Pharmacology Commons^™

Nutrient-Driven Transcription Factor-Dna Interactions And Their Signaling Mechanisms In Metabolic Disease, Evelyn A. Bates

Theses and Dissertations--Nutritional Sciences

Metabolic homeostasis is maintained through tightly coordinated signaling networks that integrate diverse physiological inputs. Central to this regulation are transcription factors, which sense nutrient, hormonal, and vitamin-derived signals and translate them into coordinated gene expression programs. Transcription factor activity is governed by DNA binding, recruitment of coregulatory proteins, and interactions with specific response elements in gene promoters, which allows them to selectively modulate diverse metabolic pathways. Owing to their multifactorial and tunable nature, transcription factors have emerged as promising targets for the treatment and diagnosis of metabolic diseases, including metabolic dysfunction-associated steatotic liver disease (MASLD). This dissertation explores the molecular …

Design And Advancement Of Analytical Frameworks For In Vivo Single-Photon Calcium Imaging To Characterize Temporal- And Treatment-Dependent Neural Adaptations To Opioid Exposure And Withdrawal In The Medial Prefrontal Cortex, Alexia R. Alsum Dr.

Theses and Dissertations--Pharmacy

Despite the availability of several approved medications for opioid use disorder (OUD), it remains a significant public health concern characterized by persistent neurobiological adaptations that drive relapse and impede successful recovery. The medial prefrontal cortex (mPFC), a region critical for executive control and decision-making, undergoes pronounced functional changes during chronic opioid exposure and withdrawal, yet the cellular mechanisms underlying these adaptations remain poorly understood. This dissertation aims to investigate longitudinal alterations in mPFC neural activity across opioid exposure and withdrawal using in vivo single-photon calcium imaging and newly developed computational frameworks.

Following standard preprocessing to extract and normalize calcium traces, …

Molecular Mechanisms And Metabolic Consequences Of Glucocorticoid Resistance, Genesee J. Martinez

Theses and Dissertations--Pharmacology and Nutritional Sciences

Glucocorticoids are vital steroid hormones that govern metabolism, stress responses, and immune functions through intricate, tissue-specific mechanisms, both genomic and non-genomic. These hormones bind to the glucocorticoid receptor (GR), which then acts as a transcription factor to modulate gene expression. Chronic elevation of glucocorticoid levels may lead to glucocorticoid resistance, resulting in adiposity, inflammation, and insulin resistance, thereby adversely affecting multiple metabolic tissues. Whether produced endogenously or administered exogenously, excessive, chronic glucocorticoid concentrations impair glucocorticoid signaling. Although there are two primary isoforms of the receptor, GR⍺ and GRβ, only GR⍺ interacts with glucocorticoids.Through the research conducted in this dissertation, we …

Could Psilocin Rescue Chronic, Stress-Accelerated, Transcriptional Aging In Brain?, Danny R. Craig, Eric M. Blalock

Journal of Pharmacology & Nutritional Sciences

Brain aging (BA) processes are complex, often affect multiple systems, and frequently lead to cognitive decline and increased susceptibility to insults. BA appears to be a primary risk for the development of many prominent neurodegenerative pathologies. The US Census Bureau predicts that the aging population (65+) will represent a greater proportion of the US population than children (under 18) by 2034, dramatically increasing the burden on health-care infrastructure.¹⁷ Several mechanisms of stress driven, aging-related neurologic dysfunction have been advanced in the past 50 years and include: Stress hormone exposure and glucocorticoid cascade;^{7, 16} calcium ion dyshomeostasis;⁸ allostatic …

Metformin In Overcoming Enzalutamide Resistance In Castration-Resistant Prostate Cancer, Kendall Simpson, Derek B. Allison, Daheng He, Jinpeng Liu, Chi Wang, Xiaoqi Liu

Markey Cancer Center Faculty Publications

Androgen deprivation is the standard treatment for patients with prostate cancer. However, the disease eventually progresses as castration-resistant prostate cancer (CRPC). Enzalutamide, an androgen receptor inhibitor, is a typical drug for treating CRPC and with continuous reliance on the drug, can lead to enzalutamide resistance. This highlights the necessity for developing novel therapeutic targets to combat the gain of resistance. Metformin has been recently investigated for its potential antitumorigenic effects in many cancer types. In this study, we used enzalutamide and metformin in combination to explore the possible rescued efficacy of enzalutamide in the treatment of enzalutamide-resistant CRPC. We first …

