of caffeine, diazepam, and ethanol on zebrafish behaviour

Zebrafish have become a popular animal model for behavioural pharmacology due to their small size, rapid development, and amenability to high throughput behavioural drug screens. Furthermore, water-soluble compounds can be administered via immersion of the fish in the drug solution, which provides a non-invasive drug delivery method. Numerous studies have demonstrated stimulant effects of alcohol. Diazepam and caffeine, on the other hand have been found to have inhibitory effect on locomotor activity in zebrafish. However, the time-dependent changes induced by these psychoactive drugs are rarely reported, and potential drug interactions have not been examined in zebrafish, despite the translational relevance of this question. In the current study, we examine time- and dose-dependent changes in zebrafish following exposure to caffeine, diazepam, and ethanol quantifying four different behavioural parameters over a 30min recording session. We subsequently analyze potential drug-drug interactions by co-administering the three drugs in different combinations. Our time-course and dose-response analyses for each of the three drugs represent so far the most detailed studies available serving as a foundation for future psychopharmacology experiments with zebrafish. Furthermore, we report significant interactions between the three drugs corroborating findings obtained with rodent models as well as in humans, providing translational relevance for the zebrafish model.

Knockout of P-glycoprotein does not alter antiepileptic drug efficacy in the intrahippocampal kainate model of mesial temporal lobe epilepsy in mice

Pharmacoresistance to antiepileptic drugs (AEDs) is a major challenge in epilepsy therapy, affecting at least 30% of patients. Thus, there is considerable interest in the mechanisms responsible for such pharmacoresistance, with particular attention on the specific cellular and molecular factors that lead to reduced drug sensitivity. Current hypotheses of refractory epilepsy include the multidrug transporter hypothesis, which posits that increased expression or function of drug efflux transporters, such as P-glycoprotein (Pgp), in brain capillaries reduces the local concentration of AEDs in epileptic brain regions to subtherapeutic levels. In the present study, this hypothesis was addressed by evaluating the efficacy of six AEDs in wildtype and Pgp deficient Mdr1a/b(-/-) mice in the intrahippocampal kainate model of mesial temporal lobe epilepsy. In this model, frequent focal electrographic seizures develop after an initial kainate-induced status epilepticus. These seizures are resistant to major AEDs, but the mechanisms of this resistance are unknown. In the present experiments, the focal nonconvulsive seizures were resistant to carbamazepine and phenytoin, whereas high doses of valproate and levetiracetam exerted moderate and phenobarbital and diazepam marked anti-seizure effects. All AEDs suppressed generalized convulsive seizures. No significant differences between wildtype and Pgp-deficient mice were observed in anti-seizure drug efficacies. Also, the individual responder and nonresponder rates in each experiment did not differ between mouse genotypes. This does not argue against the multidrug transporter hypothesis in general, but indicates that Pgp is not involved in the mechanisms explaining that focal electrographic seizures are resistant to some AEDs in the intrahippocampal mouse model of partial epilepsy. This was substantiated by the finding that epileptic wildtype mice do not exhibit increased Pgp expression in this model.

Significant effects of sex, strain, and anesthesia in the intrahippocampal kainate mouse model of mesial temporal lobe epilepsy

The intrahippocampal kainate mouse model of mesial temporal lobe epilepsy is increasingly being used for studies on epileptogenesis and antiepileptogenesis. Almost all previous studies used male mice for this purpose, and no study is available in this or other models of acquired epilepsy that directly compared epileptogenesis in female and male rodents. Epidemiological studies suggest that gender may affect susceptibility to epilepsy and its prognosis; therefore, one goal of this study was to investigate whether sex has an influence on latent period and epileptogenesis in the intrahippocampal kainate model in mice. Another aspect that was examined in the present study was whether mouse strain differences in epileptogenesis exist. Finally, we examined the effects of different types of anesthesia (chloral hydrate, isoflurane) on kainate-induced status epilepticus (SE) and epileptogenesis. Continuous (24/7) video-EEG monitoring was used during SE and the 2 weeks following SE as well as 4-6 weeks after SE. In male NMRI mice with chloral hydrate anesthesia during kainate injection, SE was followed by a seizure-free latent period of 10-14 days if hippocampal paroxysmal discharges (HPDs) recorded from the kainate focus were considered the onset of epilepsy. Anesthesia with isoflurane led to a more rapid onset and higher severity of SE, and not all male NMRI mice exhibited a seizure-free latent period. Female NMRI mice differed from male animals in the lack of any clear latent period, independently of anesthesia type. Furthermore, HPDs were only rarely observed. These problems were not resolved by decreasing the dose of kainate or using other strains (C57BL/6, FVB/N) of female mice. The present data are the first to demonstrate marked sex-related differences in the latent period following brain injury in a rodent model of acquired epilepsy. Furthermore, our data demonstrate that the choice of anesthestic agent during kainate administration affects SE severity and as a consequence, the latent period, which may explain some of the differences reported for this model in the literature.

The AMPA receptor antagonist NBQX exerts anti-seizure but not antiepileptogenic effects in the intrahippocampal kainate mouse model of mesial temporal lobe epilepsy

The AMPA receptor subtype of glutamate receptors, which mediates fast synaptic excitation, is of primary importance in initiating epileptiform discharges, so that AMPA receptor antagonists exert anti-seizure activity in diverse animal models of partial and generalized seizures. Recently, the first AMPA receptor antagonist, perampanel, was approved for use as adjunctive therapy for the treatment of resistant partial seizures in patients. Interestingly, the competitive AMPA receptor antagonist NBQX has recently been reported to prevent development of spontaneous recurrent seizures (SRS) in a neonatal seizure model in rats, indicating the AMPA antagonists may exert also antiepileptogenic effects. This prompted us to evaluate competitive (NBQX) and noncompetitive (perampanel) AMPA receptor antagonists in an adult mouse model of mesial temporal lobe epilepsy. In this model, SRS develop after status epilepticus (SE) induced by intrahippocampal injection of kainate. Focal electrographic seizures in this model are resistant to several major antiepileptic drugs. In line with previous studies, phenytoin was not capable of blocking such seizures in the present experiments, while they were markedly suppressed by NBQX and perampanel. However, perampanel was less tolerable than NBQX in epileptic mice, so that only NBQX was subsequently tested for antiepileptogenic potential. When mice were treated over three days after kainate-induced SE with NBQX (20 mg/kg t.i.d.), no effect on development or frequency of seizures was found in comparison to vehicle controls. These results suggest that AMPA receptor antagonists, while being effective in suppressing resistant focal seizures, are not exerting antiepileptogenic effects in an adult mouse model of partial epilepsy.

Animal models of temporal lobe epilepsy following systemic chemoconvulsant administration

In order to understand the pathophysiology of temporal lobe epilepsy (TLE), and thus to develop new pharmacological treatments, in vivo animal models that present features similar to those seen in TLE patients have been developed during the last four decades. Some of these models are based on the systemic administration of chemoconvulsants to induce an initial precipitating injury (status epilepticus) that is followed by the appearance of recurrent seizures originating from limbic structures. In this paper we will review two chemically-induced TLE models, namely the kainic acid and pilocarpine models, which have been widely employed in basic epilepsy research. Specifically, we will take into consideration their behavioral, electroencephalographic and neuropathologic features. We will also evaluate the response of these models to anti-epileptic drugs and the impact they might have in developing new treatments for TLE.