Abstract
Simple SummaryCongenital hearing loss (i.e., hearing impairment present at birth) is recognized in humans and other terrestrial species, but there is a lack of information on congenital malformations and associated hearing loss in pinnipeds (seals, sea lions, and walruses). Baseline knowledge on marine mammal inner ear malformations is essential to differentiate between congenital and acquired abnormalities, which may be caused by infectious agents, age, or anthropogenic interactions, such as noise exposure. Analysis of the cochlea of a neonate harbor seal (Phoca vitulina) revealed bilateral loss of inner hair cells (sensory cells responsible for transducing the auditory signal) while the outer hair cells (sensory cells responsible for sound amplification and frequency selectivity and sensitivity) were intact. The selective inner hair cell loss (up to 84.6% of loss) was more severe in the basal turn, where the high frequencies are encoded. Potential causes and consequences are discussed. This is the first report of a case of selective inner hair cell loss in a marine mammal neonate, likely congenital.Congenital hearing loss is recognized in humans and other terrestrial species. However, there is a lack of information on its prevalence or pathophysiology in pinnipeds. It is important to have baseline knowledge on marine mammal malformations in the inner ear, to differentiate between congenital and acquired abnormalities, which may be caused by infectious pathogens, age, or anthropogenic interactions, such as noise exposure. Ultrastructural evaluation of the cochlea of a neonate harbor seal (Phoca vitulina) by scanning electron microscopy revealed bilateral loss of inner hair cells with intact outer hair cells. The selective inner hair cell loss was more severe in the basal turn, where high-frequency sounds are encoded. The loss of inner hair cells started around 40% away from the apex or tip of the spiral, reaching a maximum loss of 84.6% of hair cells at 80–85% of the length from the apex. Potential etiologies and consequences are discussed. This is believed to be the first case report of selective inner hair cell loss in a marine mammal neonate, likely congenital.
Highlights
Introduction conditions of the Creative CommonsProfound congenital hearing loss is present in 1–3 children out of 1000 [1,2]
Half of all the non-genetic causes of congenital hearing loss are attributed to infectious pathogens, including Toxoplasma gondii, rubella, cytomegalovirus, herpes, and syphilis infections
The organ of Corti in mammals is formed by sensory cells that are typically arranged in one row of inner hair cells (IHCs) and three parallel rows of outer hair cells (OHCs)
Summary
Introduction conditions of the Creative CommonsProfound congenital hearing loss (i.e., hearing impairment present at birth) is present in 1–3 children out of 1000 [1,2]. Around 50 to 60% of cases of congenital hearing loss are due to a genetic etiology, while the remainder may be attributed to environmental. Half of all the non-genetic causes of congenital hearing loss are attributed to infectious pathogens, including Toxoplasma gondii, rubella, cytomegalovirus, herpes, and syphilis infections. Within these infectious agents, congenital cytomegalovirus is the most common cause of non-hereditary sensorineural hearing loss in childhood [2]. The organ of Corti (hearing organ) in mammals is formed by sensory cells that are typically arranged in one row of inner hair cells (IHCs) and three parallel rows of outer hair cells (OHCs). Low frequencies are encoded in the apex (apical region or tip of the spiral), and the high frequencies are encoded in the base of the cochlea, closer to the stapes
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