Hippocampal distribution of vesicular glutamate transporter 1 in patients with temporal lobe epilepsy.

PURPOSE: Vesicular glutamate transporters (VGLUTs) are responsible for loading synaptic vesicles with glutamate, determining the phenotype of glutamatergic neurons, and have been implicated in the regulation of quantal size and presynaptic plasticity. We analyzed VGLUT subtype expression in normal human hippocampus and tested the hypothesis that alterations in VGLUT expression may contribute to long-term changes in glutamatergic transmission reported in patients with temporal lobe epilepsy (TLE). METHODS: VGLUT immunohistochemistry, immunofluorescence, in situ hybridization, Western blotting, and quantitative polymerase chain reaction (qPCR) were performed on biopsies from TLE patients without (non-HS) and with hippocampal sclerosis (HS) and compared to autopsy controls and rat hippocampus. VGLUT1 expression was compared with synaptophysin, neuropeptide Y (NPY), and Timm's staining. RESULTS: VGLUT1 was the predominant VGLUT in human hippocampus and appeared to be localized to presynaptic glutamatergic terminals. In non-HS hippocampi, VGLUT1 protein levels were increased compared to control and HS hippocampi in all subfields. In HS hippocampi VGLUT1 expression was decreased in subfields with severe neuronal loss, but strongly up-regulated in the dentate gyrus, characterized by mossy fiber sprouting. DISCUSSION: VGLUT1 is used as marker for glutamatergic synapses in the human hippocampus. In HS hippocampi VGLUT1 up-regulation in the dentate gyrus probably marks new glutamatergic synapses formed by mossy fiber sprouting. Our data indicate that non-HS patients have an increased capacity to store glutamate in vesicles, most likely due to an increase in translational processes or upregulation of VGLUT1 in synapses from afferent neurons outside the hippocampus. This up-regulation may increase glutamatergic transmission, and thus contribute to increased extracellular glutamate levels and hyperexcitability.

Up-regulation of hippocampal metabotropic glutamate receptor 5 in temporal lobe epilepsy patients.

Metabotropic glutamate receptors (mGluRs) are G protein-coupled receptors involved in the regulation of glutamatergic transmission. Recent studies indicate that excitatory group I mGluRs (mGluR1 and mGluR5) contribute to neurotoxicity and hyperexcitability during epileptogenesis. In this study, we examined the distribution of mGluR1alpha and mGluR5 immunoreactivity (IR) in hippocampal resection tissue from pharmaco-resistant temporal lobe epilepsy (TLE) patients. IR was detected with panels of receptor subtype specific antisera in hippocampi from TLE patients without (non-HS group) and with hippocampal sclerosis (HS group) and was compared with that of non-epileptic autopsy controls (control group). By immunohistochemistry and immunoblot analysis, we found a marked increase of mGluR5 IR in hippocampi from the non-HS compared with the control group. High mGluR5 IR was most prominent in the cell bodies and apical dendrites of hippocampal principal neurons and in the dentate gyrus molecular layer. In the HS group, this increase in neuronal mGluR5 IR was even more pronounced, but owing to neuronal loss the number of mGluR5-immunoreactive neurons was reduced compared with the non-HS group. IR for mGluR1alpha was found in the cell bodies of principal neurons in all hippocampal subfields and in stratum oriens and hilar interneurons. No difference in mGluR1alpha IR was observed between neurons in both TLE groups and the control group. However, owing to neuronal loss, the number of mGluR1alpha-positive neurons was markedly reduced in the HS group. The up-regulation of mGluR5 in surviving neurons is probably a consequence rather than a cause of the epileptic seizures and may contribute to the hyperexcitability of the hippocampus in pharmaco-resistant TLE patients. Thus, our data point to a prominent role of mGluR5 in human TLE and indicate mGluR5 signalling as potential target for new anti-epileptic drugs.

Overexpression of the human major vault protein in gangliogliomas.

