Direct evidence for the specific fixation of Cl. botulinum A neurotoxin to brain matter.

Rat brain homogenate and synaptosomes from rat brain bind botulinum toxin. The binding is accompanied by partial inactivation. The binding decreases with increasing ionic strength. A considerable fixation of tetanus toxin can still be demonstrated under conditions which prevent the fixation of botulinum toxin. 2. Only the grey substance, not the white substance from bovine brain is able to bind the toxin. 3. Upon pretreatment with neuraminidase, synaptosomes lose nearly all of their binding capacity. However, neither gangliosides nor ganglioside-cerebroside mixtures nor brain extracts could replace the synaptosomes. Thus botulinum A toxin closely resembles tetanus toxin in its ability to react with (a) neuraminidase-sensitive site(s) of the grey matter of the CNS. It differs from tetanus toxin by its stronger sensitivity against ionic forces and by its failure to react with certain gangliosides.