Effect of Tetanus Toxin on Transmitter Release from the Substantia Nigra and Striatum In Vitro

: The effect of tetanus toxin on the uptake and release of radiolabelled transmitters from slices prepared from substantia nigra (SN) and striatum of rats has been investigated. Tetanus toxin-500–750 mouse lethal doses (MLD)-injected into the SN 6 h before preparing the slices significantly reduced the calcium-dependent, potassium-evoked release of [3H]GABA. Endogenous GABA levels in the SN and [3H]GABA uptake by nigral slices were unaffected by pretreatment with the toxin. Injections of tetanus toxin (1000–2000 MLD) into the striatum significantly reduced the calcium-dependent, potassium-evoked release of [14C]GABA and also [3H]dopamine, but had no effect on the K+-evoked release of [3H]5-hydroxytryptamine or [14C]acetylcholine. It is concluded that tetanus toxin inhibits GABA release directly and not by interference with synthesis or inactivation processes.