Antiepileptic drug treatment strategies in neonatal epilepsy

The highest risk of seizures across the lifespan is in the neonatal period. The enhanced excitability of the immature brain compared to the mature brain is related to the sequential development and expression of essential neurotransmitter signaling pathways. During the neonatal period there is an overabundance of excitatory receptors, and γ-amino-butyric acid (GABA) is potentially depolarizing, as opposed to hyperpolarizing in the older brain. While this enhanced excitability is required for regulation of activity-dependent synapse formation and refining of synaptic connections that are necessary for normal brain development, enhanced excitability predisposes the immature brain to seizures. In addition to being common, neonatal seizures are very difficult to treat; antiepileptic drugs used in older children and adults are less efficacious, and possibly detrimental to brain development. In an effort to target the unique features of neurotransmission in the neonate, bumetanide, an NKCC1 inhibitor which reduces intraneuronal Cl(-) and induces a significant shift of EGABA toward more hyperpolarized values in vitro, has been used to treat neonatal seizures. As the understanding of the pathophysiology of genetic forms of neonatal epilepsy has evolved there have been a few successful attempts to pharmacologically target the mutated protein. This approach, while promising, is challenging due to the findings that the genetic syndromes presenting in infancy demonstrate genetic heterogeneity in regard to both the mutated gene and its function.

Cognitive impairment in temporal lobe epilepsy: role of online and offline processing of single cell information

Cognitive impairment is a common comorbidity in temporal lobe epilepsy (TLE) and is often considered more detrimental to quality of life than seizures. While it has been previously shown that the encoding of memory during behavior is impaired in the pilocarpine model of TLE in rats, how this information is consolidated during the subsequent sleep period remains unknown. In this study, we first report marked deficits in spatial memory performance and severe cell loss in the CA1 layer of the hippocampus lower spatial coherence of firing in TLE rats. We then present the first evidence that the reactivation of behavior-driven patterns of activity of CA1 place cells in the hippocampus is intact in TLE rats. Using a template-matching method, we discovered that real-time (3-5 s) reactivation structure was intact in TLE rats. Furthermore, we estimated the entropy rate of short time scale (∼250 ms) bursting activity using block entropies and found that significant, extended temporal correlations exist in both TLE and control rats. Fitting a first-order Markov Chain model to these bursting time series, we found that long sequences derived from behavior were significantly enriched in the Markov model over corresponding models fit on randomized data confirming the presence of replay in shorter time scales. We propose that the persistent consolidation of poor spatial information in both real time and during bursting activity may contribute to memory impairments in TLE rats.

Altered short-term plasticity in the prefrontal cortex after early life seizures

Seizures during development are a relatively common occurrence and are often associated with poor cognitive outcomes. Recent studies show that early life seizures alter the function of various brain structures and have long-term consequences on seizure susceptibility and behavioral regulation. While many neocortical functions could be disrupted by epileptic seizures, we have concentrated on studying the prefrontal cortex (PFC) as disturbance of PFC functions is involved in numerous co-morbid disorders associated with epilepsy. In the present work we report an alteration of short-term plasticity in the PFC in rats that have experienced early life seizures. The most robust alteration occurs in the layer II/III to layer V network of neurons. However short-term plasticity of layer V to layer V network was also affected, indicating that the PFC function is broadly influenced by early life seizures. These data strongly suggest that repetitive seizures early in development cause substantial alteration in PFC function, which may be an important component underlying cognitive deficits in individuals with a history of seizures during development.

Neuro-QOL: brief measures of health-related quality of life for clinical research in neurology

OBJECTIVE

To address the need for brief, reliable, valid, and standardized quality of life (QOL) assessment applicable across neurologic conditions.

METHODS

Drawing from larger calibrated item banks, we developed short measures (8-9 items each) of 13 different QOL domains across physical, mental, and social health and evaluated their validity and reliability. Three samples were utilized during short form development: general population (Internet-based, n = 2,113); clinical panel (Internet-based, n = 553); and clinical outpatient (clinic-based, n = 581). All short forms are expressed as T scores with a mean of 50 and SD of 10.

RESULTS

Internal consistency (Cronbach α) of the 13 short forms ranged from 0.85 to 0.97. Correlations between short form and full-length item bank scores ranged from 0.88 to 0.99 (0.82-0.96 after removing common items from banks). Online respondents were asked whether they had any of 19 different chronic health conditions, and whether or not those reported conditions interfered with ability to function normally. All short forms, across physical, mental, and social health, were able to separate people who reported no health condition from those who reported 1-2 or 3 or more. In addition, scores on all 13 domains were worse for people who acknowledged being limited by the health conditions they reported, compared to those who reported conditions but were not limited by them.

CONCLUSION

These 13 brief measures of self-reported QOL are reliable and show preliminary evidence of concurrent validity inasmuch as they differentiate people based upon number of reported health conditions and whether those reported conditions impede normal function.

Benign focal epilepsies of childhood

Until relatively recently, genetic influences in partial seizures were thought to be of minimal importance. However, with further identification of childhood benign partial seizures it is becoming clear that inheritance plays a major role in the pathogenesis of these seizures. Diagnostic criteria proposed for benign partial seizures include absence of neurologic or intellectual deficits, family history of epilepsy, onset of seizures after age 2 years, stereotyped brief seizures, frequent nocturnal occurrence, spontaneous remission in adolescence, and electroencephalograms (EEGs) demonstrating spikes with a distinctive morphology and localization superimposed on normal background activity. The two most commonly described benign partial epilepsies of childhood are benign Rolandic epilepsy (BRE) and benign occipital epilepsy (BOE). Both disorders begin in childhood, are associated with characteristic EEG patterns, have seizures that are easily controlled with medication, often are familial, and have an excellent prognosis. The other benign partial seizure disorders in children that have been described are not as well studied as BOE and BRE, and the role of inheritance pattern, if any, is less clear.

