Naloxone-precipitated Withdrawal Research Articles

Pharmacologic profile of ITI-333: a novel molecule for treatment of substance use disorders

RationaleMedications are urgently needed to treat symptoms of drug withdrawal and mitigate dysphoria and psychiatric comorbidities that drive opioid abuse and relapse. ITI-333 is a novel molecule in development for treatment of substance use disorders, psychiatric comorbidities, and pain.ObjectiveCharacterize the preclinical profile of ITI-333 using pharmacological, behavioral, and physiological assays.MethodsCell-based assays were used to measure receptor binding and intrinsic efficacy of ITI-333; animal models were employed to assess effects on opioid reinstatement, precipitated oxycodone withdrawal, and drug abuse liability.ResultsIn vitro, ITI-333 is a potent 5-HT2A receptor antagonist (Ki = 8 nM) and a biased, partial agonist at μ-opioid (MOP) receptors (Ki = 11 nM; lacking β-arrestin agonism) with lesser antagonist activity at adrenergic α1A (Ki = 28 nM) and dopamine D1 (Ki = 50 nM) receptors. In vivo, ITI-333 blocks 5-HT2A receptor-mediated head twitch and MOP receptor-mediated effects on motor hyperactivity in mice. ITI-333 alone is a naloxone-sensitive analgesic (mice) which suppresses somatic signs of naloxone-precipitated oxycodone withdrawal (mice) and heroin cue-induced reinstatement responding without apparent tolerance or physical dependence after chronic dosing (rats). ITI-333 did not acutely impair gastrointestinal or pulmonary function (rats) and was not intravenously self-administered by heroin-maintained rats or rhesus monkeys.ConclusionsITI-333 acts as a potent 5-HT2A receptor antagonist, as well a biased MOP receptor partial agonist with low intrinsic efficacy. ITI-333 mitigates opioid withdrawal/reinstatement, supporting its potential utility as a treatment for OUD.

Model of negative affect induced by withdrawal from acute and chronic morphine administration in male mice

Opioid use disorder (OUD) is a chronic relapsing disorder that is a major burden for the lives of affected individuals, and society as a whole. Opioid withdrawal is characterized by strong physical symptoms, along with signs of negative affect. Negative affect due to opioid withdrawal is a major obstacle to recovery and relapse prevention. The mechanisms behind negative affect due to either spontaneous or antagonist-precipitated opioid withdrawal are not well known, and more animal models need be developed. Here, we present behavioral models of negative affect upon naloxone-precipitated morphine withdrawal in adult male mice. Social, anxiety, and despair-like deficits were investigated following naloxone administration in mice receiving morphine under three dosing regimens; acute, chronic constant dose and chronic escalating doses. Social behaviour in the three-chamber social preference test was decreased following withdrawal from chronic and escalating but not acute morphine. Anxiety-like behaviour in the open field was increased for all three treatments. Despair-like behaviour was increased following withdrawal from chronic and escalating but not acute morphine. Altogether, these animal models will contribute to study behavioural and neuronal circuitries involved in the several negative affective signs characterizing OUD.

Effects of CB1 receptor negative allosteric modulator Org27569 on oxycodone withdrawal symptoms in mice.

