The Effects of Histamine

Histamine is a protein that is a part of the normal immune system and is associated with the typical symptoms of allergies and hay fever. Histamine plays a large a role in allergies, but it also works as a neurotransmitter in the brain. Each study about histamine reveals more of its roles in the brain.

Inflammatory Response

Generally, histamine is stored in mast cells, which are a part of the immune system. The histamine stays within these mast cells, until some type of signal, like contact with an allergen, releases the histamine. Once the histamine is released in the bloodstream, it causes the blood vessels to become more permeable--the cells stretch further and further apart from each other, so more fluid can pass through the walls. This is what causes the local inflammation and redness in an allergic response. With the release of histamine, there is also a negative feedback loop to turn off the histamine release, which can take days or weeks, as noted by the Allergy Center.

Anaphylaxsis

The American Academy of Orthopaedic Surgeons defines anaphylaxis as an extreme allergic reaction that can be life-threatening. At least 1,000 Americans a year die of extreme allergic reactions. The major chemicals responsible for this exaggerated immune response are histamine and leukotrienes, both of which are released in large amounts. The effect from the massive release of histamine is that all the blood vessels become more permeable and start to lose components of the blood. Additionally, the smooth muscles of the lungs start to spasm. The combination of these two things make it difficult to maintain a healthy blood pressure and cause difficulty breathing. Without rapid intervention from drugs, like epinephrine (adrenaline), this condition can rapidly be fatal.

Wakefulness

Antihistamines can be taken to help with an allergy response, but they are also used to help children fall asleep, according to the Allergy Center. Antihistamines have a sedative effect. Further study of histamines has revealed that a lack of histamine not only causes drowsiness, but also it is a neurotransmitter and responsible for arousal. In May of 2004, "Neuron" published a study by J. John et al on histamines and their role in waking behavior. In this study, dogs with different types of sleep disorders were studied. The research found that histamine was a useful protein involved not only during wakefulness, but also in the actual act of waking up.

Memory

Around 1980, two different research labs discovered that histamine was an important neurotransmitter. A review study published by M.B. Passani in the April 2007 issue of "Biochemical Pharmacology" reviewed studies on histamine from the 1980s to 2007. This review study found that histamine has been found to play an important role in learning, memory, feeding and regulation of other neurotransmitters. This review study helps bring to light the importance of the use of antihistamines and how they should be altered differently for sleep aids or for decreasing allergy symptoms. For example, the use of general antihistamines for allergies can affect cognitive function and memory; however, using a different form of antihistamine will help with the allergies without affecting cognition.