Ultrastructure of the enlarged cecum in germfree rats

Summary The cecum of germfree rats, as studied by light microscopy and scanning and transmission electron microscopy, differs in many respects from the cecum of conventional rats. Epithelial cells in germfree rats are taller and have larger nuclei and longer microvilli than similar cells in conventional rats. The cecal mucosa of germfree rats shows a larger variability in the arrangement of the crypts of Lieberkühn than does the mucosa of conventional rats. Some crypts are funnel-shaped and connected close to the mucosal surface with adjacent similar crypts to form long valleys. Less wide crypts open on elevated regions of the mucosal surface. The lamina propria of germfree animals is devoid of plasma cells but rich in mast cells. Germfree animals show hypertrophy of the tunica muscularis externa.In conventional rats the cecal lumen contains a large variety of morphologically different bacteria. However, the lumen of the crypts of Lieberkühn contains only one type of elongated bacteria, which are present in large amounts. This finding suggests that symbiotic relations may be of particular importance in the crypts of Lieberkühn in the cecum.Supported by research grants from the Swedish Medical Research Council (206), Knut och Alice Wallenbergs Stiftelse and Stiftelsen Therese och Johan Anderssons Minne.