Intrathecal catheterization influences tolerance to chronic morphine in rats.

We evaluated the antinociceptive effects of acute and chronic morphine administered spinally via lumbar puncture in intrathecally catheterized and sham-surgery rats. The effects of acute morphine did not differ between groups. Catheterized rats developed tolerance to chronic morphine more rapidly, compared with sham and naive rats. Therefore, catheter presence facilitated development of opioid antinociceptive tolerance. Spinal astrogliosis, determined by measurement of 3-dimensional cell volumes, was observed in catheterized rats as indicated by significantly larger cell volumes compared with surgery-naive controls. Gliosis induced by chronic intrathecal morphine administered to surgery-naive animals was comparable to that observed in saline-treated catheterized rats. (Anesth Analg 2012; 114: 690-3)