Integrating New Neurons Into Neural Networks

By: Yovan P. Putra

In the past, the field of neuro research has a rigid belief that people can not grow new neurons well into old age. But a remarkable discovery in 1998 changed it all. It's now believed that people can grow new neurons while they're aging. Now the focus of the studies mainly placed in finding out how these new neurons integrate themselves gracefully into existing neural networks without causing any potential problems. The studies were conducted in embryonic rodents and monkeys suggested that the neurotransmitter GABA, which normally inhibits neurons from firing, may instead be stimulating new neurons to fire.

Amazed by this conclusion, a team at John Hopkins University focused to the part of the hippocampus, dentate gyrus. They penetrate a retrovirus into mice that makes dividing neurons fluoresce green. After that they can measure the responsiveness of these cells to different neurotransmitter.

Initially the neurons were sensitive to GABA that had diffused into the space between cells. After a week the new cells connected to established neurons, which transmitted GABA in pulses. In another week the cells formed connections to receive glutamate, the major stimulatory neurotransmitter in adult neurons. The results indicate that despite differences between embryos and adults, "newly formed neurons must follow this sequence," says Yehezkel Ben-Ari, director of the Mediterranean Institute of Neurobiology in France, who is not connected to the Johns Hopkins work.

Apparently, an excess of chloride ions inside the young cells is responsible for their excitation by GABA-deficient neurons that the scientists engineered showed a two-week delay in developing connections and eventually died. Johns Hopkins Neuroscientist Hongjun Song says the team hopes to test whether applying GABA to stem cells at the right time and dose could help repair central nervous system injuries.

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