Increased phosphorylation of cyclic AMP response element binding protein(CREB)in the dorsal root ganglia and superficial dorsal horn neurons following chronic constriction injury

Objective To investigate whether chronic constriction injury （CCI） of the sciatic nerve of rats could produce alterations in the phosphorylation of cyclic AMP response element binding（CREB） protein in dorsal root ganglia （DRG） and superficial dorsal horn neurons of the spinal cord. Methods Chronic constriction injury （CCI） of the sciatic nerve was employed as a model of neuropathic pain. Thirty-two Sprague-Dawley rats were randomly divided into NaYve, Sham, CCI 2w（received CCI for 2 weeks） and CCI 4w（received CCI for 4 weeks） groups. Hind paw withdrawal threshold to mechanical stimuli and withdrawal latency to thermal stimuli were used to detemline the mechanical and thermal hypemlgesia. Then all the rats were deeply anesthetized and perfused intracardiaUy with paraformaldehyde. The fixed I4-5 spinal cord and the L5 DRG ipsilateml to CCI were harvested for fixation. The pCREB-immunoreactive（pCREB-IR） cells in both DRG and superficial dorsal horn neurons were quantified for analysis using immunohistochemistry methods. Results On the 14th day after sciatic nerve injury, all the rats exhibited significant mechanical and thermal hyperalgesia. The mechanical withdrawal thresholds to yon Frey filament from CCI 2w group decreased significantly compared to both baseline values and those of Sham group（ P 〈 0.01 ） ; Thermal withdwal latencies from CCI 2w group decreased significantly compared to both baseline values and those of Sham group（ P 〈 0.01 ）. Some rats from Sham group also showed mechanical hyperalgesia compared to both baseline values and those of Naive group（ P 〈 0.01）. 28 days after CCI, both mechanical and thermal hypersensitivity were significantly alleviated, with no statistical significance compared to those of Sham group. On the 14th day after CCI, the number of pCREB-IR ceils significantly increased in ipsilateral L5 DRGs and superficial dorsal horns（ P 〈 0.01 ） compared to Sham group. The number of phosphorylated CREB-IR cells in the ipsilateral DRGs from Sham group also increased compared to that of Naive rats（ P 〈 0.05）. There were no significant statistical differences of numbers of CREB-IR neuron between Sham group and CCI 4w group. Conclusion CCI increases CREB phosphorylatian both in DRG and superficial dorsal horn neurons of the lumbar spinal cord, and may be one of the key molecular mechanisms of central and peripheral sensitization following peripheral nerve injury. Key words: Immunochemistry;  cAMP response element binding protein;  Spinal cord;  Dorsal root ganglia;  Nerve injury