Objective: To investigate the expression of neuronal nitric oxide synthase (nNOS) in spinal dorsal horn and the effect of intrathecal katemine on the expression of nNOS in the rats with formalin-induced pain.
Methods: Thirty-two Sprague-Dawley rats were randomly divided into 4 groups (n=8 in each group): a control group (C), an intrathecal saline group (NS), a katemine 50 microg group (K1), and a katemine 100 microg group (K2). The rats that were anesthetized with 10% chlroral hydrate 300 - 350 mg/kg by abdominal injection were intrathecally inserted a microspinal catheter into the lumbar region according to the method of modified Yaksh. After 5 days ,the rats in Group NS, K1 and K2 were intrathecal 20 microL saline or 10 microL katemine (50, 100 microg) followed by 10 microL saline, respectively. Thirty minutes later, 5% formalin 50 microL was subcutaneously injected into the left hindpaw. Pain intensity scoring (PIS) was used to assess antinociceptive behavior within 1 h after the formalin injection. The expression of nNOS in the spinal dorsal horn of L5 segment was assayed using immunohistochemistry 24 h later.
Results: Compared with Group NS, PIS of Group K1 and K2 was decreased obviously (P<0.01) in the second phase of formalin pain. The number of immunoreactive soma and immunohistochemistic dying grade of nNOS in the spinal dorsal horn of L5 segment was higher in Group NS than that in Group C (P<0.01), but Group K1 and K2 were lower than Group NS (P<0.01).
Conclusion: There was significant antinociception of intrathecal katemine in rats with formalin pain. Intrathecal katemine significantly inhibited the increase of nNOS expression in the spinal dorsal horn of formalin-induced pain, suggesting nNOS plays an important role in nociceptive transmission and modulation of the spinal cord.