125 Contribution of Sensory Neuron-associated Macrophages to Neuropathic Pain via Up-regulation of Calcium Channel in C Fiber Sensory Neurons in Dorsal Root Ganglion: An Animal Model Study

Abstract

INTRODUCTION: Animal models have demonstrated that sensory neuron-associated macrophages (sNAMs) play a key role in the initiation and persistence of neuropathic pain. The Cav3.2 calcium channel (Cav3.2) is also known to be involved in modulating neuropathic pain in peripheral sensory neurons. METHODS: Male Sprague-Dawley rats underwent unilateral tight ligation of the lumbar 5 spinal nerve and were divided into three groups: a control group (SHAM), a group that underwent ligation without, and with minocycline (SNL and SNL+Mino). The mechanical pain threshold of the hind paw was assessed with von-Frey filament application. Immunohistochemical staining techniques were used to evaluate the levels of sNAM, Cav3.2, and C-fiber sensory neurons with anti-Iba1, anti-Cav3.2, and IB4 antibodies, respectively. Cytokine levels were analyzed using cytokine arrays and western blotting. RESULTS: The SNL group had a significantly lower pain threshold compared to the control group (p < 0.001). In the DRG, neuropathic pain led to an accumulation of macrophages and increased their ability to attach to Cav 3.2. The expression of Cav 3.2 then triggered the activation of IB4 cells in the DRG. Additionally, cytokine array and western blot analyses revealed a higher expression rate of TNF-α in the SNL group compared to the control group (p = 0.048). Treatment with minocycline resulted in increased pain threshold, decreased number of macrophages in the DRG, and interruption of the attachment between macrophages and Cav 3.2, leading to lower expression of TNF-α. CONCLUSIONS: In conclusion, the results of this study suggest that sNAMs may play a role in the development of neuropathic pain by increasing the expression of Cav3.2 through the upregulation of TNF-α release in peripheral sensory nociceptive neurons.