Which neurotransmitter's concentration is likely increased with the use of monoamine oxidase inhibitors?

• A. Dihydroxyphenylalanine
• B. Epinephrine
• C. Tryptophan
• D. Tyrosine

Answer: (B)

Monoamine oxidase inhibitors (MAOIs) are a class of antidepressants that work by inhibiting the activity of monoamine oxidase, an enzyme responsible for breaking down monoamines such as norepinephrine, serotonin, and dopamine. When this enzyme's activity is inhibited, the concentrations of these neurotransmitters in the synaptic cleft increase due to decreased degradation.

Epinephrine, which is also known as adrenaline, is a catecholamine neurotransmitter produced from norepinephrine. Given that MAOIs prevent the breakdown of norepinephrine, the levels of epinephrine would subsequently rise as well since norepinephrine serves as a precursor for its synthesis. Therefore, the concentration of epinephrine is likely to increase with the use of MAOIs.

While dihydroxyphenylalanine (DOPA) is an important precursor in dopamine synthesis, it is not directly affected by MAOIs. Tryptophan is an amino acid that is a precursor to serotonin, and its levels are not specifically impacted by MAOIs. Tyrosine, like DOPA, is a precursor to dopamine and both can be influenced by the levels of neurotransmitters affected by MAOIs, but they are not the neurotrans