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

Light stimulates the eye's photoreceptors, sending electrical signals to the visual cortex in the brain to process visual information.

To measure the integrity of this visual pathway, start with an anesthetized, dark-adapted rat in a dark room.

Position a reference VEP electrode around the rat's lower front teeth.

Secure the rat with a fastener strip on an ERG platform in front of a Ganzfeld bowl, a light-illuminating device within a Faraday cage.

Place the reference ERG electrodes around the eye's equator, encircling the scleral ring, and secure them.

Then, attach the VEP active electrodes to the pre-implanted skull screws to detect cortical signals.

Position the ERG electrodes with lubricant on the center of the eyes to measure their responses to light stimuli.

Remove excess lubricant and insert a ground electrode into the tail to reduce electrical noise.

Move the ERG platform closer to the Ganzfeld bowl and close the Faraday cage to minimize external interference.

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.