Agonists at μ opioid receptors relieve acute pain, however, their long-term use is limited by side effects, which may involve β-arrestin2. Agonists biased against β-arrestin2 recruitment may be advantageous. However, the classification of bias may be compromised by assays utilising overexpressed μ receptors which overestimate efficacy for G-protein activation. There is a need for re-evaluation with restricted receptor availability to determine accurate agonist efficacies. We depleted μ receptor availability in PathHunter CHO cells using the irreversible antagonist, β-funaltrexamine (β-FNA), and compared efficacies and apparent potencies of twelve agonists, including several previously reported as biased, in β-arrestin2 recruitment and cAMP assays. With full receptor availability all agonists had partial efficacy for stimulating β-arrestin2 recruitment relative to DAMGO, while only TRV130 and buprenorphine were partial agonists as inhibitors of cAMP accumulation. Limiting receptor availability by prior exposure to β-FNA (100 nM) revealed morphine, oxycodone, PZM21, herkinorin, U47700, tianeptine and U47931e are also partial agonists in the cAMP assay. The efficacies of all agonists, except SR-17018, correlated between β-arrestin2 recruitment and cAMP assays, with depleted receptor availability in the latter. Furthermore, naloxone and cyprodime exhibited non-competitive antagonism of SR-17018 in the β-arrestin2 recruitment assay. Limited antagonism by naloxone was also non-competitive in the cAMP assay, while cyprodime was competitive. Furthermore, SR-17018 only negligibly diminished β-arrestin2 recruitment stimulated by DAMGO (1 μM), whereas fentanyl, morphine and TRV130 all exhibited the anticipated competitive inhibition. The data suggest that SR-17018 achieves bias against β-arrestin2 recruitment through interactions with μ receptors outside the orthosteric agonist site. This article is part of the Special Issue on \"Ligand Bias\".

Loperamide, a potent μ-opioid receptor agonist used as an antidiarrheal drug, exhibits increased bioavailability at supratherapeutic doses, causing potential central nervous system effects. Its misuse for opioid withdrawal relief and euphoria can lead to dangerously elevated blood levels, causing severe cardiac dysrhythmias and death. This study aimed to compare loperamide positive autopsy cases in Sweden and Finland after the introduction of postmortem toxicological analysis of loperamide, focusing on loperamide\'s role in fatalities and identifying common characteristics among those affected. All cases with detected loperamide in femoral blood at forensic autopsies in Sweden (2012-2022) and Finland (2017-2022) were included. In Sweden, loperamide was detected in 126 individuals, and in Finland, in 111 individuals. The incidence of individuals positive for loperamide in postmortem femoral blood increased steadily over the study duration in both Sweden and Finland. Loperamide related fatalities were observed exclusively in Sweden (n=80), predominantly involving younger males with histories of substance abuse, typically classified as accidental deaths. The group of loperamide nonrelated deaths in Sweden mirrored the entirety of cases in Finland. The concentration of loperamide in postmortem femoral blood was significantly higher in cases where loperamide was considered the cause of death (median 0.140 μg/g) compared to cases where loperamide contributed (median 0.080 μg/g), as well as in deaths unrelated to loperamide in both countries (Sweden: median 0.029 μg/g; Finland: median 0.010 μg/ml). The high limit of quantification for loperamide in Sweden may underestimate therapeutic users in epidemiological assessments. This study underscores the absence of loperamide misuse in Finland and indicates a rising trend of loperamide abuse in Sweden.

