Stereological Study Of The Structural Plasticity In The Rat Spinal Dorsal Horn Induced By Spinal Nerve Ligation

Aim: To study the effects of L5 spinal nerve ligation(SNL)- induced neuropathic pain(NP) on the number of neurons, synapses,microglia and astroglia in the rat spinal dorsal horn.Methods: Twenty-nine adult male Sprague-Dawley rats(aged 3 months) were randomly divided into 2 groups. Sixteen animals were subjected to unilateral tight ligation of the L5 spinal nerve(SNL group)and thirteen animals subjected to unilateral sham-operation(sham-operated group). 7 or 28 days after the operation, the L5 segments of the spinal cord were cut and 50 serial paraffin-embedded sections(thickness 14 μm) were prepared. 3 or 5 sections were sampled in a systematic random manner(evenly spaced) and stained with Nissl’s method and immunohistochemistry using antisynaptophysin, Iba-1 and GFAP antibody. Numbers of neurons, synapses, microglia and astroglia cells in the spinal dorsal horn were estimated using a contemporary stereological technique—the optical disector.Results: In the SNL group, compared with the non-operated side, no significant difference in the number(per unit length of the spinal cord) of synapses and the ratio between the numbers of synapses and neurons, and 210% or 62% increases in the numbers of microglia or astroglia on the operated side were found at 7 days post operation; then the number of synapses, microglia and the ratio between the numbers of synapses and neurons increased significantly by 29%, 120% and 20%, respectively, and the number of astroglia were no difference at 28 days post operation. In the sham-operated group, compared with the non-operated side, there were no significant differences in the numbers of synapses, microglia, astroglia and the ratio between the numbers of synapses and neurons on the operated side at 7 days or 28 days post operation. In the SNL group, compared to that at 7 days post operation, the numbers of microglia and astroglia on the operated side significantly reduced by 48% and 20%, respectively, 28 days post-operation.Conclusion: L5 spinal nerve ligation may lead to the structural plasticity changes in the rat spinal dorsal horn and the changes with the progress of the NP present a dynamic trend of time correlation. The trend of numbers of synapses gradually increased from non- significance to dramatically; the trend of microglia and astroglia numbers increased obviously in the early period of the NP, but then presented a decreasing trend.Microglia and astroglia might play key roles in the induce of the NP and the synapses probably associate with the maintenance of the NP.