Increased matrix metalloproteinases expression in tuberous sclerosis complex: modulation by microRNA 146a and 147b in vitro

AIM

Matrix metalloproteinases (MMPs) and their endogenous tissue inhibitors (TIMPs) control proteolysis within the extracellular matrix (ECM) of the brain. Dysfunction of this enzymatic system due to brain inflammation can disrupt the blood-brain barrier (BBB) and has been implicated in the pathogenesis of epilepsy. However, this has not been extensively studied in the epileptogenic human brain.

METHODS

We investigated the expression and cellular localization of major MMPs (MMP2, MMP3, MMP9 and MMP14) and TIMPs (TIMP1, TIMP2, TIMP3 and TIMP4) using quantitative real-time polymerase chain reaction (RT-PCR) and immunohistochemistry in resected epileptogenic brain tissue from patients with tuberous sclerosis complex (TSC), a severe neurodevelopmental disorder characterized by intractable epilepsy and prominent neuroinflammation. Furthermore, we determined whether anti-inflammatory microRNAs, miR146a and miR147b, which can regulate gene expression at the transcriptional level, could attenuate dysregulated MMP and TIMP expression in TSC tuber-derived astroglial cultures.

RESULTS

We demonstrated higher mRNA and protein expression of MMPs and TIMPs in TSC tubers compared to control and perituberal brain tissue, particularly in dysmorphic neurons and giant cells, as well as in reactive astrocytes, which was associated with BBB dysfunction. More importantly, IL-1β-induced dysregulation of MMP3, TIMP2, TIMP3 and TIMP4 could be rescued by miR146a and miR147b in tuber-derived TSC cultures.

CONCLUSIONS

This study provides evidence of dysregulation of the MMP/TIMP proteolytic system in TSC, which is associated with BBB dysfunction. As dysregulated MMP and TIMP expression can be ameliorated in vitro by miR146a and miR147b, these miRNAs deserve further investigation as a novel therapeutic approach.

Chronic activation of anti-oxidant pathways and iron accumulation in epileptogenic malformations

Aims

Oxidative stress is evident in resected epileptogenic brain tissue of patients with developmental brain malformations related to mammalian target of rapamycin activation: tuberous sclerosis complex (TSC) and focal cortical dysplasia type IIb (FCD IIb). Whether chronic activation of anti‐oxidant pathways is beneficial or contributes to pathology is not clear.

Methods

We investigated oxidative stress markers, including haem oxygenase 1, ferritin and the inflammation associated microRNA‐155 in surgically resected epileptogenic brain tissue of TSC (n = 10) and FCD IIb (n = 8) patients and in a TSC model (Tsc1^GFAP−/− mice) using immunohistochemistry, in situ hybridization, real‐time quantitative PCR and immunoblotting. Using human foetal astrocytes we performed an in vitro characterization of the anti‐oxidant response to acute and chronic oxidative stress and evaluated overexpression of the disease‐relevant pro‐inflammatory microRNA‐155.

Results

Resected TSC or FCD IIb tissue displayed higher expression of oxidative stress markers and microRNA‐155. Tsc1^GFAP−/− mice expressed more microRNA‐155 and haem oxygenase 1 in the brain compared to wild‐type, preceding the typical development of spontaneous seizures in these animals. In vitro, chronic microRNA‐155 overexpression induced haem oxygenase 1, iron regulatory elements and increased susceptibility to oxidative stress. Overexpression of iron regulatory genes was also detected in patients with TSC, FCD IIb and Tsc1^GFAP−/− mice.

Conclusion

Our results demonstrate that early and sustained activation of anti‐oxidant signalling and dysregulation of iron metabolism are a pathological hallmark of FCD IIb and TSC. Our findings suggest novel therapeutic strategies aimed at controlling the pathological link between both processes.

Dysregulation of the (immuno)proteasome pathway in malformations of cortical development

Background

The proteasome is a multisubunit enzyme complex involved in protein degradation, which is essential for many cellular processes. During inflammation, the constitutive subunits are replaced by their inducible counterparts, resulting in the formation of the immunoproteasome.

Methods

We investigated the expression pattern of constitutive (β1, β5) and immunoproteasome (β1i, β5i) subunits using immunohistochemistry in malformations of cortical development (MCD; focal cortical dysplasia (FCD) IIa and b, cortical tubers from patients with tuberous sclerosis complex (TSC), and mild MCD (mMCD)). Glial cells in culture were used to elucidate the mechanisms regulating immunoproteasome subunit expression.

Results

Increased expression was observed in both FCD II and TSC; β1, β1i, β5, and β5i were detected (within cytosol and nucleus) in dysmorphic neurons, balloon/giant cells, and reactive astrocytes. Glial and neuronal nuclear expression positively correlated with seizure frequency. Positive correlation was also observed between the glial expression of constitutive and immunoproteasome subunits and IL-1β. Accordingly, the proteasome subunit expression was modulated by IL-1β in human astrocytes in vitro. Expression of both constitutive and immunoproteasome subunits in FCD II-derived astroglial cultures was negatively regulated by treatment with the immunomodulatory drug rapamycin (inhibitor of the mammalian target of rapamycin (mTOR) pathway, which is activated in both TSC and FCD II).

Conclusions

These observations support the dysregulation of the proteasome system in both FCD and TSC and provide new insights on the mechanism of regulation the (immuno)proteasome in astrocytes and the molecular links between inflammation, mTOR activation, and epilepsy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0662-z) contains supplementary material, which is available to authorized users.

Differential expression and clinical significance of three inflammation-related microRNAs in gangliogliomas

PURPOSE

miR21, miR146, and miR155 represent a trio of microRNAs which has been shown to play a key role in the regulation of immune and inflammatory responses. In the present study, we investigated the differential expression and clinical significance of these three miRNAs in glioneuronal tumors (gangliogliomas, GGs) which are characterized by prominent activation of the innate immune response.

METHODS

The expression levels of miR21, miR146, and miR155 were evaluated using Taqman PCR in 34 GGs, including 15 cases with sufficient amount of perilesional cortex. Their expression was correlated with the tumor features and the clinical history of epilepsy. In addition, in situ hybridization was used to evaluate their cellular distribution in both tumor and peritumoral cortex.

RESULTS

Increased expression of miR146a was observed in both tumor and peritumoral cortex compared to control samples. miR146a was detected in both neuronal and astroglial cells. Tumor and peritumoral miR146a expression was negatively correlated with frequency of seizures and the density of activated microglial cells. Neuronal and astroglial expression was observed for both miR21 and miR155 with increased expression of miR21 within the tumor and miR155 in the peritumoral region. Negative correlations were observed between the miRNA levels and the expression of putative targets within the astroglial component of the tumor.

CONCLUSION

We report a differential regulation of three miRNAs, known to be related to inflammation, in both tumor and peritumoral cortex of patients with GG. Moreover, our findings suggest a functional relationship between miR146a expression and epilepsy, either directly in epileptogenesis or as modulation of seizure activity.

High frequency oscillations in intra-operative electrocorticography before and after epilepsy surgery

OBJECTIVE

Removal of brain tissue showing high frequency oscillations (HFOs; ripples: 80-250Hz and fast ripples: 250-500Hz) in preresection electrocorticography (preECoG) in epilepsy patients seems a predictor of good surgical outcome. We analyzed occurrence and localization of HFOs in intra-operative preECoG and postresection electrocorticography (postECoG).

METHODS

HFOs were automatically detected in one-minute epochs of intra-operative ECoG sampled at 2048Hz of fourteen patients. Ripple, fast ripple, spike, ripples on a spike (RoS) and not on a spike (RnoS) rates were analyzed in pre- and postECoG for resected and nonresected electrodes.

RESULTS

Ripple, spike and fast ripple rates decreased after resection. RnoS decreased less than RoS (74% vs. 83%; p=0.01). Most fast ripples in preECoG were located in resected tissue. PostECoG fast ripples occurred in one patient with poor outcome. Patients with good outcome had relatively high postECoG RnoS rates, specifically in the sensorimotor cortex.

CONCLUSIONS

Our observations show that fast ripples in intra-operative ECoG, compared to ripples, may be a better biomarker for epileptogenicity. Further studies have to determine the relation between resection of epileptogenic tissue and physiological ripples generated by the sensorimotor cortex.

SIGNIFICANCE

Fast ripples in intra-operative ECoG can help identify the epileptogenic zone, while ripples might also be physiological.

Contralateral MRI abnormalities affect seizure and cognitive outcome after hemispherectomy

OBJECTIVE

To explore whether EEG and MRI abnormalities in the "healthy" hemisphere influence seizure and cognitive outcome after functional hemispherectomy.

