Itoh

Most of us have at some point in our lives taken antihistamines–drugs that block the action of histamine (e.g., Claritin, Allegra)–to relieve allergy symptoms. And while histamine is best known for its role in the immune response, it also has many other important roles in the central nervous system.

In the brain, histamine release is important for arousal (this is why antihistamines tend to make us drowsy). It has also been implicated in regulating appetite, taste perception, learning, memory, aggressive behavior, motivation, and emotion, among others (Yoshizawa et al., 2009; see this quick summary).

Alterations in histamine signalling in the brain have been implicated in a variety of disorders, including schizophrenia (Iwabuchi et al., 2005), depression (Kano et al., 2004), and multiple sclerosis (Wikipedia has a nice summary chart; or you can read this open paper for more details, too).

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