Chronic inflammatory pain reduces fentanyl intake during early acquisition of fentanyl self-administration, but does not change motivation to take fentanyl in male and female rats.

The co-occurrence of chronic pain and opioid misuse has led to numerous preclinical investigations of pain-opioid interactions to examine how pain manipulations alter the reinforcing properties of opioids. However, preclinical investigations of chronic pain effects on opioid drug self-administration have produced inconsistent results. Our previous work demonstrated that established fentanyl self-administration is resistant to change by induction of chronic inflammatory pain (Complete Freund's Adjuvant; CFA) in male and female rats, while other laboratories have shown that CFA increased fentanyl self-administration in male but not female rats when pain induction precedes self-administration, which may be a critical factor in determining the effects of chronic pain on self-administration. The present study was designed similarly to Higginbotham et al. (2022) to test the effects of CFA on fentanyl self-administration in rats that underwent pain prior to acquisition of fentanyl self-administration. Male and female rats treated with hindpaw CFA or saline were trained to intravenously self-administer (IVSA) fentanyl for 3 weeks under limited access to fentanyl (2 h per day) conditions. After 3 weeks of fentanyl IVSA acquisition, we tested motivation to take fentanyl using progressive ratio testing and dose-response testing. CFA male and female rats self-administered less fentanyl than saline-treated controls during week 1 of acquisition, but not during weeks 2-3 of acquisition. Intra-session analysis of week 1 data demonstrated that chronic inflammatory pain suppressed fentanyl intake towards the end of week 1 and at the end of each operant session. We also report no effects of chronic inflammatory pain on motivation to take fentanyl. We discuss potential methodological explanations for differences between these results and prior reports. Our findings demonstrate that CFA temporarily suppresses fentanyl IVSA in animals without changing motivation to take fentanyl or promoting escalation of opioid use, suggesting that chronic inflammatory pain is unlikely to promote long-term risk of opioid misuse.

Systematic literature review of asthma biologic self-administration enhanced by a patient perspective.

Background: Several biologics for the treatment of severe asthma are available as self-administration devices. Objective: We performed a systematic literature review to understand the use, benefits, and challenges of these self-administration devices. Methods: Electronic databases and conference proceedings were searched using terms for asthma, biologic treatment, and at-home/self-administration (GSK study 213094). Publications were scanned for relevance using prespecified Population, Intervention, Comparison, Outcomes, Study Design (PICOS) criteria. Data on efficacy, safety, patient experience, and economic outcomes were extracted; study quality was assessed. A firsthand patient perspective was obtained. Results: Thirty-five of 504 records met the inclusion criteria. Across four phase 3 studies, ≥95% of biologic self-administrations were successful on the basis of predefined criteria. At-home self-administration was preferred over in-clinic administration by 43-96% of patients across 5 studies. Most patients (≥89%) in two phase 3 studies reported completing self-administration easily without repeated reference to instructions; high proportions of patients (≥98%) were confident in their ability to self-administer their biologic, and ≥96% rated it as extremely, very or moderately easy to self-administer. Across 16 studies reporting efficacy data, there was evidence of reduced blood eosinophil counts and improved asthma control with biologic self-administration, with improved health-related quality of life shown across 6 studies. Economic outcomes data were limited. From a patient perspective, autonomy is the major benefit of self-administration. Conclusion: Although more evidence is needed, this systematic literature review provides consistent evidence of high injection success rates and, supported by a patient perspective, preference for self-administration of biologics among patients with severe asthma.

Sex differences in nicotine intake and relapse behavior in nicotine-dependent adult wistar rats.

