Structural alterations of peripheral nerve monogalactosylceramides during development and Wallerian degeneration

Reaction products of selenite with thiols were tested for an inhibitory effect on amino acid incorporation in a cell-free system derived from rat liver and on protein synthesis in intact P815 and L1210 cells. In the cell-free system maximum inhibition, up to 96%, was reached at about 10 microM selenium. In intact cells inhibitory effect varied depending on which reaction product or cell line was used. Maximum inhibition was obtained after 30 min of incubation with selenium concentrations ranging from 0.25 microM to over 7 microM. Selenite itself also inhibited protein synthesis of L1210 cells, but only after 90 min of incubation and starting at selenium concentrations of 2 microM. Inhibition of protein synthesis in intact cells was followed by cell death. Pre-incubation of the reaction products of a monothiol (2-propanethiol) and of a vicinal dithiol (2,3-dimercapto-1-propanol) in culture medium showed a rapid decrease of the inhibitory capability of the product from the monothiol, but not of the product from the dithiol. The results indicate that selenite and a thiol react to form products which have differential toxic effects to cells in vitro.     

Desert hedgehog-patched 2 expression in peripheral nerves during Wallerian degeneration and regeneration

Hedgehog proteins are important in the development of the nervous system. As Desert hedgehog (Dhh) is involved in the development of peripheral nerves and is expressed in adult nerves, it may play a role in the maintenance of adult nerves and degeneration and regeneration after injury. We firstly investigated the Dhh-receptors, which are expressed in mouse adult nerves. The Dhh receptor patched(ptc)2 was detected in adult sciatic nerves using RT-PCR, however, ptc1 was undetectable under the same experimental condition. Using RT-PCR in purified cultures of mouse Schwann cells and fibroblasts, we found ptc2 mRNA in Schwann cells, and at much lower levels, in fibroblasts. By immunohistochemistry, Ptc2 protein was seen on unmyelinated nerve fibers. Then we induced crush injury to the sciatic nerves of wild-type (WT) and dhh-null mice and the distal stumps of injured nerves were analyzed morphologically at different time points and expression of dhh and related receptors was also measured by RT-PCR in WT mice. In dhh-null mice, degeneration of myelinated fibers was more severe than in WT mice. Furthermore, in regenerated nerves of dhh-null mice, minifascicular formation was even more extensive than in dhh-null intact nerves. Both dhh and ptc2 mRNA levels were down-regulated during the degenerative phase postinjury in WT mice, while levels rose again during the phase of nerve regeneration. These results suggest that the Dhh-Ptc2 signaling pathway may be involved in the maintenance of adult nerves and may be one of the factors that directly or indirectly determines the response of peripheral nerves to injury.     

Ultrastructural sequence of myelin breakdown during Wallerian degeneration in the rat optic nerve

Summary Adult albino rats were subjected to unilateral surgical removal of the eyeball. After survival times of 7–140 days, the numerical response of the neuroglial cells, and the progressive disintegration of the myelin sheaths in the optic nerves, were studied qualitatively and quantitatively in electron-microscopic montages. The distribution density of microglia and astroglia in degenerating optic nerve increased to peaks after 35 and 56 days respectively, whereas, the oligodendroglia gradually decreased. During the early stage of degeneration, microglial cells appeared and invaded the sheath at the intraperiod line, peeling off the outer lamellae, which were then engulfed by phagocytosis. Within the microglia, myelin sheath fragments were surrounded by a membrane curled to form a myelin ring. In the intermediate stage of degeneration, the paired electrondense lines of the ring, made up of myelin basic protein, decomposed and formed a homogenous or heterogenous osmiophilic layered structure, the myelin body, which, in the final stages, disintegrated and transformed into globoid lipid droplets and needle shaped cholesterol crystals.     

Wallerian degeneration in rabbit tibial nerve: changes in amounts of the S-100 protein

Abstract— —A soluble protein (S-100) which is unique to the nervous system was measured in rabbit tibial nerve at 0, 3, 7, 14, 21, and 28 days of degeneration. Amounts of S-100 in the degenerated peripheral segment of the transected nerve fell progressively during degeneration to 2 per cent of that measured in the corresponding portion of nerve taken from control rabbits 28 days postoperatively. Total soluble proteins increased 42 per cent during this time. Levels of S-100 and total soluble proteins remained unchanged in non-degenerated nerve segments from experimental and control rabbits. Correlations of amounts of S-100 measured in the study reported here with cellular changes demonstrated by other investigators to characterize Wallerian degeneration in peripheral nerve suggest that the S-100 protein is localized primarily in axons rather than in Schwann cells or myelin.     

Desert hedgehog‐patched 2 expression in peripheral nerves during Wallerian degeneration and regeneration

Hedgehog proteins are important in the development of the nervous system. As Desert hedgehog (Dhh) is involved in the development of peripheral nerves and is expressed in adult nerves, it may play a role in the maintenance of adult nerves and degeneration and regeneration after injury. We firstly investigated the Dhh‐receptors, which are expressed in mouse adult nerves. The Dhh receptor patched(ptc)2 was detected in adult sciatic nerves using RT‐PCR, however, ptc1 was undetectable under the same experimental condition. Using RT‐PCR in purified cultures of mouse Schwann cells and fibroblasts, we found ptc2 mRNA in Schwann cells, and at much lower levels, in fibroblasts. By immunohistochemistry, Ptc2 protein was seen on unmyelinated nerve fibers. Then we induced crush injury to the sciatic nerves of wild‐type (WT) and dhh‐null mice and the distal stumps of injured nerves were analyzed morphologically at different time points and expression of dhh and related receptors was also measured by RT‐PCR in WT mice. In dhh‐null mice, degeneration of myelinated fibers was more severe than in WT mice. Furthermore, in regenerated nerves of dhh‐null mice, minifascicular formation was even more extensive than in dhh‐null intact nerves. Both dhh and ptc2 mRNA levels were down‐regulated during the degenerative phase postinjury in WT mice, while levels rose again during the phase of nerve regeneration. These results suggest that the Dhh‐Ptc2 signaling pathway may be involved in the maintenance of adult nerves and may be one of the factors that directly or indirectly determines the response of peripheral nerves to injury. © 2005 Wiley Periodicals, Inc. J Neurobiol, 2006