Issue date: 3/25/08 Section: News

Hearing rarely returns once a human loses the ability to hear.

However, when lower vertebrates such as birds, reptiles, fish and amphibians lose the ability to hear, they are able to regenerate hearing cells, called hair cells, and regain their hearing.

The cells are called hair cells because they are tiny, hair-like projections found in the inner ear which enable humans and animals to hear. Scientists don't know why certain animals can regenerate hearing cells while higher vertebrates such as humans cannot. For more than a year, U neurobiologist Tatjana Piotrowski has been researching why certain creatures have lost the ability to regenerate these cells.

"The main focus is to understand what genes you need for hair cell regeneration," Piotrowski said. "Once we understand that, we can go back and see why mammals lost the ability to regenerate hair cells."

The National Organization for Hearing Research Foundation awarded Piotrowski a $200,000, two-year grant to conduct the study.

For about a year, Piotrowski has been studying genetic mutations in zebrafish -- small minnows found in freshwater streams throughout Southeast Asia which are also popular aquarium fish worldwide.

Zebrafish have the same hearing cells as humans but are able to regenerate their cells, which makes them prime models for understanding hair cell regeneration.

"It is remarkable how hair cells in fish die but come back days later," said Alejandro Sanchez-Alvarado, a professor in neurobiology and anatomy and co-investigator for the study. "The question we ask is, 'How do fish do this?'"

Hair cells in human ears convert vibrations and sounds into signals the brain can decipher, allowing people to hear. But if cells are exposed to too much vibration or loud noise, they die.

Humans have hundreds of hair cells in the ear, and they don't all die at once. But over the years, the number of lost cells

can add up, resulting in gradual hearing loss.

Continued...

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