This 2014 rodent study stressed the animals, measured their stress responses, then killed them and sampled genes in their amygdala, hippocampus, and blood. The researchers found that glucocorticoid receptor signaling genes were the primary pathway associated with “exposure-related individual differences“ in stress responses for the amygdala and blood. This pathway also placed first for the hippocampus in female rats (glucocorticoid receptor was second in male rats and prostate cancer signaling was first).
I’ll quote one press article’s coverage to show where the researchers wanted to go with the study’s findings:
“We found that most of the genes and pathways that are different in PTSD [post-traumatic stress disorder]-like animals compared to resilient animals are related to the glucocorticoid receptor, which suggests we might have identified a therapeutic target for treatment of PTSD.”
How about this lead sentence:
“There may some day be a blood test to determine whether someone suffers from Post-Traumatic Stress Disorder or is at risk for the psychiatric condition.”
Here’s another article’s paraphrase of a different researcher:
“Those are genes that become activated in the presence of stress. Like a key fitting into a lock, the hormone corticosterone, produced naturally by the body, connects to the receptor and has a calming effect.
In some rodents, and apparently in some people, the pathway appears to be defective, and this puts them at higher risk for PTSD.”
Also, from the study’s abstract:
“Corticosterone treatment 1 h[our] after PSS [predator-scent-stress]-exposure prevented anxiety and hyperarousal 7 d[ays] later in both sexes, confirming the GR [glucocorticoid receptor] involvement in the PSS behavioral response.”
Like other researchers continue to do, they stopped this study short of finding causes for the effects:
- What were the causes for genes in the glucocorticoid receptor signaling pathway being differentially expressed? “Exposure-related individual differences” isn’t a causal finding.
- If this pathway is “defective,” what exactly happened to make it that way?
- Did dampening the effects of stress with a shot of cortisol one hour after the stress treat the cause such that the rats were cured? Since the readers of the study and associated articles were led to infer that this treatment was a cure, why destroy the treated animals afterwards before the proofs of long-term efficacy were thoroughly documented and tested?
When studies like this are carried forward with humans, researchers should try to find the causes for these effects. It isn’t sufficient to pretend that there aren’t early-life causes for these effects. Such a pretense leads to the follow-on pretense that later-life consequences are mysteries such as “exposure-related individual differences” and not effects.
Researchers should act like the subjects are feeling human beings who can participate in treatments of both the causes and effects. They should remember that humans are not lab rats who need to be fixed.
http://www.pnas.org/content/111/37/13529.full “Expression profiling associates blood and brain glucocorticoid receptor signaling with trauma-related individual differences in both sexes”