Cognitive function in children with epilepsy

Disease-modifying effects of sodium selenate in a model of drug-resistant, temporal lobe epilepsy

There are no pharmacological disease-modifying treatments with an enduring effect to mitigate the seizures and comorbidities of established chronic temporal lobe epilepsy (TLE). This study aimed to evaluate for disease modifying effects of sodium selenate treatment in the chronically epileptic rat post-status epilepticus (SE) model of drug-resistant TLE. Wistar rats underwent kainic acid-induced SE or sham. Ten-weeks post-SE, animals received sodium selenate, levetiracetam, or vehicle subcutaneousinfusion continuously for 4 weeks. To evaluate the effects of the treatments, one week of continuous video-EEG was acquired before, during, and 4, 8 weeks post-treatment, followed by behavioral tests. Targeted and untargeted proteomics and metabolomics were performed on post-mortem brain tissue to identify potential pathways associated with modified disease outcomes. Telomere length was investigated as a novel surrogate marker of epilepsy disease severity in our current study. The results showed that sodium selenate treatment was associated with mitigation of measures of disease severity at 8 weeks post-treatment cessation; reducing the number of spontaneous seizures (p< 0.05), cognitive dysfunction (p< 0.05), and sensorimotor deficits (p< 0.01). Moreover, selenate treatment was associated with increased protein phosphatase 2A (PP2A) expression, reduced hyperphosphorylated tau, and reversed telomere length shortening (p< 0.05). Network medicine integration of multi-omics/pre-clinical outcomes identified protein-metabolite modules positively correlated with TLE. Our results provide evidence that treatment with sodium selenate results in a sustained disease-modifying effect in chronically epileptic rats in the post-KA SE model of TLE, including improved comorbid learning and memory deficits.

Neurodegenerative pathways as targets for acquired epilepsy therapy development

There is a growing body of clinical and experimental evidence that neurodegenerative diseases and epileptogenesis after an acquired brain insult may share common etiological mechanisms. Acquired epilepsy commonly develops as a comorbid condition in patients with neurodegenerative diseases such as Alzheimer's disease, although it is likely much under diagnosed in practice. Progressive neurodegeneration has also been described after traumatic brain injury, stroke, and other forms of brain insults. Moreover, recent evidence has shown that acquired epilepsy is often a progressive disorder that is associated with the development of drug resistance, cognitive decline, and worsening of other neuropsychiatric comorbidities. Therefore, new pharmacological therapies that target neurobiological pathways that underpin neurodegenerative diseases have potential to have both an anti-epileptogenic and disease-modifying effect on the seizures in patients with acquired epilepsy, and also mitigate the progressive neurocognitive and neuropsychiatric comorbidities. Here, we review the neurodegenerative pathways that are plausible targets for the development of novel therapies that could prevent the development or modify the progression of acquired epilepsy, and the supporting published experimental and clinical evidence.

Childhood epilepsy in relation to mental handicap and behavioural disorders

Epidemiological studies indicate that there is a high rate of mental retardation and behavioural problems in children with epilepsy. In some cases both the epilepsy and the mental retardation will have a common cause, such as a metabolic disorder or brain trauma. However, in other children, the epilepsy itself may cause either temporary or permanent learning problems. When permanent learning disability can be prevented it is important to treat the epilepsy early and effectively. Children with specific learning difficulties and memory problems can benefit greatly from appropriate management. There are many causes of behavioural disturbance in children with epilepsy. These causes include the epilepsy itself, treatment of the epilepsy, reactions to the epilepsy, associated brain damage/dysfunction and causes that are equally applicable to children who do not have epilepsy. Identifying the cause or causes in each child allows rational management to be provided. Antiepileptic treatment with medication or surgery can either improve the situation or make matters worse. The treatment should be tailored to the needs of the individual child. If surgery is required, there is a strong argument for performing this early in life, both to allow the greatest opportunity for brain plasticity and also to allow the child full benefit from the important developmental and educational years, without the problems that can be associated with the epilepsy. Skilled management of children with epilepsy who have mental retardation and/or behavioural problems can be very rewarding both for the family and for the professionals involved.

L-type Ca(2+) channel blocker inhibits mossy fiber sprouting and cognitive deficits following pilocarpine seizures in immature mice

Behavioral and cognitive deficits are one of the most frequent sequelae of childhood epilepsy. Accumulating evidence indicates that epilepsy induces aberrant development of the mossy fibers in the hippocampus, the region that is commonly accepted to play a key role in learning and memory. We have therefore proposed that such abnormal maturation of the central nervous system may cause the adverse prognoses following epilepsy. Based on this hypothesis, using primary cultures of the dentate granule cells, we showed that the L-type Ca(2+) channel blocker nicardipine was neuroprotective against excessive mossy fiber synaptogenesis induced by prolonged depolarization that was assumed to mimic epileptiform conditions. Therefore, we evaluated the in vivo effect of nicardipine on aversive sequelae following epileptiform seizures. We found aberrant sprouting of the mossy fibers and poor performance of spatial and contextual tasks in the mice that had received treatment with pilocarpine at their early postnatal age. Repetitive administration of nicardipine prevented the mossy fiber sprouting and ameliorated the cognitive deterioration, although it did not show anticonvulsant actions against pilocarpine seizures. In the present study, we proposed two in vitro and in vivo models for evaluating epilepsy sequelae and noticed that L-type Ca(2+) channel blocker nicardipine was effective in both models. L-type Ca(2+) channel blocker may be a good candidate for a preventive for childhood epilepsy sequelae. Likewise, these useful systems will disclose additional candidates in future.

