Is histamine crucial to normal body functioning? by Connie b. Dellobuono

Answer by Connie b. Dellobuono:

Yes. From Wiki:
Sleep-wake regulation
Histamine is released as a neurotransmitter. The cell bodies of histamine neurons are found in the posterior hypothalamus, in the tuberomammillary nuclei. From here, these neurons project throughout the brain, including to the cortex, through the medial forebrain bundle. Histamine neurons increase wakefulness and prevent sleep.[17] Classically, antihistamines (H1 histamine receptor antagonists) which cross the blood-brain barrier produce drowsiness. Newer antihistamines are designed to not cross into the brain and so do not have this effect. Similar to the effect of older antihistamines, destruction of histamine releasing neurons, or inhibition of histamine synthesis leads to an inability to maintain vigilance. Finally, H3 receptor antagonists increase wakefulness.
Histaminergic neurons have a wakefulness-related firing pattern. They fire rapidly during waking, fire more slowly during periods of relaxation/tiredness and completely stop firing during REM and NREM (non-REM) sleep.
Gastric acid release
Enterochromaffin-like cells, located within the gastric glands of the stomach, release histamine that stimulates nearby parietal cells by binding to the apical H2 receptor. Stimulation of the parietal cell induces the uptake of carbon dioxide and water from the blood, which is then converted to carbonic acid by the enzyme carbonic anhydrase. Inside the cytoplasm of the parietal cell, the carbonic acid readily dissociates into hydrogen and bicarbonate ions. The bicarbonate ions diffuse back through the basilar membrane and into the bloodstream, while the hydrogen ions are pumped into the lumen of the stomach via a K+/H+ ATPase pump. Histamine release is halted when the pH of the stomach starts to decrease. Antagonist molecules, like ranitidine, block the H2 receptor and prevent histamine from binding, causing decreased hydrogen ion secretion.
Protective effects
While histamine has stimulatory effects upon neurons, it also has suppressive ones that protect against the susceptibility to convulsion, drug sensitization, denervation supersensitivity, ischemic lesions and stress.[18] It has also been suggested that histamine controls the mechanisms by which memories and learning are forgotten.[19]
Erection and sexual function
Libido loss and erectile failure can occur during treatment with histamine H2 receptor antagonists such as cimetidine, ranitidine, and risperidone.[20] The injection of histamine into the corpus cavernosum in men with psychogenic impotence produces full or partial erections in 74% of them.[21] It has been suggested that H2 antagonists may cause sexual difficulties by reducing the uptake[clarification needed] of testosterone.[20]
Schizophrenia
Metabolites of histamine are increased in the cerebrospinal fluid of people with schizophrenia, while the efficiency of H1 receptor binding sites is decreased. Many atypical antipsychotic medications have the effect of decreasing histamine production (antagonist), because its use seems to be imbalanced in people with that disorder.[22]
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As we age we have less acid in our stomach and less histamine giving us metabolic related health issues exacerbated by many kinds of meds that most seniors take.

Is histamine crucial to normal body functioning?