Cellular neuroadaptations to chronic opioids: tolerance, withdrawal and addiction

The effect of intracerebroventricular injection of melatonin on the period of acquisition, expression, extinction, and reinstatement of morphine conditioned place preference in the male rat: A behavioral and biochemical study

BACKGROUND

Behavior in both humans and animals is significantly influenced by the brain's reward system. Many studies have shown that this dopaminergic system is the root of drug addiction and abuse. Melatonin, an indoleamine neurohormone, has been studied for its potential negative effects on addictive drugs such as morphine. This study evaluates the effect of intraventricular melatonin injection during different phases of morphine conditioning.

METHOD

Rats were conditioned with morphine [5 mg/kg; subcutaneously (SC)] for three days. The changes in conditioned place preference (CPP) scores following the injection of different doses of melatonin [25, 50, and 100 μg/kg; intracerebroventricular (ICV)] were investigated during the acquisition, expression, extinction, and reinstatement phases of morphine conditioning. After completing these steps, the c-Fos level in the nucleus accumbens (NAc) was measured using the ELISA technique.

RESULT

The results indicated that daily injections of 50 and 100 μg/kg melatonin during the acquisition and expression phases caused a dose-dependent decrease in the conditioning score. During the extinction phase, melatonin administration reduced its duration incrementally. Notably, only the 100 μg/kg dose significantly decreased morphine reinstatement. In terms of c-Fos levels, which were elevated after morphine consumption, melatonin administration led to a significant reduction across all phases.

CONCLUSION

This study demonstrates the neural interaction between melatonin and the opioid system. The evidence suggests that melatonin may be effective at decreasing drug-related rewards and has potential utility in preventing addiction.

Involvement of CXCL12/CXCR4 in CB2 receptor agonist-attenuated morphine tolerance in Walker 256 tumor-bearing rats with cancer pain

While low-dose cannabinoid 2 (CB2) receptor agonists attenuate morphine tolerance in cancer pain models, chemokine ligand 12 (CXCL12)/chemokine receptor 4 (CXCR4) expression induces morphine tolerance. Whether CB2 receptor agonists attenuate morphine tolerance by modulating CXCL12/CXCR4 signaling or whether CXCL12/CXCR4 signaling affects the mu opioid receptor (MOR) in the development of morphine tolerance in cancer pain remains unclear. In this study, we investigated the attenuation of morphine tolerance by a non-analgesic dose of the CB2 receptor agonist AM1241, focusing specifically on the modulation of CXCL12/CXCR4 signaling and its effect on the MOR. Rats received intrathecal Walker 256 tumor cell implantations and were treated with morphine combined with the intrathecal injection of AM1241 or the CB2 receptor antagonists AM630 and AM1241, or a CXCL12-neutralizing antibody, exogenous CXCL12, or the CXCR4 antagonist AMD3100. Our results show that CXCL12 and CXCR4 levels increased significantly in morphine-tolerant rats and were reduced by AM1241 pretreatment, which was reversed by AM630. CXCL12/CXCR4 expression accelerated the development of morphine tolerance and downregulated MOR expression. CXCR4 colocalized with MOR and CB2. Therefore, a non-analgesic dose of AM1241 attenuated morphine tolerance via CXCL12/CXCR4 signaling, whereas CXCL12/CXCR4 signaling participated in the development of morphine tolerance, potentially by modulating MOR expression in Walker 256 tumor-bearing rats.

Genomic factors associated with substance use disorder relapse: A critical review

Several genetic and epigenetic factors contribute to the elevated substance use disorder (SUD) relapse vulnerability, yet a comprehensive investigation into these factors is lacking. This review aims to delve into current literature to highlight key genomic factors associated with SUD relapse. Focusing on genetic predisposition and epigenetic modifications the review synthesized research findings of several genetic polymorphisms, histone modifications and DNA methylation patterns contributing to the initiation of SUD and the elevated relapse susceptibility. Notably, specific gene polymorphisms, such as Dopamine Receptor D2 gene (DRD2), Gamma-Aminobutyric Acid Receptor Alpha gene (GABRA2), Catechol-O-methyltransferase (COMT) gene, Dopamine Transporter (DAT1) gene and others were identified to be connected to various patterns of SUD relapse. Furthermore, SUD initiation and relapse has been shown to be influenced by epigenetics. Specifically, CpG hypermethylation has been associated with severe alcohol use disorder in the 5' untranslated region of the Bladder Cancer Associated Protein gene (BLCAP) and the upstream region of the Active BCR Related gene (ABR). Co-users of cannabis and tobacco showed notable variations in CpG site methylation, especially at the Aryl Hydrocarbon Receptor Repressor (AHRR), and factor II receptor-like 3 gene sites (F2RL3). In conclusion, there is good evidence of certain associations between genomic factors and relapse to SUD. However, further research is needed to ascertain causality effects of these factors and develop novel interventions for effective treatment and relapse prevention.

Alterations in Volume and Intrinsic Resting-State Functional Connectivity Detected at Brain MRI in Individuals with Opioid Use Disorder

Background Structural and functional MRI studies have revealed brain alterations associated with opioid use disorder (OUD). However, previous research has been limited by small sample sizes, few female participants, and single-modality analyses. Purpose To identify structural and functional brain alterations in individuals with OUD using whole-brain data-driven methods to analyze T1-weighted MRI and resting-state functional MRI (rsfMRI). Materials and Methods This secondary analysis of the Collaboration Linking Opioid Use Disorder and Sleep study compared participants with OUD (data collection February 2021 to February 2023) receiving methadone treatment with healthy control participants (data collection February 2018 to May 2023). T1-weighted MRI and rsfMRI were analyzed using tensor-based morphometry and intrinsic connectivity distribution, respectively. Primary outcome measures included regional brain volumes and functional connectivity. Voxel-wise linear regression was used to assess group differences, with family-wise error correction. Pearson partial correlations were used to examine structure-function relationships. Results Compared with healthy control participants (n = 105; median age, 27 years [IQR, 23-37 years]; 58 female), participants with OUD (n = 103; median age, 37 years [IQR, 31.5-46 years]; 62 male) showed smaller volumes (corrected P < .05) in the thalamus (β = -17.42 [95% CI: -26.56, -8.27]) and right medial temporal lobe (β = -8.02 [95% CI: -12.25, -3.78]). Larger volumes (corrected P < .05) were seen in the brainstem (pons and medulla, β = 15.21 [95% CI: 7.03, 23.40]; midbrain, β = 13.04 [95% CI: 6.61, 19.47]) and cerebellum (right, β = 14.96 [95% CI: 7.25, 22.67]; left, β = 14.88 [95% CI: 7.32, 22.43]). An interaction between sex and group was found for medial prefrontal cortex volume (β = -19.38, corrected P < .05), with female participants having smaller volumes than male participants in the OUD group. Increased functional connectivity (corrected P < .05) was noted in the thalamus (β = 0.50 [95% CI: 0.25, 0.75]), right medial temporal lobe (β = 0.43 [95% CI: 0.21, 0.66]), right cerebellum (β = 0.46 [95% CI: 0.21, 0.71]), and brainstem (β = 0.48 [95% CI: 0.22, 0.74]) in the OUD group. Structure and function were positively correlated in the cerebellum (Pearson r = 0.32 [95% CI: 0.17, 0.44], P < .001) and brainstem (Pearson r = 0.23 [95% CI: 0.09, 0.37], P = .002). Conclusion Individuals with OUD showed overlapping structural and functional brain alterations in opioid receptor-dense regions compared with healthy control participants. © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Filippi and Messina in this issue.

Alterations in Circular RNAs circOprm1 and circSerpini in the Striatum are Associated with Changes in Spatial Working Memory Performance after Morphine Dependence and Withdrawal in Rats

Modulating role of circRNAs and microRNAs in neurobiological changes induced by drug exposure remains unclear. We examined alterations in some circRNAs and microRNAs in the striatum after morphine dependence and withdrawal and their associations with the changes in spatial working memory performance. Male Wistar rats were used in which 10 days morphine exposure induced dependence. Withdrawal effects were assessed 30 days after stopping morphine exposure. Spatial working memory was assessed using a Y maze test on days 1 and 10 of the drug exposure and 30 days after withdrawal. The gene and protein expression were assessed after dependence and withdrawal. The results revealed that 10 days morphine exposure impaired working memory, which partially reinstated after withdrawal. After 10 days morphine exposure, significant increases in Oprm1 gene and OPRM1 protein levels were detected, which persisted even after withdrawal. The expression of circOprm1 and miR-339-3p decreased in the morphine-dependent group, but they returned to normal levels after withdrawal. The expression of Tlr4 gene and TLR4 protein levels decreased after dependence. While Tlr4 mRNA levels returned to normal after withdrawal, TLR4 protein levels remained lower than the control group. In the morphine-dependent group, both Serpini1 and circSerpini expression significantly increased, but they restored after withdrawal. Expression of miR-181b-3p, miR-181b-5p, miR-181c-3p, and miR-181c-5p decreased after dependence, but they reinstated after withdrawal. It can be concluded that circOprm1 and circSerpini via regulating the OPRM1 and TLR4 expression in the striatum are associated with the neuroadaptation underlying spatial working memory after both morphine dependence and withdrawal.

