Neurons communicate with one another by synaptic connections, where information is exchanged from one neuron to its neighbor. These connections are not static, but are continuously modulated in response to the ongoing activity or experience of the neuron. This process, known as synaptic plasticity, is a fundamental mechanism for learning and memory in humans as in all animals. In fact, we now know that alterations in synaptic plasticity are responsible for memory impairment in cognitive disorders such as Alzheimer's disease.
This latest study adds to evidence that inflammation in the brain can in fact drive the development of the disease. The findings suggest that by reducing this inflammation, progression of the disease could be halted.
The researchers at the University of Southampton used tissue samples from healthy brains and those with Alzheimer’s, both of the same age. The researchers counted the numbers of a particular type of immune cell, known as microglia, in the samples and found that these were more numerous in the brains with Alzheimer’s disease. In addition, the activity of the molecules regulating the numbers of microglia correlated with the severity of the disease.
The researchers then studied these same immune cells in mice which had been bred to develop features of Alzheimer’s. They wanted to find out whether blocking the receptor responsible for regulating microglia, known as CSF1R, could improve cognitive skills. They gave the mice oral doses of an inhibitor that blocks CSF1R and found that it could prevent the rise in microglia numbers seen in untreated mice as the disease progressed.
Importantly, the team found the healthy number of microglia needed for normal immune function in the brain was maintained, suggesting the blocking of CSF1R only reduces excess microglia.
Dr Diego Gomez-Nicola, lead author of the study and an MRC New Investigator Research Grant (NIRG), said: “These findings are as close to evidence as we can get to show that this particular pathway is active in the development of Alzheimer’s disease.
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