Scientists have created an “atlas” of synapses in the mouse brain, potentially helping other researchers better understand neurological disorders in humans.

The findings, which feature in the journal Science, provide a visual demonstration of the development of synapses across the brain’s life. Synapses connect brain cells, or neurons, in the brain.

Although the types of cells in the brain are also present in other parts of the human body, it is the ubiquity of synapses in the brain — the way that they connect everything with everything — that enables it to be so effective in processing information.

As one article notes, “[t]he connections, or synapses, among neurons in the human brain are not only more numerous but also more intricately patterned than anything that has ever been constructed to process information, including the most sophisticated supercomputer.”

Brain atlas

Over the past 20 years, scientists have learned a significant amount about this abundant and important unit of the brain. However, they do not fully understand precisely how synapses develop and the bearing that this development has on human neurological health.

In this context, the researchers behind the present study set out to create an atlas of mouse synaptic architecture.

Importantly, the researchers wanted not to look simply at the synaptic architecture at a single point in time but to track how it develops throughout the lifespan of a mouse. They hoped that doing so would enable them to gain a better understanding of the interaction of distinct synaptic regions and their role in human neurological disorders.

Mapping over time

To create the atlas of the synaptic architecture, the researchers took detailed scans of the brains of mice, color-coding the molecules of the synapses with fluorescent tags. This method allowed them to show the different types of synapse areas, as well as how they related to one another.

As they wanted to get a sense of the development of synaptic structures over time, the scientists took these images from birth until the mice were 18 months old, which, for these rodents, is old age.

The team found that the synapse architecture seems to go through three phases:

• childhood and adolescence, where the diversity of synapses begins to increase
• early adulthood, where the diversity has reached a peak, and distinct synaptic areas are distinguishable
• late adulthood, where this distinctness begins to diminish

These phases were clearly apparent in the images. Those from early adulthood were rich and vibrant, with an array of colors representing an increased density of synapse type. In contrast, the images from early or late life were more uniform and less diverse.

The authors believe that this developmental process is related to the genesis of neurological disorders and may provide a better understanding of how and why these disorders come about, as well as how best to treat them.

Future research

In the study, the authors focused on particular proteins in the synapses, using these as markers that they then color-coded. The authors suggest that future research could identify alternative synaptic markers to yield other fresh perspectives.

According to the lead researcher, Prof. Seth Grant of the Centre for Clinical Brain Sciences at the University of Edinburgh, United Kingdom, “[t]he brain is the most complex thing we know of, and understanding it at this level of detail is a momentous step forward.”

“We believe that these findings will be instrumental to helping understand why the brain is susceptible to disease at different times of life and how the brain changes as we age.”

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