TAAR1-Dependent and -Independent Actions of Tyramine in Interaction With Glutamate Underlie Central Effects of Monoamine Oxidase Inhibition.

Abstract

BACKGROUND:

Monoamine oxidase inhibitors (MAOIs) exert therapeutic actions by elevating extracellular levels of monoamines in the brain. Irreversible MAOIs cause serious hypertensive crises owing to peripheral accumulation of tyramine, but the role of tyramine in the central effects of MAOIs remains elusive, an issue addressed herein. To achieve robust inhibition of MAOA/B, the clinically used antidepressant tranylcypromine (TCP) was employed.

METHODS:

Behavioral, histological, mass spectrometry imaging, and biosensor-mediated measures of glutamate were conducted with MAOIs in wild-type and TAAR1-knockout (KO) mice.

RESULTS:

Both antidepressant and locomotion responses to TCP were enhanced in TAAR1-KO mice. A recently developed fluoromethylpyridinium-based mass spectrometry imaging method revealed robust accumulation of striatal tyramine on TCP administration. Furthermore, tyramine accumulation was higher in TAAR1-KO versus wild-type mice, suggesting a negative feedback mechanism for TAAR1 in sensing tyramine levels. Combined histoenzymological and immunohistological studies revealed hitherto unknown TAAR1 localization in brain areas projecting to the substantia nigra/ventral tegmental area. Using an enzyme-based biosensor technology, we found that both TCP and tyramine reduced glutamate release in the substantia nigra in wild-type but not in TAAR1-KO mice. Moreover, glutamate measures in freely moving animals treated with TCP demonstrated that TAAR1 prevents glutamate accumulation in the substantia nigra during hyperlocomotive states.

CONCLUSIONS:

These observations suggest that tyramine, in interaction with glutamate, is involved in centrally mediated behavioral, transcriptional, and neurochemical effects of MAOIs.

• Authors: Ioannis Mantas, Theodosia Vallianatou, Yunting Yang, Mohammadreza Shariatgorji, Maria Kalomoiri, Elva Fridjonsdottir, Mark J Millan, Xiaoqun Zhang, Per E Andrén, Per Svenningsson
• Journal: Biological psychiatry (Biol Psychiatry) Vol. 90 Issue 1 Pg. 16-27 (07 01 2021) ISSN: 1873-2402 [Electronic] United States
• PMID: 33579534 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2020 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.

Chemical References

• Monoamine Oxidase Inhibitors
• Receptors, G-Protein-Coupled
• Glutamic Acid
• Monoamine Oxidase
• Tyramine
• Trace amine-associated receptor 1

Topics

• Animals
• Glutamic Acid
• Mice
• Mice, Knockout
• Monoamine Oxidase
• Monoamine Oxidase Inhibitors (pharmacology)
• Receptors, G-Protein-Coupled (physiology)
• Tyramine