Transplantation of mouse embryonic stem cells into the cochlea of an auditory-neuropathy animal model: effects of timing after injury

Application of ouabain to the round window membrane of the gerbil selectively induces the death of most spiral ganglion neurons and thus provides an excellent model for investigating the survival and differentiation of embryonic stem cells (ESCs) introduced into the inner ear. In this study, mouse ESCs were pretreated with a neural-induction protocol and transplanted into Rosenthal's canal (RC), perilymph, or endolymph of Mongolian gerbils either 1-3 days (early post-injury transplant group) or 7 days or longer (late post-injury transplant group) after ouabain injury. Overall, ESC survival in RC and perilymphatic spaces was significantly greater in the early post-injury microenvironment as compared to the later post-injury condition. Viable clusters of ESCs within RC and perilymphatic spaces appeared to be associated with neovascularization in the early post-injury group. A small number of ESCs transplanted within RC stained for mature neuronal or glial cell markers. ESCs introduced into perilymph survived in several locations, but most differentiated into glia-like cells. ESCs transplanted into endolymph survived poorly if at all. These experiments demonstrate that there is an optimal time window for engraftment and survival of ESCs that occurs in the early post-injury period.

Scanning electron microscopic observations on the distended Reissner's and saccular membranes in the guinea pig

The surface ultrastructures of membranous labyrinths in normal and hydropic guinea pig inner ears were studied. In normal specimens differences between Reissner's and saccular membranes were observed. The endolymphatic epithelial cells of the saccule were smaller in size and their microvilli varied more in size and distribution. Mesothelial cells of the saccule were often spherical in shape and bulged toward the vestibule. In hydropic guinea pig inner ears, distension of Reissner's and saccular membranes occurred by irregular enlargement of epithelial cells. Microvilli were reduced in size and number. On the severely distended Reissner's membrane, outpouchings, infoldings and holes were observed. Transmission electron microscopic examination revealed no significant difference between the tight junctions of epithelial cells in normal or hydropic Reissner's membranes. Mesothelial cells of Reissner's membrane were more severely degenerated than those of the saccule. Cochlear sensory cells were often degenerated in the apical turn where mesothelial cells were lacking, but saccular sensory cells showed very little change in their surface structures.

Ca(2+) regulation of endocochlear potential in marginal cells

We examined the effect of the cytosolic Ca(2+) concentration ([Ca(2+)](c)) in marginal cells on the asphyxia- or furosemide-induced decrease in the endocochlear potential (EP) by perfusing the endolymph with or without a Ca(2+) chelator or inhibitors of Ca(2+)-permeable channels or Ca(2+)-pump during transient asphyxia or intravenous administration of furosemide. We obtained the following results. (1) Endolymphatic administration of SKF96365 (an inhibitor of TRPC and L-type Ca(2+) channels) or EGTA-acetoxymethyl ester (EGTA-AM) significantly inhibited both the transient asphyxia-induced decrease in EP (TAID) and the furosemide-induced decrease in EP (FUID). (2) Endolymphatic perfusion with nifedipine significantly inhibited the TAID but not the FUID. (3) The recovery from the FUID was significantly suppressed by perfusing the endolymph with EGTA-AM, nifedipine, or SKF96365. (4) Endolymphatic administration of thapsigargin inhibited both the FUID and TAID. (5) The recovery rate from the FUID was much slower than that from the TAID, indicating that furosemide may inhibit the Ca(2+)-pump. (6) A strong reaction in immunohistochemical staining for TRPC channels was observed in the luminal and basolateral membranes of marginal cells. (7) A positive staining reaction for the gamma subunit of epithelial Na(+) channels was observed in the luminal and basolateral membranes of marginal cells. (8) Positive EP was diminished toward 0 mV by the endolymphatic perfusion with 10 muM amiloride or 10 muM phenamil. Taken together, these findings suggest that [Ca(2+)](c) regulated by endoplasmic Ca(2+)-pump and Ca(2+)-permeable channels in marginal cells may regulate the positive EP, which is partly produced by the diffusion potential of Na(+) across the basolateral membrane in marginal cells.

