Tricyclics are antidepressants that block the reabsorption of neurotransmitters, in this case, serotonin, and epinephrine. As a result, these chemicals are released into a synapse.
Monoamine oxidase inhibitors (MAOIs) block the enzyme monoamine oxidase which breaks down serotonin, epinephrine, and dopamine. As a result, the levels of those neurotransmitters are increased.