FLT3 signaling inhibition abrogates opioid tolerance and hyperalgesia while preserving analgesia

Navigating the duality of opioids' potent analgesia and side effects, including tolerance and hyperalgesia, is a significant challenge in chronic pain management, often prompting hazardous dose escalation to maintain analgesic effects. The peripheral mu-opioid receptor (MOR) is known to mediate these contradictory effects. Here, we show that the fms-like tyrosine kinase receptor 3 (FLT3) in peripheral somatosensory neurons drives morphine tolerance and hyperalgesia in a male rodent model. We found that chronic morphine treatment increases FLT3 and MOR co-expression, and that inhibiting FLT3 represses MOR-induced hyperactivation of the cyclic adenosine monophosphate (cAMP) signaling pathway, mitigating maladaptive excitatory processes engaged after chronic morphine treatment. Furthermore, in postsurgical or inflammatory models of chronic pain, co-administering morphine with a FLT3-specific inhibitor not only prevents or suppresses tolerance and hyperalgesia but also potentiates the analgesic efficacy of morphine, without aggravating other morphine-induced adverse effects. Our findings suggest that pairing morphine with FLT3 inhibitors could become a promising avenue for chronic pain management to safely harness the power of opioids, without the risk of dose escalation. By enhancing morphine analgesic potency through FLT3 inhibition, this approach could minimize opioid dosage, thereby curtailing the risk of addiction and other opioid-related side effects.

Therapeutic Potential of Psychedelic Compounds for Substance Use Disorders

Psychedelics have recently (re)emerged as therapeutics of high potential for multiple mental health conditions, including substance use disorders (SUDs). Despite early mid-20th century anecdotal reports and pilot studies demonstrating the possibility of these substances in efficaciously treating conditions such as alcohol and opioid use disorders, legal restrictions and social stigma have historically hindered further research into this area. Nevertheless, concurrent with the rise in SUDs and other mental health conditions, researchers have again turned their attention to these compounds, searching for differing pharmacological targets as well as more holistic treatments that might increase patient adherence and efficacy. The aim of this review is to examine the emerging evidence-based data with regards to the therapeutic treatment of SUDs with the psychedelic compounds psilocybin, ketamine, lysergic acid diethylamide (LSD), 3,4-methylenedioxymethamphetamine (MDMA), ayahuasca, ibogaine and peyote.

Opioid system and related ligands: from the past to future perspectives

Chronic pain is a pathological condition affecting about 30% of population. It represents a relevant social-health issue worldwide, and it is considered a significant source of human suffering and disability, strongly affecting patients' quality of life. Despite several pharmacological strategies to guarantee an adequate pain management have been proposed over the years, opioids still represent one of the primary choices for treating moderate-to-severe pain in both cancer and non-cancer patients. However, chronic use of opioids often leads to numerous side effects, including respiratory depression, constipation, analgesic tolerance, and opioid-induced hyperalgesia (OIH), which can strongly limit their use. Given the fundamental role of opioid system in pain relief, this review provides a general overview about the main actors (endogenous opioid peptides and receptors) involved in its modulation. Furthermore, this review explores the action and the limitations of conventional clinically used opioids and describes the efficacy and safety profile of some promising analgesic compounds. A deeper understanding of the molecular mechanisms behind both analgesic effects and adverse events could advance knowledge in this field, thus improving chronic pain treatment.

Elucidating the molecular symphony: unweaving the transcriptional & epigenetic pathways underlying neuroplasticity in opioid dependence and withdrawal

The persistent use of opioids leads to profound changes in neuroplasticity of the brain, contributing to the emergence and persistence of addiction. However, chronic opioid use disrupts the delicate balance of the reward system in the brain, leading to neuroadaptations that underlie addiction. Chronic cocaine usage leads to synchronized alterations in gene expression, causing modifications in the Nucleus Accumbens (NAc), a vital part of the reward system of the brain. These modifications assist in the development of maladaptive behaviors that resemble addiction. Neuroplasticity in the context of addiction involves changes in synaptic connectivity, neuronal morphology, and molecular signaling pathways. Drug-evoked neuroplasticity in opioid addiction and withdrawal represents a complicated interaction between environmental, genetic, and epigenetic factors. Identifying specific transcriptional and epigenetic targets that can be modulated to restore normal neuroplasticity without disrupting essential physiological processes is a critical consideration. The discussion in this article focuses on the transcriptional aspects of drug-evoked neuroplasticity, emphasizing the role of key transcription factors, including cAMP response element-binding protein (CREB), ΔFosB, NF-kB, Myocyte-enhancing factor 2 (MEF2), Methyl-CpG binding protein 2 (MeCP2), E2F3a, and FOXO3a. These factors regulate gene expression and lead to the neuroadaptive changes observed in addiction and withdrawal. Epigenetic regulation, which involves modifying gene accessibility by controlling these structures, has been identified as a critical component of addiction development. By unraveling these complex molecular processes, this study provides valuable insights that may pave the way for future therapeutic interventions targeting the mechanisms underlying addiction and withdrawal.

3,3-Dibromoflavanone, a synthetic flavonoid derivative for pain management with antidepressant-like effects and fewer side effects than those of morphine in mice

In the pursuit of new lead compounds with fewer side effects than opioids, the novel synthetic phytochemical core, 3,3-dibromoflavanone (3,3-DBF), has emerged as a promising candidate for pain management. Acute assays demonstrated dose-dependent central and peripheral antinociceptive activity of 3,3-DBF through the μ-opioid receptor. This study aimed to explore repeated administration effects of 3,3-DBF in mice and compare them with morphine. Mice were treated with 3,3-DBF (30 mg/kg), morphine (6 mg/kg), or vehicle for 10 days, alongside single-treatment groups. Unlike morphine, 3,3-DBF demonstrated antinociceptive effects in the hot plate test without inducing tolerance. Locomotor activity and motor coordination tests (evaluated through the inverted screen and rotarod tests) revealed no significant differences between the 3,3-DBF-treated and control groups. The gastrointestinal transit assay indicated that 3,3-DBF did not induce constipation, in contrast to morphine. Furthermore, withdrawal signs assessed with the Gellert-Holtzman scale were not comparable to morphine. Additionally, 3,3-DBF exhibited antidepressant-like activity, reducing immobility time in the forced swimming and tail suspension tests, akin to imipramine. In summary, 3,3-DBF demonstrated antinociceptive effects without inducing tolerance or dependence and exhibited antidepressant properties. These findings highlight the potential of 3,3-DBF as a promising therapeutic agent for pain management and its comorbidities, offering advantages over morphine by minimizing side effects.

The Inflammation/NF-κB and BDNF/TrkB/CREB Pathways in the Cerebellum Are Implicated in the Changes in Spatial Working Memory After Both Morphine Dependence and Withdrawal in Rat

We aimed to explore the impact of the cerebellum on the decline in spatial working memory following morphine dependence and withdrawal. Two groups of male Wistar rats received intraperitoneal injections of either saline (1 ml/kg) or morphine (10 mg/kg) twice daily for 10 days, serving as the control and dependent groups. Additionally, a withdrawal group underwent a 30-day withdrawal period after the dependence phase. Spatial working memory was assessed using a Y maze test. ELISA and western blot were used to assess protein levels in the cerebellum. On day 1, morphine impaired spatial working memory, deteriorated further after 10 days of morphine use, and nearly returned to its initial level following a 30-day withdrawal period. On day 10, significant increases in TNF-α, IL-1β, and CXCL12 and a notable decrease in IL-10 levels were detected in the morphine-dependent group, which did not completely restore in the withdrawal group. The protein levels of CXCR4, TLR4, P2X7R, and NF-κB sharply increased in the morphine-dependent group. However, these levels almost returned to normal after withdrawal. In the morphine-dependent group, BDNF decreased, while TrkB and CREB1 increased noticeably. Nevertheless, after withdrawal, TrkB and CREB1 but not BDNF levels returned to normal. In the morphine-dependent group, both CACNA1 and KCNMA1 decreased significantly and after withdrawal, only KCNMA1 showed partial restoration, while CACNA1 did not. It can be concluded that inflammation/NF-κB and BDNF/TrkB/CREB pathways play key roles in neural adaptation within the cerebellum, contributing to the decline in spatial working memory after both morphine dependence and withdrawal.

