João Alberto Assirati

Hippocampal GABA and glutamate transporter immunoreactivity in patients with temporal lobe epilepsy

Objective: Sodium-coupled transporters remove extracellular neurotransmitters and alterations in their function could enhance or suppress synaptic transmission and seizures. This study determined hippocampal gamma-aminobutyric acid (GABA) and glutamate transporter immunoreactivity (IR) in temporal lobe epilepsy (TLE) patients. Methods: Hippocampal sclerosis (HS) patients (n = 25) and non-HS cases (mass lesion and cryptogenic; n = 20) were compared with nonseizure autopsies (n = 8). Hippocampal sections were studied for neuron densities along with IR for glutamate decarboxylase (GAD; presynaptic GABA terminals), GABA transporter-1 (GAT-1; presynaptic GABA transporter), GAT-3 (astrocytic GABA transporter), excitatory amino acid transporter 3 (EAAT3; postsynaptic glutamate transporter), and EAAT2-1 (glial glutamate transporters). Results: Compared with autopsies, non-HS cases with similar neuron counts showed: 1) increased GAD IR gray values (GV) in the fascia dentata outer molecular layer (OML), hilus, and stratum radiatum; 2) increased GAT-1 OML GVs; 3) increased astrocytic GAT-3 GVs in the hilus and Ammon’s horn; and 4) no IR differences for EAAT3-1. HS patients with decreased neuron densities demonstrated: 1) increased OML and inner molecular layer GAD puncta; 2) decreased GAT-1 puncta relative to GAD in the stratum granulosum and pyramidale; 3) increased GAT-1 OML GVs; 4) decreased GAT-3 GVs; 5) increased EAAT3 IR on remaining granule cells and pyramids; 6) decreased glial EAAT2 GVs in the hilus and CA1 stratum radiatum associated with neuron loss; and 7) increased glial EAAT1 GVs in CA2/3 stratum radiatum. Conclusions: Hippocampal GABA and glutamate transporter IR differ in TLE patients compared with autopsies. These data support the hypothesis that excitatory and inhibitory neurotransmission and seizure susceptibility could be altered by neuronal and glial transporters in TLE patients.

Plasticity‚ synaptic strength‚ and epilepsy: what can we learn from ultrastructural data?

Summary:  Central nervous system synapses have an intrinsic plastic capacity to adapt to new conditions with rapid changes in their structure. Such activity‐dependent refinement occurs during development and learning, and shares features with diseases such as epilepsy. Quantitative ultrastructural studies based on serial sectioning and reconstructions have shown various structural changes associated with synaptic strength involving both dendritic spines and postsynaptic densities (PSDs) during long‐term potentiation (LTP). In this review, we focus on experimental studies that have analyzed at the ultrastructural level the consequences of LTP in rodents, and plastic changes in the hippocampus of experimental models of epilepsy and human tissue obtained during surgeries for intractable temporal lobe epilepsy (TLE). Modifications in spine morphology, increases in the proportion of synapses with perforated PSDs, and formation of multiple spine boutons arising from the same dendrite are the possible sequence of events that accompany hippocampal LTP. Structural remodeling of mossy fiber synapses and formation of aberrant synaptic contacts in the dentate gyrus are common features in experimental models of epilepsy and in human TLE. Combined electrophysiological and ultrastructural studies in kindled rats and chronic epileptic animals have indicated the occurrence of seizure‐ and neuron loss‐induced changes in the hippocampal network. In these experiments, the synaptic contacts on granule cells are similar to those described for LTP. Such changes could be associated with enhancement of synaptic efficiency and may be important in epileptogenesis.

Calcified neurocysticercotic lesions and postsurgery seizure control in temporal lobe epilepsy

Background: Several studies suggest that neurocysticercosis is the main cause of symptomatic epilepsy in developing countries. In such areas, calcified cysticercotic lesions (CCL) are frequently found in patients with complex partial seizures associated with hippocampal sclerosis (HS). The authors studied whether there are clinical and pathologic differences between HS patients with and without CCL. Methods: The authors determined the clinical and pathologic findings of 30 patients with HS and compared them with 32 patients with HS + CCL. Hippocampi from both groups were measured for fascia dentata Timm staining and cell density in hippocampal subfields. Results: In the HS + CCL group, single or multiple CCL were found in all lobes with no lobar predominance. An initial precipitating event occurred in 83.3% of HS and in 62.5% of HS + CCL. First complex partial seizure occurred at 10.1 years in HS and at 11.9 years in HS + CCL. No significant differences were found for fascia dentata Timm staining and hippocampal cell densities. Good postsurgery outcome (Engel I classification) did not differ between groups, with this result occurring in 76.6% of patients with HS and 81.2% of patients with HS + CCL. Conclusions: The presence of CCL does not influence the clinical and pathologic profile of patients with hippocampal atrophy. Clinical histories and postsurgical outcomes were similar to those of patients with classic HS, suggesting that the CCL is probably, in this set of patients, a coincidental pathology and does not have a role in epileptogenesis.–1491

Hippocampal N-methyl-D-aspartate receptor subunit mRNA levels in temporal lobe epilepsy patients.