Targeting cannabinoid receptor type 1 (CB1R) has shown promise for treating opioid withdrawal symptoms. This study aimed to investigate the efficacy of a specific CB1R negative allosteric modulator (NAM), Org27569, in reducing both naloxone-precipitated and protracted withdrawal symptoms in oxycodone-dependent mice. Mice received escalating doses of oxycodone (9-33mg/kg IP) or saline twice daily for 9 days, followed by a final dose of oxycodone (33mg/kg) or saline in the morning of day 9. In one cohort, the impact of Org27569 (3, 10, and 30mg/kg) on naloxone (10mg/kg IP) precipitated withdrawal symptoms was assessed. In another cohort, Org27569 (3mg/kg) effects on the acquisition of conditioned place aversion to naloxone (0.6mg/kg) precipitated opioid withdrawal, on behaviour following a 7-9-day abstinence period, and on naloxone (0.6mg/kg) precipitated withdrawal-induced escape behaviour in a novel assay were assessed. Although Org27569 decreased opioid withdrawal-induced jumping at doses of 10 and 30mg/kg, these effects were confounded by reduced locomotion. At all doses tested, Org27569 had a modest inhibitory effect on gastrointestinal motility. At the lower dose of 3mg/kg, which was not confounded by locomotor effects, Org27569 did not impact naloxone-precipitated withdrawal-induced jumping, acquisition of oxycodone withdrawal-induced conditioned place aversion, or naloxone-precipitated withdrawal-induced escape behaviour in a novel assay. A clear protracted opioid withdrawal phenotype was not observed in assays of anxiety-like or social behaviour. Org27569 effects on negative affective-like symptoms were confounded by locomotor effects and effects on gastrointestinal motility were not opioid withdrawal specific. Further studies are needed in a model that produces a more pronounced protracted withdrawal syndrome.

Teneurin C-terminal associated peptide (TCAP)-1 attenuates the development and expression of naloxone-precipitated morphine withdrawal in male Swiss Webster mice

Teneurin C-terminal associated peptide (TCAP)-1 attenuates the development and expression of naloxone-precipitated morphine withdrawal in male Swiss Webster mice

Orally Administered N-Oleoyl Alanine Blocks Acute Opioid Withdrawal Induced-Conditioned Place Preference and Attenuates Somatic Withdrawal following Chronic Opioid Exposure in Rats

(1) Background: Intraperitoneal injections of the endogenous N-acyl amino acid N-Oleoyl alanine (OlAla) effectively reduces both the affective and somatic responses produced by opioid withdrawal in preclinical models. To increase the translational appeal of OlAla in clinical drug applications, the current experiments tested whether oral OlAla pretreatment also attenuates opioid withdrawal in rats. (2) Methods: In Experiment 1, to assess its impact on affective withdrawal behavior, OlAla (0, 5, 20 mg/kg) was orally administered during the conditioning phase of an acute naloxone-precipitated morphine withdrawal conditioned place avoidance task. In Experiment 2, to assess its impact on somatic withdrawal behavior, OlAla (5–80 mg/kg) was orally administered prior to naloxone-precipitated withdrawal from chronic heroin exposure. (3) Results: Pretreatment with oral OlAla at the higher (20 mg/kg), but not lower (5 mg/kg) dose, reduced the establishment of an acute morphine withdrawal-induced conditioned place aversion. Instead, the lower dose of oral OlAla (5 mg/kg) reduced heroin withdrawal-induced abdominal contractions and diarrhea, whereas higher doses were without effect. (4) Conclusions: The results suggest a dose-dependent reduction of opioid withdrawal responses by orally administered OlAla, and further highlight the potential utility of this compound for opioid withdrawal in clinical populations.

Blocking IL-17A prevents oxycodone-induced depression-like effects and elevation of IL-6 levels in the ventral tegmental area and reduces oxycodone-derived physical dependence in rats

Oxycodone is the most prescribed opioid for pain management and has been available in clinics for almost a century, but effects of chronic oxycodone have been studied less than morphine in preclinical and clinical studies. Newly developed depression has been coupled with chronic oxycodone use in a few clinical studies, but no preclinical studies have investigated the pathogenesis of oxycodone-induced depression. Gut microbiome changes following oxycodone use is an understudied area, and interleukin-17A (IL-17A) is linked to both the development of mood disorders and regulation of gut microbiome. The present study investigated effects of chronic oxycodone exposure on mood-related behaviors (depression and anxiety), pain hypersensitivity, physical dependence, immune markers, and the gut microbiome and tested the hypothesis that blocking IL-17A with a systemically administered monoclonal antibody reduces oxycodone-derived effects. Oxycodone (using an incremental dosing regimen) or saline was injected twice a day for 12 days. IL-17A Ab (200 µg/100 µl) or saline was administered every 3rd day during the 12-day interval. Chronic oxycodone induced a depression-like effect, but not anxiogenic- or anxiolytic-like effects; promoted hyperalgesia; increased IL-17A and IL-6 levels in the ventral tegmental area (VTA); and induced physical dependence. IL-17A Ab co-administration with oxycodone prevented the depression-like effect and hyperalgesia, reduced naloxone-precipitated withdrawal signs, and normalized the increase in cytokine levels. Chronic oxycodone exposure did not affect gut microbiome and integrity. Our results identify a role for IL-17A in oxycodone-related behavioral and neuroimmune effects and show that IL-17A Ab has potential therapeutic value in blocking these effects. Given that humanized IL-17A Ab is approved for treatment of psoriasis and psoriatic arthritis, our findings point toward studying it for use in the treatment of oxycodone use disorder.

