Efflux of GABA, glutamate and glutamine from the brain: A mass fragmentographic Study

Abstract

GABA, glutamate (GL) and glutamine (GLN) were measured by a mass-fragmentographic method in Ringer solutions filling epidural cups of freely moving rats and in cortical cups of urethane anaesthetized rats. The presence of the dura and the administration of uretane (1 g/kg) did not modify the efflux of GABA from the cerebralcortex. However the release of GL was reduced by the presence of the dura and by the administration of the anesthetic. Intracerebroventricular administrations of aminooxyacetic acid increased the brain GABA levels and its efflux from the cerebral cortex without any modification of the blood GABA concentration. The addition of KC1 (50 mM) to the cortical cups was followed by a dramatic increase in the efflux of GABA and by a parallel decrease in the efflux of glutamate and glutamine. Opposite effects were observed in animals with intact dura. The results suggest that GABA and glutamate are released from cellular structures within the brain and that their release may be inversely correlated.