PURPOSE: Recent evidence has been obtained that the major vault protein (MVP) may play a role in multidrug resistance (MDR). We investigated the expression and cellular localization of MVP in gangliogliomas (GGs), which are increasingly recognized causes of chronic pharmacoresistant epilepsy. METHODS: Surgical tumor specimens (n = 30), as well as peritumoral and control brain tissues, were examined for the cellular distribution pattern of MVP with immunocytochemistry. Western blot analysis showed a consistent increase in MVP expression in GGs compared with that in control cortex. RESULTS: In normal brain, MVP expression was below detection in glial and neuronal cells, and only low immunoreactivity (IR) levels were detected in blood vessels. MVP expression was observed in the neuronal component of 30 of 30 GGs and in a population of tumor glial cells. In the majority of the tumors, strong MVP IR was found in lesional vessels. Perilesional regions did not show increased staining in vessels or in neuronal and glial cells compared with normal cortex. However, expression of MVP was detected in the hippocampus in cases with dual pathology. CONCLUSIONS: The increased expression of MVP in GGs is another example of an MDR-related protein that is upregulated in patients with refractory epilepsy. Further research is necessary to investigate whether it could play role in the mechanisms underlying drug resistance in chronic human epilepsy.

Expression and cell distribution of group I and group II metabotropic glutamate receptor subtypes in taylor-type focal cortical dysplasia.

PURPOSE: Focal cortical dysplasia (FCD) is known to be a major cause of intractable epilepsy. The cellular mechanism(s) underlying the epileptogenicity of FCD remain largely unknown. Because recent studies indicate that metabotropic glutamate receptor subtypes (mGluRs) play a role in epileptogenesis, we investigated the expression and cellular distribution pattern of mGluRs in FCD specimens. METHODS: Immunocytochemical expression of group I and group II mGluR subtypes was investigated in 15 specimens of human FCD obtained during epilepsy surgery. RESULTS: Strong mGluR1alpha and mGluR5 (group I mGluRs) immunoreactivity (IR) was observed in the majority of FCD specimens in dysplastic as well as in heterotopic neurons. mGluR1alpha was expressed in a subpopulation of neurons (mainly large dysplastic cells), whereas mGluR5 was represented in a higher percentage of dysplastic neuronal cells. Group II mGluRs (mGluR2/3) IR was observed less frequently than that in group I mGluRs and generally appeared in <10% of the dysplastic neurons. IR for all three mGluR subtypes was observed in balloon cells. mGluR2/3 appeared to be most frequently expressed in glial fibrillary acidic protein (GFAP)-positive balloon cells (glial type), and mGluR1alpha, in microtubule-associated protein (MAP)2-positive cells (neuronal type). mGluR5 was present in the majority of balloon cells. Occasionally glial mGluR1alpha IR was observed in bizarre glial cells with di- or multinuclei. Reactive astrocytes were intensively stained, mainly with mGluR5 and mGluR2/3. CONCLUSIONS: The cellular distribution of mGluR subtypes, with high expression of mGluR1alpha and mGluR5 in dysplastic neurons, suggests a possible contribution of group I mGluRs to the intrinsic and high epileptogenicity of dysplastic cortical regions.

Interhemispheric reorganization of motor hand function to the primary motor cortex predicted with functional magnetic resonance imaging and transcranial magnetic stimulation.

The objective of this study was presurgical assessment of reorganization of motor hand function in an 11-year-old girl with intractable epilepsy and a right-sided hemiplegia resulting from an extensive perinatal left hemispheric stroke. Prior to a left functional hemispherectomy, functional magnetic resonance imaging (MRI) showed that both nonparetic and paretic motor hand function predominantly activated the right primary motor cortex, whereas no activation was found in the left hemisphere. Transcranial magnetic stimulation of the right central area yielded responses in both the nonparetic and the paretic hand, whereas no responses were obtained after stimulation of the affected hemisphere. Both techniques indicated that motor function was mediated by corticospinal fibers originating from the undamaged (primary) motor cortex and predicted no further loss of motor hand function after surgery. Indeed, subsequent functional hemispherectomy induced no new sensorimotor deficits. Functional MRI was repeated 22 months after surgery and matched preoperative sensorimotor functional MRI findings, confirming reorganization of the primary motor cortex. No additional reorganization was introduced by surgery.