Pregnancy registries in epilepsy: a consensus statement on health outcomes

Most pregnant women with epilepsy require antiepileptic drug (AED) therapy. Present guidelines recommend optimizing treatment prior to conception, choosing the most effective AED for seizure type and syndrome, using monotherapy and lowest effective dose, and supplementing with folate. The Epilepsy Therapy Project established the international Health Outcomes in Pregnancy and Epilepsy (HOPE) forum to learn more about the impact of AEDs on the developing fetus, particularly the role of pregnancy registries in studying AED teratogenicity. The primary outcome of interest in these registries is the occurrence of major congenital malformations, with some data collected on minor malformations. Cognitive and behavioral outcomes are often beyond the timeframe for follow-up of these registries and require independent study. The HOPE consensus report describes the current state of knowledge and the limitations to interpretations of information from the various sources. Data regarding specific risks for both older and newer AEDs need to be analyzed carefully, considering study designs and confounding factors. There is a critical need for investigations to delineate the underlying mechanisms and explain the variance seen in outcomes across AEDs and within a single AED.

[Relevance of basic research to clinical data: Good answers, wrong questions!]

What conclusions can be derived from experimental data on human epilepsies? This review discusses these issues, notably concerning human temporal lobe epilepsies (TLEs) and infantile epilepsies, where important advances have been achieved in both theory and the comprehension of epileptogenic mechanisms. A wide spectrum of human and animal data converge to show that the naive network transforms to one that generates seizures spontaneously. Thus, in TLE, experimental and human data suggest that the inaugurating status generates a sequence of events that lead to the sprouting of fibers and the formation of novel excitatory synapses. This reactive plasticity constitutes a basis for the generation of novel seizures by the epileptic network. Similarly, in vitro studies indicate that in immature hippocampal formation, the propagation of high- but not low-frequency seizures can transform a naive network into one that generates further seizures, thereby, giving an indication as to the types of seizure that are epileptogenic. In conclusion, it is suggested that although animal data cannot mimic human seizures in all their complex and variable etiologies, it provides essential indications on the mechanisms that enable seizure generation.

Bilateral volume reduction of the superior temporal areas in Landau-Kleffner syndrome

No specific anatomic abnormalities have been detected in typical Landau-Kleffner syndrome (LKS), an acquired epileptic aphasia with language regression in children. In four children with typical LKS without obvious anatomic abnormalities, the authors performed MRI volumetric analysis of various neocortical regions and subcortical substructures. Volume reduction was detected in bilateral superior temporal areas (26 to 51%), specifically in planum temporale (25 to 63%) and superior temporal gyrus (25 to 57%), where receptive language is localized.

GnRH-immunoreactive fiber changes with unilateral amygdala-kindled seizures

PURPOSE

To assess whether unilateral amygdala seizures are associated with a change in the number and lateral distribution of gonadotropin releasing hormone (GnRH)-staining fibers in the ventromedial hypothalamus of female rats.

METHODS

The study compared three groups of female rats: (1) amygdala seizures induced by focal injection of kainic acid (KA); (2) saline injected controls; and (3) nai;ve controls. The animals were sacrificed at 4 weeks in the diestrus phase. GnRH fibers were counted in the ventromedial hypothalamus and compared among groups.

RESULTS

GnRH fiber counts were significantly lower in KA than saline and nai;ve animals ipsilaterally but not contralaterally.

CONCLUSIONS

This finding may support a potential mechanism by which (1) temporolimbic epilepsy may promote the development of reproductive endocrine disorders and (2) the laterality of the epilepsy may influence the particular nature of the reproductive endocrine disorder.

Beneficial effects of enriched environment following status epilepticus in immature rats

BACKGROUND

There is increasing evidence that enriching the environment can improve cognitive and motor deficits following a variety of brain injuries. Whether environmental enrichment can improve cognitive impairment following status epilepticus (SE) is not known.

OBJECTIVE

To determine whether the environment in which animals are raised influences cognitive function in normal rats and rats subjected to SE.

METHODS

Rats (n = 100) underwent lithium-pilocarpine-induced SE at postnatal (P) day 20 and were then placed in either an enriched environment consisting of a large play area with toys, climbing objects, and music, or in standard vivarium cages for 30 days. Control rats (n = 32) were handled similarly to the SE rats but received saline injections instead of lithium-pilocarpine. Rats were then tested in the water maze, a measure of visual-spatial memory. A subset of the rats were killed during exposure to the enriched or nonenriched environment and the brains examined for dentate granule cell neurogenesis using bromodeoxyuridine (BrdU) and phosphorylated cyclic AMP response element binding protein (pCREB) immunostaining, a brain transcription factor important in long-term memory.

RESULTS

Both control and SE rats exposed to the enriched environment performed significantly better than the nonenriched group in the water maze. There was a significant increase in neurogenesis and pCREB immunostaining in the dentate gyrus in both control and SE animals exposed to the enriched environment compared to the nonenriched groups. Environmental enrichment resulted in no change in SE-induced histologic damage.

CONCLUSIONS

Exposure to an enriched environment in weanling rats significantly improves visual-spatial learning. Even following SE, an enriched environment enhances cognitive function. An increase in neurogenesis and activation of transcription factors may contribute to this enhanced visual-spatial memory.