METHODS

This is a retrospective consecutive cohort study of 43 children who underwent functional hemispherectomy between 1994 and 2008. Results of preoperative EEG recordings were reviewed for the existence of (inter)ictal epileptic or background abnormalities in the contralateral hemisphere. Preoperative MRIs were reexamined for the existence of unequivocal contralateral abnormalities. Postoperative seizure status was assessed, and of 34 children, IQ or mental developmental index (MDI) scores were obtained preoperatively and postoperatively. Seizure freedom was defined as Engel 1A. Contralateral EEG and MRI abnormalities were studied in relation to seizure and cognitive outcome.

RESULTS

Thirty-three children achieved seizure freedom (77%). Of the 11 patients with contralateral MRI abnormalities, only 45% were seizure free, compared with 88% of the 32 patients without contralateral MRI lesions (p = 0.030). Children with contralateral MRI abnormalities more often were severely retarded after surgery (MDI/IQ <55; 90% vs 42%, p = 0.030). Postoperative MDI/IQ scores improved in none of the children with, but in 38% of those without contralateral MRI abnormalities (p = 0.034). Contralateral epileptic or background EEG abnormalities did not affect seizure outcome or postoperative cognitive performance. Four of 6 children with bilateral epileptic encephalopathy reached seizure freedom.

CONCLUSION

Unambiguous contralateral MRI abnormalities are significantly associated with seizure recurrence, severe mental delay, and lack of cognitive improvement and may be considered a relative contraindication for hemispherectomy. Contralateral EEG abnormalities do not negatively influence postsurgical outcome.

Illusory shadow person causing paradoxical gaze deviations during temporal lobe seizures

Generally, activation of the frontal eye field during seizures can cause versive (forced) gaze deviation, while non-versive head deviation is hypothesised to result from ictal neglect after inactivation of the ipsilateral temporo-parietal area. Almost all non-versive head deviations occurring during temporal lobe seizures are directed to the side of seizure onset, so in derogatory cases it is worth while explaining the paradoxical event. We present a patient with a paradoxical direction of gaze deviation during temporal lobe seizures with an unexpected explanation. Electrocortical stimulation of the temporo-parieto-occipital junction elicited an irrepressible urge to look towards an illusory shadow person besides the patient. Paradoxical non-versive gaze deviations in temporal lobe seizures may be due to illusory experiences masked by postictal amnesia.

The intracarotid amobarbital or Wada test: unilateral or bilateral?

OBJECTIVE

In the Netherlands, presurgical screening for temporal lobe epilepsy (TLE) includes the intracarotid amobarbital procedure (IAP), consisting of two consecutive injections of amobarbital, ipsilateral and contralateral to the epileptic focus. We studied whether a bilateral IAP has added value to a unilateral, ipsilateral IAP.

METHODS

This population-based study included 183 consecutive patients referred for screening for TLE surgery who underwent bilateral IAP. Using multivariable modeling, we assessed the added value of bilateral IAP on the decision for surgery, resection size, amygdalohippocampectomy, post-operative seizure freedom, memory performance, and IQ change.

RESULTS

Given the results from the unilateral IAP, the bilateral IAP had added prognostic value for postoperative change in verbal memory (P < 0.01) and verbal IQ (P < 0.01), especially if patients had a left-sided focus. In contrast, information provided by the contralateral IAP was not associated with decision-making or surgical strategy.

CONCLUSIONS

A bilateral IAP has added value in predicting post-operative verbal memory and IQ. A bilateral IAP is currently not used to guide surgical strategy, but may be used for this purpose when verbal capacity is of particular concern in patients with a left-sided focus. In other cases, IAP is best performed unilaterally.

Gene expression profile analysis of epilepsy-associated gangliogliomas

Gangliogliomas (GG) constitute the most frequent tumor entity in young patients undergoing surgery for intractable epilepsy. The histological composition of GG, with the presence of dysplastic neurons, corroborates their maldevelopmental origin. However, their histogenesis, the pathogenetic relationship with other developmental lesions, and the molecular alterations underlying the epileptogenicity of these tumors remain largely unknown. We performed gene expression analysis using the Affymetrix Gene Chip System (U133 plus 2.0 array). We used GENMAPP and the Gene Ontology database to identify global trends in gene expression data. Our analysis has identified various interesting genes and processes that are differentially expressed in GG when compared with normal tissue. The immune and inflammatory responses were the most prominent processes expressed in GG. Several genes involved in the complement pathway displayed a high level of expression compared with control expression levels. Higher expression was also observed for genes involved in cell adhesion, extracellular matrix and proliferation processes. We observed differential expression of genes as cyclin D1 and cyclin-dependent kinases, essential for neuronal cell cycle regulation and differentiation. Synaptic transmission, including GABA receptor signaling was an under-expressed process compared with control tissue. These data provide some suggestions for the molecular pathogenesis of GG. Furthermore, they indicate possible targets that may be investigated in order to dissect the mechanisms of epileptogenesis and possibly counteract the epileptogenic process in these developmental lesions.

Inhibitory networks in epilepsy-associated gangliogliomas and in the perilesional epileptic cortex

Developmental glioneuronal lesions, such as gangliogliomas (GG) are increasingly recognized causes of chronic pharmaco-resistant epilepsy. It has been postulated that chronic epilepsy in patients with malformations of cortical development is associated with dysfunction of the inhibitory GABA-ergic system. We aimed to identify the subtypes of interneurons present within GG specimens and the expression and cellular distribution patterns of GABA receptors (GABAR) and GABA transporter 1 (GAT1). The expression of the various components of the GABA-ergic system were also analyzed in the perilesional cortex. We investigated the expression of parvalbumin, calbindin, calretinin, GABA(A)R (a1 subunit)(,) GABA(B) (R1 and R2) and GAT-1 using immunocytochemistry in 30 specimens of GG obtained during epilepsy surgery, including 10 cases with sufficient amount of perilesional cortex. Immunocytochemistry for calbindin (CB), calretinin (CR) and parvalbumin (PV) demonstrate the presence of inhibitory neurons of different subtypes within the GG specimens. Calcium-binding protein-positive interneurons represent a small fraction of the total neuronal population. Both GABA(A)R and GABA(B)R (R1 and R2) subtypes were detected within the neuronal component of GG specimens. In addition, GABA(B)R2 immunoreactivity (IR) was observed in glial cells. GG specimens displayed also expression of GAT-1 IR. Compared to normal cortex, the density of PV- and CB-immunoreactive interneurons was reduced in the perilesional cortex of GG patients, whereas CR-labeling was similar to that observed in normal cortex. GAT-1 IR was also significantly reduced in the perilesional specimens. The cellular distribution of components of the GABA-ergic system in GG, together with the perilesional changes suggest that alterations of the GABA-ergic system may contribute to the complex abnormal functional network of these highly epileptogenic developmental lesions.

Differential expression patterns of chloride transporters, Na+-K+-2Cl--cotransporter and K+-Cl--cotransporter, in epilepsy-associated malformations of cortical development

Malformations of cortical development are recognized causes of chronic medically intractable epilepsy. An increasing number of observations suggests an important role for cation-chloride co-transporters (CCTs) in controlling neuronal function. Deregulation of their expression may contribute to the mechanisms of hyperexcitability that lead to seizures. In the present study the expression and cell-specific distribution of Na+-K+-2Cl--cotransporter (NKCC1) and K+-Cl--cotransporter (KCC2) were studied immunocytochemically in different developmental lesions, including focal cortical dysplasia (FCD) type IIB (n=9), hemimegalencephaly (HMEG, n=6) and ganglioglioma (GG, n=9) from patients with medically intractable epilepsy and in age-matched controls. In normal control adult cortex, NKCC1 displayed low neuronal and glial expression levels. In contrast KCC2 showed strong and diffuse neuropil staining. Notable glial immunoreactivity (IR) was not found for KCC2. NKCC1 was highly expressed in the majority of FCD, HMEG and GG specimens. NKCC1 IR was observed in neurons of different size, including large dysplastic neurons, in balloon cells (in FCD and HMEG cases) and in glial cells with astrocytic morphology. The immunoreactivity pattern of KCC2 in FCD, HMEG and GG specimens was characterized by less neuropil staining and more intrasomatic IR compared with control. KCC2 IR was observed in neurons of different size, including large dysplastic neurons, but not in balloon cells or in glial cells with astrocytic morphology. Double-labeling experiments confirmed the differential cellular distribution of the two CCTs and their expression in GABA(A) receptor (alpha1 subunit)-positive dysplastic neurons. The cellular distribution of CCTs, with high expression of NKCC1 in dysplastic neurons and altered subcellular distribution of KCC2 resembles that of immature cortex and suggests a possible contribution of CCTs to the high epileptogenicity of malformations of cortical development.

