Opioid use disorder is a chronic, relapsing disease, with more than 85% of individuals experiencing a relapse episode within one year. One common reason patients relapse is due to intense cravings, which are defined as the compulsive urge to use the drug. In fact, craving was recently added to the DSM criteria for substance use disorder diagnosis. Counterintuitively, cravings intensify over the course of extended abstinence, especially in response to drug-paired cues, a phenomenon known as “incubation of craving”. This contributes to difficulty in maintaining long-term sobriety. The mesocorticolimbic reward pathway facilitates self-administration and cue-induced incubation of craving for drugs of abuse and natural rewards, such as sucrose. In particular, the shell sub-region of the nucleus accumbens is a critical brain region involved in context/cue-mediated reward seeking. In the experiments described here, we utilized an incubation of craving model, in which male and female rats self-administered opioids (morphine or heroin) or sucrose for 10 days. Sucrose served as an important control for delineating drug-induced changes from those caused in response to natural rewards, which are not the intended target of potential treatments. Reward delivery was paired with a cue light that was later used to elicit craving. After self-administration, rats underwent brief (one day) or extended (30 days) forced abstinence. One or 30 days later, they were returned to the chambers for a “cue test”, in which responses on the previously reward-associated lever triggered cue presentation, but no contingent reward. We used this model to further delineate behavioral and affective changes that accompany increased opioid craving in late abstinence, as well as molecular alterations underlying craving in rats that did not undergo a cue test. We found an opioid-specific behavioral signature in which peak opioid craving is accompanied by decreased grooming and hyperactivity in both sexes. We tracked the female estrous cycle throughout, as these fluctuations in reproductive hormones (akin to the menstrual cycle) are shown to affect cocaine- and nicotine-related behaviors. We found no differences between females in different phases of the estrous cycle in terms of self-administration, nor craving. RNA sequencing of the nucleus accumbens shell revealed robust changes in gene expression that occurred across extended abstinence, though the genes themselves were altered in a sex- and reinforcer-specific manner. In general, we found many behavioral and molecular changes that were unique to sex and reinforcer (sucrose versus opioids). This is promising in terms of identifying opioid-specific targets that are unlikely to affect the natural reward system in both sexes. Changes in gene expression in the brain are mediated in part by epigenetic processes that influence access of transcriptional machinery to DNA. Acetylation of histone tails, the proteins around which DNA is wrapped and packaged in the nucleus, have been identified as permissive marks that facilitate long-lasting changes in transcriptomics in response to environmental insults. Opioids promote increased acetylation, which may contribute to some of the reported changes here. We tested the efficacy of JQ1, a treatment that interferes with the read-out of opioid-induced acetylated marks, at attenuating heroin self-administration. When administered as an intracerebroventricular microinjection on self-administration day 11, JQ1 had no effect on subsequent heroin taking in either sex, suggesting that it may not be suitable as a systemic treatment at the dose given. These studies lay the groundwork for future studies to administer other treatments throughout abstinence, based on the opioid-specific genes and pathways identified here, to reduce cue-induced heroin craving and the accompanying suite of behaviors in males and females. / Psychology
| Identifer | oai:union.ndltd.org:TEMPLE/oai:scholarshare.temple.edu:20.500.12613/7782 |
| Date | January 2022 |
| Creators | Mayberry, Hannah Louise |
| Contributors | Wimmer, Mathieu, Bangasser, Debra A., Murty, Vishnu, Briand, Lisa A., Parikh, Vinay, Loweth, Jessica |
| Publisher | Temple University. Libraries |
| Source Sets | Temple University |
| Language | English |
| Detected Language | English |
| Type | Thesis/Dissertation, Text |
| Format | 142 pages |
| Rights | IN COPYRIGHT- This Rights Statement can be used for an Item that is in copyright. Using this statement implies that the organization making this Item available has determined that the Item is in copyright and either is the rights-holder, has obtained permission from the rights-holder(s) to make their Work(s) available, or makes the Item available under an exception or limitation to copyright (including Fair Use) that entitles it to make the Item available., http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | http://dx.doi.org/10.34944/dspace/7754, Theses and Dissertations |
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