The distribution of GABA in the SDH was determined by immunohistochemistry. Rats were perfused intracardially with 4% paraformaldehyde in 0.1 M phosphate buffer, and the L4–L5 segments of the spinal cord were removed, postfixed in the same solution for overnight, and cryoprotected with 30% sucrose in PBS for 2 days. Cryostat sections (35µm thickness) were incubated overnight at 4 °C with rabbit anti-GABA (1:1000; a gift from Dr. Yuan Zhu, Department of Medicine, University of Michigan, MI), mouse anti-GFAP antibody (1 : 2000, cata# G3893, Sigma, St. Louis, MO), mouse anti-OX42 antibody (1:1000, cata# CBL1512, Millipore, Billerica, MA), mouse anti-NeuN monoclonal antibody (A60) (1 : 5000, cata# MAB377, Millipore, Billerica, MA), or rabbit anti-Wnt5a (1:1000, cata# ab72583, Abcam, Cambridge, MA) followed by fluorescent IgG (Alexa Fluor 488, 1:1000 or Alexa Fluor 594, Molecular Probes, Eugene, OR, USA) for 2 hours at room temperature. Fluorescence images were captured by a fluorescent microscopy (Fluorescent M Leica/Micro CDMI 6000B)29 (link), 88 (link).