The nonmedical abuse of prescription opioids is a major socioeconomic problem in the United States. Drug abuse is known to have a genetic component and epidemiological studies indicate that individuals reporting a pleasurable experience are most likely to transition to drug abuse. Accordingly, this application seeks to identify the genetic basis of opioid reward and aversion. We will use a genetically informative panel of mouse strains and a behavioral model- the place conditioning assay- to screen for differences in the rewarding response to the commonly abused prescription opioid agonist oxycodone (OXY) and the aversive response to the opioid antagonist naloxone (NAL).
In Aim 1, we will identify genomic regions that are responsible for differences in OXY reward and NAL aversion.
In Aim 2, I will receive training in mRNA sequencing (RNA-seq) to identify differentially expressed genes and splice variants in these genomic regions as potentially causal for variation in OXY reward and NAL aversion.
In Aim 3, we will generate congenic mice carrying small portions of these genomic regions to narrow the list of potential genes responsible. Within these regions, we will choose candidate genes that are differentially expressed for further analysis via molecular genetics techniques. The outcome of this proposal will aid in identifying genes contributing to opioid reward and aversion which will have implications for understanding and treating opioid abuse. My mentor, Dr. Abraham Palmer, has several years of experience with regard to all aspects of this project, including QTL mapping, transcriptome analysis, and large-scale mouse phenotyping studies. Dr. Palmer's history of expertise for transcriptome analysis has involved microarrays;thus, I have recruited Dr. Jonathan Pritchard (Co-Mentor) and Dr. Yoav Gilad (advisory committee member) to provide mentorship and training in the analytical and technical aspects of RNA-seq. Additionally, I have formed an advisory committee consisting of Dr. Palmer, Dr. Pritchard, Dr. Gilad, Dr. Harriet de Wit, and Dr. James Zacny. Dr. de Wit has extensive background and expertise in both rodent and human studies of drug abuse and is particularly interested in the translational aspect of the proposed research. Dr. de Wit conducts genetic association studies involving sensitivity to drugs of abuse, notably with subjective phenotypes such as drug reward. Thus, Dr. de Wit is well-positioned to provide expert advice on the behavioral, genetic, and pharmacological aspects of this proposal and can offer a translational context from which to apply the results. Dr. Zacny is an expert in opioid pharmacology and human phenotyping of opioid traits and has published multiple papers regarding variability in the physiological and subjective response to opioids- in particular OXY. Dr. Zacny is interested in applying the results of this proposal to translational studies regarding the genetic basis of opioid sensitivity in humans. The institutional environment for supporting and complementing this proposal is excellent. On the genetic and genomic end of the project, there are several excellent faculty in the Department of Human Genetics with whom I interact, including members of my committee. We have several seminar series affiliated with the department that I will participate in, including Work in Progress, Monthly Seminar Series, Journal Club, and Genetics of Model Organisms. There will be at least six Illumina GA2 machines in place for my RNA-seq samples to be run, three of which are located on the U of C campus. On the neuroscience end, Dr. Paul Vezina heads a NIDA-funded T32 training program, "Neuropsychopharmacology Training for Drug abuse Research" and seminar series that meets twice per month. Dr. de Wit and Dr. Palmer are both participating P.I.'s in this program, along with several other neuroscience faculty members who are all interested in addiction biology. My long-term objective is to establish my own academic research program at a major research university aimed at identifying genes involved with phenotypes associated with drug abuse, starting with the place conditioning assay as outlined in this proposal. In the current era of QTL mapping, transcriptome analysis is now a mainstay complementary tool for finding genes contributing to complex phenotypes such as drug sensitivity. Thus, the training I receive in RNA-seq analysis will help me to realize this career goal. There is a huge gap in the field of addiction biology regarding the genetic determinants of place preference. Because this assay is so widely used in addiction biology, this area of research will undoubtedly contribute to our understanding of the multitude of existing studies and provide novel insight into the mechanisms of drug reward and abuse. Future proposals from my laboratory will be aimed at testing genes identified in this study for pleiotropic effects on other behaviors associated with drug abuse, including withdrawal, self-administration, extinction, reconsolidation, and reinstatement. I am also interested in the intersection between reward/aversion and pain pathways and would like to further explore this area of research as a future proposal.
The mouse genetics strategy outlined will likely lead to the identification of genes that regulate the motivational properties of opioids. This will have direct public health relevance because the findings will be translated into human genetic association studies and genes conferring risk for opioid abuse may be identified.