Calcium Metabolism Profile in Rat Inner Ear Indicated by MRI After Tympanic Medial Wall Administration of Manganese Chloride

Abstract

Objectives:

To evaluate the efficacy of the novel method for the targeted delivery of Mn⁺⁺ to the inner ear and monitor calcium metabolism activity in the inner ear.

Materials and Methods:

Dynamic signal changes of Mn⁺⁺ in the rat inner ear were followed using T₁-weighted magnetic resonance imaging (MRI) after administration of 2.5 µl MnCl₂ (500 mM) to the medial wall of the middle ear cavity.

Results:

Mn⁺⁺ passed through both the oval and round windows and distributed in the perilymphatic compartments, where it formed bright sharp lines along the fluid-cellular borders 12 minutes post administration and entered the endolymph sufficiently after 45 minutes. After 6 hours, the distribution of Mn⁺⁺ shifted from a fluid-dominant pattern to a cell-dominant pattern. Mn⁺⁺ concentrated in the area of the basilar membrane, periphery process, and soma of the spiral ganglion on day 2; became more distinguishable on day 4; declined on day 8; and remained detectable for 16 days post administration.

Conclusions:

The novel targeted delivery method efficiently introduced Mn⁺⁺ into the inner ear. The dynamic distribution pattern of Mn⁺⁺ in the inner ear shown by MRI indicates that this method can be used to monitor calcium metabolism activity in the inner ear.