Introduction: Tobacco use is highly addictive and the leading cause of premature mortality in the world. Long-access nicotine self-administration procedures in rats closely model human smoking behavior. However, significant gaps remain in our understanding of sex differences in the development of dependence and relapse in adult rats. Methods: In the present study, we investigated operant responding for both nicotine and saline and the development of dependence in adult rats of both sexes. The rats had daily access to nicotine or saline for 6 h per day, 7 days per week. Dependence was assessed by evaluating precipitated and spontaneous somatic withdrawal signs, measuring locomotor activity in the small open field test, and assessing anxiety-like behavior in the large open field and elevated plus maze test. The sucrose preference test was used to determine if cessation of nicotine intake leads to anhedonia. It was also investigated if a period of forced abstinence affects nicotine-seeking behavior. Results: This study showed that nicotine intake is higher in females than in males when given daily long access to nicotine. Daily nicotine self-administration led to more precipitated and spontaneous somatic withdrawal signs compared to saline self-administration, with no sex differences observed. In addition, cessation of nicotine intake led to a similar increase in activity in both males and females in the small open field test. However, cessation of nicotine intake did not increase anxiety-like behavior or cause anhedonia in either males or females. A time course analysis revealed that the nicotinic acetylcholine receptor antagonist mecamylamine affected nicotine intake differently in males and females, increasing intake in males and decreasing intake in females. Three weeks of forced abstinence led to an increase in nicotine and saline-seeking behavior. The rats exhibited more nicotine than saline seeking, and the females displayed more nicotine seeking than the males. Discussion: The present findings demonstrate that females self-administer more nicotine and display more nicotine-seeking behavior than males. Furthermore, there were no sex differences in somatic withdrawal signs or activity during abstinence from nicotine. This work underscores the importance of considering sex differences across various aspects of addiction, including intake and relapse, when developing novel treatments for tobacco use disorder.

Orbitofrontal cortex to dorsal striatum circuit is critical for incubation of oxycodone craving after forced abstinence.

Relapse is a major challenge in treating opioid addiction, including oxycodone. During abstinence, oxycodone seeking progressively increases, a phenomenon termed incubation of oxycodone craving. We previously demonstrated a causal role of orbitofrontal cortex (OFC) in this incubation. Here, we studied the interaction between glutamatergic projections from OFC and dopamine 1-family receptor (D1R) signaling in dorsal striatum (DS) in this incubation in male rats. We first examined the causal role of D1R signalling in DS in incubated oxycodone seeking. Next, we combined fluorescence-conjugated cholera toxin subunit B (CTb-555, a retrograde tracer) with Fos (a neuronal activity marker) to assess whether the activation of OFC→DS projections was associated with incubated oxycodone seeking. We then used a pharmacological asymmetrical disconnection procedure to examine the role of the interaction between projections from OFC and D1R signalling in DS in incubated oxycodone seeking. We also tested the effect of unilateral pharmacological inactivation of OFC or unilateral D1R blockade of DS on incubated oxycodone seeking. Finally, we assessed whether contralateral disconnection of OFC→DS projections impacted non-incubated oxycodone seeking on abstinence day 1. We found that D1R blockade in DS decreased incubated oxycodone seeking and OFC→DS projections were activated during incubated oxycodone seeking. Moreover, anatomical disconnection of OFC→DS projections, but not unilateral inactivation of OFC or unilateral D1R blockade in DS, decreased incubated oxycodone seeking. Lastly, contralateral disconnection of OFC→DS projections had no effect on oxycodone seeking on abstinence day 1. Together, these results demonstrated a causal role of OFC→DS projections in incubation of oxycodone craving.

Validation of drug-nondrug choice procedure to model maladaptive behavioural allocation to opioid use in rats.

Increased allocation of behaviour to substance abuse at the expense of personal and social rewards is a hallmark of addiction that is reflected in several of DSM-5 criteria for diagnosis of substance use disorder. Previous studies focused on refining the self-administration (SA) model to better emulate an addictive state in laboratory animals. Here, we employed concurrent SA of sucrose pellets and morphine as two competing natural and drug rewards, respectively, to validate the feasibility of capturing pathological behavioural allocation in rats. A custom-made three-lever operant chamber was used. With one active and one inactive lever presented, rats were trained to self-administer morphine (0.5 mg/kg/infusion; 2 h/day) under a fixed-ratio 1 (FR-1) schedule until a stable response was achieved. Next, they were trained to self-administer morphine in the presence of a third lever dispensing sucrose pellets (20 mg) under FR-1. Concurrent morphine-sucrose SA sessions (2 h/day) were continued until stable morphine taking behaviour was re-established. In another experiment, rats first established stable sucrose pellet SA (2 h/day, FR-1) and then were trained to take morphine (0.5 mg/kg/infusion; 2 h/day). Subsequently, all rats underwent extinction training, in which morphine was replaced with saline while sucrose pellets were still available upon lever pressing, followed by cue-induced reinstatement of morphine seeking behaviour. Results showed that rats retained morphine SA when sucrose pellets were also available, but they showed binge-like sucrose intake when morphine was removed during the extinction sessions. However, morphine SA did not develop in rats that had previously established sucrose pellet SA. In conclusion, morphine SA developed even in the presence of a potent competing nondrug reward in rats. Adding an effort-based contingent delivery of a natural reward to the standard SA model, this protocol may provide an improved model of drug addiction in laboratory animals.

