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Monoamine Enhancers & Their Effects on Serotonin

Monoamines are organic compounds found in the brain. The most important members of the monoamine family are the neurotransmitters dopamine, norepinephrine and serotonin. When the brain has a deficiency of these neurotransmitters, mood disorders and depression can result. Low levels of serotonin, in particular, have been linked to depression. Drugs known as monoamine enhancers can increase levels of serotonin in the brain and bring relief to people suffering from mood disorders. The major classes of monoamine enhancers are monoamine oxidase inhibitors (MAOIs), selective serotonin reuptake inhibitors (SSRIs), tri-cyclic antidepressants (TCAs) and a new experimental treatment known as Lu AA24530.

  1. MAOIs

    • MAOIs work to increase concentrations of serotonin, dopamine and norepinephrine in the brain by blocking the mechanism that breaks down these neurotransmitters. Oxidase is the protein responsible for moving the neurotransmitters out of the cells in the brain. By blocking, or inhibiting, this protein, serotonin and the other "feel good" neurotransmitters are allowed to remain in the cells longer, which can improve depression. MAOIs enhance monoamines by inhibiting their breakdown. Two commonly prescribed MAOIs are Parnate and Nardil. People taking MAOIs should not eat food containing the amino tyromine, such as aged cheeses and red wine, because its combination with the MAOI can cause sudden spikes in blood pressure.

    SSRIs

    • SSRIs were developed in the 1980s specifically to target the neurotransmitter serotonin. SSRIs block the re-absorption of serotonin in brain cells, thus allowing a higher concentration of the neurotransmitter to remain for a longer period of time. Because SSRIs target only serotonin, they have fewer side effects than MAOIs. Paxil and Prozac are two popularly prescribed SSRIs.

    TCAs

    • TCAs work like SSRIs, slowing the absorption of serotonin by nerve cells. TCAs also act on norepinephrine, however, and have more unpleasant side effects. Dry mouth and constipation are two of the most commonly reported unpleasant effects. Amitriptyline and trazodone are two examples of TCAs.

    Lu AA24530

    • Lu AA24530, a new class of drug being developed by H. Lundbeck A/S and Takeda Pharmaceutical Co. Ltd., shows promise as a treatment for depression in clinical trials. It modulates a number of serotonin receptors and actually appears to increase serotonin, dopamine and norepinephrine levels in the brain, rather than just inhibiting their re-absorption. This true monamine enhancer also appears to be well-tolerated by patients in clinical trials.

    Considerations

    • While all of these monoamine enhancers have been shown to boost levels of serotonin in the brain, some work on the other neurotransmitters as well, causing varying degrees of side effects. SSRIs are the current first line of treatment for serotonin enhancement, with TCAs and MAOIs usually reserved for second and third lines of depression therapy.

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