Identification and Pharmacological Characterization of a Low-Liability Antinociceptive Bifunctional MOR/DOR Cyclic Peptide.

Peptide-based opioid ligands are important candidates for the development of novel, safer, and more effective analgesics to treat pain. To develop peptide-based safer analgesics, we synthesized a mixture-based cyclic pentapeptide library containing a total of 24,624 pentapeptides and screened the mixture-based library samples using a 55 °C warm water tail-withdrawal assay. Using this phenotypic screening approach, we deconvoluted the mixture-based samples to identify a novel cyclic peptide Tyr-[D-Lys-Dap(Ant)-Thr-Gly] (CycloAnt), which produced dose- and time-dependent antinociception with an ED50 (and 95% confidence interval) of 0.70 (0.52-0.97) mg/kg i.p. mediated by the mu-opioid receptor (MOR). Additionally, higher doses (≥3 mg/kg, i.p.) of CycloAnt antagonized delta-opioid receptors (DOR) for at least 3 h. Pharmacological characterization of CycloAnt showed the cyclic peptide did not reduce breathing rate in mice at doses up to 15 times the analgesic ED50 value, and produced dramatically less hyperlocomotion than the MOR agonist, morphine. While chronic administration of CycloAnt resulted in antinociceptive tolerance, it was without opioid-induced hyperalgesia and with significantly reduced signs of naloxone-precipitated withdrawal, which suggested reduced physical dependence compared to morphine. Collectively, the results suggest this dual MOR/DOR multifunctional ligand is an excellent lead for the development of peptide-based safer analgesics.

AKAP150 from nucleus accumbens dopamine D1 and D2 receptor-expressing medium spiny neurons regulates morphine withdrawal

Dopamine D1 receptor-expressing medium spiny neurons (D1R-MSNs) and dopamine D2 receptor-expressing MSNs (D2R-MSNs) in nucleus accumbens (NAc) have been demonstrated to show different effects on reward and memory of abstinence. A-kinase anchoring protein 150 (AKAP150) expression in NAc is significantly upregulated and contributes to the morphine withdrawal behavior. However, the underlying mechanism of AKAP150 under opioid withdrawal remains unclear. In this study, AKAP150 expression in NAc is upregulated in naloxone-precipitated morphine withdrawal model, and knockdown of AKAP150 alleviates morphine withdrawal somatic signs and improves the performance of conditioned place aversion (CPA) test. AKAP150 in NAc D1R-MSNs is related to modulation of the performance of morphine withdrawal CPA test, while AKAP150 in NAc D2R-MSNs is relevant to the severity of somatic responses. Our results suggest that AKAP150 from D1R-MSNs or D2R-MSNs in NAc contributes to the developmental process of morphine withdrawal but plays different roles in aspects of behavior or psychology.

