Journal Club: Semi-circular canal imaging in live animal by Optical Coherence Tomography

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Today's journal article

Pan DW, Yang Z, Kim W, Biju K, Gnedeva K, Applegate BE, Oghalai JS. "Optical coherence tomography imaging demonstrates endolymphatic hydrops in the lateral and posterior semicircular canals in noise-exposed mice. "

Why I picked this article

First, this research uses live imaging of what's happening in the cochlea, using optical coherence tomography (OCT). In any species, being able to observe something happening live is so valuable for understanding the physiology and pathophysiology. 

What's more, OCT imaging is customised to target the semicircular canal, parts of our peripheral vestibular system responsible for sensing our head position/movement etc. It's really exciting that they managed to get the angle and position of the OCT relative to the animal!

And the study investigates a very interesting question around the after-effect of noise exposure. In their study, they show very striking data that suggest noise exposure increases the relative volume of the endolymph (a very important fluid for inner ear function) in both the cochlea and the vestibular system. 

Some of the research findings

Animal model:

  • CBA/CaJ (JAX#: 000654) wild-type mice, adult (6-11 week-old), both genders. 
  • Noise exposure - 100dB SPL white noise (filtered to 8 -16kHz) for 10 hours. 
  • Mice were anaesthetised, and the auditory bulla (= part of the rodent skull that contains the middle ear space) was opened so that the otic capsule bone and round window could be viewed. 

OCT system & imaging:

  • Custom-built OCT system with laser (centre wavelength 1,306 nm, 90.4 nm bandwidth, and sweeping at 100 kHz) 
  • Standard resolution -  12.5 µm axial resolution, lateral resolution of 13.2 µm
  • They also used a high-resolution OCT (HR-OCT) system with a 4x objective lens (2.45 µm axial and 3.95 µm lateral resolution) 
  • Cochlea imaging approx 45 min post-noise exposure, followed by rotating the animal to image the semi-circular canals at about 60 minutes post-noise exposure. 
Adopted from part of Figure 1, Pan et al (2025), highlighting the imaging approach. Amazing!

Image analysis: 

  • The research team has estimated the fluid volumes in the semicircular canals from imaging data obtained. 
  • They calculated an endolymph to perilymph (E/P) ratio as a normalised number. They also calculated SM and SV ratio to assess the impact of noise exposure on the Reissner's membrane.

Using the technique above, they have correlated observations in live animals with histology at both baseline and after noise exposure. Overall, the quantification from the images showed similar patterns in both the cochlea and the vestibular system: 

  • In the cochlea, the SM/SV ratio increased after noise exposure = indicating that the amount of fluid in the scala media (SM) component, or the endolymph volume, was increased. 
  • In the semi-circular canal, E/P ratio increased after the noise exposure in the exposed group = the volume of fluid was again increased relatively for endolymph.

Haruna's takeaway

This study shows very interesting acute changes in fluid volume following exposure to a very high level of noise. We don't know if this is the change that can be recovered yet, but it shows the power of this particular experimental approach to be able to monitor the change in live animals and correlate with histology. Very exciting paper. 

We do a lot of anatomical characterisation of sheep inner ear, and from that perspective, there is an observation that authors have described about the relevant size of bony labryinth and membrane labyrinth "These images demonstrated the structure of the LSCC (Fig. 2B) and PSCC (Fig. 2D) and confirmed that the membranous labyrinth (yellow arrows) was very close to the inner edge of the bony labyrinth. Thus, most of the arc of the SCC in the mouse consists of endolymph, with only a thin rim of perilymph around the edges." We have observed a similar pattern in the sheep semi-circular canal (hopefully we'll write this up sometime soon...), which may be quite different to the human semi-circular canal. 

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This is Haruna's 7/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.