GABA-A STIMULATION IN NORMAL VOLUNTEERS A ND DURING TEMPORAL EPILEPSYMEASURED BY (18)FDG WITH POSITRON EMISSION TOMOGRAPHY

The gamma-amino butyric acid (GABA) is the principal inhibitory neurot ransmitter of the brain and it has been evoked in epileptogenesis. Usi ng a GABA analog, the THIP, we tried to establish if the gabaergic neu rotransmission was modified in the epileptic focus. For this purpose, we measured the effects of this specific GABA agonist on the cerebral glucose consumption (CMRGlu) as measured by 18F-fluoro-deoxyglucose (( 18)FDG) with positron emission tomography (PET).Eight patients present ing temporal epilepsy and three normal volunteers received two (18)FDG PET studies, after placebo and THIP injection, in random order. Clini cal symptoms and electroencephalographic data demonstrated a trend tow ards sleepiness and a diminition of alpha waves after THIP injection. CMRGlu was globally increased with THIP in cortical regions, cerebellu m and caudate nuclei. The average increase was 17% in grey matter whil e it did not reach significancy in white matter. Under the placebo con dition, the asymetry between the focus and the controlateral internal temporal zone was 18% as an average, and reduced significantly to 11% after THIP injection. In the external temporal zones, the asymetry dec reased from 28% to 14%. These results suggest that gabaergic inhibitio n requires energy in the normal brain tissue and in this with temporal epilepy. Since the asymetry of glucose consumption tends to diminish, the inhibitory GABA system appears preserved in temporal epilepsy wit h an enhanced sensitivity in the focus.