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. 2021 Sep 26;11(10):1408. doi: 10.3390/biom11101408

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© 2021 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

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Schematic illustration of histamine synthesis, degradation, and types of histamine receptors. Histamine is synthesized by histidine decarboxylase (HDC) in neurons from the tuberomammillary nucleus (TMN). Histamine could interact with histamine receptors 1 to 4 (H1R, H2R, H3R, and H4R). Importantly, H3R are located presynaptically and regulates histamine release. The effect of histamine is ended by recapture in astrocytes mainly by organic cation transporter 2 (OCT2) and subsequent degradation by histamine N-methyltransferase (HNMT) which is located in the cytosol.