Investigating The Role Of Dynamic Signaling Of Nrg3-Erbb4 In The Prefrontal Cortex In Mediating Nicotine Withdrawal Phenotypes, Emily Prantzalos

Theses and Dissertations--Pharmacy

While several pharmacotherapies are currently available for nicotine use disorder (NUD), smoking cessation success rates remain below 10% each year. The molecular mechanisms underlying failed quit attempts continue to represent a critical gap in our knowledge. However, recent advances in understanding the genetic contributions to nicotine dependence offer a promising avenue for developing more effective cessation therapies. Prior research has identified genetic variation in Neuregulin 3 (Nrg3) and its cognate receptor ErbB4 as potential contributors to affective nicotine withdrawal (WD) phenotypes and cessation outcomes. Therefore, this dissertation aims to systematically investigate the region-specific, functional role of the Neuregulin Signaling Pathway …

Weighted Family History Density Of Substance Use: Influence On Participant Substance Use Onset, Escalation, And Duration, Carleigh A. Litteral

Theses and Dissertations--Psychology

Substance use disorders impose a staggering toll on the United States (U.S.), straining healthcare systems, destabilizing communities, and profoundly impacting both individuals and families. Approximately one in six Americans aged 12 and older had a past-year substance use disorder in 2022 (Key Substance Use, 2022), and nearly one-third of adults experience a substance use disorder in their lifetime (Wu, 2010), contributing to an economic burden exceeding $400 billion annually (National Drug Threat Assessment, 2011). Family history of substance use disorders is a key predictor of vulnerability, with individuals who have affected relatives being 2–8 times more …

The Effects Of Plx 3397 On Fentanyl Escalation In Male And Female Sprague-Dawley Rats, Jakob Shaykin

Theses and Dissertations--Psychology

Purpose: A hallmark characteristic of opioid use disorder (OUD) is a persons’ ‘loss of control’, which leads to the compulsion to seek and obtain opioids, resulting in increased consumption. This phenomenon is known as ‘escalation of drug intake’. Chronic opioid use causes microglial reactivity and subsequent release of proinflammatory cytokines leading to neuroinflammation, weakening one’s executive control over drug taking and ultimately leading to greater use. Previous research in our laboratory has explored heterogeneity of fentanyl intake in extended access (6-hr) sessions and identified distinct endophenotypes of fentanyl intake. Moreover, we have observed a positive correlation between Treml1 expression …

Population-Based Cross-Sectional Analysis Of Cannabis Use Among Kentucky Adults, 2020– 21, Sydney Shafer, Gunnar Kennedy, W. Jay Christian

UK CARES Faculty Publications

Purpose We conducted this study to assess cannabis use rates in the state of Kentucky relative to socioeconomic, demographic, and geographic factors, as well as reasons for use and modes of use, before the legal medical marijuana market commences in 2025.

Methods We pooled Kentucky Behavioral Risk Factor Surveillance System (BRFSS) data for 2020–2021 and used weighted responses for all analyses. We estimated current cannabis use (at least once in the past 30 days), and heavy use (at least 20 of the past 30 days) prevalence rates for Appalachian, Delta, and Central geographic regions of Ken- tucky. We tabulated descriptive …

Characterizing Gait In Young Male 5xfad Mice, Sophiya L. Sims, Kate E. Pauss, Sami L. Case, Ruei-Lung Lin, Leopoldine B. Galopin, Nicholas A. Wright, Olivier Thibault

Journal of Pharmacology & Nutritional Sciences

Gait control represents a non-cognitive domain that is affected negatively during late stages of Alzheimer’s Disease (AD) and AD Related Dementias (ADRDs). In some cases, early identification can be predictive of worsened cognitive function. Prompt detection could help define intervention windows, perhaps even years prior to formal diagnosis of dementia. In this study, the locomotor function of 3-month-old male 5xFAD mice was evaluated using several variables (speed, deviance from center, paw precision index, stride length, stride length deviation, and stride time) to characterize the change in ambulatory behavior prior to the onset of cognitive decline. The data presented here show …

What Influences Trust In And Understanding Of Clinical Trials? An Analysis Of Information And Communication Technology Use And Online Health Behavior From The Health Information National Trends Survey, Aurora Occa, Allison S. Merritt, Allison Leip, Jerod L. Stapleton

UK CARES Faculty Publications

Background: Using information and communication technologies to seek, discuss, and share health-related information influences people’s trust and knowledge of several health practices. However, we know little about the associations between individuals’ information and communication technology use and their perceptions of trust and knowledge of clinical trials. Examining these associations may lead to the identification of target audiences and channels for developing effective educational interventions and campaigns about clinical trials.

