RET and Parkinson disease: To further validate the efficacy of our optoRET-based therapeutic approach, we evaluated two additional treatments: the standard PD symptomatic medication L-DOPA (50 mg/kg46, i.p., administered daily [A1L1] or alternate days [A1L3]) and the preclinically validated RET agonist (BT4447–49, 120 μM, delivered via constant-rate direct brain infusion [A1BT]).