This article details a surgical procedure for cochlear implantation in a deafened mouse model. It outlines the steps for inserting an electrode array into the cochlea and recording auditory brainstem responses (ABR).
Take a deafened mouse with an incision behind the ear.
Position a retractor within the incision to access the bulla, a bony enclosure of the middle ear.
Obtain a cochlear implant containing an intracochlear electrode array with an insulated wire and a ground ball connected to a print board.
Insert the array through the round window at the base of the bulla into the scala tympani, the cochlea's lower chamber.
Coil the wire inside the bulla and secure it with tissue glue.
Remove the retractor and seal the incision.
Make a small incision in the neck, insert the ground ball, and seal the incision.
Connect the board to the stimulator platform, which delivers electrical stimuli.
Attach the auditory brainstem response, or ABR, electrodes to the vertex, behind the pinna, and on the hind leg.
Apply electrical stimuli and record the evoked electrical ABR response.
To insert the cochlear implant electrode array, place the retractor tool back into the incision to re-access the bulla, and insert the electrode array into the scala tympani, at a depth such that the fourth platinum ring of the array is located just inside the round window.
The insertion of the electrode array can also be tricky, so take your time to find a good insertion angle using one forcep tool, the lead wire, and another to insert the array.
Coil the lead wire inside the bulla, and glue the wire to the tissue above the bulla.
After carefully removing the retractor, enclosing the insertion with tissue glue, use a scalpel to make a 0.5-millimeter incision in the neck, perpendicular to the line between where the active and reference aVR electrodes will be. Place the ground ball in the insertion, and connect the electrode array board to the Animal Stimulator Platform.
To perform an electric aVR, place the electrodes as previously demonstrated, and open the Animal Stimulator Platform Software. Then, define the electric pulse stimulation paradigm, and present the electric pulse trains recording the evoked electric eABR responses continuously via the TDT headstage pre-amplifier and auditory processor.
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