Mechanism of spinal monocyte chemoattractant protein-1-mediated maintenance of chronic pathological pain in rats: the relationship with synaptic transmission in spinal dorsal horns / 中华麻醉学杂志

ABSTRACT

Objective To evaluate the relationship between the mechanism of spinal monocyte chemoattractant protein-1 (MCP-1)-mediated maintenance of chronic pathological pain and synaptic transmission in spinal dorsal horns of rats.Methods Female Sprague-Dawley rats,aged 2-3 weeks after birth,weighing 150-210 g,were studied.The experiment was performed in 2 parts.Experiment Ⅰ Eighteen Sprague-Dawley rats were randomly divided into 2 groups (n =9 each) on 7 days after intrathecal catheters were insertedphosphate buffer solution (PBS) group and MCP-1 group.PBS 10 μl was intrathecally injected in group PBS,and PBS 10 μ1 containing 100 ng MCP-1 was intrathecally injected in group MCP-1.The mechanical pain threshold was measured at 30 and 60 min before intrathecal injection,and 30,60,90,120,150 and 180 min and 1,2 and 3 days after intrathecal injection.Experiment Ⅱ The transverse spinal cord slices were prepared,and substantia gelatinosa neurons were selected for whole-cell patch-clamp recording.Electrophysiological recording was performed at 1 h of incubation with artificial cerebrospinal fluid (ACSF) and immediately after adding MCP-1for excitatory synaptic transmission recording,MCP-1 (final concentration 100 nmol/L),N-methyl-D-aspartate (NMDA,final concentration 100 μmol/L) and α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA,final concentration 20 μmol/L) were added to ACSF,and spontaneous excitatory postsynaptic currents (sEPSCs),AMPA receptors-mediated currents and NMDA receptors-mediated currents were recorded;for inhibitory synaptic transmission recording,MCP-1 (final concentration 100 nmol/L) and γ-aminobutyric acid (GABA,final concentration 1 mmol/L) were added to ACSF,and spontaneous inhibitory postsynaptic currents (sIPSCs) and GABA receptors-mediated currents were recorded.Results Compared with group PBS,the mechanical pain threshold was significantly decreased at 30 min-2 days after intrathecal injection in group MCP-1 (P＜0.01).Compared with those at 1 h of incubation with ACSF,the frequency and amplitude of sEPSCs were significantly increased,the amplitude of NMDA receptors-and AMPA receptors-mediated currents were increased,the frequency and amplitude of sIPSCs were decreased,and the amplitude of GABA receptors-mediated currents was decreased immediately after adding MCP-1 (P＜0.05).Conclusion MCP-1 enhances excitatory synaptic transmission through enhancing the function of NMDA and AMPA receptors in the posterior substantia gelatinosa neurons of the spinal cord;MCP-1 weakens inhibitory synaptic transmission through inhibiting GABA receptor function,which may be involved in MCP-l-mediated maintenance of chronic pathological pain in rats.