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The ability of morphine to decrease cysteine transport into neurons by inhibition of excitatory amino acid transporter 3 (EAA3) may be a key molecular mechanism underlying the acquisition of physical and psychological dependence to morphine. This study examined whether co-administration of the cell-penetrant antioxidant D-thiol ester, D-cysteine ethyl ester (D-CYSee), with morphine, would diminish the development of physical dependence to morphine in male Sprague Dawley rats. Systemic administration of the opioid receptor antagonist, naloxone (NLX), elicited pronounced withdrawal signs (e.g., wet-dog shakes, jumps, rears, circling) in rats that received a subcutaneous depot of morphine (150 mg/kg, SC) for 36 h and continuous intravenous infusion of vehicle (20 µL/h, IV). The NLX-precipitated withdrawal signs were reduced in rats that received an infusion of D-CYSee, but not D-cysteine, (both at 20.8 µmol/kg/h, IV) for the full 36 h. NLX elicited pronounced withdrawal signs in rats treated for 48 h with morphine (150 mg/kg, SC), plus continuous infusion of vehicle (20 µL/h, IV) that began at the 36 h timepoint of morphine treatment. The NLX-precipitated withdrawal signs were reduced in rats that received a 12 h infusion of D-CYSee, but not D-cysteine, (both at 20.8 µmol/kg/h, IV) that began at the 36 h timepoint of morphine treatment. These findings suggest that D-CYSee may attenuate the development of physical dependence to morphine and reverse established dependence to the opioid in male Sprague Dawley rats. Alternatively, D-CYSee may simply suppress the processes responsible for NLX-precipitated withdrawal. Nonetheless, D-CYSee and analogues may be novel therapeutics for the treatment of opioid use disorders. [ABSTRACT FROM AUTHOR]

Background and purpose: Chronic consumption of morphine (Mor) induces tolerance and dependence. This study aimed to survey the effects of pistachio extract (PX) on the induction and expression of Mor analgesic tolerance and physical dependency in mice. Experimental approach: Animals were randomly separated into six groups (n = 7): control, DMSO, Mor (10 mg/kg), Mor + saline, Mor + PX (10 mg/kg), and Mor + PX (100 mg/kg). Mor was injected (10 mg/kg, twice a day, s.c.) for 7 days to induce tolerance. PX was administered (10 and 100 mg/kg, orally) during the examination period. On each day and 20 min after Mor administration, a tail-flick test was done to measure the analgesic response and induction of tolerance. On day 7, naloxone (5 mg/kg, s.c.) was injected into the Mor-dependent animals to evaluate dependence, and animals were monitored for 30 min for jumping. Also, malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GPx) were assessed in the brain tissue. Findings/Results: Our results indicated that co-administration of PX with Mor for 7 days diminished the induction of Mor tolerance. PX administration for 7 days alongside Mor reduced the frequency of withdrawal signs in naloxone-injected animals during dependence induction. Also, Mor increased the level of MDA and decreased the activities of SOD and GPx. Treatment with PX (100 mg/kg) restored all of the mentioned abnormalities. Conclusion and implications: According to the results presented in this study, chronic administration of PX forbade the induction of Mor analgesic tolerance and dependency in mice.

Abstract N-acetyl-L-cysteine (L-NAC) is a proposed therapeutic for opioid use disorder. This study determined whether co-injections of L-NAC (500 μmol/kg, IV) or its highly cell-penetrant analogue, L-NAC methyl ester (L-NACme, 500 μmol/kg, IV), prevent acquisition of acute physical dependence induced by twice-daily injections of fentanyl (125 μg/kg, IV), and overcome acquired dependence to these injections in freely-moving male Sprague Dawley rats. The injection of the opioid receptor antagonist, naloxone HCl (NLX; 1.5 mg/kg, IV), elicited a series of withdrawal phenomena (i.e. behavioral and cardiorespiratory responses, hypothermia and body weight loss) in rats that received 5 or 10 injections of fentanyl and similar numbers of vehicle co-injections. With respect to the development of dependence, the NLX-precipitated withdrawal phenomena were reduced in rats that received had co-injections of L-NAC, and more greatly reduced in rats that received co-injections of L-NACme. In regard to overcoming established dependence, the NLX-precipitated withdrawal phenomena in rats that had received 10 injections of fentanyl (125 μg/kg, IV) were reduced in rats that had received co-injections of L-NAC, and more greatly reduced in rats that received co-injections of L-NACme beginning with injection 6 of fentanyl. This study provides compelling evidence that co-injections of L-NAC and L-NACme prevent the acquisition of physical dependence and overcome acquired dependence to fentanyl in male rats. The higher efficacy of L-NACme is likely due to its greater cell penetrability in brain regions mediating dependence to fentanyl and interaction with intracellular signaling cascades, including redox-dependent processes, responsible for the acquisition of physical dependence to fentanyl.

