Indwelling intrathecal catheter
Rats were anesthetized with ketamine/xylazine 80/12 mg/kg intraperitoneally (i.p.) (Sigma-Aldrich, St. Louis, MO), and their head was placed in a stereotaxic frame. The cisterna magna was exposed and incised. As previously reported, an 8-cm catheter (PE-10; Stoelting, Wood Dale, IL) was implanted, terminating in the lumbar region of the spinal cord (Yaksh & Rudy, 1976). Catheters were sutured (using 3–0 silk sutures) into the deep muscle and externalized at the back of the neck. Autoclips were used to close the skin, and other surgeries were performed after a 5- to 7-day recovery period.