H-89 attenuated mechanical allodynia and inhibited CREB phosphorylation in the spinal dorsal horn following chronic constriction injury in rats

Objective To investigate the effects of a highly selective cAMP-dependant protein kinase(PKA) inhibitor, H-89, on tactile allodynia, as well as cyclic AMP response element binding protein (CREB) phosphorylation in the ipsilateral spinal dorsal horn neurons induced by chronic constriction injury(CCI) of the sciatic nerve in rats. Methods In part one, after CCI model had been successfully established, twenty eight female SD rats weighing (250±20)g were randomly allocated to one of four groups(n=7): control group received solvent; H1, H2 and H4 group received H-89 1,2,and 4 nmol respectively. Drugs were delivered via L 5-6 acute puncture after briefly anesthetized with isoflurane. Mechanical withdrawal threshold (MWT) were determined at before and 15, 30, 60 min after drug-delivery. In part two, five groups (n=6), including a sham group(sham surgery received solvent), and four CCI groups received drugs(H1, H2, H4 group) or solvent(DMSO group) as described above were euthanatized 30 min after drug delivery to investigate the effect of H-89 on CREB phosphorylation in the superficial neurons of the ipsilateral spinal dorsal horn. CREB phosphorylated(pCREB) neurons were detected by immunohistochemistry. Results MWT increased after drug administration, but there were no statistical significance in the 1 nmol group, compared to baseline or control group(P>0.05). 15 min after drug delivery, MWT significantly increased(P<0.01, compared to baseline or control group) in the 4 nmol group. The number of pCREB positive neurons in the L 4-5 spinal dorsal horn and their gray level were reduced by H-89 administration(P<0.01, compared to DMSO group).Conclusion PKA inhibitor H-89 can attenuate tactile allodynia induced by chronic constriction injury of the sciatic nerve in rats, and inhibit CREB phosphorylation in the spinal dorsal horn neurons following CCI, indicating PKA/CREB signaling pathway plays an important role in the maintance of neuropathic pain.