Tetanus toxin produces spastic paralysis in situ by blocking inhibitory neurotransmitter release in the spinal cord. Although di-and trisialogangliosides bind tetanus toxin, their role as productive toxin receptors remains unclear. We examined toxin binding and action in spinal cord cell cultures grown in the presence of fumonisin B 1 , an inhibitor of ganglioside synthesis. Mouse spinal cord neurons grown for 3 weeks in culture in 20 M fumonisin B 1 develop dendrites, axons, and synaptic terminals similar to untreated neurons, even though thin layer chromatography shows a greater than 90% inhibition of ganglioside synthesis. Absence of tetanus and cholera toxin binding by toxin-horseradish peroxidase conjugates or immunofluorescence further indicates loss of mono-and polysialogangliosides. In contrast to control cultures, tetanus toxin added to fumonisin B 1 -treated cultures does not block potassiumstimulated glycine release, inhibit activity-dependent uptake of FM1-43, or abolish immunoreactivity for vesicle-associated membrane protein, the toxin substrate. Supplementing fumonisin B 1 -treated cultures with mixed brain gangliosides completely restores the ability of tetanus toxin to bind to the neuronal surface and to block neurotransmitter release. These data demonstrate that fumonisin B 1 protects against toxin-induced synaptic blockade and that gangliosides are a necessary component of the receptor mechanism for tetanus toxin.Tetanus toxin (TeNT) 1 blocks the release of inhibitory neurotransmitters in the spinal cord leading to hyperactivity of motor neurons and consequent spastic paralysis (for review, see Ref. 1). The toxin is synthesized as a single polypeptide (M r ϭ 150,000), released by bacterial lysis, and cleaved to form an active dichain toxin with the heavy and light chains linked through one disulfide bond. The carboxyl-terminal half of the heavy chain constitutes the receptor binding domain, the amino-terminal half of the heavy chain is responsible for membrane translocation of the toxin, and the light chain contains the catalytic domain (for review, see Ref.2). Upon entering the synaptic cytosol, the toxin arrests neurotransmitter release by its action as a zinc endopeptidase, which cleaves vesicle-associated membrane protein (VAMP), a synaptic vesicle integral membrane protein believed to be critical for neuroexocytosis (3, 4). Whereas TeNT has been shown to bind to the surface of neurons and to act intracellularly (for reviews, see Refs. 2 and 5-7), its cell surface receptor(s) and mechanism of delivery to the cytosol are not well understood.Since the demonstration of the affinity of TeNT for gangliosides present on the neuronal surface (8), there have been a number of studies (for review, see Ref. 6) characterizing the binding of TeNT to gangliosides in various in vitro and in vivo preparations. Although it is difficult to assign an affinity to this binding (7), there is general agreement that TeNT shows the highest affinity for GT1b and GD1b polysialogangliosides, although not nearly as ...

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