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Delayed ischemic electrocortical suppression during rapid repeated cerebral ischemia and kainate-induced seizures in rat

Authors


Dr Mihai Moldovan, 4Division of Neurophysiology, as above.
E-mail: M.Moldovan@mfi.ku.dk

Abstract

Global cerebral ischemia induces, within seconds, suppression of spontaneous electrocortical activity, partly due to alterations in synaptic transmission. In vitro studies have found that repeated brief hypoxic episodes prolong the persistence of synaptic transmission due to weakened adenosine release. The aim of this study was to investigate in vivo whether the time to ischemic electrocortical suppression (TES) could be altered during energy stress conditions such as rapid repeated global cerebral ischemia and kainate-induced seizures. Experiments were carried out in adult rats under chloral hydrate anaesthesia. Repeated episodes of 1 min of ischemia were induced by transiently clamping the carotid arteries in a ‘four-vessel occlusion’ model. We devised an automatic method of TES estimation based on the decay of the root mean square of two-channel electrocorticographic recordings. To distinguish the alterations in spontaneous electrocortical activity we compared TES with the ischemic suppression of visual evoked potentials (VEP). During the first ischemic episode, TES was ∼ 15 s and remained unchanged when five ischemic episodes were separated by 10-min reperfusion intervals. When ischemia was repeated after 2 min of reperfusion TES progressively increased, reaching a plateau value of ∼ 24 s. A similar plateau was reached during kainate-induced seizures. The TES plateau occurred prior to ischemic suppression of VEP. Our data suggest that, under conditions of acute metabolic stress in vivo, the ischemic suppression of spontaneous electrocortical activity may be delayed up to a plateau value. These findings are consistent with the hypothesis of a depletable adenosine pool; however, the restoration of synaptic transmission may be faster in vivo than in vitro.

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