New research, from King's College London and the University of Porto, has mapped the histamine system in the brain. Histamine, a molecule more commonly associated with allergies, plays a separate but poorly understood role in brain function. This study addresses this gap, building the first multiscale map of the histamine system which spans from genetics to behaviour and related mental health conditions.
The findings provide a new framework for understanding how this often-overlooked chemical system contributes to brain function and could point towards new treatment strategies for histamine-related conditions such as depression, ADHD, and schizophrenia. The study was published in Nature Mental Health and funded by the National institute for Health and Care Research (NIHR) Maudsley Biomedical Research Centre.
Histamine is a neurotransmitter, a molecule crucial for neurons to communicate with one another. Neuroscience research has classically focused on understanding other neurotransmitter systems such as dopamine and serotonin.
Dr Daniel Martins, visiting Senior Research Fellow at the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) King's College London, and first author on the paper said: "This work provides a crucial foundation for future research. By integrating molecular biology, brain imaging, and computational analysis, it offers a new perspective on how neurotransmitter systems are organized across the human brain. As neuroscience moves toward more integrated and personalized models of mental health, understanding systems like histamine may prove essential for unlocking new approaches to diagnosis and treatment."
Histamine molecules are caught by proteins called receptors, which are responsible for how the signal will influence receiver neurons. There are several types of receptors that catch histamine and they can have varied effects on neuron activity.
Through mapping the histamine system, researchers found that different histamine receptors were found on brain cells that either turn activity up (excitation) or turn it down (inhibition). This suggests histamine may be important in maintaining the balance between excitation and inhibition, a fundamental property of healthy brain function.
To build a comprehensive map of how histamine acts in the brain, researchers first combined genetic and molecular data with physical maps of the brain. This revealed which brain regions receive more input from the brain's histamine system, and which parts show greater capacity to respond to histamine. These molecular data were then linked with positron emission tomography imaging of histamine receptors in living individuals, as well as functional neuroimaging databases that map brain regions to specific cognitive processes and mental health conditions. This type of scan shows how different parts of the brain are working by tracking a tiny amount of radioactive tracer in real time.
Brain regions with higher histamine-related gene expression were consistently associated with processes such as emotional regulation, stress and fear responses, decision-making, impulsivity, reward, sleep, and memory.
The parts of the brain where histamine-related genes were most active also overlapped significantly with brain regions known to be affected in several psychiatric conditions, including attention-deficit/hyperactivity disorder, major depressive disorder, schizophrenia, and anorexia nervosa. This is in keeping with previous hypotheses linking histamine to these disorders.
Dr Daniel Martins said: "Current psychiatric treatments largely target neurotransmitters such as serotonin and dopamine, yet histamine interacts closely with these systems and influences their activity. By providing a detailed map of histamine-related pathways, this work suggests new opportunities for developing treatments that target this system more directly, particularly for symptoms such as cognitive dysfunction, fatigue, and impaired motivation. While these findings do not establish a direct causal role, they suggest that histamine signalling may contribute to regional vulnerability in these disorders. This aligns with a growing view in psychiatry that mental health conditions arise from disruptions across interacting brain systems rather than a single chemical imbalance."
This new map paints a neural picture of a previously lesser-studied molecule. It opens up future avenues of research into exactly what histamine is doing in various cell types and parts of the brain.
"We want to emphasise that these findings are hypothesis-generating and based on large-scale datasets that capture patterns rather than direct mechanisms," comments Professor Steve Williams, Professor of Neuroimaging at IoPPN King's College London and senior author on the paper.
Future studies will focus on testing how histamine signalling changes in living individuals, for example through pharmacological interventions or longitudinal imaging approaches.
Dr Daniel Van Wamelen, Clinical Senior Lecturer in Neuroscience at IoPPN, King's College London and one of the authors on the paper said: "This kind of work is already taking place at King's College London, for example in the iMarkHD project. In this project we use Positron Emission Tomography scans to study a specific histamine receptor (called H3) in people with Huntington's disease, an inherited condition that affects the brain. The goal is to see how histamine activity changes in different parts of the brain over time, and how these changes relate to symptoms such as apathy, depression, and anxiety."
