Unilateral 6-OHDA lesion

Administering 6-OHDA into the right striatum results in a lesion of the nigrostriatal pathway. Dopaminergic neurons internalize 6-OHDA, which damages striatal terminals before triggering degeneration in the substantia nigra pars compacta (SNpc) through oxidative stress and mitochondrial dysfunction (reviewed in (Duty and Jenner, 2011; Hamadjida et al., 2019; Salari and Bagheri, 2019; Gonzalez-Rodriguez et al., 2020). Animals were anesthetized with isoflurane (Sigma-Aldrich, St. Louis, MO, USA) 3%–4% with oxygen debit at 1 L/min. Mice were then placed in the stereotaxic frame (David Kopf Instruments, Los Angeles, CA, USA) and the isoflurane concentration was set at 2% and oxygen debit was set at 0.5 L/min during the surgical procedure. Four µg of 6-OHDA (Sigma-Aldrich) was dissolved at a concentration of 2 µg/µL in 0.9% saline and 0.02% ascorbic acid. A volume of 2 µL was injected with a Hamilton syringe in the right striatum at a rate of 0.5 µL/min and the injection was performed for 4 minutes at the following coordinates: AP (Bregma): +0.5 mm; ML: –1.8 mm; DV: –3.1 mm (Franklin and Paxinos, 2013). The needle was left in place for 3 minutes after the injection before complete retraction. Sham mice were subjected to the same surgical procedures but were injected with 2 µL of the vehicle solution (Coulombe et al., 2016).