ULTRASTRUCTURE OF THE ENDOLYMPHATIC DUCT IN THE RAT - FIXATION AND PRESERVATION

Ten rats were vascular-perfused at subphysiologic as well as physiolog ic pressures, 80 mmHg and 120 mmHg, respectively, employing a pressure feed-back controlled peristaltic pump and an isotonic perfusate/fixat ive with colloids (2% Dextran) and a hypertonic perfusate/fixative wit hout colloids, 300 and 530 mOsm, respectively. In both experiments the endolymphatic duct and sac were isolated by microdissection after pri mary fixation. When comparing micrographs from the two experiments we observed that rats perfused at low pressure in isotonic fixative with colloids added had non-dilated lateral intercellular spaces and a sube pithelial ground substance loaded with uniformly arranged microfibrils , not previously discovered. In rats perfused at high pressure in hype rtonic fixative with no colloids added, we observed an edematous state in the subepithelial space between the solid bony aqueduct and the en dolymphatic duct, with a concomitant derangement of previously well or ganized microfibrils. Furthermore, the epithelium was quite clearly di splaced from the capillaries, the intercellular spaces were widely dil ated and the endolymphatic duct was compressed into its lumen. Methods of fixation and current theories of endolymph resorption by the endol ymphatic duct are discussed.