The epidermis is innervated by fine nerve endings that are important in mediating nociceptive stimuli. However, their precise role in neuropathic pain is still controversial. Here, we have studied the role of epidermal peptidergic nociceptive fibers that are located adjacent to injured fibers in a rat model of neuropathic pain. Using the Spared Nerve Injury (SNI) model, which involves complete transections of the tibial and common peroneal nerve while sparing the sural and saphenous branches, mechanical hypersensitivity was induced of the uninjured lateral (sural) and medial (saphenous) area of the foot sole. At different time points, a complete foot sole biopsy was taken from the injured paw and processed for Calcitonin Gene-Related Peptide (CGRP) immunohistochemistry. Subsequently, a novel 2D-reconstruction model depicting the density of CGRP fibers was made to evaluate the course of denervation and re-innervation by uninjured CGRP fibers. The results show an increased density of uninjured CGRP-IR epidermal fibers on the lateral and medial side after a SNI procedure at 5 and 10 weeks. Furthermore, although in control animals the density of epidermal CGRP-IR fibers in the footpads was lower compared to the surrounding skin of the foot, 10 weeks after the SNI procedure, the initially denervated footpads displayed a hyper-innervation. These data support the idea that uninjured fibers may play a considerable role in development and maintenance of neuropathic pain and that it is important to take larger biopsies to test the relationship between innervation of injured and uninjured nerve areas.

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Introduction: Osteoarthritis (OA) affects millions of people worldwide. In hand OA, the thumb base is the most affected single joint. The reported radiographic prevalence ranges from 0 to 100%, making the true radiographic prevalence unclear. Hence, we conducted a meta-analysis on the age and sex-specific prevalence of radiographic thumb base OA. Methods: We performed a search in Embase, Medline Ovid, Web of Science Core Collection, Cochrane Central Register of Trials, and Google Scholar. We included studies of the general population that reported thumb base OA for males and females separately based on a hand radiograph and reported the age of these groups. Using meta-regression, we estimated the odds ratio (OR) of having radiographic thumb base OA for age and sex, while adjusting for within-study correlation. Results: The initial search yielded 4,278 articles; we finally included 16 studies that reported the age-and sex-stratified prevalence. Taken together, there were 104 age and gender specific-prevalence rates that could be derived from the 16 studies. The prevalence of radiographic OA for the 50-year-old male and female participants was 5.8% and 7.3%, respectively, while the respective prevalence for 80-year-old male and female participants was 33.1% and 39.0%. We found an OR for having radiographic OA of 1.06 (95%CI [1.055e1.065], p < 0.001) per increasing year of age, and 1.30 (95%CI: 1.05e1.61], p ¼ 0.014) for females. Conclusion: In the general population, radiographic thumb base OA is more prevalent in females and is strongly associated with age.