Fat rats stressed and forgetful, but what does that mean for us?

A recent study done with the help of USF researchers has shown that rats that consume a high-fat diet and are exposed to constant stress develop atrophy in the hippocampus, the part of the brain that is essential for learning and remembering new information.

“The hippocampus is sort of a temporary database that allows you to put information from short-term memory into long-term memory,” said David Diamond, a professor in the department of psychology and a doctor at the Veterans Hospital.

The study was conducted at USF and involved researchers from the James A. Haley Veterans Administration Medical Center, Arizona State University and the USF psychology department.

The results of the study could prove that poor eating habits in humans might result in negative effects that are more than just physical.

Although the study was conducted only on rats, the results have big implications for humans, said Cheryl Conrad, a professor in the department of psychology at Arizona State University.

“Both rats and humans share similar features,” Conrad said. “A lot of things that we see in rats also occur in humans, so we find that rats provide a great model for looking at changes in the brain that can also be observed in humans.”

In the study, stress was produced in rats by putting them into a room where they were surrounded by cats, Diamond said. Inside the room a Plexiglas container with tiny holes protected the rats. The holes in the container allowed both the cats and rats to smell each other. The rats were exposed to the room everyday for a month and were fed high-fat diets at night, Diamond said.

“There is evidence that high-fat diets alone will increase stress. We also know that stress actually has some effects that will increase damage to the heart as well as to the brain all by itself. So I figured that if we combine stress with high-fat diets, we’d get a much bigger effect,” Diamond said.

The results of the study showed that when the rats ate diets high in carbohydrates and beef fat and were exposed to constant levels of stress they developed hippocampal atrophy, Diamond said.

Hippocampal atrophy occurs when dendrites, the connections between brain cells, retract or shrivel up. This causes the hippocampal cells to become less efficient at processing information, Diamond said.

The dendrites shriveled up in the rats due to excess amounts of corticosterone, a steroid hormone produced by the adrenal glands, being produced in the rat’s bodies, Diamond said.

Corticosterone in rats is similar to a hormone produced in humans called cortisol. Both types of hormones are stress hormones produced in order to help people or animals deal with stress, Diamond said. The hormones do this by helping to break down proteins and carbohydrates into glucose, which produces more energy.

“It helps us to have more energy when life demands that we have more energy, especially if there is a threat or even when we are exercising,” Diamond said.

When corticosterone is overproduced in the brain, it results in excessive stimulation that can cause damage due to the fact that the hippocampus is overworked. When the hippocampus is overworked, the dendrites in the brain associated with it begin to shrivel up. Diamond said he believes that hippocampal atrophy occurred in the rats because of the overabundance of corticosterone produced.

“A tree protects itself by eliminating its leaves in a cold climate. That’s the same idea about what the hippocampus does. If it gets too much stimulation, it cuts back on the number of dendrites, and that will protect it because it’s actually covering up its input so it reduces the amount of stimulation,” Diamond said.

Now that Diamond knows the effects of stress and a high-fat diet on the brains of rats, he said he plans to begin research on a new project that will examine the actual learning ability of rats under these circumstances. Currently, Diamond is seeking an undergraduate student who would be interested in getting involved in this project. The ideal student would be someone majoring in psychology and is interested in the biology of memory, he said.

“They could get not only credit for this, but it could help to get them into graduate school,” Diamond said.