Complement activation in experimental and human temporal lobe epilepsy

We investigated the involvement of the complement cascade during epileptogenesis in a rat model of temporal lobe epilepsy (TLE), and in the chronic epileptic phase in both experimental as well as human TLE. Previous rat gene expression analysis using microarrays indicated prominent activation of the classical complement pathway which peaked at 1 week after SE in CA3 and entorhinal cortex. Increased expression of C1q, C3 and C4 was confirmed in CA3 tissue using quantitative PCR at 1 day, 1 week and 3-4 months after status epilepticus (SE). Upregulation of C1q and C3d protein expression was confirmed mainly to be present in microglia and in a few hippocampal neurons. In human TLE with hippocampal sclerosis, astroglial, microglial and neuronal (5/8 cases) expression of C1q, C3c and C3d was observed particularly within regions where neuronal cell loss occurs. The membrane attack protein complex (C5b-C9) was predominantly detected in activated microglial cells. The persistence of complement activation could contribute to a sustained inflammatory response and could destabilize neuronal networks involved.

[Intracranial EEG monitoring for epilepsy surgery using electrode grids--results in the first 22 Dutch patients]

OBJECTIVE

Description of initial experiences with subdural electrode grids in patients with refractory focal epilepsy as additional diagnostic tool for epilepsy surgery. Using these electrodes, the attacks were recorded during a number of days and the cerebral cortex was electrically stimulated in order to map the functional areas.

DESIGN

Retrospective.

METHOD

Data were collected from patients in whom subdural electrode grids had been placed between 1 September 1999 and 31 August 2004. All patients underwent a neurological examination and a neuropsychological test before the implantation. At the follow-up examination, the results with regard to function and the frequency of attacks were noted, as well as the complications.

RESULTS

Electrodes were placed in 22 patients: 9 women and 13 men with an average age of 27 years (range: 5-42). The implantation lasted for an average of 7 days (range: 3-10). In 4 patients, increased seizures during implantation required intravenous anticonvulsant treatment. Severe but transitory complications were seen in 4 patients (meningitis, subdural haematoma and ischaemia). 19 patients underwent a therapeutic resection. A postoperative decline in language skills was noted in 1 patient, while another 2 scored poorer in verbal tests. A permanent decline in sensorimotor function was seen in 1 patient, but this had been foreseen. Of the 16 operated patients with a duration of follow-up of at least 1 year, so were (practically) free of attacks, and another 3 patients had significantly fewer attacks.

CONCLUSION

Registration with intracranial electrodes makes it possible to treat epileptic patients surgically by excision of brain tissue near critical areas. Such intensive monitoring is, however, not without risk and this must be weighed against the potential benefits.

Verbal memory decline after temporal epilepsy surgery?: A 6-year multiple assessments follow-up study

OBJECTIVE

To assess the long-term effects of temporal lobe epilepsy surgery on verbal memory.

METHODS

We assessed verbal memory performance as measured by a verbal learning test ("15 Words Test," a Dutch adaptation of Rey's Auditory Verbal Learning Test) before surgery and at three specific times after surgery: 6 months, 2 years, and 6 years in 85 patients (34 left temporal lobe [LTL] vs. 51 right temporal lobe [RTL]). An amygdalo-hippocampectomy and a neocortical temporal resection between 2.5 and 8 cm were carried out in all patients.

RESULTS

LTL patients showed an ongoing memory decline for consolidation and acquisition of verbal material (both 2/3 SDs) for up to 2 years after surgery. RTL patients at first showed a gain in both memory acquisition and consolidation, which vanished in the long term. Breaking the group up into a mesiotemporal (MTS) group and a non-MTS group showed clear differences. The group with pure MTS showed an overall lower verbal memory performance than the group without pure MTS, in the LTL group more pronounced than in the RTL group. After surgery, both pathology groups showed an ongoing decline for up to 2 years, but the degree of decline was greater for the LTL patients with MTS compared with the non-MTS group. Becoming and remaining seizure-free after surgery does not result in a better performance in the long term. Predictors of postoperative verbal memory performance at 6 years after surgery were side of surgery, preoperative memory score, and age.

CONCLUSIONS

The results provide evidence for a dynamic decline of verbal memory functions up to 2 years after left temporal lobectomy, which then levels off.

The IL-1beta system in epilepsy-associated malformations of cortical development

Focal cortical dysplasia (FCD) and glioneuronal tumors (GNT) are recognized causes of chronic intractable epilepsy. The cellular mechanism(s) underlying their epileptogenicity remain largely unknown. Compelling evidence in experimental models of seizures indicates an important role of interleukin (IL)-1beta in the mechanisms of hyperexcitability leading to the occurrence of seizures. We immunocytochemically investigated the brain expression and cellular distribution pattern of IL-1beta, IL-1 receptor (IL-1R) types I and II and IL-1R antagonist (IL-1Ra) in FCD and GNT specimens, and we correlate these parameters with the clinical history of epilepsy in patients with medically intractable seizures. In normal control cortex, and in perilesional regions with histologically normal cortex, IL-1beta, IL-1Rs and IL-1Ra expression was undetectable. In all FCD and GNT specimens, IL-1beta and its signalling receptor IL-1RI were highly expressed by more than 30% of neurons and glia whereas the decoy receptor IL-RII and IL-Ra were expressed to a lesser extent by approximately 10% and 20% of cells, respectively. These findings show a high expression of IL-1beta and its functional receptor (IL-1RI) in FCD and GNT specimens together with a relative paucity of mechanisms (IL-1RII and IL-1Ra) apt to inactivate IL-1beta actions. Moreover, the number of IL-1beta- and IL-1RI-positive neurons was positively correlated with the frequency of seizures, whereas the number of IL-1Ra-positive neurons and astroglial cells was negatively correlated with the duration of epilepsy prior to surgery. The expression of IL-1beta family members in these developmental lesions may contribute to their intrinsic and high epileptogenicity, thus possibly representing a novel target for antiepileptic strategies.

Frameless stereotactic subcaudate tractotomy for intractable obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a chronic, disabling disorder. Psychosurgery may be indicated for a subset of patients for whom no conventional treatment is satisfactory. This paper focuses on the stereotactic subcaudate tractotomy (SST). Thus far, these procedures have been carried out using frame-based stereotactic techniques. However, modern - highly accurate - frameless stereotactic procedures have successfully been introduced in neurosurgical practice. We developed a novel frameless stereotactic subcaudate tractotomy procedure with promising initial results in a patient suffering from intractable OCD. This is the first report on frameless SST. Future studies should examine whether other ablative stereotactic psychosurgery procedures can be done using frameless stereotactic methods.

Evidence of activated microglia in focal cortical dysplasia

Focal cortical dysplasia (FCD), which is caused by malformations of cortical development, is known to be a major cause of intractable epilepsy. Cortical laminar disorganization and the presence of abnormal neuronal and astroglial cell types are histological characteristics of FCD. Though, little information is known about the microglia/macrophage cell system in FCD and its possible contribution to the high epileptogenesis of this disorder. In the present study, the distribution of cells of the microglia/macrophage lineage was studied in 20 specimens of FCD (type II) by immunocytochemistry for CD68 and human HLA-DR. A significant number of microglial cells and macrophages were observed within the dysplastic cortex. The mean number of CD68- and HLA-DR-positive cells was significantly higher in FCD specimens than in normal-appearing control cortex obtained at autopsy. HLA-DR-positive cells, which represent activated microglia, were localized around blood vessels and also clustered around dysplastic neuronal cells. The density of these activated HLA-DR-positive microglial cells correlated with the duration of epilepsy, as well as with the frequency of seizures prior to surgical resection. CD68-positive macrophages were mainly located around vessels and the number of these cells did not correlate with seizure frequency, neither with the duration of symptoms prior to surgical resection. In conclusion, our findings demonstrate a specific and persistent increase in the numerical density of HLA-DR-positive activated microglia within the dysplastic region, supporting the contribution of the inflammatory response and proinflammatory molecules to the epileptogenicity of FCD.

Distribution, characterization and clinical significance of microglia in glioneuronal tumours from patients with chronic intractable epilepsy

Cells of the microglia/macrophage lineage represent an important component of different brain tumours. However, there is little information about the microglia/macrophage cell system in glioneuronal tumours and its possible contribution to the high epileptogenecity of these lesions. In the present study, the distribution of cells of the microglia/macrophage lineage was studied by immunocytochemistry for CD68 and human leucocyte antigen (HLA)-DR in a group of glioneuronal tumours, including gangliogliomas (GG, n = 30), and dysembryoplastic neuroepithelial tumours (DNT, n = 17), from patients with chronic intractable epilepsy. A significant number of microglia/macrophage cells were observed in the large majority of glioneuronal tumours, both within the tumour and in the peritumoral region. Activated microglial cells positive for HLA-DR were localized around blood vessels and clustered around tumour neuronal cells. The density of activated microglial cells correlated with the duration of epilepsy, as well as with the frequency of seizures prior to surgical resection. These observations indicate that the presence of cells of the microglial/macrophage cell system is a feature of glioneuronal tumours and is functionally related to epilepsy, either directly in epileptogenesis or through activation following seizure activity.

