Writer: Jane Moorman, (505) 249-0527, firstname.lastname@example.org
Psychological stress can generate symptoms of depression and anxiety as well as impact the neurons in the brain, according to research conducted by a New Mexico State University professor. Furthermore, the use of anti-depressants may relieve the symptoms of depression and anxiety and damage to the brain, but only if the stress is relatively mild.
"When a female rat lives in a threatening environment, the dendrites of brain cells, or neurons, in the hippocampus of the brain are not as robust and healthy as those living in a non-stressful place," said Gail Leedy, professor of social work and coordinator of the School of Social Work program at the NMSU-Albuquerque Center.
Leedy's research conducted on female rats has been published in the Brain Research Bulletin, March issue. The bulletin publishes novel work that advances the knowledge of cellular and molecular mechanisms that underlie neural network properties associated with brain function and neuropsychiatric diseases.
"Social stress is both species- and gender-specific," Leedy said. "I was trying to find an animal model that would capture some of the complexities of depression/anxiety disorders, which would be relevant to humans."
Leedy's research is the first to use a complex social living environment, rather than physical stimulus, to induce stress in female rats. She studied ovariectomized, or spayed, female rats in four environments: living alone, pairs in small space, multiple female settings, and a visible burrow system where four females were housed with four males. The visible burrow system consists of a large open cage connected to tunnels and small, darkened "burrows."
"The prevailing wisdom was that females would not experience stress if caged with the males," she said. "It was believed what would stress them was living by themself. Both of these beliefs are based on very few studies or data."
After six weeks of observing the rats housed in the four environments, and then months of studying the dendrites of the neurons in the hippocampus, Leedy's findings were just the opposite of the previous studies.
"We observed a variety of stress-related behavior changes for those females living in the largest cages with the males," she said. "The female rats found a safe spot in the corners of the cage and stayed motionless most of the time. They also exhibited a behavior of trying to escape the males' attacks by jumping out of the cage, and once the cages were covered they would hang from the mesh screen ceiling of the cage."
Previous studies had stated that the females were attacked by the male rats, but, because there were no signs of injury, the researchers assumed that they were not stressed.
"This lack of injury is because the females do not fight back when the males attack them during the sexual acts. The female just rolled over to show they are not receptive and to prevent the act from being accomplished," she said of the females that had no sexual instinct or drive because of the lack of hormones since they were spayed.
Under the microscope, the dendrites of the neurons in the brain were less developed than those of the female rats that lived in the other three environments.
"Dendrite growth is only one way that you can observe the effects of stress in the brain. In the past it was believed that a person is born with all the neurons they would have for their life," Leedy said. "Now we know there are neurons generated in adult rats and humans in the hippocampus area of the brain. One way to determine if stress has occurred is to see if it disrupts the neurogenesis or the birth of new neurons."
During the second phase of the research, Leedy determined that the use of anti-depressant drugs, such as the generic fluoxetine, does not decrease the impact of stress on the neuron dendrites.
"In this study we compared females who lived in regular cages, females living with three other females and four males, and females living with seven other females in a visible burrow system," she said of the research that was conducted while she was on the faculty of the University of Wyoming. "In each environment half of the females received the drug."
Two questions were being answered in the second phase: do anti-depressant drugs decrease the impact of stress on the neurons and was part of the stress observed in the first phase because the rats were crowded, rather than due to the mix of females and males in one environment?
"Once again the females not with the males showed only slight signs of stress, while those living with males showed clear changes in behavior and in their neurons. These changes were not alleviated by the antidepressants," Leedy said. "Regarding the use of drugs to decrease stress, the take home message to me is that treating the symptoms of stress, such as depression and anxiety, when the stress factor is still present and is high, is ineffective."
Leedy hopes that the research will demonstrate to other researchers that studying rats in social living conditions is a good animal model that is relevant to humans.
"As a social work professional, the message I get from these findings is that until we have non-threatening environments for people the stress from those situations will affect the health of the nervous system of the people," she said. "And until that can be accomplished, when treating the symptoms of stress with medication, it is ineffective unless you also change the environment. You are throwing medicine at something without taking away the cause."
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