Variable anisotropic brain electrical conductivities in epileptogenic foci.

Source localization models assume brain electrical conductivities are isotropic at about 0.33 S/m. These assumptions have not been confirmed ex vivo in humans. This study determined bidirectional electrical conductivities from pediatric epilepsy surgery patients. Electrical conductivities perpendicular and parallel to the pial surface of neocortex and subcortical white matter (n = 15) were measured using the 4-electrode technique and compared with clinical variables. Mean (+/-SD) electrical conductivities were 0.10 +/- 0.01 S/m, and varied by 243% from patient to patient. Perpendicular and parallel conductivities differed by 45%, and the larger values were perpendicular to the pial surface in 47% and parallel in 40% of patients. A perpendicular principal axis was associated with normal, while isotropy and parallel principal axes were linked with epileptogenic lesions by MRI. Electrical conductivities were decreased in patients with cortical dysplasia compared with non-dysplasia etiologies. The electrical conductivity values of freshly excised human brain tissues were approximately 30% of assumed values, varied by over 200% from patient to patient, and had erratic anisotropic and isotropic shapes if the MRI showed a lesion. Understanding brain electrical conductivity and ways to non-invasively measure them are probably necessary to enhance the ability to localize EEG sources from epilepsy surgery patients.

Ionic charge transport between blockages: Sodium cation conduction in freshly excised bulk brain tissue.

We analyze the transient-dc and frequency-dependent electrical conductivities between blocking electrodes. We extend this analysis to measurements of ions' transport in freshly excised bulk samples of human brain tissue whose complex cellular structure produces blockages. The associated ionic charge-carrier density and diffusivity are consistent with local values for sodium cations determined non-invasively in brain tissue by MRI (NMR) and diffusion-MRI (spin-echo NMR). The characteristic separation between blockages, about 450 microns, is very much shorter than that found for sodium-doped gel proxies for brain tissue, >1 cm.

Human fascia dentata anatomy and hippocampal neuron densities differ depending on the epileptic syndrome and age at first seizure.

This study determined fascia dentata anatomy and hippocampal neuron densities in patients with different epileptic syndromes. Based on presurgical data, patients were classified into: (a) pediatric patients (n=19); (b) temporal mass lesion cases (n=14); and (c) hippocampal sclerosis patients (n=31). Surgically removed hippocampi and autopsies (n=34) were studied for: (a) hippocampal neuron densities; (b) stratum granulosum (SG) widths and lengths; and (c) hilar areas. The number of granule cells and hilar neurons per tissue section were estimated from the neuron densities and fascia dentata area measurements. Results showed that compared with autopsies (p<0.05): (a) pediatric patients had similar SG and hilar areas; granule cell density was lower (but not hilar neuron density); and the estimated number of granule cells was lower (but not the number of hilar neurons); (b) the widths of SG and hilar areas were greater in mass lesion cases; the density of granule cells and hilar neurons was lower; and the total estimated numbers of granule cells and hilar neurons were similar to those of the autopsies; and (c) hippocampal sclerosis patients had wider, yet shorter SG; hilar areas were smaller; granule cell and hilar densities were lower; and the total estimated numbers of granule cells and hilar neurons were lower than those of the autopsy cases. The duration of the seizures did not correlate with lower fascia dentata neuron densities or estimates of total granule cell and hilar neurons. Furthermore, greater SG widths correlated with lower hilar and CA4 neuron densities, but not with age at first seizure or duration of epilepsy. These results indicate that the size of the fascia dentata SG and hilus along with hippocampal neuron densities differ between surgical patients with different epileptic syndromes, and a wider SG was associated with a lower density of end folium neurons. These findings support the hypothesis that hippocampal sclerosis and granule cell dispersion are not the consequence of repetitive seizures beginning at an early developmental age, but seem to differ depending on the type of epileptic syndrome.

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 GluR1, GluR2/3, NMDAR1, and NMDAR2 IR gray values (GV) along with fascia dentata and Ammon's horn neuron densities. Compared with autopsies, non-HS cases with similar neuron densities and HS patients with decreased neuron densities showed: (a) Increased GluR1 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) GluR1 GV differences were decreased in the CA4/hilar 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.

