Next, again using precise micro-injections, the scientists transplanted hippocampal cells that had been taken from newborn transgenic mice and cultured in an incubator into the hippocampi of about half the rats. These special cells had a green fluorescent protein used to "label" and track them after transplantation. (Transgenic mice are bred with a little extra DNA that allows their cells to be grown in glass plates in incubators.)
Two months later, the scientists measured how well both the transplant and non-transplant rats learned and remembered, using two well-established maze tests of spatial learning. The rats given cell transplants had recovered completely: On both mazes, they performed as well as those rats which had not had their subiculums damaged. The rats without transplants did not recover: They had many problems learning their way through the mazes.
After studying behavior, the scientists examined what happened in the brain. Under the microscope, it appeared that the transplanted cells had settled mainly in a sub-area of the hippocampus called the dentate gyrus. There, the transplants appeared to promote the secretion of two types of growth factors, namely brain-derived neurotrophic factor and fibroblast growth factor, which boost the growth and survival of the cells that give rise to neurons. In the hippocampi of rats with cell transplants, the expression of brain-derived growth factor went up threefold.
It is significant that transplants can provide more neural growth factors in the hippocampus, because the formation of new neurons there may be critical for cognitive function.
Neural growth factors, also called neurotrophic factors, hold great promise for treating neurological problems. These specialized chemicals "provide an ideal micro-environment for making new neurons," said co
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