Developmental seizure models

GABAergic circuits drive focal seizures

Epilepsy is based on abnormal neuronal activities that have historically been suggested to arise from an excess of excitation and a defect of inhibition, or in other words from an excessive glutamatergic drive not balanced by GABAergic activity. More recent data however indicate that GABAergic signaling is not defective at focal seizure onset and may even be actively involved in seizure generation by providing excitatory inputs. Recordings of interneurons revealed that they are active at seizure initiation and that their selective and time-controlled activation using optogenetics triggers seizures in a more general context of increased excitability. Moreover, GABAergic signaling appears to be mandatory at seizure onset in many models. The main pro-ictogenic effect of GABAergic signaling is the depolarizing action of GABA_A conductance which may occur when an excessive GABAergic activity causes Cl^- accumulation in neurons. This process may combine with background dysregulation of Cl^-, well described in epileptic tissues. Cl^- equilibrium is maintained by (Na⁺)/K⁺/Cl^- co-transporters, which can be defective and therefore favor the depolarizing effects of GABA. In addition, these co-transporters further contribute to this effect as they mediate K⁺ outflow together with Cl^- extrusion, a process that is responsible for K⁺ accumulation in the extracellular space and subsequent increase of local excitability. The role of GABAergic signaling in focal seizure generation is obvious but its complex dynamics and balance between GABA_A flux polarity and local excitability still remain to be established, especially in epileptic tissues where receptors and ion regulators are disrupted and in which GABAergic signaling rather plays a 2 faces Janus role.

Magnolia officinalis Reduces Inflammation and Damage Induced by Recurrent Status Epilepticus in Immature Rats

BACKGROUND

Neuroinflammation induced in response to damage caused by status epilepticus (SE) activates the interleukin (IL)1-β pathway and proinflammatory proteins that increase vulnerability to the development of spontaneous seizure activity and/or epilepsy.

OBJECTIVES

The study aimed to assess the short-term anti-inflammatory and neuroprotective effects of Magnolia officinalis (MO) on recurrent SE in immature rats.

METHODS

Sprague-Dawley rats at PN day 10 were used; n = 60 rats were divided into two control groups, SHAM and KA, and two experimental groups, MO (KA-MO) and Celecoxib (KA-Clbx). The anti-inflammatory effect of a single dose of MO was evaluated at 6 and 24 hr by Western blotting and on day 30 PN via a subchronic administration of MO to assess neuronal preservation and hippocampal gliosis by immunohistochemistry for NeunN and GFAP, respectively.

RESULTS

KA-MO caused a decrease in the expression of IL1-β and Cox-2 at 6 and 24 h post-treatment, a reduction in iNOS synthase at 6 and 24 hr post-treatment and reduced neuronal loss and gliosis at postnatal day 30, similar to Clbx.

CONCLUSION

The results indicating that Magnolia officinalis is an alternative preventive treatment for early stages of epileptogenesis are encouraging.

Seizing the moment: Zebrafish epilepsy models

Zebrafish are now widely accepted as a valuable animal model for a number of different central nervous system (CNS) diseases. They are suitable both for elucidating the origin of these disorders and the sequence of events culminating in their onset, and for use as a high-throughput in vivo drug screening platform. The availability of powerful and effective techniques for genome manipulation allows the rapid modelling of different genetic epilepsies and of conditions with seizures as a core symptom. With this review, we seek to summarize the current knowledge about existing epilepsy/seizures models in zebrafish (both pharmacological and genetic) and compare them with equivalent rodent and human studies. New findings obtained from the zebrafish models are highlighted. We believe that this comprehensive review will highlight the value of zebrafish as a model for investigating different aspects of epilepsy and will help researchers to use these models to their full extent.

Magnolia officinalis reduces the long-term effects of the status epilepticus induced by kainic acid in immature rats