The epigenetic signatures of opioid addiction and physical dependence are prevented by D-cysteine ethyl ester and betaine

We have reported that D,L-thiol esters, including D-cysteine ethyl ester (D-CYSee), are effective at overcoming opioid-induced respiratory depression (OIRD) in rats. Our on-going studies reveal that co-injections of D-CYSee with multi-day morphine injections markedly diminish spontaneous withdrawal that usually occurs after cessation of multiple injections of morphine in rats. Chronically administered opioids are known (1) to alter cellular redox status, thus inducing an oxidative state, and (2) for an overall decrease in DNA methylation, therefore resulting in the transcriptional activation of previously silenced long interspersed elements (LINE-1) retrotransposon genes. The first objective of the present study was to determine whether D-CYSee and the one carbon metabolism with the methyl donor, betaine, would maintain redox control and normal DNA methylation levels in human neuroblastoma cell cultures (SH-SY5Y) under overnight challenge with morphine (100 nM). The second objective was to determine whether D-CYSee and/or betaine could diminish the degree of physical dependence to morphine in male Sprague Dawley rats. Our data showed that overnight treatment with morphine reduced cellular GSH levels, induced mitochondrial damage, decreased global DNA methylation, and increased LINE-1 mRNA expression. These adverse effects by morphine, which diminished the reducing capacity and compromised the maintenance of the membrane potential of SH-SY5Y cells, was prevented by concurrent application of D-CYSee (100 µM) or betaine (300 µM). Furthermore, our data demonstrated that co-injections of D-CYSee (250 μmol/kg, IV) and to a lesser extent, betaine (250 μmol/kg, IV), markedly diminished the development of physical dependence induced by multi-day morphine injections (escalating daily doses of 10-30 mg/kg, IV), as assessed by the lesser number of withdrawal phenomena elicited by the injection of the opioid receptor antagonist, naloxone (1.5 mg/kg, IV). These findings provide evidence that D-CYSee and betaine prevent the appearance of redox alterations and epigenetic signatures commonly seen in neural cells involved in opioid physical dependence/addiction, and lessen development of physical dependence to morphine.

The cell-permeant antioxidant D-thiol ester D-cysteine ethyl ester overcomes physical dependence to morphine in male Sprague Dawley rats

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.

Long-term efficacy and reduced side-effects of buprenorphine in patients with moderate and severe chronic pain

Background

Chronic pain significantly impacts quality of life and poses substantial public health challenges. Buprenorphine, a synthetic analog of thebaine, is recognized for its potential in managing moderate to severe chronic pain with fewer side effects and a lower incidence of tolerance compared to traditional opioids.

Objective

This retrospective study aimed to assess the long-term efficacy and safety of buprenorphine transdermal patches in patients with moderate and severe chronic pain, with a focus on pain relief sustainability and tolerance development.

Methods

This retrospective observational study involved 246 patients prescribed buprenorphine transdermal patches. We evaluated changes in pain intensity using the Numeric Rating Scale (NRS), assessed opioid tolerance based on FDA guidelines for morphine-equivalent doses, and measured patient-reported outcomes through the Patients' Global Impression of Change (PGIC). Any adverse events were also recorded.

Results

Over the 36-month period, there was a significant reduction in NRS scores for both moderate and severe pain patients, demonstrating buprenorphine's sustained analgesic effect. Tolerance measurement indicated that no patients required increases in morphine-equivalent doses that would meet or exceed the FDA's threshold for opioid tolerance (60 mg/day of morphine or equivalent). Additionally, patient satisfaction was high, with the PGIC reflecting significant improvements in pain management and overall wellbeing. The side effects were minimal, with skin reactions and nausea being the most commonly reported but manageable adverse events.

Conclusion

The study findings validate the long-term use of buprenorphine transdermal patches as an effective and safe option for chronic pain management, maintaining efficacy without significant tolerance development. These results support the continued and expanded use of buprenorphine in clinical settings, emphasizing its role in reducing the burdens of chronic pain and opioid-related side effects. Further research is encouraged to refine pain management protocols and explore buprenorphine's full potential in diverse patient populations.

A historical perspective on clonidine as an alpha-2A receptor agonist in the treatment of addictive behaviors: Focus on opioid dependence

Clonidine operates through agonism at the alpha-2A receptor, a specific subtype of the alpha-2-adrenergic receptor located predominantly in the prefrontal cortex. By inhibiting the release of norepinephrine, which is responsible for withdrawal symptoms, clonidine effectively addresses withdrawal-related conditions such as anxiety, hypertension, and tachycardia. The groundbreaking work by Gold et al. demonstrated clonidine's ability to counteract the effects of locus coeruleus stimulation, reshaping the understanding of opioid withdrawal within the field. In the 1980s, the efficacy of clonidine in facilitating the transition to long-acting injectable naltrexone was confirmed for individuals motivated to overcome opioid use disorders (OUDs), including physicians and executives. Despite challenges with compliance, naltrexone offers sustained blockade of opioid receptors, reducing the risk of overdose, intoxication, and relapse in motivated patients in recovery. The development of clonidine and naltrexone as treatment modalities for OUDs, and potentially other addictions, including behavioral ones, underscores the potential for translating neurobiological advancements from preclinical models (bench) to clinical practice (bedside), ushering in innovative approaches to addiction treatment.

Neuropsychiatric Effects Associated with Opioid-Based Management for Palliative Care Patients

PURPOSE OF REVIEW

The abundance of opioids administered in the palliative care setting that was once considered a standard of care is at present necessitating that providers evaluate patients for unintentional and deleterious symptomology related to aberrant opioid use and addiction. Polypharmacy with opioids is dynamic in affecting patients neurologically, and increased amounts of prescriptions have had inimical effects, not only for the individual, but also for their families and healthcare providers. The purpose of this review is to widen the perspective of opioid consequences and bring awareness to the numerous neuropsychiatric effects associated with the most commonly prescribed opioids for patients receiving palliative care.

RECENT FINDINGS

Numerous clinical and research studies have found evidence in support for increased incidence of opioid usage and abuse as well as undesirable neurological outcomes. The most common and concerning effects of opioid usage in this setting are delirium and problematic drug-related behavioral changes such as deceitful behavior towards family and physicians, anger outbursts, overtaking of medications, and early prescription refill requests. Other neuropsychiatric effects detailed by recent studies include drug-seeking behavior, tolerance, dependence, addictive disorder, anxiety, substance use disorder, emotional distress, continuation of opioids to avoid opioid withdrawal syndrome, depression, and suicidal ideation. Opioid usage has detrimental and confounding effects that have been overlooked for many years by palliative care providers and patients receiving palliative care. It is necessary, even lifesaving, to be cognizant of potential neuropsychiatric effects that opioids can have on an individual, especially for those under palliative care. By having an increased understanding and awareness of potential opioid neuropsychiatric effects, patient quality of life can be improved, healthcare system costs can be decreased, and patient outcomes can be met and exceeded.

Does Tramadol Exposure Have Unfavorable Effects on Hippocampus? A Review Study

Background

Tramadol, one of the most common opioid pain relievers, acts upon the µ-receptor in the central nervous system (CNS) to alleviate pain associated with various situations like postoperative pain, arthritis, and muscular pain. Additionally, it has been utilized to address depression and anxiety disorders. Extensive research has shown that tramadol can potentially inflict irreversible harm on different regions of the CNS, including the cerebrum, cerebellum, amygdala, and, notably, the hippocampal formation. However, the precise mechanism behind these effects remains unclear. Within this study, we conducted a comprehensive examination of the impacts of tramadol on the CNS, specifically focusing on hippocampal formation.

Methods

In this study, we collected relevant articles published between 2000 and 2022 by conducting searches using specific keywords, including tramadol, tramadol hydrochloride, central nervous system, hippocampus, and hippocampal formation, in various databases.

Findings

The results of this study proposed several processes by which tramadol may impact the CNS, including the induction of apoptosis, autophagy, excessive production of free radicals, and dysfunction of cellular organelles. These processes ultimately lead to disturbances in neural cell function, particularly within the hippocampus. Furthermore, it is revealed that tramadol administration led to a significant decrease in the neural cell count and the volume of various regions within the brain and spinal cord.

Conclusion

Consequently, neuropsychological impairments, such as memory formation, attention deficits, and cognitive impairment, may happen. This finding highlights the potential impacts of tramadol on neural structures and warrants further investigation.