Consumption of oxycodone prevents oxytocin from attenuating alcohol intake in rats.

Alcohol and opioid polysubstance use (PSU) is common and often accompanied by higher trait anxiety. Oxytocin decreases anxiety, alcohol- and opioid-seeking and -taking but has not been assessed in the context of PSU. Here we developed a rat model of sequential oxycodone and alcohol PSU to examine the relationship between anxiety, alcohol and oxycodone intake, and the efficacy of systemic oxytocin to attenuate alcohol intake. Male and female Sprague-Dawley rats were assessed for baseline anxiety-like behavior using acoustic startle and the elevated plus maze (EPM). Rats were then given 2-bottle choice access to oxycodone and/or water for 6-hr/day for 7 days, followed by 2-bottle choice access to alcohol (20% v/v) and/or water for five 24-hr sessions across 10 days. Next, monosubstance (oxycodone- or alcohol-alone) rats continued to have access to only one substance/day while PSU rats had access to oxycodone and water for 3-hr, followed by alcohol and water for 6-hr. After 12 days, rats were tested in the EPM 20 hours after alcohol access to examine withdrawal-related anxiety. Next, oxytocin (0, 0.3 or 1.0 mg/kg IP) was administered following the oxycodone/water session, 30 minutes prior to alcohol access. Rats received intragastric oxycodone (2 mg/kg) or water followed by intragastric alcohol (2 g/kg) and blood was collected to determine blood alcohol levels. Elevated baseline anxiety-like behavior was accompanied by reduced alcohol intake. Consumption of oxycodone did not alter alcohol intake but resulted in less anxiety-like behavior during withdrawal and prevented oxytocin from attenuating alcohol intake. Oxytocin (1 mg/kg) reduced alcohol intake in the alcohol-only condition, an effect that persisted for days after a single oxytocin administration. Rats that received oxycodone prior to non-contingent alcohol displayed higher blood alcohol levels than those that did not. These results support the necessity for the testing of medications for substance use in rodent models of PSU.

PKMζ alters oxycodone-taking in a dose- and sex-dependent manner.

Opioid use disorder involves disruptions to glutamate homeostasis and dendritic spine density in the reward system. PKMζ is an atypical isoform of protein kinase C that is expressed exclusively in neurons and plays a role in postsynaptic glutamate signaling and dendritic spine maturation. As opioid use leads to alterations in glutamate transmission and dendritic spine density, we hypothesized that PKMζ deletion would alter opioid-taking behaviors. The current study examined two doses of oxycodone self-administration in male and female mice with constitutive deletion of PKMζ compared to wildtype controls. At a dose of 0.25 mg/kg/infusion, PKMζ deletion significantly potentiated oxycodone self-administration in both male and female mice. However, increases in motivation for oxycodone, as indicated by increased breakpoint on a progressive ratio schedule, were only seen in male PKMζ knockout mice and not females. When we examined a lower dose of oxycodone, 0.125 mg/kg/infusion, PKMζ knockout led to increases in oxycodone self-administration only in female mice. Additionally, female PKMζ knockout mice exhibited higher breakpoints on a progressive ratio schedule at this dose compared to all other groups. In addition to the self-administration studies, we also examined locomotor sensitization in response to experimenter administered oxycodone. PKMζ KO decreased oxycodone induced locomotion in males and potentiated oxycodone sensitization in females. Together, these results suggest that PKMζ acts to dampen oxycodone taking in both sexes, but females may be more sensitive to its effects.

Sex Differences in the Development of an Opioid Addiction-Like Phenotype: A Focus on the Telescoping Effect.