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.

In contrast to kindled seizures, the frequency of spontaneous epilepsy in the limbic status model correlates with greater aberrant fascia dentata excitatory and inhibitory axon sprouting, and increased staining for N-methyl-D-aspartate, AMPA and GABA(A) receptors.

This study determined whether there were differences in hippocampal neuron loss and synaptic plasticity by comparing rats with spontaneous epilepsy after limbic status epilepticus and animals with a similar frequency of kindled seizures. At the University of Virginia, Sprague-Dawley rats were implanted with bilateral ventral hippocampal electrodes and treated as follows; no stimulation (electrode controls; n=5): hippocampal stimulation without status (stimulation controls; n=5); and limbic status from continuous hippocampal stimulation (n=12). The limbic status group were electrographically monitored for a minimum of four weeks. Four rats had no recorded chronic seizures (status controls), and all three control groups showed no differences in hippocampal pathology and were therefore incorporated into a single group (controls). Eight limbic status animals eventually developed chronic epilepsy (spontaneous seizures) and an additional eight rats were kindled to a similar number and frequency of stage 5 seizures (kindled) as the spontaneous seizures group. At the University of California (UCLA) the hippocampi were processed for: (i) Niss1 stain for densitometric neuron counts; (ii) neo-Timm's histochemistry for mossy fiber sprouting; and (iii) immunocytochemical staining for glutamate decarboxylase, N-methyl-D-aspartate receptor subunit 2, AMPA receptor subunit 1 and the GABA(A) receptor. In the fascia dentata inner and outer molecular layers the neo-Timm's stain and immunoreactivity was quantified as gray values using computer image analysis techniques. Statistically significant results (P<0.05) showed the following. Compared to controls and kindled animals, rats with spontaneous seizures had: (i) lower neuron counts for the fascia dentata hilus, CA3 and CA1 stratum pyramidale; (ii) greater supragranular inner molecular layer mossy fiber staining; and (iii) greater glutamate decarboxylase immunoreactivity in both molecular layers. Greater supragranular excitatory mossy fiber and GABAergic axon sprouting correlated with: (i) increases in N-methyl-D-aspartate receptor subunit 2 inner molecular layer staining; (ii) more AMPA receptor subunit 1 immunoreactivity in both molecular layers; and (iii) greater outer than inner molecular layer GABA(A) immunoreactivity. Furthermore, in contrast to kindled animals, rats with spontaneous seizures showed that increasing seizure frequency per week and the total number of natural seizures positively correlated with greater Timm's and GABAergic axon sprouting, and with increases in N-methyl-D-aspartate receptor subunit 2 and AMPA receptor subunit 1 receptor staining. In this rat limbic status model these findings indicate that chronic seizures are associated with hippocampal neuron loss, reactive axon sprouting and increases in excitatory receptor plasticity that differ from rats with an equal frequency of kindled seizures and controls. The hippocampal pathological findings in the limbic status model are similar to those in humans with hippocampal sclerosis and mesial temporal lobe epilepsy, and support the hypothesis that synaptic reorganization of both excitatory and inhibitory systems in the fascia dentata is an important pathophysiological mechanism that probably contributes to or generates chronic limbic seizures.

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-Timm's 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-Timm's (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.

Children with severe epilepsy: evidence of hippocampal neuron losses and aberrant mossy fiber sprouting during postnatal granule cell migration and differentiation.