Reduced glutamine synthetase in hippocampal areas with neuron loss in temporal lobe epilepsy

BACKGROUND

Increased levels of glutamate have been reported in the epileptogenic hippocampus of patients with temporal lobe epilepsy (TLE). This sustained increase, which may contribute to the initiation and propagation of seizure activity, indicates impaired clearance of glutamate released by neurons. Glutamate is predominantly cleared by glial cells through the excitatory amino acid transporter 2 (EAAT2) and its subsequent conversion to glutamine by the glial enzyme glutamine synthetase (GS).

METHODS

The authors examined the hippocampal distribution of GS, EAAT2, and glial fibrillary acidic protein (GFAP) by immunohistochemistry in TLE patients with (HS group) and without hippocampal sclerosis (non-HS group), and in autopsy controls. In hippocampal homogenates the authors measured relative protein amounts by immunoblotting and GS enzyme activity.

RESULTS

In the autopsy control and non-HS group GS immunoreactivity (IR) was predominantly found in glia in the neuropil of the subiculum, of the pyramidal cell layer of all CA fields, and in the supragranular layer of the dentate gyrus. In the HS group, GS and EAAT2 IR were markedly reduced in subfields showing neuron loss (CA1 and CA4), whereas GFAP IR was increased. The reduction in GS IR in the HS group was confirmed by immunoblotting and paralleled by decreased GS enzyme activity.

CONCLUSIONS

Glial glutamine synthetase is downregulated in the hippocampal sclerosis (HS) hippocampus of temporal lobe epilepsy (TLE) patients in areas with severe neuron loss. This downregulation appears to be pathology-related, rather than seizure-related, and may be part of the mechanism underlying impaired glutamate clearance found in the hippocampus of TLE patients with HS.

Alternative splicing of glutamate transporter EAAT2 RNA in neocortex and hippocampus of temporal lobe epilepsy patients

RATIONALE

Altered expression of glutamate transporter EAAT2 protein has been reported in the hippocampus of patients with temporal lobe epilepsy (TLE). Two alternative EAAT2 mRNA splice forms, one resulting from a partial retention of intron 7 (I7R), the other from a deletion of exon 9 (E9S), were previously implicated in the loss of EAAT2 protein in patients with amyotrophic lateral sclerosis.

METHODS

By RT-PCR we studied the occurrence of I7R and E9S in neocortical and hippocampal specimens from TLE patients and non-neurological controls.

RESULTS

Both splice forms were found in all neocortical specimens from TLE patients (100% I7R, 100% E9S). This was significantly more than in controls (67% I7R, 60% E9S; P < 0.05). We also detected I7R and E9S in all seven motor cortex post-mortem samples from patients with amyotrophic lateral sclerosis. Within the TLE patient group, both splice variants appeared significantly more in non-sclerotic (100%), than in sclerotic hippocampi (69%, P < 0.05).

CONCLUSION

These data indicate that the epileptic brain, especially that of TLE patients without hippocampal sclerosis, is highly prone to alternative EAAT2 mRNA splicing. Our data confirm that the presence of alternative EAAT2 splice forms is not disease specific.

Long-term effects of temporal lobectomy on intelligence

OBJECTIVE

To characterize the long-term effects of anterior temporal resection on intelligence.

METHODS

Twenty-eight left temporal lobectomy (LTL) and 43 right temporal lobectomy (RTL) patients were followed at standard time points for at least 6 years after surgery.

RESULTS

The average gain 6 years after operation was 3.6 Verbal IQ (VIQ) points and 10.3 Performance IQ (PIQ) points in LTL patients and 2.9 VIQ points and 7.7 PIQ points in RTL patients. A seizure-free outcome did not influence the increase in IQ, nor was the extent of resection related to IQ scores at the 6-year follow-up. Patients with exclusively mesial temporal sclerosis did not perform as well as patients with other pathologies, both before and after surgery. Major predictors of improved performance at 6 years were initial higher level of performance and lower age at surgery. Much of the observed improvement may be related to retest effects.

CONCLUSIONS

The effects of epilepsy surgery on intelligence in the long term are limited. The largest gain in VIQ is seen from 2 to 6 years after surgery.

Synaptosomal glutamate and GABA transport in patients with temporal lobe epilepsy

High-affinity glutamate and GABA transporters found in the plasma membrane of neurons and glial cells terminate neurotransmission by rapidly removing extracellular transmitter. Impairment of transporter function has been implicated in the pathophysiologic mechanisms underlying epileptogenesis. We characterized glutamate and gamma-aminobutyric acid (GABA) transport in synaptosomes, isolated from neocortical and hippocampal biopsies of patients with temporal lobe epilepsy (TLE). We analyzed K(+)-evoked release in the presence and absence of Ca(2+) to determine vesicular and transporter-mediated release, respectively. We also analyzed (3)H-glutamate and (3)H-GABA uptake, the effect of glutamate uptake inhibitors L-trans-pyrrolidine-2,4-dicarboxylic acid (tPDC) and DL-threo-beta-benzyloxyaspartate (TBOA), and GABA uptake inhibitor N-(4,4-diphenyl-3-butenyl)-3-piperidinecarboxylic acid (SK&F 89976-A). Neocortical synaptosomes from TLE patients did not show vesicular glutamate release, strongly reduced transporter-mediated release, and an increased basal release compared to that in rat synaptosomes. Furthermore, basal release was less sensitive to tPDC, and (3)H-glutamate uptake was reduced compared to that in rat synaptosomes. Vesicular GABA release from neocortical synaptosomes of TLE patients was reduced compared to that in rat synaptosomes, whereas transporter-mediated release was hardly affected. Furthermore, basal GABA release was more than doubled, but neither basal nor stimulated release were increased by SK&F 89976-A, which did significantly increase both types of GABA release in rat synaptosomes. Finally, (3)H-GABA uptake by synaptosomes from TLE patients was reduced significantly in hippocampus (0.19 +/- 0.04%), compared to that in neocortex (0.32 +/- 0.04%). Control experiments with human peritumoral cortical tissue suggest that impaired uptake of glutamate, but not of GABA, was caused in part by the hypoxic state of the biopsy. Our findings provide evidence for impaired function of glutamate and GABA transporters in human TLE.

Measurement of the conductivity of skull, temporarily removed during epilepsy surgery

The conductivity of the human skull plays an important role in source localization of brain activity, because it is low as compared to other tissues in the head. The value usually taken for the conductivity of skull is questionable. In a carefully chosen procedure, in which sterility, a stable temperature, and relative humidity were guaranteed, we measured the (lumped, homogeneous) conductivity of the skull in five patients undergoing epilepsy surgery, using an extended four-point method. Twenty-eight current configurations were used, in each of which the potential due to an applied current was measured. A finite difference model, incorporating the geometry of the skull and the electrode locations, derived from CT data, was used to mimic the measurements. The conductivity values found were ranging from 32 mS/m to 80 mS/m, which is much higher than the values reported in other studies. Causes for these higher conductivity values are discussed.

Expression and cellular distribution of multidrug transporter proteins in two major causes of medically intractable epilepsy: focal cortical dysplasia and glioneuronal tumors

The cell-specific distribution of multidrug resistance extrusion pumps was studied in developmental glioneuronal lesions, including focal cortical dysplasia (15 cases) and ganglioglioma (15 cases) from patients with medically intractable epilepsy. Lesional, perilesional, as well as normal brain regions were examined for the expression of the multidrug resistance gene 1 encoded P-glycoprotein (P-gp) and the multidrug resistance-associated protein 1 (MRP1) by immunocytochemistry. In normal brain MRP1 expression was below detection, whereas P-gp staining was present only in blood vessels. MRP1 and P-gp immunoreactivity was observed in dysplastic neurons of 11/15 cases of focal cortical dysplasia, as well as in the neuronal component of 14/15 ganglioglioma. Glial cells with astrocytic morphology within the lesion showed multidrug-resistant protein immunoreactivity (P-gp>MRP1). Moderate to strong MRP1 and P-gp immunoreactivity was observed in a population of large ballooned neuroglial cells. P-gp appeared to be most frequently expressed in glial fibrillary acidic protein-positive balloon cells (glial type), whereas MRP1 was more frequently expressed in microtubule-associated protein 2-positive balloon cells (neuronal type). In both types of lesions strong P-gp immunoreactivity was found in lesional vessels. Perilesional regions did not show increased staining in vessels or in neuronal cells compared with normal cortex. The predominant intralesional cell-specific distribution of multidrug transporter proteins supports the hypothesis of a constitutive overexpression as common mechanism underlying the intrinsic pharmaco-resistance to antiepileptic drugs of both malformative and neoplastic glioneuronal developmental lesions.

