Final answer:
Cocaine is the substance that primarily affects the reward pathway and neurotransmitter dopamine, leading to heightened pleasure and addiction.
Step-by-step explanation:
Among the substances listed, cocaine primarily affects the reward pathway and the neurotransmitter dopamine. Cocaine acts as a stimulant by preventing the reuptake of dopamine by nerve cells at the synapse. This leads to high levels of dopamine that are available to stimulate the brain's pleasure centers, which contributes to the feeling of a "high" and the substance's addictive properties. After intense use, or a binge, dopamine can be depleted rapidly, leaving the user craving more cocaine.