Temporal Lobe Epileptogenesis and Epilepsy in the Developing Brain: Bridging the Gap Between the Laboratory and the Clinic. Progression, But in What Direction?

Thalamohippocampal atrophy in focal epilepsy of unknown cause at the time of diagnosis

BACKGROUND AND PURPOSE

Patients with chronic focal epilepsy may have atrophy of brain structures important for the generation and maintenance of seizures. However, little research has been conducted in patients with newly diagnosed focal epilepsy (NDfE), despite it being a crucial point in time for understanding the underlying biology of the disorder. We aimed to determine whether patients with NDfE show evidence of volumetric abnormalities of subcortical structures.

METHODS

Eighty-two patients with NDfE and 40 healthy controls underwent magnetic resonance imaging scanning using a standard clinical protocol. Volume estimation of the left and right hippocampus, thalamus, caudate nucleus, putamen and cerebral hemisphere was performed for all participants and normalised to whole brain volume. Volumes lower than two standard deviations below the control mean were considered abnormal. Volumes were analysed with respect to patient clinical characteristics, including treatment outcome 12 months after diagnosis.

RESULTS

Volume of the left hippocampus (p_(FDR-corr)  = 0.04) and left (p_(FDR-corr)  = 0.002) and right (p_(FDR-corr)  = 0.04) thalamus was significantly smaller in patients relative to controls. Relative to the normal volume limits in controls, 11% patients had left hippocampal atrophy, 17% had left thalamic atrophy and 9% had right thalamic atrophy. We did not find evidence of a relationship between volumes and future seizure control or with other clinical characteristics of epilepsy.

CONCLUSIONS

Volumetric abnormalities of structures known to be important for the generation and maintenance of focal seizures are established at the time of epilepsy diagnosis and are not necessarily a result of the chronicity of the disorder.

Interictal epileptiform discharges shape large-scale intercortical communication

Dynamic interactions between remote but functionally specialized brain regions enable complex information processing. This intercortical communication is disrupted in the neural networks of patients with focal epilepsy, and epileptic activity can exert widespread effects within the brain. Using large-scale human intracranial electroencephalography recordings, we show that interictal epileptiform discharges (IEDs) are significantly coupled with spindles in discrete, individualized brain regions outside of the epileptic network. We found that a substantial proportion of these localized spindles travel across the cortical surface. Brain regions that participate in this IED-driven oscillatory coupling express spindles that have a broader spatial extent and higher tendency to propagate than spindles occurring in uncoupled regions. These altered spatiotemporal oscillatory properties identify areas that are shaped by epileptic activity independent of IED or seizure detection. Our findings suggest that IED-spindle coupling may be an important mechanism of interictal global network dysfunction that could be targeted to prevent disruption of normal neural activity.

Expression analysis and clinical correlation of aquaporin 1 and 4 genes in human hippocampal sclerosis

Mesial temporal sclerosis (MTS) is the most frequent cause of drug resistant symptomatic partial epilepsy. The mechanism and genetic background of this unique pathology are not well understood. Aquaporins (AQP) are regulators of water homeostasis in the brain and are expressed in the human hippocampus. We explored the role of AQP genes in the pathogenetic mechanisms of MTS through an evaluation of gene expression in surgically removed human brain tissue. We analyzed AQP1 and 4 mRNA levels by quantitative real-time polymerase chain reaction and normalized to ABL and cyclophilin genes, followed by immunohistochemistry for AQP4. Relative expressions were calculated according to the delta Ct method and the results were compared using the Mann-Whitney U test. Brain specimens of 23 patients with epilepsy who had undergone surgery for MTS and seven control autopsy specimens were investigated. Clinical findings were concordant with previous studies and 61% of the patients were seizure-free in the postoperative period. AQP1 and 4 gene expression levels did not differ between MTS patients and control groups. Immunofluorescence analysis of AQP4 supported the expression results, showing no difference. Previous studies have reported contradictory results about the expression levels of AQP in MTS. To our knowledge, only one study has suggested upregulation whereas the other indicated downregulation of perivascular AQP4. Our study did not support these findings and may rule out the involvement of AQP in human MTS.