FMRI-determined language lateralization in patients with unilateral or mixed language dominance according to the Wada test

Due to the reported variability of the language laterality index (LI) across fMRI studies, reliable distinction between patients with unilateral and mixed language dominance is currently not possible, preventing clinical implementation of fMRI as a replacement for the invasive Wada test. Variability of the LI may be related to differences in experimental and control tasks, and statistical methodology. The goal of this study was to improve detection power of fMRI for hemispheric language dominance by using a combined analysis of four different language tasks (CTA), that has previously shown more reliable and robust Lls in groups of normal volunteers than individual task analyses (see Ramsey et al). The CTA targets brain areas that are common to different language tasks, thereby focusing on areas that are critical for language processing. Further advantage of the CTA is that it is relatively independent of specific task and control conditions. 18 patients with typical (i.e., left-sided, n = 11) and atypical (i.e., right-sided or mixed, respectively, n = 3 and n = 4) language dominance according to the Wada test underwent fMRI (groups respectively denoted as WadaL, WadaR, and WadaM patients). Statistical methodology (including thresholding of activity maps) was fixed to assure a user-independent approach. CTA yielded better results than any of the individual task analyses: it was more robust (on average 2.5 times more brain activity was detected due to its higher statistical power) and more reliable (concordance for WadaL, WadaM and WadaR patients was respectively 10/11 (91%), 3/4 (75%), and 2/3 patients (67%)). Overall, a significant correlation was observed between frontal and temporoparietal LIs. Remarkably, brain activity for WadaM patients was significantly lower than for WadaL or WadaR patients, and a dissociation in lateralization was observed between frontal (right-sided) and temporoparietal (left-sided) activity in three of four patients. Of the individual task analyses, the verb generation task yielded best results for patients with unilateral language dominance (same concordance as CTA). However, in contrast to CTA results, the verb generation task was unable to identify WadaM patients (concordance in one of four patients). In conclusion, the CTA is a promising approach for clinical implementation of fMRI for the prediction of hemispheric language dominance.

Lateralization of auditory rhythm length in temporal lobe lesions

In the visual modality, short rhythmic stimuli have been proven to be better processed (sequentially) by the left hemisphere, while longer rhythms appear to be better (holistically) processed by the right hemisphere. This study was set up to see if the same holds in the auditory modality. The rhythm task as originally designed by Seashore was computerized and is part of the Fepsy Neuropsychological battery. This task was performed by 85 patients with intractable temporal lobe epilepsy (left TLE = 32; right TLE = 53) enrolled in the Dutch Collaborative Epilepsy Surgery Program. They performed the task before and 6 months after surgery. The task consists of 30 pairs of rhythmic patterns in 3 series of 10 items. The series contains patterns of 5, 6, or 7 notes. The purpose is to indicate whether the two patterns are the same or different. Reaction times are also measured. If the hypothesis is true, the short-item sequence will be better processed by patients with right temporal lobe epilepsy (nonimpaired left temporal lobe), the longer sequence will be better processed by the left temporal epilepsy group (nonimpaired right temporal lobe). No overall laterality effect on rhythm perception could be found and no difference was found between both test moments. IQ did not correlate with rhythm performance. However, there was an interaction effect of laterality and rhythm length on performance and reaction time. This effect can be explained by the increase after the operation of the score of the left focus group and a decrease in the right focus group on the longer rhythms. This effect was somewhat less strong in the reaction times: a clear tendency for faster reaction times after surgery in the left and longer reaction times in the right focus group. The effect could not be explained for by the difference in extent of resection in either temporal lobe. This study showed that memory for and discrimination of auditory rhythm is dependent on which hemisphere is used in processing. The effect could be demonstrated for the right hemisphere, which uses a holistic processing of stimuli, which outperforms the left in rhythms consisting of a long sequence. In left temporal resections an improvement occurs on the longer rhythms and in right temporal resections the performance on the longest rhythms decreases.

Development of a functional magnetic resonance imaging protocol for intraoperative localization of critical temporoparietal language areas

The aim of this study was to evaluate the use of functional magnetic resonance imaging as an alternative to intraoperative electrocortical stimulation mapping for the localization of critical language areas in the temporoparietal region. We investigated several requirements that functional magnetic resonance imaging must fulfill for clinical implementation: high predictive power for the presence as well as the absence of critical language function in regions of the brain, user-independent statistical methodology, and high spatial accuracy. Thirteen patients with temporal lobe epilepsy performed four different functional magnetic resonance imaging language tasks (ie, verb generation, picture naming, verbal fluency, and sentence comprehension) before epilepsy surgery that included intraoperative electrocortical stimulation mapping. To assess the optimal statistical threshold for functional magnetic resonance imaging, images were analyzed with three different statistical thresholds. Functional magnetic resonance imaging information was read into a surgical guidance system for identification of cortical areas of interest. Intraoperative electrocortical stimulation mapping was recorded by video camera, and stimulation sites were digitized. Next, a computer algorithm indicated whether significant functional magnetic resonance imaging activation was present or absent within the immediate vicinity (<6.4mm) of intraoperative electrocortical stimulation mapping sites. In 2 patients, intraoperative electrocortical stimulation mapping failed during surgery. Intraoperative electrocortical stimulation mapping detected critical language areas in 8 of the remaining 11 patients. Correspondence between functional magnetic resonance imaging and intraoperative electrocortical stimulation mapping depended heavily on statistical threshold and varied between patients and tasks. In 7 of 8 patients, sensitivity of functional magnetic resonance imaging was 100% with a combination of 3 functional magnetic resonance imaging tasks (ie, functional magnetic resonance imaging correctly detected all critical language areas with high spatial accuracy). In 1 patient, sensitivity was 38%; in this patient, functional magnetic resonance imaging was included in a larger area found with intraoperative electrocortical stimulation mapping. Overall, specificity was 61%. Functional magnetic resonance imaging reliably predicted the absence of critical language areas within the region exposed during surgery, indicating that such areas can be safely resected without the need for intraoperative electrocortical stimulation mapping. The presence of functional magnetic resonance imaging activity at noncritical language sites limited the predictive value of functional magnetic resonance imaging for the presence of critical language areas to 51%. Although this precludes current replacement of intraoperative electrocortical stimulation mapping, functional magnetic resonance imaging can at present be used to speed up intraoperative electrocortical stimulation mapping procedures and to guide the extent of the craniotomy.

Reproducibility of fMRI-determined language lateralization in individual subjects

This study investigated within-subject test-retest reproducibility (i.e., reliability) of language lateralization obtained with fMRI. Nine healthy subjects performed the same set of three different language tasks during two fMRI sessions on separate days (verb generation, antonym generation, and picture naming). A fourth task analysis was added in which the three tasks were analyzed conjointly (combined task analysis, CTA). The CTA targets brain areas that are commonly used in different language tasks, aiming more selectively at language-critical structures. The number of active voxels (i.e., robustness) and calculated lateralization index (LI) were compared across sessions, tasks, subjects, and two a priori defined volumes of interest (classical language regions versus whole hemisphere) for a wide range of statistical thresholds. Robustness and reliability strongly varied between task analyses. The CTA was a robust detector of language-related brain activity, in contrast to the single task approaches. The CTA and verb generation task allowed for reliable calculation of the LI. Higher thresholds yielded a clear increase in left lateralization, which was largest when calculated from active voxels in classical language regions.

