Resistance to phenobarbital extends to phenytoin in a rat model of temporal lobe epilepsy

PURPOSE: Most patients who are resistant to the first antiepileptic drug (AED) treatment are also resistant to a treatment with a second or third AED, indicating that patients who have an inadequate response to initial treatment with AEDs are likely to have refractory epilepsy. Animal models of refractory epilepsy are important tools to study mechanisms of AED resistance and develop new treatment strategies for counteracting resistance. We have recently described a rat model of temporal lobe epilepsy (TLE), in which spontaneous recurrent seizures (SRS) develop after a status epilepticus induced by sustained electrical stimulation of the basolateral amygdala. Prolonged treatment of epileptic rats with phenobarbital (PB) resulted in two subgroups, PB responders and PB nonresponders. METHODS: In the present study we examined if rats with PB-resistant seizures are also resistant to phenytoin (PHT), using continuous EEG/video recording of spontaneous seizures. RESULTS: First, a new group of 15 epileptic rats was produced and selected by treatment with PB into responders (8 rats) and nonresponders (6 rats), respectively. During subsequent treatment with PHT, the doses of PHT had to be individually adjusted for each rat to avoid toxicity. Treatment with PHT led to complete seizure control in two animals and a >50% reduction of seizure frequency in three other rats, which were considered PHT responders. In nine of the remaining rats, PHT did not exert any clear anticonvulsant effect, so that these rats were considered nonresponders. Plasma levels of PHT did not differ significantly between responders and nonresponders. When comparing the PB and PHT nonresponder groups, five of the six PB-resistant rats (83%) were also resistant to PHT, demonstrating that rats that have an inadequate response to initial treatment with PB are likely to be also resistant to treatment with a second AED. CONCLUSIONS: The AED-resistant rats of our model meet the definition of pharmacoresistance in animal models, that is, persistent seizure activity not responding to at least two AEDs at maximum tolerated doses. This new model of pharmacoresistant TLE may be useful in the targeted development of new therapies for refractory epilepsy.     

High seizure frequency prior to antiepileptic treatment is a predictor of pharmacoresistant epilepsy in a rat model of temporal lobe epilepsy

Purpose:   Progress in the management of patients with medically intractable epilepsy is impeded because we do not fully understand why pharmacoresistance happens and how it can be predicted. The presence of multiple seizures prior to medical treatment has been suggested as a potential predictor of poor outcome. In the present study, we used an animal model of temporal lobe epilepsy to investigate whether pharmacoresistant rats differ in seizure frequency from pharmacoresponsive animals.
Methods:   Epilepsy with spontaneous recurrent seizures (SRS) was induced by status epilepticus. Frequency of SRS was determined by video/EEG (electroencephalography) monitoring in a total of 33 epileptic rats before onset of treatment with phenobarbital (PB).
Results:   Thirteen (39%) rats did not respond to treatment with PB. Before treatment with PB, average seizure frequency in PB nonresponders was significantly higher than seizure frequency in responders, which, however, was due to six nonresponders that exhibited > 3 seizures per day. Such high seizure frequency was not observed in responders, demonstrating that high seizure frequency predicts pharmacoresistance in this model, but does not occur in all nonresponders.
Discussion:   The data from this study are in line with clinical experience that the frequency of seizures in the early phase of epilepsy is a dominant risk factor that predicts refractoriness. However, resistance to treatment also occurred in rats that did not differ in seizure frequency from responders, indicating that disease severity alone is not sufficient to explain antiepileptic drug (AED) resistance. These data provide further evidence that epilepsy models are useful in the search for predictors and mechanisms of pharmacoresistance.     