Background: Women develop addiction and drug-related health consequences after fewer years of drug use than men; this accelerated time course, or telescoping effect, has been observed clinically for multiple drugs, including opioids. Preclinical studies indicate that this is a biologically based phenomenon; however, these studies have focused exclusively on cocaine, and none have considered health effects. Methods: In this study, we used a rat (Sprague Dawley) model to determine sex differences in the time course for the development of an opioid addiction-like phenotype, as defined by the development of physical dependence (withdrawal-induced weight loss) and an increase in motivation for fentanyl (under a progressive-ratio schedule). Effects were determined following either 10 days (optimized, experiment 1) or 3 days (threshold, experiment 2) of extended-access fentanyl self-administration (24 hours/day, fixed ratio 1, 2- to 5-minute trials/hour) or following short-access fentanyl self-administration (subthreshold, experiment 3; fixed ratio 1, up to 40 infusions/day). Opioid-related adverse health effects were also determined (experiment 4). Results: Motivation for fentanyl was similarly increased in males and females following 10 days of extended-access self-administration (experiment 1), was transiently increased in females, but not males, following 3 days of extended-access self-administration (experiment 2) and was not increased in either sex following short-access self-administration (experiment 3). Females developed fentanyl-associated adverse health effects more readily than males (experiment 4), with particularly robust differences during extended-access self-administration and withdrawal. Conclusions: As with findings in humans, female rats developed opioid addiction-like features and adverse health consequences more readily than male rats. These data provide support for a biologically based telescoping effect in females for opioids, particularly for opioid-related adverse health consequences.

In this issue, we explore how female rats develop signs of opioid addiction and related health issues faster than male rats, a phenomenon known as the telescoping effect. This study expands on previous research by using a rat model to assess addiction-like behaviors and health consequences following different withdrawal period and durations of fentanyl self-administration. The findings underline the biological underpinnings of sex differences in addiction trajectories, previously demonstrated in humans but not yet studied in opioids until now.

Revisiting dezocine for opioid use disorder: A narrative review of its potential abuse liability.

AIMS: Opioid use disorder (OUD) remains a serious public health problem. Opioid maintenance treatment is effective but under-utilized, hard to access under existing federal regulations, and, once patients achieve OUD stability, challenging to discontinue. Fewer than 2% of persons with OUD stop using opioids completely. There have been calls from public advocacy groups, governmental agencies, and public health officials for new treatments for OUD. Dezocine, a non-scheduled opioid previously used in the United States and currently widely prescribed in China for pain management, could be a candidate for a novel OUD treatment medication in the U.S. Nonetheless, to date, there have been no reviews of the clinical and preclinical literature detailing dezocine's abuse potential, a key consideration in assessing its clinical utility. DISCUSSION: There are no English language reports of human abuse, dependence, or overdose of dezocine, despite years of extensive clinical use. There are a few case reports of dezocine abuse in the Chinese literature, but there are no reports of overdose deaths. Dezocine is perceived as an opioid and is "liked" by opioid-experienced human and non-human primates, properties that are not dose-dependent and are mitigated by ceiling effects-higher doses do not result in more "liking." There is little withdrawal, spontaneous or precipitated, in humans, monkeys, rats, or mice treated chronically with dezocine alone. However, at some doses, dezocine can precipitate withdrawal in humans and monkeys dependent on other opioids. In rodents, dezocine reduces the severity of morphine withdrawal and the rewarding properties of other opioids. CONCLUSIONS: Although dezocine is reinforcing in humans and monkeys with prior or concurrent opioid use within a restricted dose range, there are only a few anecdotal reports of dezocine abuse despite of the long history of use in humans. Given the evidence of dezocine's limited abuse potential, it could be useful both as a treatment for OUD. However, in-depth studies would be required for dezocine to be re-considered for clinical use.

Effect of chronic delivery of the NOP/MOR partial agonist AT-201 and NOP antagonist J-113397 on heroin relapse in a rat model of opioid maintenance.

RATIONALE: The opioid crisis persists despite availability of effective opioid agonist maintenance treatments (methadone and buprenorphine). Thus, there is a need to advance novel medications for the treatment of opioid use and relapse. OBJECTIVES: We recently modeled maintenance treatment in rats and found that chronic delivery of buprenorphine and the mu opioid receptor (MOR) partial agonist TRV130 decreases relapse to oxycodone seeking and taking. In contrast, chronic delivery of the buprenorphine analog BU08028 had mixed effects on different heroin relapse-related measures. Here, we tested the effect of the mixed nociceptin (NOP) receptor/MOR partial agonist AT-201 and the NOP receptor antagonist J-113397 on different heroin relapse-related measures. METHODS: We trained male and female rats to self-administer heroin (6-h/d, 14-d) in context A and then implanted osmotic minipumps containing AT-201 (0, 3.8, or 12 mg/kg/d) or J-113397 (0, 12.6, or 40 mg/kg/d). Next, we tested the effect of chronic delivery of the compounds on (1) incubation of heroin seeking in a non-drug context B, (2) extinction responding reinforced by heroin-associated discrete cues in context B, (3) context A-induced reinstatement of heroin seeking, and (4) reacquisition of heroin self-administration in context A. RESULTS: In females, AT-201 modestly increased reacquisition of heroin self-administration and J-113397 modestly decreased incubation of heroin seeking. The compounds had no effect on the other relapse-related measures in females, and no effect on any of the measures in males. CONCLUSION: The NOP/MOR partial agonist AT-201 and the NOP antagonist J-113397 did not mimic buprenorphine's inhibitory effects on relapse in a rat model of opioid maintenance treatment.

