Histamine activates four receptor types throughout the body. H1 receptors trigger allergies in mucous membranes; H2 receptors in the gut stimulate acid. Too much histamine in the brain causes neurological symptoms without visible damage, but some baseline activity is necessary for normal function.
histamine type 1 receptors a lot in your mucous membrane. If you have an allergic response in the mucous membranes, largely a histamine type 1. If it's in your GI tract and it's making hydrochloric acid, it's a histamine type 2. These things are not just for those 2 purposes. So histamine type 2 and 1 together can be very pro-inflammatory. Histamine reaction, you go to the emergency room, they will often give you 2 kinds of blocking drugs, H1 and H2 receptor blockers. There are also histamine receptors of type 1 and 2 and 3 and 4 in our brain. People who are having huge histamine dumps can have all sorts of neurological and neuropsychiatric symptoms that are not because they have an organic problem with their brain. It's just their brain is participating in all this extra histamine and it's getting overstimulated. If you had no histamine in your brain, your brain would quit working appropriately and might quit working altogether.