Antiepileptic drug resistant rats differ from drug responsive rats in GABA A receptor subunit expression in a model of temporal lobe epilepsy

Epidemiological data indicate that 20–40% of the patients with epilepsy are refractory to treatment with antiepileptic drugs (AEDs). The mechanisms underlying pharmacoresistance in epilepsy are unclear, but several plausible hypotheses have emerged, including loss of AED target sensitivity in the epileptic brain, decreased AED concentrations at brain targets because of localized overexpression of drug efflux transporters in epileptogenic brain tissue, and network alterations in response to brain damage associated with epilepsy. Rat models of epilepsy in which part of the animals are resistant to treatment with AEDs offer a means to investigate the mechanisms underlying AED resistance. In the present study, AED-responsive and AED-resistant rats were selected from a model in which spontaneous recurrent seizures develop after a status epilepticus induced by electrical stimulation of the basolateral amygdala. For selection into responders and nonresponders, epileptic rats were treated over two weeks by phenobarbital. Subsequent histological examination showed neurodegeneration of the CA1, CA3 and dentate hilus in only one of eight responders but five of six nonresponders (P = 0.0256). Based on previous studies in AED-resistant rats of this model, we hypothesized that changes in the structure and function of inhibitory GABA_A receptors may contribute to drug resistance. We therefore analyzed the distribution and expression of several GABA_A receptor subunits (α1, α2, α3, α4, α5, β2/3, and γ2) immunohistochemically with specific antibodies in the hippocampal formation of responders, nonresponders and nonepileptic controls. In nonresponders, decreased subunit staining was observed in CA1, CA2, CA3, and dentate gyrus, whereas much less widespread alterations were determined in responders. Furthermore, upregulation of the α4-subunit was observed in the CA1 of nonresponders. Our data suggest that alterations in GABA_A receptor subtypes may be involved in resistance to AEDs.     

Striking differences in individual anticonvulsant response to phenobarbital in rats with spontaneous seizures after status epilepticus

PURPOSE: More than one third of patients with epilepsy have inadequate control of seizures with drug therapy, but mechanisms of intractability are largely unknown. Because of this large number of pharmacoresistant patients with epilepsy, the existing process of antiepileptic drug (AED) discovery and development must be reevaluated with a focus on preclinical models of therapy-resistant epilepsy syndromes such as mesial temporal lobe epilepsy (TLE). However, although various rodent models of TLE are available, the pharmacoresponsiveness of most models is not well known. In the present study, we used a post-status epilepticus model of TLE to examine whether rats with spontaneous recurrent seizures (SRSs) differ in their individual responses to phenobarbital (PB). METHODS: Status epilepticus was induced in Sprague-Dawley rats by prolonged electrical stimulation of the basolateral amygdala. Once the rats had developed SRSs, seizure frequency and severity were determined by continuous EEG/video recording over a 6-week period (i.e., a predrug control period of 2 weeks, followed by PB treatment for 2 weeks, and a postdrug control period of 2 weeks). PB was administered twice daily at maximal tolerated doses. RESULTS: Analysis of plasma drug concentrations showed that drug concentrations within the therapeutic range (10-40 microg/ml) were maintained in all rats throughout the period of treatment. In six (55%) of 11 rats, complete control of seizures was achieved, and another rat exhibited a >90% reduction of seizure frequency. These seven rats were considered responders. The remaining four (36%) rats showed either no response at all (n=3) or only moderate reduction in seizure frequency and were therefore considered nonresponders. Plasma drug concentrations did not differ between these two groups of rats. CONCLUSIONS: These data demonstrate that, similar to patients with epilepsy, rats with SRSs markedly differ in their individual responses to AED treatment. Pharmacoresistant rats selected by prolonged drug treatment from groups of rats with SRSs may provide a unique model to study mechanisms of pharmacoresistance and to identify novel AEDs for treating seizures of patients currently not controlled with existing therapies.     

A kindling model of pharmacoresistant temporal lobe epilepsy in Sprague-Dawley rats induced by Coriaria lactone and its possible mechanism

