Intrathecal Drug Administration in Rats

The lumbar catheterization was performed as previously described (Størkson et al., 1996 (link); Chen et al., 2014 (link)). Briefly, under isoflurane (4%) anesthesia, a midline incision was made to expose the intervertebral space between L5 and L6. After a clear exposure, a polyethylene-10 catheter (0.28 mm i.d. and 0.61 mm o.d., Becton Dickinson, Sparks, MD, USA) was inserted into the subarachnoid space and pushed rostrally to terminate at the level of L4–L5 spinal segments. Then the PE-10 tube was tunneled under the skin and the incisions were sutured. Three days after catheterization, 10 μl of lidocaine (2%; followed by 10 μl saline for flushing) was injected into the catheter to test the successful insertion. Rats with signs of bilateral hind limbs paralysis immediately after lidocaine injection were selected for further experiments. All rats were housed separately to recover for 5–7 days. The following drugs were administered in this study, EM2 (No. E3148; Sigma-Aldrich), SP (No. 1156; Tocris) and L-732138, (NK1R antagonist, No. 0868; Tocris). The drugs were dissolved in sterile saline and administered intrathecally in a volume of 10 μl solution followed by 10 μl saline for flushing.