Abnormal targeting of developing hippocampal mossy fibers after epileptiform activities via L-type Ca2+ channel activation in vitro

The hippocampal mossy fibers, which originate from the dentate granule cells, develop mainly in the early postnatal period and are involved in numerous pathological processes. In this study, hippocampal slices prepared from premature rats were cultivated in the presence of convulsants to evaluate the influences of epileptiform activities on mossy fiber ontogeny. Electrophysiological and histochemical analyses revealed that prolonged hyperexcitability inhibited proper growth of the mossy fibers and caused ectopic innervation to the stratum oriens and the dentate molecular layer. These phenomena were prevented by pharmacological blockade of L-type Ca2+ channels, which did not affect convulsant-evoked ictal bursts. After single-pulse stimulation of the stratum granulosum in the slices cultured under paroxysmal conditions, the dentate gyrus displayed excessive excitation, but synaptic transmission to the CA3 region was hypoactive. However, brief repetitive stimulation elicited delayed epileptiform discharges in the CA3 region that were inhibited by an NMDA receptor antagonist. Chronic treatment with an L-type Ca2+ channel blocker ameliorated such aberrant neurotransmissions. These results suggest that ictal neuron activities at the developmental stage of the mossy fibers bring about the errant maturation associated with hippocampal dysfunction, which may form a cellular basis for the sequelae of childhood epilepsy, including chronic epilepsy or cognitive deficits. Thus I propose that L-type Ca2+ channel blockers can ameliorate the aversive prognosis of childhood epilepsy.

Altered cognitive functioning in children with idiopathic epilepsy receiving valproate monotherapy

Once a child is diagnosed with epilepsy, a primary concern is whether or not the child's behavior and cognitive abilities will be affected by the disease, by the drug prescribed for seizure control, or both. Direct cognitive effects by the epileptic condition have been described. On the other hand, cognitive effects in epilepsy have been attributed to antiepileptic drug therapy. Valproate is an antiepileptic drug of choice in managing the commonest childhood epilepsy syndromes. Although frequently prescribed in pediatric neurology practice, there have been relatively few studies investigating the cognitive effects of valproate therapy in children. Cognitive effects of valproate reported in normal adult volunteers and in adults with epilepsy cannot be generalized to the pediatric population. The results of investigations on children are less conclusive. Guidelines for antiepileptic drug trials in children have recently been formulated. Carefully designed studies are required in determining the cognitive effects of valproate in the pediatric population. Neuropsychological measures that are likely to assess subtle changes in higher brain functions crucial to learning in children should be employed. We propose a test battery to assess for cognitive changes associated with anticonvulsant therapy in children.

Chronic phenytoin induced impairment of learning and memory with associated changes in brain acetylcholine esterase activity and monoamine levels

Groups of adult, male, Wistar rats were administered phenytoin (DPH) at 5, 12.5, 25, 50, or 75 mg/kg i.p. for 21 days. The learning and memory of these rats were assessed using the T-maze and passive avoidance tests. The plasma DPH levels, acetylcholine esterase (AChE) activity in different brain regions, and the levels of monoamines in the hippocampus were measured. The results indicate that DPH below the therapeutic plasma level did not significantly impair learning and memory. Correspondingly, no changes were noted in the brain 5-HT or AChE activity. However, DPH, at therapeutic plasma concentrations (i.e., 10.5 micrograms/ml in the dosage range of 50 and 75 mg/kg, respectively), significantly impaired learning and memory in rats. The impaired learning and memory functions were associated with increased 5-HT levels and decreased AChE activity in the hippocampus. With a dose of 75 mg/kg DPH, there was a reduction in the AChE activity in the striatum, in addition to hippocampus. It is conjectured that the neurochemical changes brought about by DPH at therapeutic plasma levels may account for the impairment of learning, memory, and cognitive functions in epilepsy.

