Table 1.

The distribution and function of histamine receptors in human body.

Receptor	Distribution	Effects
H1 Receptor	Central nervous system, especially in thalamus, cortex and other regions (210)	Activate neurons and astrocytes (211); Activate H1R, leading to the production of cyclic guanosine monophosphate (cGMP) and nitric oxide (NO), thus inducing the production of arachidonic acid (21, 23)
H2 Receptor	Mainly in basal ganglia, hippocampus, amygdala and cerebral cortex (210, 212)	Induce an increase in intracellular cyclic adenosine phosphate (cAMP) production (41); Block Ca2+ activated potassium conduction and inhibit the release of PLA2 and arachidonic acid (21, 23)
H3 Receptor	Widely in the central nervous system, especially in the cortex, hippocampus and caudate nucleus, but low in peripheral tissues (213, 214)	Mediate feedback inhibition of histamine release and synthesis, and regulate the release of other neurotransmitters such as dopamine and GABA (215)
H4 Receptor	Mainly on hematopoietic cells and immune cells such as mast cells, eosinophils, dendritic cells, and microglia (41)	Play a role in histamine-mediated inflammation, but the specific mechanism is still unclear (41)