Timing of cognitive deficits following neonatal seizures: relationship to histological changes in the hippocampus

Neonatal seizures are frequently associated with cognitive impairment and reduced seizure threshold. Previous studies in our laboratory have demonstrated that rats with recurrent neonatal seizures have impaired learning, lower seizure thresholds, and sprouting of mossy fibers in CA3 and the supragranular region of the dentate gyrus in the hippocampus when studied as adults. The goal of this study was to determine the age of onset of cognitive dysfunction and alterations in seizure susceptibility in rats subjected to recurrent neonatal seizures and the relation of this cognitive impairment to mossy fiber sprouting and expression of glutamate receptors. Starting at postnatal day (P) 0, rats were exposed to 45 flurothyl-induced seizures over a 9-day period of time. Visual-spatial learning in the water maze and seizure susceptibility were assessed in subsets of the rats at P20 or P35. Brains were evaluated for cell loss, mossy fiber distribution, and AMPA (GluR1) and NMDA (NMDAR1) subreceptor expression at these same time points. Rats with neonatal seizures showed significant impairment in the performance of the water maze and increased seizure susceptibility at both P20 and P35. Sprouting of mossy fibers into the CA3 and supragranular region of the dentate gyrus was seen at both P20 and P35. GluR1 expression was increased in CA3 at P20 and NMDAR1 was increased in expression in CA3 and the supragranular region of the dentate gyrus at P35. Our findings indicate that altered seizure susceptibility and cognitive impairment occurs prior to weaning following a series of neonatal seizures. Furthermore, these alterations in cognition and seizure susceptibility are paralleled by sprouting of mossy fibers and increased expression of glutamate receptors. To be effective, our results suggest that strategies to alter the adverse outcome following neonatal seizures will have to be initiated during, or shortly following, the seizures.

Outcome of severe refractory status epilepticus in children

PURPOSE

Refractory status epilepticus (RSE) is the persistence of seizure activity despite appropriate therapy; it is treated with high-dose suppressive anesthetic agents. We report here the outcome of RSE in a large series of children.

METHODS

We retrospectively reviewed cases of RSE treated at Children's Hospital, Boston, between 1992 and 2000. Factors evaluated included age, history of seizures or neurologic impairment, etiology, outcome, including mortality or return to baseline, and initial EEG findings.

RESULTS

Twenty-two patients ages 4.5 months to 18 years were admitted to the intensive care unit for RSE. All were treated with high-dose suppressive therapy consisting of pentobarbital, midazolam, propofol infusion, or high-dose phenobarbital, either alone, or in combination, for < or =146 days. The overall mortality was seven of 22. Mortality was related to etiology, age, and EEG findings. No death occurred in the remote symptomatic group, and three of four younger than 3 years died, whereas only four of 18 older than 3 years died. The mortality rate among patients with focal abnormalities on the EEG was lower than that among those with multifocal or generalized abnormalities. None of the children with normal premorbid neurologic status returned to baseline.

CONCLUSIONS

Our data demonstrate a high mortality and morbidity for childhood RSE. Mortality is related to etiology and is higher in younger children and with multifocal or generalized abnormalities on the initial EEG.

Enhanced auditory reversal learning by genetic activation of protein kinase C in small groups of rat hippocampal neurons

The hippocampus has a central role in specific types of learning, but there is only limited evidence identifying the requisite molecular changes in ensembles of hippocampal neurons. To investigate the role of protein kinase C (PKC) pathways in hippocampal mediated learning, a constitutively active, catalytic domain of rat PKC betaII was delivered into hippocampal dentate granule neurons using a Herpes Simplex Virus (HSV-1) vector. This PKC causes a long-lasting, activation-dependent increase in neurotransmitter release from cultured cells. Activation of PKC pathways in a small percentage (< or =0.26%) of dentate granule neurons was sufficient to enhance rat auditory discrimination reversal learning. The affected neurons altered hippocampal physiology as revealed by elevated NMDA receptor densities in specific hippocampal areas. Thus, these results directly suggest that activation of PKC pathways in a specific hippocampal area alters rat auditory discrimination reversal learning. Because each rat may contain a unique pattern of affected neurons, there appears to be considerable flexibility and/or redundancy in the groups of neurons that can modify learning.

Prediction of safe duration of hypothermic circulatory arrest by near-infrared spectroscopy

OBJECTIVE

Hypothermic circulatory arrest is widely used for adults with aortic arch disease as well as for children with congenital heart disease. At present, no method exists for monitoring safe duration of circulatory arrest. Near-infrared spectroscopy is a new technique for noninvasive monitoring of cerebral oxygenation and energy state. In the current study, the relationship between near-infrared spectroscopy data and neurologic outcome was evaluated in a survival piglet model with hypothermic circulatory arrest.

METHODS

Thirty-six piglets (9.36 +/- 0.16 kg) underwent circulatory arrest under varying conditions with continuous monitoring by near-infrared spectroscopy (temperature 15 degrees C or 25 degrees C, hematocrit value 20% or 30%, circulatory arrest time 60, 80, or 100 minutes). Each setting included 3 animals. Neurologic recovery was evaluated daily by neurologic deficit score and overall performance category. Brain was fixed in situ on postoperative day 4 and examined by histologic score.

RESULTS

Oxygenated hemoglobin signal declined to a plateau (nadir) during circulatory arrest. Time to nadir was significantly shorter with lower hematocrit value (P <.001) and higher temperature (P <.01). Duration from reaching nadir until reperfusion ("oxygenated hemoglobin signal nadir time") was significantly related to histologic score (r (s) = 0.826), neurologic deficit score (r (s) = 0.717 on postoperative day 1; 0.716 on postoperative day 4), and overall performance category (r (s) = 0.642 on postoperative day 1; 0.702 on postoperative day 4) (P <.001). All animals in which oxygenated hemoglobin signal nadir time was less than 25 minutes were free of behavioral or histologic evidence of brain injury.

CONCLUSION

Oxygenated hemoglobin signal nadir time determined by near-infrared spectroscopy monitoring is a useful predictor of safe duration of circulatory arrest. Safe duration of hypothermic circulatory arrest is strongly influenced by perfusate hematocrit value and temperature during circulatory arrest.

