CXCL12 Promotes Sympathetic Sprouting And Participates In The Cell Biological Mechanisms Of Neuropathic Pain

OBJECTIVE:The roles of CXCL12 and its receptors in the axon morphogenesis of primary cultured sympathetic neuron were explored in our present study.We aim to discuss the morphological plasticity of sympathetic axon terminals which may be involved in the development of Sympathetically maintained neuropathic pain and may provide a new target for clinical treatment.METHODS:For immunocytochemistry and co-localization of tyrosine hydroxylase(TH).CXCR4,and CXCR7,primary sympathetic neurons from Sprague-Dawley rats or ICR mice were cultured at a low density.Images were acquired by confocal or fluorescence microscope for observation or co-expression count.Sympathetic neurons were cultured at a very low density for axonal morphological analysis.After treated with CXCL12 for 12 hours,neurons were fluorescently labeled with vital dye,and all neuronal images were acquired by fluorescence microscope and analyzed to obtain total neurite length,number of branch point and profiles of Sholl analysis for the axonal complexity study.RESULTS:We found that CXCR4 was co-expressed with TH at 100% on rat sympathetic neuron,as well as CXCR7 at 100%.Both CXCR4 and CXCR7 were expressed on cultured mice sympathetic neurons,too.CXCR4,the pain related CXCL12 receptor,is express on the sympathetic neuron somas,axons and growth cones.Neurons treated with CXCL12 showed more complexed axonal Sholl morphology(P<0.001)and more branch points(P<0.05),but no significant total cable length of axons(P>0.05).However,when we focused on the root(first process)of the exposed axons,Sholl plot showed less complexity compared with the control group(P<0.0001),suggested that CXCL12 added the complexity of sympathetic axon by increase branch points of non-first-process axons.CONCLUSION:Both CXCR4 and CXCR7 were expressed on the primary cultured rat sympathetic neurons.Sympathetic neurons treated with CXCL12 showed more complex axon morphogenesis.