Isolated febrile seizures are not associated with structural abnormalities of the limbic system

The nature of the relationship between childhood febrile seizures (CFSs) and temporal lobe epilepsy (TLE) remains unknown. The purpose of this study was to perform a comprehensive analysis of measures of structural changes of the hippocampus and limbic white matter to determine whether structural abnormalities previously demonstrated in TLE were present in adults with isolated CFS. Twenty-three adults with past CFS but no history of nonfebrile seizures and 21 controls underwent research MRI for measurement of volume, T2 and mean diffusivity of the hippocampus and fractional anisotropy of the fornix and cingulum. No significant group differences were found in any of the measured parameters. These findings suggest that structural abnormalities of the hippocampus and limbic white matter that have been demonstrated in TLE are not associated with isolated CFS.

Phenotypic characteristics of temporal lobe epilepsy: the impact of hippocampal sclerosis

OBJECTIVES

Whether mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) is a condition with a unique biological background that can be delineated from other TLE, is unresolved. Here we performed a comparative analysis of two TLE patient cohorts - one cohort with HS and one without HS - in order to identify phenotypic characteristics specifically associated with MTLE-HS.

METHODS

Epidemiological data and clinical and diagnostic features were compared between patients with MTLE-HS and TLE patients without HS. When appropriate, data were compared with healthy controls.

RESULTS

Fifty-six (26%) patients were diagnosed with MTLE-HS and 162 (74%) with other TLE. Age at epilepsy onset was lower in patients with MTLE-HS (P = 0.003) than in TLE patients without HS. Incidence of simple partial seizures was higher in the MTLE-HS group (P = 0.006), as were complex partial seizures (P = 0.001), ictal psychiatric symptoms (P = 0.015), and autonomic symptoms (P < 0.001). Interictal psychiatric symptoms, including depression, were less frequent in MTLE-HS (P = 0.043). MTLE-HS patients had a higher incidence of childhood febrile seizures (FS; P = 0.043) than TLE patients without HS. In contrast, the former group had the lower frequency of first-grade family members with childhood FS (P = 0.019).

CONCLUSIONS

We identified phenotypic characteristics that distinguish MTLE-HS from other types of TLE. These characteristics will be important in diagnostics, treatment, and determination of prognosis, and provide a basis for future phenotype-genotype studies.

Nitric oxide regulates activity-dependent neuroprotective protein (ADNP) in the dentate gyrus of the rodent model of kainic acid-induced seizure

The dentate gyrus (DG) of the normal rat brain contains activity-dependent neuroprotective protein (ADNP) which is widely distributed in the cytoplasm of neurons and astrocytes. Treatment with nitric oxide (NO) synthase (NOS) inhibitor N(G)-nitro-L: -arginine methyl ester (L: -NAME) caused a decrease in ADNP expression in granule cells which persisted 3 days post-treatment. However, treatment with neuronal-specific NOS inhibitor, 7-nitroindazole (7-NI), or soluble guanylyl cyclase inhibitor, ODQ, did not change ADNP expression in the DG. We have previously shown that kainic acid (KA)-induced seizure increases neuronal NOS in neurons and inducible NOS in glia cells and suppresses ADNP in the hippocampus (Cosgrave et al., Neurobiol Dis 30(3):281-292, 2008). In the DG, L: -NAME treatment prior to KA causes ADNP synthesis in granule cells by 3 h which was later restricted to the subgranular zone by 3 days. 7-NI and ODQ had no effect. Double immunostaining for neuronal marker NeuN and ADNP revealed a significant decrease of both ADNP(+) neurons and of total neuron numbers (NeuN(+)) in the hilus of animals having KA-induced seizure that had been pretreated with L: -NAME implying that NO and ADNP may act together to protect hilar neurons. Overall, these observations suggest that NO regulates ADNP in the DG under both basal and pathophysiological conditions.

Regulation of activity-dependent neuroprotective protein (ADNP) by the NO-cGMP pathway in the hippocampus during kainic acid-induced seizure

Activity-dependent neuroprotective protein (ADNP) is widely distributed in the cytoplasm of neurons and astrocytes of the hippocampus. Kainic acid (KA)-induced seizures increases neuronal nitric oxide synthase (nNOS) in neurons and inducible NOS (iNOS) in glia cells which coincides with a reduction in ADNP in the hippocampus. Inhibitors of NOS or soluble guanylyl cyclase (sGC) activity reduce ADNP under basal conditions in the absence of seizures. Treating animals with these inhibitors prior to KA-induced seizure, in particular, L-NAME (N(G)-nitro-l-arginine methyl ester), advances the onset of the first seizure but reverses the loss of ADNP by 3 days after the first seizure. This suggests that the NO-cGMP pathway has a role in regulating ADNP under both basal physiological conditions and in the pathophysiological changes produced during epileptogenesis.

