Effects Of Intrathecal Ketamine On Rat's Pain Threshold And Changes Of Neuronal Fractalkine Expression In Rat Spinal Dorsal Horn Following CCI

ObjectivePain is the disable and uncomfortable feeling that the senior centers (cerebral cortex) reflect the tissue injury, the subjective feeling under the condition of human consciousness. Pain has become the fifth important life sign behind the T, pulse, respiratory, BP.The neuropathic pain usually comes from the tissue injury, inflammation and neuronal tissue injury, and the main symptom is the hyperalgesia, allodynia, spontaneous pain. Recently more and more research show that immune and inflammation mechanism is very important to the development of the neuropathic pain. Fractalkine which is quite different to the other factors, is a kind of transmembrane glucoprotein; and the cellular formation, biochemical character, tissue distribution and chromosome location show the great difference. So the fractalkine make the special function in the development of the neuropathic pain.So this study was initiated to observe the effect of intrathecal ketamine on rat's pain threshold and changes of chemokine fractalkine expression in rat spinal dorsal horn following chronic constriction injury of the sciatic nerve, and to explore the mechanism of neuropathic pain and the effect of intrathecal ketamine on these changes.MethodsThirty-six healthy male Sprague-Dawley rats (200-250g) were randomly devided into four groups (n=9 in all groups):Sham group; NS control group(CCI group); ketamine I group (CCI+K I group); ketamine II group (CCI+KII group). All rats were anesthetized and a microspinal catheter was inserted intrathecally into the lumbar region. After 4 days, these weren't operative procedure in Sham group; the rats in the other groups received a lesion of the sciatic nerve (chronic constriction injury CCI). The group CCI was intrathecally injected 10μl normal saline; the group CCI+K I and CCI+KII were injected ketamine 25μg and 50μg respectively after 4 days post-surgery. Mechanical allodynia and radiogenic heat pain thresholds were measured pre-surgery and on the day 1,3,4,7 post-surgery and 30,60 min after infection. All rats were killed and the L5 spinal cord was dissected for determination of the expression of fractalkine using the immunohistochemical techniques.Results(1) In all group there were no difference on the statistics in pain threshold and body weight before pre-surgery (P>0.05); (2) There were significant difference on the statistics in pain mechanical and heat threshold in group CCI, CCI+K I, CCI+K II as compared with group Sham. The intrathecal injection of ketamine can reduce pain mechanical and heat threshold (P<0.05). (3) The number of immunoreactive soma in group CCI, CCI+K I and CCI+K II increased significantly compared with that in group Sham (P<0.05). The number in group with ketamine decreased clearly (P<0.05).Conclusion(1) Hyperpathia may be caused in the injured side limbs of rats following CCI. Intrathecal administration of ketamine provide significant antinociception in the rat of CCI model; (2)The pain of CCI model can produced the increase of neuronal fractalkine expression in rat spinal dorsal horn; (3) Intrathecal ketamine significantly inhibited the increase of fractalkine expression in rat spinal dorsal horn of CCI.