Scientists have found a new type of neuron that has the ability to tell stem cells to make more neurons. The work is in its early stages, but by identifying this first piece of a new brain-repair circuit, the researchers suggest that the adult brain is capable of rebuilding itself after an injury.
Neuroscientists have long suspected that the brain is capable of directing the manufacturing of new neurons -- a process called neurogenesis -- but it’s been difficult to figure out where these instructions come from.
By conducting experiments with mice, a team led by Duke University’s Chay Kuo has found a previously unknown group of neurons in the subventricular zone (SVZ) of the adult brain mouse brain. The newly discovered neurons expressed an enzyme called choline acetyltransferase (ChAT), which is required to make the neurotransmitter acetylcholine.
When the team tuned the firing frequency of these neurons up and down with laser light, they could see clear changes in the production of neural stem cells in the brain.
The mature ChAT+ neuron population is just one part of an undescribed neural circuit that apparently talks to stem cells and tells them to increase new neuron production, Kuo explains in a news release. They don't know all the parts of the circuit yet or even the code it's using, but by controlling the electrical signals generated by ChAT+ neurons, the team has shown that these neurons are necessary and sufficient to control the production of new brain cells.
In mice, the young neurons produced by these signals were headed for the olfactory bulb, which makes sense since a large amount of mouse brains are devoted to processing smells. With humans, who have much less impressive olfactory bulbs, Kuo thinks the new neurons are produced for other brain regions -- likely parts involved with motor and cognitive control.
"The brain gives up prime real estate around the lateral ventricles for the SVZ niche housing these stem cells," Kuo says. "Is it some kind of factory taking orders?" He thinks there might a way to combine behavioral therapy and stem cell treatments after a brain injury to rebuild some of the damage.
The work was published in Nature Neuroscience this week.
Image: Duke University/O'Reilly Science Art