Several studies demonstrated the existence of marked changes in pH, potassium and cerebral blood flow during the activation of epileptiform discharges. The sequential correlation between changes in neuronal activity, extracellular ionic changes and modifications in blood flow has never been investigated in detail. We performed a preliminary study to test the possibility to approach this problem in the the isolated guinea pig brain preparation. Epileptiform interictal and ictal discharges were induced in the piriform and entorhinal cortex by application of bicuculline, applied either by local intracerebral ejection or by arterial perfusion. Conventional extracellular recordings were performed simultaneously to extracellular pH and potassium measurements with ionselective electrodes. An indirect measurement of cerebral blood flow was obtained by recording the changes in vascular tone via a pressure transducer positioned along the perfusion line, below the perfusion cannula inserted in the basilar artery. The preservation of the arterial and endothelial functions is demonstrated by the ability of the cerebral vessels to constrict in the presence of vasoactive drugs (such as noradrenaline and tromboxane A2 agonists) and to dilate via nitric oxide release when perfused with acethylcholine. During interictal discharges (single spikes or short afterdischarges) we observed a simultaneous extracellular increase in potassium concentration and an alkalinization. No changes in vascular tone could be detected. During ictal discharges the potassium increase was coupled with an early extracellular alkalinization followed by a pronounced and lasting acidification. A vasodilation was consistently observed during ictal events. Its onset preceded the onset of the extracellular acidification. Laminar profiles of field potential, pH and potassium performed in the piriform cortex demonstrated a non-homogeneous distribution of pH shifts within cortical layers. These preliminary results demonstrate that it is feasible to study the temporal correlation between changes in the extracellular environment and vascular responses in the isolated brain preparation, during epileptiform events.
|Number of pages||1|
|Journal||Italian Journal of Neurological Sciences|
|Publication status||Published - 1999|
ASJC Scopus subject areas
- Clinical Neurology