After behavioral test, rats were deeply anesthetized with pentobarbital sodium (50 mg/kg). The spinal cord was removed quickly and the lumber segments of the dorsal horn (L4-L5) were punched (13 (link)) and homogenized in the lysis buffer. The total and nuclear protein were prepared and processed for immunoblotting. The following antibodies were used: polyclonal antibodies against NR2B (1:1000, Millipore), GluR1 (1:1000, Millipore), or monoclonal anti-β-actin antibody (1:1000; Santa Cruz Biotechnology), and the horseradish peroxidase-conjugated anti-mouse or anti-rabbit IgG secondary antibody (1:10,000; Jackson ImmunoResearch Laboratories). The immunoreactivity was detected using enhanced chemiluminescence (ECL Advance Kit, Amersham Biosciences). The intensity of bands was analyzed quantitatively with ImageJ software.