2.5. Dopaminergic lesion with neurotoxin 6-hydroxydopamine

Rats were anesthetized with 2,2,2-tribromoethanol (250 mg kg⁻¹ ip) and fixed into the stereotaxic apparatus. The incisor bar was set at 3.3 mm below the interaural line. Rats received one injection (coordinates from bregma: AP = −4.3; LL = −1.6; DV = −8.3) of 2.0 μl 6-Hydroxydopamine (6-OHDA, Sigma-Aldrich, St Louis, MO, USA) into the left medial forebrain bundle as described by Gomes et al. (2008) (6-OHDA - 2.5 μg μl⁻¹ in 0.9% NaCl supplemented with 0.02% ascorbic acid, 1 μL min⁻¹).

Motor asymmetry following unilateral lesioning of the nigrostriatal pathway was assessed 15 days after the lesion by apomorphine (0.5 mg kg−1 in 0.9% NaCl, subcutaneous, Sigma) -induced rotational behavior analysis using automated rotameter bowls (Columbus Instruments International, Ohio, USA; Ungerstedt and Arbuthnott, 1970). The rats were placed in a rotameter bowl and connected to the recording harness. Total turns and net turns ipsilateral to the lesioning were recorded by online input into a microcomputer over 45 min. Only rats showing more than 90 total full turns (contralateral to the lesion) per 45 min were selected for the study (Sup. Table 2). Rats meeting this criterion have striatal DA depletion greater than 95% 1. L-DOPA treatment started two days after the apomorphine rotational test. The lesions were immunohistochemically analyzed and a staining for tyrosine hydroxylase (TH) was used to rate the limiting enzyme in catecholamine synthesis pathway in the substantia nigra.