It is well-established that cyclophosphamide (CYP) can sensitize the pelvic afferent nerve arising from the urinary bladder, and therefore, induce suprapubic pain. To test the possibility that CYP might facilitate spinal activity-dependent neural plasticity to mediate the development of visceral hypereflexia/hyperalgesia, we compared pelvic-urethra reflex activity and spinal NR2B phosphorylation in vehicle solution (Veh)- and CYP-treated rats. In accompanied with up-regulation of phosphorylated NR2B expression in lumbosacral (L6-S2) dorsal horn, CYP facilitated repetitive stimulation (1 stimulation/ 1 sec)-induced spinal reflex potentiation by increasing the evoked spikes when compared with vehicle solution. Moreover, the facilitation of reflex potentiation and NR2B phosphorylation caused by CYP were reversed both by L-NAME and roscovitine, NOS and Cdk5 antagonists respectively. When compared with negative control, Si-RNA of NR2B, which decreased the expression of NR2B expression, abolished CYP-dependent reflex facilitation and spinal NR2B phosphorylation. These results suggested that CYP might facilitate spinal N-methyl-D-aspartate receptors (NMDARs)-mediated reflex potentiation to participate in the development of visceral hypereflexia/hyperalgesia through NO- and Cdk5-dependent NR2B phosphorylation at lumbosacral dorsal horn.