Comparison of the reinforcing, antinociceptive, and respiratory depressant effects of prototypical and G-protein biased mu-opioid receptor agonists in male and female Sprague-Dawley rats.

RATIONALE: G-protein biased mu-opioid receptor (MOR) agonists have been reported to exhibit superior therapeutic windows compared to prototypical MOR agonists when relating antinociception to respiratory depression. However, there is relatively little research on the abuse potential of G-protein biased MOR agonists in relation to other behavioral endpoints. OBJECTIVES: The aim of the present study was to quantitatively compare the reinforcing, antinociceptive, and respiratory-depressant effects of the prototypical MOR agonists, fentanyl and oxycodone, to the G-protein biased MOR agonists, SR14968 and SR17018, in male and female rats. METHODS: In the self-administration study, four separate groups of Sprague-Dawley (SD) rats self-administered intravenous (i.v.) fentanyl, oxycodone, SR14968, and SR17018 under a progressive-ratio schedule of reinforcement. Using a within-subjects design, separate cohorts of SD rats were tested with i.v. fentanyl, oxycodone, SR14968, and SR17018 using a hot-plate assay, assays of neuropathic and inflammatory antinociception, and whole-body plethysmography. RESULTS: All MOR agonists functioned as reinforcers, but SR14968 and SR17018 were less efficacious relative to oxycodone and fentanyl. Moreover, all MOR agonists produced dose-dependent and fully efficacious antinociception across all nociception modalities. Oxycodone and fentanyl, but not SR14968 or SR17018, produced respiratory depression in a dose-dependent manner. CONCLUSION: The present results indicate that the G-protein biased MOR agonists tested herein produce MOR-typical antinociception, exhibit reduced but apparent abuse potential, and do not produce respiratory effects at doses that are above the antinociceptive range. Atypical MOR agonists within the SR series should be further studied as foundational molecules for the development of safter analgesics.

Astrocyte Ca2+ in the dorsal striatum suppresses neuronal activity to oppose cue-induced reinstatement of cocaine seeking.

Recent literature supports a prominent role for astrocytes in regulation of drug-seeking behaviors. The dorsal striatum, specifically, is known to play a role in reward processing with neuronal activity that can be influenced by astrocyte Ca2+. However, the manner in which Ca2+ in dorsal striatum astrocytes impacts neuronal signaling after exposure to self-administered cocaine remains unclear. We addressed this question following over-expression of the Ca2+ extrusion pump, hPMCA2w/b, in dorsal striatum astrocytes and the Ca2+ indicator, GCaMP6f, in dorsal striatum neurons of rats that were trained to self-administer cocaine. Following extinction of cocaine-seeking behavior, the rats over-expressing hMPCA2w/b showed a significant increase in cue-induced reinstatement of cocaine seeking. Suppression of astrocyte Ca2+ increased the amplitude of neuronal Ca2+ transients in brain slices, but only after cocaine self-administration. This was accompanied by decreased duration of neuronal Ca2+ events in the cocaine group and no changes in Ca2+ event frequency. Acute administration of cocaine to brain slices decreased amplitude of neuronal Ca2+ in both the control and cocaine self-administration groups regardless of hPMCA2w/b expression. These results indicated that astrocyte Ca2+ control over neuronal Ca2+ transients was enhanced by cocaine self-administration experience, although sensitivity to acutely applied cocaine remained comparable across all groups. To explore this further, we found that neither the hMPCA2w/b expression nor the cocaine self-administration experience altered regulation of neuronal Ca2+ events by NPS-2143, a Ca2+ sensing receptor (CaSR) antagonist, suggesting that plasticity of neuronal signaling after hPMCA2w/b over-expression was unlikely to result from elevated extracellular Ca2+. We conclude that astrocyte Ca2+ in the dorsal striatum impacts neurons via cell-intrinsic mechanisms (e.g., gliotransmission, metabolic coupling, etc.) and impacts long-term neuronal plasticity after cocaine self-administration differently from neuronal response to acute cocaine. Overall, astrocyte Ca2+ influences neuronal output in the dorsal striatum to promote resistance to cue-induced reinstatement of cocaine seeking.

