Dorsal striatal mu opioid receptor function and alcohol use Project Summary: The proposal presented here seeks to better understand the role of mu opioid receptors (MORs) in the dorsal striatum in the transition from alcohol use to abuse. One brain region where MORs may play a significant role is the dorsal striatum, which is a critical structure in the transition from goal-directed to habitual drug use, including alcohol use One of the few effective pharmacological treatments for alcohol use disorders is an opioid receptor antagonist. Additionally, transgenic mice that lack MOR appear to find alcohol aversive. On the other hand, long-term consumption of alcohol may alter the levels and functional coupling of MORs in the dorsal striatum. My preliminary data reveal that long-term alcohol exposure disrupts normal MOR- dependent long-term synaptic plasticity in the dorsal striatum. Thus, there appears to be an interaction between alcohol consumption and the function of MOR in this brain region, which may underlie the transition from drug use to addiction. I hypothesize here that ethanol exposure alters MOR-mediated plasticity at specific striatal synapses and that manipulating MOR function at these same synapses will alter ethanol consummatory behaviors. To test these hypotheses, I propose the following three specific aims. 1.
In Specific Aim 1, I wil determine whether alcohol-mediated disruption of dorsal striatal MOR-dependent long-term plasticity of striatal inputs is global or synapse-specific. I will use optogenetics and pharmacology to specifically probe distinct striatal inputs and determine which are MOR-sensitive and whether chronic alcohol disrupts this plasticity. This will provide clues as to what types of input (executive, associative, sensory, etc.) to the dorsal striatum are altered by alcohol use, and provide new hypotheses regarding MOR-regulated effects of alcohol on behavior. 2.
In Specific Aim 2, I will identify the effects of alcohol on MOR-mediated regulation of dopaminergic signaling. It is not known how MOR regulates dorsal striatal dopamine release as well as whether this regulation is altered by alcohol exposure. Furthermore, dopaminergic neuroadaptations in the dorsal striatum to prolonged alcohol exposure may result from a disruption of normal, MOR-dependent processes. MORs found on dorsal striatal cholinergic interneurons are in a prime location to modulate dopamine release. Therefore, in this aim I specifically address the hypotheses that MORs on cholinergic interneurons are the critical component of the effects of MOR on dopamine release and that ethanol disrupts this normal MOR-regulated dopamine release. 3. In my final aim, I will pharmacologically and genetically manipulate dorsal striatal MOR function and observe the effects these alterations have on alcohol consumption. I will test the hypothesis that dorsal striatal activation of MOR results in increased alcohol consumption, and conversely that MOR inhibition will reduce ethanol consumption. Additionally, I will use transgenic mice to ablate MOR expression from specific neuron types and observe whether these genetically modified mice still consume alcohol. These experiments will reveal whether MORs in the dorsal striatum, and more specifically in distinct cell types, control alcohol consummatory behavior. Throughout my time as an undergraduate research assistant, graduate student, and postdoctoral fellow, I have had an intense interest in how drugs of abuse change synapses in the brain. I have had the privilege of working with great scientists such as Drs. Ken Mackie and David Lovinger, among others, who have taught me invaluable skills of not just research techniques, but engaging in hypothesis-driven science. These mentors have taught me to ask many questions, design careful and focused experiments, and critically interpret data. In addition, they have provided me with many opportunities to direct the course of the work I performed, allowing me to fail at times and learn from those failures. I am a better scientist because of the mentorship of these individuals and my many other colleagues. During the mentored phase of this award, I will have the support of the Division of Intramural Clinical and Biological Research and will be under the mentorship of Dr. Lovinger. I have a number of highly qualified colleagues that are readily available to teach me the new techniques necessary to accomplish the work presented here. As a result of the mentored phase of this project, I will learn and become proficient in new skills such as fast-scan cyclic voltammetry, ethanol administration paradigms, and infusion of drugs into brain tissue. I will also develop skills that I have limited training in, such as stereotaxic surgeries and optogenetic protocols. In addition, at NIAAA I have access to high quality research equipment and supplies that will allow me to achieve the work that will be performed during the mentored phase. Throughout the mentored and transition phases, I will gain additional mentoring experience and skills that will enable me to independently oversee my own research laboratory in the future. Furthermore, I am in close association with many experts in the field of alcohol research from whom I can learn much and become a fully integrated member of this research community. I am confident that with Dr. Lovinger's principal mentorship, the additional mentorship of a committee of select colleagues, and the institutional environment at NIAAA, I will be able to achieve my goals of becoming a fully independent neuroscientist.
One of the few effective pharmacological therapies for alcohol use disorders is an opioid receptor antagonist, naltrexone, suggesting that the endogenous opioid system is critical to alcohol use and abuse. In turn, long- term alcohol use alters the expression and function of many components of this opioid system, especially the mu opioid receptor, suggesting a bidirectional relationship between alcohol use and mu opioid receptor function. It is unclear how the changes in the opioid system translate into changes in neuronal communication and animal behavior. This project aims to provide a better understanding of how alcohol's effects on the opioid system remodel opioid receptor signaling at specific synapses in the dorsal striatum, a brain region that is important in the transition from casual drug use to dru abuse and addiction, and how this receptor at these synapses influences drinking behavior.
| Fritz, Brandon M; Muñoz, Braulio; Yin, Fuqin et al. (2018) A High-fat, High-sugar 'Western' Diet Alters Dorsal Striatal Glutamate, Opioid, and Dopamine Transmission in Mice. Neuroscience 372:1-15 |
