Expression of phosphorylated cyclic AMP response element binding protein (pCREB) in the dorsal root ganglia and superficial dorsal horn neurons following chronic constriction injury in rats

Objective To determine whether chronic constriction injury (CCI) to sciatic nerve is associated with changes in the phosphorylation of CREB in dorsal root ganglia ( DRG) and superficial dorsal horn neurons of the spinal cord.Methods Thirty-two adult female SD rats weighing 230-270 g were randomly divided into 4 groups (n = 8 each): Ⅰ blank control;Ⅱ sham operation; Ⅲ CCI 2w and Ⅳ CCI 4w. The animals were anesthetized with intraperitoneal pentobarbital 40 mg·kg-1. Right sciatic nerve was exposed and 4 ligatures were placed on the right sciatic nerve at 1 mm interspace with 3-0 silk suture. Paw withdrawal threshold to mechanical stimulation (von Frey filament) applied to plantar surface ( MWT) and paw withdrawal latency to thermal stimulation (radiant heat) (TWL) were measured before operation (baseline) and 14 days (group Ⅰ,Ⅱ and Ⅲ) or 28 days (group Ⅳ) after nerve ligation. The animals were killed the next day and the L4,5 segment of the spinal cord and L5 dorsal root ganglion were removed for determination of expression of phosphorylated-CREB-immuno-reaction(pCREB-IR) using immuno-histochemistry. The pCREB-IR cells both in DRG and superficial dorsal horn neurons were quantified and analyzed. Results The animals developed mechanical and thermal hyperalgesia on the 14th day after CCI (in group CCI 2w) . The hyperalgesia was greatly attenuated on the 28th day after CCI. Interestingly enough the animals in sham operation group (Ⅱ) also developed mechanical hyperalgesia to some extent on the 14th day after operation. The number of pCREB-IR cells was significantly increased in the ipsilateral L5 DRG and superficial dorsal horn in group Ⅲ(CCI 2w) as compared to sham operation group ( P 0.01) , but was significantly decreased in group Ⅳ (CCI 4w) . The number of phosphorylated CREB-IR cell was also significantly larger in the ipsilateral DRGs in sham operation group than in blank control group.Conclusion CCI to sciatic nerve increases CREB phosphorylation both in DRG and in superficial dorsal horn neurons of the spinal cord, which may partly explain the molecular mechanisms underlying central and peripheral sensitization following peripheral nerve injury.