This article describes a method for recording direct-coupled electroretinograms (DC-ERG) from the retinal pigment epithelium (RPE) of anesthetized mice. The procedure involves careful electrode placement and maintenance of eye conductivity to ensure accurate measurements of retinal responses.
Begin with a dark-adapted, anesthetized mouse.
Apply anesthetic and dilating drops to the cornea.
Place the mouse on a raised platform in front of a dome with a dim red light.
Secure a ground electrode subcutaneously on the hind leg and a reference electrode inside the mouth.
Take an electrode holder with a capillary filled with salt solution. Flick to remove air bubbles.
Fill the capillary tip fully with the salt solution.
Position the capillary on the cornea to record a direct-coupled electroretinogram or DC-ERG.
The DC-ERG measures subtle electrical responses of the retinal pigment epithelium or RPE.
RPE is a specialized cell monolayer that maintains the health and structural integrity of photoreceptor cells.
Apply a drop of eye lubricant to maintain conductivity and prevent desiccation.
Check the resistance values for each eye to ensure they are similar and within range.
Establish a stable baseline, and then start recording the DC-ERG.
To position the mouse and electrodes for an experiment, anesthetize the cornea of a sedated mouse with a drop of 0.5% Proparacaine Hydrochloric acid before dilating the cornea with a drop of 2.5% Phenylephrine HCl and 0.5% tropicamide.
Use step one of six to turn on a dim red light inside the dome and place the mouse on a heated recording table. Use forceps to carefully tent the skin of the rear leg, and using one hand to firmly hold the needle electrode, use the other hand to insert the electrode subcutaneously into the rear leg to secure the electrode into place.
Place the reference silver/silver chloride electrode into the animal's mouth so that the centered pellet rests along the back cheek, and is held in place behind the teeth.
Before placing the capillary electrodes onto the eye, position the electrode holder with the glass capillaries oriented vertically, and flick the electrode holder with an index finger to remove any bubbles that may have been introduced.
Use a 25-gauge needle to fill the capillary tips with HBSS and inspect the capillaries to ensure that there are no air bubbles trapped in the tips. Position the electrode holder stand so that the open tips of the HBSS-filled capillaries are in gentle contact with the cornea, and taking care to avoid introducing bubbles, invert the lubricant eye gel dispenser to discard the initial drops. Then, place a drop of lubricant eye gel onto each eye to maintain conductivity and to prevent desiccation during the recording.
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