PURPOSE: The aim of this study was to develop a new animal model of pharmacoresistant temporal lobe epilepsy (TLE) by repeated intramuscular injection of Coriaria lactone (CL) at subthreshold dosages and to explore the mechanisms that might be involved. METHODS: Healthy male Sprague-Dawley rats (n = 160) were randomized into four groups during the kindling process: three groups (n = 50 for each group) received CL injection at subthreshold dosages (1.25, 1.5, and 1.75 mg/kg, respectively), and ten received normal saline (NS) injection as a control group. The maximal human adult dosage of carbamazepine (CBZ), valproate (VPA), and phenytoin (PHT) was administered as monotherapy to different groups of kindled rats for 1 month (n = 20 for each group). Changes in EEG recording, seizure number, intensity (expressed as grade 1-5 according to Racine stage), and duration, including spontaneous seizures during different interventions, were compared. The expression of P-170, a multiple drug resistance gene (MDR1) encoding P-glycoprotein, was measured in brain samples from different groups of experimental rats by using an image analysis and measurement system (ImagePro-Plus 4.0). RESULTS: A total of 70 (46.7%) rats were fully kindled with a median of 15 (seven to 20) CL injections. Electrocorticogram (ECoG) including hippocampal (EHG) monitoring revealed the temporal lobe origins of epileptiform potentials, which were consistent with the behavioral changes observed. Spontaneous seizures occurred with frequency and diurnal patterns similar to those of human TLE. The antiepileptic drugs (AEDs) tested lacked a satisfactory seizure control. The maximal P-170 expression was in the kindled rats with AED treatment; the next highest was in the kindled rats without AED intervention. Nonkindled SD rats with CL injection also had increased P-170 expression compared with control SD rats. CONCLUSIONS: The study provided a simple and stable animal TLE kindling model with pharmacoresistant properties. The pharmacoresistance observed in the kindled rats to CBZ, VPA, and PHT at maximal human adult dosages together with the increased P-170 expression was a distinct feature of this model. This model might be used in further investigations of the mechanisms involved in pharmacoresistant TLE and for developing new AEDs.     

Predictors of pharmacoresistant epilepsy

Outcome data were analysed from 780 patients newly diagnosed with epilepsy and followed up at a single centre over a 20-year period to investigate which clinical factors predicted pharmacoresistance. Patients were divided at the time of analysis into those whose seizures had been controlled for at least the last 12 months of follow up (n=462) and those whose epilepsy remained refractory (n=318). Numbers of pre-treatment seizures were greater in uncontrolled patients. Those reporting more than 10 seizures prior to initiation of therapy were more than twice as likely to develop refractory epilepsy. Univariate and multivariate logistic regression analyses demonstrated that pharmacoresistance was also associated with family history of epilepsy, previous febrile seizures, traumatic brain injury as the cause of the epilepsy, intermittent recreational drug use, and prior or current psychiatric comorbidity, particularly depression. Factors not predicting poorer outcome included gender, neurological deficit and mental retardation. The most interesting new finding was the correlation between psychiatric comorbidity and lack of response to antiepileptic drug therapy. The deleterious neurobiological processes that underpin depression, anxiety and psychosis may interact with those producing seizures to increase the extent of brain dysfunction and thereby the likelihood of developing pharmacoresistant epilepsy.     

Inter-individual variation in the anticonvulsant effect of phenobarbital in the pilocarpine rat model of temporal lobe epilepsy

Despite a large therapeutic arsenal of old and new antiepileptic drugs (AEDs), there remains a substantial unmet need for the patients with refractory (AED-resistant) epilepsy. Animal models of refractory epilepsy are needed for at least two goals; (1) better understanding of the mechanisms underlying resistance to AEDs, and (2) development of more efficacious AEDs for patients with refractory seizures. It is only incompletely understood why two patients with seemingly identical types of epilepsy and seizures may respond differently to the same AED. Prompted by this well-known clinical phenomenon, we tested whether epileptic rats from the same epilepsy model respond differently to AEDs and previously discovered phenobarbital (PB) responsive and resistant animals in groups of rats in which epilepsy had been induced by sustained electrical stimulation of the basolateral amygdala (BLA). In the present study, we used the same approach for the widely used pilocarpine model of temporal lobe epilepsy. Epileptic rats from this model were continuously video/EEG monitored over seven consecutive weeks, starting with a predrug control period of two weeks, then two weeks of daily treatment with PB at maximum tolerated doses, and finally a postdrug control period of three weeks. In those rats that were included in response selection, 50% did not adequately respond to PB, whereas PB significantly decreased seizure frequency and severity in another 50% of the animals. Responders and nonresponders did not differ in predrug seizure frequency, PB plasma levels or hippocampal neurodegeneration, but behavioral differences were observed in anxiety models. These findings demonstrate that in the pilocarpine model, similar to epilepsy patients, epileptic rats differ in their response to an AED, which is most likely due to as yet unknown genetic factors.     

