🧬 Cambridge Scientists Reverse "Irreversible" Nerve Damage in Lab-Grown Human Brain-Spinal Cord Model

Researchers at the University of Cambridge have built a miniature human brain-spinal cord system in the lab and used it to overturn a long-held assumption: that nerve damage in the central nervous system is permanent.

The team, led by Dr. András Lakatos, grew pea-sized brain and spinal cord organoids from human stem cells and kept them physically separate. Axons from the brain tissue grew across the gap and connected with the spinal cord tissue, forming a functional neural circuit that could even trigger muscle contractions.

Key findings:

— Neurons could regrow damaged axons until roughly day 150 of development (mid-pregnancy equivalent). After that, a sharp decline in regenerative ability sets in — a biological switch hardwired into maturing human neurons.

— The team identified the gene network responsible for this switch. When they blocked its key regulators, neurons regained the ability to grow axons again.

— An existing drug, lynestrenol (a hormone currently approved for menstrual disorders), significantly improved axon regrowth when tested on the damaged neurons.

— While lynestrenol itself is unlikely to be the clinical answer, it proves the principle: human neurons can be directly targeted to regenerate.

Quote from Dr. Lakatos: "When the brain and spinal cord are damaged, the nerve fibers that carry movement signals rarely grow back. That's why paralysis is usually permanent. But our model shows this block can be reversed."

This matters because most nerve regeneration research has relied on rodents, whose neurons behave differently from human ones. Human organoid models bridge that gap and may accelerate the path to treating conditions like spinal cord injury, motor neurone disease, and multiple sclerosis.

Original paper (Cell Reports): https://www.cell.com/cell-reports/fulltext/S2211-1247(26)00477-8

ScienceDaily summary: https://www.sciencedaily.com/releases/2026/05/260528082459.htm

#neuroscience #organoids #regeneration #spinalcordinjury #cambridge

🧠 Scientists Replaced Most of a Mouse’s Cortex With Human Brain Tissue

This sounds like science fiction, but the experiment is real.

Stanford researchers genetically engineered mice so that most of their cerebral cortex and hippocampus never developed. The adult animals were left with only about 2% of the normal amount of corresponding cortical tissue.

Then, shortly after birth, scientists implanted tiny human cortical organoids — brain-like structures grown from human stem cells — into the empty space.

Three months later, more than 90% of the cortical tissue by volume was human-derived.

And it did not simply sit there.

Human neurons became integrated into the mouse nervous system, developed organized electrical activity and sent long-range projections — some extending as far as the spinal cord. The mice retained broadly normal movement, although researchers found specific differences in coordination and spontaneous behavior.

Then came an unexpected discovery.

Inside the transplanted human tissue, researchers found cells resembling von Economo neurons — extremely rare, large neurons associated with brain regions involved in social awareness and decision-making. They occur in humans, great apes, elephants, dolphins and whales, but scientists had never previously succeeded in generating them in laboratory brain cultures.

The team also demonstrated why the model could matter medically. When the animals experienced several hours of reduced oxygen, the human cortical tissue was severely damaged while comparable mouse tissue was largely spared — potentially giving researchers a living model for studying why the developing human brain is particularly vulnerable to oxygen deprivation.

An important distinction: these are not mice with human intelligence or a human brain. The transplanted tissue remained developmentally immature, and the experiment provides no evidence of human-like cognition or consciousness. It is a new animal model for studying human neural development and disease.

But the boundary scientists have crossed is remarkable.

We can now grow substantial amounts of developing human neural tissue not just in a dish —

but inside a living brain, connected to a living nervous system.

Where should the ethical boundary for experiments like this be?

#Neuroscience #Brain #Organoids #StemCells #Biotechnology #Stanford #Science

https://www.nature.com/articles/s41586-026-11032-2