*2.3. Retina Axotomy Explant Model*

Compounds were tested using a retinal axotomy model that has been previously described [9]. Mice were euthanized by cervical dislocation, and eyes were enucleated immediately. Subsequently, retinas were dissected free in cold HBSS and either fixed immediately with PFA for 1 h (0 days ex vivo; control) or flat mounted on cell culture inserts (Millicell 0.4 μm pore; Merck, Kenilworth, NJ, USA) and maintained in culture (37 ◦C, 5% CO2) with Neurobasal-A media supplemented by 2 mM L-glutamate (GlutaMAX, Gibco, Thermo Fisher Scientific, Waltham, MA, USA), 1% N-2 supplement, 2% B-27 supplement, and 1% penicillin/streptomycin (all Gibco) in six-well culture plates (3 days ex vivo). For treated retinas, valproic acid (1 mM), folic acid (50 μg/mL), SB-431542 (10 μM), WY-14,463 (100 μM), and genistein (10 μM) were dissolved in the culture media (all drugs from Merck). Half of the media volume was replaced at 48 h. After 72 h (3 days ex vivo), the retinas were removed from culture, fixed in 3.7% PFA for 30 min, and immunolabelled as detailed below.
