Unilateral 6-OHDA Lesioning and Apomorphine-Induced Rotations

The in vivo study timeline is show in Figure 1A. At day 0, under isofluorane anesthesia (5% induction, 2–3% maintenance), all 20 rats were infused (0.5 μl/min) with 12.5 μg 6-hydroxydopamine (6-OHDA.HCl, Sigma-Aldrich) in 2.5 μl saline containing 0.2% ascorbic acid, into the left medial forebrain bundle (AP-2.6 mm, ML + 2.0 mm and DV-8.8 mm relative to bregma). Two weeks post-lesion, the full extent of the 6-OHDA lesion was confirmed using apomorphine-induced rotation (Duty and Jenner, 2011). Briefly, after 30 min acclimatization in rotometers, rats were injected with apomorphine (0.5 mg/kg, s.c.) and the net contraversive rotations were recorded over 90 min using Rotorat software (MedAssociates). This revealed 19 of the 20 rats to be fully lesioned (displayed 382 ± 32 net contraversive rotations over 90 min) and therefore valid for inclusion in the subsequent study.

Timeline and confirmation for induction of dyskinesia in rats. (A) Timeline for induction and assessment of L-DOPA-induced abnormal involuntary movements (AIMs), reflective of dyskinesia, in rats subject to a 6-hydroxydopamine-lesion of the median forebrain bundle (MFB) on day 0. Full description is contained within the manuscript text. (B) Graph displaying individual AIMs scores obtained on the final day of priming with either L-DOPA (6.25 mg/kg s.c. with benserazide [15 mg/kg s.c.]; n = 7) or saline (n = 10). Horizontal bars indicate mean ± SEM. ****p < 0.0001 (Mann–Whitney U test) versus saline controls.