Opioid exposure is known to cause transcriptomic changes in the nucleus accumbens (NAc). However, no studies to date have investigated cell type-specific transcriptomic changes associated with volitional opioid taking. Here, we use single nucleus RNA sequencing (snRNAseq) to comprehensively characterize cell type-specific alterations of the NAc transcriptome in rats self-administering morphine. One cohort of male Brown Norway rats was injected with acute morphine (10 mg/kg, i.p.) or saline. A second cohort of rats was allowed to self-administer intravenous morphine (1.0 mg/kg/infusion) for 10 consecutive days. Each morphine-experienced rat was paired with a yoked saline control rat. snRNAseq libraries were generated from NAc punches and used to identify cell type-specific gene expression changes associated with volitional morphine taking. We identified 1106 differentially expressed genes (DEGs) in the acute morphine group, compared to 2453 DEGs in the morphine self-administration group, across 27 distinct cell clusters. Importantly, we identified 1329 DEGs that were specific to morphine self-administration. DEGs were identified in novel clusters of astrocytes, oligodendrocytes, and D1R- and D2R-expressing medium spiny neurons in the NAc. Cell type-specific DEGs included Rgs9, Celf5, Oprm1, and Pde10a. Upregulation of Rgs9 and Celf5 in D2R-expressing neurons was validated by RNAscope. Approximately 85% of all oligodendrocyte DEGs, nearly all of which were associated with morphine taking, were identified in two subtypes. Bioinformatic analyses identified cell type-specific upstream regulatory mechanisms of the observed transcriptome alterations and downstream signaling pathways, including both novel and previously identified molecular pathways. These findings show that volitional morphine taking is associated with distinct cell type-specific transcriptomic changes in the rat NAc and highlight specific striatal cell populations and novel molecular substrates that could be targeted to reduce compulsive opioid taking.

The University of Pennsylvania Summer Undergraduate Internship Program (SUIP) is a 10-week intensive research opportunity for visiting undergraduate students. This summer, the Schmidt Lab was fortunate to welcome Camille Carthy, Lafayette College Class of 2023, as a SUIP intern.  During her short time in the lab, Camille contributed to various complex behavioral projects that furthered the labs understanding of the role of amygdalar GLP-1R signaling in the reinstatement of cocaine seeking during withdrawal. Most notably, Camille used her previous research experiences to aid in the lab’s exploration of cocaine administration and GLP-1R activation on amygdala neural dynamics using in vivo calcium imaging techniques. In addition to all her hard work in the lab, as a SUIP intern Camille also participated in weekly seminars, professional development workshops, and had the opportunity to present her summer research at both the SUIP Symposium and the Leadership Alliance National Symposium in Hartford, CT.

The Schmidt Lab thanks Camille for a great summer and wishes her the best of luck during her senior year at Lafayette where she is expected to graduate with a BS in Neuroscience next spring!!

Congratulations to Amanda Moreno (B.A.), Riley Merkel (B.A.), Kamryn Stecyk (B.S.), and Suditi Rahematpura (B.S.) (pictured left to right) on their recent graduation from the University of Pennsylvania and the Schmidt Lab as a part of the Undergraduate Class of 2021!

The four graduates have been invaluable members of the Schmidt Lab team during their time as students at Penn. All have been awarded grants, fellowships, and/or awards for their research endeavors over the years. Most recently, and mentored by Dr. Schmidt, Moreno and Merkel successfully defended their senior honors theses at the Annual Neuroscience Research Symposium. This feat landed both Moreno and Merkel Neuroscience degrees with Honors Distinction at graduation and Moreno with the 2021 Elliot Stellar Award for best research talk.