Surgically resected hippocampi from children with extrahippocampal seizures and structurally non-atrophic brains were examined to determine the relationship of neuron losses and aberrant mossy fiber (MF) sprouting to the postnatal migration and differentiation of the fascia dentata (FD) granule cells (GC). Percent neuron loss compared to age-matched autopsy controls was determined by quantitative cell densities, and aberrant MF sprouting by neo-Timm histochemistry. Postnatal immature GC migration and differentiation was demonstrated by the transient but GC-specific expression of the immature form of neural cell adhesion molecule (NCAM-H). Results showed that the hippocampi from children with seizures appeared microanatomically intact without focal areas of damage. However, significant neuron losses were found by neuron counts in the fascia dentata (P < 0.01), CA4 (P < 0.01), and CA2 (P < 0.05). Aberrant supragranular inner molecular layer MF sprouting was found in hippocampi of children with seizures, and the MFs showed smaller puncta in specimens resected under 2 years of age (n = 3) compared to the larger puncta in older children (n = 5). Hippocampi from children under 2 years of age also demonstrated NCAM-H positive primitive cells in the infragranular and stratum granulosum of the fascia dentata consistent with the postnatal migration and differentiation of GCs, the parent neurons of the MFs. These results indicate that seizures in the immature but structurally intact human hippocampus are associated with decreased neuron densities and aberrant MF sprouting very early in postnatal development. The data also show that aberrant MF sprouting is found during postnatal migration, differentiation and axogenesis of GCs.(ABSTRACT TRUNCATED AT 250 WORDS)

Anoxia during kainate status epilepticus shortens behavioral convulsions but generates hippocampal neuron loss and supragranular mossy fiber sprouting.

In rats, this study determined the impact of systemic hypoxia during late kainate-induced status epilepticus on hippocampal neuron loss and mossy fiber sprouting. Non-fasted Sprague Dawley rats were prepared as follows: Naive controls (n=5); rats placed 2 min in a hypoxia chamber (hypoxia only; n=6); rats that seized for more than 6 h from kainic acid (KA-status; 12 mg/kg; i.p.; n=7); and another KA-status group placed into the hypoxia chamber 75 min after the convulsions started (KA-status/hypoxia; n=16). All rats, except for half of the KA-status/hypoxia animals, were perfused 2 weeks later (short-term). The other 8 KA-status/hypoxia rats were perfused after 2 months (long-term). Hippocampal sections were studied for neuron densities and aberrant mossy fiber sprouting at three ventral to dorsal levels. Fascia dentata (FD) mossy fiber sprouting was quantified as an increase in the inner minus outer molecular layer (IML-OML) gray value (GV) difference. Behaviorally, KA-status/hypoxia rats had a shorter duration of convulsive status epilepticus than KA-status animals without anoxia. Hippocampal sections showed that compared to controls: (1) hypoxia-only rats showed no differences in ventral neuron densities and neo-Timm's stained IML-OML GVs; (2) KA-status rats had decreased CA3 densities and a non-significant increase in ventral IML-OML GV differences; and (3) KA-status/hypoxia short-term animals showed decreased hilar, CA3 and CA1 densities and increased ventral IML-OML GV differences. Compared to KA-status/hypoxia short-term rats, long-term animals showed no differences in ventral hippocampal neuron densities, but middle and dorsal sections demonstrated increased IML-OML GV differences and animals were observed to have spontaneous limbic epilepsy. These results indicate that rats exposed to kainate-induced status epilepticus for over 1 h and then a hypoxic insult had a shorter duration of convulsive status, decreased hippocampal neuron densities and greater FD mossy fiber sprouting than controls and the amount of neuronal damage and sprouting was slightly more than animals subjected to 6 h of kainate-induced status. This supports the hypothesis that a physiologic insult during status can shorten the convulsive episode, but still produce hippocampal pathology with a number of clinical and pathologic similarities to human mesial temporal lobe epilepsy (MTLE).

The pathophysiologic relationships between lesion pathology, intracranial ictal EEG onsets, and hippocampal neuron losses in temporal lobe epilepsy.

