Abstract
Correlations between inner ear morphology and auditory sensitivity in the same individual are extremely difficult to obtain for stranded cetaceans. Animals in captivity and rehabilitation offer the opportunity to combine several techniques to study the auditory system and cases of hearing impairment in a controlled environment. Morphologic and auditory findings from two beluga whales (Delphinapterus leucas) in managed care are presented. Cochlear analysis of a 21-year-old beluga whale showed bilateral high-frequency hearing loss. Specifically, scanning electron microscopy of the left ear revealed sensory cell death in the first 4.9 mm of the base of the cochlea with scar formation. Immunofluorescence microscopy of the right ear confirmed the absence of hair cells and type I afferent innervation in the first 6.6 mm of the base of the cochlea, most likely due to an ischemia. Auditory evoked potentials (AEPs) measured 1.5 years prior this beluga's death showed a generalized hearing loss, being more pronounced in the high frequencies. This individual might have had a mixed hearing loss that would explain the generalized hearing impairment. Conversely, based on AEP evaluation, her mother had normal hearing and subsequent cochlear analysis did not feature any apparent sensorineural pathology. This is believed to be the first study to compare two cochlear analysis techniques and hearing sensitivity measurements from AEPs in cetaceans. The ability to combine morphological and auditory data is crucial to validate predictions of cochlear frequency maps based on morphological features. In addition, our study shows that these three complementary analysis techniques lead to comparable results, thus improving our understanding of how hearing impairment can be detected in stranding cases.
Highlights
Correlations between inner ear morphology and auditory sensitivity in the same individual are extremely difficult to obtain for cetaceans
There is some degree of acoustic crosstalk between the two ears with this arrangement, it is likely that the Auditory evoked potentials (AEPs) are dominated by activity from by the ear closest to the jawphone, especially at threshold [11,12,13]
This type of projector is commonly used in AEP threshold audiometry with odontocete cetaceans, and threshold data obtained with jawphones produce audiograms that are comparable, especially in shape and high-frequency hearing limit, to those obtained underwater in a direct field [14]
Summary
Correlations between inner ear morphology and auditory sensitivity in the same individual are extremely difficult to obtain for cetaceans. Previous studies on hearing loss in humans and terrestrial mammals have demonstrated structural alterations of the organ of Corti (or hearing organ) and associated innervation These lesions have been attributed to mechanical damage and metabolic fatigue of the sensory cells and associated with highintensity and/or long-duration sound exposure [1], exposure to ototoxic drugs, genetic, infectious (bacterial and viral), and geriatric processes [2]. The presence of scarring among hair cell rows is an important criterion to assess for any possible history of hearing loss These scars can be differentiated from artifactual exfoliation of hair cells that occurs with autolysis [7, 8]. When the differentiated supporting cells are absent, the basilar membrane is covered by a layer of simple squamous or cuboidal epithelia, termed “flat epithelium” [9]. It is unclear whether the flat epithelium represents de-differentiated supporting cells or cells that migrated from adjoining regions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
