HIGH-RESOLUTION AMS IMAGING OF RADIOCARBON IN BIOMEDICAL APPLICATIONS

Radiocarbon has been an important labelling element in biological meta bolism studies. By interfacing an accelerator mass spectrometer (AMS) with a scanning microprobe secondary ion source, we have imaged the up take of radiocarbon labelled metabolic or neurotransmitter amino acids by neurons and glial cells of rats and gerbils at high resolution (1 micron), high sensitivity and in a short time. The biological samples are prepared and sectioned serially at 0.5 mu m thickness using standa rd histological procedures. The adjacent sections to those used for AM S imaging were either immunolabelled with antibodies to GABA to reveal GABA-containing cells, or stained with toluidine blue to visualise ev ery cell. Therefore, the distribution of radiocarbon revealed by AMS c ould be matched to that of the cells. By simultaneously measuring the C-14, C-13 and C-12 signals, we can demonstrate that the localised pea ks of radiocarbon could be readily identified and matched to GABA-immu nopositive neurons and glial cells by aligning the radiocarbon deficie nt blood vessels with the vessels in the adjacent histologically stain ed section. The results revealed the selective uptake of the neurotran smitter, GABA and that of metabolic amino acid, leucine. The technique compares favourably with high resolution autoradiography and provides great potential for improving the analysis of molecular interactions in and between cells.