Biomedical subjects
Publications and source records attributed to D Tonge.
An improved method using HRP for visualizing axons in whole-mount preparations is described. Application of this method to preparations of regenerating frog peripheral nerves maintained in organ culture was used to show that regeneration following nerve crush begins after about 3 days.
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.
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.
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.
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