Department of Psychological Science

Title: Female Sprague Dawley Rats Show Enhanced Oral Self-Administration of Fentanyl

Authors: Joesph Gilbert, Taylor Trejo, Finn Wise, and Justin R. Yates, Ph.D.

Department: Psychological Science

Abstract: Fentanyl is a synthetic opioid substance that was developed in 1960 as an analgesic for heart surgery. However, fentanyl use rates have significantly increased over the last decade, with a spike in fentanyl-related overdose deaths during the COVID-19 pandemic. Because fentanyl is now often pressed into counterfeit pills, the present experiment was conducted with rats to test oral self-administration of fentanyl. In total, 27 Sprague Dawley rats (12 males, 15 females) were given access to fentanyl citrate (25 ug/ml) during 60-minute sessions. In contrast to our previous work, rats were trained to self-administer fentanyl under a variable interval 10-sec (VI-10) schedule of reinforcement. Female rats self-administered fentanyl at significantly higher rates than male rats. Female rats also self-administered more saccharin when tested on a VI-10 schedule of reinforcement, suggesting a general increased sensitivity to rewards in females relative to males.

Title: Modulation of Effort-Based Decision Making by Muscarinic Receptors

Authors: Kaitlyn Strange, Ana Rey Caldera, Christina Gogzheyen, Paityn Barrett, Tyler Downnen

Department: Psychological Science

Abstract: Effort-based decision making (EBDM) refers to choosing to expend cognitive or physical energy to satisfy needs and desires. The neurotransmitter, acetylcholine, may contribute to the biological basis of EBDM. This study investigated the influence of partial agonists and antagonists at muscarinic receptors for acetylcholine on EBDM. Sixteen rats received injections of saline or the partial agonist, xanomeline, and were tested for EBDM using a concurrent-choice task, where they could choose to exert effort to press a lever to receive a high-carb sugar pellet or eat freely available chow. Xanomeline decreased bar pressing and increased chow consumption, suggesting that it decreases EBDM. A second experiment determined if xanomeline could reduce the effects of scopolamine, a full antagonist of muscarinic receptors, on EBDM. Scopolamine decreased the latency to press the bar, and reduced overall bar pressing and chow consumption, suggesting a sedative effect. Xanomeline did not significantly alter these responses to scopolamine.