Motherhood is a costly life-history transition accompanied by behavioral and neural plasticity necessary for offspring care. Motherhood in the monogamous prairie vole is associated with decreased pair bond strength, suggesting a trade-off between parental investment and pair bond maintenance. Neural mechanisms governing pair bonds and maternal bonds overlap, creating possible competition between the two. We measured mRNA expression of genes encoding receptors for oxytocin (oxtr), dopamine (d1r and d2r), mu-opioids (oprm1a), and kappa-opioids (oprk1a) within three brain areas processing salience of sociosensory cues (anterior cingulate cortex; ACC), pair bonding (nucleus accumbens; NAc), and maternal care (medial preoptic area; MPOA). We compared gene expression differences between pair bonded prairie voles that were never pregnant, pregnant (~day 16 of pregnancy), and recent mothers (day 3 of lactation). We found greater gene expression in the NAc (oxtr, d2r, oprm1a, and oprk1a) and MPOA (oxtr, d1r, d2r, oprm1a, and oprk1a) following the transition to motherhood. Expression for all five genes in the ACC was greatest for females that had been bonded for longer. Gene expression within each region was highly correlated, indicating that oxytocin, dopamine, and opioids comprise a complimentary gene network for social signaling. ACC-NAc gene expression correlations indicated that being a mother (oxtr and d1r) or maintaining long-term pair bonds (oprm1a) relies on the coordination of different signaling systems within the same circuit. Our study suggests the maternal brain undergoes changes that prepare females to face the trade-off associated with increased emotional investment in offspring, while also maintaining a pair bond.

Opioid addiction is a relapsing disorder marked by uncontrolled drug use and reduced interest in normally rewarding activities. The current study investigated the impact of spontaneous withdrawal from chronic morphine exposure on emotional, motivational and cognitive processes involved in regulating the pursuit and consumption of food rewards in male rats. In Experiment 1, rats experiencing acute morphine withdrawal lost weight and displayed somatic signs of drug dependence. However, hedonically driven sucrose consumption was significantly elevated, suggesting intact and potentially heightened reward processing. In Experiment 2, rats undergoing acute morphine withdrawal displayed reduced motivation when performing an effortful response for palatable food reward. Subsequent reward devaluation testing revealed that acute withdrawal disrupted their ability to exert flexible goal-directed control over reward seeking. Specifically, morphine-withdrawn rats were impaired in using current reward value to select actions both when relying on prior action-outcome learning and when given direct feedback about the consequences of their actions. In Experiment 3, rats tested after prolonged morphine withdrawal displayed heightened rather than diminished motivation for food rewards and retained their ability to engage in flexible goal-directed action selection. However, brief re-exposure to morphine was sufficient to impair motivation and disrupt goal-directed action selection, though in this case, rats were only impaired in using reward value to select actions in the presence of morphine-paired context cues and in the absence of response-contingent feedback. We suggest that these opioid-withdrawal induced deficits in motivation and goal-directed control may contribute to addiction by interfering with the pursuit of adaptive alternatives to drug use.

Over 50 million Americans endure chronic pain where many do not receive adequate treatment and self-medicate to manage their pain by taking substances like opioids and cannabis. Research has shown high comorbidity between chronic pain and substance use disorders (SUD) and these disorders share many common neurobiological underpinnings, including hypodopaminergic transmission. Drugs commonly used for self-medication such as opioids and cannabis relieve emotional, bothersome components of pain as well as negative emotional affect that perpetuates misuse and increases the risk of progressing towards drug abuse. However, the causal effect between chronic pain and the development of SUDs has not been clearly established. In this review, we discuss evidence that affirms the proposition that chronic pain is a risk factor for the development of opioid and cannabis use disorders by outlining the clinical evidence and detailing neurobiological mechanisms that link pain and drug misuse. Central to the link between chronic pain and opioid and cannabis misuse is hypodopaminergic transmission and the modulation of dopamine signaling in the mesolimbic pathway by opioids and cannabis. Moreover, we discuss the role of kappa opioid receptor activation and neuroinflammation in the context of dopamine transmission, their contribution to opioid and cannabis withdrawal, along with potential new treatments.