Seizure-related injuries are underreported in pharmacoresistant localization-related epilepsy

Purpose:   To investigate and compare injury rates, associated risk factors, circumstances, and medical record documentation in patients with pharmacoresistant temporal lobe epilepsy (TLE) and extratemporal lobe epilepsy (ETLE).
Methods:   The study cohort consisted of fifty-two consecutive adults with treatment-resistant epilepsy and seizure classification confirmed by video-electrocardiography (EEG) (28 with TLE and 24 with ETLE) who consented to participate. All subjects had their seizures classified with prior video-EEG monitoring, were followed in a tertiary-care center in northwest New York City, and received a semistructured phone interview regarding injuries experienced since being diagnosed with epilepsy.
Results:   Injuries were reported in 16 (57%) of the patients with TLE and 4 (17%) of the patients with ETLE (p = 0.004 after controlling for duration of epilepsy and seizure burden); 83% of all injuries were designated by patients as seizure-related. Most injuries (22 of 41; 54%) were classified as moderate or greater in severity. In addition, one motor vehicle accident (MVA) was reported in the TLE group and one episode of sudden unexpected death (SUDEP) was identified in the ETLE group. More than half (55%) of the injuries were not documented as seizure-related in medical records.
Conclusion:   A substantial number of potentially serious injuries are not documented as seizure related, even in a tertiary-care setting. Patients with pharmacoresistant TLE may be at higher risk for experiencing an injury than patients with pharmacoresistant ETLE.     

Determinants of health-related quality of life in pharmacoresistant epilepsy: results from a large multicenter study of consecutively enrolled patients using validated quantitative assessments

Purpose: To evaluate the relative contribution of demographic and epilepsy‐related variables, depressive symptoms, and adverse effects (AEs) of antiepileptic drugs (AEDs) to health‐related quality of life (HRQOL) in adults with pharmacoresistant epilepsy. Methods: Individuals with epilepsy whose seizures failed to respond to at least one AED were enrolled consecutively at 11 tertiary referral centers. HRQOL was assessed by the Quality of Life in Epilepsy Inventory‐31 (QOLIE‐31), AEs by the Adverse Event Profile (AEP), and depressive symptoms by the Beck Depression Inventory‐II (BDI‐II). Multivariate linear regression models were used to identify variables associated with QOLIE‐31 total score and subscale scores. Key Findings: Of 933 enrolled individuals aged 16 years or older, 809 (87%) were able to complete the self‐assessment instruments and were included in the analysis. Overall, 61% of the variance in QOLIE‐31 scores was explained by the final model. The strongest predictors of HRQOL were AEP total scores (β = −0.451, p < 0.001) and BDI‐II scores (β = −0.398, p < 0.001). These factors were also the strongest predictors of scores in each of the seven QOLIE‐31 subscales. Other predictors of HRQOL were age (β = −0.060, p = 0.008), lack of a driving license (β = −0.053, p = 0.018), pharmacoresistance grade, with higher HRQOL in individuals who had failed only one AED (β = 0.066, p = 0.004), and location of the enrolling center. Epilepsy‐related variables (seizure frequency, occurrence of tonic–clonic seizures, age of epilepsy onset, disease duration) and number of AEDs had no significant predictive value on HRQOL. The AEP total score was the strongest negative predictor of HRQOL in the subgroup of 362 patients without depressive symptoms (BDI‐II score <10), but even in this subgroup the BDI‐II score was retained as a significant predictor. Significance: In individuals with pharmacoresistant epilepsy, AEs of medication and depressive symptoms are far more important determinants of HRQOL than seizures themselves. When seizure freedom cannot be achieved, addressing depressive comorbidity and reducing the burden of AED toxicity is likely to be far more beneficial than interventions aimed at reducing the frequency of seizures.     