Recurrent neonatal seizures: relationship of pathology to the electroencephalogram and cognition

Seizures in preterm infants are associated with a high risk of neurological sequelae. In the neonatal rat recurrent seizures have been associated with long-term changes in cerebral excitability and cognition as well as sprouting of mossy fiber terminals in the granule cell layer of the dentate gyrus and hippocampal CA3 subfield. To evaluate the relationship between seizure-induced morphological changes and cognitive function we subjected newborn rats to 55 seizures with flurothyl during the first 12 days of life. During adolescence rats with prior recurrent seizures were compared with controls in electroencephalographic power and performance in the Morris water maze and open field test. Rats subjected to recurrent seizures had marked impairment in water maze performance and never reached the level of learning seen in controls despite a total of 54 trials. Recurrent seizures were also associated with an overall reduction in spectral power which was most pronounced in the theta range. On histological examination rats with recurrent neonatal seizures had sprouting of mossy fiber terminals in CA3 and the granule cell layer of the dentate gyrus without any accompanying cell loss. Sprouting in CA3, but not the granule cell layer of the dentate gyrus, correlated with water maze performance. This study demonstrates that recurrent neonatal seizures can result in profound impairment of water maze performance and reduction of electroencephalographic power despite the lack of discernible cell loss and that this cognitive impairment correlates with mossy fiber sprouting in CA3.

Reduced neurogenesis after neonatal seizures

Although neonatal seizures are quite common, there is controversy regarding their consequences. Despite considerable evidence that seizures may cause less cell loss in young animals compared with mature animals, there are nonetheless clear indications that seizures may have other potentially deleterious effects. Because it is known that seizures in the mature brain can increase neurogenesis in the hippocampus, we studied the extent of neurogenesis in the granule cell layer of the dentate gyrus over multiple time points after a series of 25 flurothyl-induced seizures administered between postnatal day 0 (P0) and P4. Rats with neonatal seizures had a significant reduction in the number of the thymidine analog 5-bromo-2'-deoxyuridine-5'-monophosphate- (BrdU) labeled cells in the dentate gyrus and hilus compared with the control groups when the animals were killed either 36 hr or 2 weeks after the BrdU injections. The reduction in BrdU-labeled cells continued for 6 d after the last seizure. BrdU-labeled cells primarily colocalized with the neuronal marker neuron-specific nuclear protein and rarely colocalized with the glial cell marker glial fibrillary acidic protein, providing evidence that a very large percentage of the newly formed cells were neurons. Immature rats subjected to a single seizure did not differ from controls in number of BrdU-labeled cells. In comparison, adult rats undergoing a series of 25 flurothyl-induced seizures had a significant increase in neurogenesis compared with controls. This study indicates that, after recurrent seizures in the neonatal rat, there is a reduction in newly born granule cells.

Brain development and generation of brain pathologies

The timing of brain development is genetically programmed and can be profoundly altered by a number of abnormal genes that control proliferation, differentiation, migration, synapse formation, and elimination of cells and synapses. With advances in genetic techniques both the gene and gene product responsible for brain malformation are being identified which will permit a better understanding of the pathophysiology of brain malformations. In addition to genetic abnormalities, brain development can be influenced by a variety of acquired disorders. The type of brain abnormality is highly dependent on the stage of brain development during which the insult occurs. While our understanding of experience- or activity-dependent processes on brain development is limited, it is now clear that this activity can significantly alter the timing of a number of maturational events including receptor maturation and neurogenesis. The future challenge will be both to understand the biological basis of these processes and to use this information to enhance brain development.

Topiramate and metabolic acidosis in pediatric epilepsy

PURPOSE

Topiramate (TPM) has been widely used as an adjunctive therapy for treating epilepsy. TPM is reported to have multiple mechanisms of action, including inhibition of carbonic anhydrase, which may result in metabolic acidosis from decreased serum bicarbonate (HCO3-).

METHODS

Clinical data from 30 children who received TPM as adjunctive therapy for medically refractory epilepsy were reviewed at Children's Hospital, Boston. Serum HCO3- levels were assessed before, during, and after discontinuing TPM (n = 9). When multiple data were available, mean values were used for analysis.

RESULTS

Of the 30 patients, 21 had a >10% decrease in HCO3- levels. The mean decrease in HCO3- among the 21 patients was 4.7 mEq/L, and maximum was 10 mEq/L. No clinical symptoms occurred, and HCO3- supplement was not needed, except for one patient who developed tachypnea from worsened acidosis after prolonged status epilepticus during a suspected viral illness. Among the 21 patients, TPM was discontinued in seven children because of a lack of efficacy, and in two because of anorexia. After discontinuing TPM, the serum HCO3- returned to the previous level before starting TPM in all nine.

CONCLUSIONS

Decreased HCO3- levels occurred in the majority of patients reviewed, usually only to a small to moderate extent, but by 8 and 10 mEq/L in two cases. In patients at risk for acidosis, the decrease in HCO3- may cause significant consequences, such as severe acidosis or renal calculi. Monitoring HCO3- levels before and during TPM therapy may be indicated, especially with conditions that predispose to acidosis.

The neurobiology and consequences of epilepsy in the developing brain

Epilepsy is a disorder in which the balance between cerebral excitability and inhibition is tipped toward uncontrolled excitability. There is now clear evidence that there are distinct differences between the immature and mature brain in the pathophysiology and consequences of seizures. Both the enhanced excitability of the immature brain compared with the mature brain and the unique pathologic consequences of seizures are related to the sequential development and expression of essential signaling pathways. Although the immature brain is less vulnerable than the mature brain to seizure-induced cell death, seizures in the developing brain can result in irreversible alterations in neuronal connectivity. Developing novel strategies to treat and avert the consequences of seizures in children will require further understanding of the unique mechanisms of seizure initiation and propagation in the immature brain.

