Which agents can inhibit ACh release from presynaptic vesicles?

Botulinum toxin is the correct choice as it specifically acts on the presynaptic mechanisms involved in neurotransmitter release. This neurotoxin produced by the bacterium Clostridium botulinum interferes with the fusion of synaptic vesicles containing acetylcholine (ACh) with the presynaptic membrane, effectively preventing the release of ACh into the synaptic cleft. This inhibition of ACh release is responsible for the muscle paralysis and other symptoms associated with botulism.

In contrast, anticholinergics are agents that block the action of ACh at its receptor sites without influencing its release from presynaptic vesicles. Beta blockers primarily affect the adrenergic system by blocking the effects of norepinephrine and do not have a direct role in modulating ACh release. Selective serotonin reuptake inhibitors (SSRIs) function mainly by increasing serotonin levels in the synaptic cleft, which does not directly involve the modulation of ACh release either. Thus, botulinum toxin is uniquely relevant to the inhibition of ACh release among the listed agents.