Neuropathic pain is a chronic condition caused by damage or dysfunction in the nervous system. While the spleen may influence neuropathic pain, its role has been poorly understood. This study demonstrates that the spleen plays a crucial role in regulating neuropathic pain through the bed nucleus of the stria terminalis (BNST) - paraventricular nucleus of the hypothalamus (PVN) neural circuit in a chronic constriction injury (CCI) mouse model. Splenectomy, splenic denervation, or splenic sympathectomy significantly increased the mechanical withdrawal threshold (MWT) and reduced macrophage infiltration in the dorsal root ganglia (DRG) of CCI mice. Pseudorabies virus injections into the spleen revealed connections to the BNST and PVN in the brain. Chemogenetic inhibition of the BNST-PVN circuit increased macrophage infiltration in the DRG and decreased the MWT; these effects were reversed by splenectomy, splenic denervation, or sympathectomy. These findings underscore the critical role of the spleen, regulated by the BNST-PVN circuit, in neuropathic pain.
Animals ; Neuralgia/pathology* ; Septal Nuclei/physiopathology* ; Male ; Spleen/physiopathology* ; Paraventricular Hypothalamic Nucleus/physiopathology* ; Mice, Inbred C57BL ; Splenectomy ; Mice ; Neural Pathways/physiopathology* ; Disease Models, Animal ; Ganglia, Spinal/physiopathology* ; Sympathectomy ; Macrophages

Objective:To evaluate the role of splenic sympathetic nerve-regulated infiltration and polarization of dorsal root ganglion (DRG) macrophages in diabetic neuropathic pain (DNP) in mice.Methods:Forty-eight specific pathogen-free male C57BL/6 mice, aged 6 weeks, weighing 20-22 g, were divided into 4 groups ( n=12 each) using a random number table method: control group (Con group), DNP group, DNP plus sham operation group (DNP+ Sham group), and diabetes mellitus induced by DNP plus splenic sympathetic denervation group (DNP+ SS group). In DNP+ SS group, the splenic sympathetic denervation procedures were performed using 6-hydroxydopamine solution, while a solvent of 0.2% ascorbic acid saline solution was used as a substitute for 6-hydroxydopamine solution in DNP+ Sham group. After a two-week recovery, the diabetes mellitus was induced by intraperitoneal injection of streptozotocin 120 mg/kg in mice at 8 weeks of age. The mechanical paw withdrawal threshold (MWT) were measured on day 1 before developing the model and on days 7, 14, 21 and 28 after developing the model. After the last behavioral testing, the DRG was taken after anesthesia for determination of the expression of the macrophage marker ionized calcium-binding adaptor molecule 1(Iba1), calcitonin gene-related peptide (CGRP), and tumor necrosis factor-α (TNF-α) (by immunofluorescence) and expression of M1 phenotype markers (CD16, TNF-α, inducible nitric oxide synthase [iNOS]) and M2 phenotype markers (interleukin-10 [IL-10], transforming growth factor-β1 [TGF-β1], and CD206) mRNA (using quantitative real-time polymerase chain reaction). Results:Compared with Con group, the MWT was significantly decreased on days 14, 21 and 28 after developing the model, the expression of CGRP and TNF-α in the DRG was up-regulated, the count of Iba1-positive cells was increased, the expression of CD16, TNF-α and iNOS mRNA was up-regulated ( P<0.05), and no significant change was found in the expression of IL-10, TGF-β1 and CD206 in DNP group ( P>0.05). Compared with DNP group and DNP+ Sham group, the MWT was significantly increased on days 14, 21 and 28 after developing the model, the expression of CGRP and TNF-α in the DRG was down-regulated, the count of Iba1-positive cells was decreased, the expression of CD16, TNF-α and iNOS mRNA was down-regulated, and the expression of IL-10, TGF-β1 and CD206 mRNA was up-regulated in DNP+ SS group ( P<0.05), and no significant change was found in the aforementioned parameters at each time point in DNP and DNP+ Sham groups ( P>0.05). Conclusions:Activation of splenic sympathetic nerve can promote the infiltration and polarization of DRG macrophages, thus participating in the process of diabetic neuropathic pain in mice.

Objective:To evaluate the role of splenic sympathetic nerve-regulated infiltration and polarization of dorsal root ganglion (DRG) macrophages in diabetic neuropathic pain (DNP) in mice.Methods:Forty-eight specific pathogen-free male C57BL/6 mice, aged 6 weeks, weighing 20-22 g, were divided into 4 groups ( n=12 each) using a random number table method: control group (Con group), DNP group, DNP plus sham operation group (DNP+ Sham group), and diabetes mellitus induced by DNP plus splenic sympathetic denervation group (DNP+ SS group). In DNP+ SS group, the splenic sympathetic denervation procedures were performed using 6-hydroxydopamine solution, while a solvent of 0.2% ascorbic acid saline solution was used as a substitute for 6-hydroxydopamine solution in DNP+ Sham group. After a two-week recovery, the diabetes mellitus was induced by intraperitoneal injection of streptozotocin 120 mg/kg in mice at 8 weeks of age. The mechanical paw withdrawal threshold (MWT) were measured on day 1 before developing the model and on days 7, 14, 21 and 28 after developing the model. After the last behavioral testing, the DRG was taken after anesthesia for determination of the expression of the macrophage marker ionized calcium-binding adaptor molecule 1(Iba1), calcitonin gene-related peptide (CGRP), and tumor necrosis factor-α (TNF-α) (by immunofluorescence) and expression of M1 phenotype markers (CD16, TNF-α, inducible nitric oxide synthase [iNOS]) and M2 phenotype markers (interleukin-10 [IL-10], transforming growth factor-β1 [TGF-β1], and CD206) mRNA (using quantitative real-time polymerase chain reaction). Results:Compared with Con group, the MWT was significantly decreased on days 14, 21 and 28 after developing the model, the expression of CGRP and TNF-α in the DRG was up-regulated, the count of Iba1-positive cells was increased, the expression of CD16, TNF-α and iNOS mRNA was up-regulated ( P<0.05), and no significant change was found in the expression of IL-10, TGF-β1 and CD206 in DNP group ( P>0.05). Compared with DNP group and DNP+ Sham group, the MWT was significantly increased on days 14, 21 and 28 after developing the model, the expression of CGRP and TNF-α in the DRG was down-regulated, the count of Iba1-positive cells was decreased, the expression of CD16, TNF-α and iNOS mRNA was down-regulated, and the expression of IL-10, TGF-β1 and CD206 mRNA was up-regulated in DNP+ SS group ( P<0.05), and no significant change was found in the aforementioned parameters at each time point in DNP and DNP+ Sham groups ( P>0.05). Conclusions:Activation of splenic sympathetic nerve can promote the infiltration and polarization of DRG macrophages, thus participating in the process of diabetic neuropathic pain in mice.