Despite their shared learning experiences in the Schmidt lab, the young women have all forged their own unique paths for the future. This coming year Moreno will be serve as co-President and Director of Be Body Positive Philly, a nonprofit organization she co-founded dedicated to decreased eating disorder risk in marginalized youth. Moreno is expected to attend medical starting in the fall of 2022 and hopes to one day be a pediatrician working at the intersection of clinical care and public health. Stecyk plans to spend time interning at New England Aquarium and Small Animals Clinic and will attend veterinary school in the near future. Rahematpura will be working as a Hepatology Clinical Research Assistant in the Perelman School of Medicine conducting various clinical studies for patients with liver disease, many of whom struggle with opioid use disorder. Rahematpura aspires to take her knowledge from Schmidt Lab into the clinical world as an Emergency Medicine Physician to serve and discover new solutions for those who suffer from substance use disorders. Merkel, on the other hand, will be staying in Schmidt Lab as a Neuroscience Research Specialist.

For Carpenter’s high school capstone project, she had the opportunity to observe and shadow Dr. Schmidt and other members of the Schmidt lab team. Carpenter’s project involved researching an “essential question” for possible answers and solutions. Her question was, “how do substance use disorder in animals change due to the environment and social interactions that these animals have?” Through her research, Carpenter was able to learn more about a field that she is very interested in pursuing and used the words “intriguing” and “inspiring” to describe her experience shadowing the Schmidt Lab.

“I hope to take the experiences and knowledge I have acquired from the Schmidt Lab with me as I continue on to my future endeavors and career path,” says Carpenter.

Carpenter will be attending the University of Pittsburgh this fall with the intentions to study neuroscience. We wish her the best of luck in Pittsburgh and a huge congratulations on the completion of a fantastic project in the lab!

There has been a dramatic increase in illicit fentanyl use in the United States over the last decade. In 2018, more than 31,000 overdose deaths involved fentanyl or fentanyl analogs, highlighting an urgent need to identify effective treatments for fentanyl use disorder. An emerging literature shows that glucagon-like peptide-1 receptor (GLP-1R) agonists attenuate the reinforcing efficacy of drugs of abuse. However, the effects of GLP-1R agonists on fentanyl-mediated behaviors are unknown. The first goal of this study was to determine if the GLP-1R agonist exendin-4 reduced fentanyl self-administration and the reinstatement of fentanyl-seeking behavior, an animal model of relapse, in rats. We found that systemic exendin-4 attenuated fentanyl taking and seeking at doses that also produced malaise-like effects in rats. To overcome these adverse effects and enhance the clinical potential of GLP-1R agonists, we recently developed a novel dual agonist of GLP-1Rs and neuropeptide Y2 receptors (Y2Rs), GEP44, that does not produced nausea-like behavior in drug-naïve rats or emesis in drug-naïve shrews. The second goal of this study was to determine if GEP44 reduced fentanyl self-administration and reinstatement with fewer adverse effects compared to exendin-4 alone. In contrast to exendin-4, GEP44 attenuated opioid taking and seeking at a dose that did not suppress food intake or produce adverse malaise-like effects in fentanyl-experienced rats. Taken together, these findings indicate a novel role for GLP-1Rs and Y2Rs in fentanyl reinforcement and highlight a potential new therapeutic approach to treating opioid use disorders.

Dr. Schmidt is currently an Associate Professor in the Department of Biobehavioral Health Science and holds a secondary appointment in the Department of Psychiatry, Perelman School of Medicine. His area of inquiry and teaching have added tremendous value to the School of Nursing’s research and teaching missions. Given the enormous effects of smoking and obesity on chronic illness and the devastating impact of substance use disorders, his work addresses some of the most pressing and intractable health issues today. Dr. Schmidt has shown leadership in developing undergraduate curricula in this area of expertise and demonstrated excellence in teaching. For example, he co-developed with Peggy Compton , PHD, RN, FAAN an undergraduate course on opioids, opioid use disorders and pain, and a second course on the pharmacology of performance-enhancing drugs that is of interest to students enrolled in all four undergraduate schools at Penn! He has directly supervised 19 undergraduate researchers at Penn who have all gone on to matriculate in top-tier graduate programs and are authors on empirical publications in high-impact journals and conference abstracts.  It is clear – Dr. Schmidt not only educates but also inspires our undergraduate students.

The appointment is effective July 1, 2021. Congrats to a wonderful PI!

Amanda Moreno ’21 has been named a University Scholar by the Center for Undergraduate Research and Fellowships (CURF).

