Histamine is a neurotransmitter that plays a key role in allergenic responses, sleep, alertness, cognition and gastric acid synthesis and secretion. It binds primarily to the four types of histamine receptors:

  • H1, responsible for alertness, cognition, allergenic responses.
  • H2, responsible for gastric acid and intestinal excretions and motility in general.
  • H3, which serves as the histamine autoreceptor.
  • H4, which seems to play a role in immune function.
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