In temporal lobe epilepsy (TLE) lesion patients the pathology, location of intracranial ictal EEG onsets, and hippocampal neuron losses were compared. Patients (n = 63) were classified into: (1) Tumors (n = 26, e.g. astrocytomas, gangliogliomas); (2) vascular (n = 9, e.g. cavernous and venous angiomas); (3) developmental (n = 17, e.g. cortical dysplasia, heterotopias); or (4) atrophic (n = 11, e.g. cortical or white matter encephalomalacia). Other variables were; (1) the location of the temporal lesion in the mesial to lateral, and anterior to posterior plane, (2) a clinical history of an initial precipitating injury (IPI) prior to the onset of TLE (e.g. prolonged first seizure, head trauma), (3) hippocampal neuron densities, (4) focal or regional location by intracranial depth EEG of ictal onsets, and (5) seizure outcomes. Results showed that severe hippocampal neuron losses were associated with two statistically significant findings. First, patients with mesial lesions in or adjacent to the body of the hippocampus had greater neuron losses compared to mesial lesions anterior or posterior to the hippocampus (P = 0.04). Second, lesion patients with an IPI history had greater Ammon's horn (AH) neuron losses compared to those without IPI histories (P = 0.0005), and the profile of loss was similar to hippocampal sclerosis (HS). Granule cell losses correlated in a complex manner in that; 1) by regression analysis densities decreased with longer intervals of TLE (P = 0.006), (2) tumor patients with IPIs had less granule cell loss compared to those without IPIs intervals of TLE (P = 0.006), (2) tumor patients with IPIs had less granule cell loss compared to those without IPIs (P = 0.05), and (3) developmental patients with IPIs had greater granule cell loss than patients without IPIs (P = 0.009). Mesial-temporal depth EEG electrodes were the first areas of ictal activity in 15 of 16 patients (94%), and greater hippocampal neuron losses were not associated with focal mesial-temporal EEG onsets. Seizure outcomes were worse in tumor patients compared to HS patients (P = 0.01), and patients with post-resection seizures had incomplete resections of their lesions and/or hippocampi. These results indicate that in TLE lesion patients the amount and pattern of hippocampal neuron loss depends on the location of the lesion, the pathologic classification, and a history of an IPI. Further, despite variable neuron losses, in temporal lesion patients the hippocampus was nearly always involved in the genesis or propagation of the chronic seizures.

Traumatic compared to non-traumatic clinical-pathologic associations in temporal lobe epilepsy.

This study determined differences in clinical-pathologic characteristics of intractable temporal lobe epilepsy (TLE) patients whose mechanism of cerebral injury and chronic seizures involved a prior history of cerebral trauma compared to those with non-traumatic initial injuries. TLE patients (n = 120) from a single epilepsy center were retrospectively and blindly catalogued into pathogenic groups (independent variables) based on if there was a significant Birth injury (n = 11) or Cerebral trauma (n = 26). These two 'trauma' categories were compared to TLE patients with non-seizure non-trauma histories (Non-Sz/Non-Trauma; n = 17), or a first Prolonged seizure (n = 66). The four groups were compared for differences in the time course of their clinical injuries and seizures, quantified hippocampal neuron counts, other temporal neocortical pathologies, and seizure outcomes (dependent variables). Between group statistically significant (at least P < 0.05) results showed: (1) In Birth injury, 33% had Ammon's Horn (AH) neuron loss under 50%, 54% had other temporal neocortical pathologies, they showed the most CA4 neuron loss, and the worse seizure outcomes. (2) Cerebral trauma were older when injured, 29% had AH loss under 50%, 50% showed other pathologies, and they had the best seizure outcomes. (3) Non-Sz/Non-Trauma showed the least AH and CA4 neuron losses, only 12% had other temporal pathologies, and they had seizure outcomes that were intermediate. (4) Prolonged seizure showed the youngest age of habitual TLE onsets, the greatest AH, CA1, and prosubiculum neuron loss, only 11% had other temporal pathologies, and their seizure outcomes were excellent. These results indicate that in intractable surgically treated TLE, a history of cerebral trauma or birth injury as the pathogenic mechanism of their seizures show different clinical-pathologic features and seizure outcomes compared to non-trauma patients. This supports the notion that in TLE there are different pathogenic mechanisms associated with different types of initial injuries and that patients will have different responses to surgical therapy.

The pathogenic and progressive features of chronic human hippocampal epilepsy.