EEG-fMRI in children with pharmacoresistant focal epilepsy

PURPOSE: To evaluate the usefulness of EEG-combined functional magnetic resonance imaging (EEG-fMRI) to localize epileptogenic sources. METHODS: Six children (age 8-15 years) with lesional or nonlesional pharmacoresistant focal epilepsy were studied. RESULTS: We found significant activations in four children, activation and deactivation in one child, and widespread deactivation in another. In four children, activations colocalized with the presumed location of the epileptic focus, one of which was confirmed by intracranial EEG. CONCLUSIONS: EEG-fMRI is a promising tool to noninvasively localize epileptogenic regions in children with pharmacoresistant focal epilepsy.     

Psychiatric comorbidity in patients with pharmacoresistant focal epilepsy and psychiatric outcome after epilepsy surgery

There are only a few studies in which both preoperative psychiatric comorbidity in pharmacoresistant focal epilepsy and its outcome after epilepsy surgery have been investigated. In this study, 144 patients evaluated for epilepsy surgery received psychiatric examination, 84 proceeding to intervention were reassessed postoperatively. Preoperatively, 60% met criteria for ICD-10- or epilepsy-specific psychiatric diagnosis. Twenty-seven percent, predominantly female, suffered from dysphoric disorder (DD) associated with temporal epileptogenic foci. Prevalence of DD correlated with complex partial seizure frequency and presence of ictal fear suggesting limbic-cortical dysregulation. Psychotic syndromes were linked to a history of febrile convulsions and left-sided temporomesial epileptogenic foci. High seizure frequency and early epilepsy onset predisposed to the development of personality disorders. Postoperative assessment revealed 18% of patients with "de novo" interictal affective disorders after surgery. Symptoms in 48% of patients with preoperative affective syndromes and 60% of patients with DD remitted after surgery. Seizure freedom and improved psychosocial status predicted remission of preoperative psychopathology.     

De novo psychogenic nonepileptic attacks after adult epilepsy surgery: An underestimated entity

We retrospectively assessed all patients in a large cohort of patients with epilepsy surgery at the National Hospital for Neurology and Neurosurgery (NHNN) over 12 years, to identify patients with postoperative psychogenic nonepileptic attacks (PNEA). Twenty‐nine patients (23 women) were identified of a total of 790 patients, a frequency of 3.7%. Female gender and presurgical psychiatric diagnosis, other than psychosis, were significant risk factors for PNEA development. In female patients with a preoperative psychiatric diagnosis the chance of developing PNEA after epilepsy surgery was 8.5%. PNEA developed between 2 weeks and 10 years after epilepsy surgery, independently of outcome of epileptic seizures. In most cases, PNEA differed from the present or past epileptic seizures, and motor symptoms were the most common manifestations. Seizures after epilepsy surgery should be carefully evaluated. Physicians should consider the possibility of PNEA, especially in female patients with preoperative psychiatric comorbidity developing “atypical” seizures with motor manifestations postoperatively, even many years after epilepsy surgery.     

Multifactorial etiology of interictal behavior in frontal and temporal lobe epilepsy

Purpose: Based on discussions on the so called “epileptic personality” in patients with epilepsy, interictal behavioral impairments in frontal and temporal lobe epilepsies were examined in a multivariate approach that took demographic, clinical, and neuropsychological determinants into consideration. Methods: A total of 428 patients with epilepsies originating from the temporal (TLE; 84%) or frontal (FLE; 16%) lobes were examined in regard to personality (Fragebogen zur Persönlichkeit bei zerebralen Erkrankungen [FPZ], a clinical personality questionnaire) and mood (Beck Depression Inventory [BDI I]). Prevalence of impaired behavioral domains was determined. Etiologically relevant determinants of behavioral problems were identified via multiple regression analyses. Key Findings: Elevated depression scores (BDI) were evident in 42% of the patients, and not different in TLE and FLE. In regard to personality, introversion together with low mood, sociability, and self‐determination, as well as problems with interpersonal communication were frequent. The TLE group tended to show greater neuroticism and introversion, while FLE appeared more associated with behavioral aspects of an organic psychosyndrome. Multivariate analyses revealed demographic characteristics (age, gender, education), clinical aspects (psychiatric history, affected hemisphere, mesial pathology, seizure frequency, cognitive functions), and treatment (antiepileptic drug treatment) as relevant determinants, explaining up to 30% of the behavior. Significance: Behavioral abnormalities in patients with frontal or temporal lobe epilepsy are common but on the average mostly mild. Within a multivariate etiological model, localization (mesial yes/no) and lateralization (left > right) dependent behavioral problems in TLE and FLE seem to be overshadowed by other variables, of which patients’ and their families’ psychiatric history, patient characteristics and pharmacological treatment appear of major importance. Better education and cognitive capabilities may be discussed as protective features.     