Distribution of glutamate transporters in the hippocampus of patients with pharmaco-resistant temporal lobe epilepsy

In patients suffering from temporal lobe epilepsy (TLE), increased extracellular glutamate levels in the epileptogenic hippocampus both during and after clinical seizures have been reported. These increased glutamate levels could be the result of malfunctioning and/or downregulation of glutamate transporters (also known as EAATs; excitatory amino acid transporters). In this study, the distribution of protein and mRNA of EAAT subtypes was examined in the hippocampus of TLE patients with hippocampal sclerosis (HS group) and without hippocampal sclerosis (non-HS group), and in autopsy controls without neurological disorders. EAAT protein localization was studied by immunohistochemistry on paraffin sections using specific poly- and monoclonal antibodies against the glial glutamate transporters EAAT1 and EAAT2 and the neuronal glutamate transporter EAAT3. Antibody specificity was shown by immunoblotting. In the HS group, a small decrease in EAAT1-immunoreactivity (IR) was observed in CA4 and in the polymorphic and supragranular layer of the dentate gyrus, compared with the control group. The strongest changes were found for EAAT2 levels. In the non-HS group, increased EAAT2-IR was detected in the CA1 and CA2 field, compared with non-epileptic controls. EAAT2-IR was decreased in the HS compared with the non-HS group. Fewer EAAT3-positive cells were found in the HS group than in the non-HS and control group. In both TLE groups, increased EAAT3 levels were observed in individual neurones. In the HS group, the percentage of EAAT3-IR neurones was increased in CA2 and in the granule cell layer of the dentate gyrus. Radioactive in situ hybridization for EAAT1-3 confirmed our immunohistochemical results. Non-radioactive in situ hybridization showed that not only astrocytes, but also neurones express EAAT2 mRNA. Taken together, differences in both mRNA and protein levels of glutamate transporter subtypes were found in specific regions in the TLE hippocampus, with most severe changes found for EAAT2 and EAAT3 levels. The results indicate an upregulation of EAAT2 protein expression in CA1 and CA2 in neurones in the non-HS group. This is in line with decreased EAAT2 protein levels in the HS group, since these hippocampi are characterized by severe neuronal cell loss. The functional consequences (glutamate transport capacity) of the reported changes in EAAT2 and EAAT3 remain to be determined.

[Dutch Collaborative Epilepsy Surgery Program: reduction of seizures, operative complications and tapering of medication in 338 patients, 1973-1998]

OBJECTIVE

To determine the results of surgical treatment in patients with drug-resistant epilepsy, referred to the Dutch Epilepsy Surgery Program, who were treated in the University Medical Centre Utrecht, the Netherlands, in the period January 1973-December 1998.

DESIGN

Retrospective descriptive.

METHOD

A total of 338 patients were operated on; 269 underwent temporal lobe resection, 41 extratemporal resection, 12 a functional hemispherectomy and 10 callosotomy. Six patients were treated with vagus nerve stimulation. For seven of the patients no follow-up data was available.

RESULTS

After a minimum follow-up of 1 year class I or class II results (in accordance with the University of California in Los Angeles classification (UCLA) where class I = seizure-free and class II < or = 3 seizures per year) were obtained in 91% of patients who underwent temporal lobe resections, 67% of patients who underwent extratemporal resections, 81% of patients who underwent functional hemispherectomy and 10% of patients who underwent anterior callosotomy. In five of these patients an improvement in their behaviour occurred. Of the 6 patients who underwent vagus nerve stimulation only I experienced a beneficial seizure reduction (UCLA class III). Transient physical complications occurred in 4% of the patients treated and permanent damage in 1%. Postoperative psychiatric complications occurred almost exclusively following temporal resections; in 11% of which 7% de novo. After 4 postoperative years this had decreased to 5%. In a group of 143 patients who were seizure-free for 2 or more years, post-surgery medication was tapered in 75 cases, stopped in 33 cases and remained unchanged in 35 cases. The relapse rate following a tapering or stopping of the medication was 30% and with unchanged medication 17%. Although the majority of patients were once again seizure-free upon restarting the medication, a significant number continued to experience seizures.

CONCLUSION

For a number of carefully selected epilepsy patients with intractable seizures, surgery is a successful treatment with few serious complications.

A grading system for hippocampal sclerosis based on the degree of hippocampal mossy fiber sprouting

In patients suffering from temporal lobe epilepsy (TLE) a highly variable degree of hippocampal sclerosis (HS) can be observed. For standard neuropathological evaluation after hippocampal resection, neuronal cell loss in the hippocampal subareas is assessed (Wyler score 0-4) [Wyler et al. (1992) J Epilepsy 5: 220-225]. Other marked morphological changes in the sclerotic hippocampus are gliosis and loss of mossy fibers in the hilus and mossy fiber sprouting in the supragranular layer. In this study we quantified changes in mossy fiber density using Timm's stain in resected hippocampal tissue from patients with various degrees of sclerosis. We found that tissue specimens from patients without sclerosis (W0) show almost no mossy fiber sprouting. Patients with moderate sclerosis show sprouting without fiber loss in the hilus, whereas specimens from patients with severe sclerosis show sprouting as well as fiber loss in the hilus. Thus, analysis of mossy fiber abundance in hilus and supragranular layer by the rapid and simple Timm's stain is a sensitive measure for hippocampal sclerosis. It provides a reliable rapid tool for neuropathological evaluation, even if the tissue only contains dentate gyrus due to the sectioning procedure.

Glioneuronal tumors and medically intractable epilepsy: a clinical study with long-term follow-up of seizure outcome after surgery

The present study intends to identify factors that predict postoperative clinical outcome in patients with gangliogliomas (GG) and dysembryoplastic neuroepithelial tumors (DNT). We evaluated the medical records of 45 patients with GG and 13 patients with DNT, treated surgically between 1985 and 1995. We assessed several clinical and histopathological features and analyzed the data statistically. At 5 years postoperatively, 63% of patients with GG and 58% of patients with DNT were seizure-free (Engel's class I). Younger age at surgery (P<0.01 for GG and P<0.05 for DNT), total resection (P<0.01 for GG), shorter duration of epilepsy (P<0.01), absence of generalized seizures (P<0.01 for GG; P<0.05 for DNT) and absence of epileptiform discharge in the post-operative EEG (P<0.01 for GG; P=0.01 for DNT) predicted a better postoperative seizure outcome. Tumor recurrence with malignant progression occurred in eight histologically benign GG and two anaplastic GG and was associated which older age at surgery (P=0.01) and subtotal resection of the tumor (P<0.01). Our results indicate that a prompt diagnosis, relatively soon after seizure onset, followed by complete resection of glioneuronal tumors provides the best chance for curing epilepsy and preventing their malignant transformation.

Localization of implanted EEG electrodes in a virtual-reality environment

In the planning of epilepsy surgery procedures, intracranial electrodes are implanted in a significant fraction of the patients. Accurate localization of the individual electrode contacts with respect to the brain cortex is imperative. Because the manual tracking of an EEG electrode in a CT scan in a slice-by-slice fashion is cumbersome and subjective, the goal of this study was to develop an easier and more accurate way to localize implanted EEG electrodes. In this paper, we present our solution in the form of a virtual-reality environment with interactive tools to assist the clinician with EEG localization. With the help of a high-quality and fast volume renderer, a view is created of the inside of the patient's skull to obtain an overview of the electrodes in relation to the cortical structures. Depth, grid, and reed electrodes are characterized semi-interactively using different methods. For depth electrodes, the contacts (which are not visible in the CT scan) are derived by measuring off the theoretical distance between the contact and the end of the electrode from the central axis produced by a three-dimensional (3D) line tracker. For grid electrodes, the contacts are visible in a CT, so the 3D view is merely used to find the contacts and to resolve the overlap of grids with other grids, tail wires, or bone ridges. For reed electrodes, the contacts, which are again not visible in this case, are calculated from a line model fitted to the positions of lead markers. After letting the user place artificial spheres on the lead markers and wire, a B-spline is fitted to the spheres' centers to estimate the positions of the contacts. The approach was evaluated by applying it to CT scans of seven patients. It appeared that the method is generally applicable (even crossing electrodes or electrodes with gaps were correctly characterized), and that the display via 3D views and slices is so good that manual placement of spheres performed as well as semi-automatic placement. From computer experiments, it appeared that the final localization error in the position of EEG contacts could be estimated to lie in the order of the dimensions of one voxel.

Proton magnetic resonance spectroscopy of temporal lobe white matter in patients with histologically proven hippocampal sclerosis

The purpose of this study was to assess temporal lobe white matter changes accompanying hippocampal sclerosis on magnetic resonance (MR) imaging using single-voxel 1H MR spectroscopy and to strengthen the hypothesis that these white matter changes are caused by myelin alterations. In 11 patients with histologically proven hippocampal sclerosis, preoperative coronal fluid-attenuated inversion recovery images were visually assessed by two experienced neuroradiologists for hippocampal signal increase and size decrease, atrophy of collateral white matter, and temporal lobe gray/white matter demarcation loss. Single-voxel 1H MR spectroscopy of the white matter of each anterior temporal lobe was also performed, excluding the amygdala and hippocampus. The N-acetyl-aspartate (NAA)/choline and NAA/creatine ratios were calculated. In 12 healthy volunteers both temporal lobes were spectroscopically examined. In all patients the excised hippocampi were histologically assessed for the presence of sclerosis, and the excised neocortical temporal lobes were examined for gray and white matter abnormalities. MRI abnormalities were found on the right in six patients, on the left in four, and one scan was normal. Hippocampal signal increase was seen in nine patients, hippocampal size decrease in ten, atrophy of collateral white matter in nine, and gray/white matter demarcation loss in six. A significant decrease in the NAA/choline ratio was found in temporal lobe white matter ipsilateral to the pathologic hippocampus (symptomatic side), compared with the contralateral, asymptomatic side (P < 0.01), and also compared with controls (P < 0.001). The ipsilateral NAA/creatine ratio was also significantly decreased (P < 0.05) compared with the contralateral side and the control subjects (P < 0.001). Histological examination showed hippocampal sclerosis to a different degree in all patients. Neither gliosis nor cortical dysplasia was found in the ipsilateral, symptomatic temporal lobe. Significant decrease in the mean of NAA/choline ratios is found in temporal lobe white matter of patients with histologically confirmed hippocampal sclerosis. As this indicates neuronal loss or dysfunction, the number of axons may be reduced, with associated decrease in myelin density.

