Tetanus toxin inhibits the evoked outflow of an inhibitory (GABA) and an excitatory (D-aspartate) amino acid from particulate brain cortex.

In order to elucidate the mode of action of tetanus toxin, particles from rat forebrain were preloaded with tritiated GABA or D-aspartate, pre-incubated with tetanus toxin and then depolarized with K+, either in a batch procedure or by superfusion. The toxin depresses, but does not abolish, the evoked outflow of both amino acids in either system. Omission of Ca2+ decreases the outflow in the batch procedure by about 40%. The remaining outflow of either amino acid is insensitive to tetanus toxin, whereas the Ca2+ dependent outflow is completely inhibited. Antitoxin neutralizes the toxin but does not reverse its in vitro effects, once manifest. The toxin effects increase with time and temperature of pre-incubation. Pretreatment of the particles with V. cholerae neuraminidase, which is known to convert the long-chain gangliosides quantitatively into GM1, does not decrease the sensitivity to tetanus toxin. Besides particles from rat brain, those from chicken, but not those from frog brain, are toxin-sensitive when tested for GABA outflow in the batch procedure. Frog brain does not yield the typical ganglioside pattern, and also does not measurably bind 125I-tetanus toxin. The homoexchange diffusion of GABA, but not of D-aspartate, is slightly facilitated by tetanus toxin. We confirmed that tetanus toxin slightly inhibits the uptake of GABA, whereas that of D-aspartate is not measurably influenced. The accumulation, driven by a Na+/K+ gradient, of GABA into membrane vesicles from rat cortex is not affected by tetanus toxin. The present data support the hypothesis that tetanus toxin influences a process involved in the outflow of many transmitters, both excitatory and inhibitory.