By Pranav Parikh
The ear, just like any other organ in the human body, uses nerves to function properly. One of the most vital nerves that the ear uses is the cochlear nerve, which connects the inner ear to the brain, or more specifically to the tonotopically-based regions of the cochlear nuclear complex located in the brainstem. This nerve shares the same shape and design of most nerves in the body, with dendrites absorbing information from various sources, sending the signal down the axon of the nerve through action potentials, and terminating the signal in a synapse so the message can be spread. In order to allow for this process to occur expediently, the nerve encounters a process known as myelination (providing a myelin sheath to propagate a signal faster). This is done through a glial cell known as an oligodendrocyte. Oligodendrocytes form a layer of lipid (fat) and protein around the axon to provide insulation, thereby allowing for signals to be sent to the brain more efficiently.
The immunoreactivity of Olig2 was detected during postnatal day (PND) 0 to 7, which became weaker after PND 10. Before PND 7, the majority of Olig2-expressing cells were found within the modiolus at the basal cochlear turn, while a few cells were located peripherally to the DIC-PCTZ and in close proximity to the spiral lamina at the basal cochlea turn. After PND 7, Olig2-expressing cells were fully overlapped with the DIC-PCTZ within modiolus at the spiral lamina in the basal cochlea.
A team of scientists led by Dr. Zhengqing Hu, funded by Hearing Health Foundation through its Emerging Research Grants program (2010 & 2011) was able to analyze oligodendrocyte protein expression in the cochlear nerve of postnatal mice. Through the use of Differential Interference Contrast (DIC) microscopy, they were able to investigate the cochlear nerve at staggered postnatal days, meaning the period following birth.
Their findings indicate oligodendrocytes are found to migrate along with the transition zone between the central and peripheral nervous systems. As the fetus develops after birth, and myelination occurs in the nerves connecting to the brain, the oligodendrocyte protein marker Oligo2 was observed. This could mean loss of hearing function could be connected to unmyelinated axons. There are many other neurodegenerative autoimmune diseases, such as multiple sclerosis, caused by demyelination, and hearing loss could potentially be added to that list. Dr. Hu’s work improves clarity of the neural network connecting the inner ear and the brain.
Zhengqing Hu, M.D., Ph.D. , is a 2010 and 2011 Emerging Research Grants recipient. Hu's research was published by Otolaryngology-Head and Neck Surgery on July 11, 2017.
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