We examined whether co-injections of the cell-permeant D-cysteine analogues, D-cysteine ethyl ester (D-CYSee) and D-cysteine ethyl amide (D-CYSea), prevent acquisition of physical dependence induced by twice-daily injections of fentanyl, and reverse acquired dependence to these injections in freely-moving male Sprague Dawley rats. Injection of the opioid receptor antagonist, naloxone HCl (NLX, 1.5 mg/kg, IV), elicited a series of withdrawal phenomena that included cardiorespiratory and behavioral responses, and falls in body weight and body temperature, in rats that received 5 or 10 injections of fentanyl (125 µg/kg, IV), and the same number of vehicle co-injections. Regarding the development of physical dependence, the NLX-precipitated withdrawal phenomena were markedly reduced in fentanyl-injected rats that had received co-injections of D-CYSee (250 µmol/kg, IV) or D-CYSea (100 µmol/kg, IV), but not D-cysteine (250 µmol/kg, IV). Regarding reversal of established dependence to fentanyl, the NLX-precipitated withdrawal phenomena in rats that had received 10 injections of fentanyl (125 µg/kg, IV) was markedly reduced in rats that received coinjections of D-CYSee (250 µmol/kg, IV) or D-CYSea (100 µmol/kg, IV), but not D-cysteine (250 µmol/kg, IV), starting with injection 6 of fentanyl. This study provides evidence that co-injections of D-CYSee and D-CYSea prevent the acquisition of physical dependence, and reverse acquired dependence to fentanyl in male rats. The lack of effect of D-cysteine suggests that the enhanced cell-penetrability of D-CYSee and D-CYSea into cells, particularly within the brain, is key to their ability to interact with intracellular signaling events involved in acquisition to physical dependence to fentanyl. [ABSTRACT FROM AUTHOR]

The ability of morphine to decrease cysteine transport into neurons by inhibition of excitatory amino acid transporter 3 (EAA3) may be a key molecular mechanism underlying the acquisition of physical and psychological dependence to morphine. This study examined whether co-administration of the cell-penetrant antioxidant D-thiol ester, D-cysteine ethyl ester (D-CYSee), with morphine, would diminish the development of physical dependence to morphine in male Sprague Dawley rats. Systemic administration of the opioid receptor antagonist, naloxone (NLX), elicited pronounced withdrawal signs (e.g., wet-dog shakes, jumps, rears, circling) in rats that received a subcutaneous depot of morphine (150 mg/kg, SC) for 36 h and continuous intravenous infusion of vehicle (20 μL/h, IV). The NLX-precipitated withdrawal signs were reduced in rats that received an infusion of D-CYSee, but not D-cysteine, (both at 20.8 μmol/kg/h, IV) for the full 36 h. NLX elicited pronounced withdrawal signs in rats treated for 48 h with morphine (150 mg/kg, SC), plus continuous infusion of vehicle (20 μL/h, IV) that began at the 36 h timepoint of morphine treatment. The NLX-precipitated withdrawal signs were reduced in rats that received a 12 h infusion of D-CYSee, but not D-cysteine, (both at 20.8 μmol/kg/h, IV) that began at the 36 h timepoint of morphine treatment. These findings suggest that D-CYSee may attenuate the development of physical dependence to morphine and reverse established dependence to the opioid in male Sprague Dawley rats. Alternatively, D-CYSee may simply suppress the processes responsible for NLX-precipitated withdrawal. Nonetheless, D-CYSee and analogues may be novel therapeutics for the treatment of opioid use disorders.

We examined whether co-injections of the cell-permeant D-cysteine analogues, D-cysteine ethyl ester (D-CYSee) and D-cysteine ethyl amide (D-CYSea), prevent acquisition of physical dependence induced by twice-daily injections of fentanyl, and reverse acquired dependence to these injections in freely-moving male Sprague Dawley rats. Injection of the opioid receptor antagonist, naloxone HCl (NLX, 1.5 mg/kg, IV), elicited a series of withdrawal phenomena that included cardiorespiratory and behavioral responses, and falls in body weight and body temperature, in rats that received 5 or 10 injections of fentanyl (125 μg/kg, IV), and the same number of vehicle co-injections. Regarding the development of physical dependence, the NLX-precipitated withdrawal phenomena were markedly reduced in fentanyl-injected rats that had received co-injections of D-CYSee (250 μmol/kg, IV) or D-CYSea (100 μmol/kg, IV), but not D-cysteine (250 μmol/kg, IV). Regarding reversal of established dependence to fentanyl, the NLX-precipitated withdrawal phenomena in rats that had received 10 injections of fentanyl (125 μg/kg, IV) was markedly reduced in rats that received co-injections of D-CYSee (250 μmol/kg, IV) or D-CYSea (100 μmol/kg, IV), but not D-cysteine (250 μmol/kg, IV), starting with injection 6 of fentanyl. This study provides evidence that co-injections of D-CYSee and D-CYSea prevent the acquisition of physical dependence, and reverse acquired dependence to fentanyl in male rats. The lack of effect of D-cysteine suggests that the enhanced cell-penetrability of D-CYSee and D-CYSea into cells, particularly within the brain, is key to their ability to interact with intracellular signaling events involved in acquisition to physical dependence to fentanyl.

