Hippocampal cell density and subcortical metabolism in temporal lobe epilepsy.

PURPOSE: Correlations between hippocampal cell density and subcortical metabolism in patients with temporal lobe epilepsy (TLE) were studied to explore possible links between subcortical function and the regulation of hippocampal excitability. METHODS: Resected hippocampal cell densities were correlated with cortical and subcortical regional cerebral metabolic rate for glucose (CMRglu), as measured by [18F]-fluorodeoxyglucose positron emission tomography (18-FDG-PET), in 39 patients with intractable TLE who underwent anterior temporal lobectomy (ATL). CMRglu was measured ipsilateral and contralateral to the resected temporal lobe. Linear regression techniques were used for statistical analysis. RESULTS: Hilar cell densities correlated positively and significantly with CMRglu in the bilateral thalamus, putamen and globus pallidus, and the ipsilateral caudate. Dentate granule cell densities correlated positively and significantly with CMRglu in the bilateral thalamus and putamen. There was no significant correlation between cell densities and CMRglu in any cortical region, including the hippocampus. CONCLUSIONS: We postulate that hippocampal cell loss results in decreased efferent synaptic activity to the thalamus and basal ganglia, causing decreased neuronal activity in these structures with consequent hypometabolism. This synaptic activity has a significant bilateral component. Subcortical hypometabolism in patients with TLE may reinforce the epileptogenic potential of mesial temporal lobe discharges.

Adenovirus vector-mediated gene transfer into human epileptogenic brain slices: prospects for gene therapy in epilepsy.

As a first step in the development of a gene therapy approach to epilepsy, we evaluated the ability of adenovirus vectors to direct the transfer into and expression of a marker gene in human brain slices obtained from patients undergoing surgery for medically intractable epilepsy. Following injection of adenovirus vectors containing the Escherichia coli lacZ gene into hippocampal and cortical brain slices, lacZ mRNA, beta-galactosidase protein, and enzymatic activity were detected, confirming successful gene transfer, transcription, and translation into a functional protein. Transfected cells were predominantly glial, with some neurons expressing beta-galactosidase as well. These results support the potential of adenovirus vectors to transfer genetic information into human epileptogenic brain, resulting in expression of the gene into a functional protein. These findings also have implications for the development of gene therapy approaches to certain seizure disorders. A number of potential therapeutic approaches are discussed, including the elevation of inhibitory neurotransmitter or neuropeptide levels, expression or modulation of postsynaptic receptors, and manipulation of signal transduction systems.

Direct gene transfer into human epileptogenic hippocampal tissue with an adeno-associated virus vector: implications for a gene therapy approach to epilepsy.

PURPOSE: Virus vectors capable of transferring genetic information into human cells provide hope for improved therapy in several neurological diseases, including epilepsy. We evaluated the ability of an adeno-associated virus (AAV) vector to transfer and cause expression of a lacZ marker gene in brain slices obtained from patients undergoing temporal lobectomy for control of medically intractable seizures. METHODS: Human brain slices were injected with an AAV vector (AAVlacZ) encoding Escherichia coli beta-galactosidase and incubated for as long as 24 h. The presence of lacZ mRNA. beta-galactosidase protein and enzymatic activity were assayed by reverse transcriptase polymerase chain reaction (rtPCR), immunocytochemistry, and the X-Gal technique, respectively. RESULTS: AAVlacZ directed the expression in human epileptogenic brain of E. coli beta-galactosidase that had functional activity. Expression was observed in < or =5 h and was sustained for as long as the slices were viable. Morphological analysis indicated that neurons were preferentially transfected, and there was no evidence of cytotoxicity. CONCLUSIONS: Our results confirm the feasibility of using AAV vectors to transfer genes into the human CNS and in particular, into neurons. Replacement of the lacZ gene with a functional gene modulating hippocampal neuronal physiology, might allow a localized genetic intervention for focal seizures based on the stereotaxic or endovascular delivery of such a vector system into the appropriate brain region.

Mossy fiber reorganization and its possible physiological consequences in the dentate gyrus of epileptic humans.