Biasing Gβγ Downstream Signaling with Gallein Inhibits Development of Morphine Tolerance and Potentiates Morphine-Induced Nociception in a Tolerant State

Opioid analgesics are widely used as a treatment option for pain management and relief. However, the misuse of opioid analgesics has contributed to the current opioid epidemic in the United States. Prescribed opioids such as morphine, codeine, oxycodone, and fentanyl are mu-opioid receptor (MOR) agonists primarily used in the clinic to treat pain or during medical procedures, but development of tolerance limits their utility for treatment of chronic pain. Here we explored the effects of biasing Gβγ signaling on tolerance development after chronic morphine treatment in vivo. We hypothesized that biasing Gβγ signaling with gallein could prevent activation of regulatory signaling pathways that result in tolerance to antinociceptive effects of MOR agonists. Gallein has been shown to bind to Gβγ and inhibit interactions of Gβγ with phospholipase-Cβ3 (PLCβ3) or G-protein-coupled receptor kinase 2 (GRK2) but not G-protein inwardly rectifying potassium (GIRK) channels. In mice, morphine-induced antinociception was evaluated in the 55°C warm water tail withdrawal assay. We used two paradigms for gallein treatment: administration during and after three times-daily morphine administration. Our results show that gallein cotreatment during repeated administration of morphine decreased opioid tolerance development and that gallein treatment in an opioid-tolerant state enhanced the potency of morphine. Mechanistically, our data suggest that PLCβ3 is necessary for potentiating effects of gallein in an opioid-tolerant state but not in preventing the development of tolerance. These studies demonstrate that small molecules that target Gβγ signaling could reduce the need for large doses of opioid analgesics to treat pain by producing an opioid-sparing effect. SIGNIFICANCE STATEMENT: Biasing Gβγ signaling prevents tolerance to repeated morphine administration in vivo and potentiates the antinociceptive effects of morphine in an opioid-tolerant state. Mechanistically, phospholipase-Cβ is necessary for potentiating effects of gallein in an opioid-tolerant state but not in preventing the development of tolerance. This study identifies a novel treatment strategy to decrease the development of tolerance to the analgesic effects of mu-opioid receptor agonists, which are necessary to improve pain treatment and decrease the incidence of opioid use disorder.

Repeated Morphine Exposure Alters Temporoamonic-CA1 Synaptic Plasticity in Male Rat Hippocampus

In this study, the electrophysiological and biochemical consequences of repeated exposure to morphine in male rats on glutamatergic synaptic transmission, synaptic plasticity, the expression of GABA receptors and glutamate receptors at the temporoammonic-CA1 synapse along the longitudinal axis of the hippocampus (dorsal, intermediate, ventral, DH, IH, VH, respectively) were investigated. Slice electrophysiological methods, qRT-PCR, and western blotting techniques were used to characterize synaptic plasticity properties. We showed that repeated morphine exposure (RME) reduced excitatory synaptic transmission and ability for long-term potentiation (LTP) in the VH as well as eliminated the dorsoventral difference in paired-pulse responses. A decreased expression of NR2B subunit in the VH and an increased expression GABAA receptor of α1 and α5 subunits in the DH were observed following RME. Furthermore, RME did not affect the expression of NR2A, AMPA receptor subunits, and γ2GABAA and GABAB receptors in either segment of the hippocampus. In sum, the impact of morphine may differ depending on the region of the hippocampus studied. A distinct change in the short- and long-term synaptic plasticity along the hippocampus long axis due to repeated morphine exposure, partially mediated by a change in the expression profile of glutamatergic receptor subunits. These findings can be useful in further understanding the cellular mechanism underlying deficits in information storage and, more generally, cognitive processes resulting from chronic opioid abuse.

Lipophilic analogues of D-cysteine prevent and reverse physical dependence to fentanyl in male rats

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.

Small G-Protein Rheb Gates Mammalian Target of Rapamycin Signaling to Regulate Morphine Tolerance in Mice

BACKGROUND

Analgesic tolerance due to long-term use of morphine remains a challenge for pain management. Morphine acts on μ-opioid receptors and downstream of the phosphatidylinositol 3-kinase signaling pathway to activate the mammalian target of rapamycin (mTOR) pathway. Rheb is an important regulator of growth and cell-cycle progression in the central nervous system owing to its critical role in the activation of mTOR. The hypothesis was that signaling via the GTP-binding protein Rheb in the dorsal horn of the spinal cord is involved in morphine-induced tolerance.

METHODS

Male and female wild-type C57BL/6J mice or transgenic mice (6 to 8 weeks old) were injected intrathecally with saline or morphine twice daily at 12-h intervals for 5 consecutive days to establish a tolerance model. Analgesia was assessed 60 min later using the tail-flick assay. After 5 days, the spine was harvested for Western blot or immunofluorescence analysis.

RESULTS

Chronic morphine administration resulted in the upregulation of spinal Rheb by 4.27 ± 0.195-fold (P = 0.0036, n = 6), in turn activating mTOR by targeting rapamycin complex 1 (mTORC1). Genetic overexpression of Rheb impaired morphine analgesia, resulting in a tail-flick latency of 4.65 ± 1.10 s (P < 0.0001, n = 7) in Rheb knock-in mice compared to 10 s in control mice (10 ± 0 s). Additionally, Rheb overexpression in spinal excitatory neurons led to mTORC1 signaling overactivation. Genetic knockout of Rheb or inhibition of mTORC1 signaling by rapamycin potentiated morphine-induced tolerance (maximum possible effect, 52.60 ± 9.56% in the morphine + rapamycin group vs. 16.60 ± 8.54% in the morphine group; P < 0.0001). Moreover, activation of endogenous adenosine 5'-monophosphate-activated protein kinase inhibited Rheb upregulation and retarded the development of morphine-dependent tolerance (maximum possible effect, 39.51 ± 7.40% in morphine + metformin group vs. 15.58 ± 5.79% in morphine group; P < 0.0001).

CONCLUSIONS

This study suggests spinal Rheb as a key molecular factor for regulating mammalian target of rapamycin signaling.

EDITOR’S PERSPECTIVE

Rethinking ketamine as a panacea: adverse effects on oxygenation and postoperative outcomes

Ketamine is receiving renewed interest in perioperative medicine as an anaesthetic adjunct and a treatment for chronic conditions, including depression. Ketamine's complex pharmacologic profile results not only in several desirable effects, such as anaesthesia and analgesia, but also multiple adverse effects affecting the central nervous, cardiovascular, and respiratory systems. In addition to defining patient-centred outcomes in future clinical studies on the perioperative uses of ketamine, careful monitoring for its numerous adverse effects will be paramount.

Amiloride alleviates morphine tolerance by suppressing ASIC3-dependent neuroinflammation in the spinal cord

BACKGROUND

The use of morphine in clinical medicine is severely constrained by tolerance. Therefore, it is essential to examine pharmacological therapies that suppress the development of morphine tolerance. Amiloride suppressed the expression of inflammatory cytokines by inhibiting microglial activation. Microglia play a crucial role in the establishment of morphine tolerance. Thus, we anticipated that amiloride might suppress the development of morphine tolerance. During this investigation, we assessed the impact of amiloride on mouse morphine tolerance.

METHODS

Mice received morphine (10 mg/kg, s.c.) twice daily with intrathecally injected amiloride (0.3 μg/5 μl, 1 μg/5 μl, and 3 μg/5 μl) for nine continuous days. To assess morphine tolerance, mice underwent the tail-flick and hot plate tests. BV-2 cells were used to investigate the mechanism of amiloride. By using Western blotting, real-time PCR, and immunofluorescence labeling methods, the levels of acid-sensing ion channels (ASICs), nuclear factor kappa B (NF-kB) p65, p38 mitogen-activated protein kinase (MAPK) proteins, and neuroinflammation-related cytokines were determined.

RESULTS

The levels of ASIC3 in the spinal cord were considerably increased after long-term morphine administration. Amiloride was found to delay the development of tolerance to chronic morphine assessed via tail-flick and hot plate tests. Amiloride reduced microglial activation and downregulated the cytokines IL-1β and TNF-a by inhibiting ASIC3 in response to morphine. Furthermore, amiloride reduced p38 MAPK phosphorylation and inhibited NF-κB expression.

CONCLUSIONS

Amiloride effectively reduces chronic morphine tolerance by suppressing microglial activation caused by morphine by inhibiting ASIC3.

In vivo photopharmacology with light-activated opioid drugs

Traditional methods for site-specific drug delivery in the brain are slow, invasive, and difficult to interface with recordings of neural activity. Here, we demonstrate the feasibility and experimental advantages of in vivo photopharmacology using "caged" opioid drugs that are activated in the brain with light after systemic administration in an inactive form. To enable bidirectional manipulations of endogenous opioid receptors in vivo, we developed photoactivatable oxymorphone (PhOX) and photoactivatable naloxone (PhNX), photoactivatable variants of the mu opioid receptor agonist oxymorphone and the antagonist naloxone. Photoactivation of PhOX in multiple brain areas produced local changes in receptor occupancy, brain metabolic activity, neuronal calcium activity, neurochemical signaling, and multiple pain- and reward-related behaviors. Combining PhOX photoactivation with optical recording of extracellular dopamine revealed adaptations in the opioid sensitivity of mesolimbic dopamine circuitry in response to chronic morphine administration. This work establishes a general experimental framework for using in vivo photopharmacology to study the neural basis of drug action.

L-cysteine ethyl ester prevents and reverses acquired physical dependence on morphine in male Sprague Dawley rats

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.

