June 18, 2014
Stress Hormone Cortisol May Speed Up Short-Term Memory Loss
Brett Smith for redOrbit.com - Your Universe Online
While cognitive decline is a relatively normal part of the aging process, some factors could amplify or speed up that process.
Working with laboratory rats, researchers at the University of Iowa have found that the stress hormone cortisol could be one of those factors contributing to cognitive decline, according to a new report published in the Journal of Neuroscience.
The UI study team found that elevated amounts of cortisol slowly leads to a loss of synapses in the prefrontal cortex, the area of the brain responsible for short-term memory.
"Stress hormones are one mechanism that we believe leads to weathering of the brain," said study author Jason Radley, assistant professor in psychology at UI the paper.
"Older animals with higher levels of stress hormones in their blood have 'older' frontal cortexes than animals with less stress hormones," commented Robert Sapolsky, a brain expert from Stanford University who was not involved with this study. "Thus, stress may act as a pacemaker of aging in this key brain region."
Expanding on previous research that showed the general negative effects of cortisol on cognitive function, UI scientists assessed the quantity of cortisol in the blood of young and old rats and evaluated cells in the prefrontal cortex. The scientists discovered that older animals with elevated levels of the stress hormone had a lot fewer connections between prefrontal cortex cells than the older rodents with lower levels of cortisol. Finally, the team found prefrontal cortex cells looked the same in younger animals despite cortisol levels.
The groups of young and old rats were then segregated further based on if the rats had naturally high or naturally low levels of the hormone comparable to cortisol in humans. The scientists placed the rats in a T-shaped maze that they were trained to navigate by recalling which direction they had turned 30, 60 or 120 seconds ago and then turn the reverse direction each time they ran the maze.
The researchers found memory dropped across all groups as the time the rats waited prior to running the maze again elevated, older rats with high stress hormone levels reliably performed the worst -- choosing the right direction only 58 percent of the time, as opposed to older rats with lower stress levels who did 80 percent of the time.
"These findings are not meant to indicate that high stress hormones are the only factor in determining the decline of mental abilities during aging," Radley cautioned. "Nonetheless, this study suggests that the effects of these stress hormones on the brain may be much more widespread than we previously thought."
Researchers in that study identified ten lipids, or fats, that predict cognitive disease. The study team said the new test could be ready for use in clinical trials in as little as two years.