Cocaine's euphoric rush and addictive properties are primarily due to its effect on increasing dopamine levels in the brain by preventing its reuptake into nerve cells.
The cocaine rush is principally due to its effects on the neurotransmitter dopamine. Cocaine acts as a stimulant, blocking the reuptake of dopamine into nerve cells, which allows for higher levels of this neurotransmitter to stimulate the brain's pleasure centers. The significant increase in dopamine is directly correlated with the intense feeling of euphoria, often described as a "high", and the subsequent addictive nature of cocaine usage.
the main neurotransmitter affected by cocaine that is responsible for its euphoric effects and addictive properties is dopamine, making option (a) the correct answer to the question.