To design useful experimental models of epilepsy, it is necessary to clearly understand the known clinical-pathologic features of the disease process. Studies of mesial temporal lobe epilepsy (MTLE) patients have identified several distinctive clinical and pathophysiologic characteristics and many of these can be analyzed in experimental models. For example, patients with typical MTLE have medical histories that often contain an initial precipitating injury (IPI), are likely to have hippocampal sclerosis in the surgical specimen, and have better seizure outcomes than patients with typical idiopathic temporal seizures (i.e. cryptogenic). Hippocampal from children as young as age 1 year with IPI histories also demonstrate neuron damage similar to adults with hippocampal sclerosis. Compared to IPI patients without seizures (i.e. trauma, hypoxia, etc.), IPI cases with severe seizures showed younger ages at the IPI, shorter latent periods, and longer durations of habitual MTLE. Hippocampal damage is often bilateral, however, the epileptogenic side shows hippocampal sclerosis and the opposite side usually shows only mild neuron losses. Moreover, MTLE patients show declines in hippocampal neuron densities with very long histories of habitual seizures (15 to 20 years), however, the additional neuron loss adds to the template of hippocampal sclerosis and occurs in limited subfields (granule cells, CA1 and prosubiculum). Hippocampal axon and synaptic reorganization is another pathologic feature of MTLE, and involves granule cell mossy fibers and axons immunoreactive for neuropeptide upsilon, somatostatin, and glutamate decarboxylase (which synthesizes GABA). Finally, MTLE patients with hippocampal sclerosis show increased granule cell mRNA levels for brain derived neurotropic factor, nerve growth factor, and neurotrophin-3 that correlate with mossy fiber sprouting or with declines in Ammon's horn neuron densities. Taken together, our data support the following concepts: (1) The pathogenesis of MTLE is associated with IPI histories that probably injure the hippocampus at some time prior to habitual seizure onsets, (2) most of the damage seems to occur with the IPI, (3) there can be additional neuron loss associated with long histories, (4) another pathologic feature of MTLE is axon reorganization of surviving fascia dentata and hippocampal neurons, and (5) reorganized axon circuits probably contribute to seizure or propagation.

Glutamate AMPA receptors in the fascia dentata of human and kainate rat hippocampal epilepsy.

The present study examined the relationship between the patterns and densities of glutamate AMPA receptor sub-units GluR1 and GluR2/3 in the molecular layer of the fascia dentata and aberrant mossy fiber neoinnervation in human and kainate rat hippocampal epilepsy. Because AMPA sub-units modulate the fast glutamate synaptic transmission, we hypothesized that the AMPA receptor densities would be related to the glutamate-secreting mossy fibers, which could then contribute to seizure generation. In human hippocampal epilepsy, we found that the immunocytochemical labeling of GluR1 and GluR2/3 dendrites was positively related to the densities and spatial locations of the densest, aberrant neo-Timm stained supragranular mossy fibers. We used quantitative densitometry for the mossy fibers. However, the relatively faint and punctate immunocytochemical staining of the receptors did not allow true quantitative densitometry of the dendritic trees because in human epilepsy granule cell densities were decreased on average 50% of normal. Nevertheless, visual observations did confirm spatial relations between dense fascia dentata inner molecular layer mossy fibers and dense AMPA receptor staining. In the outer molecular layer, the mossy fibers were present only in the lower portion, were not densely-stained, and the AMPA receptors were only faintly-labeled. Nevertheless, outer molecular layer AMPA receptor densities were usually present more distally than were the mossy fibers. Experiments were done using intrahippocampal kainate epileptic rats to test the time courses for the changes in mossy fibers and AMPA receptors. The upregulation of inner and outer molecular layer AMPA receptors occurred maximally within 5 days post-kainate injection, prior to any mossy fiber supragranular ingrowth. One hundred and eighty days after ipsilateral kainate the AMPA receptors were increased bilaterally in the inner and outer molecular layers despite the fact that the contralateral aberrant supragranular mossy fibers were minor in comparison to the dense ipsilateral mossy fiber hyperinnervation. These results suggest that in hippocampal epilepsy AMPA receptor numbers increase throughout the length of the molecular layer dendrites; however the AMPA receptor densities are greater in rough relation to the greatest aberrant mossy fiber presynaptic inputs. Interestingly, the receptor upregulation precedes the mossy fiber ingrowth and may play a role in initiating axonal sprouting or in maintaining the aberrant mossy fiber synapses.

Neuron loss, mossy fiber sprouting, and interictal spikes after intrahippocampal kainate in developing rats.

