Experimental animals were anesthetized and perfused transcardially with 0.9% saline followed by 4% paraformaldehyde. Brain samples were postfixed with 4% paraformaldehyde overnight and equilibrated in 30% sucrose. Coronal sections of 40 μm were prepared with a sliding microtome. IHC was performed using mouse anti-tyrosine hydroxylase (Chemicon). Unbiased quantification of TH-immunoreactive neurons in the SN was performed according to the optical fractionator principle (Gundersen et al., 1988). See Supplemental Experimental procedures for full methods.