The effects of (2R,6R)-hydroxynorketamine on oxycodone withdrawal and reinstatement

Despite the thousands of lives lost during the ongoing opioid crisis, a scarcity of new and effective clinical treatments for opioid use disorder (OUD) remains. To address this unmet need, some researchers have turned to dissociative and psychedelic drugs to treat multiple psychiatric conditions. In particular, low doses of ketamine have been shown to attenuate opioid withdrawal and drug use in clinical and preclinical studies. However, ketamine has misuse liability and dissociative side effects that may limit its widespread application as a treatment for OUD. More recently, (2R,6R)-hydroxynorketamine (HNK), a ketamine metabolite that lacks misuse potential, has gained attention for its effectiveness in depression and stress models. To uncover its role in OUD, we tested the time-dependent effects of (2R,6R)-HNK on oxycodone withdrawal and reinstatement of oxycodone conditioned place preference (CPP). In male and female oxycodone-dependent mice, we found that 24h pretreatment with (2R,6R)-HNK (10 or 30mg/kg, s.c.) reduced the frequency of withdrawal-like behaviors and global withdrawal scores during naloxone-precipitated withdrawal, whereas 1h pretreatment with (2R,6R)-HNK only reduced paw tremors and the sum of global withdrawal scores but not GWS Z-scores. In other experiments, both 1h and 24h pretreatment with (2R,6R)-HNK (30mg/kg, s.c.) blocked drug-induced reinstatement of oxycodone CPP. Finally, we found (2R,6R)-HNK (30mg/kg, sc) had no effect on locomotor activity and thigmotaxis. Together, these results indicate that acute (2R,6R)-HNK has efficacy in some preclinical models of OUD without producing locomotor or anxiety-like side effects.

Selective activation of AKAP150/TRPV1 in ventrolateral periaqueductal gray GABAergic neurons facilitates conditioned place aversion in male mice

Aversion refers to feelings of strong dislike or avoidance toward particular stimuli or situations. Aversion can be caused by pain stimuli and has a long-term negative impact on physical and mental health. Aversion can also be caused by drug abuse withdrawal, resulting in people with substance use disorder to relapse. However, the mechanisms underlying aversion remain unclear. The ventrolateral periaqueductal gray (vlPAG) is considered to play a key role in aversive behavior. Our study showed that inhibition of vlPAG GABAergic neurons significantly attenuated the conditioned place aversion (CPA) induced by hindpaw pain pinch or naloxone-precipitated morphine withdrawal. However, activating or inhibiting glutamatergic neurons, or activating GABAergic neurons cannot affect or alter CPA response. AKAP150 protein expression and phosphorylated TRPV1 (p-TRPV1) were significantly upregulated in these two CPA models. In AKAP150flox/flox mice and C57/B6J wild-type mice, cell-type-selective inhibition of AKAP150 in GABAergic neurons in the vlPAG attenuated aversion. However, downregulating AKAP150 in glutamatergic neurons did not attenuate aversion. Knockdown of AKAP150 in GABAergic neurons effectively reversed the p-TRPV1 upregulation in these two CPA models utilized in our study. Collectively, inhibition of the AKAP150/p-TRPV1 pathway in GABAergic neurons in the vlPAG may be considered a potential therapeutic target for the CPA response.

Distinctive roles of L-type calcium channels subtypes within the dorsal hippocampus in formation of morphine withdrawal-induced aversion in rats

Although the negative effects coming along with opiate withdrawal are in part modulated by L-type calcium channels (LTCCs), the distinctive physiological properties and functions of LTCCs subtypes suggest differential roles of subtypes during withdrawal. The present study aimed to examine the contributions of LTCC subtypes, Cav1.2 and Cav1.3, within the dorsal hippocampus (DH) in naloxone-precipitated morphine withdrawal using the conditioned place aversion (CPA) paradigm. Firstly, we injected the non-specific LTCCs antagonist verapamil into the DH of morphine-dependent rats before conditioning an environment with naloxone-precipitated withdrawal. Our results showed that verapamil blocked the acquisition of CPA. Then, to explore the molecular mechanisms of LTCCs subtypes during withdrawal, we measured the protein expression of Cav1.2 and Cav1.3 in morphine-dependent rats under different conditions. In morphine-dependent rats, conditioning with withdrawal increased Cav1.2 expression in the membrane, while only acute naloxone injection increased the membrane expression of Cav1.3. To further determine the causal roles of LTCCs subtypes in the withdrawal process, we used Cav1.2 siRNA or Cav1.3 shRNA to knock down the expression of subtypes and detected the effects on CPA and somatic withdrawal signs in morphine-dependent rats. Cav1.2 siRNA, but not Cav1.3 shRNA, inhibited the acquirement of CPA and relieved somatic withdrawal symptoms. Together, our findings reveal that Cav1.2, but not Cav1.3 plays an important role in mediating morphine withdrawal, suggesting this subtype may serve as a potential therapeutic target for the treatment of negative effects in opiate dependence.