This study determined neuron losses, mossy fiber sprouting, and interictal spike frequencies in adult rats following intrahippocampal kainic acid (KA) injections during postnatal (PN) development. KA (0.4 micrograms/0.2 microliters; n = 64) was injected into one hippocampus and saline into the contralateral side between PN 7 to 30 days. Animals were sacrificed 28 to 256 days later, along with age-matched naive animals (controls; n = 20). Hippocampi were studied for: (1) Fascia dentata granule cell, hilar, and CA3c neuron counts; (2) neo-Timm's stained supragranular mossy fiber sprouting; and (3) hippocampal and intracerebral interictal spike densities (n = 13). Mossy fiber sprouting was quantified as the gray value differences between the inner and outer molecular layer. Statistically significant results (p < 0.05) showed the following: (1) Compared to controls, CA3c and hilar neuron counts were reduced in KA-hippocampi with injections at PN 7-10 and PN 12-14 respectively and counts decreased with older PN injections. Granule cell densities on the KA-side and saline injected hippocampi were not reduced compared to controls. (2) In adult rats, supragranular mossy fiber sprouting was observed in 2 of 7 PN 7 injected animals. Compared to controls, increased gray value differences, indicating mossy fiber sprouting, were found on the KA-side beginning with injuries at PN 12-14 and increasing with older PN injections. On the saline-side only PN 30 animals showed minimal sprouting. (3) Mossy fiber sprouting progressively increased on the KA-side with longer survivals in rats injured after PN 15. Sprouting correlated positively with later PN injections and longer post-injection survival intervals, and not with reduced hilar or CA3c neuron counts. (4) On the KA-side, mossy fiber gray value differences correlated positively with in vivo intrahippocampal interictal spike densities. These results indicate that during postnatal rat development intrahippocampal kainate excitotoxicity can occur as early as PN 7 and increases with older ages at injection. This rat model reproduces many of the pathologic, behavioral, and electrophysiologic features of human mesial temporal lobe epilepsy, and supports the hypothesis that hippocampal sclerosis can be the consequence of focal injury during early postnatal development that progressively evolves into a pathologic and epileptic focus.

Hippocampal AMPA and NMDA mRNA levels and subunit immunoreactivity in human temporal lobe epilepsy patients and a rodent model of chronic mesial limbic epilepsy.

This study compared temporal lobe epilepsy patients, along with kindled animals and self sustained limbic status epilepticus (SSLSE) rats for parallels in hippocampal AMPA and NMDA receptor subunit expression. Hippocampal sclerosis patients (HS), non-HS cases, and autopsies were studied for: hippocampal AMPA GluR1-3 and NMDAR1&2b mRNA levels using in situ hybridization: GluR1, GluR2/3, NMDAR1, and NMDAR2(a&b) immunoreactivity (IR); and neuron densities. Similarly, spontaneously seizing rats after SSLSE, kindled rats, and control animals were studied for: fascia dentata neuron densities: GluR1 and NMDAR2(a&b) IR; and neo-Timm's staining. In HS and non-HS cases, the mRNA hybridization densities per granule cell, as well as molecular layer IR, showed increased GluR1 (relative to GluR2/3) and increased NMDAR2b (relative to NMDAR1) compared to autopsies. Likewise, the molecular layer of SSLSE rats with spontaneous seizures demonstrated more neo-Timm's staining, and higher levels of GluR1 and NMDAR2(a&b) IR compared to kindled animals and controls. These results indicate that hippocampal AMPA and NMDA receptor subunit mRNAs and their proteins are differentially increased in association with spontaneous, but not kindled, seizures. Furthermore, there appears to be parallels in fascia dentata AMPA and NMDA receptor subunit expression between HS (and non-HS) epileptic patients and SSLSE rats. This finding supports the hypothesis that spontaneous seizures in humans and SSLSE rats involve differential alterations in hippocampal ionotrophic glutamate receptor subunits. Moreover, non-HS hippocampi were more like HS cases than hippocampi from kindled animals with respect to glutamate receptors; therefore, hippocampi from kindled rats do not accurately model human non-HS cases, despite some similarities in neuron densities and mossy fiber axon sprouting.

Quantified patterns of mossy fiber sprouting and neuron densities in hippocampal and lesional seizures.