During critical periods of neurodevelopment, the immature brain is susceptible to neuronal hyperexcitability, alterations such as hyperthermia, hypoxia, brain trauma or a preexisting neuroinflammatory condition can trigger, promote and prolong epileptiform activity and facilitate the development of epilepsy. The goal of the present study was to evaluate the long-term neuroprotective effects Magnolia officinalis extract, on a model of recurrent status epilepticus (SE) in immature rats. Sprague-Dawley rats were treated with kainic acid (KA) (3 mg/kg, dissolved in saline solution) beginning at day 10 P N every 24 h for five days (10 P N-14PN). Two experimental groups (KA) received two treatments for 10 days (14-24 P N): one group was treated with 300 mg/kg Magnolia Officinalis (MO) (KA-MO), and another was treated with 20 mg/kg of celecoxib (Clbx) (KA-Clbx) as a control drug. A SHAM control group at day 90 P N was established. Seizure susceptibility was analyzed through an after-discharge threshold (ADT) evaluation, and electroencephalographic activity was recorded. The results obtained from the ADT evaluation and the analysis of the electroencephalographic activity under basal conditions showed that the MO and Clbx treatments protected against epileptiform activity, and decreases long-term excitability. All rats in the KA-MO and KA-Clbx groups presented a phase I seizure on the Racine scale, corresponding to the shaking of a wet dog. In contrast, the KA group showed phase V convulsive activity on the Racine scale. Similarly, MO and Clbx exerted neuroprotective effects on hippocampal neurons and reduced gliosis in the same areas. Based on these results, early intervention with MO and Clbx treatments to prevent the inflammatory activity derived from SE in early phases of neurodevelopment exerts neuroprotective effects on epileptogenesis in adult stages.

Evidence for the involvement of the GABA-ergic pathway in the anticonvulsant activity of the roots bark aqueous extract of Anthocleista djalonensis A. Chev. (Loganiaceae)

BACKGROUND

The root bark of Anthocleista djalonensis A. Chev. (Loganiaceae) is widely used in traditional medicine in Northern Cameroon to treat epilepsy and related conditions, such as migraine, insomnia, dementia, anxiety, and mood disorders.

METHODS

To investigate the anticonvulsant effects and the possible mechanisms of this plant, an aqueous extract of Anthocleista djalonensis (AEAD) was evaluated by using animal models of bicuculline-, picrotoxin-, pilocarpine-, and pentylenetetrazole-induced convulsions. Their effects on brain γ-aminobutyric acid (GABA) concentration and GABA-T activity were also determined.

RESULTS

This extract significantly protected mice against bicuculline-induced motor seizures. It provided 80% protection against picrotoxin-induced tonic-clonic seizures, and strongly antagonized convulsions induced by pilocarpine. AEAD also protected 100% of mice against pentylenetetrazole-induced seizures. Flumazenil, a central benzodiazepine receptor antagonist and FG7142, a partial inverse agonist in the benzodiazepine site of the GABAA receptor complex, were found to have an inhibitory effect on the anticonvulsant action of AEAD in pentylenetetrazole test. Finally, the brain GABA concentration was significantly increased and GABA-T activity was inhibited by AEAD.

CONCLUSIONS

The effects of Anthocleista djalonensis suggested the presence of anticonvulsant properties that might involve an action on benzodiazepine and/or GABA sites in the GABAA receptor complex or by modulating GABA concentration in the central nervous system (CNS).

Dissociation of spontaneous seizures and brainstem seizure thresholds in mice exposed to eight flurothyl-induced generalized seizures

Objective

C57BL/6J mice exposed to eight flurothyl‐induced generalized clonic seizures exhibit a change in seizure phenotype following a 28‐day incubation period and subsequent flurothyl rechallenge. Mice now develop a complex seizure semiology originating in the forebrain and propagating into the brainstem seizure network (a forebrain→brainstem seizure). In contrast, this phenotype change does not occur in seizure‐sensitive DBA/2J mice. The underlying mechanism was the focus of this study.

Methods

DBA/2J mice were exposed to eight flurothyl‐induced seizures (1/day) followed by 24‐h video‐electroencephalographic recordings for 28 days. Forebrain and brainstem seizure thresholds were determined in C57BL/6J and DBA/2J mice following one or eight flurothyl‐induced seizures, or after eight flurothyl‐induced seizures, a 28‐day incubation period, and final flurothyl rechallenge.

Results

Similar to C57BL/6J mice, DBA/2J mice expressed spontaneous seizures. However, unlike C57BL/6J mice, DBA/2J mice continued to have spontaneous seizures without remission. Because DBA/2J mice did not express forebrain→brainstem seizures following flurothyl rechallenge after a 28‐day incubation period, this indicated that spontaneous seizures were not sufficient for the evolution of forebrain→brainstem seizures. Therefore, we determined whether brainstem seizure thresholds were changing during this repeated‐flurothyl model and whether this could account for the expression of forebrain→brainstem seizures. Brainstem seizure thresholds were not different between C57BL/6J and DBA/2J mice on day 1 or on the last induction seizure trial (day 8). However, brainstem seizure thresholds did differ significantly on flurothyl rechallenge (day 28), with DBA/2J mice showing no lowering of their brainstem seizure thresholds.