Anticonvulsant action and long-term effects of gabapentin in the immature brain

The anticonvulsant action and the long-term effects on learning, memory and behavior of the new generation antiepileptic drug gabapentin (GBP) were investigated in immature animals. Kainic acid (KA) was administered to rats on postnatal day (P) 35. Animals were treated with GBP or saline from P36 to P75 and spontaneous seizure frequency was monitored. After tapering the drug, the rats were tested in the water maze and open field test. Brains were then analyzed for histological lesions. Animals treated with GBP following KA-induced status epilepticus had a reduced incidence of spontaneous recurrent seizures, a better pathology score, and less aggressiveness compared to saline-treated controls. Effectiveness of GBP on seizure threshold was tested using flurothyl inhalation in 10 separate age groups of animals ranging from the newborn period to adulthood. Furthermore, GBP plasma concentration peaks were determined in all age groups. At all ages, GBP pre-treated animals demonstrated a higher seizure threshold. Plasma GBP concentrations did not significantly change with age. These data suggest that acute administration of a single therapeutic dose of GBP increases the seizure threshold at all ages studied, while chronic treatment following the status reduces spontaneous seizure frequency and cell damage and has no long-term adverse consequences on cognitive processes during development.

Timing of ketogenic diet initiation in an experimental epilepsy model

Following kainic acid (KA)-induced status epilepticus (SE), the ketogenic diet (KD) retards the development of epileptogenesis, with fewer spontaneous recurrent seizures (SRS) and less mossy fiber sprouting than rats on a normal diet. In this study, we investigated whether there is a critical period for initiation of the KD, in terms of the diet's effectiveness in reducing SRS. In addition, we investigated whether early treatment with the KD prevents the deficits in spatial learning and memory that ordinarily follow KA-induced SE. Young rats (P30) underwent KA-induced SE, followed by assignment to one of three treatment groups: control diet ('KA'), KD begun 2 days after SE ('KD2'), and KD begun fourteen days after SE ('KD14'). For 12 weeks following SE, rats were monitored by closed circuit video recording (12 h/wk) to detect SRS. KD2 rats had significantly fewer SRS than rats in the control or KD14 groups. On water maze testing to assess spatial learning and memory, KD2 rats had significantly poorer acquisition of place learning than control (KA alone) or KD14 rats. KD2 rats also failed to gain weight well. There was no difference between groups on routine histologic examination of the hippocampus. In summary, P30 rats placed on the KD 2 days after SE were relatively protected from recurrent seizures, but showed behavioral and physical impairment. Rats placed on the KD 14 days after KA-induced SE did not differ from controls with regard to spontaneous seizure rate.

Protective effects of prenatal choline supplementation on seizure-induced memory impairment

Choline is an essential nutrient for rats and humans, and its availability during fetal development has long-lasting cognitive effects (Blusztajn, 1998). We investigated the effects of prenatal choline supplementation on memory deficits associated with status epilepticus. Pregnant rats received a control or choline-supplemented diet during days 11-17 of gestation. Male offspring [postnatal day 29 (P29)-32] were tested for their ability to find a platform in a water maze before and after administration of a convulsant dose of pilocarpine at P34. There were no differences between groups in water maze performance before the seizure. One week after status epilepticus (P41-P44), animals that had received the control diet prenatally had a drastically impaired performance in the water maze during the 4 d testing period, whereas prenatally choline-supplemented rats showed no impairment. Neither the seizures nor the prenatal availability of choline had any effect on hippocampal choline acetyltransferase or acetylcholinesterase activities. This study demonstrates that prenatal choline supplementation can protect rats against memory deficits induced by status epilepticus.

Increased susceptibility to generalized seizures after immunolesions of the basal forebrain cholinergic neurons in rats

We investigated whether basal forebrain cholinergic neurons influence the expression of generalized seizures. Animals received intracerebroventricular injections of saporin (lesioned) or saline (controls) and were tested for susceptibility to flurothyl- or pentylenetetrazole-induced seizures. Lesioned rats had significantly shorter latencies to onset of generalized tonic-clonic seizures than controls. Our findings suggest that basal forebrain cholinergic neurons may participate in the modulation of generalized seizures.

Efficacy of gabapentin as adjunctive therapy in a large, multicenter study. The Steps Study Group

The objective of this study was to determine the efficacy of gabapentin as adjunctive therapy in doses required to achieve the most effective seizure control. There were 2016 patients with partial seizures requiring adjunctive therapy who received gabapentin at doses up to 3600 mg/day in this open-label, multicenter, 16-week study. Of the 1055 patients evaluable for efficacy, 573 received gabapentin < or =1800 mg/day and 482 received > 1800 mg/day as the highest dose received. For the overall efficacy evaluable population, the percentage of patients achieving at least a 50% reduction in seizure frequency was 76.0%; 46.4% of the patients were seizure free. Patients whose highest gabapentin dose did not require > 1800 mg/day had, at baseline, fewer seizures and were receiving fewer concomitant antiepileptic drugs (AEDs) at baseline than those patients requiring > 1800 mg/day. This suggests that patients requiring higher doses of gabapentin were more refractory to drug treatment at the start of the study. Gabapentin was well tolerated at all doses in this study. The results of the study demonstrate that gabapentin is effective as adjunctive therapy in patients with partial seizures whose seizures are inadequately controlled by traditional AEDs.

Neonatal seizures induced persistent changes in intrinsic properties of CA1 rat hippocampal cells

We investigated the effects of repeated early-life seizures induced by flurothyl inhalation on intrinsic membrane properties of hippocampal pyramidal neurons from young rats (postnatal day 15-20). Intracellular recordings of CA1 and CA3 pyramidal neurons from flurothyl-treated and control rats revealed no significant differences in resting membrane potential, input resistance, membrane time constant, and action potential characteristics. In CA1 pyramidal cells from flurothyl-treated rats, the spike frequency adaptation and afterhyperpolarizing potential following a spike train were markedly reduced when compared with controls. In contrast, no significant alterations in the firing properties of CA3 pyramidal neurons were found. It is concluded that neonatal seizures lead to persistent changes in intrinsic membrane properties of CA1 pyramidal neurons. These alterations are consistent with an increase in neuronal excitability and may contribute to the behavioral deficit and epileptogenic predisposition observed in rats that experienced repeated neonatal seizures.