Bilateral white matter diffusion changes persist after epilepsy surgery

PURPOSE

Bilateral white matter diffusion tensor imaging (DTI) abnormalities have been reported in patients with temporal lobe epilepsy (TLE) and unilateral mesial temporal sclerosis (MTS), but it is unknown whether these are functional or structural changes. We performed a longitudinal study in patients with unilateral MTS who were seizure-free for 1 year after surgery to determine whether the observed presurgical white matter diffusion abnormalities were reversible.

METHODS

Eight TLE patients with unilateral MTS who were seizure-free after anterior temporal resection and 22 healthy subjects were recruited. DTI was performed before surgery and at 1-year follow-up. Tractography and region-of-interest (ROI) analyses were performed in the fornix, cingulum, genu, and splenium of the corpus callosum and external capsules. Diffusion tensor parameters were compared between groups and before and after surgery in the patient group.

RESULTS

The fornix, cingulum, and external capsules showed preoperative bilateral abnormal diffusion parameters (i.e., decreased diffusion anisotropy and increased mean and perpendicular diffusivities). The fornix and cingulum ipsilateral to the resected mesial temporal structures showed signs of wallerian degeneration at 1-year follow-up. The contralateral tracts of the fornix, cingulum, and external capsules, as well as the genu of the corpus callosum, failed to show a normalization of their diffusion parameters.

CONCLUSIONS

The irreversibility of the white matter DTI abnormalities on seizure freedom suggests underlying structural abnormalities (e.g., axonal/myelin degradation) as opposed to functional changes (e.g., fluid shifts due to seizures) in the white matter.

Hippocampal mossy fiber sprouting and elevated trkB receptor expression following systemic administration of low dose domoic acid during neonatal development

We have previously reported that serial systemic injections of low-dose (subconvulsive) domoic acid (DOM) during early postnatal development produces changes in both behavior and hippocampal cytoarchitecture in aged rats (17 months) that are similar to those seen in existing animal models of temporal lobe epilepsy. Herein we report further hippocampal changes, consisting of mossy fiber sprouting and associated changes in the trkB receptor population in young adult (3 months) rats, and further, report that these changes show regional variation throughout the septo-temporal axis of the hippocampus. Groups of Sprague Dawley rat pups were injected daily from postnatal day 8-14 with either saline (n = 23) or 20 microg/kg DOM (n = 25), tested for key indicators of neonatal neurobehavioral development, and then left undisturbed until approximately 90 days of age, at which time brain tissue was removed, hippocampi were dissected, fixed and processed using either Timm's stain to visualize hippocampal mossy fiber sprouting (MFS) or trkB immunohistochemistry to visualize full length trkB receptors. Multiple sections from dorsal, mid, and ventral hippocampus were analyzed separately and all measures were conducted using image analysis software. The results indicate significant increases in MFS in the inner molecular layer in treated animals with corresponding changes in trkB receptor density. Further we identified significant increases in trkB receptor density in the hilus of the dentate gyrus and area CA3 and report increased mossy fiber terminal density in the stratum lucidum in treated rats. The magnitude of these changes differed between sections from dorsal, mid, and ventral hippocampus. We conclude that low dose neonatal DOM produces cytoarchitectural changes indicative of abnormal development and/or synaptic plasticity that are progressive with age and show regional variation within the hippocampal formation.

