Acetylcholine inhibition botulinum neurotoxins

Tetanus toxin poisoning produces tetanus, i.e. muscle contractions resulting in spastic paralysis. In contrast, Botulinum neurotoxins cause botulism, which is characterized by flaccid paralysis. This difference reflects differences in the anatomical level of action of these toxins. TeTx acts primarily on the CNS where it blocks exocytosis from inhibitory glycinergic synapses in the spinal cord. Loss of inhibitory control results in motoneuron firing. BoNTs act primarily in the periphery where they inhibit acetylcholine release at the neuromuscular junctions. 

Mochida S, Saisu H, Kobayashi H etal. (1995) Impairment of synatxin by botulinum neurotoxin Ci or antibodies inhibits acetylcholine release but not Ca channel activity. Neuroscience. 65 905—15. 

The botulinum neurotoxins (BoNTs) comprise a family of seven distinct neurotoxic proteins (A-G) produced by immunologically discrete strains of the anaerobic bacterium Clostridium botulinum and in rare cases by Clostridium baratii and Clostridium butyricum (Habermann and Dreyer, 1986 Harvey et ah, 2002 Simpson, 2004). These toxins act on peripheral cholinergic synapses to inhibit spontaneous and impulse-dependent release of acetylcholine (ACh) (Brooks, 1956 Kao et al., 1976). Intoxication by BoNT results in muscle weakness, which can be fatal when the diaphragm and intercostal muscles become sufficiently compromised to impair ventilation (Dickson and Shevky, 1923). The BoNTs are the most potent substances in nature, and exposure to as httle as 1-3 ng/kg may be sufficient to cause human lethahty (GUI, 1982 Middlebrook and Franz, 1997 Amon et al., 2001). 

Type Cl and D botulinum neurotoxins as ADP-ribosyl transferases. As shown by Knight et al. (3), type D botulinum neurotoxin was able to inhibit exocytosis in cultured chromaffin cells. Fig. 1 represents the results of our experiments showing the time course of this inhibition. When cultured bovine adrenal chromaffin cells were incubated with type D botulinum neurotoxin, inhibition of acetylcholine-evoked catecholamine release appeared. This inhibition, however, did not occur instantaneously but appeared and increased with days of incubation, suggesting involvement... 

Fig. 1. Geft) Inhibition of acetylcholine-induced catecholamine release by botulinum toxin in cultured adtenal chromaffin cells. Bovine adrenal chromaffin cells were isolated and cultured at a density of 5 x lOVml. After two days of culture, the cells were washed and suspended in a fresh medium containing 20 pg/ml of type D botulinum neurotoxin. After incubation for indicated days, the cells were washed and stimulated 500 with pM acetylcholine. Catecholamines in the media and cells were extracted separately and quantified electrochemically. Catecholamine release is expressed as % of the total amount , acetylcholine-evoked release O, basal release.

Botulinum neurotoxins, produced by the anaerobic bacterium Clostridium bo-tulinum, are the most toxic poisons known to man. The neurotoxins are food poisons. Once ingested, the neurotoxin is absorbed through the intestinal mucosal layer into the blood stream. It acts at the neuromuscular junction to inhibit the release of acetylcholine (a neurotransmitter) from nerve endings (Simpson, 1989). The result is the dreaded botulism disease, which is manifested by flaccid muscle paralysis. 

Several toxic proteins act as neurotoxins by disrupting the activity of synapses. (A synapse is a junction between two neurons or between a neuron and a muscle cell.) The pain, tremors, and irritability that result from black widow spider bites are caused by a-latrotoxin (125,000 D). This molecule, a single polypeptide, stimulates a massive release of the neurotransmitter acetylcholine (ACh). In contrast, ACh release is inhibited by botulinum toxin, a mixture of several proteins produced by the bacterium Clostridium botulinum. Botulism, a malady most commonly caused by eating contaminated canned food, is characterized by vomiting, dizziness, and sometimes paralysis and death. A related species,... 

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