Composition Of Perilymph Research Articles

A study of intra-cochlear electrodes and tissue interface by electrochemical impedance methods in vivo

This paper presents methods, results and analysis for measurements of the electrochemical impedance of platinum electrodes (∼0.43 mm 2) over a 6-month implantation in the cat cochlea. The study aimed to improve our understanding of the effects of tissue response on impedance behaviour. An increase in impedance in the post-operative period was evident with a rise of the distorted arc at high frequencies in the complex plane, correlating to anomalous charge transport at the electrode–tissue interface. The impedance at low frequencies generally showed a capacitive dispersion modelled as a constant phase element, indicating a blocking characteristic of the electrodes. The study suggests that a reduction and changes in composition of perilymph or extracellular fluid adjacent to the electrodes, as a consequence of tissue response, causes the elevated “contact impedance”. This affects the efficiency and quality of neural stimulating electrodes and neural recording electrodes. The finding of the crucial role of perilymph or extracellular fluid thin layer provides a new strategy for surface materials of neural electrodes, which is discussed in the paper. The interface characteristics must be considered during interpretation of studies undertaken in vitro or in acute experiments in vivo, where physiological fluid is abundant.

Apical cochlear nerve exposed to perilymph in the gerbil and rat

There is considerable controversy regarding the origin and composition of perilymph in the scala vestibuli and scala tympani and the barriers and transport mechanisms between them. To elucidate the anatomical separation between perilymph and the extracellular fluid which surrounds the cochlear nerve in Mongolian gerbils ( Meriones unguiculatus) and Sprague Dawley rats ( Rattus rattus) we examined the modiolus, osseous spiral lamina and the bone of the perilymphatic scalae using light and electron microscopy. Although the cochlear nerve, spiral ganglion and their extracellular fluid are separated from perilymph by the bone of the modiolus in the middle and basal turns, no bone separates these neural structures from perilymph in the apical turn in the two species examined. Instead, the spiral ganglion and axonal elements of the apical turn were covered by a continuation of the bone lining cell layer of the scala tympani. Gaps between lining cells appeared to provide direct communication between the perilymphatic fluid and the extracellular fluid investing the cochlear nerve. Various authors have described openings in modiolar bone in both the scala vestibuli and the scala tympani. While the bone and cellular covering of the modiolus in the basal middle turns of the cochlea is not presumed to be a complete barrier to fluid exchange between the two scalac and the modiolar canal it can be expected to impose some limitation on the rate of passive diffusion. Therefore our data indicates that in the apical turn of the Mongolian gerbil and Sprague-Dawley rat there may be a more significant communication between perilymph and the extracellular fluid and neural elements of the apical modiolar canal than previously reported.

Effects of Experimental Renal Insufficiency on the Osmotic Pressure and the Biochemical Composition of Perilymph

The biochemical effects of experimental renal insufficiency produced by bilateral nephrectomy on perilymph were studied. Rats were used for the experiments; measurements were carried out at various intervals after nephrectomy. Statistically significant changes in perilymph (osmolality, Na, K, Cl, and urea), and serum (osmolality, urea and creatinine) were found. These findings represent a marked labyrinth alteration, and may partly explain the pathophysiology of labyrinthine disturbances in chronic renal disease.

Biochemical differences between perilymph, cerebrospinal fluid and blood plasma in the guinea pig.

Seven selected biochemical substances were systematically analyzed in perilymph (PL), cerebrospinal fluid (CSF) and blood plasma or serum of anesthetized guinea pigs in order to compare the composition of these fluids with regard to the origin and biochemical nature of PL. Compositional differences between the fluids were expressed by PL/CSF and PL/plasma concentration ratios of the chemical components measured. Contrary to the prevailing notion, the results suggest that the specific biochemical composition of PL corresponds neither to that of CSF nor to that of a simple ultrafiltrate of blood plasma. Furthermore, except for the total protein concentration, no significant differences were found in the composition of PL between the scala tympani and scala vestibuli.

The effect of intracisternally injected ouabain on perilymph electrolyte concentrations.

A means for altering the ionic composition of perilymph utilizing the cochlear aqueduct and cerebrospinal fluid in chinchillas is introduced. A decrease in sodium and an increase in potassium concentration in perilymph was observed after ouabain was injected into cerebrospinal fluid. The time course of changes in the perilymph paralleled the CSF change but with a time lag which had not reached equilibrium within 60 minutes.

Ethacrynic acid effect on the composition of cochlear fluids.

Ethacrynic acid, when administered to six dogs, caused a fall in the concentration of potassium in endolymph from 145 to 21 milliequivalents per liter and a rise in the concentration of sodium from 5.9 to 146 milliequivalents per liter. The composition of perilymph is unaffected. Perilymph and endolymph are slightly hypertonic as compared to plasma.