Changes in the subunit stoichiometry of the N‐methyl‐D‐aspartate (NMDA) receptor (NMDAR) alters its channel properties, and may enhance or reduce neuronal excitability in temporal lobe epilepsy patients. This study determined whether hippocampal NMDA receptor subunit mRNA levels were increased or decreased in temporal lobe epilepsy patients compared with nonseizure autopsy cases. Hippocampal sclerosis (HS; n = 16), non‐HS (n = 10), and autopsy hippocampi (n = 9) were studied for NMDAR1 (NR1) and NR2A–D mRNA levels by using semiquantitative in situ hybridization techniques, along with neuron densities. Compared with autopsy hippocampi, non‐HS and HS patients showed increased NR2A and NR2B hybridization densities per dentate granule cell. Furthermore, non‐HS hippocampi showed increased NR1 and NR2B mRNA levels per CA2/3 pyramidal neuron compared with autopsy cases. HS patients, by contrast, showed decreased NR2A hybridization densities per CA2/3 pyramidal neuron compared with non‐HS and autopsy cases. These findings indicate that chronic temporal lobe seizures are associated with differential changes in hippocampal NR1 and NR2A–D hybridization densities that vary by subfield and clinical–pathological category. In temporal lobe epilepsy patients, these findings support the hypothesis that in dentate granule cells NMDA receptors are increased, and excitatory postsynaptic potentials should be strongly NMDA mediated compared with nonseizure autopsies. HS patients, by comparison, showed decreased pyramidal neuron NR2A mRNA levels, and this suggests that NMDA‐mediated pyramidal neuron responses should be reduced in HS patients compared with non‐HS cases.

Increased hippocampal AMPA and NMDA receptor subunit immunoreactivity in temporal lobe epilepsy patients

This study determined if hippocampal AMPA and NMDA subunit immunoreactivity (IR) in temporal lobe epilepsy patients was increased compared with nonseizure autopsies. Hippocampi from hippocampal sclerosis patients (HS; n=26) and nonsclerosis cases (non-HS; n=12) were compared with autopsies (n=6) and studied for GluRl, GluR2/3, NMDAR1, and NMDAR2 IR gray values (GV) along with fascia dentata and Ammons horn neuron densities. Compared with autopsies, non-HS cases with similar neuron densities and HS patients with decreased neuron densities showed: (a) Increased GluRl GVs in the fascia dentata molecular layer; (b) increased NMDAR1 GVs in the CA3-1 stratum radiatum and greater IR within pyramids; and (c) increased GluR2/3 and NMDAR2 GVs throughout all hippocampal subfields. Furthermore, HS patients showed that relative to the outer molecular layer; (a) GluRl GV differences were decreased in the CA4/hiIar region and CA1 stratum radiatum compared with autopsies; and (b) NMDAR2 GV differences were increased in the inner molecular layer compared with non-HS cases. In temporal lobe seizure patients, these results indicate that AMPA and NMDA receptor subunit IR was increased in HS and non-HS hippocampi compared with nonseizure autopsies. In humans, these findings support the hypothesis that glutamate receptor subunits are increased in association with chronic temporal lobe seizures, which may enhance excitatory neurotransmission and seizure susceptibility.

Seizure outcome after surgery for epilepsy due to focal cortical dysplastic lesions

Neocortical development is a highly complex process encompassing cellular proliferation, neuronal migration and cortical organization. At any time this process can be interrupted or modified by genetic or acquired factors causing malformations of cortical development (MCD). Epileptic seizures are the most common type of clinical manifestation, besides developmental delay and focal neurological deficits. Seizures due to MCD are frequently pharmacoresistant, especially those associated to focal cortical dysplasia (FCD). Surgical therapy results have been reported since 1971, however, currently available data from surgical series are still limited, mainly due to small number of patients, distinct selection of candidates and surgical strategies, variable pathological diagnosis and inadequate follow-up. This study addresses the possibilities of seizure relief following resection of focal cortical dysplasia, and the impact of presurgical evaluation, extent of resection and pathological findings on surgical outcome. We included 41 patients, 22 adults and 19 children and adolescents, with medically intractable seizures operated on from 1996 to 2002. All were submitted to standardized presurgical evaluation including high-resolution MRI, Video-EEG monitoring and ictal SPECT. Post-surgical seizure outcome was classified according to Engels schema. Univariate and multivariate analysis were performed. Fifteen patients had temporal and 26 extratemporal epilepsies. Of the total 26 patients (63.4%) reached seizure-free status post-operatively. There was no correlation between outcome and age at surgery, duration of epilepsy, frequency of seizures, and pathological findings. There was, however, a clear correlation with topography of FCD (temporal versus extratemporal) and regional ictal EEG onset, on univariate as well as multivariate analysis.