SR9883 is a novel small-molecule enhancer of α4ß2* nicotinic acetylcholine receptor signaling that decreases intravenous nicotine self-administration in rats.

Background: Most smokers attempting to quit will quickly relapse to tobacco use even when treated with the most efficacious smoking cessation agents currently available. This highlights the need to develop effective new smoking cessation medications. Evidence suggests that positive allosteric modulators (PAM) and other enhancers of nicotinic acetylcholine receptor (nAChR) signaling could have therapeutic utility as smoking cessation agents. Methods: 3-[3-(3-pyridyl)-1,2,4-oxadiazol-5-yl]benzonitrile (NS9283) was used as a starting point for medical chemistry efforts to develop novel small molecule enhancers of α4ß2* nAChR stoichiometries containing a low-affinity agonist binding site at the interface of α4/α4 and α4/α5 subunits. Results: The NS9283 derivative SR9883 enhanced the effect of nicotine on α4ß2* nAChR stoichiometries containing low-affinity agonist binding sites, with EC50 values from 0.2-0.4 µM. SR9883 had no effect on α3ß2* or α3ß4* nAChRs. SR9883 was bioavailable after intravenous (1 mg kg-1) and oral (10-20 mg kg-1) administration and penetrated into the brain. When administered alone, SR9883 (5-10 mg kg-1) had no effect on locomotor activity or intracranial self-stimulation (ICSS) thresholds in mice. When co-administered with nicotine, SR9883 enhanced locomotor suppression and elevations of ICSS thresholds induced by nicotine. SR9883 (5 and 10 mg kg-1) decreased responding for intravenous nicotine infusions (0.03 mg kg-1 per infusion) but had no effect on responding for food rewards in rats. Conclusions: These data suggest that SR9883 is useful for investigating behavioral processes regulated by certain α4ß2* nAChR stoichiometries. SR9883 and related compounds with favorable drug-like physiochemical and pharmacological properties hold promise as novel treatments of tobacco use disorder.

Exploring the progression of drug dependence in a methamphetamine self-administration rat model through targeted and non-targeted metabolomics analyses.

Persistent neurochemical and biological disturbances resulting from repeated cycles of drug reward, withdrawal, and relapse contribute to drug dependence. Methamphetamine (MA) is a psychostimulant with substantial abuse potential and neurotoxic effects, primarily affecting monoamine neurotransmitter systems in the brain. In this study, we aimed to explore the progression of drug dependence in rat models of MA self-administration, extinction, and reinstatement through targeted and non-targeted metabolomics analyses. Metabolic profiles were examined in rat plasma during the following phases: after 16 days of MA self-administration (Group M); after 16 days of self-administration followed by 14 days of extinction (Group MS); and after self-administration and extinction followed by a reinstatement injection of MA (Group MSM). Each group of MA self-administration, extinction, and reinstatement induces distinct changes in the metabolic pathways, particularly those related to the TCA cycle, arginine and proline metabolism, and arginine biosynthesis. Additionally, the downregulation of glycerophospholipids and sphingomyelins in Group MSM suggests their potential role in MA reinstatement. These alterations may signify the progressive deterioration of these metabolic pathways, possibly contributing to drug dependence following repeated cycles of drug reward, withdrawal, and relapse. These results provide valuable insights into the metabolic changes associated with MA use at various stages, potentially facilitating the discovery of early diagnostic biomarkers and therapeutic targets for MA use disorders.

Artificial intelligence-based analysis of behavior and brain images in cocaine-self-administered marmosets.

