S. Andrew Aston
Corticotropin-releasing hormone (CRH) acts as one of the primary coordinators of the physiological, behavioral, and autonomic stress response. CRH secreted from the paraventricular nucleus (PVN) of the hypothalamus initiates the hypothalamic pituitary adrenal (HPA) axis response by signaling the secretion of adrenocorticotropic hormone (ACTH) from the anterior pituitary. ACTH then travels to the adrenal glands, leading to the release of cortisol Thus, CRH plays a key role in preparing an individual to adaptively respond to a stressful situation.
Dysregulation of the CRH system, however, may lead to psychopathology. Studies have found elevated levels of CRH in individuals suffering from stress-related, depressive, and anxiety related disorders including anorexia nervosa, posttraumatic stress disorder (PTSD), and, perhaps most commonly, major depression. Excessive CRH may also contribute to psychopathology by dysregulating downstream elements of the stress response as previous research also implicates abnormal levels cortisol in psychopathology. Together these studies indicate that malfunctioning of the CRH system may lead to physiological and behavioral abnormalities.
Experiences early in development appear to influence CRH system functioning and later vulnerability to psychopathology. Studies using rhesus macaques indicate that disruption of the mother-infant relationship contributes to elevated levels of CRH in infants and dysregulation of the HPA axis. The influence of developmental experience on future neurophysiology suggests gene by environment (GxE) interactions may affect an individual’s vulnerability to psychopathology. A 2011 study found that a repeat polymorphism in the rhesus macaque serotonin transporter gene interacted with early developmental experiences leading to elevated levels of CRH. Research has uncovered similar GxE interactions that may contribute to psychopathology in humans.
A single nucleotide polymorphism (SNP) in the promoter region of the rhesus macaque CRH gene (CRH-248 C>T) dysregulates glucocorticoid negative feedback and upregulates transcription of CRH in vitro. Behavioral studies indicate that this SNP interacts with early adverse rearing to disrupt activity of the HPA axis and promotes stress induced alcohol consumption. Our lab is currently preparing research for publication that indicates that this SNP interacts with adverse rearing leading to potentially psychopathological dysregulation of the HPA axis and affecting anxious behavior in juvenile rhesus macaques. Because the T allele is rare, we wanted to be able to replicate our findings using different animals and a larger sample size.
I wrote my ORCA proposal intending to genotype 250-300 animals that participated in a biobehavioral assessment (BBA) at the California National Primate Research Center (CNPRC) in Davis, CA. The BBA involves a battery of biological and behavioral that measure, among other things, the functionality of subjects’ HPA axis and behavioral responses to stressors. Subjects in the BBA come from distinct, controlled rearing environments, allowing us to investigate GxE interactions that may influence psychopathology.
During a research internship at the CNPRC, I worked with researchers to analyze previously extracted DNA samples for their suitability for genotyping. Analysis involved pulling samples of BBA tested animals from a collection of DNA samples, aliquoting half of the sample into new tubes, and then quantifying the DNA using a Nanodrop® 2000c photospectrometer. I started working with a list of approximately 600 subjects for whom we expected to find DNA. Many samples could not be found, others samples were found at such a low volume that they could not be divided into two tubes, and other samples were found to have such low concentrations of DNA in solution that they could not be used. After analyzing the DNA, we determined that we had 268 samples from which we could draw 75 ng of DNA for shipment to the National Institutes of Health, where collaborators could run TaqMan® assays to determine subjects’ genotype at 5 psychophysiologically significant genetic loci, including the CRH-248 C>T SNP. We diluted the samples to a standard concentration of 15 ng/μl and placed them in boxes for shipping.
The samples have not yet been shipped, but after these samples are shipped and genotyped, they will make a significant addition to the BBA and help researchers, including future undergraduate students from Brigham Young University (BYU), investigate the effects of genotype on the physiological and behavioral stress response. Not only will these data help researchers better understand the way that genetic variation contributes to psychopathology of the stress response, but it will also help future BYU students as they learn about the scientific research process. Working on this project has helped me better understand how research works, taught me how to collaborate with principal investigators, and given me the opportunity to develop relationships with scientists that will help me as I pursue a career in neurogenetic research.
In the interest of space, references are available upon request.