Electron microscopy of degenerative changes in the chick basilar papilla after gentamicin exposure

Abstract

We present a sequential study of the substructural alterations in the chick basilar papilla at the earliest signs of hair cell degeneration. Three-day posthatch chicks received a single injection of gentamicin (300 mg/kg) and were killed at 6, 8, 12, 15, 18, 21, and 24 hours after the injection. The basilar papillae were studied by conventional transmission electron microscopy. Examination was limited to the basal region, where all hair cells are eliminated by this treatment. As early as 8 hours and clearly by 12 hours, altered fine structure was seen in hair cells. Changes included rounding and swelling of the hair cells, condensation of nuclear chromatin, dissolution of ribosomes, dilatation of the mitochondria, and accumulation of inclusion bodies and lysosomes. By 15-18 hours, lysosomes increased and became denser, afferent terminals appeared swollen, and the first cell extrusion was seen. Efferents were unaffected, and supporting cells, though having inclusion bodies now, retained normal intercellular junctions. By 21-24 hours, large regions of complete hair cell loss were composed of expanded supporting cell processes with normal-appearing intercellular junctions and portions of extruded hair cells, partially attached to the supporting cell surface. These observations demonstrate that auditory hair cells undergo a rapid and controlled process of hair cell extrusion that allows preservation of the reticular lamina and minimal contamination of surrounding structures by intracytoplasmic contents of the damaged hair cells.

Disruption and restoration of cell–cell junctions in mouse vestibular epithelia following aminoglycoside treatment

“…In contrast to the present Wndings, no disruptions in the epithelial cell junctions following aminoglycoside treatment have been observed in previous studies Forge and Li, 2000;Hirose et al, 2004). This may be associated with the diVerence in drug application routes; local application of aminoglycoside into the inner ear was used in the present study, while previous studies used systemic application.…”

Fluorescent aminoglycosides reveal intracellular trafficking routes in mechanosensory hair cells

“…Lastly, we evaluated whether lysosomes are enriched in Neo-TR. In HCs of the neonatal chick, accumulations of injected kanamycin were previously found in lysosomes identified by acid phosphatase cytochemistry (52), and dramatic increases in the density of lysosomes following gentamicin exposure are seen in chick hair cells prior to hair cell death (53,54). We assessed whether Neo-TR was present in lysosomes labeled with the vital dye LysoTracker Green.…”

How to Bury the Dead: Elimination of Apoptotic Hair Cells from the Hearing Organ of the Mouse

“…In some cases, only the apical portions of hair cells are extruded (Cotanche and Dopyera 1990;Gale et al 2002;Hirose et al 2004;Hordichok and Steyger 2007;Bird et al 2010). Decapitation is a predominant mechanism of hair cell elimination in the adult organ of Corti (Forge 1985).…”