Morphine is a frequently used analgesic that activates the mu-opioid receptor (MOR), which has prominent side effects of tolerance. Although the inefficiency of morphine in inducing the endocytosis of MOR underlies the development of morphine tolerance, currently, there is no effective therapy to treat morphine tolerance. In the current study, we aimed to develop a monoclonal antibody (mAb) precisely targeting MOR and to determine its therapeutic efficacy on morphine tolerance and the underlying molecular mechanisms. We successfully prepared a mAb targeting MOR, named 3A5C7, by hybridoma technique using a strategy of deoxyribonucleic acid immunization combined with cell immunization, and identified it as an immunoglobulin G mAb with high specificity and affinity for MOR and binding ability to antigens with spatial conformation. Treatment of two cell lines, HEK293T and SH-SY5Y, with 3A5C7 enhanced morphine-induced MOR endocytosis via a G protein-coupled receptor kinase 2 (GRK2)/β-arrestin2-dependent mechanism, as demonstrated by immunofluorescence staining, flow cytometry, Western blotting, coimmunoprecipitation, and small interfering ribonucleic acid (siRNA)-based knockdown. This mAb also allowed MOR recycling from cytoplasm to plasma membrane and attenuated morphine-induced phosphorylation of MOR. We established an in vitro morphine tolerance model using differentiated SH-SY5Y cells induced by retinoic acid. Western blot, enzyme-linked immunosorbent assays, and siRNA-based knockdown revealed that 3A5C7 mAb diminished hyperactivation of adenylate cyclase, the in vitro biomarker of morphine tolerance, via the GRK2/β-arrestin2 pathway. Furthermore, in vivo hotplate test demonstrated that chronic intrathecal administration of 3A5C7 significantly alleviated morphine tolerance in mice, and withdrawal jumping test revealed that both chronic and acute 3A5C7 intrathecal administration attenuated morphine dependence. Finally, intrathecal electroporation of silencing short hairpin RNA illustrated that the in vivo anti-tolerance and anti-dependence efficacy of 3A5C7 was mediated by enhanced morphine-induced MOR endocytosis via GRK2/β-arrestin2 pathway. Collectively, our study provided a therapeutic mAb, 3A5C7, targeting MOR to treat morphine tolerance, mediated by enhancing morphine-induced MOR endocytosis. The mAb 3A5C7 demonstrates promising translational value to treat clinical morphine tolerance.

The molecular mechanisms underlying the acquisition of addiction/dependence on morphine may result from the ability of the opioid to diminish the transport of L-cysteine into neurons via inhibition of excitatory amino acid transporter 3 (EAA3). The objective of this study was to determine whether the coadministration of the cell-penetrant L-thiol ester, L-cysteine ethyl ester (L-CYSee), would reduce physical dependence on morphine in male Sprague Dawley rats. Injection of the opioid-receptor antagonist, naloxone HCl (NLX; 1.5 mg/kg, IP), elicited pronounced withdrawal phenomena in rats which received a subcutaneous depot of morphine (150 mg/kg) for 36 h and were receiving a continuous infusion of saline (20 μL/h, IV) via osmotic minipumps for the same 36 h period. The withdrawal phenomena included wet-dog shakes, jumping, rearing, fore-paw licking, 360° circling, writhing, apneas, cardiovascular (pressor and tachycardia) responses, hypothermia, and body weight loss. NLX elicited substantially reduced withdrawal syndrome in rats that received an infusion of L-CYSee (20.8 μmol/kg/h, IV) for 36 h. NLX precipitated a marked withdrawal syndrome in rats that had received subcutaneous depots of morphine (150 mg/kg) for 48 h) and a co-infusion of vehicle. However, the NLX-precipitated withdrawal signs were markedly reduced in morphine (150 mg/kg for 48 h)- treated rats that began receiving an infusion of L-CYSee (20.8 μmol/kg/h, IV) at 36 h. In similar studies to those described previously, neither L-cysteine nor L-serine ethyl ester (both at 20.8 μmol/kg/h, IV) mimicked the effects of L-CYSee. This study demonstrates that 1) L-CYSee attenuates the development of physical dependence on morphine in male rats and 2) prior administration of LCYSee reverses morphine dependence, most likely by intracellular actions within the brain. The lack of the effect of L-serine ethyl ester (oxygen atom instead of sulfur atom) strongly implicates thiol biochemistry in the efficacy of L-CYSee. Accordingly, L-CYSee and analogs may be a novel class of therapeutics that ameliorate the development of physical dependence on opioids in humans. [ABSTRACT FROM AUTHOR]

Background: Drugs that act on the central nervous system (CNS) and have sedative effects can lead to abuse in humans. New CNS-active drugs often require evaluation of their abuse potential in dedicated animal models before marketing approval. Daridorexant is a new dual orexin receptor antagonist (DORA) with sleep-promoting properties in animals and humans. It was approved in 2022 in the United States and Europe for the treatment of insomnia disorder. Aims: Nonclinical evaluation of abuse potential of daridorexant using three specific rat models assessing reinforcement, interoception, and withdrawal. Methods: Reinforcing effects of daridorexant were assessed in an operant rat model of intravenous drug self-administration. Similarity of interoceptive effects to those of the commonly used sleep medication zolpidem was tested in an operant drug discrimination task. Withdrawal signs indicative of physical dependence were evaluated upon sudden termination of chronic daridorexant treatment. Rat experiments were conducted at a dose range resulting in daridorexant plasma concentrations equaling or exceeding those achieved at the clinically recommended dose of 50 mg in humans. Results: Daridorexant had no reinforcing effects, was dissimilar to zolpidem in the drug discrimination task, and did not induce any withdrawal-related signs upon treatment discontinuation that would be indicative of physical dependence. Outcomes: Daridorexant showed no signs of abuse or dependence potential in rats. Our data indicate that daridorexant, like other DORAs, has a low potential for abuse in humans. [ABSTRACT FROM AUTHOR]

