Electroencephalographic and histological characteristics of a model of limbic status epilepticus permitting direct control over seizure duration

Hippocampal atrophy and abnormal brain development following a prolonged hyperthermic seizure in the immature rat with a focal neocortical lesion

In rats subjected to a focal cortical lesion soon after birth, hyperthermia at P10 induces a prolonged epileptic seizure, often followed by temporal lobe epilepsy in the adult. To determine whether brain damage and notably hippocampal atrophy occur early on in this model, whole brain as well as hemispheric, cortical, subcortical and hippocampal volumes was measured in non-lesioned and lesioned rat pups, 2 days (P12) and 12 days (P22) after the hyperthermic seizure. All pups with a cortical lesion showed reductions in whole brain and in ipsilateral hemispheric, cortical and hippocampal volumes at P12, which persisted at P22 in pups having also sustained a prolonged hyperthermic seizure at P10. Limiting the duration of the seizure with Diazepam prevented the hippocampal atrophy. Thus, a prolonged hyperthermic seizure in immature brain with a subtle neocortical lesion impairs normal brain development, and the duration of the seizure appears to be a key factor in generating hippocampal atrophy.

Antiepileptic drugs and neuroprotection: current status and future roles

There has been a growing interest in the use of antiepileptic drugs (AEDs) for neuroprotection, and in the possible role of AEDs in disease modification (i.e., antiepileptogenesis). Increased understanding of the mechanisms underlying brain injury has led to advances in the study of neuroprotection. However, defining the clinical paradigm and selecting appropriate outcomes to detect neuroprotective effects present challenges to clinicians studying the neuroprotective properties of drugs. Established AEDs, such as phenytoin, phenobarbital, and carbamazepine, have shown neuroprotective activity in an ischemic/hypoxic model of neuronal injury. Animal model studies also have suggested that newer AEDs, such as levetiracetam, topiramate, and zonisamide, may have neuroprotective or antiepileptogenic properties. However, the prevention of epileptogenesis by an AED has yet to be demonstrated in clinical trials. The future of neuroprotection may involve established and newer AEDs, as well as other compounds, such as immunophilins, caspase inhibitors, endocannabinoids, and antioxidants.

Induction of prolonged electrographic seizures in vitro has a defined threshold and is all or none: implications for diagnosis of status epilepticus

PURPOSE

To study whether induction of prolonged (>30-min duration) in vitro electrographic seizure discharges resembling status epilepticus (SE) is graded or all-or-none, and to determine the critical factors mediating SE induction.

METHODS

Prolonged electrographic seizure discharges were induced in combined hippocampal-entorhinal cortical (HEC) brain slices by electrical stimulation of the Schaeffer collaterals. Discharges were recorded by using field-potential electrodes in the dentate gyrus, CA3, CA1, and entorhinal cortex. Slices were prepared from rats that were (a). 21- to 30-day-old naive, (b). 60- to 120-day old naive, (c). epileptic, and (d). status post a prior traumatic brain injury.

RESULTS

Induction of SE discharges was dependent on the duration, but not amplitude of the preceding stimulus train-induced afterdischarge in HEC slices from 21- to 30-day-old control, brain-injured, and epileptic animals, but not from 60- to 120-day-old animals. In slices from 21- to 30-day-old control animals, once afterdischarges exceeded 4 min in duration, SE was induced in 50% of slices, and after >or=6 min 37 s seizure activity; SE was induced in 95% of slices. A defined SE threshold also was evident in brain-damaged rats, including rats in which an epileptic condition was induced by pilocarpine injection 4-16 weeks before recording, and rats subjected to a fluid percussive head trauma 1-8 weeks before recording. However, in these brain-damaged animals, mean SE threshold was considerably lower (24 and 44 s, respectively). HEC slices from 60- to 120-day-old controls for the brain-injured and epileptic animals did not develop SE even after 20 stimulations, demonstrating the pronounced effect of brain injury and epilepsy on the development of SE in the HEC slice preparation compared with that in age-matched controls.

CONCLUSIONS

In vitro, SE discharges have a defined temporal threshold for initiation. Once a seizure exceeds 6-7 min in duration in control animals, and 30-55 s in brain-damaged animals, the probability of SE induction is greatly increased. This demonstrates that brain injury lowers the afterdischarge duration required to produce SE and suggests that brains injured from trauma or SE are more susceptible to develop status epilepticus.

Do prolonged febrile seizures produce medial temporal sclerosis? Hypotheses, MRI evidence and unanswered questions

Whether or not severe febrile seizures in infancy cause hippocampal injury and subsequent medial temporal sclerosis is an often debated question in epilepsy. Recent magnetic resonance imaging (MRI) of infants suffering from febrile seizures has provided preliminary evidence that abnormally increased T2 signal intensity can be seen in the hippocampi of infants following prolonged and focal febrile seizures. Follow-up MRIs in a few of these infants have confirmed that medial temporal sclerosis can develop following these acute MRI signal changes. In this article, we review the hypotheses and MRI evidence relating to hippocampal injury during prolonged febrile seizures and the later development of medial temporal sclerosis.

Neuroprotective effects of early vs. late administration of dantrolene in experimental status epilepticus

We examined the effects of dantrolene, an inhibitor of intracellular calcium release, on hippocampal neuronal damage associated with 140 min of limbic status epilepticus in the rat. Dantrolene (10 mg/kg i.p.) was administered after either 30 min or 140 min of status epilepticus. Early administration was associated with a significant reduction in the amount of neuronal injury in all hippocampal subregions, while late administration was associated with less neuronal injury in area CA3 only. These findings suggest that a substantial portion of seizure-induced hippocampal injury is associated with release of calcium from intracellular stores, and that early administration of dantrolene may be a useful adjunct to anticonvulsant treatment of status epilepticus.

Topiramate reduces neuronal injury after experimental status epilepticus

Prolonged seizures are associated with injury to vulnerable neurons, particularly in the hippocampus. Identification of compounds that attenuate injury after prolonged seizures could be of value in the management of refractory status epilepticus. We hypothesized that topiramate, an anticonvulsant with multiple mechanisms of action, would attenuate hippocampal neuronal injury when given after experimental status epilepticus. Limbic status epilepticus was induced in adult male Wistar rats for 140 min by unilateral hippocampal electrical stimulation. Rats then received intraperitoneal injections of either vehicle (n=6) or topiramate at 20 mg/kg (n=6), 40 mg/kg (n=7) or 80 mg/kg (n=7). Three days later, hippocampal sections were processed for neuronal degeneration using a silver impregnation stain. Seizure-induced damage was assessed by measuring the density of silver staining in hippocampal regions CA1, CA3 and dentate hilus. Administration of topiramate at each dose was associated with a significant reduction in staining density bilaterally in area CA1 and the dentate hilus. Reduction in staining density in area CA3 was seen contralateral to the side of stimulation at the two higher topiramate doses only. The results indicate that administration of topiramate after experimental status epilepticus can attenuate seizure-induced hippocampal neuronal injury.