In medicine and pharmacology, tricyclic antidepressants are antidepressants that are adrenergic uptake inhibitors that "contain a fused three-ring moiety and are used in the treatment of depression. These drugs block the uptake of norepinephrine and serotonin into axon terminals and may block some subtypes of serotonin, adrenergic, and histamine receptors. However the mechanism of their antidepressant effects is not clear because the therapeutic effects usually take weeks to develop and may reflect compensatory changes in the central nervous system."
Tertiary amine tricyclics
Secondary amine tricyclics
Secondary amine tricyclics include desipramine, nortriptyline, and others. These medications have less affect on serotonin receptors and more on norepinephrine receptors. These medications have less anticholinergic drug toxicity and less sedation.
Mirtazapine, a tetracyclic compound, is classified as a tricyclic antidepressant by the National Library of Medicine in the United States. However, mirtazapine is also considered a second-generation antidepressant.
Mechanism of action
It is generally accepted that they antagonize catechol-O-methyl transferase in postsynaptic neurons. Blocking this enzyme means that it slows the metabolism of serotonin and norepinephrine in the postsynaptic neuron, keeping a higher concentration in the synapse that continues to affect receptors. In contrast, most second-generation antidepressants operate on the presynaptic neuron to maintain high synaptic levels of these neurotransmitters.
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