Quantified hippocampal mossy fiber synaptic reorganization and neuron losses were measured to determine the pathological features associated with epileptogenic fascia dentata. Twenty-five patients with temporal lobe epilepsy (TLE) were classified as having either mesial temporal sclerosis (MTS; 16 patients), with seizure genesis in the hippocampus, or temporal mass lesions (nine patients), with seizures that were probably extrahippocampal. Neo-Timm's histochemistry identified mossy fiber sprouting, and aberrant fascia dentata puncta densities were objectively measured by light microscopic analysis on an image-analysis computer. neuron densities determined cell losses and the two seizure groups were compared to control specimens obtained from autopsies. Results showed significantly greater fascia dentata mossy fiber puncta densities and neuron losses in TLE patients compared to autopsy specimens (p < 0.026). Furthermore, there were significant differences between the two seizure groups: 1) mossy fiber puncta densities in the inner molecular layer were significantly greater in MTS compared to lesions (p < 0.02), and 2) mossy fiber puncta densities were greater in the inner molecular layer than in the stratum granulosum in 14 of 16 MTS patients (88%) compared to four of nine patients with lesions (44%, p < 0.01). Neuron densities were significantly different comparing MTS, lesion and control groups for stratum granulosum (p = 0.0001) and Ammon's horn (p = 0.0001), with each group significantly different (p < 0.05) compared to another. All patients were either seizure-free or significantly improved 1 year or more after en bloc temporal lobectomy. There were no significant correlations between fascia dentata mossy fiber puncta densities and counts of hilar neurons, CA4 pyramids, granule cells, or years of seizures. This indicates that inner molecular layer mossy fiber puncta densities and neuron losses are greater in patients with MTS than in those with lesions, and mossy fiber sprouting probably contributes to the pathophysiology of hippocampal seizures. Furthermore, these data show that some patients with extrahippocampal lesions have mossy fiber sprouting similar to MTS patients, suggesting that hippocampi in lesion patients may be capable of epileptogenesis from synaptic reorganization.

Influence of the type of initial precipitating injury and at what age it occurs on course and outcome in patients with temporal lobe seizures.

The type of initial precipitating injury and the age at which it occurred in 20 patients with nonlesional temporal lobe epilepsy (TLE) were related to clinical features, presurgical neuroimaging, quantified hippocampal pathologies, and seizure outcomes. Clinical data, neuroimaging records, and seizure outcomes were abstracted from medical records and confirmed with patient and family contacts. Hippocampal neuron losses and mossy fiber reactive synaptogenesis were quantified independently. Results showed that the type of initial precipitating injury and the patient's age at which it occurred were related to the clinicopathological features of TLE. An initial precipitating injury occurred in 18 patients (90%), all of whom had mesial temporal sclerosis (MTS). Patients with a prolonged initial seizure or a nonseizure initial precipitating injury before age 5 years were significantly more likely to have unilateral hippocampal atrophy (p < 0.05) shown on magnetic resonance (MR) imaging, and had significantly greater inner molecular layer mossy fiber puncta densities (p < 0.001) than patients with nonprolonged childhood initial precipitating injuries and/or seizures after age 5 years. Furthermore, nonseizure injuries in patients before age 5 years had significantly longer latent periods (p < 0.05), and the patients did not respond to surgical treatment as well as other MTS patients. Those with an initial precipitating injury after age 5 years had MTS but showed significantly less inner molecular layer mossy fiber sprouting (p < 0.05) than patients whose injuries appeared before age 5 years. Patients without an initial precipitating injury (idiopathic TLE) had significantly fewer neuron losses (p < 0.05) and inner molecular layer mossy fiber puncta densities (p < 0.05) and had worse outcomes following en bloc temporal lobectomy compared to patients with MTS who had experienced initial precipitating injuries. Patients with unilateral hippocampal abnormalities on MR imaging did not show significant differences in neuron losses or aberrant mossy fiber puncta densities compared to patients without asymmetry. These results support the hypothesis that the type of initial precipitating injury and the age at which the injury occurred initiates and influences the pathophysiological process that eventually develops into MTS. These data support the notion that the pathophysiology of hippocampal damage and mossy fiber sprouting after an initial precipitating injury may be a progressive process.