Immunohistochemical characterization of mossy fibre sprouting in the hippocampus of patients with pharmaco-resistant temporal lobe epilepsy

Hippocampal sclerosis (HS) is a common derangement in many patients with temporal lobe epilepsy. As a result of neuronal cell loss in the hilar region of the hippocampus, it is proposed that mossy fibres sprout and re-innervate new regions of the dentate gyrus. This sprouting may cause recurrent excitation that may lead to the generation of seizures. Here, we determined neuronal density, and synaptophysin and glial fibrillary acidic protein (GFAP) immunoreactivity in hippocampal specimens from patients with pharmaco-resistant temporal lobe epilepsy. Patients were classified into two groups: those with severe and those with no HS. Non-epileptic autopsy tissue served as controls. Mossy fibre sprouting was investigated in these two groups of epilepsy patients using Timm's staining and an immunohistochemical staining of the presynaptic growth-associated protein B-50 (also known as GAP-43, neuromodulin, F1). B-50 immunoreactivity in the different sub-areas of the hippocampus was quantified by image analysis. Our results show the following: (i) in both groups of temporal lobe epilepsy patients, there was a significant loss in cell number in all major hippocampal sub-areas compared with autopsy control tissue; (ii) in HS patients, when compared with non-HS patients, there was a further decline in the number of principal cells in all hippocampal sub-areas analysed, which was associated with an increase in GFAP immunoreactivity; (iii) the decline in cell density was accompanied by a reduced number of synaptic terminals; (iv) in the HS group, there were sprouted mossy fibres in the supragranular layer (SGL) of the dentate gyrus; (v) there was an increase in synaptophysin immunostaining in the SGL indicating that functionally active nerve terminals were formed; and (vi) B-50 immunoreactivity was also increased in the SGL in the HS group compared with the non-HS and control groups. These data showed that all temporal lobe epilepsy hippocampi investigated had severe neuronal cell loss which was most dramatic in the HS group, where it was accompanied by a severe loss of synapses. In the HS group, mossy fibre sprouting into the SGL was found. The increase in B-50 immunoreactivity in the SGL indicated that there was still active sprouting. This sprouting was accompanied by an increased density of synapses, indicating that mossy fibre terminals are not only anatomically present, but probably also functional. Thus, functional glutamatergic mossy fibre terminals are in the right position to synapse on to the dendrites of granule cells and thus may contribute to the onset of seizures.

Non-linear analysis of intracranial human EEG in temporal lobe epilepsy

OBJECTIVE

Intracranial EEG recordings from patients suffering from medically intractable temporal lobe epilepsy were analyzed with the aim of characterizing the dynamics of EEG epochs recorded before and during a seizure and comparing the classification of the EEG epochs on the basis of visual inspection to the results of the numerical analysis.

METHODS

The stationarity of the selected EEGs was assessed qualitatively. The coarse-grained correlation dimension and coarse-grained correlation entropy were used for the non-linear characterization of the EEG epochs.

RESULTS

High-pass filtering was necessary in order to make the majority of the epochs appear stationarity beyond a time scale of about 2 s. It was found that the dimension of the ictal EEGs decreased with respect to the epochs containing ongoing (interictal) activity. The entropy of the ictal recordings however increased. A scaling of the entropy was applied and it was found that the scaled entropy of the ictal EEG decreased, consistent with the increased regularity of the ictal EEG. The coarse-grained quantities discriminated well between EEG epochs recorded prior to and during seizures at locations displaying ictal activity and classification improved by including the linear autocorrelation time in the analysis.

CONCLUSIONS

It is concluded that ictal and non-ictal EEG can be well distinguished on the basis of non-linear analysis. The results are in good agreement with the visual analysis.

Language area localization with three-dimensional functional magnetic resonance imaging matches intrasulcal electrostimulation in Broca's area

In this study, intraoperative electrocortical stimulation mapping (ioESM), the current gold standard for the localization of critical language areas, is compared with functional magnetic resonance imaging (fMRI) in a 14-year-old girl with medically intractable epilepsy caused by a tumor in the region of Broca's area. Prior to the operation, four different fMRI tasks that target inferior frontal language areas were applied. Prior to the resection, ioESM as well as fMRI detected no language areas at the exposed cortical area. After removal of the tumor, a unique opportunity presented itself, where ioESM could be performed in the depth of a now exposed and intact gyrus. One specific locus that was indicated to be a critical language area by multiple-task fMRI was targeted. IoESM selectively confirmed the location of this language area to within an estimated 3 mm. We propose that the combined use of different fMRI tasks increases the sensitivity and specificity for the detection of essential language areas.

Characterization of neocortical and hippocampal synaptosomes from temporal lobe epilepsy patients

To investigate epilepsy-associated changes in the presynaptic terminal, we isolated and characterized synaptosomes from biopsies resected during surgical treatment of drug-resistant temporal lobe epilepsy (TLE) patients. Our main findings are: (1) The yield of synaptosomal protein from biopsies of epilepsy patients was about 25% of that from rat brain. Synaptosomal preparations were essentially free of glial contaminations. (2) Synaptosomes from TLE patients and naive rat brain, quickly responded to K(+)-depolarization with a 70% increase in intrasynaptosomal Ca(2+) ([Ca(2+)](i)), and a 40% increase in B-50/GAP-43 phosphorylation. (3) Neocortical and hippocampal synaptosomes from TLE patients contained 20-50% of the glutamate and gamma-aminobutyric acid (GABA) contents of rat cortical synaptosomes. (4) Although the absolute amount of glutamate and GABA released under basal conditions from neocortical synaptosomes of TLE patients was lower than from rat synaptosomes, basal release expressed as percentage of total content was higher (16.4% and 17.3%, respectively) than in rat (11.5% and 9. 9%, respectively). (5) Depolarization-induced glutamate and GABA release from neocortical synaptosomes from TLE patients was smaller than from rat synaptosomes (3.9% and 13.0% vs. 21.9% and 25.0%, respectively). (6) Analysis of breakdown of glial fibrillary acid protein (GFAP) indicates that resection time (anoxic period during the operation) is a critical parameter for the quality of the synaptosomes. We conclude that highly pure and viable synaptosomes can be isolated even from highly sclerotic human epileptic tissue. Our data show that in studies on human synaptosomes it is of critical importance to distinguish methodological (i.e., resection time) from pathology-related abnormalities.

Comparison of combined versus subdural or intracerebral electrodes alone in presurgical focus localization

PURPOSE

The yield of subdural versus intracerebral electrodes for ictal localization remains a point of controversy. We assessed the relative sensitivity of these two types of electrodes per case.

METHODS

Eighty-three intracranial recordings obtained from 82 patients were retrospectively reviewed to establish which type of electrode performed best in which patients and which seizure types.

RESULTS

Sixty (73%) of 82 patients had temporal lobe seizure onsets, eight frontal, nine widespread or multifocal/multilobar or both, whereas in five, seizure onset was not localized. Exclusive use of intracerebral electrodes would have been sufficient for accurate localization of the seizure-onset zone in all 35 patients with strictly mesial temporal seizure onsets. In only 20 (57%) of these 35 patients, the same decision would have been reached with exclusive use of subdural electrodes. In widespread neocortical and mesial temporal seizures (n = 25), yield of both electrode types was at about the same level, but neither was sufficient to identify the zone of ictal onset on its own. In frontal or multilobar seizures (n = 22), yield of subdural electrodes was slightly better then that of the intracerebral electrodes, but was not sufficient in all cases.

CONCLUSIONS

This study indicates that, depending on the characteristics of the seizure disorder, exclusive use of either intracerebral or subdural electrodes may easily result in erroneous diagnosis because of insufficient sampling of the brain. These findings are in contrast with other studies emphasizing the high yield of reliable EEG findings in evaluations with a single type of electrode and corroborate the results of one of our previous studies.