Significance

These results demonstrate that DBA/2J mice exposed to the repeated‐flurothyl model develop spontaneous seizures without evidence of seizure remission and provide a new model of epileptogenesis. Moreover, these findings indicated that the transition of forebrain ictal discharge into the brainstem seizure network occurs as a result of changes in brainstem seizure thresholds that are independent of spontaneous seizure expression.

Anticonvulsant effects of agomelatine in mice

Agomelatine is a potent MT1 and MT2 melatonin receptor agonist and a 5-HT2C serotonin receptor antagonist. We analyzed whether agomelatine has anticonvulsant properties. The anticonvulsant activity of agomelatine (25, 50 or 75 mg/kg, i.p.) was evaluated in mouse models of pentylenetetrazole (PTZ-85 mg/kg, i.p.), pilocarpine (400mg/kg, i.p.), picrotoxin (7 mg/kg, i.p.), strychnine (75 mg/kg, i.p.) or electroshock-induced convulsions. In the PTZ-induced seizure model, agomelatine (at 25 or 50mg/kg) showed a significant increase in latency to convulsion, and agomelatine (at 50 or 75 mg/kg) also increased significantly time until death. In the pilocarpine-induced seizure model, only agomelatine in high doses (75 mg/kg) showed a significant increase in latency to convulsions and in time until death. In the strychnine-, electroshock- and picrotoxin-induced seizure models, agomelatine caused no significant alterations in latency to convulsions and in time until death when compared to controls. Our results suggest that agomelatine has anticonvulsant activity shown in PTZ- or pilocarpine-induced seizure models.

Experimental models of seizures and epilepsies

Epilepsy is one of the most common neurological conditions that affect people of all ages. Epilepsy is characterized by occurrence of spontaneous recurrent seizures. Currently available drugs are ineffective in controlling seizures in approximately one-third of patients with epilepsy. Moreover, these drugs are associated with adverse effects, and none of them are effective in preventing development of epilepsy following an insult or injury. To develop an effective therapeutic strategy that can interfere with the process of development of epilepsy (epileptogenesis), it is crucial to study the changes that occur in the brain after an injury and before epilepsy develops. It is not possible to determine these changes in human tissue for obvious ethical reasons. Over the years, experimental models of epilepsies have contributed immensely in improving our understanding of mechanism of epileptogenesis as well as of seizure generation. There are many models that replicate at least some of the characteristics of human epilepsy. Each model has its advantages and disadvantages, and the investigator should be aware of this before selecting a specific model for his/her studies. Availability of a good animal model is a key to the development of an effective treatment. Unfortunately, there are many epilepsy syndromes, specifically pediatric, which still lack a valid animal model. It is vital that more research is done to develop animal models for such syndromes.

Neonatal Seizures: Gaps Between the Laboratory and the Clinic

Seizures in neonates (NBs) remain the most frequent neurological problem in the nursery. Considerable debate about their consequences exists between data and deductions reached through animal experimentations and those obtained through clinical investigations. The main conflicting issues are whether seizures in NBs can plant the roots for epileptogenesis and cause long-term deficits. The purpose of this chapter is to evaluate both laboratory and clinical results.

METHODS

Clinical data will be presented, including a 20-year-long cohort of NBs. This will be followed by the main seminal discoveries obtained in neonatal models. The phenomenon of transient or persistent dysmaturity following NB seizures will be discussed in relation to etiological factors.

RESULTS

The findings and deductions from animal models support the notions that epileptogenesis and cognitive deficits result from NB seizures. These conclusions contrast with clinical investigations maintaining that NB seizures, per se, are symptomatic markers of preexisting or of ongoing morbidities. The reasons for contrasting views will be discussed. Suggestions will be advanced for more animal models whose seizures are consistent with the etiologies and the phenotypes of human NB seizures.