Unilateral hippocampal mossy fiber sprouting and bilateral asymmetric neuron loss with episodic postictal psychosis.

Rarely are both sides of the hippocampus available for pathological study in a patient with intractable temporal lobe epilepsy (TLE). The authors report a patient with TLE investigated with bilateral depth electrodes who had an episode of postictal psychosis. The patient died 4 weeks after temporal lobectomy of unknown reasons, despite complete postmortem examination and clinical evidence of postsurgery seizure control. Pathological examination of surgical and autopsy hippocampal specimens found bilateral asymmetric neuron losses. However, only the resected epileptogenic hippocampus showed the profile of neuron loss typical of mesial temporal sclerosis (MTS) and abnormal mossy fiber synaptic reorganization. Quantitative depth electroencephalographic (EEG) analysis of the postictal psychotic event showed that it was not associated with a cluster of seizures, increased postictal depth EEG spike activity, or insufficient antiepileptic medication. These results support the hypothesis that ipsilateral hippocampal epileptogenesis is associated with MTS and mossy fiber sprouting. The results also suggest that the etiology of postictal psychosis in this patient was initiated by an ictal event and the behavior apparently depended on seizure propagation outside the hippocampus. The relevance of these two findings to the literature is discussed.

Spoken language outcomes after hemispherectomy: factoring in etiology.

We analyzed postsurgery linguistic outcomes of 43 hemispherectomy patients operated on at UCLA. We rated spoken language (Spoken Language Rank, SLR) on a scale from 0 (no language) to 6 (mature grammar) and examined the effects of side of resection/damage, age at surgery/seizure onset, seizure control postsurgery, and etiology on language development. Etiology was defined as developmental (cortical dysplasia and prenatal stroke) and acquired pathology (Rasmussen's encephalitis and postnatal stroke). We found that clinical variables were predictive of language outcomes only when they were considered within distinct etiology groups. Specifically, children with developmental etiologies had lower SLRs than those with acquired pathologies (p =.0006); age factors correlated positively with higher SLRs only for children with acquired etiologies (p =.0006); right-sided resections led to higher SLRs only for the acquired group (p =.0008); and postsurgery seizure control correlated positively with SLR only for those with developmental etiologies (p =.0047). We argue that the variables considered are not independent predictors of spoken language outcome posthemispherectomy but should be viewed instead as characteristics of etiology.

Removing interictal fast ripples on electrocorticography linked with seizure freedom in children.

BACKGROUND: Fast ripples (FR, 250-500 Hz) detected with chronic intracranial electrodes are proposed biomarkers of epileptogenesis. This study determined whether resection of FR-containing neocortex recorded during intraoperative electrocorticography (ECoG) was associated with postoperative seizure freedom in pediatric patients with mostly extratemporal lesions. METHODS: FRs were retrospectively reviewed in 30 consecutive pediatric cases. ECoGs were recorded at 2,000 Hz sampling rate and visually inspected for FR, with reviewer blinded to the resection and outcome. RESULTS: Average age at surgery was 9.1 ± 6.7 years, ECoG duration was 11.8 ± 8.1 minutes, and postoperative follow-up was 27 ± 4 months. FRs were undetected in 6 ECoGs with remote or extensive lesions. FR episodes (n = 273) were identified in ECoGs from 24 patients, and in 64% FRs were independent of spikes, sharp waves, voltage attenuation, and paroxysmal fast activity. Of these 24 children, FR-containing cortex was removed in 19 and all became seizure-free, including 1 child after a second surgery. The remaining 5 children had incomplete FR resection and all continued with seizures postoperatively. In 2 ECoGs, the location of electrographic seizures matched FR location. FR-containing cortex was found outside of MRI and FDG-PET abnormalities in 6 children. CONCLUSION: FRs were detected during intraoperative ECoG in 80% of pediatric epilepsy cases, and complete resection of FR cortex correlated with postoperative seizure freedom. These findings support the view that interictal FRs are excellent surrogate markers of epileptogenesis, can be recorded during brief ECoG, and could be used to guide future surgical resections in children.