Characterization of the cochlear aqueduct

This proposal will determine the morphological, molecular, and functional mechanisms on
how the cochlear aqueduct (CA) changes over the lifespan. This will be the first histological
and molecular characterization of the cochlear aqueduct over the lifespan of CBA/CaJ mice.
Aim 1: A complete characterization of passage of tracers, spheres, or immune cells through the
CA with increasing age is lacking and therefore this information is needed for the future
development of using the cochlear aqueduct as a point of entry to the cochlea for rescue strategies
for the inner ear. The route used to deliver these substances will be through the CA by injecting
into the CSF in the cisternae magna. Experiments are designed to determine the relative
distribution of tracers throughout the cochlea by using Gadovist and contrast-enhanced MR
imaging at different ages. The highest resolution of pre-clinical MRI (a 9.4 T Bruker machine) will
be used for cochlear fluid imaging in living animals. The study will determine the size limitations
of passage through the barrier membrane (located at the cochlear end of the aqueduct) and if it
changes with increasing age. To determine the accessibility of microspheres (0.2-2µm), which is
a new technology that can deliver drugs, stem cells, and other therapeutics, histological
investigations will be performed after they are injected into the cisterna magnum and then
histologically quantified. We have found macrophages and lymphoid markers in the CA and we
hypothesize that the CA could be a source of immune cells that enter the cochlea. We will inject
GFP-labelled CX3CR1 monocytes isolated from Cx3cr1CreER-Eyfp/wt mice available in our facility,
into the cisternae magnum before or after a PTS-inducing noise exposure (110 dB, 2h, 6-12 kHz
in awake animals) known to trigger inflammatory processes in the cochlea and evaluate by
histology whether these cells delivered in the CSF have been populating the cochlea in greater
abundance than in sham exposed animals. Aim 2: A complete characterization of the cellular
identity of the tissue surrounding the CA is needed to better understand its role as a cochlear gate
keeper. Laser capture microdissection coupled with next generation sequencing (LCM- Smart-
seq3) developed at the Karolinska Institute and will determine the molecular composition and the
cellular identify of the inner tissue layer. This unique work will establish a morphological,
physiological, and molecular characterization of the CA. Knowledge will be generated regarding
how the influx of fluids from the CA aqueduct is regulated during the lifespan. The results from this
project will establish a fundamental basis for understanding the CA as a passage route to and
from the cochlea and its use for pre-clinical delivery strategies to treat cochlear disorders.

Grant Number: 5R21DC021730-02
NIH Institute/Center: NIH
Principal Investigator: BARBARA CANLON