It is unlikely that MF reorganization is the cause of epilepsy, but it may affect the progression of the disease, i.e., the frequency or severity of seizures. We propose that early events, yet undiscovered, lead to an increased likelihood of excitability. This hyperexcitability, which initially may not be manifested in overt seizures, may erode vulnerable hilar neurons that serve an important inhibitory function, as illustrated in Fig. 6-15. As inhibition is lost, hyperexcitability reaches the level of clinically manifested seizures that are severe enough to lead to substantial loss of hilar neurons. When the loss of these cells is sufficiently high, MF reorganization occurs, first to neighboring hilar neurons and later to dendrites of granule cells (Fig. 6-15). Thus, the functional consequence of MF reorganization may provide a compensatory form of inhibition, as well as a circuit for feedback excitation. Although definitive evidence indicating that MF reorganization contributes to the acceleration or progression of epilepsy is missing, the findings to date are consistent with this hypothesis. In the event that reorganization contributes to the epileptic condition, treatments that reduce indicators of neuropathology may lead to a reduction of seizure frequency and severity. Evidence suggests that reorganization in the dentate gyrus may follow the pathways of neuronal processes of hilar neurons that have died. Thus, further study of the events that guide MF reorganization may hold important clues for developing methods for targeting regenerating axons following central nervous system injury.

Prospects for gene therapy in Parkinson's disease.

Numerous advances in in vivo and ex vivo gene-therapy approaches to Parkinson's disease offer promise for direct clinical trials in patients in the next several years. These systems are predicated on introducing gene that encode enzymes responsible for dopamine biosynthesis or neurotrophic factors that may delay nigrostriatal degeneration or facilitate regeneration. We review the current status of experimental approaches to gene therapy for Parkinson's disease. Comparative advantages and disadvantages of each system are enumerated, and preclinical trials of some of the systems are evaluated. Although the specific in vivo or ex vivo methods used for gene transfer into the brain are likely to be supplanted by newer technology over the next decade, the principles and approaches developed in current studies likely will remain the same.

Hippocampal cell distributions in temporal lobe epilepsy: a comparison between patients with and without an early risk factor.

Neuronal cell distributions were measured for anterior and posterior locations in the hippocampi of epilepsy patients who were seizure-free after temporal lobectomy. Patients were divided into two groups, those with an early risk factor, defined as a neurologic insult occurring in the first 4 years of life, and those with no early risk factor. Early-risk patients had lower hilar cell densities, lower granule cell densities, and fewer granule cells per millimeter, a measured related to total granule cell number, than to early risk patients. Moreover, each risk group had different anteroposterior density gradients for granule cells and hilar cells. These differences in cell distribution may arise from different patterns of cell loss of cell migration in the dentate gyrus during development. In the early-risk group, there was also a distinction between patients with a history of febrile convulsions without CNS infection and patients with a history of meningitis or encephalitis. These two subgroups had similar numbers of granule cells, However, the meningitis/encephalitis subgroup exhibited a wider granule cell layer, suggesting that the granule cell layer was more dispersed. Our results support the hypothesis of a predominantly anterior hippocampal insult in temporal lobe epilepsy (TLE). In nonepileptic hippocampus, the ratio of putatively excitatory granule neurons to putatively inhibitory hilar neurons is highest in the anterior hippocampus. This ratio may explain in part why the anterior hippocampus is more prone to cell loss and seizures.

Longitudinal variation in cell density and mossy fiber reorganization in the dentate gyrus from temporal lobe epileptic patients.

Variation in cell loss and mossy fiber reorganization was examined along the longitudinal axis of the dentate gyrus from temporal lobe epileptic (TLE) patients. Previous evidence has indicated that the anterior hippocampus is prone to seizure activity. We compared granule and hilar cell number in addition to Timm stain density of the molecular layer and hilus in more anterior and more posterior specimens of hippocampus obtained from patients surgically treated for intractable epilepsy by the removal of the anterior half of the hippocampus. Granule cells/mm in the more anterior specimen were less than or equal to those in the more posterior specimen locations in 77% of the patients, while there was no significant difference in hilar neuron density between the two blocks. These results demonstrate a significantly greater pathology in the granule cell layer in more anterior specimens and no difference in pathology for hilar neurons. Molecular layer Timm stain density was significantly greater in the more anterior specimen of 71% of the patients. The molecular layer Timm stain density ratio was inversely related to hilar cell density in more anterior specimens, whereas in more posterior specimens there was no significant relationship with hilar cell density. Our observations show that although differences exist among TLE patients for these neuroanatomic measures, pathology was greater in more anterior specimens. The latter result is consistent with the conclusion that seizure activity may originate in the anterior region of the hippocampus in a majority of patients.

Adult levels of meridional anisotropy and contrast threshold in 5-year olds.

This study, using a forced-choice technique, shows that 5-yr-old children have greater sensitivity for vertical and horizontal sinusoidal gratings than for obliques. Contrast thresholds for all orientations were similar to those of adults as was the magnitude of the meridional anisotropy. These results suggest that meridional anisotropy does not develop over an extended period of childhood as was previously reported (Mayer, 1977). Reasons for the discrepancy between the two studies are discussed.