Summary: A new study reports mice who were exposed to allergens produced new hippocampal neurons during allergic reactions.
Source: Frontiers.
Hay fever may do more than give you a stuffy nose and itchy eyes, seasonal allergies may change the brain.
Hay fever may do more than give you a stuffy nose and itchy eyes, seasonal allergies may change the brain, says a study published in the open-access journal Frontiers in Cellular Neuroscience.
Scientists found that brains of mice exposed to allergen actually produced more neurons than controls, they did this using a model of grass pollen allergy.
The research team examined the hippocampus, the part of the brain responsible for forming new memories, and the site where neurons continue be formed throughout life. During an allergic reaction, there was an increase in the numbers of new neurons in the hippocampus, raising the question: what could be the consequences of allergies on memory?
The formation and functioning of neurons is linked to the brain’s immune cells, the microglia.
To the scientists surprise, they found that the same allergic reaction that kicks the body’s immune system in high gear, has opposite effect on resident immune cells of the brain. The microglia in the brain were deactivated in brains of these animals.
“It was highly unexpected to see the deactivation of microglia in the hippocampus,” explained Barbara Klein, one of the authors of the study: “Partly because other studies have shown the reverse effect on microglia following bacterial infection.
“We know that the response of immune system in the body is different in case of an allergic reaction vs a bacterial infection. What this tells us is that the effect on the brain depends on type of immune reaction in the body.”
According to a report by the WHO, 10-30% of the population worldwide suffers from allergic rhinitis, commonly called hay fever.
Allergic reaction also causes an increase in neurogenesis, the growth and development of nervous tissue, which is known to decline with age. In individuals prone to allergies, would brain ageing progress differently than in those who are not allergic?
This was a joint study led by Ludwig Aigner from the University of Salzburg and Richard Weiss from Paracelsus Medical University and the Paris Lodron University of Salzburg, Austria.
Funding: The study was funded by European Union, Research Fund of the Paracelsus Medical University Salzburg, and others.
Source: Emily Barker – Frontiers
Image Source: This NeuroscienceNews.com image is credited to the NIH and is in the public domain.
Original Research: Full open access research for “Allergy Enhances Neurogenesis and Modulates Microglial Activation in the Hippocampus” by Barbara Klein, Heike Mrowetz, Josef Thalhamer, Sandra Scheiblhofer, Richard Weiss and Ludwig Aigner in Frontiers in Cellular Neuroscience. Published online June 28 2016 doi:10.3389/fncel.2016.00169
[cbtabs][cbtab title=”MLA”]Frontiers. “Seasonal Allergies Could Change Your Brain.” NeuroscienceNews. NeuroscienceNews, 8 August 2016.
<https://neurosciencenews.com/allergies-hippocampus-neuroscience-4797/>.[/cbtab][cbtab title=”APA”]Frontiers. (2016, August 8). Seasonal Allergies Could Change Your Brain. NeuroscienceNews. Retrieved August 8, 2016 from https://neurosciencenews.com/allergies-hippocampus-neuroscience-4797/[/cbtab][cbtab title=”Chicago”]Frontiers. “Seasonal Allergies Could Change Your Brain.” https://neurosciencenews.com/allergies-hippocampus-neuroscience-4797/ (accessed August 8, 2016).[/cbtab][/cbtabs]
Abstract
Allergy Enhances Neurogenesis and Modulates Microglial Activation in the Hippocampus
Allergies and their characteristic TH2-polarized inflammatory reactions affect a substantial part of the population. Since there is increasing evidence that the immune system modulates plasticity and function of the central nervous system (CNS), we investigated the effects of allergic lung inflammation on the hippocampus—a region of cellular plasticity in the adult brain. The focus of the present study was on microglia, the resident immune cells of the CNS, and on hippocampal neurogenesis, i.e., the generation of new neurons. C57BL/6 mice were sensitized with a clinically relevant allergen derived from timothy grass pollen (Phl p 5). As expected, allergic sensitization induced high serum levels of allergen-specific immunoglobulins (IgG1 and IgE) and of TH2 cytokines (IL-5 and IL-13). Surprisingly, fewer Iba1+ microglia were found in the granular layer (GL) and subgranular zone (SGZ) of the hippocampal dentate gyrus and also the number of Iba1+MHCII+ cells was lower, indicating a reduced microglial surveillance and activation in the hippocampus of allergic mice. Neurogenesis was analyzed by labeling of proliferating cells with bromodeoxyuridine (BrdU) and determining their fate 4 weeks later, and by quantitative analysis of young immature neurons, i.e., cells expressing doublecortin (DCX). The number of DCX+ cells was clearly increased in the allergy animals. Moreover, there were more BrdU+ cells present in the hippocampus of allergic mice, and these newly born cells had differentiated into neurons as indicated by a higher number of BrdU+NeuN+ cells. In summary, allergy led to a reduced microglia presence and activity and to an elevated level of neurogenesis in the hippocampus. This effect was apparently specific to the hippocampus, as we did not observe these alterations in the subventricular zone (SVZ)/olfactory bulb (OB) system, also a region of high cellular plasticity and adult neurogenesis.
“Allergy Enhances Neurogenesis and Modulates Microglial Activation in the Hippocampus” by Barbara Klein, Heike Mrowetz, Josef Thalhamer, Sandra Scheiblhofer, Richard Weiss and Ludwig Aigner in Frontiers in Cellular Neuroscience. Published online June 28 2016 doi:10.3389/fncel.2016.00169