BACKGROUND: The sophisticated behavioral and cognitive repertoires of non-human primates (NHPs) make them suitable subjects for studies involving cocaine self-administration (SA) schedules. However, ethical considerations, adherence to the 3Rs principle (replacement, reduction and refinement), and other factors make it challenging to obtain NHPs individuals for research. Consequently, there is a need for methods that can comprehensively analyze small datasets using artificial intelligence (AI). NEW METHODS: We employed AI to identify cocaine dependence patterns from collected data. First, we collected behavioral data from cocaine SA marmosets (Callithrix jacchus) to develop a dependence prediction model. SHapley Additive exPlanations (SHAP) values were used to demonstrate the importance of various variables. Additionally, we collected positron emission tomographic (PET) images showing dopamine transporter (DAT) binding potential and developed an algorithm for PET image segmentation. RESULTS: The prediction model indicated that the Random Forest (RF) algorithm performed best, with an area under the curve (AUC) of 0.92. The top five variables influencing the model were identified using SHAP values. The PET image segmentation model achieved an accuracy of 0.97, a mean squared error of 0.02, an intersection over union (IoU) of 0.845, and a Dice coefficient of 0.913. COMPARISON WITH EXISTING METHODS AND CONCLUSION: Utilizing data from the marmoset SA experiment, we developed an ML-based dependence prediction model and analyzed variable importance rankings using SHAP. AI-based imaging segmentation methods offer a valuable tool for evaluating DAT availability in NHPs following chronic cocaine administration.

Time-course concentration of ethanol, acetaldehyde and acetate in rat brain dialysate following alcohol self-administration.

The unclear mechanisms of ethanol metabolism in the brain highlight the need for a deeper understanding of its metabolic pathways. This study used in vivo microdialysis to simultaneously sample ethanol and its metabolites, acetaldehyde and acetate, in the rat striatum following self-administration of ethanol, emphasizing the natural oral exposure route. To enhance the self-administration, rats underwent two-bottle-choice and limited access training. Dialysate samples, collected every 10 minutes for 2.5 hours, were analyzed using gas chromatography with flame ionization detection (GC-FID). The measured time courses of dialysate concentrations of ethanol, acetaldehyde, and acetate provided insights into dynamics of ethanol metabolism. Notably, in a subject with low ethanol consumption (0.29 g/kg), the concentration of acetaldehyde remained below the limit of detection throughout the experiment. However, the acetate concentration was clearly increased after ethanol consumption in this subject and was comparable to that of other rats with higher ethanol consumption. Compared with focusing only on peak values in the time-courses of concentrations of ethanol and its metabolites, calculating areas under curves provided better models of the relationships between ethanol intake and individual ethanol metabolites, as indicated by the r-square values for the linear regressions. This approach of using the area under the curve accounts for both the amplitude and duration of the concentration profiles, reducing the impact of variations in individual drinking patterns. In vivo microdialysis enables concurrent sampling of brain metabolites during oral ethanol administration, contributing insights into metabolite dynamics. To our knowledge, this paper is the first to report measurement of all three analytes in the brain following self-administration of ethanol. Future studies will explore regional variations and dynamics post-ethanol dependence, further advancing our understanding of ethanol metabolism in the brain.

Biological sex modulates the efficacy of 2,5-dimethoxy-4-iodoamphetamine (DOI) to mitigate fentanyl demand.

BACKGROUND: Overdose deaths remain high for opioid use disorder, emphasizing the need to pursue innovative therapeutics. Classic psychedelic drugs that engage many monoamine receptors mitigate opioid use. Here, we tested the hypothesis that the preferential serotonin 5-HT2AR agonist, 2,5-dimethoxy-4-iodoamphetamine (DOI) could reduce the demand for fentanyl in a preclinical model of fentanyl self-administration. METHODS: Male and female Sprague-Dawley rats (n = 25-29) were implanted with indwelling jugular catheters and allowed to self-administer fentanyl (3.2µg/kg/infusion). Rats progressed to a novel low price twice within-session threshold procedure where rats sampled the lowest price twice before decreasing the dose of fentanyl by a » log every 10minutes across 11 doses. Once stable, rats were pretreated with saline or DOI (0.01, 0.03, 1mg/kg). Fentanyl consumption was analyzed using an exponentiated demand function to extract the dependent variables, Q0 and α. RESULTS: Male and female rats acquired fentanyl self-administration in the lowest price twice within-session threshold procedure. DOI dose-dependently altered fentanyl intake such that 5-HT2AR activation decreased Q0 in female rats but increased Q0 in male rats. For demand elasticity, DOI increased α in male rats but did not alter α in female rats. DOI did not alter inactive lever presses or latency. CONCLUSION: DOI reduces consumption at minimally constrained costs but did not affect the reinforcement value of fentanyl in female rats. Alternatively, DOI significantly reduced the reinforcement value of fentanyl in male rats. Biological sex alters the therapeutic efficacy of DOI and 5-HT2AR activation sex-dependently alters opioid reinforcement.

