Metz, Marissa Joan, authorHentges, Shane T., advisorTamkun, Michael M., committee memberVigh, Jozsef, committee memberHenry, Charles S., committee member2022-01-072022-01-072021https://hdl.handle.net/10217/234277For thousands of years, humans have been using various forms of opioid drugs as analgesics, recreational drugs, and more. The power of these opioid drugs rests in the availability of opioid receptors expressed within the human brain and body. Opioid receptors sense opioid agonists and confer various actions in the cell through inhibitory g-proteins. One type of opioid receptor, the mu-opioid receptor (MOR), is especially important for sensing both currently used analgesic drugs and opioids of abuse. Thus the MOR is of focus in the following chapters. Understanding particular signaling states of MORs is important because each function of the MOR corresponds to specific cellular and behavioral effects. In Chapter 2, an attempt was made to better observe MOR activities through direct observation of mobility states within the cell membrane. Experiments were performed to examine if specific mobility states of the MOR within the cell membrane correspond to specific functional states of the MOR. Particular mobility states did not always correspond to single functional states, but the variation in mobility states observed at baseline hinted at the potential for a rich variety of functional states before agonist was applied. Therefore, the experiments in Chapter 3 investigated if the functional state of MORs could be shifted towards more active, or sensitized receptors. Using a clinically relevant antagonist treatment, low dose naltrexone (LDN), the response of MORs to subsequent agonist treatment was tested using electrophysiology and found to be no different from MOR responses in cells from animals not treated with LDN. Further, the activity of cells producing endogenous opioids in the brain, proopiomelanocortin (POMC) neurons, was investigated to understand if LDN could alter endogenous opioid systems. This was not the case, however, and LDN actions appeared to be independent of enhancement of MOR activity or endorphin production from POMC neurons in the brain. Therefore, Chapter 4 focused on how the circuitry of POMC neurons is set up to handle many different functions. Dual retrograde tracing was used to examine whether individual POMC neurons project to more than one location, with the expectation that POMC neurons might form subpopulations based on the region they project to. This hypothesis was largely supported, as very few individual POMC neurons projected to more than one of the examined target regions. These findings help in understanding the organization of neurons that make β-endorphin and other peptides. Overall, the work presented in this dissertation reveals the complexity and heterogeneity of the opioid system from receptor to circuit. While the application of LDN does not appear to affect this complex system within POMC neurons, the circuitry of POMC neurons themselves lends promise to manipulating opioid processes with more precision in the future.born digitaldoctoral dissertationsengCopyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.complexityheterogeneityopioid systemLDNPOMC neuronsText