Buprenorphine reduces somatic withdrawal in a mouse model of early-life morphine exposure

The rising prevalence of early-life opioid exposure has become a pressing public health issue in the U.S. Neonates exposed to opioids in utero are at risk of experiencing a constellation of postpartum withdrawal symptoms commonly referred to as neonatal opioid withdrawal syndrome (NOWS). Buprenorphine (BPN), a partial agonist at the mu-opioid receptor (MOR) and antagonist at the kappa-opioid receptor (KOR), is currently approved to treat opioid use disorder in adult populations. Recent research suggests that BPN may also be effective in reducing withdrawal symptoms in neonates who were exposed to opioids in utero. We sought to determine whether BPN attenuates somatic withdrawal in a mouse model of NOWS. Our findings indicate that the administration of morphine (10mg/kg, s.c.) from postnatal day (PND) 1–14 results in increased somatic symptoms upon naloxone-precipitated (1mg/kg, s.c.) withdrawal. Co-administration of BPN (0.3mg/kg, s.c.) from PND 12–14 attenuated symptoms in morphine-treated mice. On PND 15, 24h following naloxone-precipitated withdrawal, a subset of mice was examined for thermal sensitivity in the hot plate test. BPN treatment significantly increased response latency in morphine-exposed mice. Lastly, neonatal morphine exposure elevated mRNA expression of KOR, and reduced mRNA expression of corticotropin-releasing hormone (CRH) in the periaqueductal gray when measured on PND 14. Altogether, this data provides support for the therapeutic effects of acute low-dose buprenorphine treatment in a mouse model of neonatal opioid exposure and withdrawal.

Cannabidiol attenuates the expression of conditioned place aversion induced by naloxone-precipitated morphine withdrawal through the activation of 5-HT1A receptors

The misuse of and addiction to opioids are serious public health problems in some countries, such as the USA. Drug addiction is a chronic and relapsing medical condition that involves motivational and memory-related processes due to the strong associations between drugs and consuming-related stimuli. These stimuli usually trigger continuous and compulsive use and are associated with relapses after periods of withdrawal. Several factors contribute to relapse, including withdrawal-induced mood changes. Therefore, drugs attenuating withdrawal-induced affective alterations could be useful alternative treatments for relapse prevention. Cannabidiol (CBD), a non-psychotomimetic component from the Cannabis sativa plant, has anti-anxiety and anti-stress properties and has been investigated as an alternative for the treatment of several mental disorders, including drug addiction. Here, we evaluated if CBD administered 30 min prior to test for a conditioned place aversion (CPA) would attenuate the aversion induced by morphine withdrawal precipitated by the opioid receptor antagonist naloxone in male C57BL/6 mice. We also investigated if this effect involves the activation of 5-HT1A receptors, a mechanism previously associated with CBD anti-aversive effects. As expected, morphine-treated mice spent less time exploring the compartment paired with the naloxone-induced withdrawal, indicating a CPA induced by naloxone-precipitated morphine withdrawal. This effect was not observed in animals treated with CBD, at 30 and 60 mg/kg, prior to the CPA test, indicating that CBD attenuated the expression of CPA induced by naloxone-precipitated morphine withdrawal. Pretreatment with the 5-HT1A receptor antagonist WAY100635 (0.3 mg/kg) blocked CBD effects. Our findings suggest that CBD may reduce the expression of a previously established conditioned aversion induced by morphine withdrawal by a mechanism involving the activation of 5-HT1A receptors. Thus, CBD may be a therapeutic alternative for preventing relapse to opioid addiction by decreasing withdrawal-induced negative affective changes.