Time course evaluation of behavioral impairments in the pilocarpine model of epilepsy

Epilepsy is a brain function disorder characterized by unpredictable and recurrent seizures. The majority of patients with temporal lobe epilepsy (TLE), which is the most common type of epilepsy, have to live not only with seizures but also with behavioral alterations, including anxiety, psychosis, depression, and impaired cognitive functioning. The pilocarpine model has been recognized as an animal model of TLE. However, there are few studies addressing behavioral alterations in the maturation phase when evaluating the time course of the epileptogenic process after pilocarpine administration. Therefore, the present work was designed to analyze the neurobehavioral impairments of male adult Wistar rats during maturation and chronic phases in the pilocarpine model of epilepsy. Behavioral tests included: open-field tasks, olfactory discrimination, social recognition, elevated plus maze, and the forced swimming test. The main behavioral alterations observed in both maturation and chronic phases of the pilocarpine model were olfactory and short-term social memory deficits and decrease in the immobility time in the forced swimming test. Moreover, increased anxiety-like responses were only observed in the maturation phase. These findings indicate that early behavioral impairments can be observed in the pilocarpine model during the maturation phase, and these behavioral deficits also occur during the acquired epilepsy (chronic phase). Several of the neurobehavioral impairments that are associated with epilepsy in humans were observed in the pilocarpine-treated rats, thus, rendering this animal model a useful tool to study neuroprotective strategies as well as neurobiological and psychopathological mechanisms associated with epileptogenesis.     

Psychogenic nonepileptic seizures in patients with surgically treated temporal lobe epilepsy: Presurgical and de novo postsurgical occurrence

Whether occurring before or after an epilepsy surgery, psychogenic nonepileptic seizures (PNES) impact treatment options and quality of life of patients with epilepsy. We investigated the frequency of pre- and postsurgical PNES, and the postsurgical Engel and psychiatric outcomes in patients with drug-resistant temporal lobe epilepsy (TLE). We reviewed 278 patients with mean age at surgery of 37.1 ± 12.4 years. Postsurgical follow-up information was available in 220 patients, with average follow-up of 4 years.Nine patients (9/278 or 3.2%) had presurgical documented PNES. Eight patients (8/220 or 3.6%) developed de novo PNES after surgery. Pre- and postsurgery psychiatric comorbidities were similar to the patients without PNES. After surgery, in the group with presurgical PNES, five patients were seizure-free, and three presented persistent PNES. In the group with de novo postsurgery PNES, 62.5% had Engel II–IV, and 37.5% had Engel I. All presented PNES at last follow-up.Presurgical video-EEG monitoring is crucial in the diagnosis of coexisting PNES. Patients presenting presurgical PNES and drug-resistant TLE should not be denied surgery based on this comorbidity, as they can have good postsurgical epilepsy and psychiatric outcomes. Psychogenic nonepileptic seizures may appear after TLE surgery in a low but noteworthy proportion of patients regardless of the Engel outcome.     