Volumetric Evidence of Bilateral Damage in Unilateral Mesial Temporal Lobe Epilepsy

Summary:  Purpose: We sought to analyze the contralateral volumes of the temporal pole, posterior segment of the temporal lobe, amygdala, hippocampus, and parahippocampal gyrus in patients with temporal lobe epilepsy (TLE) due to histologically proven mesial temporal lobe sclerosis (MTLS), seizure free for ≥4 years of postsurgical follow‐up.

Do psychiatric comorbidities predict postoperative seizure outcome in temporal lobe epilepsy surgery

Clinical and demographic presurgical variables may be associated with unfavorable postsurgical neurological outcome in patients with mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS). However, few reports include preoperative psychiatric disorders as a factor predictive of long-term postsurgical MTLE-HS neurological outcome. We used Engels criteria to follow 186 postsurgical patients with MTLE-HS for an average of 6 years. DSM-IV criteria and psychiatric comorbidity criteria specific to epilepsy (interictal dysphoric disorder, postictal and interictal psychosis) were used to assess presurgical psychiatric disorders. Kaplan-Meier event-free survival and adjusted hazard ratios were estimated with unconditional logistic regression. Seventy-seven (41.4%) patients had a preoperative Axis I psychiatric diagnosis. Thirty-six patients had depression, 11 interictal dysphoric disorder, 14 interictal psychosis, 6 postictal psychosis, and 10 anxiety disorders. Twenty-three (12.4%) patients had Axis II personality disorders. Regarding seizure outcome, preoperative anxiety disorders (P=0.009) and personality disorders (P=0.003) were positively correlated with Engel class 1B (remaining auras) or higher. These findings emphasize the importance of presurgical psychiatric evaluation, counseling, and postsurgical follow-up of patients with epilepsy and psychiatric disorders.

Aberrant hippocampal mossy fiber sprouting correlates with greater NMDAR2 receptor staining.

THIS study determined in temporal lobe epilepsy patients and rats injected with intrahippocampal kainate (KA) whether fascia dentata molecular layer mossy fiber sprouting was associated with increases in NMDAR2 immunoreactivity (IR). Patients with hippocampal sclerosis (n = 11) were compared with those with temporal mass lesions (n = 7) and material obtained at autopsies (n = 4); and unilateral KA-injected rat hippocampi (n = 7) were compared with the contralateral saline-injected side and non-lesioned animals (n = 7; control). Hippocampi were studied for neo-Timms stained mossy fiber sprouting and NMDAR2 IR. The staining was quantified as gray values (GV) using computer image analysis. Hippocampal sclerosis patients and KA-injected rats showed the greatest inner molecular layer (IML) mossy fiber sprouting and NMDAR2 staining. Compared with autopsies and patients with mass lesions, hippocampal sclerosis patients had greater IML neo-Timms (p = 0.0018) and NMDAR2 staining (p = 0.0063). Similarly, compared with controls and saline-injected rats, KA-injected hippocampi showed greater IML mossy fiber sprouting and NMDAR2 IR (p = 0.0001). Furthermore, IML mossy fiber sprouting positively correlated with greater IML NMDAR2 staining in both human and experimental rat groups (p < 0.0099). These results support the hypothesis that in severely damaged hippocampi abnormal mossy fiber sprouting and concordant increases in IML NMDAR2 receptor staining may contribute or partially explain granule cell hyperexcitability and the pathophysiology of hippocampal epilepsy.

Clinical features of patients with posterior cortex epilepsies and predictors of surgical outcome

Summary:  Purpose: Posterior cortex epilepsies (PCEs) encompass a group of epilepsies originating from the occipital, parietal, or occipital border of the temporal lobe, or from any combination of these regions. When their seizures are refractory to pharmacologic treatment, these patients are usually referred for surgery. The aim of our study was to analyze clinical characteristics of all PCE patients referred for surgery from 1994 to 2003, and to search for predictors of surgical outcome.