Interictal aggression in rats with chronic seizures after an early life episode of status epilepticus.

OBJECTIVE: In spite of anecdotal reports describing an association between chronic epilepsy and interictal aggressiveness, and of a few studies suggesting that such an association is common in temporal lobe epilepsy, this concept has not been generally accepted by epileptologists. In the course of studies of the long-term consequences of limbic status epilepticus (SE) in juvenile rats, we noticed that experimental animals, unlike littermate controls, could not be housed together because of severe fighting. We now report a study of interictal aggression in those rats. METHODS: Long-term behavioral consequences of lithium/pilocarpine SE were studied 3 months after SE had been induced with lithium and pilocarpine in male Wistar rats at age 28 days. Chronic spontaneous seizures developed in 100% of animals. We tested rats for territorial aggression under the resident-intruder paradigm. We measured the number of episodes of dominance (mounting and pinning), and agonistic behavior (attacks, boxing, and biting). RESULTS: Untreated lithium/pilocarpine SE induced a large increase in aggressive behavior, which involved all aspects of aggression in the resident-intruder paradigm when tested 3 months after SE. The experimental rats were dominant toward the controls, as residents or as intruders, and showed episodes of biting and boxing rarely displayed by controls. They also displayed increased aggressiveness compared with controls when tested against each other. SIGNIFICANCE: This robust model offers an opportunity to better understand the complex relationship between seizures, epilepsy, and aggression, and the role of age, SE vs. recurrent spontaneous seizures, and focal neuronal injury in the long-term behavioral effects of SE.

Treatment of early life status epilepticus: What can we learn from animal models?

Treatment of status epilepticus (SE) in infants and children is challenging. There is a recognition that a broad set of developmental processes need to be considered to fully appreciate the physiologic complexity of severe seizures, and seizure outcomes, in infants and children. The development and use of basic models to elucidate important mechanisms will help further our understanding of these processes. Here we review some of the key experimental models and consider several areas relevant to treatment that could lead to productive translational research. Terminating seizures quickly is essential. Understanding pharmacoresistance of SE as it relates to receptor trafficking will be critical to seizure termination. Once a severe seizure is terminated, how will the developing brain respond? Basic studies suggest that there are important acute and long-term histopathologic, and pathophysiologic, consequences that, if left unaddressed, will produce long-lasting deficits on the form and function of the central nervous system. To fully utilize the evidence that basic models produce, age- and development- and model-specific frameworks have to be considered carefully. Studies have demonstrated that severe seizures can cause perturbations to developmental processes during critical periods of development that lead to life-long deficits. Unfortunately, some of the drugs that are commonly used to treat seizures may also produce negative outcomes by enhancing Cl--mediated depolarization, or by accelerating programmed cell death. More research is needed to understand these phenomena and their relevance to the human condition, and to develop rational drugs that protect the developing brain from severe seizures to the fullest extent possible.

Rational polytherapy in the treatment of acute seizures and status epilepticus.

We used a model of severe cholinergic status epilepticus (SE) to study polytherapy aimed at reversing the effects of seizure-induced loss of synaptic GABA(A) receptors and seizure-induced gain of synaptic NMDA receptors. Combinations of a benzodiazepine with ketamine and valproate, or with ketamine and brivaracetam, were more effective and less toxic than benzodiazepine monotherapy in this model of SE.

Brain energy metabolism during experimental neonatal seizures.

During flurothyl seizures in 4-day-old rats, cortical concentration of ATP, phosphocreatine and glucose fell while lactate rose. Cortical energy use rate more than doubled, while glycolytic rate increased fivefold. Calculation of the cerebral metabolic balance during sustained seizures suggests that energy balance could be maintained in hyperglycemic animals, and would decline slowly in normoglycemia, but would be compromised by concurrent hypoglycemia, hyperthermia or hypoxia. These results suggest that the metabolic challenge imposed on the brain by this model of experimental neonatal seizures is milder than that seen at older ages, but can become critical when associated with other types of metabolic stress.

Treatment of experimental status epilepticus in immature rats: dissociation between anticonvulsant and antiepileptogenic effects.

We studied the effects of treating status epilepticus (SE) induced by lithium and pilocarpine at postnatal day 15 (P15) or 28 (P28), on the severity of acute SE and of SE-induced epileptogenesis. Rats received topiramate (10 or 50 mg/kg, IP) or diazepam (5 mg/kg, IP) 20, 40 or 70 min after pilocarpine, and three months after SE 24-h video/EEG recordings were obtained for one (P28) or two weeks (P15) continuously. In P15 rats, topiramate did not modify the course of SE, yet treatment at 20 or 40 min completely prevented the development of spontaneous recurrent seizures (SRS) while later treatment (70 min) was partially effective in reducing the severity and frequency of SRS. Diazepam was effective against acute SE at all time points tested. Early (20 min) but not late treatment with diazepam had the effect of reducing the frequency and severity of SRS. In P28 rats, both drugs reduced the cumulative seizure time. Early treatment (20 min) with either drug reduced the incidence of chronic epilepsy. Late treatment (40/70 min) did not alter the incidence of SRS, but decreased their frequency. This study demonstrates that, in the treatment of SE, anticonvulsant and antiepileptogenic effects can be dissociated in a development-specific manner: topiramate was antiepileptogenic without being an effective anticonvulsant in P15 animals at the doses tested. Diazepam, on the other hand, was a better anticonvulsant than an antiepileptogenic agent in the P15 animals at the dose tested. Such effects were not seen in the older animals.

