sections were incubated for 1 h at RT in an avidin-biotin-peroxydase complex solution (Vector Laboratories) diluted 1/100 in the blocking solution. Sections were then rinsed and the bound peroxidase revealed by incubating the sections for 3 min at RT in a 0.025% solution of 3,3′diaminobenzidine tetrahydrochloride (DAB; catalog no. D5637; Sigma-Aldrich) diluted in Tris-buffered saline (TBS; 50 mM; pH 7.4), to which 0.005% of H2O2 was added. The reaction was stopped and the sections mounted on gelatin-coated slide and air-dried. Sections were then dehydrated in graded alcohol, cleared in toluene and coverslipped with Permount (catalog no. SP15-500; Fisher Scientific). The TH-immunostained sections taken through the midbrain were used to assess the number of DA cell bodies in the SNc and VTA, as delineated based on the mouse brain atlas of Franklin et Paxinos70. On these sections, all TH+ cell bodies were counted and results expressed as percentage of control side.
