Interaction of labelled tetanus toxin with substructures of rat spinal cord in vivo
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The in vivo interaction of 125I-labelled toxin with substructures of rat spinal cord has been studied. The rats were poisoned by i.v. injection about 40–50 h before sacrifice.
The labelled material accumulates in the grey substance, which is, on microdissection, about 6 times more active than the white. Autoradiography reveals that the toxin is particularly enriched in the ventrolateral part of the grey substance.
On ultracentrifugation of the homogenates, the label is preferentially fixed to the dense fractions known to contain the synaptosomes. However, a considerable part of the toxin is fixed to the lighter fractions too.
Upon gel filtration, the labelled material in SDS-homogenates from spinal cords poisoned in vivo is indistinguishable from toxin added to the homogenates already prepared. The same is true for the bulk of radioactivity when subjected to disc gel electrophoresis.
The labelled material is degraded by enzymes from spinal cord at pH 3.5, but not at pH 7.5.
The labelled material is relatively firmly bound to structures of spinal cord. The bonding is fairly resistant against washing, even in the presence of an excess of cold toxin, but it can be partially released by treatment with antitoxin.
According to these findings, the labelled material is firmly but not irreversibly bound in vivo to discrete structures, corresponding preferentially to the synaptosomal fractions in the homogenates and the ventrolateral grey in the slices. No evidence has been found for its degradation in vivo. So far, the bulk of labelled material in the spinal cord is indistinguishable from tetanus toxin.
Key wordsTetanus Toxin Iodine Labelling Spinal Cord Autoradiography Antitoxin
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