Immunohistochemical changes of synaptophysin in the rat spinal cord after chronic constriction injury of sciatic nerve and ketamine intervention study

Objective To study the changes of synaptophysin in the rat spinal cord after chronic constriction injury of sciatic nerve and the influence of ketamine intervention.Methods Twenty-four female SD rats weighing 180-250 mg were divided randomly into 4 groups (n=6 in each group).Group I:The right sciatic nerve chronic constriction injury (CCI) model was established.Group Ⅱ:Sham-operative control.Group Ⅲ:Ketamine 5 mg/kg was administered intraperitoneally on day 4 after CCI,twice everyday and continuously for 10 days.Group Ⅳ:The same procedure as Group Ⅲ was taken and the dosage of ketamin was changed to 10 mg/kg.Thermal nociceptive and mechanical withdrawal thresholds were measured before the constriction injury and on the day 4,7 and 14 post-chronic constriction injury.The changes of synaptophysin in the spinal cord was detected quantitatively by using immuneohistochemistry and computerized image analysis.Results Pain threshold in groups I,Ⅲ,Ⅳ was reduced significantly on the day 4 after sciatic nerve ligation as compared with that in group Ⅱ (P 0.05) and the established heat hyperalgesia and mechanical allodynia in groups I,Ⅲ was maintained for 10 days.Thermal pain threshold and mechanic pain threshold in group Ⅳ were increased on the day 14 as compared with those in group I (P 0.05). The density of synaptophysin immunoreactivity in the superficial dorsal horn as compared with that in control group was remarkably increased by 58% on the 14th day after CCI (P0.01).The synaptophysin-positivity in group Ⅳ was significantly reduced by 25% as compared with that in CCI model rats (P 0.05). Conclusion There is an increase of synaptophysin immunoreactivity in the superficial layers of the dorsal horn during the development of neuropathic pain and ketamine can restrain this change.