Time courses of aspartate and glutamate concentrations in the focus area during penicillin induced epileptiform activity in awake rats.

Abstract

1. In 16 awake rats, the time courses of cortical aspartate (ASP) and glutamate (GLU) concentrations were investigated before, during and after penicillin-induced epileptiform activity (PCN-EA). The amino acids were collected by means of the microdialysis technique from a site within the motor cortex located close to the PCN focus. PCN-EA was recorded by means of 12 cortical electrodes. 2. The median time courses of ASP and GLU concentrations demonstrated no relation to the time course of PCN-EA. In contrast, the analysis of individual time courses revealed three response types for both ASP and GLU which could not be related to specific sites within the motor cortex. 3. The ASP concentration was i) not affected by epileptiform activity (8 of 16 rats), ii) changed synchronously with the PCN-EA (3 of 16), or iii) increased transiently or in a long-lasting manner during or after disappearance of PCN-EA (5 of 16). 4. The GLU concentration was i) not effected or only slightly affected by epileptiform activity (5 of 16), ii) decreased strongly during the activity (7 of 16), or iii) increased during the epileptiform activity (4 of 16). 5. If all rats were taken into account, the overall observation was absence of a uniform correlation type between the time courses of ASP and GLU concentrations; i.e. epileptiform activity affects the time courses of ASP and GLU concentrations in an independent manner. 6. These results demonstrate that consideration of median values alone can mask significant effects of epileptiform activity on the biochemistry of the brain in individual animals. The study also shows that a consideration of individual time courses of physiological and biochemical parameters is mandatory for the understanding of basic mechanisms of epilepsy. The results support the hypothesis about the activation of neuroprotective mechanisms by epileptiform activity.