Introduction: Women are more vulnerable than men in many aspects of opioid use disorder (OUD); a major theory of sex differences in substance use disorders is that these differences are due to ovarian hormones with estradiol enhancing vulnerability in females. However, most of this evidence is for psychostimulants and alcohol; evidence with opioids is sparse. Thus, the goal of this study was to determine the impact of estradiol on vulnerability in females in a rat model of OUD. Method: Following self-administration training, ovariectomized (OVX) females with (E) or without (V) estradiol replacement were given extended (24 h/day), intermittent access (2, 5-min trials/h) to fentanyl for 10 days. Then, the development of three key features of OUD were assessed, including physical dependence, defined by the magnitude and time course of weight loss during withdrawal; an enhanced motivation for fentanyl, assessed using a progressive-ratio schedule; and relapse vulnerability, assessed using an extinction/cue-induced reinstatement procedure. These later two characteristics were examined following 14 days of withdrawal when the phenotypes are known to be highly expressed. Results: OVX+E females self-administered markedly higher levels of fentanyl under extended, intermittent-access conditions and showed a longer time course of physical dependence, a greater increase in motivation for fentanyl, and an enhanced sensitivity to the reinstating effects of fentanyl-associated cues compared to OVX+V rats. Severe health complications were also observed in OVX+E, but not OVX+V females, during withdrawal. Conclusion: These results indicate that, as with findings with psychostimulants and alcohol, estradiol enhances vulnerability in females to developing opioid addiction-like features and serious opioid-related health complications. [ABSTRACT FROM AUTHOR]

Morphine is a frequently used analgesic that activates the mu-opioid receptor (MOR), which has prominent side effects of tolerance. Although the inefficiency of morphine in inducing the endocytosis of MOR underlies the development of morphine tolerance, currently, there is no effective therapy to treat morphine tolerance. In the current study, we aimed to develop a monoclonal antibody (mAb) precisely targeting MOR and to determine its therapeutic efficacy on morphine tolerance and the underlying molecular mechanisms. We successfully prepared a mAb targeting MOR, named 3A5C7, by hybridoma technique using a strategy of deoxyribonucleic acid immunization combined with cell immunization, and identified it as an immunoglobulin G mAb with high specificity and affinity for MOR and binding ability to antigens with spatial conformation. Treatment of two cell lines, HEK293T and SH-SY5Y, with 3A5C7 enhanced morphine-induced MOR endocytosis via a G protein-coupled receptor kinase 2 (GRK2)/β-arrestin2-dependent mechanism, as demonstrated by immunofluorescence staining, flow cytometry, Western blotting, coimmunoprecipitation, and small interfering ribonucleic acid (siRNA)-based knockdown. This mAb also allowed MOR recycling from cytoplasm to plasma membrane and attenuated morphine-induced phosphorylation of MOR. We established an in vitro morphine tolerance model using differentiated SH-SY5Y cells induced by retinoic acid. Western blot, enzyme-linked immunosorbent assays, and siRNA-based knockdown revealed that 3A5C7 mAb diminished hyperactivation of adenylate cyclase, the in vitro biomarker of morphine tolerance, via the GRK2/β-arrestin2 pathway. Furthermore, in vivo hotplate test demonstrated that chronic intrathecal administration of 3A5C7 significantly alleviated morphine tolerance in mice, and withdrawal jumping test revealed that both chronic and acute 3A5C7 intrathecal administration attenuated morphine dependence. Finally, intrathecal electroporation of silencing short hairpin RNA illustrated that the in vivo anti-tolerance and anti-dependence efficacy of 3A5C7 was mediated by enhanced morphine-induced MOR endocytosis via GRK2/β-arrestin2 pathway. Collectively, our study provided a therapeutic mAb, 3A5C7, targeting MOR to treat morphine tolerance, mediated by enhancing morphine-induced MOR endocytosis. The mAb 3A5C7 demonstrates promising translational value to treat clinical morphine tolerance. [Display omitted] • A monoclonal antibody targeting MOR named 3A5C7 was developed. • 3A5C7 alleviates morphine tolerance and physical dependence. • 3A5C7 facilitates morphine-induced MOR endocytosis via GRK2/β-arrestin2 pathway. [ABSTRACT FROM AUTHOR]

The molecular mechanisms underlying the acquisition of addiction/dependence on morphine may result from the ability of the opioid to diminish the transport of L-cysteine into neurons via inhibition of excitatory amino acid transporter 3 (EAA3). The objective of this study was to determine whether the co-administration of the cell-penetrant L-thiol ester, L-cysteine ethyl ester (L-CYSee), would reduce physical dependence on morphine in male Sprague Dawley rats. Injection of the opioid-receptor antagonist, naloxone HCl (NLX; 1.5 mg/kg, IP), elicited pronounced withdrawal phenomena in rats which received a subcutaneous depot of morphine (150 mg/kg) for 36 h and were receiving a continuous infusion of saline (20 μL/h, IV) via osmotic minipumps for the same 36 h period. The withdrawal phenomena included wet-dog shakes, jumping, rearing, fore-paw licking, 360° circling, writhing, apneas, cardiovascular (pressor and tachycardia) responses, hypothermia, and body weight loss. NLX elicited substantially reduced withdrawal syndrome in rats that received an infusion of L-CYSee (20.8 μmol/kg/h, IV) for 36 h. NLX precipitated a marked withdrawal syndrome in rats that had received subcutaneous depots of morphine (150 mg/kg) for 48 h) and a co-infusion of vehicle. However, the NLX-precipitated withdrawal signs were markedly reduced in morphine (150 mg/kg for 48 h)-treated rats that began receiving an infusion of L-CYSee (20.8 μmol/kg/h, IV) at 36 h. In similar studies to those described previously, neither L-cysteine nor L-serine ethyl ester (both at 20.8 μmol/kg/h, IV) mimicked the effects of L-CYSee. This study demonstrates that 1) L-CYSee attenuates the development of physical dependence on morphine in male rats and 2) prior administration of L-CYSee reverses morphine dependence, most likely by intracellular actions within the brain. The lack of the effect of L-serine ethyl ester (oxygen atom instead of sulfur atom) strongly implicates thiol biochemistry in the efficacy of L-CYSee. Accordingly, L-CYSee and analogs may be a novel class of therapeutics that ameliorate the development of physical dependence on opioids in humans.

