An axon terminal releases dopamine into the extracellular space primarily by which mechanism?

• A. Passive diffusion of dopamine directly through the phospholipid bilayer
• B. Transport through gap junction channels connecting the neuron to the extracellular space
• C. Ca$2^{+}$-triggered fusion of synaptic vesicles with the plasma membrane (exocytosis)
• D. Engulfment of extracellular fluid containing dopamine followed by vesicle rupture (endocytosis)

Answer: (C)