The Spinal Role Of PSD-95 In NR2B-Mediated Neuropathic Pain

BACKGROUND:Neuropathic pain,usually caused by a primary lesion in the nervous system,is a serious public health problem worldwide.N-methyl-D-aspartate(NMDA)receptor subtype 2B(NR2B),a critical subunit of the glutamatergic NMDA receptor,contributes to the maintenance of neuropathic pain and is involved in pain-related behaviors including hyperalgesia and allodynia.Postsynaptic density-95(PSD-95)is a synaptic scaffolding protein that anchors glutamatergic NMDA receptors to intracellular signaling molecules at the level of synapses;its binding to NR2B plays a crucial role in the development of neuropathic pain.However,the underlying mechanism between these interactions remains unclear.To address the role of PSD-95 in NR2B-mediated chronic pain,we investigated the relationship between PSD-95 activation and NR2B function in the spinal cord,by using a rat model of sciatic nerve chronic constriction injury(CCI).METHODS:We induced CCI by loose ligation of the left sciatic nerve in rats and measured their behavioral hypersensitivity to mechanical and thermal stimuli.At day 7 after CCI,the expression levels of total NR2B and PSD-95 were detected by immunoblotting,as well as phosphorylated NR2B and PSD-95.We assessed the expression of PSD-95 inpain sensitivity,by administering the NR2B antagonist Ro 25-6981 through a pre-established intrathecal catheter.The behavioral hypersensitivity to mechanical and thermal stimuli was evaluated after PSD-95 inhibitor NA-1 application.RESULTS:We demonstrate that the expression levels of total NR2B and PSD-95,as well as phosphorylated NR2B and PSD-95,in the spinal dorsal horn,were increased in the CCI animals.Repeated treatment with the selective NR2B antagonist Ro 25-6981 markedly attenuated the thermal hypersensitivity,in a time-dependent manner,and inhibited the CCI-induced upregulation of PSD-95 in the spinal dorsal horn.Furthermore,intrathecal injection of the PSD-95 inhibitor strikingly reversed the thermal and mechanical hyperalgesia.CONCLUSIONS:Our results indicates up-regulated PSD-95 expression was mediated by NR2B in CCI rats and blocking of NR2B signaling in the spinal cord could be used as a therapeutic candidate for treating neuropathic pain.