Ringing in the good news for tinnitus research

New research from UWA has reshaped the medical community’s understanding of tinnitus, bringing us closer to potential treatments for the condition.

School of Biomedical, Biomolecular and Chemical Sciences Associate Professor Wilhelmina Mulders says before this research it was believed tinnitus was only generated in the dorsal cochlear nucleus.

“But now that we find it is generated in the ventral cochlear nucleus; it’s possible both are involved,” Prof Mulders says.

The discovery, published in the Journal of Neuroscience in the paper “Hyperactivity in the Ventral Cochlear Nucleus after Cochlear Trauma”, is the result of research in an animal model.

In the lab, Prof Mulders and the research team, student Darryl Vogler and Professor Donald Robertson, caused restricted hearing loss in a guinea pig under anaesthesia by playing a pure 10khz tone for one or two hours, depending on the experiment.

Several tests are then conducted to determine whether the animal is hearing something that is not there, considered to be tinnitus – a condition characterised by hearing non-existent sounds, often ringing or roaring.

“Before the hearing loss, you teach the animal to lick a water spout when it hears a sound,” Prof Mulders says.

“After the hearing loss, if the animal then doesn’t lick the spout when there is no sound, you can infer that the animal is hearing something else that is stopping them from licking the spout.”

Once the team determined the guinea pig was experiencing tinnitus, electrodes were connected to the brain to record the nerve cell activity from individual neurons situated in the ventral cochlear nucleus.

In a normal animal model, there will always be a measure of spontaneous background electrical activity in the brain. The normal model was then compared with the hearing loss model.

“We found the animals with hearing loss showed a much higher degree of spontaneous activity – what we call ‘hyperactivity’,” Prof Mulders says.

Prof Mulders says because this hyperactivity was originally found in the dorsal cochlear nucleus, researchers only built on the initial research largely and ignored the other parts of the brain.

“We thought to look in the ventral cochlear nucleus because it is one of the nuclei that receives direct input from the auditory nerves,” she says.

Although the new insight has complicated the work of tinnitus research Prof Mulders says researchers can now consider other parts of the brain that may be targeted for therapy.

“It may be a long way off but I believe if we unravel the mechanisms, we can target specific problems.”

(Source: Science Network Western Australia: The Journal of Neuroscience)