A NOVEL METHOD FOR THE VISUALIZATION OF THE IN-SITU MUCUS LAYER IN RAT AND MAN

1, The observed thickness of the gastric mucus barrier varies widely, even appearing discontinuous, depending on the methods used. Here we d escribe the development and application of a modified periodic acid Sc hiff/Alcian Blue staining technique for use on cryostat sections of ga stric mucosa. This technique for the first time enables the preservati on and visualization of the full thickness of the adherent gastric muc us layer and the underlying mucosa. 2, In designing this novel method we have selected those procedures which would result in the least alte ration to the mucus layer. The methods used were snap freezing, cryost at sectioning of the whole stomach followed by brief ethanol pretreatm ent (10 min in 100% ethanol), a prolonged staining with periodic acid Schiff/Alcian Blue (15 min and 2.5 h respectively), a gentle post-fixa tion (45 min paraformaldehyde vapour at 37 degrees C) and the use of a water-soluble mountant. 3. A continuous, adherent mucus layer was obs erved over the surface of the rat gastric mucosa (periodic acid Schiff /Alcian Blue stained) and human gastric antral biopsies (periodic acid Schiff stained). In the rat the mean (S.D.) mucus thickness measureme nts along the antrum to oesophageal axis (which; was divided histologi cally into four regions, A to D) were: A, 166 (47) mu m; B, 179 (48) m u m; C, 184 (50) mu m; D (the non-glandular stratified epithelium at t he top of the stomach), Absent. In human gastric antral biopsies the m ean (S.D.) mucus thickness was 144 (52) mu m. 4, This new technique ha s enabled the visualization and precise measurement of thickness of th e gastric mucus layer in rat and man. The adherent gastric mucus layer was observed to be continuous in the rat glandular stomach and human antrum. In validation experiments in rat the mean mucus thickness meas urements were found to be twice those measured by conventional histolo gical techniques, in which the mucus layer appeared discontinuous and patchy. However, they were within the range of thickness values seen i n unfixed tissues and in the rat in vivo preparation.