Antiepileptic drug-resistant rats differ from drug-responsive rats in hippocampal neurodegeneration and GABA(A) receptor ligand binding in a model of temporal lobe epilepsy

The disabling seizures associated with mesial temporal lobe epilepsy (TLE) are often resistant to antiepileptic drugs (AEDs). The biological basis of this refractoriness is unknown but may include alterations in AED targets in the epileptogenic brain tissue, reduced AED penetration to the seizure focus, and neuropathological brain alterations such as hippocampal sclerosis typically found in patients with refractory TLE. In the present study, we used a rat model of TLE to examine whether AED responders differ from non-responders in their structural alterations and GABA(A) receptor characteristics in the hippocampal formation. In this model, spontaneous recurrent seizures develop after a status epilepticus induced by prolonged electrical stimulation of the basolateral amygdala. The frequency of these seizures was recorded by continuous video/EEG monitoring before, during, and after daily treatment with phenobarbital, which was given at maximum tolerated doses for 2 weeks. Based on their individual response to phenobarbital, rats were grouped into responders and non-responders. The severity or duration of the initial brain insult (the status epilepticus) did not differ between responders and non-responders, indicating that the difference between the two subgroups is genetically determined. Subsequent histological examination showed a significant loss of neurons in the CA1, CA3c/CA4, and dentate hilus of non-responders, whereas responders did not differ in this respect from non-epileptic controls. The morphological alterations in the non-responders were associated with striking alterations in autoradiographic imaging of diazepam-sensitive and diazepam-insensitive GABA(A) receptor binding in the dentate gyrus with a significant shift to enhanced diazepam-insensitive binding. The present data indicate that neurodegeneration and associated GABA(A) receptor changes in the dentate gyrus are critically involved in the mechanisms underlying refractoriness of seizures in TLE.     

Short-term withdrawal of antiepileptic medication: effects on attention and memory

Introduction – The aim of this study was to determine the effect of routine withdrawal of antiepileptic drugs (AEDs) during preoperative evaluation on cognitive functions and also to clarify whether short-term withdrawal of AED would help to lateralize the epileptic focus and to highlight focal dysfunction of memory in patients with temporal lobe epilepsy. Material & methods – Cognitive function was evaluated in 25 patients on full medication and after 1-week during the ongoing AED withdrawal. Six additional patients without AED withdrawal were studied during the same time interval and served as controls. The effect of AED withdrawal on memory tests was evaluated in a subgroup of 11 patients with temporal lobe epilepsy (TLE group). Results – In the TLE group, verbal recurrent-sequences learning tasks deteriorated significantly in patients with left-sided foci during AED withdrawal. In the whole group, attention, concentration and mental flexibility improved both in patients and in controls; the improvement was interpreted as being the result of the practice effect. During AED withdrawal, the number of errors in these tests decreased or remained unchanged. Conclusion – We suggest that preoperative neuropsychological testing can be scheduled at any time in patients referred for epilepsy surgery. In patients with temporal lobe epilepsy, the lateralizing results of selective memory tests may be most reliable if the testing is performed during AED withdrawal.     

Ex vivo study of dentate gyrus neurogenesis in human pharmacoresistant temporal lobe epilepsy

M. Paradisi, M. Fernández, G. Del Vecchio, G. Lizzo, G. Marucci, M. Giulioni, E. Pozzati, T. Antonelli, G. Lanzoni, G. P. Bagnara, L. Giardino and L. Calzà (2010) Neuropathology and Applied Neurobiology 36, 535–550
Ex vivo study of dentate gyrus neurogenesis in human pharmacoresistant temporal lobe epilepsy Aims: Neurogenesis in adult humans occurs in at least two areas of the brain, the subventricular zone of the telencephalon and the subgranular layer of the dentate gyrus in the hippocampal formation. We studied dentate gyrus subgranular layer neurogenesis in patients subjected to tailored antero‐mesial temporal resection including amygdalohippocampectomy due to pharmacoresistant temporal lobe epilepsy (TLE) using the in vitro neurosphere assay. Methods: Sixteen patients were enrolled in the study; mesial temporal sclerosis (MTS) was present in eight patients. Neurogenesis was investigated by ex vivo neurosphere expansion in the presence of mitogens (epidermal growth factor + basic fibroblast growth factor) and spontaneous differentiation after mitogen withdrawal. Growth factor synthesis was investigated by qRT‐PCR in neurospheres. Results: We demonstrate that in vitro proliferation of cells derived from dentate gyrus of TLE patients is dependent on disease duration. Moreover, the presence of MTS impairs proliferation. As long as in vitro proliferation occurs, neurogenesis is maintained, and cells expressing a mature neurone phenotype (TuJ1, MAP2, GAD) are spontaneously formed after mitogen withdrawal. Finally, formed neurospheres express mRNAs encoding for growth (vascular endothelial growth factor) as well as neurotrophic factors (brain‐derived neurotrophic factor, ciliary neurotrophic factor, glial‐derived neurotrophic factor, nerve growth factor). Conclusion: We demonstrated that residual neurogenesis in the subgranular layer of the dentate gyrus in TLE is dependent on diseases duration and absent in MTS.     

