DA levels from the midbrain containing VTA and SN samples were analysed by Biomedical Research Center, Asan Institute for Life Sciences (Asan Medical Center, Seoul, Korea) and were presented as pmole mg−1 of tissue. Briefly, dopamine hydrochloride and dopamine-1,1,2,2-d4 hydrochloride were purchased from Sigma-Aldrich (St Louis, MO, USA). Oasis wax cartridges were from Waters (Milford, MA, USA). All solvents including water were purchased from J.T. Baker (Center Valley, PA, USA).
