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D Tonge

Publications and source records attributed to D Tonge.

11 recordsLinked to original sources
PubMed1996

Protein kinase C and mouse sciatic nerve regeneration.

We have studied the role of protein kinase C (PKC) in peripheral nerve regeneration by using the cultured adult mouse sciatic nerve, which displays regrowth of sensory axons under serum-free conditions. By the use of immunohistochemistry we show that one of the isoforms of PKC, PKC beta, is present in the nerve cell bodies of normal nerves and is upregulated after injury. In spite of this, the specific PKC inhibitor chelerythrine at 5 microM, a concentration well above its IC50 value for PKC, failed to reduce the outgrowth distance of new axons. This was not due to impermeability of the drug, since the same concentration caused a clear reduction of the injury-induced proliferation of Schwann cells in the crush region. Likewise, HA-1004, an inhibitor of cyclic nucleotide-dependent protein kinases, also lacked effect on outgrowth when used on its own, even at very high concentrations (100 microM). In contrast, outgrowth was significantly reduced when 5 microM chelerythrine and 5 microM HA-1004 were used in combination. In conclusion, the present results suggest that PKC-activity is important but not indispensable for the regeneration process. Successful completion of the latter could be achieved by several, perhaps redundant, phosphorylation systems.

Alkaloids↗
PubMed1996

Axonal outgrowth and neuronal apoptosis in cultured adult mouse dorsal root ganglion preparations: effects of neurotrophins, of inhibition of neurotrophin actions and of prior axotomy.

Dorsal root ganglia (L4 and L5) with attached spinal roots and nerve stumps were isolated from young adult mice and cultured in a layer of extracellular matrix material (matrigel). Within one day, a large number of axons grew out from the cut ends of the nerve and the dorsal root. The average outgrowth length was more than doubled by nerve growth factor, which also strongly increased the number of fibres, showing extensive branching. There was also a significant outgrowth stimulation by neurotrophin-3, but no observable effect by brain-derived neurotrophic factor. In preparations isolated and cultured six days after peripheral nerve transection in vivo, there was an increase in both the outgrowth length (about 1.5- to 2-fold) and in the number of axons. Stimulation of axonal outgrowth, which concerned outgrowth from both the peripheral nerve and the dorsal root, could be further enhanced by the addition of nerve growth factor to the culture. K-252a, a selective inhibitor of neurotrophin receptor-associated tyrosine kinase activity, did not affect either the normal outgrowth or the increased outgrowth in pre-axotomized preparations, at a concentration which abolished the stimulating effects by exogenous nerve growth factor and neurotrophin-3. Under the culturing conditions used, spontaneous apoptosis occurred, but none of the neurotrophins tested, nor K-252a, affected the number of apoptotic neuronal cells analysed by nick-labelling DNA breaks at the end of a 48-h culturing period. Altogether, the present data suggest that for most dorsal root ganglia neurons, signalling through the trk receptors does not influence the apoptosis in vitro and is not required for either the spontaneous axonal outgrowth in matrigel or the increased outgrowth which occurs after prior axotomy in vivo.

Animals↗
PubMed1994

Early regeneration in vitro of adult mouse sciatic axons is dependent on local protein synthesis but may not involve neurotrophins.

The sensory axons of the adult mouse sciatic nerve were shown to regenerate after a local test crush lesion in vitro in a serum-free medium. The average outgrowth distance of the leading axons after culturing for 3 days was 2.8 +/- 0.1 mm, which was shorter than in vivo (3.8 +/- 0.2 mm). With the use of a compartmentalised culture system we could show that regeneration was partially dependent on local protein synthesis in the injury region. The initial stages of regeneration did not seem to involve neurotrophins since both K252a and K252b, selective and nontoxic inhibitors of the neurotrophin actions, failed to inhibit axonal growth. The present in vitro model system offers favourable conditions to investigate the early events of the regeneration process in an adult mammalian peripheral nerve.

Animals↗
PubMed1992

A study of the expression of laminin in the spinal cord of the frog during development and regeneration.

In the present experiments, we have used an affinity-purified polyclonal antibody to laminin to determine the time course of expression of laminin in the central nervous system (CNS) of Rana temporaria tadpoles during normal development and during restoration of the dorsal columns of the spinal cord. Immunoblotting analysis indicated that in the peripheral nervous system (PNS) of adult frogs the antibody recognized proteins of molecular weights 350-400 and 205-220 kDa, corresponding to the A and B chains respectively of mammalian laminin. Immunohistochemistry with our antibody suggested that laminin was absent from the tadpole spinal cord, and did not appear even in the basal lamina of the blood vessels within the spinal cord until after metamorphosis. Furthermore, there was no evidence of laminin expression in the dorsal columns after hemisection of the spinal cord. However, throughout development laminin was present in basal lamina outside the CNS, in particular in the pial membranes, and in the basal lamina of blood vessels and sheath cells in the dorsal and ventral roots. Electron microscopy showed that the blood vessels of CNS capillaries had basal laminae throughout development that was morphologically indistinguishable from that seen in peripheral vessels.

Animals↗
PubMed1987

Pathfinding by dorsal column axons in the spinal cord of the frog tadpole.

Sensory fibres from dorsal root ganglia (DRG) enter the spinal cord and run within a clearly defined ipsilateral pathway, the dorsal column, which lies in the dorsal funiculus. We have examined the characteristics of this pathway as a defined substrate for dorsal column axons in Rana temporaria tadpoles by rotating the thoracic spinal cord through 180 degrees from dorsal to ventral. Using HRP as a neuronal tracer we establish that many dorsal column axons from the hindlimb locate the ipsilateral or contralateral dorsal column pathway in the rotated cord. Other axons locate and grow caudally down the contralateral dorsal column returning to the lumbar region. Axons of the dorsal column never take an inappropriate pathway except at the transection sites where they negotiate abnormal routes to reach the contralateral or ipsilateral dorsal columns in normally positioned or rotated cord. The results demonstrate that the dorsal columns act as highly specific pathways for axons from DRG neurones but the axons' interactions with the pathway do not control the craniocaudal or left-right options for growth.

Animals↗
PubMed1977

The labelling of motor end-plates in skeletal muscle of mice with 125I tetanus toxin.

Twelve hours after injection of 125I labelled tetanus toxin into the shank of one hindlimb of mice radioactivity was found in the end-plate region of soleus muscles. The ratio between the radioactivity of the end-plate and the end-plate-free region was 2.5 +/- 0.4 S.D. Autoradiographs showed intense labelling of end-plates and a slight but clear labelling of axons. When 125I tetanus toxin was injected 3 days after denervation of the soleus muscle the former end-plate region still accumulated a higher radioactivity (ratio 2.0 +/- 0.5 S.D.), however, autoradiographs showed a diffuse distribution of labelled tetanus toxin. It can be concluded that tetanus toxin binds to the presynaptic nerve terminal. This binding is not dependent on activity of the nerve terminal or transmitter release.

Animals↗
PubMed1974

Levodopa.

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Humans↗