Morphological and histochemical peculiarities of the gut in the white sturgeon, Acipenser transmontanus

The gut of adult sturgeon was examined. The oesophageal mucosa contained nu merous caliciform cells, synthesizing both neutral and acidic glycoconjugat es, the latter of the sialylated type. The deep tunica propria-submucosa co ntained lobules of multilocular adipose tissue, specially abundant during t he cold season. The oesophageal tunica muscularis was made up of a large sh eath of striated muscle fibres, arranged orthogonally to a thin, subserous smooth muscle layer. The siphon-shaped stomach showed a ciliated epithelium in cardiac and gastric proper gland zones, where tubular glands were prese nt in the tunica propria. The columnar cells which composed the superficial epithelium and gastric pits were demonstrated to synthesize almost exclusi vely neutral glycoconjugates. Appendices pyloricae constituted a glandular body equipped with intestinal mucosa. The intestinal mucosa was organized i n folds, containing numerous caliciform cells which synthesized neutral or acidic glycoconjugates, the latter either of the sialylated and sulphated t ype. The sulphoglycoconjugates were more abundant in the caliciform cells o f the distal intestinal tracts. The tunica propria-submucosa of the spiral valve (medium intestine) contained lymphatic tissue and large lymphatic fol licles. A muscularis mucosae was present only in the rectum, where in addit ion a peculiar granular cell type was present in the superficial tunica pro pria-submucosa, possibly related to defensive properties. The subserous con nective tissue contained pancreatic lobules all along the stomach and intes tine. The enteric nervous system showed some special aspects, the most intr iguing of which was the presence of large, longitudinally oriented nerve bu ndles in the t. propria-submucosa of oesophagus and cardiac stomach. The ne rve bundles contained, near unmyelinated nerves, some myelinated nerves, as well as neuronal bodies. Both these aspects are exceptional in vertebrates and obscure in their significance. The structural and histochemical aspect s we here describe are in part different from those described for other fis h. Some of these special features are possibly related with special functio nal roles, others require a deeper insight and different approaches to clar ify them functionally.