A real mindbender

In our adult brains, right now, new neurons are being born. That’s the good news; a healthy brain needs all the neurons it can get. The bad news is that most of those baby neurons die before they could help with cognition, memory or mood regulation.

Why do most new neurons die while a few survive? Song, a UNC School of Medicine neuroscientist, has some answers.

Her study, published in the journal Nature Neuroscience, is the first to show how specific brain cells communicate with each other during adult neurogenesis – the creation of new neurons. She also found that one cell type – PV+ interneurons – can be stimulated to help baby neurons survive and thrive even as older neurons die.

Neurodegenerative conditions such as dementia or Alzheimer’s disease

“We now know how newborn neurons can be regenerated in specific regions of the brain,” said Song, assistant professor in the department of pharmacology and the UNC Neuroscience Center. The finding has wide implications for people with neurodegenerative conditions, such as dementia or Alzheimer’s disease, and perhaps for patients with brain damage. “By showing how interneurons are a part of neurogenesis, we can see how it’s possible to regenerate cells in parts of the brain that are damaged, for example, because of a stroke.”

Photo of baby neurons attached to the terminals of interneurons.

Baby neurons (green) attached to terminals of interneurons (orange).

Neurogenesis, which occurs throughout the brain during pre-natal development, continues throughout adulthood in just two brain regions – the hippocampus and subventricular zone.

It works like this: neural stem cells produce progenitor cells, more than half of which die within four days. The progenitor cells don’t have axons or dendrites – the cell parts that adult neurons use to create and transmit signals to each other.

The surviving progenitor cells – also known as newborn or baby neurons – then turn into immature neurons; these do form axons and dendrites and evolve into mature neurons that connect with other neurons through synapses. These mature neurons then integrate into the complex neural networks involved in cognition, memory and mood.

Chemical signals

Previously, when Song was a postdoctoral fellow at Johns Hopkins University, she studied how stem cells create neurons. She was first author and lead researcher of a study published in Nature that showed how neural stem cells “sense” the transmission of chemical signals between mature neurons and PV+ interneurons.

Song’s team used words such as “sensed” and “listened” and “eavesdropped” because they found that the stem cells did not form synaptic connections with either the mature neurons or the interneurons. They somehow “heard” the chemical signaling between the two other cell types. And depending on the signal, the stem cells either stayed dormant or began creating progenitor cells.

Continued . . . read more from the UNC Health Care article by Mark Derewicz.

Published December 5, 2013.