Noxacusis Research Paper Summary: Pain Signals in Cochlear Neurons and Supporting Cells

by | Apr 3, 2024 | Research | 0 comments

By Megan Beers Wood

One hallmark of skin pain is release of ATP causing a rise in calcium within epithelial cells. Around a point of damage, this produces a ‘calcium wave’ spreading from the site of damage. These calcium waves contribute to activation of pain-sensing neurons in the skin that transmit the pain signal to the brain. Calcium waves also occur in the inner ear. In our previous publication (Nowak and Wood et al., 2020), we showed that an increase in calcium occurred in both epithelial cells and type II afferents after focal damage caused by a laser. In this mini-review we focus on cochlear epithelial cells to highlight another tool for studying damage-evoked calcium waves.  This is an increase in fluorescence that is visible without calcium-sensitive dyes or geneticallyencoded calcium indicators.  This signal is thought to result from an increase in fluorescent NADH.  The damage-evoked calcium wave enters mitochondria to increase synthesis of NADH from non-fluorescent NAD.  The resulting waves of increased fluorescence propagate similarly (speed and dissipation with distance) to those described previously in cochlea and skin using genetically-encoded calcium indicators. Importantly, these waves can be studied in any tissue since no calcium indicators are required.  Previous work showed that ATP released from damaged tissue can activate type II cochlear afferents.  We will continue to explore the activity of epithelial cells and type II cochlear afferent fibers as the cellular basis for painful hyperacusis.

The diagram is a top-down view of the organ of Corti with three rows of outer hair cells (OHC) (represented by gray circles) and a single row of inner hair cells (IHC). The dark gray rectangles represent the supporting cells underneath the hair cell layer. From top to bottom, there is one row of Claudius cells (CC), three rows of Deiters’ cells (DC) and two rows of pillar cells (OPC and IPC). The outer and inner pillar cells are separated by the tunnel of Corti. The top row is a schematic showing how fluorescence (green cells) propagates from the site of damage (OHC marked with red X). The arrow indicates time. The bottom row is the same schematic with a single type II afferent added to show the timing of type II activation relative to the fluorescent wave in the epithelial cells. After noise exposure, the type II afferent calcium-associated fluorescence occurs after the initial epithelial cell wave.


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