Irvine, Calif., October 25, 1999
Certain experiences in infancy can alter levels of a stress hormone, causing changes in the brain that result in impaired memory and learning in adulthood, a UC Irvine research team has found.
The findings of the research conducted in rats suggest that stress early in life can lead directly to later disabilities. The research could lead to new ways to prevent stress-related injuries in the brain that occur during childhood. The researchers will present their findings Monday, Oct. 25, at the annual meeting of the Society for Neuroscience in Miami, Fla.
Dr. Tallie Z. Baram, a professor of pediatrics and neurology in the UCI College of Medicine, and researchers Kristen Brunson and Carolyn Hatalski found that if they raised levels of the stress hormone CRH (corticotropin-releasing hormone) in young rats, the rats were less able to learn simple tasks when they reached adulthood.
In addition, the researchers discovered that some stressful events in infancy elevated CRH levels in the brain's hippocampus, an area responsible for handling memory and learning.
These stresses did not raise CRH levels in other areas of the brain such as the hypothalamus, which is responsible for handling immediate hormonal reactions to stress. CRH is released by nerve cells during stressful events and helps enhance communication between brain cells.
"We now have a better idea of how CRH is regulated in the young brain, and how certain changes in the brain can affect levels of this hormone," said Baram, the Danette (Dee Dee) Shepard Chair in Neurological Studies. "In children, early stresses in life like neglect or abuse are often linked to poor performance in school. This study brings us closer to finding out exactly how poor performance arises, how it may affect learning and memory during adulthood and how some performance problems may be prevented."
The researchers found that only those experiences that activated brain cells in the hippocampus raised CRH levels there. Then, the researchers found that rats that had levels of CRH raised artificially when they were young were less able as adults to find a platform hidden in cloudy water. Rats that had grown up with normal CRH levels had no difficulty finding the platform as adults.
"This is the first time we've seen that CRH in the hippocampus can be influenced by experience and that raised hormone levels can impair learning later in life," Baram said. "Many behaviors associated with stress—freezing, appetite loss and anxiety—are controlled by CRH in other areas of the brain, such as the amygdala and hypothalamus. Now, we also see that CRH has a profound effect on memory and development by working in the hippocampus."
The researchers are now looking at whether CRH can work the same way in humans and whether its increased levels can be curbed. "The CRH molecule is identical in rats and humans. Now we need to see if CRH production is regulated in the same way in humans as it is in rats. Eventually, we may be able to design treatments that could protect the brain from the effects of stress and CRH early in life," Baram said.
The research was supported by an award from the National Institute of Neurological Disorders and Stroke.