Elemental composition of the developing inner ear.

The elemental composition of the inner ear fluid-filled compartments has been analyzed using the x-ray energy dispersive technique (CBA mouse). Special attention has been focused on the maturation of endolymph. A few days before and after birth the relative peak intensity of potassium (RK) in the vestibular endolymphatic compartment was slightly surpassing that in the cochlear part of the labyrinth. From the fourth day after birth (DAB) a rapid increase occurred concerning the RK. The highest RK was found in the endolymphatic space in the basal part of the cochlea followed by that in the vestibular endolymph. The lowest RK was measured in endolymph of the apical part of the cochlea. These obvious differences were abandoned already on the sixth DAB. A mature composition of endolymph was reached on the eighth DAB. The present technique does not allow analyses of differences between cochlear and vestibular endolymph with regard to minimal shifts.