Loss of Astrocytic µ Opioid Receptors Exacerbates Aversion Associated with Morphine Withdrawal in Mice: Role of Mitochondrial Respiration.

Astrocytes express mu/µ opioid receptors, but the function of these receptors remains poorly understood. We evaluated the effects of astrocyte-restricted knockout of µ opioid receptors on reward- and aversion-associated behaviors in mice chronically exposed to morphine. Specifically, one of the floxed alleles of the Oprm1 gene encoding µ opioid receptor 1 was selectively deleted from brain astrocytes in Oprm1 inducible conditional knockout (icKO) mice. These mice did not exhibit changes in locomotor activity, anxiety, or novel object recognition, or in their responses to the acute analgesic effects of morphine. Oprm1 icKO mice displayed increased locomotor activity in response to acute morphine administration but unaltered locomotor sensitization. Oprm1 icKO mice showed normal morphine-induced conditioned place preference but exhibited stronger conditioned place aversion associated with naloxone-precipitated morphine withdrawal. Notably, elevated conditioned place aversion lasted up to 6 weeks in Oprm1 icKO mice. Astrocytes isolated from the brains of Oprm1 icKO mice had unchanged levels of glycolysis but had elevated oxidative phosphorylation. The basal augmentation of oxidative phosphorylation in Oprm1 icKO mice was further exacerbated by naloxone-precipitated withdrawal from morphine and, similar to that for conditioned place aversion, was still present 6 weeks later. Our findings suggest that µ opioid receptors in astrocytes are linked to oxidative phosphorylation and they contribute to long-term changes associated with opioid withdrawal.

Natural Polyphenols-Resveratrol, Quercetin, Magnolol, and β-Catechin-Block Certain Aspects of Heroin Addiction and Modulate Striatal IL-6 and TNF-α.

We have examined the effects of four different polyphenols in attenuating heroin addiction using a conditioned place preference (CPP) paradigm. Adult male Sprague Dawley rats received heroin (alternating with saline) in escalating doses starting from 10 mg/kg, i.p. up to 80 mg/kg/d for 14 consecutive days. The rats were treated with distilled water (1 mL), quercetin (50 mg/kg/d), β-catechin (100 mg/kg/d), resveratrol (30 mg/kg/d), or magnolol (50 mg/kg/d) through oral gavage for 7 consecutive days, 30 min before heroin administration, starting on day 8. Heroin withdrawal manifestations were assessed 24 h post last heroin administration following the administration of naloxone (1 mg/kg i.p). Heroin CPP reinstatement was tested following a single dose of heroin (10 mg/kg i.p.) administration. Striatal interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α) were quantified (ELISA) after naloxone-precipitated heroin withdrawal. Compared to the vehicle, the heroin-administered rats spent significantly more time in the heroin-paired chamber (p < 0.0001). Concomitant administration of resveratrol and quercetin prevented the acquisition of heroin CPP, while resveratrol, quercetin, and magnolol blocked heroin-triggered reinstatement. Magnolol, quercetin, and β-catechin blocked naloxone-precipitated heroin withdrawal and increased striatal IL-6 concentration (p < 0.01). Resveratrol administration was associated with significantly higher withdrawal scores compared to those of the control animals (p < 0.0001). The results of this study show that different polyphenols target specific behavioral domains of heroin addiction in a CPP model and modulate the increase in striatal inflammatory cytokines TNF-α and IL-6 observed during naloxone-precipitated heroin withdrawal. Further research is needed to study the clinical utility of polyphenols and to investigate the intriguing finding that resveratrol enhances, rather than attenuates naloxone-precipitated heroin withdrawal.