Methods: In this study, we analyzed Health Information National Trends Survey data to document perceptions of clinical trial-related knowledge and trust that were recently added as questions in this annual national …

Design Of Kappa Opioid Receptor Agonists For Potential Treatment Of Multiple Sclerosis, Lindsay Kornberger

Theses and Dissertations--Pharmacy

Multiple Sclerosis (MS) is a neurodegenerative disease of the central nervous system characterized by demyelination and neuroinflammation. There is currently no cure for MS. There is a critically unmet need for the development of pharmacotherapies that can induce remyelination promoting both repair and recovery. The kappa opioid receptor (KOR) has been identified as a potential target for the development of remyelinating pharmacotherapies. KOR activation has been shown to promote functional recovery and remyelination preclinically. However, typical KOR agonists like U50,488 have limitations such as sedation and dysphoria limiting their use. This necessitates further development of new KOR agonists that maintain …

Sensitizing Keap1 Loss Non-Small Cell Lung Cancer To Artesunate Anti-Cancer Activity, Keng Hee Peh

Theses and Dissertations--Pharmacy

Lung cancer is the global leading cause of cancer related death. Non-small cell lung cancer (NSCLC) accounts for 80% of lung cancer diagnoses conferring a significant disease burden. However, certain mutations in tumor suppressors such as Kelch-like ECH-associated protein 1 (KEAP1) confers resistance to standard of care therapy in NSCLC. KEAP1 is known to regulate multiple cellular processes such as oxidative stress response and anti-apoptotic pathways. Furthermore, KEAP1 loss of function in NSCLC is associated with poorer clinical outcomes and there are no currently approved therapies for KEAP1 loss NSCLC and represents an unmet clinical need. Artesunate (Art) demonstrated anti-cancer …

Abl1/2 And Ddr1 Cooperate To Stabilize Braf/Craf To Drive Erk1/2 Reactivation And Promote Mek Inhibitor Resistance In Nras-Mutant Melanomas, Anastasia Lyon

Theses and Dissertations--Pharmacology and Nutritional Sciences

This study addresses the escalating incidence of NRAS-mutant melanomas, a type of skin cancer lacking FDA-approved targeted therapies. Despite ongoing research targeting the RAF/MEK/ERK pathway, existing drugs fail to enhance progression-free survival due to acquired resistance. This project identifies a novel role for ABL1/2 and DDR1 kinases in driving drug resistance and proliferation of NRAS-mutant melanoma cells. ABL1/2 and DDR1 cooperate to promote RAF homodimerization and protein stability in order to reactivate MEK/ERK signaling to drive MEK1/2 inhibitor (MEKi) resistance and promote survival of resistant cells. By targeting ABL1/2 and DDR1 with nilotinib, a FDA-approved anti-leukemic inhibitor, we …

Enhancing Translation: A Need To Leverage Complex Preclinical Models Of Addictive Drugs To Accelerate Substance Use Treatment Options, Christa Corley, Ashley Craig, Safiyah M. Sadek, Julie A. Marusich, Samar N. Chehimi, Ashley M. White, Lexi J. Holdiness, Benjamin C. Reiner, Cassandra D. Gipson

Markey Cancer Center Faculty Publications

Preclinical models of addictive drugs have been developed for decades to model aspects of the clinical experience in substance use disorders (SUDs). These include passive exposure as well as volitional intake models across addictive drugs and have been utilized to also measure withdrawal symptomatology and potential neuro- behavioral mechanisms underlying relapse to drug seeking or taking. There are a number of Food and Drug Administration (FDA)-approved medications for SUDs, however, many demonstrate low clinical efficacy as well as potential sex differences, and we also note gaps in the continuum of care for certain aspects of clinical ex- periences in individuals …

Impacts Of Xylazine On Fentanyl Demand, Body Weight, And Acute Withdrawal In Rats: A Comparison To Lofexidine, Safiyah M. Sadek, Shailesh N. Khatri, Zachary A. Kipp, Kelly E. Dunn, Joshua S. Beckmann, William W. Stoops, Terry D. Hinds, Jr., Cassandra D. Gipson

