T12-L1 segments of spinal cord from various groups were homogenized and total RNAs were isolated using RNeasy Mini Kit (Qiagen, Valencia, CA) according to the manufacturer’s protocol. Approximately 1 µg of total RNA from each sample was reverse transcribed into cDNA according to the manufacturer’s instructions using the iScrip™ cDNA Synthesis Kit (Bio-Rad Laboratories, Hercules, CA). Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was applied as an internal control. We used the following sequences for the forward and reverse primers: