Research: Gene-Enhanced Mice Improve Understanding of Hearing Loss

Scientists have developed mice with improved hearing to learn more about the mysteries surrounding hearing loss.

To accomplish this, University of Michigan neurobiologist Lingchao Ji and his team amplified neurotrophin-3 (Ntf3) expression. According to Science Alert, their research showed that boosting Ntf3 expression improves hearing in middle-aged mice and helps animals with damaged inner ears recover.

The method enhances synaptic amplification between cochlear hair cells and the brain. Through these connections, hair cells transmit sound vibration impulses to brain neurons.

Breakthrough Findings

Gabriel Corfas, a neurobiologist at the University of Michigan, noted that furnishing Ntf3 to the inner ear in young mice "increased the number of synapses between inner hair cells and auditory neurons." However, he said they still have no idea "what having more synapses would do to hearing."

The startle reaction is unaffected by synaptic density; hence, sound detection stays unaltered. Increased synapse density improves sound discrimination by changing the gap detection threshold, the shortest silence between two sounds.

This threshold is longer when there are fewer synapses, as Ji and his team demonstrated in mice with lower Ntf3 expression. Loss of inner hair cell connections may delay the brain's sound information processing, similar to hearing disorders. These delays make speech comprehension difficult, especially in noisy surroundings.

Mice with increased Ntf3 expression had denser synapses, enhancing their ability to process and distinguish sound characteristics. Corfas noted that animals possessing inner ear synapses have "normal thresholds," which an audiologist defines as normal hearing. "They can process the auditory information in supranormal ways," he said.

The researchers believe this development might improve human hearing. Several neurodegenerative diseases begin with brain synaptic degeneration. Thus, inner ear studies may lead to novel treatments for some health disorders.

Billions Impacted by Hearing Loss

Through this breakthrough research, experts have illuminated auditory processing pathways, paving the way for the treatment of hearing loss and other neurological disorders.

The World Health Organization estimates that by 2050, nearly 2.5 billion people will have lost their hearing, with at least 700 million requiring hearing rehabilitation. Over 1 billion young individuals risk irreversible, preventable hearing damage from hazardous listening. Scaling up ear and hearing care requires an annual expenditure of less than US$1.40 per person. Every US dollar invested in this investment will yield roughly US$16 over a decade.

Over 5% of the world's population, equivalent to 430 million people, needs hearing loss rehabilitation, including 34 million children. By 2050, over 700 million people will have debilitating hearing loss.

Hearing loss beyond 35 dB in the better ear is considered disabling. Nearly 80% of deaf people reside in low-and middle-income nations, and over 25% of those over 60 have hearing loss.

Depending on the severity of their condition, people with hearing loss can use hearing aids, cochlear implants, captioning, and other assistive equipment to speak.

Most adults last received hearing tests in grade school. Experts recommend that adults get hearing tests during their yearly physicals. According to Hopkins Medicine, this first test sets a benchmark for subsequent comparisons. If hearing loss occurs later, an audiologist can compare current hearing levels to baselines to determine the severity and treatment.