Two other double BAC transgenic mice received bilateral injections of colchicine (catalog no. C9754; Sigma-Aldrich) in the striatum, a drug that block axonal transport, allowing optimal immunostaining of neuropeptides contained in MSNs cell bodies. For intra-cerebral injections of colchicine, the following stereotaxic coordinates were used: anteroposterior (bregma) = 0.14 mm; mediolateral = 2.00 mm; dorsoventral = 3.20 mm, corresponding to the dorsal part of the striatum at the commissural level, according to the mouse brain atlas of Franklin and Paxinos70. One μL of colchicine diluted at 23 mg/mL in saline was pressure-injected in each side of the brain. One week after injections, colchicine-injected mice were transcardially perfused, as described above. Their whole brains were dissected out and cut with a vibratome into 50 μm-thick transverse sections.