In this paper, we develop statistical inference tools for high-dimensional functional time series. We introduce a new concept of physical dependent processes in the space of square integrable functions, which adopts the idea of basis decomposition of functional data in these spaces, and derive Gaussian and multiplier bootstrap approximations for sums of high-dimensional functional time series. These results have numerous important statistical consequences. Exemplarily, we consider the development of joint simultaneous confidence bands for the mean functions and the construction of tests for the hypotheses that the mean functions in the panel dimension are parallel. The results are illustrated by means of a small simulation study and in the analysis of Canadian temperature data. [ABSTRACT FROM AUTHOR]

Despite the prevalence of opioid misuse, opioids remain the frontline treatment regimen for severe pain. However, opioid safety is hampered by side-effects such as analgesic tolerance, reduced analgesia to neuropathic pain, physical dependence, or reward. These side effects promote development of opioid use disorders and ultimately cause overdose deaths due to opioid-induced respiratory depression. The intertwined nature of signaling via m-opioid receptors (MOR), the primary target of prescription opioids, with signaling pathways responsible for opioid side-effects presents important challenges. Therefore, a critical objective is to uncouple cellular and molecular mechanisms that selectively modulate analgesia from those that mediate side-effects. One such mechanism could be the transactivation of receptor tyrosine kinases (RTKs) via MOR. Notably, MOR-mediated sideeffects can be uncoupled from analgesia signaling via targeting RTK family receptors, highlighting physiological relevance of MOR-RTKs crosstalk. This review focuses on the current state of knowledge surrounding the basic pharmacology of RTKs and bidirectional regulation of MOR signaling, as well as how MOR-RTK signaling may modulate undesirable effects of chronic opioid use, including opioid analgesic tolerance, reduced analgesia to neuropathic pain, physical dependence, and reward. Further research is needed to better understand RTK-MOR transactivation signaling pathways, and to determine if RTKs are a plausible therapeutic target for mitigating opioid side effects. [ABSTRACT FROM AUTHOR]

Despite the prevalence of opioid misuse, opioids remain the frontline treatment regimen for severe pain. However, opioid safety is hampered by side-effects such as analgesic tolerance, reduced analgesia to neuropathic pain, physical dependence, or reward. These side effects promote development of opioid use disorders and ultimately cause overdose deaths due to opioid-induced respiratory depression. The intertwined nature of signaling via μ-opioid receptors (MOR), the primary target of prescription opioids, with signaling pathways responsible for opioid side-effects presents important challenges. Therefore, a critical objective is to uncouple cellular and molecular mechanisms that selectively modulate analgesia from those that mediate side-effects. One such mechanism could be the transactivation of receptor tyrosine kinases (RTKs) via MOR. Notably, MOR-mediated side-effects can be uncoupled from analgesia signaling via targeting RTK family receptors, highlighting physiological relevance of MOR-RTKs crosstalk. This review focuses on the current state of knowledge surrounding the basic pharmacology of RTKs and bidirectional regulation of MOR signaling, as well as how MOR-RTK signaling may modulate undesirable effects of chronic opioid use, including opioid analgesic tolerance, reduced analgesia to neuropathic pain, physical dependence, and reward. Further research is needed to better understand RTK-MOR transactivation signaling pathways, and to determine if RTKs are a plausible therapeutic target for mitigating opioid side effects.

Opioids like fentanyl remain the mainstay treatment for chronic pain. Unfortunately, opioid's high dependence liability has led to the current opioid crisis, in part, because of side‐effects that develop during long‐term use, including analgesic tolerance and physical dependence. Both tolerance and dependence to opioids may lead to escalation of required doses to achieve previous therapeutic efficacy. Additionally, altered sleep and circadian rhythms are common in people on opioid therapy. Opioids impact sleep and circadian rhythms, while disruptions to sleep and circadian rhythms likely mediate the effects of opioids. However, the mechanisms underlying these bidirectional relationships between circadian rhythms and opioids remain largely unknown. The circadian protein, neuronal PAS domain protein 2 (NPAS2), regulates circadian‐dependent gene transcription in structure of the central nervous system that modulate opioids and pain. Here, male and female wild‐type and NPAS2‐deficient (NPAS2−/−) mice were used to investigate the role of NPAS2 in fentanyl analgesia, tolerance, hyperalgesia and physical dependence. Overall, thermal pain thresholds, acute analgesia and tolerance to a fixed dose of fentanyl were largely similar between wild‐type and NPAS2−/− mice. However, female NPAS2−/− exhibited augmented analgesic tolerance and significantly more behavioral symptoms of physical dependence to fentanyl. Only male NPAS2−/− mice had increased fentanyl‐induced hypersensitivity, when compared with wild‐type males. Together, our findings suggest sex‐specific effects of NPAS2 signaling in the regulation of fentanyl‐induced tolerance, hyperalgesia and dependence. [ABSTRACT FROM AUTHOR]