Childhood mesial temporal sclerosis

The prevalence and clinical characteristics of mesial temporal sclerosis have not been well studied in children. All brain magnetic resonance imaging (MRI) reports of children less than 14 years of age were reviewed from two tertiary institutions. A 52-month period from one institution and a 37-month period from the other were reviewed. All reports of definite or possible mesial temporal sclerosis were noted. These patients' MRIs were then reviewed to confirm the MRI diagnostic criteria of mesial temporal sclerosis. The charts of the patients who satisfied these criteria were reviewed in detail. Three thousand one hundred brain MRI reports were reviewed. Twenty-six reports of mesial temporal sclerosis were found. Twenty-four of the 26 films satisfied the criteria of mesial temporal sclerosis by MRI after the films were reviewed. The prevalence among all pediatric brain MRI studies was 0.77%. All patients had presented with seizures, that is, there were no "incidental" findings of mesial temporal sclerosis. Four patients had a history of febrile seizures. Mesial temporal sclerosis is an uncommon finding in children, but when it occurs, it is always associated with epilepsy. Asymptomatic mesial temporal sclerosis or mesial temporal sclerosis not associated with a seizure disorder did not occur in our series. Febrile seizures can occur in association with mesial temporal sclerosis presenting in childhood.

Meditation and epilepsy: A still hung jury

Meditation has been advocated as a treatment for several medical problems, including epilepsy. Conversely, concern has been raised that meditation may aggravate or even precipitate epilepsy. We present a case of new onset mesial temporal lobe epilepsy in a young woman meditator lacking other apparent risk factors for epilepsy as a springboard for a balanced discussion concerning the potential relationship between meditation and epilepsy, and a criticism of the current literature in this field. Prospective clinical studies of meditators with video-electroencephalography and clinical trials of meditation in refractory epilepsy patients are needed to resolve current controversies concerning meditation and epilepsy.

Different types of status epilepticus lead to different levels of brain damage in rats

We investigated a possible correlation between behavior during status epilepticus (SE) and underlying brain damage. Adult rats were electrically stimulated in the left amygdala to induce SE, which was stopped 2 hours later. We observed two different types of SE: (1) typical SE (TSE), with facial automatisms, neck and forelimb myoclonus, rearing and falling, and tonic-clonic seizures; (2) ambulatory SE (ASE), with facial automatisms, neck myoclonus, and concomitant ambulatory behavior. TSE was behaviorally more severe than ASE (P<0.05). Histology revealed neuronal loss in several brain areas. There was a positive correlation between SE type and amount of injured areas 24 hours and 14 days after SE (P<0.01). The areas more affected were piriform cortex and hippocampal formation. We suggest quality of seizures during SE may be considered in further SE studies, as our results indicate its influence on the severity of brain damage following this paradigm.

Time course changes of estrogen receptor alpha expression in the adult rat hippocampus after kainic acid-induced status epilepticus

Although estrogens possess neuroprotective and epileptogenic properties, the expression pattern of the estrogen receptor (ER) following status epilepticus (SE) remains unclear. We therefore examined the expression pattern of ER alpha in the adult rat hippocampus after SE. SE was induced in rats by kainic acid (KA; 12 mg/kg, i.p.). ER alpha expression was assessed by immunostaining and Western blotting at various times (24 h, and 7, 14, and 21 days) after SE onset. Immunohistochemistry disclosed ER alpha expression in the CA1 and CA3 pyramidal cells of control rats, whereas, after SE, ER alpha-immunoreactive neurons decreased in number due to neuronal death in the CA1 from days 7 to 21. On the other hand, ER alpha-immunoreactive cells with astrocytic morphology were observed in the CA1 beginning on day 7 after SE. This immunoreactivity increased in proportion to the hypertrophy of astrocytes up to day 21. Western blotting revealed a significant decrease in ER alpha expression on day 7 after SE in comparison with control level. However, ER alpha expression on days 14 and 21 were similar when comparing KA-treated and control rats. These results indicate that reactive astrocytes are important sites of estrogen action in the hippocampal CA1 after SE.

Progressive hippocampal and extrahippocampal atrophy in drug resistant epilepsy

PURPOSE OF REVIEW

This article reviews recent experimental and clinical evidence for seizure-related progressive brain damage and discusses possible mechanisms of ongoing brain atrophy in epilepsy.

