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.