Background & Aims
Alcohol induced peripheral neuropathy is a major result of chronic alcohol intake and makes up 10% of polyneuropathies. AIPN affects peripheral nerves and leads to neuropathic symptoms primarily in the lower extremities. Mechanisms of this disease are poorly understood. A lack of well characterized AIPN animal models led to gaps in mechanistic research and ultimately, inefficacious treatment strategies. Most animal models of AIPN relied primarily on the use of evoked behaviors and male animals. Therefore, a crucial need exists to better characterize animal models of AIPN to elucidate novel targets involved in the development of AIPN. We aimed to fully characterize an AIPN mouse model and determine the impact of chronic daily EtOH intake on characteristics of AIPN that have yet to be fully explored. We investigated the impact of EtOH % and duration of intake on: evoked and spontaneous behaviors, caudal electrophysiology, intra-epidermal nerve fiber density (IENF) and neuroinflammation.
Methods
Male and female C57BL/6J mice were habituated to a control liquid diet for 7 days. Mice were then chronically given an EtOH or control liquid diet. The impact of EtOH dose (2.5 or 5%) on the development of mechanical and cold sensitivity was investigated. The impact of duration of 5% EtOH intake on changes in spontaneous pain-related behaviors (nesting, wheel running, burrowing, hanging, rearing, locomotor activity and grimace score) was evaluated at 2, 4 and 6 weeks of EtOH intake. The impact of 5% EtOH intake for 4 weeks on electrophysiology was evaluated using caudal nerve conduction. Additionally, the impact of 5% EtOH intake on IENF density was determined. Finally, the impact of the duration of 5% EtOH intake on neuroinflammation was evaluated by measuring the RNA expression of pro-inflammatory cytokines (IL-6, IL-1b and TNFa) using qrt-PCR.
Results
Mice on chronic EtOH for 4 weeks dose-dependently developed mechanical hypersensitivity and cold sensitivity. 5% chronic EtOH treatment produced deficits in nesting deficits at 4 weeks of EtOH intake, but not weeks 2 or 6. Alternatively, chronic EtOH intake did not impact spontaneous hanging or rearing behaviors. Burrowing behavior was lower in mice on 5% EtOH diets versus control and significant at weeks 2 and 6 of EtOH intake. Similarly, mice on 5% EtOH diets showed reduced wheel running activity beginning at week 4 of EtOH intake through week 6. However, chronic EtOH intake did not impact grimace scores nor general locomotor activity. Caudal nerve conduction showed 4 weeks of 5% EtOH intake induced deficits in action potential amplitude but not velocity. Additionally, 4 week of 5% EtOH intake resulted in deficits of IENF density in the hind paws. Finally, mice on chronic EtOH intake showed an upregulation of specific PIC, such as IL-6 and IL-1b, in the spinal cord.
Conclusions
Our studies showed that EtOH dose and duration of intake are key factors in the development of AIPN in mice. Furthermore, we characterized the impact of chronic EtOH intake on a wide variety of behavioral, electrophysiological, morphological and molecular endpoints in mice that emulate clinical characteristics of AIPN. It is well established that the exclusive evaluation of evoked behaviors in animal models leads to a lack of translation to clinical studies in terms of mechanisms and treatment efficacy. The results from this study pave the way for future research in a well characterized model of AIPN that includes a wide range of testable and clinically-relevant endpoints. In addition to evoked behaviors, future AIPN mouse studies should consider the evaluation of additional behaviors (i.e., nesting, burrowing and wheel running), caudal nerve conduction, IENF density and neuroinflammation when investigating potential mechanisms and treatment strategies.
References
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(4) De Logu, F.; Li Puma, S.; Landini, L.; Portelli, F.; Innocenti, A.; de Araujo, D. S. M.; Janal, M. N.; Patacchini, R.; Bunnett, N. W.; Geppetti, P.; Nassini, R. Schwann Cells Expressing Nociceptive Channel TRPA1 Orchestrate Ethanol-Evoked Neuropathic Pain in Mice. J Clin Invest 2019, 129 (12), 5424–5441. https://doi.org/10.1172/JCI128022.
Presenting Author
Lauren Moncayo
Poster Authors
Topics
- Models: Chronic Pain - Neuropathic