Many thanks to Dr. Christina S. Barr from the National Institutes of Health/National Institute on Alcohol Abuse and Alcoholism-Laboratory of Clinical and Translational Studies, National Institutes of Health Animal Center for taking the time to comment on her team’s recent publication, “Functional CRH variation increases stress-induced alcohol consumption in primates” [doi:10.1073/pnas.0902863106] which was covered here. On behalf of students and interested readers, I am so grateful to her for doing this! Thank you Dr. Barr!
For readers who are unfamiliar with the extensive literature on this topic, can you give them some basic background context for the study?
“In rodents, increased CRH system functioning in parts of the brain that drive anxious responding (ie, amygdala) occurs following extended access to alcohol and causes animals to transition to the addicted state. In rodent lines in which genetic factors drive increased CRH system functioning, those animals are essentially phenocopies of those in the post-dependent state. We had a variant in the macaque that we expected would drive increased CRH expression in response to stress, and similar variants may exist in humans. We, therefore, hypothesized that this type of genetic variation may interact with prior stress exposure to increase alcohol drinking.”
Can you tells us more about the experimental design strategy and methods?
“This was a study that relied on use of archived NIAAA datasets. The behavioral and endocrine data had been collected years ago, but we took a gene of interest, and determined whether there was variation. We then put a considerable amount of effort into assessing the functional effects of this variant, in order to have a better understanding of how it might relate to individual variation. We then genotyped archived DNA samples in the colony for this polymorphism.”
“I am actually a veterinarian in addition to being a neuroscientist- we have the “3 R’s”. Reduce, refine, and replace…..meaning that animal studies should involve reduced numbers, should be refined to minimize pain/distress and should be replaced with molecular studies if possible. This is an example of how you can marry use of archived data and sophisticated molecular biology techniques/data analysis to come up with a testable hypothesis without the use of animal subjects. (of course, it means you need to have access to the datasets….;)”
How do the results relate to broader questions and your field at large?
“I became interested in this system because it is one that appears to be under intense selection. In a wide variety of animal species, individuals or strains that are particularly stress-reactive may be more likely to survive and reproduce successfully in highly variable or stressful environments. Over the course of human evolution, however, selective pressures have shifted, as have the nature and chronicity of stress exposures. In fact, in modern society, highly stress-reactive individuals, who are no less likely to be eaten by a predator (predation not being a major cause of mortality in modern humans), may instead be more likely to fall susceptible to various-stress related disorders, including chronic infections, diabetes, heart disease, accelerated brain aging, stress-related psychiatric disorders, and even drug and alcohol problems. Therefore, these genetic variants that are persistent in modern humans may make individuals more vulnerable to “modern problems.”
I do hope this helps. Let me know if it doesn’t, and I will try to better answer your questions.”
THANK YOU AGAIN VERY MUCH DR. BARR!!
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