Which of the following manipulations would reduce the release of neurotransmitter from a presynaptic neuron terminal?
I. reduction in extracellular calcium ion concentration at the axon terminal
II. increase in extracellular sodium ion concentrations at the axon terminal
III. addition of tetrodotoxin to the extracellular fluid at the axon terminal
A) only I
B) only II
C) only III
D) only II and III
E) only I and II

Question

Quizplus · Accepted Answer

I. A reduction in extracellular calcium ion concentration at the axon terminal would lead to a decrease in the amount of calcium entering the neuron upon depolarization. Since calcium influx is crucial for the vesicles containing neurotransmitters to fuse with the presynaptic membrane and release their contents into the synaptic cleft, a decrease in calcium levels would reduce neurotransmitter release. II. An increase in extracellular sodium ion concentrations would not directly reduce neurotransmitter release; it might actually enhance depolarization of the neuron. III. Tetrodotoxin blocks sodium channels, preventing action potentials from occurring, which indirectly affects neurotransmitter release by inhibiting the initial depolarization needed for calcium influx, but this option is not included in the correct answer choice.

Which of the Following Manipulations Would Reduce the Release of Neurotransmitter