Behavioral alterations in the pilocarpine model of temporal lobe epilepsy in mice

Psychiatric disorders frequently occur in patients with epilepsy, but the relationship between epilepsy and psychopathology is poorly understood. Frequent comorbidities in epilepsy patients comprise major depression, anxiety disorders, psychosis and cognitive dysfunction. Animal models of epilepsy, such as the pilocarpine model of acquired epilepsy, are useful to study the relationship between epilepsy and behavioral dysfunctions. However, despite the advantages of mice in studying the genetic underpinning of behavioral alterations in epilepsy, mice have only rarely been used to characterize behavioral correlates of epilepsy. This prompted us to study the behavioral and cognitive alterations developing in NMRI mice in the pilocarpine model of epilepsy, using an anxiety test battery as well as tests for depression, drug-induced psychosis, spatial memory, and motor functions. In order to ensure the occurrence of status epilepticus (SE) and decrease mortality, individual dosing of pilocarpine was performed by ramping up the dose until onset of SE. This protocol was used for studying the consequences of SE, i.e. hippocampal damage, incidence of epilepsy with spontaneous recurrent seizures, and behavioral alterations. SE was terminated by diazepam after either 60, 90 or 120 min. All mice that survived SE developed epilepsy, but the severity of hippocampal damage varied depending on SE length. In all anxiety tests, except the elevated plus maze test, epileptic mice exhibited significant increases of anxiety-related behavior. Surprisingly, a decrease in depression-like behavior was observed in the forced swimming and tail suspension tests. Furthermore, epileptic mice were less sensitive than controls to most of the behavioral effects induced by MK-801 (dizocilpine). Learning and memory were impaired in epileptic mice irrespective of SE duration. Thus, the pilocarpine-treated mice seem to reflect several of the behavioral and cognitive disturbances that are associated with epilepsy in humans. This makes these animals an ideal model to study the neurobiological mechanisms underlying the association between epilepsy and psychopathology.     

Behavioral alterations in a mouse model of temporal lobe epilepsy induced by intrahippocampal injection of kainate

Patients with temporal lobe epilepsy are frequently afflicted with psychiatric comorbidity and deficits in spatial and other forms of declarative memory. The relationship between epilepsy and psychopathology is poorly understood, so that systematic research in this area is important. In the present study, we characterized various behaviors and learning and memory in a mouse model in which major aspects of mesial temporal lobe epilepsy can be reproduced. In this model, a single unilateral injection of kainate into the dorsal hippocampus induces a nonconvulsive status epilepticus, followed by development of spontaneous recurrent seizures and ipsilateral lesions of CA1, CA3c and dentate hilus neurons. Unexpectedly, the epileptic mice exhibited only few alterations in a behavioral test battery used to investigate locomotor activity and function, emotionality, depression-related behavior and learning and memory. In contrast to recent experiments with the same test battery in epileptic mice generated by systemic administration of pilocarpine, mice with focal kainate administration did not exhibit reduced explorative behavior or increases of anxiety-related behavior. However, similar to pilocarpine-treated mice, a decrease in depression-like behavior was observed in the forced swimming test. In the Morris water maze test, kainate-treated animals exhibited retarded acquisition and impaired retention of visual-spatial information. Our data suggest that the focal kainate model of mesial temporal lobe epilepsy may contribute to understanding the neurobiological mechanisms underlying the association between epilepsy and behavioral or cognitive alterations.