FATE OF l‐GLUTAMATE IN THE BRAIN

It is shown, using aminooxyacetate as metabolic inhibitor, that the process of oxidation of endogenous glutamate in incubated rat brain cortex slices follows a different course from that of exogenous l ‐glutamate. Whereas endogenous glutamate is largely oxidized by an initial reaction with glutamate dehydrogenase with release of ammonia, exogenous l ‐glutamate undergoes initial transamination to aspartate and α‐oxoglutarate before oxidation occurs. In the presence of 2·5 m m l ‐glutamate, it is found that, of the total exogenous glutamate utilized, 49 per cent is converted to aspartate, 37 per cent is converted to glutamine and the rest is f uily oxidized through glutamate dehydrogenase. It is suggested that endogenous glutamate is normally oxidized in the neurons, and that glutamate released from neurons during excitation, and acting therefore as exogenous glutamate, is taken up by the glia where, besides conversion to glutamine, it largely undergoes initial transamination before oxidation takes place.