For more than a century, scientists thought the adult brain could only lose nerve cells, not gain them, but in fact, new neurons do form during adulthood in all mammals, including humans, and become a working part of the adult brain in mice at the very least.
In the first study to show how these "baby" neurons are integrated into the brain's existing networks, the Johns Hopkins researchers show that a brain chemical called GABA readies baby neurons to make connections to old ones. The discovery is described in the Dec. 11 advance online section of Nature.
"GABA is important during fetal development, but most scientists thought it would have the same role it has with adult neurons, which is to inhibit the cells' signals," says Hongjun Song, Ph.D., an assistant professor in the Neuroregeneration and Repair Program within ICE. "We've shown that GABA instead excites new neurons and that this is the first step toward their integration into the adult brain."
Song added that their discovery might help efforts to increase neuron regeneration in the brain or to make transplanted stem cells form connections more efficiently.
The researchers, including postdoctoral fellows Shaoyu Ge and Eyleen Goh, discovered that a constant flood of GABA is required as a first step. Next, the new neuron receives specific connections that communicate using GABA, which shifts the constant barrage of GABA in step one to a pulsed exposure. The third and final step occurs when the new neuron receives connections that communicate via another chemical, the critical excitatory messenger glutamate.
In the adult brain, glutamate is the most prevalent excitatory chemical, and GABA is a major inhibitory chemical. But it turns out that new neurons are excited by GABA, whether
Source:Johns Hopkins Medical Institutions