Post-Traumatic Stress Replicated in Mice
Researchers have found a way to trigger the symptoms of post-traumatic stress disorder in mice, which they say may help reveal a way to treat PTSD in people.
By coupling an electric shock with an injection of steroid hormones, researchers caused mice to behave as though they had PTSD, their study says.
People with PTSD have vivid recollections of a traumatic eventand an inability to place that memory in context. They are plagued by fearful memories that come on suddenly, often triggered by harmless cues.
"In an extremely stressful situation, because all the attention of the patient is focused on one single, salient, trauma-related cue," other details surrounding the traumatic event are not processed by the brain well enough to be remembered, explained lead researcher Aline Desmedt, a neuroscientist at the University of Bordeaux in France.
In the study, Desmedt and her colleagues set out to see if they could bring on PTSD-like memory impairmentsin mice — that is, if they could cause the mice to show fear in response to incorrect threat cues.
Shock and stress
The researchers placed mice in a Plexiglas chamber and gave them foot shocks immediately after playing a tone, causing the mice to associate the noise with the painful experience. They then shocked a different group of mice without the tone — a method known to cause mice to associate the shocks with the chamber they're in (the "context" of their trauma).
Immediately after the shocks, the researchers injected corticosterone into each rodent's hippocampus, a brain region that is important to memory and seems impaired in PTSD patients. Corticosterone is a hormone involved in stress responses.
The mice that hadn't heard the tone showed fear in response to the noise, but not to being placed in the chamber — they seemingly forgot which cue was connected to being shocked.
In another experiment, instead of injecting mice with the hormone, the researchers restrained the mice in a cylinder for 20 minutes, which triggering a release of the animals' own stress hormones. Again, the mice forgot their predictive cue.
In all, the results suggest that a PTSD-like memory impairment results from excessive stress hormone production along with an exposure to an intense threat, Desmedt said.
Looking at the brains of mice, the researchers found that when PTSD-like memories form, activity in the hippocampus becomes very low and activity in the amygdala— a brain area involved in the processing and remembering of emotional reactions — becomes very high.
What the findings mean for people
These findings could "open the way to the understanding of the molecular bases [of PTSD] and, as a consequence, to the development of efficient therapies," Desmedt said.
Not everyone is convinced the mice in this experiment make a good model of PTSD in people. The study's findings "are extremely relevant to understanding normative stress responses, but it is hard to see how the findings relate to PTSD," said Rachel Yehuda, a psychiatrist and neuroscientist who specializes in PTSD at the Mount Sinai School of Medicine in New York City.
To Yehuda, a major issue with the study is that there was no variation between the mice's responses. "The fact is that we don't all get PTSD from traumatic events," Yehuda told MyHealthNewsDaily.
Further, she said PTSD symptoms are present long after the traumatic event, something the researchers didn't show with their mice. "Everyone looks like they have PTSD right after something bad happens — that's normal," Yehuda said.
The study appears online today (Feb. 24) in the journal Science.
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By Kiley Price