The Therapeutic Potential of Cannabidiol in Revolutionising Opioid Use Disorder Management

Opioid use disorder (OUD) is a significant cause of morbidity and mortality worldwide and is linked to a complex interplay of biopsychosocial factors as well as the increasing overprescription and availability of opioid medications. Current OUD management relies on the controlled provision of opioid medications, such as methadone or buprenorphine, known as opioid replacement therapy. There is variable evidence regarding the long-term efficacy of these medications in improving the management of OUD, thereby necessitating an exploration into innovative approaches to complement, or even take the place of, existing treatment paradigms. Cannabidiol (CBD), a non-psychoactive compound derived from the cannabis plant, has garnered attention for its diverse pharmacological properties, including anti-inflammatory, analgesic, and anxiolytic effects. Preliminary studies suggest that CBD may target opioid withdrawal pathways that make CBD a potential therapeutic option for OUD. This narrative review synthesises current literature surrounding OUD and offers a nuanced review of the current and future role of CBD in managing this condition. In doing so, we highlight the potential avenues to explore with respect to CBD research for the guidance and development of further research opportunities, framework and policy development, and clinical considerations before medicinal CBD can be integrated into evidence-based clinical guidelines.

Repurposing EGFR Inhibitors for Oral Cancer Pain and Opioid Tolerance

Oral cancer pain remains a significant public health concern. Despite the development of improved treatments, pain continues to be a debilitating clinical feature of the disease, leading to reduced oral mobility and diminished quality of life. Opioids are the gold standard treatment for moderate-to-severe oral cancer pain; however, chronic opioid administration leads to hyperalgesia, tolerance, and dependence. The aim of this review is to present accumulating evidence that epidermal growth factor receptor (EGFR) signaling, often dysregulated in cancer, is also an emerging signaling pathway critically involved in pain and opioid tolerance. We presented preclinical and clinical data to demonstrate how repurposing EGFR inhibitors typically used for cancer treatment could be an effective pharmacological strategy to treat oral cancer pain and to prevent or delay the development of opioid tolerance. We also propose that EGFR interaction with the µ-opioid receptor and glutamate N-methyl-D-aspartate receptor could be two novel downstream mechanisms contributing to pain and morphine tolerance. Most data presented here support that repurposing EGFR inhibitors as non-opioid analgesics in oral cancer pain is promising and warrants further research.

The use of ketamine infusion to dramatically reduce opioid requirements in a patient whose high-dose intrathecal opioid pump was inadvertently cut during surgery

BACKGROUND

Chronic opioid therapy may lead to high level tolerance development, hyperalgesia, and central sensitization, which further complicates long-term therapeutic management of chronic pain patients. In this case, we encounter a patient who was receiving over 15,000 morphine milligram equivalents through their intrathecal pain pump. Unfortunately, the intrathecal pump was inadvertently cut during a spinal surgery. It was deemed unsafe to delivery IV equivalent opioid therapy in this case; instead, the patient was admitted to the ICU and given a four-day ketamine infusion.

METHOD

The patient was started on a ketamine infusion at a rate of 0.5mg/kg/h, which was continued for three days. On the fourth day, the infusion rate was tapered over 12 h before being completely stopped. No coinciding opioid therapy was given during this time, which was only restarted in the outpatient setting.

RESULTS

Despite chronic high levels of opioid therapy immediately prior to the ketamine infusion, the patient did not experience florid withdrawals during the infusion period. Additionally, the patient experienced remarkable improvement in their subjective pain rating, which decreased from 9 to 3-4 on an 11-point Number Rating Scale, while simultaneously being managed on an MME <100. These results were sustained through a 6-month follow-up period.

CONCLUSION

Ketamine may play an important role in attenuating not only tolerance but also acute withdrawal in a setting where rapid or instant weaning from high dose chronic opioid therapy is needed.

μ-opioid receptor agonists and psychedelics: pharmacological opportunities and challenges

Opioid misuse and opioid-involved overdose deaths are a massive public health problem involving the intertwined misuse of prescription opioids for pain management with the emergence of extremely potent fentanyl derivatives, sold as standalone products or adulterants in counterfeit prescription opioids or heroin. The incidence of repeated opioid overdose events indicates a problematic use pattern consistent with the development of the medical condition of opioid use disorder (OUD). Prescription and illicit opioids reduce pain perception by activating µ-opioid receptors (MOR) localized to the central nervous system (CNS). Dysregulation of meso-corticolimbic circuitry that subserves reward and adaptive behaviors is fundamentally involved in the progressive behavioral changes that promote and are consequent to OUD. Although opioid-induced analgesia and the rewarding effects of abused opioids are primarily mediated through MOR activation, serotonin (5-HT) is an important contributor to the pharmacology of opioid abused drugs (including heroin and prescription opioids) and OUD. There is a recent resurgence of interest into psychedelic compounds that act primarily through the 5-HT2A receptor (5-HT 2A R) as a new frontier in combatting such diseases (e.g., depression, anxiety, and substance use disorders). Emerging data suggest that the MOR and 5-HT2AR crosstalk at the cellular level and within key nodes of OUD circuitry, highlighting a major opportunity for novel pharmacological intervention for OUD. There is an important gap in the preclinical profiling of psychedelic 5-HT2AR agonists in OUD models. Further, as these molecules carry risks, additional analyses of the profiles of non-hallucinogenic 5-HT2AR agonists and/or 5-HT2AR positive allosteric modulators may provide a new pathway for 5-HT2AR therapeutics. In this review, we discuss the opportunities and challenges associated with utilizing 5-HT2AR agonists as therapeutics for OUD.

The Role of Ryanodine Receptor 2 in Drug-Associated Learning

Type-2 ryanodine receptor (RyR2) ion channels facilitate the release of Ca 2+ from stores and serve an important function in neuroplasticity. The role for RyR2 in hippocampal-dependent learning and memory is well established and chronic hyperphosphorylation of RyR2 (RyR2P) is associated with pathological calcium leakage and cognitive disorders, including Alzheimer's disease. By comparison, little is known about the role of RyR2 in the ventral medial prefrontal cortex (vmPFC) circuitry important for working memory, decision making, and reward seeking. Here, we evaluated the basal expression and localization of RyR2 and RyR2P in the vmPFC. Next, we employed an operant model of sucrose, cocaine, or morphine self-administration (SA) followed by a (reward-free) recall test, to reengage vmPFC neurons and reactivate reward-seeking and re-evaluated the expression and localization of RyR2 and RyR2P in vmPFC. Under basal conditions, RyR2 was expressed in pyramidal cells but not regularly detected in PV/SST interneurons. On the contrary, RyR2P was rarely observed in PFC somata and was restricted to a different subcompartment of the same neuron - the apical dendrites of layer-5 pyramidal cells. Chronic SA of drug (cocaine or morphine) and nondrug (sucrose) rewards produced comparable increases in RyR2 protein expression. However, recalling either drug reward impaired the usual localization of RyR2P in dendrites and markedly increased its expression in somata immunoreactive for Fos, a marker of highly activated neurons. These effects could not be explained by chronic stress or drug withdrawal and instead appeared to require a recall experience associated with prior drug SA. In addition to showing the differential distribution of RyR2/RyR2P and affirming the general role of vmPFC in reward learning, this study provides information on the propensity of addictive drugs to redistribute RyR2P ion channels in a neuronal population engaged in drug-seeking. Hence, focusing on the early impact of addictive drugs on RyR2 function may serve as a promising approach to finding a treatment for substance use disorders.

Stigmata that are desired: Contradictions in addiction

Many experts in the etiology, assessment, and treatment of substance use/addiction view stigma and stigmatization - negatively branding addiction and substance users - as obstacles to the solution of the substance misuse problem. Discussions on this topic impact research and policy, and result in oft-repeated calls to remove the stigma from substance use and users. The goal of the article is to analyze the stigmatization concept as applied to substance use/addiction. It is widely accepted in the literature that stigmatization negatively affects substance users because addiction stigma interferes in both seeking and receiving professional care. It is argued that the societal disapproval of substance use/addiction is inappropriate because it is a mental disorder, involving biological processes. Nonetheless, neither those processes nor negative attitudes to substance use affirm the concept of stigmatization as currently applied. This concept conflates potential mistreatment and malpractice with the prosocial justified societal disapproval of a lethally dangerous behavior. Consequently, the stigmatization concept suffers from internal contradictions, is either misleading or redundant, and may do more harm than the supposed mistreatment of substance users that stigmatization connotes. On the contrary, the justified disapproval of harmful behavior may be a factor raising individual resistance to substance use. Instead of mitigating the effects of that disapproval, it may need to be capitalized on. If it is employed explicitly, conscientiously, and professionally, its internalization may be one of the resistance mechanisms needed to achieve any progress in the still elusive prevention of substance use and addiction.

