Preparing a Rat Model to Assess Visual Pathway Integrity Using an Electrophysiology Setup

For scotopic recordings, all the procedures are performed in a dark room. For illustration purposes, electrode positioning is conducted under normal room lighting here. The animal was dark-adapted for 12 hours, and anesthetized with ketamine and xylazine.

After pupil dilatation and topical anesthesia, hook the inactive EP electrode around the bottom incisors. Then, place the animal on the ERG platform in front of the ganzfeld bowl situated in the Faraday cage. Secure the animal to the platform with a strip of hook and loop fastener, placed firmly but not tightly around the nape.

Next, position the ERG-inactive electrodes by encircling the scleral ring non-invasively around the eye's equator, approximately three millimeters behind the limbus. Stabilize this by attaching the electrodes to the hook and loop fastener strip around the nape. Repeat the procedure for the contralateral eye.

Now, fasten the VEP-active electrodes by attaching alligator clips to the stainless steel screws pre-implanted on the skull. Prior to the ERG-active electrode placement, place a small drop of 1% carboxymethylcellulose sodium on the electrode to improve signal quality. Position the ERG-active electrodes to lightly touch the central corneal surface using a micromanipulator attached to the custom-built stereotaxic arm.

Ensure the carboxymethylcellulose sodium only contacts the cornea and not the sclera, by wiping excess fluid away. Then, insert 2 to 5 millimeters of the stainless steel ground needle electrode subcutaneously into the tail. Slide the platform closer to the ganzfeld bowl, and ensure the animal's eyes align with the opening of the bowl to enable even illumination of both retinas.

Subsequently, close the Faraday cage to reduce extraneous noise.