Flurothyl-induced seizures in rats activate Fos in brainstem catecholaminergic neurons

Autonomic changes accompany seizures in both animals and humans. While ictal autonomic dysfunction can be life-threatening, the participating neural networks involved are poorly understood. In this study we examined the activation of Fos following generalized seizures in brainstem structures known to mediate autonomic function. Adult female rats were sacrificed 2 h after flurothyl-induced seizures. Double-immunostaining for c-Fos and dopamine-beta-hydroxylase (DBH), and c-Fos and phenylethanol-N-methyl-transferase (PNMT) were performed in brainstem slices. Numbers of DBH-labeled neurons expressing Fos-like immunoreactivity (FLI) (DBH/Fos) and PNMT labeled neurons expressing FLI (PNMT/Fos) were counted in the noradrenergic (A1, A2, A5, A7) and adrenergic (C1, C2) cell groups localized in pons and medulla oblongata. Among the experimental animals, the highest degree of co-localization of DBH/Fos neurons was observed in the locus coeruleus (A6; 87.7%), and in the A1(72.8%) cell group located in the caudal ventrolateral medulla (VLM). No co-localization of DBH/Fos neurons was observed in control animals. The highest degree of co-localization of PNMT/Fos neurons was observed in the C1 adrenergic cell group (84.2%) located in the rostral VLM. Control animals showed very few (5.5%) PNMT/Fos co-localized neurons in the C1 adrenergic cell group. Our results indicate that flurothyl-induced generalized seizures in rats activate catecholaminergic neurons in the pons and medulla oblongata. Further studies are necessary to determine whether activation of brainstem catecholaminergic neurons contribute to the autonomic manifestations that frequently accompany epileptic seizures.

Lateral asymmetry in activation of hypothalamic neurons with unilateral amygdaloid seizures

PURPOSE

Reproductive disorders are unusually frequent among women with temporal lobe seizures. The particular type of disorder may be related to the laterality and focality of epileptiform discharges. Here we examined whether unilateral amygdaloid seizures activate hypothalamic neurons involved in reproductive function and reproductive endocrine secretion in female rats and whether such activation shows lateral asymmetry.

METHODS

Numbers of Fos-immunoreactive (Fos-ir) neurons in various hypothalamic regions were compared for three groups of animals: (a) unilateral amygdala-kindled, (b) implanted but unstimulated, and (c) unimplanted.

RESULTS

Fos-ir neurons showed strong ipsilateral occurrence in the medial preoptic, ventrolateral part of the ventromedial, and ventral premammillary nuclei, sexually dimorphic regions involved in reproductive endocrine regulation. No significant lateral asymmetry was observed for other investigated hypothalamic regions.

CONCLUSIONS

Unilateral amygdaloid seizures activate hypothalamic neurons that regulate reproductive endocrine secretion in a laterally asymmetric fashion. This may explain the clinical association of different reproductive endocrine disorders with left and right temporal epileptiform discharges.

Long-term effects of neonatal seizures: a behavioral, electrophysiological, and histological study

Previous studies have demonstrated that recurrent seizures during the neonatal period lead to permanent changes in seizure threshold and learning and memory. The pathophysiological mechanisms for these changes are not clear. To determine if neonatal seizures cause changes in hippocampal excitability or inhibition, we subjected rats to 50 flurothyl-induced seizures during the first 10 days of life (five seizures per day). When the rats were adults, we examined seizure threshold using flurothyl inhalation, and learning and memory in the water maze. In separate groups of animals, we evaluated in vivo paired-pulse facilitation and inhibition in either CA1 with stimulation of the Schaffer collaterals or dentate gyrus with stimulation of the perforant path. Following these studies, the animals were sacrificed and the brains evaluated for mossy fiber sprouting with the Timm stain. Compared to control animals, rats with 50 flurothyl seizures had a reduced seizure threshold, impaired learning and memory in the water maze, and sprouting of mossy fibers in the CA3 pyramidal cell layer and molecular layer of the dentate gyrus. No significant differences in impaired paired-pulse inhibition was noted between the flurothyl-treated and control rats. This study demonstrates that recurrent neonatal seizures result in changes of neuronal connectivity and alterations in seizure susceptibility, learning and memory. However, the degree of impairment following 50 seizures was modest, demonstrating that the immature brain is remarkably resilient to seizure-induced damage.

Effects of neonatal seizures on subsequent seizure-induced brain injury

BACKGROUND

Although seizures are very common in neonates and are often the harbinger of poor neurologic outcome, there is controversy regarding the degree of brain damage induced by seizures during early development. Here, we evaluated the effect of neonatal seizures on subsequent brain injury induced by status epilepticus.

METHODS

Twenty-five seizures were induced by the inhalant flurothyl in neonatal rats during the first 5 days of life. Flurothyl reliably produced generalized seizures with concomitant electroencephalographic changes and a low mortality rate. During adolescence or early adulthood, animals were subjected to status epilepticus using either kainic acid or perforant path stimulation.

RESULTS

Although flurothyl-induced neonatal seizures did not cause cell death, animals that had neonatal seizures had significantly more severe brain injury after both kainic acid and perforant path stimulation than did animals without a history of neonatal seizures.

CONCLUSIONS

Neonatal seizures increase the susceptibility of the developing brain to subsequent seizure-induced injury.