RECENT FINDINGS

Experimental data indicate that seizures induce brain plasticity that may result in either damage or protection. Brief seizures or status epilepticus may promote resistance to additional damage but also induce cumulative neuronal loss and increase susceptibility to network synchronization. Some experimental studies indicated that, following the initial damage caused by status epilepticus, further brief seizures may not produce significant continuing neuronal loss and hippocampal atrophy, whereas other studies showed the contrary. There is recent evidence that progressive damage and atrophy may occur after an acute insult but are not directly associated with recurrent seizures. Clinical research data continue to show discrepancies regarding whether ongoing seizures cause progressive atrophy. Some cross-sectional and longitudinal magnetic resonance imaging studies in patients with partial epilepsies have shown progressive hippocampal and extrahippocampal atrophy, the severity of which correlated with the duration of epilepsy, seizure frequency, or lifetime seizure number, whereas others have failed to show a clear association.

SUMMARY

Experimental data indicate that epileptogenesis in developing brain may not require significant neuronal loss, which is in keeping with clinical observations that progressive cognitive and behavioural impairment may occur in patients with no detectable brain atrophy. A better understanding of why, when and how progressive brain atrophy occurs will lead to better clinical management, earlier surgical intervention when necessary and, ultimately, prevention of epileptogenesis.

Lipopolysaccharide-induced Febrile Convulsions in the Rat: Short-term Sequelae

PURPOSE

Febrile convulsions (FCs) occur in children as a result of fever. The mechanisms involved in the genesis of FCs and their long-term consequences on brain development remain unclear. We have developed a model of FC, by using fever as a parameter, to test the hypothesis that fever can lower seizure threshold and to examine the neurologic sequelae of FCs.

METHODS

Fourteen-day-old rat pups equipped with body-temperature telemetry devices exhibited approximately 1.5 degrees C fevers after lipopolysaccharide (Escherichia coli, 200 microg/kg). During such fevers, concurrently administered doses of kainic acid that are normally subconvulsant were used to induce convulsions with fever. Animals were then killed at varying times for pathological and immunohistochemical studies.

RESULTS

The pairing of lipopolysaccharide and subconvulsant kainic acid resulted in convulsions in approximately 50% of febrile animals, with very low mortality. To study the neural correlates of these FCs, we used fos immunohistochemistry and found that animals with FCs had fos-positive immunoreactivity in brain regions involved in seizures. After a period of 72 h, we also examined brains for pathologic changes and found no differences among our groups.

CONCLUSIONS

Our data indicate that a neuroimmune challenge and its accompanying fever reduce the seizure threshold. Furthermore, the FCs induced by fever in this model do not have short-term adverse effects on the brain. In addition, this model, by incorporating physiologic fever, may be useful for examining the role of fever and its constituent mediators in the genesis of FCs.

Differential effects of chronic ethanol administration and withdrawal on gamma-aminobutyric acid type A and NMDA receptor subunit proteins in male and female rat brain

BACKGROUND

Investigations have shown that chronic ethanol exposure results in selective alterations in levels of gamma-aminobutyric acid (GABA)A and NMDA receptor subunits. We previously reported significant sex differences in these chronic ethanol-induced adaptations. Because we have more recently found important sex differences in timing for the development of and recovery from ethanol dependence, we wanted to ascertain whether there were associations between overt expression of withdrawal and neuroadaptations at the level of GABAA and NMDA receptors.

METHODS

Western blot analysis was used to assay protein levels for several GABAA and NMDA receptor subunits in rat cerebral cortex and hippocampus by using subunit-selective antibodies. Rats were fed 6% ethanol in a liquid diet with pair-fed controls. Feeding, harvesting of tissue, and Western blot experiments were all conducted while maintaining the paired design. Tissue was harvested after 3 days of ethanol exposure, 9 days of ethanol exposure, or 3 days of ethanol withdrawal after 14 days of liquid diet administration.

RESULTS

We again found sex-, subunit-, and brain region-selective effects of ethanol administration and withdrawal for GABAA and NMDA receptors. There was a strong association between increased GABAA receptor alpha4 subunit levels and previously determined withdrawal-induced changes in seizure susceptibility, highlighted by the sex differences in ethanol exposure length required to cause withdrawal signs. In addition, results obtained after 9 days of ethanol administration were in general agreement with previous findings after 14 days of ethanol administration.

CONCLUSIONS

These data further support the suggestion that alterations in subunit assembly of GABAA and NMDA receptors may have some mechanistic role in neuroadaptations underlying ethanol dependence and withdrawal. Furthermore, significant sex differences in these adaptations suggest that multiple types of adaptations may be elicited, depending on innate differences in the actions/effects of ethanol.