Electrochemical potentials and potassium concentration profiles recorded from perilymph, endolymph and associated inner ear tissues in adrenalectomized rats

This study evaluated the electrochemical potentials and potassium concentration (Ck+) profiles in the perilymph, endolymph, marginal cells, and spiral ligament of adrenalectomized rats in which endogenous corticosteroids had been removed. Electrochemical potentials recorded at the four cochlear sites were not affected by adrenalectomy (ADX). Ck+ was greater in the endolymph of the ADX animals as compared to control animals. Additionally, there was an increase of Ck+ in the marginal cells, perilymph, and spiral ligament tissues of the ADX animals as compared to control animals, although the observed increases were not statistically significant. In a previous study (Ma et al., 1995a), it was found that potassium levels in the blood plasma of ADX animals were higher than those identified in normal rats; thus, ADX may have a systemic effect on Ck+ that is detectable in both tissues and fluids within the cochlea. Even though Ck+ was elevated within the cochlea in the ADX model, the functional response of the inner ear, as assessed electrophysiologically, was not altered.

Endocytosis and transepithelial transport of endolymph in the endolymphatic sac

The fate of cationized ferritin (CF) injected into the endolymphatic space of the endolymphatic sac was observed by transmission electron microscopy. At 10 min after the injection, CF particles bound to the apical plasma membrane of epithelial cells of the sac and were then endocytosed with coated pits. However, they never passed through the junctional complexes between the epithelial cells. At 30 min after the injection, the CF particles were transferred to endosomes and lysosomes by small vesicles of 100-150 nm in diameter. CF particles were also found in small vesicles close to Golgi cisternae and in multivesicular bodies. Acid phosphatase positive lysosomes were found close to endosomes containing CF particles. In addition, a small fraction of the small vesicles containing CF particles became inserted into the basolateral plasma membrane. At 60 min after the injection, many CF particles were found in acid phosphatase positive secondary lysosomes. These observations suggest that endocytosis of endolymph is actively performed by the epithelial cells of the sac, and transepithelial vesicular transport across the epithelial cells occurs.

Ultracytochemical localization of Na+, K(+)-ATPase activity in the tegmentum vasculosum of the developing chick cochlea

We studied the morphological changes and the precise localization of Na+, K(+)-ATPase activity in the developing chick tegmentum vasculosum (TV) with a cytochemical method utilizing K(+)-p-nitrophenylphosphatase (K(+)-NPPase). At stage 37, epithelial folds (lamellae) were relatively well developed, and the light and the dark cells were clearly identified. At stage 41 to 42, Na+, K(+)-ATPase activity appeared in the folded cytoplasmic processes of the dark cells which interdigitated with those of the light cells. The present results indicate that the TV is involved in the production of the cochlear endolymph prenatally (at least up to stage 41), and that the dark cell plays a central role in the maintenance of the ionic composition of the endolymph.

[The pathogenesis of the acute symptoms of Menière's disease (author's transl)]

The pathogenesis of vertigo attacks and hearing fluctuations in Menière's disease is discussed on the basis of new electronmicroscopic observations on the perilymph endolymph barrier. The zonulae occludentes (z.o.) of the epithelial cells lining the endolymphatic space are the main sealing elements which control the passive ion transport. They consist of parallel running intramembranous fibrils (cell membrane fusion lines). Recent investigations demonstrated conditions which partially destruct some of such fibrils (e.g. increased osmotic pressure, endocrine disorders). This also may be true in Menière's attacks: tight z.o. are transformed to leaky z.o. such that a high transepithelial ion exchange developes. This would result in reduced generation of the receptor potentials as well as in decreased activities of the first order afferent neurons as it was supposed earlier by other authors. This mechanism may be combined with a decompensation of active ion transport processes due to microcirculation disturbances. Finally it will be pointed out that true ruptures of the endolymphatic walls cannot be the usual mode of reversible lesions in Menières disease but a diffuse leakage of the perilymph-endolymph barrier.