Changes in respiratory-modulated neural activities, consistent with obstructive and central apnea, during fictive seizures in an in situ anaesthetized rat preparation

Sudden unexplained death in epilepsy (SUDEP) has been proposed to result from seizure-induced changes in respiratory and cardiac function. Our purpose was to characterize changes in respiration during seizures. We used a preparation of the anaesthetized, perfused in situ rat. This preparation has the advantage over in vivo preparations in that delivery of oxygen to the brain does not depend upon the lungs or cardiovascular system. Electroencephalographic activity was recorded as were activities of the hypoglossal, vagus and phrenic nerves. The hypoglossal and vagus nerves innervate muscles of the upper airway and larynx while the phrenic nerve innervates the diaphragm. Fictive seizures were elicited by injections of penicillin into the parietal cortex or the carotid artery. Following elicitation of the fictive seizures, activities of the hypoglossal and vagal nerves declined greatly while phrenic activity was little altered. Such a differential depression of activities of nerves to the upper airway and larynx, compared to that to the diaphragm, would predispose to obstructive apnea in intact preparations. With more time, activity of the phrenic nerve also declined or ceased. These changes characterize central apnea. The major conclusion is that seizures may result in recurrent periods of obstructive and central apnea. Thus, seizures can adversely alter respiratory function in a profound manner.

Effects of Status Epilepticus Early in Life on Susceptibility to Ischemic Injury in Adulthood

PURPOSE

Status epilepticus (SE) commonly occurs in children, whereas ischemic stroke is the most frequent neurologic insult in adults. The purpose of this study was to determine the effect of SE induced in immature (15 days old; PN15) male rats, on susceptibility to subsequent transient focal cerebral ischemia induced in adulthood.

METHODS

SE was induced by flurothyl ether (FE) or kainic acid (KA). Rats that did not develop seizures after FE or KA served as controls. Five weeks later, the now-adult rats were subjected to middle cerebral artery occlusion (MCAo) for 1 or 2 h by using the intraluminal filament technique. The extent of the infarct volume was evaluated 24 h later.

RESULTS

In rats submitted to 1-h-long FE-SE, the volume of infarction was significantly reduced compared with that in rats exposed to FE without SE. Longer duration of FE-SE was acutely lethal. KA-SE induced prolonged behavioral SE (156 +/- 17.5 min). In these rats, the volume of infarction was significantly larger compared with that in rats that did not show any electrographic seizures after KA administration. Comparison of FE and KA groups revealed that differences in the size of infarction were confined into cortical areas served by the MCA. Neither type of SE induced any obvious histologic changes in these neocortical regions before stroke induction.

CONCLUSIONS

Early in life, SE can influence the outcome of a subsequent focal ischemic insult in adulthood. The extent of the infarct is related to the duration and cause of SE. Prolonged SE induced by KA worsens the outcome, whereas FE-SE has a neuroprotective effect.

Infantile spasms: criteria for an animal model

Infantile spasms is an epilepsy syndrome with several distinctive features, including age specificity during infancy, characteristic semiology (epileptic spasms), specific electroencephalographic patterns (interictal hypsarrhythmia and ictal voltage suppression), and responsiveness to the adrenocorticotropic hormone (ACTH). There is no adequate animal model of infantile spasms, perhaps due to these clinically unique features, that is specific for the developing human brain. An informative animal model would provide insights into the pathophysiology of this syndrome and form the basis for the development of innovative therapies. This chapter considers criteria for an "ideal" animal model of infantile spasms, as well as "minimal" criteria that we consider essential to yield useful information. Two animal models of infantile spasms have been described in rodents: seizures induced by corticotropin-releasing factor and N-methyl-D-aspartic acid. Neither of these models conforms exactly to the human analog, but each possesses intriguing similarities that provide testable hypotheses for future investigations.

Consequences of epilepsy in the developing brain: implications for surgical management

The developing brain is highly susceptible to seizures, as demonstrated by both human and animal studies. Until recently, the brain has been considered to be relatively resistant to damage induced by seizures early in life. Accumulating evidence in animal models now suggests that early seizures can cause structural and physiologic changes in developing neural circuits that result in permanent alterations in the balance between neuronal excitation and inhibition, deficits in cognitive function, and increased susceptibility to additional seizures. The disruption of normal neuronal activity by seizures can affect multiple developmental processes, resulting in these long-lasting changes. These data should be considered in the clinical approach to children with intractable epilepsy and suggest that early intervention may avoid some of these long-term neurologic deficits.

