Two-photon microscopy offers look inside intact cochlea

For the first time, researchers have snapped pictures of mouse inner ear cells using an approach that doesn’t damage tissue or require elaborate dyes. The approach could offer a way to investigate hearing loss and may help guide the placement of cochlear devices or other implants.

The small delicate cochlea and associated parts are encased in the densest bone in the body.  With standard anatomical imaging techniques such as MRI, the inner ear just looks like a small grey blob. “We can’t biopsy it, we can’t image it, so it’s very difficult to figure out why people are deaf,” said ear surgeon and neuroscientist Konstantina Stankovic of the Massachusetts Eye and Ear Infirmary in Boston.  

Stankovic and her colleagues took a peek at inner ear cells using an existing technique called two-photon microscopy. Stankovic and her colleagues took a peek at inner ear cells using an existing technique called two-photon microscopy. This approach shoots photons at the target tissue, exciting particular molecules that then emit light. The researchers worked with mice exposed to 160 decibels of sound for two hours. Then they removed the rodents’ inner ears, which includes the spiraled, snail-shaped cochlea and other organs. Instead of cutting into the cochlea, the researchers peered through the “round window” — a middle ear opening covered by a thin membrane that leads to the cochlea.

The approach yielded clear images of rows of the inner ear’s hair cells, tiny hairlike structures that detect sound vibrations, enabling hearing. Unlike in control mice, ears of noise-exposed mice had visible damage: Whole sections of ear cells were wiped out, Stankovic reported February 17 at the annual meeting of the American Association for the Advancement of Science.

She hopes the approach will not only shed light on the various kinds of damage that lead to hearing loss, but that it also will help guide the insertion of implants.  In the future, the imaging approach might help guide the placement of an experimental device that extracts energy from the inner ear, acting as a tiny battery. The new device, developed by Stankovic and colleagues, doesn’t generate enough power to run a cochlear implant. It could, however, act as a sensor, monitoring for infections or sensing drug levels.

Such devices might prove very useful for monitoring all sorts of physiological responses, says biomedical engineer Philippe Renaud of Swiss Federal Institute of Technology in Lausanne. They could prove especially useful, he says, in patients for whom devices need to be small, delicate and efficient, such as those undergoing deep brain stimulation.

Citations:

K. M. Stankovic. Treating deafness with better vision: cellular level optical imaging of the inner ear. Annual meeting of the American Association for the Advancement of Science, Boston. Presented February 17, 2013

Imaging technique offers look inside hearing loss
By Rachel Ehrenberg in Science news

http://www.sciencenews.org/view/generic/id/348394/description/Imaging_technique_offers_look_inside_hearing_loss