Consequences of recurrent seizures during early brain development

It is well documented that prolonged seizures (status epilepticus) can cause neuronal injury and result in synaptic reorganization in certain brain regions. However, the effect of recurrent, relatively short seizures in young animals on subsequent brain development is not known. To study the consequences of recurrent seizures on the developing brain, we subjected immature rats to a total of 50 flurothyl-induced seizures from postnatal day 11 until day 23. Immunohistochemistry for c-fos was performed to characterize the pattern of neuronal activation following the seizures. Cell counting of dentate granule cells, CA3, CA1, and hilar neurons, using unbiased stereological methods, and the silver impregnation method were used to evaluate neuronal death following the recurrent seizures. Timm and Golgi staining were performed four weeks after the 50th seizure to evaluate the effects of recurrent seizures on synaptic organization. Our results show that recurrent flurothyl-induced seizures progressively increased excitability of the brain, as revealed by a dramatic increase in the extent and intensity of c-fos immunostaining. While no cell loss was detected in the hippocampus with either Cresyl Violet or silver stains, animals experiencing multiple daily seizures developed increased mossy fiber sprouting in both the supragranular layer of the dentate gyrus and the infrapyramidale layer of the CA3 region. Golgi staining confirmed that there was an increase in mossy fibers in the pyramidal cell layer. Our results suggest that serial recurrent seizures in the immature brain can lead to significant changes in mossy fiber distribution even though the seizures do not cause significant hippocampal cell loss.

EEG and clinical predictors of medically intractable childhood epilepsy

OBJECTIVES

To identify electroencephalographic and clinical factors associated with both seizure control and medical intractability in children with epilepsy.

METHODS

We retrospectively reviewed EEGs and medical records from children with well-controlled epilepsy or medically intractable epilepsy.

SUBJECTS

Features of the initial EEG and clinical findings were compared in 39 children with well controlled seizures and 144 with intractable epilepsy using both univariate and multivariate analyses.

RESULTS

Strong univariate associates were noted between intractability and several EEG factors: abnormal EEG background including diffuse slowing, asymmetry, abnormal amplitude, a high frequency of spikes or sharp waves, and focal spike and wave activity. With multiple logistic regression, independent predictors of intractability were diffuse slowing and focal spike and wave activity. Strong univariate associates of clinical factors with intractability included: an early age of onset, simple partial, tonic, and myoclonic seizures, a history of status epilepticus, a symptomatic etiology of the seizures, and abnormal magnetic resonance imaging of the head. Multivariate analysis detected 4 independent clinical features associated with intractable epilepsy: symptomatic etiology, tonic seizures, simple partial seizures, and an early age of onset.

CONCLUSIONS

There are a number of EEG and clinical features that can be identified early in the course of childhood epilepsy that are predictive of outcome. These findings will need to be verified in a prospective study.

Effects of hyperthermia and continuous hippocampal stimulation on the immature and adult brain

Whether febrile seizures lead to hippocampal necrosis is a question of paramount clinical importance. This study attempted to simulate a complex febrile seizure, compared with hyperthermia (HYP) alone and prolonged seizure alone (produced by continuous hippocampal stimulation (CHS)). Four groups of rats were studied at each of two ages, immature (postnatal day, P20) and adult (P60). Group 1 was subjected to 45 min of HYP (body temperature 40 degrees C) plus CHS, Group 2 received 45 min of HYP alone, Group 3 got 45 min of CHS alone, and Group 4 was sham-handled control rats. Baseline and post-session EEGs were recorded in all groups. Subsequently, brains were examined histologically for evidence of hippocampal damage. Both CHS-treated groups (with and without HYP) exhibited behavioral and EEG seizures while the group undergoing HYP alone did not have seizures. There were no gross histological lesions in any group. Cell counts in regions CA1, CA3, dentate gyrus and dentate hilus did not differ in rats under any condition of hyperthermia and CHS, in either P20 or P60 rats compared to age-matched controls. These results indicate that both immature and mature rodents are resistant to hyperthermic brain damage and raises the question of whether febrile seizures play a role in the genesis of mesial temporal sclerosis.

Safety and tolerability of gabapentin as adjunctive therapy in a large, multicenter study

PURPOSE

To evaluate the tolerability and safety of gabapentin (GBP) as add-on therapy for seizure control.

METHODS

Conducted in an outpatient setting and reflecting usual practice, this study compared tolerability of GBP dosages < or = 1,800 versus >1,800 mg/day, when these doses were required to achieve the most effective seizure control. Two analyses of adverse events are presented: tolerability and safety. In the tolerability analysis, each patient served as his or her own control to compare the occurrence of adverse events at GBP < or =1,800 versus >1,800 mg/day. The safety analysis required patients to receive at least one dose of GBP and have a follow-up contact.

RESULTS

A total of 2,216 patients enrolled in this open-label, 16-week study and were evaluable for safety. Of these, 74.0% completed the 16-week study, and 281 met the tolerability criteria. Within these 281 patients, two mutually exclusive groups were compared (a) those reporting adverse events at only < or =1,800 mg/day (low dose); and (b) those reporting adverse events at only >1,800 mg/day (high dose). Three adverse events (asthenia, headache, and dizziness) were observed in a statistically significantly larger number of patients at only the low dose than in the group reporting these same adverse events at only the high dose, suggesting that patients who tolerated GBP at < or = 1,800 mg/day did not experience a significant increase in adverse events with dosages >1,800 mg/day. Overall, 10.6% of the 2,216 patients in the safety population prematurely withdrew because of adverse events, and 3.5% discontinued because of lack of efficacy. Safety and tolerability of GBP was rated as excellent or good for 78.5% of all patients.

CONCLUSIONS

Gabapentin doses >1,800 mg/day were as well tolerated as doses < or =1,800 mg/day and were not associated with more adverse events.

Lamictal (lamotrigine) monotherapy for typical absence seizures in children

PURPOSE

To investigate whether lamotrigine (LTG) monotherapy is effective and safe for newly diagnosed typical absence seizures in children and adolescents (aged 3-15 years, n = 45).

METHODS

A "responder-enriched" study design was used: open-label dose escalation was followed by placebo-controlled, double-blind testing of LTG. Conventional hyperventilation testing with EEG recording was used to confirm diagnoses and assess treatment success defined as complete freedom from seizures. Ambulatory 24-h EEG recordings provided supporting evidence of effectiveness. Safety was assessed by evaluation of adverse events, vital signs, and physical, neurologic, and laboratory examinations. Plasma samples were taken to evaluate the pharmacokinetics of LTG.

