Researchers induce PTSD symptoms in mice

(Medical Xpress) -- Post-traumatic stress disorder (PTSD) is a condition in which people find themselves experiencing intense fear following a traumatic experience due to unrelated circumstances. It’s quite common in soldiers returning from the battlefield but can also be found in people that have experienced an assault, abuse or tragedy such as surviving a hurricane or tornado. And because it can persist for years after the initial trauma, those that suffer from it can find their lives seriously disrupted. Because of this, research into ways to treat the condition has been ongoing by both military and civilian entities. Now, a French team of researchers has found, as they describe in their paper published in Science, a way to induce what appears to be PTSD symptoms in mice. This move could help scientists better understand the chemical processes in the brain in people with the disorder.

To replicate the traumatizing effects of conditions that cause people to experience PTSD, the researchers set a group of mice in a plastic cage. They were subsequently shocked on the feet with an electric probe right after a tone was played. Naturally, this caused them to become conditioned to expect pain upon hearing the tone. To make the experience more heightened, a main component of PTSD, the mice were also given a dose of corticosterone (a stress response hormone) injected directly into their hippocampus right after being shocked. In highly high-stress situations, corticosterone levels in the hippocampus (an area of the brain associated with memory) are naturally higher. In a second experiment, they did precisely the same thing, except they omitted the part where the tone was played before the shock.

In testing the mice afterwards, the dose of corticosterone given after the traumatic event caused confusion about what should be tied to the fear. Some mice who had not heard the tone before the shock displayed fear when hearing it nonetheless.

In a wholly different experiment, the team also attempted to induce PTSD symptoms by restraining the mice inside their cage, causing stress hormones to be released naturally after the tone and shock were administered. They found virtually the same results.

This all suggests, the team writes, that very traumatic and stressful situations cause hormone levels to rise, at least in some mice (and perhaps humans), leading to PTSD.

The team also found in studying the brains of the mice after the experiment that hippocampus activity levels were lower than average while the amygdala, a part of the brain involved in processing and emotional memory, showed more.

More information: Glucocorticoids Can Induce PTSD-Like Memory Impairments in Mice, Published Online February 23 2012, Science DOI: 10.1126/science.1207615

ABSTRACT 
Post-traumatic stress disorder (PTSD) is characterized by a hypermnesia of the trauma and memory impairment that decreases the ability to restrict fear to the appropriate context. Infusion of glucocorticoids in the hippocampus after fear conditioning induces PTSD-like memory impairments and an altered pattern of neural activation in the hippocampal-amygdalar circuit. Mice cannothttp:// identify the context as the right predictor of the threat and show fear responses for a discrete cue non-predicting the threat in normal conditions. These data demonstrate PTSD-like memory impairments in rodents and identify a potential pathophysiological mechanism of this condition.

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"Researchers induce PTSD symptoms in mice." February 24th, 2012. http://medicalxpress.com/news/2012-02-ptsd-symptoms-mice.html

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Robert Karl Stonjek