Herniated intervertebral disc may be a consequence of age-related degeneration, strenuous activities, trauma, obesity or poor posture. It affects about 1-3% of the US population with the highest prevalence among 30-50 years old men. A crucial minority suffer spinal cord compression (SCComp) with nerve damage, loss of bladder and bowel control and chronic pain. The nitric oxide (NO·) / soluble Guanylate Cyclase (sGC) / cyclic GMP (cGMP) pathway has been demonstrated to be a mediator of pain transmission and processing and may be involved in both enhancement and inhibition of pain following spinal cord injury [1]. We have developed a mouse model of SCComp, assessed pelvic and peripheral pain and bladder function in SCComp mice and tested the effect of cinaciguat, a sGC activator, in alleviating SCComp-associated symptoms.

Adult male C57Bl6 mice were anesthetized with 2-5% isoflurane, and the back skin and muscle surgically opened to expose the column after which the animals were stabilized using a specialized holder. A precision microdrill system was used to bore a 1.6 mm hole into the column at segment L1 without damaging the dura (Figure 1A-B). A small clear surgical grade silicon disc (~0.1 mm thick x 3 mm dia) was then inserted under the column (Figure 1C), spinal cord covered with hemostatic sponge and the muscle layer sutured. Immediately after SCComp, mice were implanted with bladder catheters routed under the skin to the back of the animal and connected to an externalized access port. Sham mice were operated in the same manner without the disc insertion. Recovering mice received prophylactic antibiotics and analgesics.

Starting 1 week after recovery, 1 hour urine spot tests were performed followed by foot and pelvic pain evaluation with an automatic testing system (Topcat methodology, 5-6 repeats per mouse every 1-2 minutes) and awake cystometries (saline instillation at 0.01 ml/min). Some of the mice were implanted with ALZET osmotic pumps delivering cinaciguat at 1 mg/kg/day/14 days starting approximately 4 weeks following SCComp surgery.

While immediately after surgery all operated mice exhibited heightened sensitivity in both perineum and feet, sham mice sensitivity returned to control levels about a week following surgery. At the end of experiments, SCComp animals were very sensitive in both the perineum and feet. Cinaciguat decreased sensitivity of treated animals to control levels (Figure 2A). The urine spot tests of SCC mice presented with many small spots suggestive of bladder overactivity. Average voided volumes calculated from the urine spot tests were significantly smaller in SCComp animals and increased nearly to control levels following cinaciguat treatment (Figure 2B). Cystometries confirmed shortened intercontractile intervals and higher baseline and threshold pressures in SCComp animals, contrasting with improved parameters using cinaciguat (Figure 2C).

Our new SCComp mouse model exhibits increased sensitivity in the both perineum and feet, suggestive of painful sensation. Bladder function is dramatically affected following SCComp showing increased frequency, decreased voided volume and higher bladder pressures. Two weeks of cinaciguat treatment improved bladder function and decreased sensitivity in SCComp animals.

We have developed and demonstrated a new mouse model for SCComp presenting with features representative of patients with herniated discs. Cinaciguat treatment improved both bladder function and pain sensitivity in SCComp mice suggesting that the NO·/cGMP pathway may have an analgetic function in herniated disc patients.

PMID: 36254980