Background: The more the cancer treatments progress, the more the needs increase to taper and discontinue opioids in cancer patients. Furthermore, opioid dependence of cancer survivors has become a bigger problem. However, a safe opioid tapering and discontinuation method has not yet been established in cancer patients. Objective: To suggest a safe opioid tapering and discontinuation method in cancer patients. Design: We reviewed opioid type, dose, administration route, administration duration, reason for tapering and discontinuation, and presence/absence of opioid withdrawal symptoms in cancer patients whose opioids needed to be tapered and discontinued. Setting/Subjects: We recruited cancer patients referred to the palliative care team of Kyoto University Hospital-Japan whose opioids were tapered and discontinued. Measurements: Opioid withdrawal symptoms were assessed by two physicians, one nurse, and one pharmacist of palliative care team. Results: Opioids were tapered and discontinued in 25 out of 145 cancer patients (17%). Opioid withdrawal symptoms were observed in 3 of the 25 cases (12%). In withdrawal symptom cases and nonwithdrawal symptom cases, the mean maximum oral morphine-equivalent doses of opioids were 352.0 and 55.7?mg/day, and the mean administration duration of opioid were 82.3 and 28.7 days, respectively. Withdrawal symptoms occurred in patients receiving higher-dose opioids with longer administration duration and their symptoms tended to appear at approximately 10% of the maximum dose. Conclusions: We suggest that withdrawal symptoms may be prevented by using a two-stage method rather than a monotonous tapering method in cancer patients whose higher-dose opioid with longer administration duration needed to be tapered and discontinued.

Background and purpose: Opiates are traditionally used for the treatment of pain. Chronic consumption of opiates such as morphine (MOR) induces tolerance and dependence. This study aimed to investigate the effects of valsartan (VAL), as an angiotensin II receptor blocker, on the induction and expression of MOR analgesic tolerance and physical dependence in rats. Experimental approach: MOR 10 mg/kg was injected s.c. twice a day for 7 days to induce tolerance and dependence. For evaluating the effect of VAL on the induction of MOR analgesic tolerance and physical dependence, 20 mg/kg VAL was administered orally (once a day) during the 7 days of the examination period. The tail-flick test was performed every day. On day 7, 5 mg/kg naloxone () was injected s.c. into the morphine-dependent rats and the rats were monitored for 30 min for the frequency of withdrawal signs such as jumping, diarrhea, defecation, head tremor, rearing, scratching, sniffing, teeth chattering, and wet-dog shake. For evaluating the effect of VAL on the expression of MOR-analgesic tolerance and physical dependence, 45 min before the last MOR injection, VAL was administered only on day 7. The tail-flick test was performed and naloxone was injected into the addicted rats and they were monitored for 30 min for the frequency of withdrawal signs such as jumping, diarrhea, defecation, head tremor, rearing, scratching, sniffing, teeth chattering, and wet-dog shake. Findings/Results: Our results revealed that the co-administration of VAL with MOR for 7 consecutive days reduced the induction of MOR tolerance. Moreover, VAL administration for 7 days along with MOR reduced the frequency of diarrhea and defecation in naloxone-injected animals. Conclusion and implications: According to the results presented in this study, chronic administration of VAL prevented the induction of MOR-analgesic tolerance and dependence in rats.

Opioid use disorder (OUD) is a major epidemic in the United States, and fentanyl is a major culprit. The National Institute on Drug Abuse has highlighted an urgent need for research on the risks and outcomes of OUD with fentanyl; a better understanding of sex/gender differences is also critically needed given that the opioid epidemic has been particularly impactful on women. In response to this need, we developed a rat model of OUD with fentanyl and showed that sex impacts relapse vulnerability following extended-access self-administration under a low fentanyl dose. Here, our goal was to determine sex differences across a broad dose range, including high doses expected to maximize the expression of addiction-like features (e.g., vulnerability to relapse and physical dependence). Male and female rats were assigned to self-administer one of four fentanyl doses (0.25, 0.75, 1.5, and 3.0 µg/kg/infusion), and once they acquired, they were given extended (24-h/day), intermittent access (2, 5 min trials/h, fixed-ratio 1) to fentanyl for 10 days. Physical dependence (spontaneous weight loss) was assessed during early withdrawal, and relapse vulnerability was assessed on withdrawal day 15 using an extinction/cue-induced reinstatement procedure. Despite markedly higher intake in the high- versus low-dose groups, each group responded similarly during relapse testing (extinction and cue-induced reinstatement). However, number of infusions, or frequency of use, during extended access was predictive of later vulnerability to relapse, whereas total intake impacted physical dependence given that weight loss only occurred following the discontinuation of fentanyl self-administration at the three highest doses. Females self-administered more fentanyl each day and within each binge (active trial), and had longer lasting weight loss during withdrawal than males. Relapse vulnerability was also higher in females than males and highest in females tested during estrus. These findings indicate that sex is an important risk factor for patterns and levels of fentanyl intake, relapse, and physical dependence, and while fentanyl intake predicts physical dependence, frequency of use predicts relapse. [ABSTRACT FROM AUTHOR]

Nociceptin opioid peptide (NOP) receptor modulates pain transmission and is considered a prospective target for pain management. Under acute pain conditions in rodents, however, no definitive conclusions about effects of systemically intervening NOP receptors on nociception, classical opioid-induced antinociception, tolerance and physical dependence have been drawn. Given that opioid analgesia has sex differences, and females experience greater pain and consume more opioids, clarifying these issues in females will help develop novel analgesics. To clarify the role of NOP receptors on the pharmacological profiles of µ-opioid receptor agonists, in this study, a selective agonist (SCH221510) and antagonist (SB612111) of the NOP receptor were subcutaneously administered in female mice in multiple animal models. In hot-plate test, neither SCH221510 (3 and 10 mg/kg, sc) nor SB612111 (10 mg/kg, sc) produced significant antinociception. SCH221510 (3 mg/kg, sc) attenuated but SB612111 (10 mg/kg, sc) enhanced morphine-induced antinociception, with rightward and leftward shift of morphine dose-response curves, respectively. SCH221510 (3 mg/kg, sc) combined with morphine (10 mg/kg, sc) accelerated the development of morphine antinociceptive tolerance. Conversely, SB612111 (10 mg/kg, sc) delayed morphine tolerance development. Neither SCH221510 (3 mg/kg, sc) nor SB612111 (10 mg/kg, sc) statistically significantly altered the development of morphine-induced physical dependence. Therefore, systemic activation of NOP receptors attenuated morphine antinociception to acute thermal stimuli, facilitated morphine-induced antinociceptive tolerance but did not robustly alter physical dependence in female mice. Systemic blockade of NOP receptors produced opposite actions. These findings demonstrate that N/OFQ-NOP receptor system plays diverse roles in modulating pharmacological profiles of µ-opioid receptor agonists. [ABSTRACT FROM AUTHOR]

