THE SPONTANEOUS AND ELECTRICALLY EVOKED RELEASE, FROM SLICES OF GUINEA‐PIG CEREBRAL CORTEX, OF ENDOGENOUS AMINO ACIDS LABELLED VIA METABOLISM OF d‐[U‐14C]GLUCOSE

Publisher Website
Google Scholar
Abstract
Abstract— In an effort to identify neurotransmitters in slices of guinea‐pig cerebral cortex, a study was made of the release of endogenous amino acids which had become labelled via metabolism of d‐[U‐14C]glucose. While incorporation of 14C into endogenous glutamate, aspartate, GABA, alanine and threonine‐serine‐glutamine (unseparated) was large enough to permit measurement of their release, that into other amino acids was not. In parallel experiments, the release of exogeneous labelled glutamate, aspartate, GABA and α‐aminoisobutyrate was examined. Electrical field stimulation evoked a transient increase in the release of all the adequately labelled endogenous amino acids and all the exogenous amino acids. The stimulated ‘increase’ in the release of each of the endogenous 14C‐labelled transmitter candidates (glutamate, aspartate and GABA) was larger than that of any other amino acid (except that of exogenous GABA). When the experiments were performed without the glucose (5 mm) usually present in the medium bathing the slices, larger amounts of each labelled amino acid were released from the slices than in the presence of glucose. Moreover, the pattern of selective release of the endogenous labelled transmitter candidates was much more pronounced in the absence of glucose. It is likely that in the absence of glucose, release from the tissue was larger because cells in the slice were relatively depolarized and uptake of amino acids into cells was impaired. Because previous evidence suggests that over 90% of glucose consumption occurs in the ‘large metabolic compartment’ which is thought to be composed of neuronal elements, neurons were probably the main site from which the larger release of endogenous 14C‐labelled transmitter candidates was evoked. The exogenous amino acids were probably released from several cellular elements in the slices. It was concluded that the pattern of a selective release of the endogenous labelled transmitter candidates may have been indicative of a transmitter releasing mechanism in nerve terminals.