Partial Aminoglycoside Lesions in Vestibular Epithelia Reveal Broad Sensory Dysfunction Associated with Modest Hair Cell Loss and Afferent Calyx Retraction.

David R Sultemeier,Larry F Hoffman

doi:10.3389/fncel.2017.00331

David R Sultemeier, Larry F Hoffman

Open Access

https://doi.org/10.3389/fncel.2017.00331

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Abstract

Although the effects of aminoglycoside antibiotics on hair cells have been investigated for decades, their influences on the dendrites of primary afferent neurons have not been widely studied. This is undoubtedly due to the difficulty in disassociating pathology to dendritic processes from that resulting from loss of the presynaptic hair cell. This was overcome in the present investigation through development of a preparation using Chinchilla laniger that enabled direct perilymphatic infusion. Through this strategy we unmasked gentamicin’s potential effects on afferent calyces. The pathophysiology of the vestibular neuroepithelia after post-administration durations of 0.5 through 6 months was assessed using single-neuron electrophysiology, immunohistochemistry, and confocal microscopy. Hair cell densities within cristae central zones (0.5-, 1-, 2-, and 6-months) and utricle peri- and extrastriola (6-months) regions were determined, and damage to calretinin-immunoreactive calyces was quantified. Gentamicin-induced hair cell loss exhibited a profile that reflected elimination of a most-sensitive group by 0.5-months post-administration (18.2%), followed by loss of a second group (20.6%) over the subsequent 5.5 months. The total hair cell loss with this gentamicin dose (approximately 38.8%) was less than the estimated fraction of type I hair cells in the chinchilla’s crista central zone (approximately 60%), indicating that viable type I hair cells remained. Extensive lesions to afferent calyces were observed at 0.5-months, though stimulus-evoked modulation was intact at this post-administration time. Widespread compromise to calyx morphology and severe attenuation of stimulus-evoked afferent discharge modulation was found at 1 month post-administration, a condition that persisted in preparations examined through the 6-month post-administration interval. Spontaneous discharge was robust at all post-administration intervals. All calretinin-positive calyces had retracted at 2 and 6 months post-administration. We found no evidence of morphologic or physiologic recovery. These results indicate that gentamicin-induced partial lesions to vestibular epithelia include hair cell loss (ostensibly reflecting an apoptotic effect) that is far less extensive than the compromise to stimulus-evoked afferent discharge modulation and retraction of afferent calyces (reflecting non-apoptotic effects). Additionally, calyx retraction cannot be completely accounted for by loss of type I hair cells, supporting the possibility for direct action of gentamicin on the afferent dendrite.

Highlights

The vestibulotoxic effects of aminoglycosides became apparent shortly after implementation of streptomycin therapy in the treatment of tuberculosis (Bignall et al, 1951; Robson and Goulding, 1952)
These results indicate that gentamicin-induced partial lesions to vestibular epithelia include hair cell loss that is far less extensive
Cytoarchitecture of the Chinchilla Crista Central Zones The cytoarchitecture of central zone epithelia from non-lesioned chinchilla cristae are presented first to provide the histologic perspective for the balance of the physiologic and morphologic correlates presented in this investigation. This was achieved through quantitative morphometry of normal, vehicle control (HBSS-infused) and contralesion control cristae

Summary

Introduction

The vestibulotoxic effects of aminoglycosides became apparent shortly after implementation of streptomycin therapy in the treatment of tuberculosis (Bignall et al, 1951; Robson and Goulding, 1952). Gentamicin is an agent commonly used in investigations of mammalian vestibular pathophysiology (Imamura and Adams, 2003a,b; Hirvonen et al, 2005; Hong et al, 2006; Day et al, 2007; Lue et al, 2009; Ding et al, 2010; Warchol, 2010a; Bremer et al, 2014; King et al, 2017) These studies have considerable translational value to enhance the understanding of gentamicin’s use in ablative therapy for intractable vertigo associated with Mèniére’s syndrome (Schuknecht, 1956, 1957; Nedzelski et al, 1993; Halmagyi et al, 1994; Minor, 1999; De Waele et al, 2002; Magnusson et al, 2007; Nguyen et al, 2009; Marques et al, 2015; Junet et al, 2016). There is evidence suggesting that type I hair cells, those in cristae central zones and utriclar striolae, are the most sensitive and are the first to be compromised or eliminated after aminoglycoside administration (Wersall and Hawkins, 1962; Lindeman, 1969b; Watanuki et al, 1972; Hirvonen et al, 2005). Lyford-Pike et al (2007) provided evidence indicating that type I hair cells accumulated higher gentamicin concentrations than type II hair cells, supporting the notion that type I hair cells exhibit enhanced susceptibility to gentamicin toxicity than other constituents of the vestibular epithelia

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