Pharmacodynamic interaction between phenytoin and sodium valproate changes seizure thresholds and pattern

1. In this study we used cortical stimulation to assess the effects of phenytoin (PHT), sodium valproate (VPA), and their interaction on total motor seizure and on the constituent elements of the seizure. 2. PHT (40 mg kg(-1)) was administered as an intravenous bolus infusion to animals receiving either a continuous infusion of VPA or saline. VPA plasma concentration was maintained at levels that produced no detectable anticonvulsant effect. 3. Analysis of ictal components (eyes closure, jerk, gasp, forelimb, clonus, and hindlimb tonus) and their durations revealed both qualitative and quantitative differences in drug effects. 4. The anticonvulsant effect is represented by the increase in the duration of the stimulation required to reach a given seizure threshold. PHT significantly increased the duration of the stimulation and of the motor seizure. This increase was greatly enhanced by VPA. In addition, ictal component analysis revealed that the combination of PHT and VPA causes the reduction of a specific seizure component (JERK). 5. Neither the free fraction of PHT nor the biophase equilibration kinetics changes in the presence of VPA. It is concluded that the synergism may be due to a pharmacodynamic rather than a pharmacokinetic interaction.

Further studies on anti- and proconvulsant effects of inhibitors of nitric oxide synthase in rodents

We confirmed that the effects of inhibitors of nitric oxide (NO) synthase, such as Nomega-nitro-L-arginine methyl ester and Nomega-nitro-L-arginine, differ depending on several experimental factors. Both compounds but not their less active enantiomers delayed picrotoxin-induced clonus in mice yet increased the incidence of clonus following low-dose picrotoxin. Nomega-nitro-L-arginine methyl ester significantly reduced the latencies of both myoclonus and clonus in older but not younger Sprague-Dawley rats receiving pentylenetetrazol s.c. By contrast, there was no significant change in the latencies for myoclonus and clonus in Wistar rats (older and younger). However, when pentylenetetrazol was administered i.p. rather than s.c., Nomega-nitro-L-arginine methyl ester dramatically increased latencies of convulsive indicators, including tonus, in both Sprague-Dawley and Wistar rats. Nomega-nitro-L-arginine methyl ester also delayed tonus but not myoclonus or clonus in mice, regardless of the systemic route of administration of pentylenetetrazol. Both Nomega-nitro-L-arginine methyl ester and NG-nitro-L-arginine increased the tonic CD50 of pentylenetetrazol in mice and Nomega-nitro-L-arginine methyl ester delayed 4-aminopyridine-induced tonus. However, Nomega-nitro-L-arginine methyl ester reduced the tonic CD50 of both picrotoxin and 4-aminopyridine in mice and failed to suppress tonus following maximal electroshock. Evidently, inhibitors of NO synthase are not universally effective antitonic drugs.

Critical review of the animal models of generalized epilepsies

The state of the art for models of generalized seizures in animals is satisfactory, but improvable for what concerns primary generalized seizures of Petit-Mal type. Other models of secondary generalized seizures are available allowing acceptable ways of studying some mechanisms of epileptogenesis, and/or screening potentials new AEDs. For other forms of seizures, such as amyotonic fits, there are no models. By and large, models of epilepsy are lagging behind models of seizures as most of the former when reproduced in the laboratory are short lived. Spontaneously occurring epilepsies in cats should be studied more widely as they may provide a wide variety of epileptic conditions not dissimilar from the ones seen in humans. Overall, models of seizures and epilepsies are more advanced than the models of most neuropsychiatric conditions.

Critical evaluation of animal models for localization-related epilepsies

There are many forms of human partial seizures and many human localization-related epilepsies. Idiopathic epilepsies undoubtedly have pathophysiologic substrates different from those of symptomatic epilepsies, and there is evidence that some forms of limbic epilepsy involve different epileptogenic mechanisms than neocortical epilepsies. Although these mechanisms are best studied and understood by direct investigations of patients, this is often impractical and experimental animal models are also necessary. The use of experimental animals requires that the relevance of each model to a human condition be determined. Human epilepsies are comprised of multiple component parts which can be modeled independently. For instance, acute animal models provide opportunities to study epileptic seizures, but chronic models are necessary for investigation of processes relevant to epileptic conditions, such as epileptogenesis, transition from interictal to ictal state, and long-term consequences of epilepsy. Interactions between localized epileptic activity and cerebral maturation can also be studied in the animal laboratory. Experimental animal models of human partial seizures and localization-related epilepsies can be used to further investigations on basic mechanisms that cannot be pursued in patients, and to develop hypotheses concerning the fundamental neuronal processes underlying epilepsy and epilepsy-related phenomena that subsequently can be validated in patients. In addition, it would be of great clinical utility to develop animal models of partial seizures or localization-related epilepsy that could be used cost-effectively to screen potential anti-epileptic drugs.