Chronic administration of opioids produces physical dependence and opioid-induced hyperalgesia. Users claim the Thai traditional tea "kratom" and component alkaloid mitragynine ameliorate opioid withdrawal without increased sensitivity to pain. Testing these claims, we assessed the combined kratom alkaloid extract (KAE) and two individual alkaloids, mitragynine (MG) and the analog mitragynine pseudoindoxyl (MP), evaluating their ability to produce physical dependence and induce hyperalgesia after chronic administration, and as treatments for withdrawal in morphine-dependent subjects. C57BL/6J mice (n = 10/drug) were administered repeated saline, or graded, escalating doses of morphine (intraperitoneal; i.p.), kratom alkaloid extract (orally, p.o.), mitragynine (p.o.), or MP (subcutaneously, s.c.) for 5 days. Mice treated chronically with morphine, KAE, or mitragynine demonstrated significant drug-induced hyperalgesia by day 5 in a 48 °C warm-water tail-withdrawal test. Mice were then administered naloxone (10 mg/kg, s.c.) and tested for opioid withdrawal signs. Kratom alkaloid extract and the two individual alkaloids demonstrated significantly fewer naloxone-precipitated withdrawal signs than morphine-treated mice. Additional C57BL/6J mice made physically dependent on morphine were then used to test the therapeutic potential of combined KAE, mitragynine, or MP given twice daily over the next 3 days at either a fixed dose or in graded, tapering descending doses. When administered naloxone, mice treated with KAE, mitragynine, or MP under either regimen demonstrated significantly fewer signs of precipitated withdrawal than control mice that continued to receive morphine. In conclusion, while retaining some liabilities, kratom, mitragynine, and mitragynine pseudoindoxyl produced significantly less physical dependence and ameliorated precipitated withdrawal in morphine-dependent animals, suggesting some clinical value. [ABSTRACT FROM AUTHOR]

Bulleyaconitine A (BAA), a C19-diterpenoid alkaloid, has been prescribed as a nonnarcotic analgesic to treat chronic pain over four decades in China. The present study investigated its inhibition in morphine-induced withdrawal symptoms, conditioned place preference (CPP) and locomotor sensitization, and then explored the underlying mechanisms of actions. Multiple daily injections of morphine but not BAA up to 300 μg/kg/day into mice evoked naloxone-induced withdrawal symptoms (i.e., shakes, jumps, genital licks, fecal excretion and body weight loss), CPP expression, and locomotor sensitization. Single subcutaneous BAA injection (30–300 μg/kg) dose-dependently and completely attenuated morphine-induced withdrawal symptoms, with ED50 values of 74.4 and 105.8 μg/kg in shakes and body weight loss, respectively. Subcutaneous BAA (300 μg/kg) also totally alleviated morphine-induced CPP acquisition and expression and locomotor sensitization. Furthermore, subcutaneous BAA injection also specifically stimulated dynorphin A expression in microglia but not astrocytes or neurons in nucleus accumbens (NAc) and hippocampal, measured for gene and protein expression and double immunofluorescence staining. In addition, subcutaneous BAA-inhibited morphine-induced withdrawal symptoms and CPP expression were totally blocked by the microglial metabolic inhibitor minocycline, dynorphin A antiserum, or specific KOR antagonist GNTI, given intracerebroventricularly. These results, for the first time, illustrate that BAA attenuates morphine-induced withdrawal symptoms, CPP expression, and locomotor sensitization by stimulation of microglial dynorphin A expression in the brain, suggesting that BAA may be a potential candidate for treatment of opioids-induced physical dependence and addiction.

Purpose of Review: Pain is a multi-faceted symptom. Effective pain assessment involves properly defining the pain syndrome, utilizing various assessment tools, and recognizing different conditions which may affect the expression and the management of pain. Recent Findings: Pain results from multiple physical and psychosocial etiological interplay. It has traditionally been categorized as acute or chronic with chronic pain having been categorized further into 6 categories in ICD 11. At the same time, the opioid epidemic and the recent surge in cannabis popularity further complicates pain assessment and effective pain management. Summary: Adequate management of pain begins with proper assessment including conducting extensive medical and psychosocial history and physical examination, and utilizing various pain and substance risk assessment tools. An interdisciplinary team approach may be more effective in managing complex pain behaviors compared to a solo approach. [ABSTRACT FROM AUTHOR]

