The effect of electroacupuncture on pain behaviors and noxious stimulus-evoked fos expression in a rat model of neuropathic pain

Chronic-constriction injury (CCI) of the sciatic nerve causes mechanical an d heat hyperalgesia and mechanical allodynia in the plantar surface of the hindpaw. The underlying mechanism thought to account for these phenomena in clude central sensitization induced by peripheral nerve injury, ie, the inc rease in neuronal activity of spinal dorsal horn neurons. As a marker of ne uronal activation of the central nervous system, Fos expression has been us ed widely to monitor the change in neuronal activity evoked by peripheral i nput. In this study, we examined the antinociceptive effect of electroacupu ncture (EA) on pain behavior and noxious stimulus-evoked Fos expression in dorsal horn neurons of the spinal cord in CCI rats 14 days after injury. Ma le Sprague-Dawley rats (180 to 200 g) received loose ligation of the left s ciatic nerve. Heat and mechanical hyperalgesia and mechanical allodynia wer e examined by the plantar foot test, the pin-prick test, and the von Frey t est before and after the EA treatment (100 Hz, 0.3 millisecond, 3 or 1 mA, 20 minutes) into the Zusanli point (536). When EA stimulation to the Zusanl i point was applied, the mechanical and heat hyperalgesia were significantl y suppressed; however, mechanical allodynia was not affected. The EA stimul ation to nonacupuncture point did not show any significant effect. Next, pi nch stimulation was applied to the plantar surface of the operated hindpaw of the CCI rats for 10 minutes, and the stimulus-evoked Fos expression in d orsal horn neurons in L4-L6 spinal cord levels was then examined by using i mmunohistochemistry. The number of noxious stimulus-evoked Fos-labeled neur ons in both the superficial and deep laminae of the dorsal horn in the CCI rats was increased significantly compared with those in sham-operated rats, suggesting an increased excitability of dorsal horn neurons to noxious sti muli. Concurrent EA treatment to the Zusanli point with the pinch stimulus suppressed the increase in the number of Fos-labeled cells in the spinal do rsal horn in the CCI rats. The present results show that EA treatment has a ntinociceptive effects on both pain behavior and neuronal activation of the spinal dorsal horn neurons in CCI rats.(C) 2001 by the American Pain Socie ty.