Glucocorticoids and Memory Loss (Michael Meaney Study 1988)
Glucocorticoids and memory loss
Michael Meaney (1988) carried out a study with
rats to find out what the effect of glucocorticoids is
on memory. He found that high levels of
glucocorticoids - stress hormones - in the early life
of a rat resulted in changes that affected the rats in
old age.
He and his team used an independent samples
design. One set of rats were taken away from their
mother and did not experience the normal
grooming that baby rats experienced. These rats
were labeled the "non-handled" rats. The second
set of rats were not taken away from their
mothers. These rats served as a control group.
Rats that were not handled secreted more glucocorticoids in response to stress than did handled
rats. At later ages, non-handled rats also showed elevated basal glucocorticoid levels, with the
result that there was a greater cumulative exposure to glucocorticoids in non-handled rats.
Increased exposure to adrenal glucocorticoids can accelerate hippocampal neuron loss and
cognitive impairments in aging. To test the effect, aged rats were put into a pool of milky water.
In the pool was a platform. Meaney and his team tracked the route of the rats as they sought
out the platform based on the rats' memories of previous attempts to escape the water. The
paths that he traced can be seen in the image below.
1 © John Crane, InThinking
www.tok-inthinking.co.ukYou can see that the non-handled rats took a much more circuitous route to get to the platform.
Hippocampal cell loss and pronounced spatial memory deficits emerged with age in the nonhandled
rats, but were almost absent in the handled rats. So, what does this mean? Can we
generalize the findings to human beings? And if so, what are the implications?
There are several studies that show a link between glucocorticoid levels and the onset of
Alzheimer’s. There are acetylcholine receptor sites in the hippocampus. Loss of hippocampal
cells also correlates with lower levels of acetylcholine. This may play a key role in the
development of dementia.
In addition, it appears that a rat mother’s grooming helps to activate genes which are
responsible for the reaction to the stress response. This is an example of epigenetics - the
grooming process “turns on” the genes which help the young rat cope with stress - which then
leads to a longer and healthier life.
Meany’s research was able to establish a cause and effect relationship between stress and the
effect on memory. However, further research has shown that epigenetics is the reason why the
hippocampal cell loss happens. Even though the cause and effect was established, it did not
explain the exact process of what was happening. Since the original study in 1988, Meaney has
shown the complex interaction between the hippocampus, glucocorticoids and our genes in the
development of dementia.
References
Meaney, M et al (1988). Effect of Neonatal Handling on Age-related Impairments associated
with the Hippocampus. Science 12 February 1988: Vol. 239 no. 4841 pp. 766-768
For more information on how rat grooming affects genes and one’s level of stress, see the
following site: http://learn.genetics.utah.edu/content/epigenetics/rats/
Michael Meaney (1988) carried out a study with
rats to find out what the effect of glucocorticoids is
on memory. He found that high levels of
glucocorticoids - stress hormones - in the early life
of a rat resulted in changes that affected the rats in
old age.
He and his team used an independent samples
design. One set of rats were taken away from their
mother and did not experience the normal
grooming that baby rats experienced. These rats
were labeled the "non-handled" rats. The second
set of rats were not taken away from their
mothers. These rats served as a control group.
Rats that were not handled secreted more glucocorticoids in response to stress than did handled
rats. At later ages, non-handled rats also showed elevated basal glucocorticoid levels, with the
result that there was a greater cumulative exposure to glucocorticoids in non-handled rats.
Increased exposure to adrenal glucocorticoids can accelerate hippocampal neuron loss and
cognitive impairments in aging. To test the effect, aged rats were put into a pool of milky water.
In the pool was a platform. Meaney and his team tracked the route of the rats as they sought
out the platform based on the rats' memories of previous attempts to escape the water. The
paths that he traced can be seen in the image below.
1 © John Crane, InThinking
www.tok-inthinking.co.ukYou can see that the non-handled rats took a much more circuitous route to get to the platform.
Hippocampal cell loss and pronounced spatial memory deficits emerged with age in the nonhandled
rats, but were almost absent in the handled rats. So, what does this mean? Can we
generalize the findings to human beings? And if so, what are the implications?
There are several studies that show a link between glucocorticoid levels and the onset of
Alzheimer’s. There are acetylcholine receptor sites in the hippocampus. Loss of hippocampal
cells also correlates with lower levels of acetylcholine. This may play a key role in the
development of dementia.
In addition, it appears that a rat mother’s grooming helps to activate genes which are
responsible for the reaction to the stress response. This is an example of epigenetics - the
grooming process “turns on” the genes which help the young rat cope with stress - which then
leads to a longer and healthier life.
Meany’s research was able to establish a cause and effect relationship between stress and the
effect on memory. However, further research has shown that epigenetics is the reason why the
hippocampal cell loss happens. Even though the cause and effect was established, it did not
explain the exact process of what was happening. Since the original study in 1988, Meaney has
shown the complex interaction between the hippocampus, glucocorticoids and our genes in the
development of dementia.
References
Meaney, M et al (1988). Effect of Neonatal Handling on Age-related Impairments associated
with the Hippocampus. Science 12 February 1988: Vol. 239 no. 4841 pp. 766-768
For more information on how rat grooming affects genes and one’s level of stress, see the
following site: http://learn.genetics.utah.edu/content/epigenetics/rats/