SUBCELLULAR FRACTIONATION ON PERCOLL GRADIENT OF MESSY FIBER SYNAPTOSOMES - EVOKED RELEASE OF GLUTAMATE, GABA, ASPARTATE AND GLUTAMATE-DECARBOXYLASE ACTIVITY IN CONTROL AND DEGRANULATED RAT HIPPOCAMPUS

Using discontinuous density gradient centrifugation in isotonic Percol l sucrose, we have characterized two subcellular fractions (PII and PI II) enriched in messy fiber synaptosomes and two others (SII and SIII) enriched in small synaptosomes. These synaptosomal fractions were com pared with those obtained from adult hippocampus irradiated at neonata l stage to destroy granule cells and their messy fibers. Synaptosomes were viable as judged by their ability to release aspartate, glutamate and GABA upon Kf depolarization, After irradiation, compared to the c ontrol values, the release of glutamate and GABA was decreased by 57 a nd 74% in the PIII fraction, but not in the other fractions and the co ntent of glutamate, aspartate and GABA was also decreased in PIII frac tion by 62, 44 and 52% respectively. These results suggest that messy fiber (MF) synaptosomes contain and release glutamate and GABA. Measur ement of the GABA synthesizing enzyme, glutamate decarboxylase, exhibi ted no significant difference after irradiation, suggesting that GABA is not synthesized by this enzyme in messy fibers.