Scientists develop a new way to test autism & epilepsy treatments: Why traditional mice cannot explain complex human brain disorders

Through the use of mice, researchers have been able to discover a lot about different areas of the brain including learning, movement and diseases among others. Mice have also been widely used in testing of new drugs to determine whether they can be administered on humans.

Autism, epilepsy and certain types of cerebral palsy are diseases characterized by complex brain cells, connections and developmental problems. Since there is a difference between the brains of humans and that of mice, what works on one species may not work on the other.

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A group of researchers based at Stanford University together with other institutes has developed a new experiment model. The researchers inserted human brain cells into lab-grown mice and were able to prove that the cells survived, developed and integrated within the bodies of the mice.

This experiment which was done at Stanford is detailed in the journal Nature and does not mean that the mice had human brains. Rather, it means that scientists can study human brain cells in a live subject where the cells connect to blood vessels, nerve circuits and surrounding tissues.

How human brain tissue was introduced into mice

Scientists employed genetically modified mice, which did not grow any or very little of their own cerebral cortex—a part of the brain responsible for decision making, perceptions, and memories. This way, there was enough room left for human brain tissue to develop without interference of the existing mouse cortex.

Scientists reprogrammed human skin cells into brain organoids such as three-dimensional structures containing brain neurons and other cells. While often referred to as “mini-brains,” they are much more primitive than a human brain and cannot generate human thoughts or behavior.

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Once the brain organoids have been cultivated, they were introduced into genetically modified mice. Human cells survived, multiplied, and mixed with other mouse tissues. They were able to make connections with mice neural networks, some even stretching out towards the spine.

At the same time, human brain cells received nourishment from the mouse brain—they got the supply of blood and other signals from the neighboring cells. That way, scientists were able to study human brain cells in the living organism nervous system and not only in laboratory test tubes, where cells behave differently.

What the implanted cells revealed

The implanted tissue developed several cell types associated with human and primate brain development. Some of these cells are missing from mice or differ considerably from their mouse counterparts.

Researchers also identified human-specific features in the developing tissue. These included cell populations and patterns of development that are difficult to examine using standard mouse models.

The findings suggest that human cells can respond to signals from a mouse brain while retaining important elements of their human identity.

That combination could help scientists investigate how genetic changes influence brain development. It may also allow researchers to examine how human neurons communicate and respond to medicines in a living environment.

A dish containing human cells can provide valuable information, but it cannot reproduce every interaction that takes place inside a brain. The new model offers an intermediate approach: human tissue can be studied inside a living organism while researchers retain more control than they would in a human patient.

The model still has important limitations. The implanted tissue was not organised exactly like a naturally developed human cortex. Brain scans showed some irregularities, and the mice did not display obvious changes in intelligence or behaviour.

After roughly six months, the animals generally behaved like ordinary mice in the tests carried out by the researchers. This suggests that human brain tissue did not automatically produce human-like cognition.

Potential applications in autism and epilepsy research

The most important use of the model may be in early-stage research into neurological and psychiatric conditions.

Autism is a developmental condition involving differences in communication, behaviour and sensory processing. Its causes are complex and include many genetic factors. Some of the biological processes involved may not be accurately reproduced in mice.

Epilepsy involves abnormal electrical activity in the brain. Animal models are used to study seizures and test medicines, but differences between mouse and human neurons can make it difficult to predict how a treatment will work in patients.

Human brain tissue inside a living mouse could allow researchers to study these differences more directly.

For example, scientists could create organoids from cells carrying genetic variants associated with autism or epilepsy. They could then implant those organoids into engineered mice and compare them with tissue made from cells without the variants.

Researchers might measure changes in electrical activity, neuron growth, communication between cells and responses to experimental medicines. These observations could reveal disease mechanisms that are difficult to identify in ordinary mice or isolated cell cultures.

The approach could also be used to study cerebral palsy, neurodevelopmental disorders and certain psychiatric conditions.

However, the model would not replace human research. A medicine that performs well in this system would still need to be tested in other models and eventually in carefully controlled human trials.

Questions that people ask frequently

1. Have scientists created mice with human brains?

Scientists have injected the mice with human brain tissue organoids, but the brains of these animals are still mouse brains. The tissue did not grow into a complete human brain cortex.

2. Were the mice more intelligent after that?

No significant increase in intelligence or behavior was noticed. In most cases, the mice were acting as usual for mice.

3. How can this benefit autism research?

Researchers can conduct experiments on brain development, neuron interaction and response to medication using the cells containing the mutations linked to autism.

4. Can this be an alternative for clinical trials on humans?

No. The new model can be useful in early-stage studies but the treatment will still need more testing and human trials.