Chronic pain is associated with higher rates of psychiatric comorbidity, including substance use disorders. Patients with chronic pain often require opioids for their pain relief. Often, clinicians are reluctant to prescribe opioids to patients with chronic pain due to fear of patients becoming dependent on opioids. Diagnosing opioid addiction in chronic pain with comorbid prescription opioid use is challenging, as some of the symptoms of addiction overlap with those of physical dependence. A 28-year-old female presented with a history of recurrent abdominal pain beginning at the age of 16 years. The patient was diagnosed with chronic pancreatitis and was prescribed tramadol orally or injections for pain. The patient started experiencing craving with repeated administration of tramadol. She started using it daily and increased her dose to about 6-7 ampoules per day. She also developed complications due to injections. She was not able to work due to her pain, as well as injection use. She would go to multiple chemist shops for getting herself injected with tramadol injections. She also developed depressive symptoms in this period. Due to abdominal pain, the patient was admitted in the gastroenterology ward, from where she was shifted to the psychiatry ward for the management of opioid misuse and depressive symptoms. The patient was diagnosed to be suffering from opioid dependence syndrome with depressive episodes, for which she was provided tablet buprenorphine 14 mg/day dose along with tablet sertraline 150 mg/day. The case demonstrates several challenges in the diagnosis and management of opioid dependence and chronic pain when they occur simultaneously. [ABSTRACT FROM AUTHOR]

Background: Alcoholism is one of the most challenging public health problem in most of the countries including India. In India it has shown a prevalence of 15-60 % for alcoholism. The study was conducted to determine the severity of alcohol dependence and also to determine the relationship between severity of alcohol dependence and age of onset of drinking. Materials and Method: The study was conducted among above 18 year ols males from rural field practice area attached to SSIMS & RC, Davangere. Systematic random sampling was used to select the houses. Participants were interviewed for socio-demographic and alcohol related information with the use of pre-tested questionnaire. Written consent was taken before starting the study. AUDIT and SADQ was used. Results: Total 265 participants were included in this study. 77% participants started drinking at the age of 18-20years. 57% participants showed the mild physical dependence. Severity of alcohol dependence is shown in those who have started drinking in early age. Conclusion: Majority of participants were young to start drinking alcohol and early initiation of alcohol showed the mild physical dependence among them.

Opiate tolerance and dependence is a worldwide public health problem and gives a significant burden to society. The aim of this study was to evaluate the effects of metformin (MET) on development and expression of morphine tolerance and dependence in rats. For induction of tolerance, morphine sulfate was injected (10 mg/kg, twice a day, s.c.) for 7 days. Animals received metformin (5 and 50 mg/kg, orally, daily) during the examination period for assessing the development of morphine tolerance and dependence. In order to evaluate the expression of morphine tolerance and dependence, single doses of MET (5 and 50 mg/kg, orally) were administered on day 7. Tail flick test was performed to assess the induction of morphine tolerance. For evaluation of morphine dependence, naloxone-induced jumping (5 mg/kg, s.c.) was monitored. Our results showed that 7 days coadministration of 50 mg/kg of MET significantly reduced the development of morphine analgesic tolerance versus morphine + saline treated rats (P < 0.001). Treatment with 50 mg/kg MET reduced the incidence and frequency of jumping in naloxone injected animals (P < 0.01). It is notable that single dose administration of MET, did not prevent the expression of analgesic tolerance and physical dependence to morphine. Based on these results, it can be concluded that MET attenuates the development of morphine analgesic tolerance and dependence in rats.

Background & Objective: Coriandrum sativum L (CS) has different pharmacological properties such as analgesic, anti-inflammatory, and anti-stress effects. Hence, in the present study the effects of CS essential oil on naloxone -induced jumping in morphine-dependent mice was investigated. Material & Methods: In this experimental study, 60 male albino mice were used. The animals were divided into 10 groups of 6, including carrier (10 ml/kg), clonidine (3.5 mg/kg), and different doses of CS essential oil (400, 600, and 800 mg/kg). Tolerance and dependency on morphine were induced by administration of different doses of morphine (50, 50, 75, and 50 mg/kg, respectively) in a 4-day schedule. On the last day, after administration of single dose of morphine, Naloxone (5 mg /kg) was injected and the number of jumps was recorded within 30 minutes. Results: Results showed that all doses of CS essential oil and clonidine, compared to control group, significantly decreased the number of jumping in both tolerance and dependence stage (P

Introduction: Previous studies revealed that anise (Pimpinella anisum L.) has several pharmacological effects including analgesic, antidepressant, anxiolytic, anti-inflammatory and antispasmodic activities. This study aimed to evaluate its effect on morphine physical dependence in mice. Methods: In this experimental study, 40 male NMRI mice (25-30 g) were randomly divided into 5 groups of 8. Control group received morphine and normal saline (10 mL/kg, i.p.) and other groups received diazepam (5 mg/kg) plus one of three doses of P. anisum (50,100 or 200 mg/kg, i.p.). Dependence was induced by administration of increasing doses (50-75 mg/kg, i.p.) of morphine. A time of 30 minutes after naloxone injection was considered for the critical period of the withdrawal syndrome. The number of jumps and scores of 0 to 3 were given for incidences of wet dog shakes, teeth chattering, climbing, writing, diarrhea, grooming, and rearing during a 30-minute period. Results: All doses of P. anisum (P < 0.01) reduced the number of jumps. Additionally, all doses of the extract reduced the behaviors of grooming (P < 0.05, P < 0.01 and P < 0.01, respectively) and writhing (P < 0.05, P < 0.001and P < 0.001, respectively). None doses of the extract could reduce diarrhea (P > 0.05). Climbing, rearing and wet dog shakes reduced only by the high dose of the extract (P < 0.05). Teeth chattering reduced by 100 and 200 mg/kg of the extract (P < 0.05). Conclusion: These results obviously show that P. anisum ethanolic extract is effective in suppression of morphine physical dependence and further studies are needed to find out the responsible constituents and also the exact mechanisms of actions.