Mitigation of neuroma induced neuropathic pain through prophylactic regenerative peripheral nerve interfaces (RPNIs) is sexually dimorphic in rats
Amir Dehdashtian, MD, MPH1, Shelby Svientek, MD2, Mary Jane Risch, BS1, Jarred Bratley, BS1, Allison B Vittert, MS1, Daniel C. Ursu, MS3, Paul S Cederna, MD4 and Stephen WP Kemp, PhD1, (1)University of Michigan, Ann Arbor, MI, (2)The University of Michigan, Ann Arbor, MI, (3)Plastic Surgery, The University of Michigan, Ann Arbor, MI, (4)Plastic Surgery, University of Michigan, Ann Arbor, MI
Introduction:
Approximately two million people are affected by major limb amputations in the United States. One of the major limitations for rehabilitation of these patients is painful neuroma formation. Nerve transection following amputation triggers a cascade of changes, resulting in hypersensitivity of both central and peripheral nervous systems. Recent evidence suggests that underlying hypersensitivity mechanisms are different between males and females Regenerative peripheral nerve interfaces (RPNIs) have been previously shown to effectively treat neuroma pain by providing physiologic muscle targets for the severed axons. In the present study, we investigated the effect of prophylactic RPNIs to reduce both central and peripheral pain hypersensitivity in male and female rats.
Methods:
Thirty-six F344 rats (n=18/gender) were randomly assigned to one of the following groups (n=6/group): (1) neuroma without treatment, (2) prophylactic RPNI, and (3) sham surgery. For the neuroma group, the right side tibial nerve was transected at the mid-thigh level, and the proximal nerve segment was relocated and placed directly underneath the skin. In contrast, for the prophylactic RPNI group, the transected nerve was implanted into an autologous extensor digitorum longus (EDL) muscle, and the RPNI was placed underneath the skin and was situated between the biceps femoris muscle. Weekly behavioral tests were performed for eight weeks post-operatively. Neuroma pain was measured by five trials of five gentle tappings over neuroma location using a single Von-Frey filament (similar to Tinel's test). A series of Von-Frey filaments were applied to the middle of the hind-paw to assess mechanical allodynia. Also, cold and heat allodynias were evaluated using the acetone and Hargreaves tests, respectively. At the endpoint, neuroma bulb, RPNI, L4-5 dorsal root ganglia (DRGs), and lumbar spinal cord were harvested. Macrophage proliferation in DRGs, as well as, microglial expansion in the spinal cord sections were quantified after immunostaining.
Results:
Although prophylactic RPNI reduced the neuroma pain over time in both sexes, females displayed significantly higher pain initially, and a longer convalescence before the pain was attenuated. Similarly, mechanical allodynia was attenuated faster in males as compared to females. Prophylactic RPNI significantly mitigated thermal allodynia in males, while the intervention was not effective in females. Regardless of gender, prophylactic RPNI did not attenuate cold allodynia.
Conclusion:
Treatment with prophylactic RPNIs substantially mitigates neuroma pain and mechanical allodynia in both sexes, while the response was faster in males. In addition, cold and heat allodynia in females was refractory to the prophylactic RPNI.
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