Which neurotransmitter system is directly involved in the euphoric effects of narcotics according to the described mechanism?

• A. Acetylcholine
• B. Endorphin receptor activation
• C. Norepinephrine
• D. GABA

Answer: (B)

The main concept is that narcotic-induced euphoria is driven by activation of the brain’s endogenous opioid system. When narcotics bind to mu-opioid receptors (endorphin receptors), they inhibit GABA-releasing neurons in the ventral tegmental area. This reduces GABA’s suppression of dopamine neurons, leading to increased dopamine release in the mesolimbic pathway, especially in the nucleus accumbens, which produces the rewarding, euphoric feeling. In other words, direct engagement of the opioid receptor system triggers the downstream dopamine surge that underlies the euphoria. The other neurotransmitters listed don’t directly drive this euphoric effect: acetylcholine isn’t the primary mediator here, norepinephrine relates more to arousal, and while GABA is involved in the circuit, the euphoric response specifically stems from opioid receptor activation and the resulting dopamine boost.