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gold particles of different sizes (5, 20 and 4Onm). We have been able to localise insulin, together with glucagon, somatostatin or pancreatic polypeptide to separate cells in normal pancreatic islets of man and other mammals. In addition, C-peptide, which is a component of pro-insulin, has been localised to a morphologically distinct sub-population of secretory granules in B-cells of normal pancreas and also in insulinomas. We have also localised VIP and substance P to separate nerve terminals within one tissue section thus confirming the heterogeneous nature of the enteric peptidergic nervous system. Phe development of such a double staining method at the EM level will facilitate studies on the co-existence of peptides with classical neurotransmitters and hormones in single cells or nerve terminals, and also demonstrate the topographic distribution of pro-hormones and their smaller bioactive molecules within single organelles.

IDENTIFICATION OF ENTEROCHROMAFFIN (EC) CELLS WITH DIFFERENT STAINING TECHNIQUES. G.M. Portela-Gomes, L. Grimelius. Department of Pathology, Uni- versity of Uppsala. Sweden.

Three staining reactions - argentaffin reaction (modified Masson technique), formaldehyde-induced fluorescence (FIF) and serotonin i~unoreactivity - were compared with restaining technique in human and rat gastrointestinal mucosa. In the intestinal mucosa virtually the same cells showed a positive reaction with the three staining methods, but sometimes serotonin im~nunoreac- tivity was seen in a larger cytoplasmic area than the other two staining reactions. In antral mucosa, one cell population showed staining reactions similar to those described above, but there were also cells with serotonin immunoreactivity but no FIF-argentaffin reaction and a small cell population which had a FIF-argentaffin reaction but no serotonin immunoreactivity. This discrepancy between the FIF-argentaffin reaction, on the one hand, and the immunocytochemical reaction on the other, was more apparent in rat than in man. The discrepancy in staining reactions will be discussed. Conclusions: The three staining techniques can be used to visualize the EC cells in the intestinal mucosa both in man and the rat. However, in the antrum three cell populations are distinguishable from their staining characteristics. In this region it is better to avoid the term EC cells and instead use terms based on the staining reactions.

IMMUNOHISTOCHEMICAL STUDIES OF THE PANCREACTIC GABA SYSTEM

Steven R. Vincent, Tomas HSkfelt and Jang-Yen Wu, Department of Histology, Karolinska Institutet, S-I04 01 Stockholm, Sweden.

In the brain, the amino acid y-aminobutyrate (GABA) appears to be the major inhibitory neurotransmitter. GABA has been thought to be confined to the central nervous system in vertebrates since its discovery there in 1950. Recently, however, biochemical studies have demonstrated high concentrations of GABA and its synthesizing enzyme glutamate decarboxylase (GAD) in the pancreatic islets of Langerhans. In the present study we have examined the location of this pancreactic GABA system using indirect immunofluorescence with specific antibodies raised against purified mouse brain GAD. In sections of rat pancreas, intense GAD immunoreactivity was observed within the islets, but not in nerve fibres or exocrine tissue. The GAD-positive cells were confined to the center of the islets and appeared to correspond to the B-cells. By comparing the localization of GAD immunoreactivity with that of somatostatin (D-cells), gastric inhibitory polypeptide (A-cells) and pancreatic polypeptide (F-cells), it was found that only the 8-cells were GAD-positive. This indicates that the insulin cells have the capacity to