Objective To evaluate the effect of dexmedetomidine on synaptic transmission in the spinal dorsal horn of rats.Methods Male Sprague-Dawley rats,aged 4-6 weeks,weighing 150-200 g,were used in the study.The lumbar enlargemnent segments of the spinal cord were harvested,and the parasagittal lumbosacral spinal cord slices with attached dorsal roots were prepared and incubated in artificial cerebro-spinal fluid.The whole-cell patch-clamp technique was used to record each index,and 4 spinal cord slices were selected and used for each index records.Experiment Ⅰ Dexmedetomidine was added cumulatively in concentration increments.Aδ and C fibers-mediated evoked excitatory postsynaptic currents (eEPSCs) were recorded before administration (baseline) and during perfusion with dexmedetomidine 4 and 10 μg/ml.Experiment Ⅱ The neurons innervated by Aδ and C fibers were selected,and Aδ and C fibers-mediated eEPSCs were recorded before administration (baseline),at 5 min of perfusion with yohimbine (alpha 2 adrenergic receptor antagonist) 2 μmol/L,and during continuous perfusion with yohimbine 2 μmol/L plus dexmedetomidine 4 μg/ml.Experiment Ⅲ The evoked excitatory postsynaptic potentials (eE-PSPs) and evoked inhibitory postsynaptic potentials (eIPSPs) were recorded before administration (baseline) and during perfusion with dexmedetomidine 4 μg/ml.Results Dexmedetomidine could dose-dependently inhibit Aδ and C fibers-mediated eEPSCs,dexmedetomidine could inhibit Aδ and C fibers-mediated eEPSPs and produced no effect on eIPSPs,and yohimbine could inhibit dexmedetomidine-induced inhibitory effect on eEPSCs.Conclusion The mechanism by which dexmedetomidine inhibits nociceptive information transmission in the spinal dorsal horn is related to inhibition of excitatory synaptic transmission through activating α2-adrenergic receptors,but not related to activation of inhibitory synaptic transmission in rats.

AIM:Early calcification of atherosclerotic plaques are colocalized with macrophage and high mobility group box 1 (HMGB1), a cytokine associated with biomineralizing process under physiological and pathological conditions .Our study aims to evaluate whether HMGB1 induces ectopic mineralization via promoting the secretion of matrix vesicles ( MVs) from macrophages .METHODS:HMGB1 was added to the medium of macrophages , the secretion of MVs in the supernatant was tested by flow cytometry analysis .The mineral deposition in calcifying medium was detected by Alizarin Red staining and von Kossa staining .Transmission electron microscopy showed the formation of hydroxyapatite crystals in MVs .Then we subcutaneous injection into mice with MVs to induce regional minera-lization.RESULTS:HMGB1 significantly promoted secretion of MVs from macrophages as raveled by flow cytometry analysis .TNAP activity, considered as a marker of MVs maturation , was higher in HMGB1-induced MVs compared to the control-MVs.HMGB1-MVs also led to mineral deposition in an in vitro MVs-collagen mineralization model .Subcutaneous injection into mice with MVs derived from HMGB1-treated cells showed a greater potential to initiate regional mineralization .Mechanistic experiments revealed that HMGB 1 activated neutral sphingomyelinase 2 ( nSMase2 ) that involved the receptor for advanced glycation end products ( RAGE ) and p38 MAPK (upstream of nSMase2).Inhibition of nSMase2 with GW4869 or p38 MAPK with SB-239063 prevented MVs secretion and min-eral deposition .CONCLUSIONS: HMGB1 induces MVs secretion from macrophages at least in part , via the RAGE/p38 MAPK/nSMase2 signaling pathway .Our findings thus reveal a novel mechanism by which HMGB 1 may participated in the early calcification of atherosclerotic plaques .