It is estimated that addiction and its associated costs: crime, domestic violence and child abuse, health care costs, and loss of employment and family structure, exceed half of a trillion dollars per year. Fighting addiction is not a matter of willpower, it is a battle to understand how drugs affect the brain and can permanently alter its function. One of the key limitations to understanding the cellular and genetic basis of a complex disease like addiction is the availability of good models to test hypotheses related to cells and genes and their functions. The laboratory rat is one model which has tremendous value because of its intensely studied physiological, biochemical, and behavioral characteristics and their genome sequence similarities to humans. More than 2000 genetic determinants of disease-related traits have been initially described in the rat, however, it has been difficult to precisely correlate specific genes with these traits because of limitations in technology for manipulating the rat genome. In the past 4 years, we have been developing new tools to close this technology gap. We have developed new and efficient ways of making transgenic rats using transposable elements which are highly reproducible and we were the first to apply zinc-finger nuclease (ZFN) technology to target and disrupt, or knock out, specific genes in the rat. These are two very important technologies that allow us to do many things, but more work is needed. Many times, knocking out a gene in the whole animal precludes studying its role in a particular cell or tissue because the gene is essential for early embryo development and so knocking it out causes the animal to die. In other cases, knocking out the gene in the whole animal doesn't allow one to distinguish what organ (or part of the brain, for example) the gene is functioning in to cause the disease. In this pilot/feasibility study, we propose to develop the next key technological step toward this goal - to be able to specifically disrupt genes in a particular cell or tissue at a particular time. We will develop transgenic rats which express an inducible CRE/loxP recombinase system in specific tissues. This system will allow us to create conditional knockout rats where we can control where and when a gene function is removed from a cell. We will focus brain neuron systems known to be important for studying addiction and behavior - the dopaminergic and serotonergic neurons. As a proof of principal that the system is working, we will knock out the gene that produces serotonin, a hormone that is important in the reward system of the brain and an integral player in addiction and other psychiatric disorders, specifically in neurons of the hindbrain. If successful, this approach will change the way we can approach genes, cells and diseases in the laboratory rat model to impact the socioeconomic burdens of addiction and drug abuse.
The key to developing effective therapies for the treatment of addiction and other psychiatric disorders is the identification of genes and the cells they work in to target new drugs and approaches. Lab rats are the preferred model for studying addiction by many resources, but the technology to study a particular gene by knocking out its function in a particular cell or tissue has not been demonstrated. This pilot and feasibility study aims to develop that technology in the lab rat so we can enable studies of specific genes and their roles in addictive behavior and other diseases.