Probing different paradigms of morphine withdrawal on sleep behavior in male and female C57BL/6J mice

Opioid misuse has dramatically increased over the last few decades resulting in many people suffering from opioid use disorder (OUD). The prevalence of opioid overdose has been driven by the development of new synthetic opioids, increased availability of prescription opioids, and more recently, the COVID-19 pandemic. Coinciding with increases in exposure to opioids, the United States has also observed increases in multiple Narcan (naloxone) administrations as a life-saving measures for respiratory depression, and, thus, consequently, naloxone-precipitated withdrawal. Sleep dysregulation is a main symptom of OUD and opioid withdrawal syndrome, and therefore, should be a key facet of animal models of OUD. Here we examine the effect of precipitated and spontaneous morphine withdrawal on sleep behaviors in C57BL/6 J mice. We find that morphine administration and withdrawal dysregulate sleep, but not equally across morphine exposure paradigms. Furthermore, many environmental triggers promote relapse to drug-seeking/taking behavior, and the stress of disrupted sleep may fall into that category. We find that sleep deprivation dysregulates sleep in mice that had previous opioid withdrawal experience. Our data suggest that the 3-day precipitated withdrawal paradigm has the most profound effects on opioid-induced sleep dysregulation and further validates the construct of this model for opioid dependence and OUD.

The antidepressant agomelatine attenuates morphine-induced reinstatement but not self-administration or precipitated withdrawal

BackgroundExogenous melatonin appears to have anti-addictive properties and was recently shown to improve mental health and metabolic measures in patients receiving chronic opioid maintenance therapy. Agomelatine is a marketed antidepressant which acts as a melatonin agonist. We evaluated its effects using a rat model of morphine-reinforced behavior. MethodsAfter pretreatment with noncontingent morphine, male Wistar rats were trained to self-administer intravenous morphine (1.0 mg/kg-injection) under a progressive-ratio schedule. Rats were pretreated with vehicle or agomelatine during extinction, reinstatement, and reacquisition of morphine-reinforced behavior. ResultsDaily treatment with 10 mg/kg-day of agomelatine decreased the number of ratios completed and prolonged latency during morphine-induced reinstatement. There were no significant effects on cue-induced reinstatement, morphine self-administration, or naloxone-precipitated withdrawal. Treatment with 32 mg/kg-day of agomelatine caused postural changes. That dose prolonged withdrawal-induced loss of body weight and caused delayed reductions in food reinforcement. SummaryIn addition to postural effects, high-dose agomelatine worsened the course of spontaneous withdrawal and produced nonspecific effects on food-reinforced behavior. When administered at a selective dose, agomelatine did not modify morphine self-administration or precipitated withdrawal, but decreased morphine-induced reinstatement. Our findings show potential detrimental effects of high-dose agomelatine, with reductions in opioid-seeking behavior after a lower, more selective dose.

Selective M5 muscarinic acetylcholine receptor negative allosteric modulator VU6008667 blocks acquisition of opioid self-administration

Recent evidence suggests that inhibition of the M5 muscarinic acetylcholine receptor (mAChR) may provide a novel non-opioid mechanism for the treatment of opioid use disorder (OUD). Previous studies from our group and others have demonstrated that acute administration of the long-acting M5 negative allosteric modulator (NAM) ML375 attenuates established self-administration of cocaine, ethanol, oxycodone, and remifentanil in rats. In the present study, we characterized the effects of acute and repeated administration of the novel, short-acting M5 NAM VU6008667 on the reinforcing effects of oxycodone and reinstatement of oxycodone-seeking behaviors in male Sprague-Dawley rats, as well as on physiological withdrawal from oxycodone. Acute VU6008667 decreased oxycodone self-administration under both fixed ratio 3 (FR3) and progressive ratio (PR) schedules of reinforcement and attenuated cue-induced reinstatement of lever pressing following extinction from oxycodone self-administration, a commonly used relapse model. When administered daily to opioid-naïve rats, VU6008667 prevented acquisition of oxycodone self-administration behavior. VU6008667 had minimal effects on naloxone-precipitated withdrawal. After acute administration, VU6008667 did not inhibit sucrose self-administration and, when given chronically, delayed but did not prevent acquisition of sucrose maintained self-administration. VU6008667 also did not impact oxycodone induced anti-nociception or motor coordination, but mildly decreased novelty exploration. Finally, acute or daily VU6008667 administration did not impair cued fear conditioning. Overall, these results suggest that inhibition of the M5 mAChR may provide a novel, non-opioid based treatment for distinct aspects of OUD by inhibiting opioid intake in established OUD, reducing relapse during abstinence, and by reducing the risk of developing OUD.