Transplants of cells engineered to produce GABA suppress spontaneous seizures.

PURPOSE: Cell transplantation into the brain is an aggressive clinical alternative. The hopes of treating diseases like intractable temporal lobe epilepsy have been subdued because the preclinical successes thus far have shown only slowing of epileptogenesis, or suppression of electrically induced seizures. Because the hallmark of epilepsy is spontaneous seizures, the clinical relevance of these studies has been questioned. The purpose of this study was to establish that cells genetically engineered to produce gamma-aminobutyric acid (GABA) could suppress spontaneous seizures in an accepted model of temporal lobe epilepsy. METHODS: Conditionally immortalized neurons were engineered to produce GABA under the control of tetracycline. These cells were transplanted into the substantia nigra of spontaneously seizing animals. After transplantation, the animals were monitored for 3 days immediately after surgery and again for 3 days beginning 7-8 days after surgery. Seizures and epileptiform spikes were recorded and later analyzed with detection software combined with video monitoring. RESULTS: Animals that received genetically engineered GABA-producing cells had significantly fewer spontaneous seizures than did animals that received control cells, or animals that received GABA-producing cells plus doxycycline at the observation period starting 1 week after transplantation. A significant suppression of epileptiform spikes also was noted between the group that received GABA-producing cells and the group that received the same cells but were given doxycycline. The engineered cells show evidence of integration with the host but limited survival. CONCLUSIONS: These data demonstrate that genetically engineered cells have the ability to suppress spontaneous seizures when transplanted into seizure-modulating nuclei. This is an important step toward defining a clinical potential for this approach in epilepsy. The fact that the gene of interest can be regulated suggests that individualizing transplant therapy may be possible.

Seizure-induced neuronal death in the immature brain.

The response of the developing brain to epileptic seizures and to status epilepticus is highly age-specific. Neonates with their low cerebral metabolic rate and fragmentary neuronal networks can tolerate relatively prolonged seizures without suffering massive cell death, but severe seizures in experimental animals inhibit brain growth, modify neuronal circuits, and can lead to behavioral deficits and to increases in neuronal excitability. Past infancy, the developing brain is characterized by high metabolic rate, exuberant neuronal and synaptic networks and overexpression of receptors and enzymes involved in excitotxic mechanisms. The outcome of seizures is highly model-dependent. Status epilepticus may produce massive neuronal death, behavioral deficits, synaptic reorganization and chronic epilepsy in some models, little damage in others. Long-term consequences are also highly age- and model-dependent. However, we now have some models which reliably lead to spontaneous seizures and chronic epilepsy in the vast majority of animals, demonstrating that seizure-induced epileptogenesis can occur in the developing brain. The mode cell death from status epilepticus is largely (but not exclusively) necrotic in adults, while the incidence of apoptosis increases at younger ages. Seizure-induced necrosis has many of the biochemical features of apoptosis, with early cytochrome release from mitochondria and capase activation. We speculate that this form of necrosis is associated with seizure-induced energy failure.

Genetically engineered GABA-producing cells demonstrate anticonvulsant effects and long-term transgene expression when transplanted into the central piriform cortex of rats.

Local application of GABA-potentiating agents can prevent or reduce the development and maintenance of behavioral seizures induced by limbic kindling in rats. Microinjection and lesion studies suggest that the transition zone between anterior and posterior piriform cortex (PC), termed here central PC, is a potential target for transplantation of GABA-producing cells. In the present study, we transplanted conditionally immortalized mouse cortical neurons, engineered with the GABA-synthesizing enzyme GAD(65), to the central PC of rats. Suspensions of 1.5 x 10(5) cells in 1 microl were transplanted bilaterally. Control animals received transplantation of beta-galactosidase (beta-gal)-expressing cells. All rats were subsequently kindled through a chronically implanted electrode placed in the basolateral amygdala. The pre- and postkindling threshold currents for eliciting behavioral seizures were determined before and after kindling. We found the prekindling partial seizure threshold to be significantly increased by about 200% in the rats that received the GABA-producing cells compared to rats receiving beta-gal-producing transplants. After kindling, the seizure threshold tended to be higher by 100% in rats that received GABA-producing cells, although the difference from controls was not statistically significant. GABA-producing transplants had no significant effect on the rate of amygdala kindling, but the latency to the first generalized seizure during kindling was significantly increased in animals receiving GABA-producing cells. The transplanted cells showed long-term GAD(65) expression as verified immunohistologically after termination of the experiments. The findings substantiate and extend previous findings that the central PC is part of the anatomical substrate that facilitates propagation from partial to generalized seizures. The data demonstrate that genetically engineered cells have the potential to raise seizure thresholds when transplanted to the central PC.