Markey Cancer Center Faculty Publications

The opioid use landscape has recently shifted to include xylazine, a veterinary anesthetic, as an adulterant in the fentanyl supply. The health impacts of xylazine as an emerging fentanyl adulterant has raised alarm regarding xylazine as a public health threat, warranting research on the impacts of xylazine on fentanyl’s behavioral effects. No prior studies have evaluated the effects of xylazine on fentanyl consumption at various unit doses, fentanyl demand, or withdrawal as compared to the Food and Drug Administration-approved opioid withdrawal medication, lofexidine (Lucemyra®). This is important because lofexidine and xylazine are both adrenergic α2a (A2aR) agonists, however, lofexidine is …

Oxycodone Withdrawal Is Associated With Increased Cocaine Self-Administration And Aberrant Accumbens Glutamate Plasticity In Rats, Shailesh N. Khatri, Hanaa Ulangkaya, Erin E. Maher, Safiyah M. Sadek, Mei Hong, Andrea M. Woodcox, William W. Stoops, Cassandra D. Gipson

Markey Cancer Center Faculty Publications

Individuals with opioid use disorder (OUD) frequently use other substances, including cocaine. Opioid with- drawal is associated with increased likelihood of cocaine use, which may represent an attempt to ameliorate opioid withdrawal effects. Clinically, 30% of co-using individuals take opioids and cocaine exclusively in a sequential manner. Preclinical studies evaluating mechanisms of drug use typically study drugs in isolation. However, polysubstance use is a highly prevalent clinical issue and thus, we established a novel preclinical model of sequential oxycodone and cocaine self-administration (SA) whereby rats acquired oxycodone and cocaine SA in an A-B-A-B design. Somatic signs of withdrawal were evaluated …

Synthetic Contraceptive Hormones Occlude The Ability Of Nicotine To Reduce Ethanol Consumption In Ovary-Intact Female Rats, Erin E. Maher, Ashley M. White, Ashley Craig, Shailesh N. Khatri, Percell T. Kendrick Jr., Mary E. Matocha, Emma O. Bondy, Nikhil Pallem, Grace W. Breakfield, Madison Botkins, Olivia Sweatt, William C. Griffin, Brent A. Kaplan, Jessica Jane Weafer, Joshua S. Beckmann, Cassandra D. Gipson

Markey Cancer Center Faculty Publications

Rates of tobacco and alcohol use in women are rising, and women are more vulnerable than men to escalating tobacco and alcohol use. Many women use hormonal birth control, with the oral contraceptive pill being the most prevalent. Oral contraceptives contain both a progestin (synthetic progesterone) and a synthetic estrogen (ethinyl estradiol; EE) and are contraindicated for women over 35 years who smoke. Despite this, no studies have examined how synthetic contraceptive hormones impact this pattern of polysubstance use in females. To address this critical gap in the field, we treated ovary-intact female rats with either sesame oil (vehicle), the …

Adipocyte-Derived Pxr Signaling Is Dispensable For Diet-Induced Obesity And Metabolic Disorders In Mices, Fang Wang, Jinwei Liu, Rebecca Hernandez, Se-Hyung Park, Ying-Jing Lai, Shuxia Wang, Bruce Blumberg, Changcheng Zhou

UK CARES Faculty Publications

Pregnane X receptor (PXR) is a xenobiotic receptor that can be activated by numerous chemicals including endogenous hormones, dietary steroids, pharmaceutical agents, and environmental chemicals. PXR has been established to function as a xenobiotic sensor to coordinately regulate xenobiotic metabolism by regulating the expression of many enzymes and transporters required for xenobiotic metabolism. Recent studies have implicated a potentially important role for PXR in obesity and metabolic disease beyond xenobiotic metabolism, but how PXR action in different tissues or cell types contributes to obesity and metabolic disorders remains elusive. To investigate the role of adipocyte PXR in obesity, we generated …

New Insights On The Differential Interaction Of Sulfiredoxin With Members Of The Peroxiredoxin Family Revealed By Protein-Protein Docking And Experimental Studies, Murli Mishra, Hong Jiang, Qiou Wei

