Concomitant in vivo electrophysiological and voltammetric analysis indicate that ascorbic acid is a biochemical index of early ischaemia.

A number of in vitro studies or in vivo cortical microdialysis measurements have observed that changes in the levels of ascorbic acid (AA), uric acid (UA), tryptophan (TRY), indoles and other compounds may be biochemical markers of cerebral ischaemic damages following occlusion of the rat middle cerebral artery (MCAO). The aim of the present work was to study the influence of early ischaemia upon presynaptic and postsynaptic activities in the cerebral cortex of rats. These activities have been studied by means of electrophysiological and electro-biochemical (voltammetric) measurements performed concomitantly every 5 min and applied with the same biosensor. The biosensor was inserted in the cerebral cortex of anaesthetised adult male rats which were then submitted to focal ischaemia via MCAO. Since changes in electrophysiological activity are considered marker of rise of ischaemia, the choice of simultaneous electrophysiological and electrochemical (voltammetric) analysis could allow the observation of specific biochemical(s) correlation(s) with the initial phase of ischaemia. The data obtained indicated that electrophysiological and voltammetric changes can be monitored simultaneously in the same brain region (i.e. effected by MCAO) by means of a single biosensor with an improved time resolution when compared with previous biochemical in vivo studies. In addition, a high correlation was observed between MCAO reduced functional responses of the neurons monitored by electrophysiology and increased levels of AA measured by voltammetry. This original observation suggests that AA is a biochemical marker of the very early stages of focal ischaemia and could be a useful tool for the evaluation of initial ischaemic damage.