Closed-perfusion transretinal ERG setup for preclinical drug and nanostructure testing

Objective: The isolated mammalian retina may serve as a sensitive biosensor for preclinical drug testing, including eye drugs and a broader range of pharmaceuticals. To facilitate testing with minimal amounts of drug molecules or nanostructures, we developed a closed-perfusion transretinal electroretinography (tERG) setup. Methods: The major challenge with small amounts of circulating perfusate was maintaining retinal viability and stability during long experiments. We conducted ex vivo tERG using WT C57BL/6J and Gnat1
^-/-
mice to assess rod- and cone-mediated light signals. The dark-adapted retina was stimulated with full-field light flashes while perfused at 5-6 ml/min. Results: The minimum perfusate needed in our closed-circulation was around 50 ml. Penicillin-Streptomycin (Pen-Strep) was indispensable for long recordings. Rod responses remained stable for at least 42 hours, the longest recording we conducted, with the retina still responsive, and rod and cone bipolar cell responses for up to 12 hours. IBMX (3-isobutyl-1-methylxanthine), a non-specific phosphodiesterase (PDE) inhibitor with reversible effects, validated our setup. We used our setup to test the zwitterionic polymer poly(sulfobetaine methacrylate) (PSMBA), serving as a promising material for thermoresponsive nanostructures, and the corresponding monomer SBMA for possible harmful effects on mouse rod and bipolar cell functioning. Conclusion: Our closed-perfusion tERG setup enables long experiments with small amounts of perfusate. PSMBA or SBMA had no effect on rod and bipolar cell responses. Significance: This method is applicable for assessing drug functionality, as well as conducting preliminary biocompatibility and toxicity testing using small amounts of molecules or nanostructures that could impact neuronal or synaptic function.