Injury to the peripheral nervous system can lead to spontaneous pain, hyperalgesia and allodynia. Previous studies have shown sprouting of Aβ-fibres into lamina II of the spinal cord dorsal horn after nerve injury and the formation of new synapses by these sprouts. Synaptophysin is a presynaptic vesicle protein, useful in the identification of synaptogenesis. Here we investigated whether synaptogenesis as measured by the expression of synaptophysin protein correlates with symptoms of neuropathic pain in rats with a chronic constriction injury (CCI) of the sciatic nerve. We used immunohistochemistry, Western immunoblotting and densitometry to study the distribution of synaptophysin and to quantify relative protein. Synaptophysin was increased in the ipsilateral dorsal horn with a peak level on day 14 and returned to baseline on day 21 post-CCI. Synaptophysin levels temporally correlated with thermal hyperalgesia but not with tactile allodynia. Our results indicate that thermal hyperalgesia in CCI significantly correlates with synaptogenesis within the superficial layers of the dorsal horn.
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