Mu Opioid Receptor Activation Mediates (S)-ketamine Reinforcement in Rats: Implications for Abuse Liability

BACKGROUND

(S)-ketamine is an NMDA receptor antagonist, but it also binds to and activates mu opioid receptors (MORs) and kappa opioid receptors in vitro. However, the extent to which these receptors contribute to (S)-ketamine's in vivo pharmacology is unknown.

METHODS

We investigated the extent to which (S)-ketamine interacts with opioid receptors in rats by combining in vitro and in vivo pharmacological approaches, in vivo molecular and functional imaging, and behavioral procedures relevant to human abuse liability.

RESULTS

We found that the preferential opioid receptor antagonist naltrexone decreased (S)-ketamine self-administration and (S)-ketamine-induced activation of the nucleus accumbens, a key brain reward region. A single reinforcing dose of (S)-ketamine occupied brain MORs in vivo, and repeated doses decreased MOR density and activity and decreased heroin reinforcement without producing changes in NMDA receptor or kappa opioid receptor density.

CONCLUSIONS

These results suggest that (S)-ketamine's abuse liability in humans is mediated in part by brain MORs.

Increased Excitability and Synaptic Plasticity of Drd1- and Drd2-Expressing Prelimbic Neurons Projecting to Nucleus Accumbens after Heroin Abstinence Are Reversed by Cue-Induced Relapse and Protein Kinase A Inhibition

Dysregulation of the input from the prefrontal cortex (PFC) to the nucleus accumbens (NAc) contributes to cue-induced opioid seeking but the heterogeneity in, and regulation of, prelimbic (PL)-PFC to NAc (PL->NAc) neurons that are altered has not been comprehensively explored. Recently, baseline and opiate withdrawal-induced differences in intrinsic excitability of Drd1+ (D1+) versus Drd2+ (D2+) PFC neurons have been demonstrated. Thus, here we investigated physiological adaptations of PL->NAc D1+ versus D2+ neurons after heroin abstinence and cue-induced relapse. Drd1-Cre+ and Drd2-Cre+ transgenic male Long-Evans rats with virally labeled PL->NAc neurons were trained to self-administer heroin followed by 1 week of forced abstinence. Heroin abstinence significantly increased intrinsic excitability in D1+ and D2+ PL->NAc neurons and increased postsynaptic strength selectively in D1+ neurons. These changes were normalized by cue-induced relapse to heroin seeking. Based on protein kinase A (PKA)-dependent changes in the phosphorylation of plasticity-related proteins in the PL cortex during abstinence and cue-induced relapse to cocaine seeking, we assessed whether the electrophysiological changes in D1+ and D2+ PL->NAc neurons during heroin abstinence were regulated by PKA. In heroin-abstinent PL slices, application of the PKA antagonist (R)-adenosine, cyclic 3',5'-(hydrogenphosphorothioate) triethylammonium (RP-cAMPs) reversed intrinsic excitability in both D1+ and D2+ neurons and postsynaptic strength in only D1+ neurons. Additionally, in vivo bilateral intra-PL infusion of RP-cAMPs after abstinence from heroin inhibited cue-induced relapse to heroin seeking. These data reveal that PKA activity in D1+ and D2+ PL->NAc neurons is not only required for abstinence-induced physiological adaptations but is also required for cue-induced relapse to heroin seeking.SIGNIFICANCE STATEMENT Neuronal plasticity in the medial prefrontal cortex is thought to underlie relapse to drug seeking, yet the subpopulation of neurons that express this plasticity to functionally guide relapse is unclear. Here we show cell type-specific adaptations in Drd1-expressing versus Drd2-expressing prelimbic pyramidal neurons with efferent projections to nucleus accumbens. These adaptations are bidirectionally regulated during abstinence versus relapse and involve protein kinase A (PKA) activation. Furthermore, we show that disruption of the abstinence-associated adaptations via site-specific PKA inhibition abolishes relapse. These data reveal the promising therapeutic potential of PKA inhibition for preventing relapse to heroin seeking and suggest that cell type-specific pharmacologies that target subpopulations of prefrontal neurons would be ideal for future therapeutic developments.

Calcium/calmodulin-dependent protein kinase II is involved in the transmission and regulation of nociception in naïve and morphine-tolerant rat nucleus accumbens

Background

Synaptic plasticity contributes to nociceptive signal transmission and modulation, with calcium/calmodulin-dependent protein kinase II (CaMK II) playing a fundamental role in neural plasticity. This research was conducted to investigate the role of CaMK II in the transmission and regulation of nociceptive information within the nucleus accumbens (NAc) of naïve and morphine-tolerant rats.

Methods

Randall Selitto and hot-plate tests were utilized to measure the hindpaw withdrawal latencies (HWLs) in response to noxious mechanical and thermal stimuli. To induce chronic morphine tolerance, rats received intraperitoneal morphine injection twice per day for seven days. CaMK II expression and activity were assessed using western blotting.

Results

Intra-NAc microinjection of autocamtide-2-related inhibitory peptide (AIP) induced an increase in HWLs in naïve rats in response to noxious thermal and mechanical stimuli. Moreover, the expression of the phosphorylated CaMK II (p-CaMK II) was significantly decreased as determined by western blotting. Chronic intraperitoneal injection of morphine resulted in significant morphine tolerance in rats on Day 7, and an increase of p-CaMK II expression in NAc in morphine-tolerant rats was observed. Furthermore, intra-NAc administration of AIP elicited significant antinociceptive responses in morphine-tolerant rats. In addition, compared with naïve rats, AIP induced stronger thermal antinociceptive effects of the same dose in rats exhibiting morphine tolerance.

Conclusions

This study shows that CaMK II in the NAc is involved in the transmission and regulation of nociception in naïve and morphine-tolerant rats.

Evaluation of the antinociceptive effect of valerian and hops combination in experimental animal models: Involvement of the opioid system

Pain is a common undertreated worldwide complaint. The need to explore the antinociceptive potential of alternative herbal products is essential. Although used as a mild sedative, limited evidence focused on the potential antinociceptive effect of valerian and hops combination. The present study was carried out to evaluate the in vivo anti-nociceptive effect of the valerian-hops combination to justify its use as an effective and safe analgesic agent. Anti-nociceptive effects of valerian-hops combination (50, 100, and 200 mg/kg) were assessed in swiss albino mice for performing the acetic acid-induced writhing test, the paw licking test using formalin, the paw licking test using glutamate, and the tail immersion test. The effects were compared to those of diclofenac or morphine in the presence or absence of the opioid receptor antagonist naloxone. Valerian-hops" extract of 100 and 200 mg/kg demonstrated a significant reduction in the number of writhing episodes induced by acetic acid compared to the control (p < 0.05), a significant reduction in the licking number at doses of 100 and 200 mg/kg in the late phase formalin-induced paw licking, significantly reduced the number of lickings after glutamate injection compared to control (p < 0.05). And significantly increased pain reaction after 60 and 90 min of tail immersion test, this effect was opposed by naloxone treatment. The valerian-hops combination produced a significant antinociceptive effect that involved the opioid system. Further studies are required to fully uncover the underlying active constituents and their mechanisms.

Psychometric validity and the appropriateness of tolerance as a criterion for internet gaming disorder: A systematic review

Tolerance is a controversial but still an omnipresent criterion in measuring problematic gaming and Internet Gaming Disorder (IGD). Despite criticisms, a systematic review of its suitability has not been conducted until now. The aim of this study was to assess the evidence of psychometric validity and the appropriateness of tolerance as a criterion for IGD. A total of 61 articles were included in the review, 47 quantitative, 7 qualitative studies,plus 7 studies that introduce potential item wordings for operationalizing tolerance. Results showed that the tolerance item tends to have acceptable to high factor loadings on the single IGD factor. While tolerance sometimes did not adequately differentiate the engaged gamers from those with a probable disorder, it was endorsed at medium to high levels of IGD severity and had a good performance in the interviews. It, however, showed weak relations with distress and well-being. In qualitative studies, tolerance as currently defined by DSM-5 and measured by questionnaires (i.e., increasing amounts of time spent on gaming) was almost unequivocally rejected by gamers. The solid performance of tolerance in psychometric studies was probably due to deficiencies of the IGD construct, which also contains other disputed criteria. Tolerance lacks relevance in measuring IGD and care should be taken when using and interpreting IGD measures with this criterion.

In vivo photopharmacology with light-activated opioid drugs

Traditional methods for site-specific drug delivery in the brain are slow, invasive, and difficult to interface with recordings of neural activity. Here, we demonstrate the feasibility and experimental advantages of in vivo photopharmacology using "caged" opioid drugs that are activated in the brain with light after systemic administration in an inactive form. To enable bidirectional manipulations of endogenous opioid receptors in vivo , we developed PhOX and PhNX, photoactivatable variants of the mu opioid receptor agonist oxymorphone and the antagonist naloxone. Photoactivation of PhOX in multiple brain areas produced local changes in receptor occupancy, brain metabolic activity, neuronal calcium activity, neurochemical signaling, and multiple pain- and reward-related behaviors. Combining PhOX photoactivation with optical recording of extracellular dopamine revealed adaptations in the opioid sensitivity of mesolimbic dopamine circuitry during chronic morphine administration. This work establishes a general experimental framework for using in vivo photopharmacology to study the neural basis of drug action.

