New findings help understand the impact of severe allergies on postnatal brain development

^{Eglish version by Diana Taborda}

Although the connection between severe allergies and attention deficit hyperactivity disorder (ADHD) is already known, the reason for the comorbidity of ADHD and allergic diseases has yet to be clear. Now, research conducted by the University of Coimbra (UC) reveals that the link between allergies and ADHD is related to a postnatal neuroimmune critical period for cerebellar development, during which an exacerbated allergic response has been detected, disrupting the maturation of this region of the brain.

The identification of this postnatal neuroimmune critical period for cerebellar development provides new insights into the mechanisms of neurodevelopment, highlighting the importance of healthy development of the immune system, and how any disruptions to this process can affect the brain.

The scientific article "IL-4 shapes microglia-dependent pruning of the cerebellum during postnatal development", published in NEURON, a prestigious journal in the field of neuroscience, aimed to "study the interaction of the allergic response in the cerebellum, a brain region that develops essentially in the postnatal period", explains the head of the Neural Circuits and Behaviour Research Group at the Centre for Neuroscience and Cell Biology of the University of Coimbra (CNC-UC), João Peça. "We know that the brain's immune cells [microglia] respond to messages and "instructions" from the periphery, but we know very little about this interaction during the critical period after birth," explains the professor from the Department of Life Sciences at the Faculty of Sciences and Technology of the University of Coimbra (DCV/FCTUC).

Under normal circumstances, the early postnatal stage, "the developing cerebellum needs to 'grow', but it also needs to be 'pruned', with surplus neurons being eliminated by cells called microglia. When there is an allergic response, the microglia do not carry out this 'pruning' efficiently, resulting in the survival of surplus neurons, which in turn disrupts the proper functioning of the cerebellum”, Peça explains. The research team was also able to observe that in the absence of this "pruning" in animal models, "there are changes in the cerebellar circuit function, with hyperlocomotion and hyperactivity, characteristics associated with ADHD".

In terms of future research in this field, João Peça stresses the importance of "understanding in more detail why the cerebellum is particularly involved in these processes, as well as the critical time window of ʽpruningʼ. At later stages, this window closes and neurobehavioural alterations do not occur in the presence of an allergic stimulus”.

The CNC-UC Neural Circuits and Behaviour Research Group is now studying how the cerebellum regulates dopamine release in ADHD because "understanding this circuit and this neurotransmitter could help us better understand this disorder," says the researcher. [ADHD typically manifests in children between the ages of 6 and 12, can persist into adulthood [or be diagnosed only in adulthood] and is associated with impulsive behaviour and difficulty concentrating - which may impact children's academic performance.]

The research was led by scientists from the University of Coimbra, João Peça, Joana Guedes, Ana Luísa Cardoso and Pedro Ferreira, and involved other researchers from the University of Coimbra and the University of Manchester.

The scientific article is available here.