Changes in learning and memory, acetylcholinesterase activity and monoamines in brain after chronic carbamazepine administration in rats

Groups of adult male Wistar rats were administered carbamazepine (CBZ) in doses of 5, 10, 20, 40 or 80 mg/kg/day intraperitoneally (i.p.) for 21 days. The learning and memory of the rats were assessed by the T-maze and passive avoidance tests. The CBZ plasma levels, the activity of acetylcholinesterase (AChE) in different brain regions, and the levels of monoamines in the hippocampus were also measured. None of the administered doses of CBZ impaired learning and memory. Rats with CBZ plasma levels of 2.5 and 4.5 micrograms/ml corresponding to the doses of 20 and 40 mg/kg, learned significantly better than controls. AChE activity was decreased in hippocampus and pyriform cortex (19%) in these groups. Simultaneously, an increase in the serotonin (5-HT) (36%) and dopamine (137%) levels in the hippocampus was noted in the 20-mg/kg CBZ group. 5-Hydroxyindole acetic acid (5-HIAA) and homovanillic acid (HVA) levels were increased at 10-, 20-, and 40-mg/kg CBZ doses. However, a dose of 80-mg/kg caused no change in learning performance as compared with that of controls. Correspondingly, no changes were evident in the AChE activity or monoamine levels. We postulated that the decreased AChE activity caused by CBZ in the therapeutic range may lead to increased ACh levels in brain, thus producing improvement in learning and memory. The increased turnover of 5-HT and dopamine (DA) in the hippocampus may play a role in long-term potentiation and improvement in memory.

Age-dependent cognitive and behavioral deficits after kainic acid seizures

The long-term behavioral and cognitive effects of seizures at different ages were studied using the kainic acid (KA) seizure model. Rats of postnatal (P) ages (in days) 5, 10, 20, 30, and 60 were administered KA intraperitoneally (i.p.), which induced status epilepticus for several hours, or an equivalent volume of saline. Occurrence of spontaneous recurrent seizures (SRS) was then monitored for 3 months by a closed-circuit videotaping system. Rats began behavioral testing on P80; a separate group of rats that received KA on P60 began testing on P120. Behavioral tests included the Morris water maze (visuospatial learning and memory), the open field test (response to a novel environment), and the handling test (emotionality). When tested on P80, KA-treated P5 and P10 rats had no demonstrable deficits on any test as compared with controls. KA-Treated P20 rats differed from controls only on the water maze spatial bias test. KA-Treated P30 rats had deficits in spatial bias, were more active in the open field, and were more aggressive when handled. KA-Treated P60 rats, whether tested on P80 or P120, had deficits in learning platform position and spatial bias in the water maze, were more active in the open field, and were more aggressive when handled. P60 rats with SRS performed poorer in water maze place learning and spatial bias testing, although the number of SRS did not correlate with overall task acquisition. Our findings suggest age-related behavioral and cognitive deficits after KA-induced seizures. Pubescents and adults had alterations in learning, memory, exploratory behavior, and response to handling, whereas younger animals had no obvious behavioral or cognitive deficits.

Behavioral effects of kainic acid administration on the immature brain

Prepubescent male rats with an amygdaloid electrode in place were administered kainic acid (KA) intraperitoneally (i.p.) while controls received phosphate-buffered saline (PBS). All KA-treated animals developed status epilepticus with bilateral forelimb clonus and ictal discharges on the EEG. The rats were then tested as adults for learning, memory, emotionality, social interaction, and activity level using the T maze, water maze, handling test, home cage intruder test, and open field test. KA-treated rats learned at a slower rate in the water maze and T maze than the controls. In addition, KA-treated rats had evidence of impaired memory during spatial bias testing in the water maze. In the home cage intruder test, KA-treated animals were more submissive and less aggressive than control animals. Finally, KA-treated animals were significantly more active than control animals in the open field test. This study demonstrates that KA administration to the immature brain, in a convulsant dose, results in permanent changes in behavior, learning, and memory.

The effects of various antiepileptic drugs on E-shock-induced amnesia in mice: dissociability of effects on convulsions and effects on memory

Antiepileptic drugs prevent tonic convulsions induced by cerebral electroshocks. The present study investigated whether these drugs can also modulate the amnestic effect of the cerebral electroshock. It could be shown that phenytoin, ethosuximide, valproinate sodium, phenobarbitone, and clonazepam dose-dependently worsened the amnestic effect of electroshock (despite prevention of the convulsion). Carbamazepine, in contrast, significantly reduced the amnestic effect of the cerebral electroshock even at doses below the threshold for anticonvulsant activity.

Cognitive and behavioural characteristics of children with idiopathic epilepsy in a low-income area of Ankara, Turkey

Fifteen school-age children with idiopathic epilepsy but with no other neurological symptoms were compared with non-epileptic children, matched for age, on four cognitive tests selected to measure specific cognitive skills at two levels of functioning, and a behaviour rating scale. All children were from a low-income district of Ankara, Turkey. Epileptic children did as well as controls on the recognition of a geometric designs test but were significantly inferior at drawing these designs, suggesting some deficit at a cognitive level involving coordination of perception and motor activity. In language functioning, they were significantly poorer on the receptive test but not on the expressive test. They had significantly more behavioural problems than either the control group or their own siblings, those related to fears and anxiety being most prominent. However, in comparison with their siblings, they also had significantly more problems related to conduct- disobedience and inattention. These findings provide further evidence for the importance of some form of counselling for school-age epileptic children and their families.