Highlights

A photoactivatable opioid agonist (PhOX) and antagonist (PhNX) for in vivo photopharmacology. Systemic pro-drug delivery followed by local photoactivation in the brain. In vivo photopharmacology produces behavioral changes within seconds of photostimulation. In vivo photopharmacology enables all-optical pharmacology and physiology.

A distinct impact of repeated morphine exposure on synaptic plasticity at Schaffer collateral-CA1, temporoammonic-CA1, and perforant pathway-dentate gyrus synapses along the longitudinal axis of the hippocampus

We aimed to study how morphine affects synaptic transmission in the dentate gyrus and CA1 regions along the hippocampal long axis. For this, recording and measuring of field excitatory postsynaptic potentials (fEPSPs) were utilized to test the effects of repeated morphine exposure on paired-pulse evoked responses and long-term potentiation (LTP) at Schaffer collateral-CA1 (Sch-CA1), temporoammonic-CA1 (TA-CA1) and perforant pathway-dentate gyrus (PP-DG) synapses in transverse slices from the dorsal (DH), intermediate (IH), and ventral (VH) hippocampus in adult male rats. After repeated morphine exposure, the expression of opioid receptors and the α1 and α5 GABA_A subunits were also examined. We found that repeated morphine exposure blunt the difference between the DH and the VH in their basal levels of synaptic transmission at Sch-CA1 synapses that were seen in the control groups. Significant paired-pulse facilitation of excitatory synaptic transmission was observed at Sch-CA1 synapses in slices taken from all three hippocampal segments as well as at PP-DG synapses in slices taken from the VH segment in the morphine-treated groups as compared to the control groups. Interestingly, significant paired-pulse inhibition of excitatory synaptic transmission was observed at TA-CA1 synapses in the DH slices from the morphine-treated group as compared to the control group. While primed-burst stimulation (a protocol reflecting normal neuronal firing) induced a robust LTP in hippocampal subfields in all control groups, resulting in a decaying LTP at TA-CA1 synapses in the VH slices and at PP-DG synapses in both the IH and VH slices taken from the morphine-treated rats. In the DH of morphine-treated rats, we found increased levels of the mRNAs encoding the α1 and α5 GABA_A subunits as compared to the control group. Taken together, these findings suggest the potential mechanisms through which repeated morphine exposure causes differential changes in circuit excitability and synaptic plasticity in the dentate gyrus and CA1 regions along the hippocampal long axis.

Plasma Brain-Derived Neurotrophic Factor and Opioid Therapy: Results of Pilot Cross-Sectional Study

Objective: The neurotoxic effect of opioid has not been thoroughly described. No studies have been conducted to explain the effect of opioids in chronic non-cancer pain therapy on the neurotrophic factors level. Due to the ability to cross the blood-brain barrier, it seems the determination of serum Brain-derived neurotrophic factor (BDNF) concentration is a reliable presentation of the concentration in the central nervous system. The aim of the study was to explore the changes of plasma BDNF concentration during long-term opioid therapy.Methods: The study group included 28 patients with chronic low back pain treated with opioid therapy buprenorphine (n=10), tramadol (n=8), oxycodone (n=6), morphine (n=3), fentanyl (n=1). The control group included 11 patients. Measurements of plasma BDNF concentrations were performed, and information about opioid therapy were recorded (age, sex, opioid substance type, daily dose and the duration of opioid therapy). Data were analyzed using nonparametric tests.Results: The median BDNF level in the study group was significantly lower (2.73 ng/mL) than that in the control group (5.04 ng/mL, P<0.05). BDNF levels did not differ among groups based on the type of opioid substance used, but the lowest median value was observed for tramadol (2.62 ng/mL), and the highest median value was observed for buprenorphine (2.73 ng/mL). The widest minimum-maximum ranges of BDNF for oxycodone were noted, minimum 1.23 ng/mL and maximum 4.57 ng/mL, respectively. BDNF concentrations were correlated with age in the tramadol group and with the duration of opioid therapy in the buprenorphine group.Conclusion: Chronic opioid therapy for noncancer pain induces specific changes in the BDNF concentration. Tramadol and buprenorphine exerted an important effect on BDNF levels in the examined patients. The BDNF level depends on duration of opioid therapy with buprenorphine, and age in tramadol therapy.

Opioid epidemic: lessons learned and updated recommendations for misuse involving prescription versus non-prescription opioids

INTRODUCTION

In the past decades, the opioid crisis has heavily impacted parts of the US society and has been followed by an increase in the use of opioids worldwide. It is of paramount importance that we explore the origins of the US opioid epidemic to develop best practices to tackle the rising tide of opioid overdoses.

AREAS COVERED

In this expert review, we discuss opioid (over)prescription, change in perception of pain, and false advertisement of opioid safety as the leading causes of the US opioid epidemic. Then, we review the evidence about opioid dependence and addiction potential and provide current knowledge about predictors of aberrant opioid-related behavior. Lastly, we discuss different approaches that were considered or undertaken to combat the rising tide of opioid-related deaths by regulatory bodies, pharmaceutical companies, and health-care professionals. For this expert review, we considered published articles relevant to the topic under investigation that we retrieved from Medline or Google scholar electronic database.

EXPERT OPINION

The opioid epidemic is a dynamic process with many underlying mechanisms. Therefore, no single approach may be best suited to combat it. In our opinion, the best way forward is to employ multiple strategies to tackle different underlying mechanisms.

Mechanism of opioid addiction and its intervention therapy: Focusing on the reward circuitry and mu-opioid receptor

Opioid abuse and addiction have become a global pandemic, posing tremendous health and social burdens. The rewarding effects and the occurrence of withdrawal symptoms are the two mainstays of opioid addiction. Mu-opioid receptors (MORs), a member of opioid receptors, play important roles in opioid addiction, mediating both the rewarding effects of opioids and opioid withdrawal syndrome (OWS). The underlying mechanism of MOR-mediated opioid rewarding effects and withdrawal syndrome is of vital importance to understand the nature of opioid addiction and also provides theoretical basis for targeting MORs to treat drug addiction. In this review, we first briefly introduce the basic concepts of MORs, including their structure, distribution in the nervous system, endogenous ligands, and functional characteristics. We focused on the brain circuitry and molecular mechanism of MORs-mediated opioid reward and withdrawal. The neuroanatomical and functional elements of the neural circuitry of the reward system underlying opioid addiction were thoroughly discussed, and the roles of MOR within the reward circuitry were also elaborated. Furthermore, we interrogated the roles of MORs in OWS, along with the structural basis and molecular adaptions of MORs-mediated withdrawal syndrome. Finally, current treatment strategies for opioid addiction targeting MORs were also presented.

Age-Induced Changes in µ-Opioid Receptor Signaling in the Midbrain Periaqueductal Gray of Male and Female Rats

Opioids have decreased analgesic potency (but not efficacy) in aged rodents compared with adults; however, the neural mechanisms underlying this attenuated response are not yet known. The present study investigated the impact of advanced age and biological sex on opioid signaling in the ventrolateral periaqueductal gray (vlPAG) in the presence of chronic inflammatory pain. Assays measuring µ-opioid receptor (MOR) radioligand binding, GTPγS binding, receptor phosphorylation, cAMP inhibition, and regulator of G-protein signaling (RGS) protein expression were performed on vlPAG tissue from adult (2-3 months) and aged (16-18 months) male and female rats. Persistent inflammatory pain was induced by intraplantar injection of complete Freund's adjuvant (CFA). Adult males exhibited the highest MOR binding potential (BP) and highest G-protein activation (activation efficiency ratio) in comparison to aged males and females (adult and aged). No impact of advanced age or sex on MOR phosphorylation state was observed. DAMGO-induced cAMP inhibition was highest in the vlPAG of adult males compared with aged males and females (adult and aged). vlPAG levels of RGS4 and RGS9-2, critical for terminating G-protein signaling, were assessed using RNAscope. Adult rats (both males and females) exhibited lower levels of vlPAG RGS4 and RGS9-2 mRNA expression compared with aged males and females. The observed age-related reductions in vlPAG MOR BP, G-protein activation efficiency, and cAMP inhibition, along with the observed age-related increases in RGS4 and RGS9-2 vlPAG expression, provide potential mechanisms whereby the potency of opioids is decreased in the aged population.SIGNIFICANCE STATEMENT Opioids have decreased analgesic potency (but not efficacy) in aged rodents compared with adults; however, the neural mechanisms underlying this attenuated response are not yet known. In the present study, we observed age-related reductions in ventrolateral periaqueductal gray (vlPAG) µ-opioid receptor (MOR) binding potential (BP), G-protein activation efficiency, and cAMP inhibition, along with the observed age-related increases in regulator of G-protein signaling (RGS)4 and RGS9-2 vlPAG expression, providing potential mechanisms whereby the potency of opioids is decreased in the aged population. These coordinated decreases in opioid receptor signaling may explain the previously reported reduced potency of opioids to produce pain relief in females and aged rats.