Riley Merkel ’21 has been awarded the BBB Summer 2020 Fellowship for Neuroscience Research based on her proposal “A Paradoxical Role of Amygdalar GLP-1 Signaling in Drug-Seeking Behavior.”

Jennifer Ben Nathan ’22 has been awarded a research position through Penn Undergraduate Research Mentoring Program (PURM) and will join the lab in summer 2020.

Congrats to all our undergraduate researchers and thank you for your commitment and contributions to our work!

Schmidt Lab alumni Christopher Turner, Jordan Wolfheimer, and Dr. Nicole Hernandez, in collaboration with Drs. De Luca and Madsen of the University of Copenhagen, recently published a paper in Neuropharmacology . Find the abstract below:

Protein interacting with C kinase-1 (PICK1) regulates intra-cellular trafficking of GluA2-containing AMPA receptors, a process known to play a critical role in cocaine-seeking behavior. This suggests that PICK1 may represent a molecular target for developing novel pharmacotherapies to treat cocaine craving-induced relapse. Emerging evidence indicates that inhibition of PICK1 attenuates the reinstatement of cocaine-seeking behavior, an animal model of relapse. Here, we show that systemic administration of TAT-P₄-(DATC5)₂, a novel high-affinity peptide inhibitor of the PICK1 PDZ domain, dose-dependently attenuated the reinstatement of cocaine seeking in rats at doses that did not produce operant learning deficits or suppress locomotor activity. We also show that systemic TAT-P₄-(DATC5)₂ penetrated the brain where it was visualized in the nucleus accumbens shell. Consistent with these effects, infusions of TAT-P₄-(DATC5)₂ directly into the accumbens shell reduced cocaine, but not sucrose, seeking. The effects of TAT-P₄-(DATC5)₂ on cocaine seeking are likely due, in part, to inhibition of PICK1 in medium spiny neurons (MSNs) of the accumbens shell as TAT-P₄-(DATC5)₂ was shown to accumulate in striatal neurons and bind PICK1. Taken together, these findings highlight a novel role for PICK1 in the reinstatement of cocaine seeking and support future studies examining the efficacy of peptide inhibitors of PICK1 in animal and human models of cocaine relapse.

Congratulations!

Find the abstract below:

Despite the effectiveness of current medications to treat opioid use disorder, there is still a high rate of relapse following detoxification. Thus, there is critical need for innovative studies aimed at identifying novel neurobiological mechanisms that could be targeted to treat opioid use disorder. A growing body of preclinical evidence indicates that glucagon-like peptide-1 (GLP-1) receptor agonists reduce drug reinforcement. However, the efficacy of GLP-1 receptor agonists in attenuating opioid-mediated behaviors has not been thoroughly investigated. Using recently established models of opioid-taking and -seeking behaviors, we showed that systemic administration of the GLP-1 receptor agonist exendin-4 reduced oxycodone self-administration and the reinstatement of oxycodone-seeking behavior in rats. We also identified behaviorally selective doses of exendin-4 that reduced opioid-taking and -seeking behaviors and did not produce adverse feeding effects in oxycodone-experienced rats. To identify a central site of action, we showed that systemic exendin-4 penetrated the brain and bound putative GLP-1 receptors on dopamine D1 receptor- and dopamine D2 receptor-expressing medium spiny neurons in the nucleus accumbens shell. Consistent with our systemic studies, infusions of exendin-4 directly into the accumbens shell attenuated oxycodone self-administration and the reinstatement of oxycodone-seeking behavior without affecting ad libitum food intake. Finally, exendin-4 did not alter the analgesic effects of oxycodone, suggesting that activation of GLP-1 receptors attenuated opioid reinforcement without reducing the thermal antinociceptive effects of oxycodone. Taken together, these findings suggest that GLP-1 receptors could serve as potential molecular targets for pharmacotherapies aimed at reducing opioid use disorder.

The University of Pennsylvania School of Nursing also highlighted our research on opioids and satiety factors in a news article . Find the full paper in Neuropsychopharmacology published here.