Markey Cancer Center Faculty Publications

Sulfiredoxin (Srx) is the enzyme that restores the peroxidase activity of peroxiredoxins (Prxs) through catalyzing the reduction of hyperoxidized Prxs back to their active forms. This process involves protein-protein interaction in an enzyme-substrate binding manner. The integrity of the Srx-Prx axis contributes to the pathogenesis of various oxidative stress related human disorders including cancer, inflammation, cardiovascular and neurological diseases. The purpose of this study is to understand the structural and molecular biology of the Srx-Prx interaction, which may be of significance for prediction of target site for the novel drug-discovery. Homology modeling and protein-protein docking approaches were applied to examine …

Validation Of Monitoring Septic Thymus Involution In Mice Using Ultrasound., Jianyao Xue, Xiang-An Li

Journal of Pharmacology & Nutritional Sciences

Sepsis is a dangerous condition commonly seen in the intensive care unit (ICU) of hospitals. It causes the thymus, a crucial immune organ, to shrink. This process is known as thymus involution. Although thymus involution is a natural process that occurs as we age, it is accelerated during sepsis. This process is associated with poor outcomes in septic patients, yet it had never been studied using ultrasonography in a septic mouse model. Researchers from the University of Kentucky have validated a non-invasive ultrasound imaging approach to monitor septic thymus involution in a cecum ligation and puncture (CLP) sepsis mouse model. …

The Last Of Us In Therapy: How Mind-Controlling Fungi And Gut Bacteria Affect Your Mental Health, Anastasia Lyon

Journal of Pharmacology & Nutritional Sciences

The "psilocybiome" represents the mutually beneficial relationship between ourselves, our bacteria, and psychedelic drugs. This short review briefly discusses the benefits and limitations surrounding the potential for psychedelic therapy to synergize with gut bacteria to help regulate and maintain proper balance in the immune system, diet, and stress levels. Psychedelic therapy is a novel treatment strategy that has the potential to improve patient mental health, and, by identifying the types of gut bacteria present in patients, it can aid in personalizing medicine by determining how well their "psilocybiome" may respond.

(Pro)Renin Receptor And Its Soluble Form In Metabolic Dysfunction: Friend Or Foe?, Gertrude Arthur

Journal of Pharmacology & Nutritional Sciences

(Pro)renin receptor is component of the renin angiotensin system which has been shown to be involved in several physiological and pathophysiological processes including blood pressure regulation and hypertension, water and electrolyte balance, kidney injury, obesity, and metabolic dysfunction. Enzymatic cleavage of prorenin receptor produces soluble prorenin receptor which can also activate the renin angiotensin system stimulate similar pathophysiological process like its full form receptor. This review explores findings on the role of prorenin receptor and soluble prorenin receptor in metabolic dysfunction and discusses the conflicting findings on soluble prorenin receptor in metabolic dysfunction.

Effect Of Lifestyle-Based Lipid Lowering Interventions On The Relationship Between Circulating Levels Of Per-And Polyfluoroalkyl Substances And Serum Cholesterol, Stephanie Morgan, M. Abdul Mottaleb, Maria P. Kraemer, Debra K. Moser, Jessica Worley, Andrew J. Morris, Michael C. Petriello

UK CARES Faculty Publications

Exposure to certain per-and polyfluoroalkyl substances (PFAS) has been shown to be positively associated with total and/or low-density lipoprotein cholesterol. Examining this association in lipid lowering interventions may provide additional evidence linking PFAS to cardiovascular risk. We examined the relationship of 6 PFAS with cholesterol in a 6-month lifestyle-based intervention. We quantitated PFAS in 350 individuals at baseline and post intervention and examined associations of PFAS with cholesterol before and after intervention. Food frequency questionnaires and GIS analyses were used to investigate PFAS hotspots and possible exposure routes. Cholesterol significantly decreased following intervention and in parallel, PFOS, PFOA, PFHxS, and …

Effects Of Elevated Extracellular Dopamine On Astrocytes In The Nucleus Accumbens, Mengfan Xia

Theses and Dissertations--Pharmacology and Nutritional Sciences

Nucleus accumbens is involved in processing of motivational and affective behaviors and plays a significant role in development and maintenance of substance use. Released from the ventral tegmental area into the nucleus accumbens, the mesolimbic dopamine controls incentive salience and facilitates learning of reinforcement and reward-related motor functions. Recent studies reveal that, in the context of cocaine exposure, dopamine transmission in the ventromedial striatum is pivotal to the regulation of initial drug use. Astrocytes, a major subpopulation of the brain glial cells, are an active component of the so-called tripartite synapse and communicate with neurons through the release of transmitters …

