Role of Projections between Piriform Cortex and Orbitofrontal Cortex in Relapse to Fentanyl Seeking after Palatable Food Choice-Induced Voluntary Abstinence

Abstract

We recently developed a rat model of relapse to drug seeking after food choice-induced voluntary abstinence. Here, we used this model to study the role of the orbitofrontal cortex (OFC) and its afferent projections in relapse to fentanyl seeking. We trained male and female rats to self-administer palatable food pellets for 6 d (6 h/d) and intravenous fentanyl (2.5 g/kg/infusion) for 12 d (6 h/d). We assessed relapse to fentanyl seeking after 13-14 voluntary abstinence days, achieved through a discrete choice procedure between fentanyl infusions and palatable food (20 trials/d). In both sexes, relapse after food choice-induced abstinence was associated with increased expression of the activity marker Fos in the OFC. Pharmacological inactivation of the OFC with muscimol plus baclofen (50 ϩ 50 ng/side) decreased relapse to fentanyl seeking. We then determined projection-specific activation of OFC afferents during the relapse test by using Fos plus the retrograde tracer cholera toxin B (injected into the OFC). Relapse to fentanyl seeking was associated with increased Fos expression in the piriform cortex (Pir) neurons projecting to the OFC, but not in projections from the basolateral amygdala and thalamus. Pharmacological inactivation of the Pir with muscimol plus baclofen decreased relapse to fentanyl seeking after voluntary abstinence. Next, we used an anatomical disconnection procedure to determine whether projections between the Pir and OFC are critical for relapse to fentanyl seeking. Unilateral muscimol plus baclofen injections into the Pir in one hemisphere plus unilateral muscimol plus baclofen injections into the OFC in the contralateral, but not ipsilateral, hemisphere decreased relapse. Our results identify Pir-OFC projections as a new motivation-related pathway critical to relapse to opioid seeking after voluntary abstinence.

Role of BNST CRFR1 Receptors in Incubation of Fentanyl Seeking

“…In addition, we used only male rats in this study which is an important limitation as it has been shown that a subpopulation of females is more sensitive to CRF-induced reinstatement of cocaine seeking compared to males ( Buffalari et al, 2012 ). While there is limited evidence for sex differences in incubation of fentanyl seeking ( Reiner et al, 2020 ), evidence for BNST-mediated sex differences in opioid withdrawal ( Luster et al, 2020 ) encourage future studies investigating sex differences in BNST CRFR1 action. We used a single dose of R121919 (1 μg/hemisphere) based on a prior study ( Pomrenze et al, 2019 ) to test the role of BNST CRFR1 receptors in fentanyl craving.…”

A buprenorphine-validated rat model of opioid use disorder optimized to study sex differences in vulnerability to relapse

“…They are also consistent with previous preclinical findings showing that females self-administer more heroin and oxycodone under extended access conditions than males (Carroll et al 2002 ; Towers et al 2019 ; Kimbrough et al 2020 ) and with previous findings with other drugs of abuse showing that females have higher levels of drug-seeking than males following extended access self-administration and abstinence (Lynch 2018 ). Our current findings showing that sex differences were apparent in some conditions, but not others, may also explain some discrepancies in the occurrence of sex differences under extended access conditions (e.g., Carroll et al 2002 ; Towers et al 2019 ; Kimbrough et al 2020 ; Reiner et al 2020 ; Fredriksson et al 2020 ; Venniro et al 2017 , 2019 ) since differences are likely to depend on both the training and extended access conditions. As with the current findings, these previous reports of sex differences in drug-seeking have typically revealed effects during extinction, but not following exposure to drug-associated cues (Lynch 2018 ).…”

“…Similar effects may also occur with opioids considering findings showing that female rats and mice given extended access (≥ 6 h/day) to heroin or oxycodone self-administer more drug and/or show greater escalation of intake over time than their male counterparts (Carroll et al 2002 ; Towers et al 2019 ; Kimbrough et al 2020 ). However, sex differences with opioids may be less robust than with other drugs given that several other studies have reported no differences between males and females in levels or patterns of drug intake under extended access conditions (Venniro et al 2017 , 2019 ; Reiner et al 2020 ) or for subsequent levels of drug-seeking following voluntary (Reiner et al 2020 ) or forced abstinence (Venniro et al 2019 ). One the other hand, it is possible that sex differences were obscured in these latter studies given that intake was restricted in each of these studies to either 12 (Reiner et al 2020 ) or 15 infusions/h (Fredriksson et al 2020 ; Venniro et al 2017 , 2019 ).…”

“…However, sex differences with opioids may be less robust than with other drugs given that several other studies have reported no differences between males and females in levels or patterns of drug intake under extended access conditions (Venniro et al 2017 , 2019 ; Reiner et al 2020 ) or for subsequent levels of drug-seeking following voluntary (Reiner et al 2020 ) or forced abstinence (Venniro et al 2019 ). One the other hand, it is possible that sex differences were obscured in these latter studies given that intake was restricted in each of these studies to either 12 (Reiner et al 2020 ) or 15 infusions/h (Fredriksson et al 2020 ; Venniro et al 2017 , 2019 ). These latter studies also included choice testing between heroin/fentanyl and a non-drug reward within the extended access training period which may have impacted the occurrence of sex differences as well as the development of an addiction-like phenotype.…”

“…These latter studies also included choice testing between heroin/fentanyl and a non-drug reward within the extended access training period which may have impacted the occurrence of sex differences as well as the development of an addiction-like phenotype. Indeed, the main findings from three of these studies was that, like contingency management in humans, the availability of a non-drug reward (palatable food or social interaction) could be used to maintain voluntary abstinence and reduce/prevent the development of incubated drug-craving (Reiner et al 2020 ; Venniro et al 2017 , 2019 ). This interpretation is also consistent with their findings showing that both males and females showed a high preference for the non-drug versus drug reward even when tested following protracted abstinence (Reiner et al 2020 ; Venniro et al 2017 , 2019 ).…”