Elsevier

Brain Research

Volume 42, Issue 2, 20 July 1972, Pages 297-309
Brain Research

Reactions of unmyelinated nerve fibers to injury. An ultrastructural study

https://doi.org/10.1016/0006-8993(72)90532-XGet rights and content

Abstract

Reactions of unmyelinated nerves to injury were studied in the distal stumps of rabbit anterior mesenteric nerves following transection. These nerves, chosen because they are almost exclusively unmyelinated, were examined by phase contrast and electron microscopy at intervals from 12 h to 2 weeks after transection. Swollen axons containing mitochondria and other organelles were prominent in the proximal few mm of the distal stump of anterior mesenteric nerve trunks during the first 4 days after transection. As early as 6 days after injury, regenerative changes consisting of numerous small axons with an increased axon-Schwann cell ratio were observed; there was little trace of degenerating axons, or their debris. Thus the capacity of unmyelinated nerve fibers for rapid regeneration has been demonstrated. It is anticipated that this delineation of reactions in unmyelinated nerves will contribute to a greater understanding of functional and morphologic abnormalities in disorders of peripheral nerves.

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      Small-diameter, unmyelinated axons ensheathed by Schwann cell were not associated with macrophages (arrows in Figures 7G and 7H). This is in keeping with previous studies showing that, following injury, macrophages are not recruited into purely unmyelinated peripheral nerves to clear the minimal debris that is present (Bray et al., 1972). Interestingly, macrophages lacking phagocytosed material and with morphological features of highly motile cells were also occasionally detected in cut/ligated nerves, suggesting that they continue to be recruited into nerves lacking myelin (Figure 7C).

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