Fentanyl self-administration is accelerated by methamphetamine co-use and results in worsened hypodopaminergia in male, but not female rats.

Combined use of fentanyl and methamphetamine (FENT + METH) has increased in recent years and has been documented in a growing number overdose deaths each year. The impact of FENT + METH on behavior and neurobiology is not well understood. In this study, male and female Long Evans rats were tested on a limited access, fixed ratio 1 self-administration schedule for increasing doses (1.25-5 µg/kg/infusion; iv) of fentanyl, with and without a single dose (0.1 mg/kg/infusion; iv) of methamphetamine, for 15 days. FENT + METH abolished dose responsiveness to fentanyl in all rats and accelerated intake in males, resulting in patterns of responding that may be more likely to result in adverse effects. Ex vivo slice voltammetry in the nucleus accumbens core showed decreases in dopamine release and reuptake (Vmax) following FENT + METH exposure, compared with saline, fentanyl, and methamphetamine alone groups at baseline parameters. Further, significant decreases in dopamine release were observed across a range of stimulation intensities following FENT + METH exposure. Overall, male and female rats displayed sex-specific behavioral and neurobiological responses to FENT + METH exposure, with males displaying increased vulnerability.

The ventral tegmental area dopamine to basolateral amygdala projection supports acquisition of cocaine self-administration.

Dopamine signaling in the amygdala is known to play a role in associative learning and memory, including the process of learning to associate environmental cues with the reinforcing properties of drugs like cocaine. Evidence suggests that the ventral tegmental area (VTA) dopamine (DA) projection specifically to the basolateral amygdala (BLA) participates in establishing cocaine-cue associations that can promote later craving- and relapse-like responses to the cue alone. In order to further investigate the specific role of VTA-BLA projections in cocaine-reinforced learning, we used chemogenetics to manipulate VTA DA inputs to the BLA during cocaine self-administration, cue- and cocaine-primed reinstatement, and conditioned place preference. We found inhibiting DA input to the BLA during cocaine self-administration inhibited acquisition and weakened the ability of the previously cocaine-paired cue to elicit cocaine-seeking, while acutely inhibiting the pathway on the day of cue-induced reinstatement testing had no effect. Conversely, exciting the projection during self-administration boosted the salience of the cocaine-paired cue as indicated by enhanced responding during cue-induced reinstatement. Importantly, interfering with DA input to the BLA had no impact on the ability of cocaine to elicit a place preference or induce reinstatement in response to a priming cocaine injection. Overall, we show that manipulation of projections underlying DA signaling in the BLA may be useful for developing therapeutic interventions for substance use disorders.

Psilocybin administered following extinction sessions does not affect subsequent cocaine cue reinstatement in male and female rats and mice.

There are currently no pharmacological treatments for cocaine use disorder. Recently there has been a great deal of interest in the potential of psychedelic drugs such as psilocybin to treat psychiatric disorders. Human studies have indicated that a single administration of psilocybin can have long-lasting effects. Few preclinical studies have examined a role for psilocybin in addiction models. The goal of the current study was to determine whether psilocybin would enhance extinction following cocaine self-administration in male and female mice and rats and thus result in an attenuation of cue-induced drug-seeking. In experiments in mice, 16 female and 19 male mice underwent 8d of cocaine self-administration (0.5 mg/kg/infusion) and extinction training. Immediately following extinction trials, mice were injected with vehicle or 1.0 mg/kg psilocybin. Following the conclusion of extinction training, mice were tested for cue-induced reinstatement. In experiments in rats, 24 female and 23 male rats underwent 15d of cocaine self-administration (0.8 mg/kg/infusion) and extinction training. Immediately following extinction trials, rats were injected with vehicle, 1.0 mg/kg psilocybin, or 2.5 mg/kg psilocybin. Following the conclusion of extinction training, rats were tested for cue-induced reinstatement. Psilocybin administered following extinction trials had no effect, as both female and male mice and rats demonstrated significant cue-induced reinstatement. These data suggest that psilocybin is ineffective at altering cocaine-seeking behavior in the paradigm and doses used in the current study. It remains to be seen whether treatment with psilocybin under different conditions may be useful in the long-standing goal of finding pharmacotherapies to treat CUD.