Cannabidivarin alleviates neuroinflammation by targeting TLR4 co-receptor MD2 and improves morphine-mediated analgesia

Toll-like receptor 4 (TLR4) is a pattern-recognition receptor (PRR) that regulates the activation of immune cells, which is a target for treating inflammation. In this study, Cannabidivarin (CBDV), an active component of Cannabis, was identified as an antagonist of TLR4. In vitro, intrinsic protein fluorescence titrations revealed that CBDV directly bound to TLR4 co-receptor myeloid differentiation protein 2 (MD2). Cellular thermal shift assay (CETSA) showed that CBDV binding decreased MD2 stability, which is consistent with in silico simulations that CBDV binding increased the flexibility of the internal loop of MD2. Moreover, CBDV was found to restrain LPS-induced activation of TLR4 signaling axes of NF-κB and MAPKs, therefore blocking LPS-induced pro-inflammatory factors NO, IL-1β, IL-6 and TNF-α. Hot plate test showed that CBDV potentiated morphine-induced antinociception. Furthermore, CBDV attenuated morphine analgesic tolerance as measured by the formalin test by specifically inhibiting chronic morphine-induced glial activation and pro-inflammatory factors expression in the nucleus accumbent. This study confirms that MD2 is a direct binding target of CBDV for the anti-neuroinflammatory effect and implies that CBDV has great translational potential in pain management.

A potential paradigm shift in opioid crisis management: The role of pharmacogenomics

Pharmacogenetic investigations into the opioid crisis suggest genetic variation could be a significant cause of opioid-related morbidity and mortality. Variability in opioid system genes, including single nucleotide polymorphisms, manifest after pharmacogenetic testing, as previously invisible risk factors for addiction and overdose. Pharmacodynamic genes regulate opioid-sensitive brain networks and neural reward circuitry. Pharmacokinetic genes expressed in drug metabolic pathways regulate blood levels of active vs. inactive opioid metabolites. Elucidating the complex interplay of genetic variations in pharmacokinetic and pharmacodynamic pathways will shed new light on the addictive and toxic properties of opioids. This narrative review serves to promote understanding of key genetic mechanisms affecting the metabolism and actions of opioids, and to explore causes of the recent surge in opioid-related mortality associated with COVID-19. Personalised treatment plans centred around an individual's genetic makeup could make opioid-based pain management and opioid use disorder (OUD) treatments safer and more effective at both the individual and system levels.

Yokukansan Inhibits the Development of Morphine Tolerance by Regulating Presynaptic Proteins in DRG Neurons

Opioids, such as morphine, are used in clinical settings for the management of acute and chronic pain. However, long-term use of morphine leads to antinociceptive tolerance and hypersensitivity. The cellular and molecular mechanisms of morphine tolerance seem to be quite complex, with suggestions including internalization of the μ-opioid receptor (MOR), neuroinflammation with activation of microglia and astrocytes, and changes in synaptic function in the central nervous system. Yokukansan (YKS), a traditional Kampo medicine consisting of seven herbs, has been used to treat emotional instability, neurosis, and insomnia. Interestingly, recent studies have begun to reveal the inhibitory effect of YKS on the development of morphine tolerance. In the present study, we determined the effect of YKS on morphine tolerance formation and its mechanisms in a rat model, focusing on the synapses between primary sensory neurons and spinal dorsal horn secondary neurons. We found that morphine tolerance formation was significantly inhibited by YKS (0.3 or 1.0 g/kg/day) preadministration for 7 days. Repeated administration of morphine (10 mg/kg/day) increased the expression of presynaptic proteins, including synaptotagmin I, in the spinal cord, which was suppressed by YKS. Furthermore, these changes in presynaptic protein expression were more pronounced at isolectin B4 (IB4)-positive excitatory synapses around the lamina II of the dorsal horn. These results suggest that YKS suppresses the development of morphine tolerance by inhibiting the enhancement of presynaptic function of dorsal root ganglia neurons projecting to spinal dorsal horn neurons caused by continuous morphine administration.

Iatrogenic opioid withdrawal syndromes in adults in intensive care units: a narrative review

Background and Objective

In hospitalized patients, opiates are essential analgesics and sedatives used in intensive care unit (ICU) patients. However, the iatrogenic opioid withdrawal syndrome (IOWS) in ICU patients has been poorly characterized, and there are no well accepted, standardized diagnostic tools for hospitalized adults. This review analyzed recent clinical studies to determine the frequency, characteristics, and treatment of IOWS in critically ill adults.

Methods

The initial literature search used the PubMed MeSH terms “Analgesics”, “Opioids”, “Iatrogenic Disease”, and “Neurobiology”. The main focus was on clinical studies describing IOWS in adults receiving intravenous opioids in ICUs.

Key Content and Findings

Review of 8 studies indicated that IOWS occurs in 15% to 40% of patients in intensive care units who required opioid infusions. These reports included patients in medical ICUs, trauma ICUs, surgical ICUs, and burn ICUs; many patients also received sedative drugs. Most of the studies used DSM-5 criteria to identify the syndrome. Factors which predicted the development of this syndrome varied from study to study; important considerations included the weaning rate for the opioid, the duration of opioid infusion, and the concomitant infusion of benzodiazepines. Treatment approaches included the reinstitution of the opioid infusion with slower reductions in the rate and the use of an alpha-2 agonist, such dexmedetomidine or clonidine. Many patients appeared to recover without specific treatment.

Agonist-Specific Regulation of G Protein-Coupled Receptors after Chronic Opioid Treatment

Chronic treatment of animals with morphine results in a long lasting cellular tolerance in the locus coeruleus and alters the kinase dependent desensitization of opioid and nonopioid G protein-coupled receptors (GPCRs). This study examined the development of tolerance and altered regulation of kinase activity after chronic treatment of animals with clinically relevant opioids that differ in efficacy at the µ-opioid receptors (MOR). In slices from oxycodone treated animals, no tolerance to opioids was observed when measuring the MOR induced increase in potassium conductance, but the G protein receptor kinase 2/3 blocker, compound 101, no longer inhibited desensitization of somatostatin (SST) receptors. Chronic fentanyl treatment induced a rightward shift in the concentration response to [Met5]enkephalin, but there was no change in the kinase regulation of desensitization of the SST receptor. When total phosphorylation deficient MORs that block desensitization, internalization, and tolerance were virally expressed, chronic treatment with fentanyl resulted in the altered kinase regulation of SST receptors. The results suggest that sustained opioid receptor signaling initiates the process that results in altered kinase regulation of not only opioid receptors, but also other GPCRs. This study highlights two very distinct downstream adaptive processes that are specifically regulated by an agonist dependent mechanism. SIGNIFICANCE STATEMENT: Persistent signaling of MORs results in altered kinase regulation of nonopioid GPCRs after chronic treatment with morphine and oxycodone. Profound tolerance develops after chronic treatment with fentanyl without affecting kinase regulation. The homeostatic change in the kinase regulation of nonopioid GPCRs could account for the systems level in vivo development of tolerance that is seen with opioid agonists, such as morphine and oxycodone, that develop more rapidly than the tolerance induced by efficacious agonists, such as fentanyl and etorphine.

Digital Analgesic Comprising a Second-Generation Digital Health System: Increasing Effectiveness by Optimizing the Dosing and Minimizing Side Effects

Opioids remain an essential part of the treatment of chronic pain. However, their use and increasing rates of misuse are associated with high morbidity and mortality. The development of tolerance to opioids and analgesics further complicates dosing and the need to reduce side effects. First-generation digital systems were developed to improve analgesics but are not always capable of making clinically relevant associations and do not necessarily lead to better clinical efficacy. A lack of improved clinical outcomes makes these systems less applicable for adoption by clinicians and patients. There is a need to enhance the therapeutic regimens of opioids. In the present paper, we present the use of a digital analgesic that consists of an analgesic administered under the control of a second-generation artificial intelligence system. Second-generation systems focus on improved patient outcomes measured based on clinical response and reduced side effects in a single subject. The algorithm regulates the administration of analgesics in a personalized manner. The digital analgesic provides advantages for both users and providers. The system enables dose optimization, improving effectiveness, and minimizing side effects while increasing adherence to beneficial therapeutic regimens. The algorithm improves the clinicians’ experience and assists them in managing chronic pain. The system reduces the financial burden on healthcare providers by lowering opioid-related morbidity and provides a market disruptor for pharma companies.