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Primates, Mice, and Neuronal Plasticity

QPS Neuropharmacology

When you think of a mouse compared to a primate – a chimpanzee, for example – it’s pretty easy to determine which animal is “smarter.” After all, chimpanzees have a rich communication style and strictly organized communities. With that in mind, it’s easy to assume that primates are more sophisticated than mice. But a recent study indicates that mice actually have more synapses connecting the neurons in their brains, suggesting a higher level of neuronal plasticity. Read on to find out what that means for neurological research.

Graohic illustration depicting signals in neurons

Neuronal Plasticity: What Does It Mean?

According to a 2017 volume published in the National Library of Medicine, neuronal plasticity, sometimes known as “neural plasticity,” refers to the “capacity of the nervous system to modify itself, functionally and structurally, in response to experience and injury.” This plasticity is key to neuronal development and functioning. Neuronal plasticity is governed by the central nervous system’s synapses, which are the gaps at the end of each neuron that transmit signals between nerve cells. And while it may seem that a higher number of synapses per neuron would indicate higher neurological function, a recent study found that this may not be the case.

A New Study Explores Neuronal Plasticity

Researchers explored neuronal plasticity in a study published on September 14, 2021, in Cell Reports. In the study, researchers compared the brains of two kinds of specimens: macaques, which are primates, and mice. When the study concluded, the researchers found that the primates had significantly fewer synapses per neuron compared to the mice. Specifically, the researchers identified more than 9,700 synapses in the mouse samples, but only about 6,000 synapses in the macaque samples. Once again, this may be surprising given the assumption that primates seem more intelligent than mice. Eventually, the researchers were able to explain the discrepancy: they found that the “metabolic cost” of building and maintaining synapses can create “sparser neural networks.” In other words, mice may have a high number of synapses, but maintaining those synapses comes at a cost to their neural functioning.

A Surprising Outcome

The researchers behind the study were understandably surprised at its results. “The reason why this is surprising is that there’s this quiet sort of assumption among neuroscientists and, I think, people in general that having more neuronal connections means that you’re smarter,” researcher Gregg Wildenberg told U Chicago News. “This work clearly shows that while there are more total connections in the primate brain overall because there are more neurons, if you look on a per-neuron basis, primates actually have fewer synapses.”

Researcher Matt Rosen echoed Wildenberg’s thoughts. “We’ve had this expectation forever that the density of synapses in primates would be similar to what’s seen in rodents, or maybe even higher because there’s more space and more neurons in the primate brain,” Rosen told U Chicago News. “In light of Gregg’s surprising finding, we thought about why primate neurons would make fewer connections than expected. And we thought that perhaps it was driven by evolutionary forces – that perhaps the energetic costs associated with maintaining a brain might be driving this difference.”

Implications for the Future

These results aren’t just surprising; they could also have major implications for future neurological research, particularly when making connections between primates and mice. “Fundamentally, I think all neuroscientists want to understand what makes us human – what separates us from other primates, and from mice,” Wildenberg told U Chicago News. Ideally, this study will help scientists further understand neural evolution and the mechanisms behind different kinds of brains. Additionally, this kind of research could inform the understanding of several neurological conditions.

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Understanding the differences in primate and rodent neuronal plasticity may not seem like the most groundbreaking pursuit. However, studies like this one further the scientific community’s understanding of brain evolution. That can, in turn, lead to major revelations in the understanding of human neurology.

QPS Neuropharmacology is a division of QPS, a GLP/GCP-compliant contract research organization (CRO) delivering the highest grade of discovery, preclinical, and clinical drug development services since 1995. QPS Neuropharmacology focuses on preclinical studies related to central nervous system (CNS) diseases, rare diseases, and mental disorders. With highly predictive disease models available on site and unparalleled preclinical experience, QPS Neuropharmacology can handle most CNS drug development needs for biopharmaceutical companies of all sizes. To study neuronal plasticity, QPS Neuropharmacology offers several in vitro and in vivo models. For more information about QPS visit www.qps.com, and for more information about QPS Neuropharmacology, visit www.qpsneuro.com.