Understanding endogenous opioid drive of alcohol consumption

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PROJECT SUMMARY Endogenous opioids released in the Central Nervous System by drinking alcohol promote continued consumption. The endogenous opioid peptides are fragments of larger precursor peptides (preproenkephalin (PPENK), preprodynorphin (PPDYN) and pro-opiomelanocortin (POMC)) are implicated in regulating alcohol intake. The fragments that are actually released are unknown, however the known POMC and PPENK derived peptide fragments act both the mu and delta opioid receptors (MORs and DORs, respectively). We found that endogenous opioids acting at the DOR can protect against high levels of alcohol consumption, while opioids acting the MOR promote alcohol consumption. To better understand how endogenous opioids control ethanol consumption and to develop new opioid based therapeutic agents we need to determine how MORs and DORs are dynamically regulated and interact. Furthermore, a full understanding of how they regulate ethanol consumption will require identification of which opioid peptides fragments are released by drinking and then testing the action of these peptides at synaptic elements that express both receptors and are involved in regulating ethanol consumption. The ventral tegmental area (VTA) is a site where opioids act to control ethanol consumption. MOR selective antagonists injected into the VTA reduce while DOR antagonists increase ethanol consumption. Both MOR and DOR selective ligands have synaptic actions in the VTA that correlate with alcohol consumption. In this project we will study the interaction of MOR, DOR and kappa opioid receptor agonists on VTA synaptic function. We will collect and identify endogenous opioid peptides released in the VTA during voluntary ethanol drinking, then test the action of these peptides on opioid receptor expressing synaptic elements in the VTA. We will also use optogenetic approaches to activate and inhibit specific sources of opioid peptide input to the VTA to determine the critical circuit inputs that modify drinking behavior. This information will be used to better understand the molecular mechanisms that promote and inhibit alcohol consumption and to design new, more effective opioid ligands for the treatment of alcohol abuse.