The Antinociceptive Effect of Sympathetic Block is Mediated by Transforming Growth Factor β in a Mouse Model of Radiculopathy.

Although sympathetic blockade is clinically used to treat pain, the underlying mechanisms remain unclear. We developed a localized microsympathectomy (mSYMPX), by cutting the grey rami entering the spinal nerves near the rodent lumbar dorsal root ganglia (DRG). In a chemotherapy-induced peripheral neuropathy model, mSYMPX attenuated pain behaviors via DRG macrophages and the anti-inflammatory actions of transforming growth factor-β (TGF-β) and its receptor TGF-βR1. Here, we examined the role of TGF-β in sympathetic-mediated radiculopathy produced by local inflammation of the DRG (LID). Mice showed mechanical hypersensitivity and transcriptional and protein upregulation of TGF-β1 and TGF-βR1 three days after LID. Microsympathectomy prevented mechanical hypersensitivity and further upregulated Tgfb1 and Tgfbr1. Intrathecal delivery of TGF-β1 rapidly relieved the LID-induced mechanical hypersensitivity, and TGF-βR1 antagonists rapidly unmasked the mechanical hypersensitivity after LID+mSYMPX. In situ hybridization showed that Tgfb1 was largely expressed in DRG macrophages, and Tgfbr1 in neurons. We suggest that TGF-β signaling is a general underlying mechanism of local sympathetic blockade.