Scientists Grow Part-Human Brain Tissue in Mice for Disorder Research

Researchers have developed a novel approach to studying human brain disorders by implanting lab-grown human brain organoids into genetically engineered mice. The goal is to gain a deeper understanding of complex neurological conditions for which current treatments are lacking.

Developed at Stanford University, the method involves genetically modifying mice so they produce significantly less of their own cerebral cortex, the brain's outer layer responsible for higher-level cognitive functions, memory, and senses. Human neurons, derived from reprogrammed skin cells, are then grown into organoids—collections of connected, living cells. These organoids are subsequently implanted into the mouse brains.

Once implanted, the human cells integrate into the animal's existing neural circuitry, connecting with the brain and spinal cord. While not perfectly structured like a natural cortex, these human brain cells begin to organize and function over several months, resembling the outer layer of the mouse's brain.

Lead researcher Professor Sergiu Pașca of Stanford University highlighted the limitations of current research methods, noting that psychiatry has one of the lowest success rates in clinical trials. "Even drugs that actually make it to clinical trial - that seem to be working really well in animal models - fail dramatically in clinic," he stated. He believes this new model can capture aspects of human brain function previously inaccessible, potentially aiding research into conditions like epilepsy, autism, and cerebral palsy.

Neuroscientists not involved in the study have expressed interest in the technical achievement. Dr. Ilary Allodi from St. Andrews University described the work as "very impressive," particularly noting the spontaneous formation of human-specific cell types within the implanted mice. She likened the mouse to an "incubator" for the human brain tissue.

Despite the technical success, ethical considerations have been raised. Dr. Sarah Chan, a bioethicist at the University of Edinburgh, commented that the study "prompts us to think about what it might mean when we start changing animal cognition." She raised questions about how to understand and account for the experience of these modified animals.

Researchers emphasize that these mice are engineered and handled under strict ethical and welfare guidelines. The organoids themselves are not whole human brains and there is no indication that the mice gain human-like cognitive abilities. The researchers suggest that the implanted mice, likely to be used in a limited number of specialized labs, could offer a new avenue for understanding human diseases that are difficult to model using existing methods, such as traditional animal models or cell cultures.