rh-795 and Epilepsy

Seizures commonly occur in glioma patients, but their pathogenesis is poorly understood, in part due to a lack of valid and versatile experimental models. We have established a new model that enables comprehensive neuropathological and neurophysiological analysis on identical tissue preparations. Rat C6 glioma cells stably transfected with a green fluorescence protein (GFP) gene are transplanted into rat neocortex, giving rise to diffusely invading gliomas histologically resembling human glioblastomas. After 2 weeks, 500- micro m-thick cerebral slices are prepared, stained with the voltage-sensitive dye RH795, and fluorescence changes associated with origin and spread of abnormal bioelectric activity upon washout of Mg(2+) are detected by a 464-element photodiode array at a rate of 785 frames/s. GFP fluorescence promotes identification of tumor cells during electrophysiological experiments and in neuropathological analyses using frozen and paraffin-embedded tissue sections. By performing subsequent histological analysis of the slices examined neurophysiologically, origin and spread of abnormal activity can be correlated with structural and molecular (immunohistochemical) features. Specifically, we found that ictaform activity was initiated in cortical areas diffusely invaded by single tumor cells. This model is useful for further elucidating the electrophysiological, molecular and structural basis of glioma-associated epileptogenesis.

Topics: Animals; Brain Neoplasms; Disease Models, Animal; Electrophysiology; Epilepsy; Fluorescent Dyes; Glioblastoma; Glioma; Green Fluorescent Proteins; Immunohistochemistry; Luminescent Proteins; Male; Neocortex; Rats; Rats, Wistar; Seizures; Stereotaxic Techniques; Styrenes; Tumor Cells, Cultured

The spatio-temporal distribution of evoked activity in guinea pig neocortical slices was investigated during partial suppression of gamma-aminobutyric acid (GABA)A-mediated synaptic inhibition with different concentrations of bicuculline. Activity patterns were recorded by use of a voltage-sensitive dye and a fast optical recording technique. At non-epileptogenic concentrations of bicuculline (0.6-2.5 microM), evoked potentials were of longer duration and larger amplitude, but the spatial extent of spread in the horizontal direction was unaffected. At threshold epileptogenic concentrations of bicuculline (1.25-5 microM), spatially restricted epileptiform activity developed at a distance from the stimulation site which was clearly separated from potentials with non-epileptic characteristics close to the stimulation site. It is concluded that, under moderate disinhibition, stimulus-evoked activity has a suppressive effect on spread and development of epileptiform activity, probably through synchronous activation of still-functioning inhibitory circuits.

Topics: Animals; Cerebral Cortex; Electric Stimulation; Epilepsy; Evoked Potentials; Fluorescent Dyes; GABA-A Receptor Antagonists; Guinea Pigs; Neural Inhibition; Organ Culture Techniques; Styrenes

The spread of epileptiform activity was monitored in guinea-pig neocortical slices by the use of a voltage-sensitive dye (RH795) and a fast optical recording technique. Epileptiform activity induced by bicuculline methiodide (10-20 microM) and single-pulse stimulation spread from the stimulation site in layer I or in the white matter across most of the slice. Different lesions were made in the slice in order to specify the neuronal connections used for spread in the horizontal direction. In the slice, intracortical connections are necessary for the spread of epileptiform activity, as shown by vertical cuts through all cortical layers but sparing the white matter. Horizontal connections were interrupted by cuts parallel to the axis of pyramidal neurons through either supragranular or infragranular layers. Vertical connections were interrupted by cuts perpendicular to the axis of pyramidal neurons separating supragranular and infragranular layers. Spread of epileptiform activity in the horizontal direction was not hindered by horizontal cuts. Vertical cuts through infragranular layers also did not hinder the spread of epileptiform activity. In contrast, vertical cuts through supragranular layers either abolished completely (nine slices) or delayed significantly (ten slices) the spread of epileptiform activity. The mean delay at the supragranular lesion was 44 ms in layer III and 30 ms in layer V; at the infragranular lesion the mean delay was 2 ms in layer III and 6 ms in layer V. Also, with horizontal cuts, in three out of five slices the velocity of spread was significantly lower in infragranular as compared to supragranular layers. It is concluded that both supra- and infragranular layers if isolated possess the ability to initiate and propagate epileptiform activity independently. However, in the intact slice the influence of the supragranular networks on initiation and propagation of epileptiform activity appears to dominate.

Topics: Animals; Bicuculline; Cerebral Cortex; Denervation; Electric Stimulation; Electrophysiology; Epilepsy; Guinea Pigs; Neural Pathways; Optics and Photonics; Styrenes