Espirros, Sexo, Sono e Histamina.

"Heat--Research on the ability to withstand heat stress identified histamine receptors as contributing to increased blood flow during heat stress, but only the H1 histamine receptor was involved in skin blood flow changes.
Sleep--It has been shown that histaminergic cells have the most "wakeful" firing pattern of any neuronal type. They fire rapidly during waking, and completely stop firing during sleep. The cell bodies of neurons which release histamine as a neurotransmitter are found in the posterior hypothalamus, in various tuberomammillary nuclei. From here, these histaminergic neurons project throughout the brain, to the cortex through the medial forebrain bundle. Antihistamines, that is substances that block the H1 histamine receptors improve sleep. Likewise, destruction of histamine releasing neurons, or inhibition of histamine synthesis leads to an inability to maintain vigilance. Finally, H3 receptor antagonists (which stimulate histamine release) increase wakefulness
Sex--Histamine is released as part of sexual arousal from mast cells in the genitals, and histamine release has been connected to the sex flush in women. The female orgasm can be facilitated by supplemental folic acid along with niacin, which will increase histamine release. Conversely, men with high histamine levels may suffer from premature ejaculations.
Allergies--Histamine is an important protein involved in many allergic reactions. An antigen must first be attached to cell surface receptors on mast cells. This triggers a response that often includes the release of histamine. Most allergies involve the release of histamine and other pro-inflammatory substances."[...]