Activation of spinal GABAB receptors normalizes N-methyl-D-aspartate receptor in diabetic neuropathy

N-methyl-D-aspartate receptor (NMDAR) activity is increased, while GABA(B) receptor is downregulated in the spinal cord dorsal horn in diabetic neuropathy. In this study, we determined the interaction of NMDARs and GABA(B) receptors in streptozotocin (STZ) -induced diabetic neuropathy. The paw withdrawal threshold (PWT) was significantly lower in STZ-treated rats than in vehicle-treated rats. Intrathecal injection of baclofen, a GABA(B) receptor agonist, significantly increased the PWT in STZ-treated rats, an effect that was abolished by pre-administration of the GABA(B) receptor specific antagonist CGP55845. Spinal NR2B, an NMDA receptor subunit, protein and mRNA expression levels were significantly higher in STZ-treated rats than in vehicle-treated rats. Intrathecal baclofen significantly reduced the NR2B protein and mRNA expression levels in STZ-treated rats. Intrathecal administration of CGP55845 eliminated baclofen-induced reduction of NR2B protein and mRNA levels in STZ-treated rats. In addition, the phosphorylated cAMP response element-binding (CREB) protein level was significantly higher in the spinal cord dorsal horn in STZ-treated rats compared with vehicle-treated rats. Intrathecal injection of baclofen significantly decreased phosphorylated CREB protein level in STZ-treated rats; an effect was blocked by CGP55845. These data suggest that activation of GABA(B) receptors in the spinal cord dorsal horn normalizes NMDAR expression level in diabetic neuropathic pain. (C) 2014 Elsevier B.V. All rights reserved.