Nutritional & Colorectal Health, Tariq A. Alam, Brittany R. Rice, Sara B. Police

Journal of Pharmacology & Nutritional Sciences

Kentucky has the highest incidence and mortality rate of all site cancers, and Kentuckians residing in the Appalachian region often have worse outcomes, where cancer is a leading cause of death. Focusing on colorectal cancer (CRC) specifically, Kentucky ranks first nationwide for incidence (50 cases per 100,000 people) and fifth for mortality (about 17 deaths per 100,000 people). The Kentucky Colon Cancer Screening Program increased screening rates and reduced mortality since its launch. Yet, CRC remains a leading cause of death for Kentuckians. Risk factors for CRC include increasing age as well as a history of inflammatory bowel disease (IBD) …

Effectiveness Of A Long-Acting Cocaine Hydrolase In Metabolizing Cocaine And Its Physiologically Active Metabolites, Linyue Shang

Theses and Dissertations--Pharmacy

Cocaine is a widely abused, hepatotoxic drug without an FDA-approved pharmacotherapy specific for cocaine addiction or overdose. Cocaine-induced toxicity in animals and humans is due to its multiple physiological effects on the central nervous system, cardiovascular system, etc. The toxicity of cocaine is highly complex, as its metabolites also contribute to the toxicity. Notably, the combination of cocaine and alcohol is common among drug users and can produce additional metabolites. Some of the metabolites are more toxic than cocaine itself. Hence, to develop an ideal therapeutic candidate, the candidate should not only account for cocaine but should also detoxify other …

Age-Associated Increase Of Gamma Delta T Cells In Visceral Adipose Tissue And Mechanisms Of Their Accumulation, Sujata Mukherjee

Theses and Dissertations--Pharmacology and Nutritional Sciences

Chronic systemic inflammation, known as inflammaging is considered a hallmark of aging and associated diseases. While adipose tissue has long been considered only as a caloric reservoir regulating systemic energy homeostasis, research in the past couple of decades substantiate its endocrine function to secrete an array of inflammatory mediators and hormones, which have physiological effects on multiple organ systems, and contribute to inflammaging. Redistribution of adipose tissue from subcutaneous to visceral depots, changes in the immune profile and the chronic inflammatory state are among the major sources of adipose tissue dysfunction with aging.

This dissertation is focused on identifying and …

Chemical Immobilization Of Helicopter-Captured Elk (Cervus Canadensis) And Survival Of Elk Calves In Southeastern Kentucky, Kathleen E. Williams

Theses and Dissertations--Forestry and Natural Resources

Safe and effective chemical immobilization is critical to minimize stress and risk of injury when capturing free-ranging, wild ungulates. Many traditionally favored high potency opioids have been phased out or become unavailable because of increased regulations, leading to the development of two pre-mixed combination drugs, butorphanol-azaperone-medetomidine (BAM) and nalbuphine-medetomidine-azaperone (NalMed-A). Both drugs have been used to chemically immobilize ungulates, but their efficacy has not been documented in elk captured and transported via helicopter. During 2020 – 2022, we chemically immobilized helicopter-captured female elk (Cervus canadensis) with a single IM-injection of BAM (n = 41) or NalMed-A (n = …

Xylazine Suppresses Fentanyl Consumption During Self-Administration And Induces A Unique Sex-Specific Withdrawal Syndrome That Is Not Altered By Naloxone In Rats, Shailesh N. Khatri, Safiyah M. Sadek, Percell T. Kendrick, Emma O. Bondy, Mei Hong, Sally Pauss, Dan Luo, Thomas E. Prisinzano, Kelly E. Dunn, Julie A. Marusich, Joshua S. Beckmann, Terry D. Hinds Jr., Cassandra D. Gipson

Markey Cancer Center Faculty Publications

Prescription and illicit opioid use are a public health crisis, with the landscape shifting to fentanyl use. Since fentanyl is 100-fold more potent than morphine, its use is associated with a higher risk of fatal overdose that can be remediated through naloxone (Narcan) administration. However, recent reports indicate that xylazine, an anesthetic, is increasingly detected in accidental fentanyl overdose deaths. Anecdotal reports suggest that xylazine may prolong the fentanyl “high,” alter the onset of fentanyl withdrawal, and increase resistance to naloxone-induced reversal of overdose. To date, no preclinical studies have evaluated the impacts of xylazine on fentanyl self-administration (SA; 2.5 …