RESULTS

During initial open-label dose escalation, 71.4% of patients (intent-to-treat) or 82% (per protocol analysis) became seizure free; individual patients responded at doses ranging from 2 to 15 mg/kg/day (median, 5.0). In the placebo-controlled, double-blind phase of the study, statistically significantly more patients remained seizure free when treated with LTG (62%) than with placebo (21%; p < 0.02; for the intent-to-treat analysis). Mean plasma concentrations of LTG, were linearly related to dose, although there was substantial interindividual variation. No patients were withdrawn from the study for any safety-related reason.

CONCLUSIONS

LTG monotherapy is effective for typical absence seizures in children and is generally well tolerated.

Consciousness in congenitally decorticate children: developmental vegetative state as self-fulfilling prophecy

According to traditional neurophysiological theory, consciousness requires neocortical functioning, and children born without cerebral hemispheres necessarily remain indefinitely in a developmental vegetative state. Four children between 5 and 17 years old are reported with congenital brain malformations involving total or near-total absence of cerebral cortex but who, nevertheless, possessed discriminative awareness: for example, distinguishing familiar from unfamiliar people and environments, social interaction, functional vision, orienting, musical preferences, appropriate affective responses, and associative learning. These abilities may reflect 'vertical' plasticity of brainstem and diencephalic structures. The relative rarity of manifest consciousness in congenitally decorticate children could be due largely to an inherent tendency of the label 'developmental vegetative state' to become a self-fulfilling prophecy.

Neuroprotective effects of brain-derived neurotrophic factor in seizures during development

Although the immature brain is highly susceptible to seizures, it is more resistant to seizure-induced neuronal loss than the adult brain. The developing brain contains high levels of neurotrophins which are involved in growth, differentiation and survival of neurons. To test the hypothesis that neurotrophins may protect the developing brain from seizure-induced neuronal loss, brain-derived neurotrophic factor up-regulation was blocked by intracerebroventricular infusion of an 18mer antisense oligodeoxynucleotide sequence to brain-derived neurotrophic factor in 19-day-old rats using micro-osmotic pumps. Control rats were infused with sense or missense oligodeoxynucleotide. Status epilepticus was induced by intraperitoneal administration of kainic acid 24 h after the start of oligodeoxynucleotide infusion. Seizure duration was significantly increased in the antisense oligodeoxynucleotide plus kainic acid group compared to groups that received kainic acid alone or kainic acid plus sense or missense oligodeoxynucleotide. There was no difference between groups in the latency to forelimb clonus. A twofold increase in brain-derived neurotrophic factor levels was observed in the hippocampus 20 h following kainic acid-induced seizures. This kainic acid-induced increase was absent in animals receiving infusion of antisense oligodeoxynucleotide to brain-derived neurotrophic factor at time of seizure induction. Hippocampi of rats in this group (antisense oligodeoxynucleotide plus kainic acid) showed a loss of CA1 and CA3 pyramidal cells and hilar interneurons. This neuronal loss was not dependent upon seizure duration since animals injected with diazepam to control seizure activity in the antisense plus kainic acid group also showed similar neuronal loss. Administration of kainic acid or infusion of antisense alone did not produce any cell loss in these regions. Induction of seizures at postnatal day 20, in the presence or absence of antisense oligonucleotide, did not produce an impairment in learning and memory when tested 15 days later in the Morris water maze. The hippocampi of these animals did not show any synaptic reorganization as assessed by growth-associated protein-43 immunostaining and Timm staining. Our findings confirm prior studies demonstrating that seizures in the immature brain are associated with little, if any, cell loss. However, when seizure-induced increase in brain-derived neurotrophic factor is blocked, seizures do result in neuronal loss in the developing brain. Thus, brain-derived neurotrophic factor appears to provide protection against kainic acid seizure-induced neuronal damage in the developing brain.

Ketogenic diet reduces spontaneous seizures and mossy fiber sprouting in the kainic acid model

The high fat, low carbohydrate, low protein ketogenic diet (KD) has been used to control refractory epilepsy in children since 1920, although its mechanism of action is unknown. Previous animal studies have shown that the KD can increase acute seizure threshold, but the effect of the KD on the process of epileptogenesis has not been studied. We tested the effect of an experimental KD on epileptogenesis in adult rats using the kainic acid (KA) model. P54 rats underwent KA-induced status epilepticus, followed by assignment to a control diet or a KD consisting of (by weight), 14% protein, 70% fat and no carbohydrate. KD-fed animals tolerated the diet and maintained ketosis. KD-fed rats had significantly fewer and briefer spontaneous recurrent seizures and less supragranular mossy fiber sprouting, although the degree of hippocampal pyramidal cell damage was similar in both groups. These results provide the first evidence that the KD retards epileptogenesis in an experimental model.

Consequences of cortical dysplasia during development in rats

PURPOSE

To determine whether focal cortical dysplasia alters excitability in regions distant to the region of the dysplasia.

METHODS

We studied the physiological consequences of cortical dysplasia induced by either one or three freeze lesions at birth. Seizure susceptibility was assessed at age 35 days by amygdala kindling. c-fos immunostaining was performed after kainic acid-induced seizures at 10, 20, or 30 days to evaluate the patterns of neuronal activation.

RESULTS

Freeze lesions consistently produced uniform regions of dysplasia. No significant differences in seizure susceptibility, as measured by afterdischarge threshold and kindling rate, were seen between controls and rats receiving either one or three freeze lesions. c-fos activation after kainic acid injection was not observed in the region of the dysplasia. However, rats with freeze lesions at age 30 days demonstrated asymmetric c-fos staining with greater staining in CA1 ipsilateral, than contralateral, to the lesion.

CONCLUSIONS

Focal cortical dysplasia results in enhancement of c-fos activation in regions outside the borders of the dysplasia. However, as indicated by kindling rate, the functional consequences of these alterations do not appear to be robust.