Abstracts

RATIONALE: Gamma-aminobutyric acid (GABA) is the most important inhibitory neurotransmitter in the central nervous system. GABA uptake and catabolism may be altered in epileptic patients. GABA transaminase (GABA-T) in blood platelets exhibits characteristics similar to those of GABA-T in the brain. We evaluated now the differences in platelet GABA uptake and GABA-T activity in different epileptic syndromes. METHODS: The blood samples were collected from 20 patients with generalized epilepsy syndromes (GES), 20 patients with refractory localization related epilepsies (RFE) and 20 healthy volunteers. The patients were on a variety of antiepileptic drugs but not on gamma-vinyl-GABA (vigabatrin). The patients and volunteers where matched by age and sex. There were 14 male and 26 female patients with an average age of 32 years, and 7 male and 13 female volunteers with an average age of 35 years. The study was approved by the ethics committee of Tampere University Hospital. GABA-T activity was assessed with carbon-labeled GABA as a substrate and GABA uptake with tritium-labeled GABA as a tracer. RESULTS: GABA-T activity was significantly higher in the GES patients. However, the patients RFE did not differ in this respect from the healthy volunteers. GABA uptake was measured in the concentration range of 5-500 M. The kinetic parameters, maximal velocity and transport constant, were estimated by non-linear regression analysis. GABA uptake was slowest in the GES group and fastest in healthy volunteers. CONCLUSIONS: Marked differences in platelet GABA uptake and metabolism seem to exist between patients with generalized and localization related epilepsies. The observed peripheral alterations may indicate impairment in the function of brain GABAergic systems.