Effect of valproic acid on sodium currents in cortical neurons from patients with pharmaco-resistant temporal lobe epilepsy

In a selected group of temporal lobe epilepsy patients with seizures refractory to pharmacological treatment, pharmacological seizure control can be attained by surgical resection of the epileptic zone. We investigated to what extent pharmaco-resistance is reflected in a reduced response at the cellular level, in neurons acutely isolated from the temporal cortex resected in 20 patients. We studied the effect of valproic acid (VPA) on the transient sodium current, measured under whole-cell voltage-clamp conditions. We compared neurons from patients with temporal lobe sclerosis (S) with neurons from patients without hippocampal sclerosis (nS) and compared hippocampal CA1 neurons (CA) with neocortical neurons (NC). We could not detect differences in the voltage dependence and kinetics of sodium current activation and inactivation in any of the group comparisons. VPA shifted the voltage dependence of steady-state inactivation (expressed as V(h,i) in a Boltzmann fit) to more hyperpolarized levels. The shift induced by 2 mM VPA was -5.1 +/- 0.7 mV in CA-S (n = 13), -5.1 +/- 0.7 mV in CA-nS (n = 25), -4.3 +/- 0.5 mV in NC-S (n = 17) and -4.9 +/- 0.5 mV in NC-nS (n = 16) The relation between concentration and voltage shift had an EC50 of 1.4 +/- 0.2 mM VPA (n = 16) and a maximal shift of 9.6 +/- 0.9 mV. We conclude that pharmaco-resistance in these patients is not associated with a changed modulation of the sodium current by VPA. Results are discussed in the light of a reduced sodium current modulation by carbamazepine in CA1 neurons of patients with hippocampal sclerosis and of similar observations in the kindling model of epileptogenesis.

Intracranial EEG seizure-offset termination patterns: relation to outcome of epilepsy surgery in temporal lobe epilepsy

PURPOSE

Studies using stereo-EEG (SEEG) and electrocorticography (ECoG) should not only identify a patient's epileptogenic zone, but also should provide prognostic information for surgical outcome. In this respect, seizure-offset patterns have so far been the subject of only one study, in which they were shown to be associated with poor outcome when recorded over cortical areas outside the temporal lobe of seizure onset. To clarify whether seizure-offset patterns are reliable in predicting seizure outcome, we studied SEEG/ECoG in a similar group of patients with temporal lobe epilepsy (TLE).

METHODS

SEEG/ECoG records of 44 patients with refractory TLE were analyzed. The areas of seizure termination were classified as ipsilateral or contralateral (mesial and/or lateral) temporal, (temporal and) frontal, and diffuse/bilateral. Patients were classified with respect to seizure outcome as either seizure-free (UCLA class 1a) or not seizure free (UCLA class 2-4); both groups were correlated with specific seizure-offset categories using Fisher's exact probability test and analysis of variance (ANOVA).

RESULTS

Of the 44 patients, the majority (n = 36) had at least part of their seizure offsets in the ipsilateral temporal lobe, whereas 8 patients manifested no seizure offsets in this lobe. Only 9 patients (20%) showed exclusive offsets in the ipsilateral temporal lobe. No statistically significant difference was evident between patients with all seizure offsets in the ipsilateral temporal lobe and those with offsets elsewhere. Similarly, no statistically significant difference was evident between patients with a diffuse seizure offset and those with seizure offsets of a different category.

CONCLUSIONS

Seizure-offset patterns in SEEG/ECoG are unreliable in predicting seizure outcome after resective activity surgery for TLE.

Fast spin-echo MR of contact points on implanted intracerebral stainless steel multicontact electrodes

A three-dimensional fast spin-echo MR technique is proposed for locating contact points on implanted intracerebral multicontact electrode bundles, Coronal or sagittal reformatting shows the entire trajectory of the electrode bundles. The contract points are clearly visible owing to the absence of coating material associated with a slightly larger susceptibility artifact. Potentially, this technique may preclude postimplantation thin-section CT, with its associated high radiation dose.

Effects of dextromethorphan on rat brain during ischemia and reperfusion assessed by magnetic resonance spectroscopy

Using proton and phosphorus magnetic resonance spectroscopy, we evaluated the metabolic effects of preischemic administration of the N-methyl-D-aspartate antagonist dextromethorphan (50 mg/kg i.p.) during global forebrain ischemia and subsequent reperfusion in rats. Dextromethorphan-treated animals (n = 10) showed less lactate formation during ischemia than untreated animals (n = 11, p less than 0.001). During reperfusion, the lactate level in the treated group was reduced (p less than 0.05). Tissue pH declined less in the treated group during ischemia (p less than 0.01). There was no difference in the phosphocreatine/inorganic phosphate peak height ratio between groups. During ischemia, the N-acetylaspartate resonance peaks decreased in both groups. Histologic damage assessed in the hippocampal CA1 region 7 days after the ischemic insult was more severe in the untreated group (p less than 0.05). There was a significant correlation between end-ischemic tissue pH and hippocampal damage (r = -0.73, p less than 0.05). In the dextromethorphan-treated animals, 90% of the rats survived compared with 47% of the untreated animals (p less than 0.05). These results support findings in previous studies that dextromethorphan attenuates ischemic damage.

Age-dependent changes in localized proton and phosphorus MR spectroscopy of the brain

After birth the human brain is subject to major maturational changes, which are associated with changes in the biochemical composition of the brain and brain metabolism. Magnetic resonance (MR) spectroscopy has special capabilities in the analysis of in vivo metabolism. Volume-selective proton and phosphorus MR spectroscopy of the brain was performed on a 1.5-T magnet in 41 healthy children aged 1 month to 16 years. With advancing age, phosphorus spectra revealed a decrease in the ratios of phosphomonoesters (PMEs) to beta-adenosine triphosphate (ATP) and PMEs to phosphocreatine (PCr) and an increase in the ratios of phosphodiesters to beta-ATP, PCr to beta-ATP, and PCr to inorganic phosphate (Pi). No significant changes were observed in Pi/beta-ATP and pH. No changes occurred after the age of 3 years. Proton spectroscopy revealed an increase in the ratios of N-acetylaspartate (NAA) to choline (Ch) and NAA to creatine (Cr) and a decrease in Ch/Cr with increasing age. The most rapid changes were noted during the first 3 years of life, but changes were still observed at the age of 16 years.

1H and 31P NMR measurement of cerebral lactate, high-energy phosphate levels, and pH in humans during voluntary hyperventilation: associated EEG, capnographic, and Doppler findings

In order to explore the sensitivity of spatially resolved 1H and 31P NMR spectroscopy on a whole-body NMR instrument, cerebral metabolic changes in human volunteers were measured during hyperventilation provocation. During hyperventilation the flow velocity in the middle cerebral artery decreased significantly and the EEG showed a marked increase in slow activity. 1H NMR spectra revealed an increase in cerebral lactate concentration. 31P NMR spectra showed no changes in ATP or PCr peak heights, but a shift toward tissue alkalosis was derived from changes in Pi chemical shift. During subsequent recovery, lactate concentration decreased and a slight intracellular acidosis was detected. In three experiments broadening of the lactate resonance peak resulted in separation into two components at 1.32 and 1.48 ppm, in which the latter signal possibly arose from alanine.

Cerebral lactate detected by regional proton magnetic resonance spectroscopy in a patient with cerebral infarction

Water-suppressed image-guided localized proton magnetic resonance spectroscopy was performed in a 59-year-old woman with two major brain infarcts. Spectra were measured in the infarcts, in an area between the infarcts, and in the healthy hemisphere. The volumes of interest were selected on the basis of a fast T2-weighted image. A 1331-2662 Hahn spin-echo sequence was used to suppress the water in the 8-cm3 volume that was selected by means of spatially resolved spectroscopy or stimulated echoes. The spectra were obtained in 5 minutes' accumulation time. Spectral editing was applied to separate the resonance of lactate from that of other substances. Our results show no increase of lactate concentration within the infarcts after 6 months; however, a resonance was observed at 1.6 ppm, which is assigned to fatty acids. Peak intensities of brain-specific compounds were decreased. Six months after the onset of clinical symptoms (at the time of bypass surgery), a fivefold increase in lactate concentration compared with normal values was observed in the area between the two infarcts. Four months after bypass surgery, the lactate concentration in this area had decreased to only twice normal. We speculate that lactate is a marker of reversible or impending brain damage.

Proton magnetic resonance imaging in experimental cerebral ischaemia

MRI was performed on 11 primates, 7 with a proximal and 4 with a distal MCA occlusion. Chronic implanted electrodes created only minor image disturbances. The development of oedema formation was visualised in repetitive imaging. The site of the MCA occlusion determined the infarct-size.