Sciatic Nerve Intrafascicular Lidocaine Injection-induced Peripheral Neuropathic Pain: Alleviation by Systemic Minocycline Administration

Local Administration of Minocycline Improves Nerve Regeneration in Two Rat Nerve Injury Models

Peripheral nerve injuries are quite common and often require a surgical intervention. However, even after surgery, patients do not often regain satisfactory sensory and motor functions. This, in turn, results in a heavy socioeconomic burden. To some extent, neurons can regenerate from the proximal nerve stump and try to reconnect to the distal stump. However, this regenerating capacity is limited, and depending on the type and size of peripheral nerve injury, this process may not lead to a positive outcome. To date, no pharmacological approach has been used to improve nerve regeneration following repair surgery. We elected to investigate the effects of local delivery of minocycline on nerve regeneration. This molecule has been studied in the central nervous system and was shown to improve the outcome in many disease models. In this study, we first tested the effects of minocycline on SCL 4.1/F7 Schwann cells in vitro and on sciatic nerve explants. We specifically focused on the Schwann cell repair phenotype, as these cells play a central role in orchestrating nerve regeneration. Finally, we delivered minocycline locally in two different rat models of nerve injury, a sciatic nerve transection and a sciatic nerve autograft, demonstrating the capacity of local minocycline treatment to improve nerve regeneration.

Sciatic Nerve Intrafascicular Injection Induces Neuropathy by Activating the Matrix Modulators MMP-9 and TIMP-1

Background: Peripheral nerve block (PNB) under echo guidance may not prevent intrafascicular anesthetic injection-induced nerve injury. This study investigated whether unintended needle piercing alone, or the intrafascicular nerve injectant could induce neuropathy.

Methods: 120 adult male Sprague-Dawley rats were divided into four groups: 1) group S, only the left sciatic nerve was exposed; 2) group InF-P, the left sciatic nerve was exposed and pierced with a 30 G needle; 3) group InF-S, left sciatic nerve was exposed and injected with saline (0.9% NaCl 30 µL); 4) group InF-R, left sciatic nerve was exposed and injected with 0.5% (5 mg/mL, 30 µL) ropivacaine. Behaviors of thermal and mechanical stimuli responses from hindpaws, sciatic nerve vascular permeability and tight junction protein expression, and macrophage infiltration were assessed. Pro-inflammatory cytokine expression and TIMP-1 and MMP-9 activation at the injection site and the swollen, and distal sites of the sciatic nerve were measured by cytokine array, western blotting, and immunofluorescence of POh14 and POD3.

Results: Intrafascicular saline and ropivacaine into the sciatic nerve, but not needle piercing alone, significantly induced mechanical allodynia that lasted for seven days. In addition, the prior groups increased vascular permeability and macrophage infiltration, especially in the swollen site of the sciatic nerve. Thermal hypersensitivity was induced and lasted for only 3 days after intrafascicular saline injection. Obvious upregulation of TIMP-1 and MMP-9 on POh6 and POh14 occurred regardless of intrafascicular injection or needle piercing. Compared to the needle piercing group, the ratio of MMP-9/TIMP-1 was significantly higher in the intrafascicular injectant groups at the injected and swollen sites of the sciatic nerve. Although no gross changes in the expressions of tight junction proteins (TJPs) claudin-5 and ZO-1, the TJPs turned to apparent fragmentation and fenestration-like degenerative change in swollen endothelial cells and thickened microvessels.

Conclusion: Intrafascicular nerve injection is a distinct mechanism that induces neuropathy. It is likely that the InF nerve injection-induced neuropathy was largely due to dramatic, but transient, increases in enzymatic activities of MMP-9 and activating TIMP-1 in the operated nerves. The changes in enzymatic activities then contributed to certain levels of extracellular matrix degradation, which leads to increases in endoneurial vascular permeability.

Advances in Experimental Medicine and Biology: Intrafascicular Local Anesthetic Injection Damages Peripheral Nerve-Induced Neuropathic Pain

Peripheral nerve blockade (PNB) is advantageous for patients undergoing surgery to decrease the perioperative opioid consumptions and enhance recovery after surgery.Inadvertent local anesthetic (LA) administration into nerve fiber intrafascicularly easily results in unrecognized nerve injury. Using nerve block guidance either by ultrasound, electrical nerve stimulator, or using pressure devices does not prevent nerve damage, even though most of the nerve injury is transiently. The incidence of neurologic symptoms or neuropathy is in the range of 0.02-2.2%, and no significant difference of postoperative neurologic symptoms is found as compared with using ultrasound or guided nerve stimulator technique. However, intrafascicular lidocaine brought about macrophage migration into the damaged fascicle, Schwann cell proliferation, increased intensity of myelin basic protein, and shorten withdrawal time to mechanical stimuli. In dorsal root ganglion (DRG), intrafascicular LA injection increased the activated transcriptional factor 3 (ATF-3) and downregulated Nav1.8 (Nav1.8). In spinal dorsal horn (SDH), the microglia and astrocytes located in SDH were activated and proliferated after intrafascicular LA injection and returned to baseline gradually at the end of the month. This is a kind of neuropathic pain, so low injection pressure should be maintained, the correct needle bevel used, nerve stimulator or ultrasound guidance applied, and careful and deliberately slow injection employed as important parts of the injection technique to prevent intrafascicular LA administration-induced neuropathic pain.