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The distribution of collagen types I, III, and V and fibronectin was investigated by means of immunofluorescent techniques in denervated and normal rat skeletal muscle. During a period of 28 days, a distinct atrophy developed in the denervated gastrocnemius muscle and was accompanied by an increase in types I and III collagen in the endomysium and perimysium. The amount of type V collagen showed little change, whereas fibronectin increase closely parallelled types I and III collagen. The results indicate that denervation atrophy in muscles is accompanied by striking fibrotic changes due to mesenchymal types I and III collagen.

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Northern hybridization of total RNA isolated from adult human sciatic nerve demonstrated a readily detectable hybridization signal for glucose transporter 1 (GLUT 1) mRNA. Western blot analysis demonstrated that GLUT 1 proteins extracted from adult human and from mature rat sciatic nerves had different electrophoretical mobilities. The migration positions of human and rat GLUT 1 proteins corresponded to 60-70 kDa and 55-60 kDa, respectively, as estimated by markers with known molecular masses. Indirect immunofluorescence staining localized GLUT 1 to the perineurium in the adult human sciatic nerve. Only a few endoneurial capillaries of human adult nerve stained positively for GLUT 1, which was in contrast to rat peripheral nerve where most endoneurial capillaries were positive for GLUT 1. In developing human nerves, the staining pattern for GLUT 1 was markedly different from that of the adult nerves: at 14 weeks, the perineurial cells were entirely negative for GLUT 1. Between 22 and 26 weeks of gestation, the staining reaction for GLUT 1 in the perineurium became markedly more prominent, and by 35 weeks the intense perineurial staining resembled that observed in the adult human nerves. In contrast to adult nerves, both endo- and epineurial blood vessels stained intensely for GLUT 1 in the fetal samples. Thus, the immunoreactivity for GLUT 1 in the perineurium seems to increase concomitant with the maturation of barrier properties of perineurium, whereas the transient expression of GLUT 1 in the vasculature of developing nerve may have a specific role in the proliferating endothelial cells.

The changes in Schwann cell basement membrane associated with degeneration and regeneration during 50 weeks after transection of rat sciatic nerve were studied immunohistochemically with antibodies to laminin. In half of the animals, regeneration was prevented by suturing the nerve stumps aside, whereas in the rest spontaneous regeneration was allowed. Axonal regeneration was monitored with anti-neurofilament protein antibodies. In control nerves, basement membranes surrounding Schwann cells were visualized as circular, laminin-positive structures within the endoneurium. By 8 weeks after transection, Schwann cells had formed columns which were laminin-positive throughout their cross-sectional area and indistinguishable from basement membrane zones in both non-regenerating and regenerating nerves. As axons repopulated the distal stump, the normal shape of Schwann cell basement membrane tubes was slowly restored in freely regenerating nerves. In non-regenerating nerves, however, a striking atrophy of Schwann cell columns was observed. Regenerating axons were only seen inside laminin-positive tubular structures in all phases after 8 weeks in regenerating nerves. On the other hand, restoration of normal shape in laminin-positive basement membrane zones was coincident with appearance of axons in the distal stump, but it did not take place in chronically degenerating nerves. The results show that chronic degeneration leads to an atrophy of Schwann cell columns and results in a decrease in laminin immunoreactivity associated with them.