Assessment of abuse potential of carfentanil.

Carfentanil, as a fentanyl analogue, is a potent synthetic opioid. It has been controlled in many countries, and its emergence has been highlighted by many recent reports. However, although discriminative stimulus effects of carfentanil in rats had been reported, its abuse potential has not been fully evaluated. In this study, we evaluated the abuse potential of carfentanil via the tests of conditioned place preference (CPP), drug self-administration and naloxone-precipitated opioid withdrawal assay, compared with fentanyl and heroin. Carfentanil exhibited significant place preference at a minimum dose of 1μg/kg in mice, whereas fentanyl and heroin induced significant place preference at the minimum doses of 100 μg/kg and 1000 μg/kg, respectively. In the drug-substitution test in heroin self-administered rats (50 μg/kg/infusion), carfentanil and fentanyl acquired significant self-administrations above saline levels from 0.05-0.1 and 0.1-10.0μg/kg/infusion, respectively. Carfentanil induced the maximum number of infusions at 0.1μg/kg, whereas fentanyl and heroin at 1 and 25 μg/kg, respectively. In short, carfentanil showed the highest potency to induce CPP and self-administration. Furthermore, repeated treatment with escalating doses of carfentanil, fentanyl or heroin induced typical withdrawal symptoms in mice, including a greater number of jumping and weight loss than saline group. This indicated that carfentanil could produce physical dependence similar to fentanyl and heroin. Taken together, the present study demonstrated the higher abuse potential of carfentanil compared with fentanyl and heroin. The rank order of abuse potential for these compounds is carfentanil > fentanyl > heroin.

Cannabidiol Reduced the Severity of Gastrointestinal Symptoms of Opioid Withdrawal in Male and Female Mice.

Introduction: Opioid withdrawal is a powerful driver of drug-seeking behavior as relief from this aversive state through drug-taking is a strong negative reinforcer. There are currently limited treatment options available for opioid withdrawal and cannabidiol (CBD) has been identified as a potential novel therapeutic. This study explored the efficacy and dose dependency of CBD for reducing the severity of naloxone-precipitated and spontaneous oxycodone withdrawal (PW and SW, respectively) in male and female mice. Methods: Mice were administered saline or escalating doses of oxycodone, whereby 9, 17.8, 23.7, and 33 mg/kg oxycodone IP was administered twice daily on days 1-2, 3-4, 5-6, and 7-8, respectively. On the 9th day, a single 33 mg/kg dose of oxycodone (or saline) was administered. To precipitate withdrawal, on day 9, mice in the withdrawal conditions were administered an IP injection of 10 mg/kg naloxone 2 h after the final oxycodone injection and immediately before withdrawal testing. To elicit SW, a separate group of mice underwent withdrawal testing 24 h after their final oxycodone injection. Mice were treated with an IP injection of 0, 10, 30 or 100 mg/kg of CBD 60 min before testing. Withdrawal symptoms examined included gastrointestinal symptoms (fecal boli, diarrhea, and body weight loss), somatic symptoms (paw tremors), and negative affect (jumping). Results: A robust PW syndrome was observed in both male and female mice, whereas only male mice displayed an SW syndrome. CBD dose dependently reduced gastrointestinal symptoms during both PW and SW in male mice and during PW in female mice. CBD had no effect on PW- or SW-induced jumping in male mice. However, in female mice, the PW-induced increase in jumps was less pronounced in CBD-treated mice. The highest dose of CBD inhibited paw tremors during PW, but not SW, in male mice. Neither PW- nor SW-induced paw tremors were observed in female mice. Conclusions: The magnitude of effects on the gastrointestinal symptoms, their consistency across PW and SW, and both sexes, alongside the availability of CBD for clinical use, suggest further exploration of the potential for CBD to treat these symptoms could be justified.