Description of Cochlear Morphology and Hair Cell Variation in the Beluga Whale

Abstract

Environmental change and decreased ice cover in the Arctic make new areas accessible to humans and animals. It is important to understand how these changes impact marine mammals, such as beluga whales (Delphinapterus leucas Pallas, 1776). Hearing is crucial in the daily lives of cetaceans. Consequently, we need normal baselines to further understand how anthropogenic noise affects these animals. Relatively little is known about the inner ear morphology of belugas, particularly the organ of Corti, or hearing organ, found within the cochlea. The base of the cochlea encodes for high-frequency sounds, while low frequencies are detected in the apex. We showed differences between the apex, or centremost point of the cochlea, and the base, the region closest to the stapes. Our results showed that average outer hair cell density changed from 148 cells/mm in the apex to 117 cells/mm in the base. Cell width varied between the two regions, from 5.8 μm in the apex to 8.4 μm in the base. These results revealed variation throughout the cochlea, and thus the need to understand the basic morphology, to give further insight on hearing function in belugas and allow us to recognize damage if or when we find it.

Ultrastructure of the organ of Corti in harbor seals (Phoca vitulina)

“…The results for width of the reticular lamina and distances between hair cell rows showed a significant decrease from apex to base (Figure 5A). This decreasing pattern and the values obtained coincide with previous studies of the organ of Corti in mammals (Lim, 1986;Roth et al, 1992;Girdlestone et al, 2017).…”

“…Decreasing OHC density along the cochlear spiral was found from the apex area (19 cells/100 µm) to the 85% location (10 cells/ 100 µm). This decreasing trend in cell density with proximity to the spiral base is consistent with observations for other mammalian species and is associated with changes in OHC morphology depending on location in the cochlear spiral (U ́lehlováet al, 1987;Burda and Branis, 1988;Vater and Kössl, 2011;Girdlestone et al, 2017). In Ind5A, a peak of increased cell number was found at the 95% location of the cochlear spiral.…”

Cochlear apical morphology in toothed whales: Using the pairing hair cell—Deiters' cell as a marker to detect lesions

“…There are some studies of the cochlear sensory epithelium in toothed whales (Girdlestone et al, 2018; Morell et al, 2015; Morell et al, 2017; Morell, Raverty, et al, 2020; Morell, Vogl, et al, 2020; Wever, McCormick, Palin, & Ridgway, 1971a, 1971b; Wever, Ridgway, Palin, & McCormic, 1972) focusing on describing anatomical features, structural adaptations and morphometric variations of the organ of Corti along the cochlear spiral in harbor porpoises ( Phocoena phocoena ), striped dolphins ( Stenella coeruleoalba ), bottlenose dolphins ( Tursiops truncatus ), Atlantic white‐sided dolphins ( Lagenorhynchus acutus ), and beluga whales ( Delphinapterus leucas ). However, to the best of our knowledge, no previous reports have described the arrangement of hair cells in the apex of the cochlea.…”

Neuroanatomy of the Cetacean Sensory Systems

“…Detailed descriptions of the cochlear morphology using light microscopy were conducted for bottlenose dolphin and Pacific white-sided dolphin [ 67 , 68 , 69 , 70 ], while the cochlear fibres in diverse species [ 71 ] and features of the basilar membrane in different odontocete species have been compared and related to their hearing capabilities [ 72 , 73 , 74 ]. Morphological description of the ultrastructure of the cochlea and associated innervation from several species of odontocetes using electron [ 75 , 76 , 77 , 78 , 79 ] and confocal microscopy [ 79 , 80 , 81 ] were presented. Unique ultrastructural features of the sensory cells and supporting cells of the organ of Corti of odontocetes are found in the basal turn of the cochlea, where the high frequencies are encoded [ 76 , 77 ].…”