[The vessels of the inner ear (author's transl)]

Kinetic experiments with radionuclides concerning the perilymph-blood barrier in a guinea pig model

Since 1950 many animal radiotracer experiments have been performed to study inner ear kinetics. For the most part in these studies, radionuclides were applied systemically, following which a discontinuous probing of inner ear fluids or of inner ear tissues was done. Two techniques have been developed in the Section for Experimental Otorhinolaryngology of the University of Würzburg. These have been adapted to the direct and continuous measurements of inner ear efflux kinetics for several hour periods. For this purpose, only a tiny amount of radiotracer need be applied directly to the inner ear. Experiments were done on the anesthetized guinea pig as an animal model. In the first technique, a collimator-detector system is focused precisely on the cochlea, which had been quickly resealed after application of the radionuclide bolus via two small holes in the basal turn of the cochlea. The second technique makes use of a perilymph cycling system, whereby a small outer volume includes a microcuvette with a so-called artificial round window. By this latter cycling technique, perilymph clearance kinetics of all kinds of radiotracers--with the exception of tritium labelled ones--can be measured. Calculations from clearance kinetics show that quite small particles with particle weights up to 100, such as the chlorine anion and the potassium cation, as well as urea, glycerol, pyruvate, and lactate, exhibit perilymphatic half-lives varying from 45 to 60 min. These half-live data are plausible in regard to cochlear blood flow measured previously via an independent technique developed by Angelborg et al.(ABSTRACT TRUNCATED AT 250 WORDS)

[The effect of alpha receptor-blocking agents on inner ear function (author's transl)]

Nicergolin is used in the treatment of tinnitus, cerebral insufficiency, and sensorineural hearing loss. An increase of cerebral blood flow was observed after i.v. injection of Nicergolin (0.1 mg/kg). The effect of this drug on the inner ear was studied by measuring the DC potential and K+ activity in the endolymph. A rapid fall of the DC potential and hypocapnea were observed after the injection of Nicergolin (0.2 mg/kg). An increase of expiratory PCO2 (10-20 mm Hg) was also observed. Arteficial respiration with pure oxygen prevented the fall of the DC potential. The present investigation demonstrates that this drug primarily acts on the respiratory center with secondary PCO2 increase in the blood which then causes the dilatation of cerebral vessels. The fall of the DC potential after the injection of Nicergolin appears to be caused by hypoxia and not by direct effect on the inner ear.

The blood vessels of the limbus spiralis

The capillaries of the spiral limbus in the cochlea of the laboratory rat were investigated under light and electron microscopy. A stereological examination of the capillary volumes of specimens injected with horseradish peroxidase was performed. The volume of capillaries amounted to 2.87%, and, as such, is very high. The ultrastructure of the capillaries showed continuous endothelial cells and basal laminae, discontinuous pericytes and varying relations towards the surrounding tissue. Morphological criteria, such as microvilli and plasmalemmal vesicles, suggest a significant transendothelial transport. The causes for the abundance of vessels in the spiral limbus are discussed: the transport of oxygen to the perilymph and the need of substances for the formation of the tectorial membrane seem to be important factors. The transport processes are obviously controlled by the endothelial cells as well as by the spiral limbus cells.