The role and mechanism of glutamic NMDA receptor in the mechanical hyperalgesia in diabetic rats

Some studies have shown that painful neuropathy is a common and costly complication of both type 1 and type 2 diabetes mellitus, and glutamate is involved in the process although the mechanisms are not clear. The purpose of the present study was to investigate the effect of N-methyl-D-aspartate (NMDA) receptor on mechanical hyperalgesia in diabetic rats and the possible mechanism.Diabetic rat model was established by intraperitoneal injection of streptozotocin (STZ, 1%, 70 mg/kg) once, and evaluated by the change in the fasting blood glucose. The mechanical hyperalgesia was estimated by mechanical withdrawal threshold (MWT) using a set of calibrated Von Frey's filaments. In addition, the expressions of phosphorylated NMDA NR1 and phosphorylated cAMP response element binding protein (pCREB) in L4/L5 dorsal horns of spinal cord were observed.Behavioral results showed that MK-801, an antagonist of NMDA receptor, could reduce the proportion of mechanical hyperalgesia in diabetic rats from 76.67 to 20.00%. Meanwhile, the mean MWTs in STZ group or saline-treated STZ group decreased significantly at 3-8 week, while, the MWTs in MK-801 treated STZ group were significant higher than those in STZ or saline-treated STZ group. In addition, the expressions of NMDA NR1 and pCREB in L4/5 dorsal horns of spinal cord were significant higher in diabetic rats, and MK-801 down-regulated their expressions partly.All these results suggested that NMDA receptor and pCREB in the spinal cord were involved in the regulation of mechanical hyperalgesia in diabetic rats.