Botulinum toxin and amphetamines ___________________.
  | 
   
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   increase the release of acetylcholine and norepinephrine from the presynaptic membrane, respectively; | 
   
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   act at axoaxonic synapses; | 
   
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   stimulate presynaptic facilitative heteroreceptors; | 
   
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   stimulate calcium ion influx; | 
   
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   all of the alternatives above are correct; |