OBJECTIVE: Opioid use disorder is a cause of significant morbidity and mortality. In order to reverse opioid overdose as quickly as possible, many institutions and municipalities have encouraged people with no professional medical training to carry and administer naloxone. This study sought to provide preliminary data for research into the rates of adverse effects of naloxone when administered by bystanders compared to Emergency Medical Services (EMS) personnel, since this question has not been studied previously.
METHODS: This was a retrospective cohort study performed at an urban, tertiary, academic medical center that operates its own EMS service. A consecutive sample of patients presenting to EMS with opioid overdose requiring naloxone was separated into two groups based on whether naloxone was administered by bystanders or by EMS personnel. Each group was analyzed to determine the incidence of four pre-specified adverse events.
RESULTS: There was no significant difference in the rate of adverse events between the bystander (19%) and EMS (16%) groups (OR = 1.23; 95% CI, 0.63 - 2.32; P = .499) in this small sample. Based on these initial results, a study would need a sample size of 6,188 in order to reach this conclusion with 80% power. Similarly, there were no significant differences in the rates of any of the individual adverse events. Secondary analysis of patients\' demographics showed differences between the two groups which generate hypotheses for further investigation of disparities in naloxone administration.
CONCLUSIONS: This preliminary study provides foundational data for further investigation of naloxone administration by bystanders. Adverse events after the prehospital administration of naloxone are rare, and future studies will require large sample sizes. These preliminary data did not demonstrate a statistically significant difference in adverse event rates when comparing naloxone administration by bystanders and EMS clinicians. This study provides data that will be useful for conducting further research on multiple facets of this topic.

Dynorphin is an endogenous opiate localized in many brain regions and spinal cord, but the activity of dynorphin neurons during sleep is unknown. Dynorphin is an inhibitory neuropeptide that is coreleased with orexin, an excitatory neuropeptide. We used microendoscopy to test the hypothesis that, like orexin, the dynorphin neurons are wake-active. Dynorphin-cre mice (n = 3) were administered rAAV8-Ef1a-Con/Foff 2.0-GCaMP6M into the zona incerta-perifornical area, implanted with a GRIN lens (gradient reflective index), and electrodes to the skull that recorded sleep. One month later, a miniscope imaged calcium fluorescence in dynorphin neurons during multiple bouts of wake, non-rapid-eye movement (NREM), and rapid-eye movement (REM) sleep. Unbiased data analysis identified changes in calcium fluorescence in 64 dynorphin neurons. Most of the dynorphin neurons (72%) had the highest fluorescence during bouts of active and quiet waking compared to NREM or REM sleep; a subset (20%) were REM-max. Our results are consistent with the emerging evidence that the activity of orexin neurons can be classified as wake-max or REM-max. Since the two neuropeptides are coexpressed and coreleased, we suggest that dynorphin-cre-driven calcium sensors could increase understanding of the role of this endogenous opiate in pain and sleep.

The United States (US) opioid epidemic is a persistent and pervasive public health emergency that claims the lives of over 80,000 Americans per year as of 2021. There have been sustained efforts to reverse this crisis over the past decade, including a number of measures designed to decrease the use of prescription opioids for the treatment of pain. This study analyzed the changes in federal production quotas for prescription opioids and the distribution of prescription opioids for pain and identified state-level differences between 2010 and 2019. Data (in grams) on opioid production quotas and distribution (from manufacturer to hospitals, retail pharmacies, practitioners, and teaching institutions) of 10 prescription opioids (codeine, fentanyl, hydrocodone, hydromorphone, meperidine, methadone, morphine, oxycodone, oxymorphone, and tapentadol) for 2010 to 2019 were obtained from the US Drug Enforcement Administration. Amounts of each opioid were converted from grams to morphine milligram equivalent (MME), and the per capita distribution by state was calculated using population estimates. Total opioid production quotas increased substantially from 2010 to 2013 before decreasing by 41.5% from 2013 (87.6 MME metric tons) to 2019 (51.3). The peak year for distribution of all 10 prescription opioids was between 2010 and 2013, except for codeine (2015). The largest quantities of opioid distribution were observed in Tennessee (520.70 MME per person) and Delaware (251.45) in 2011 and 2019. There was a 52.0% overall decrease in opioid distribution per capita from 2010 to 2019, with the largest decrease in Florida (-61.6%) and the smallest in Texas (-18.6%). Southern states had the highest per capita distribution for eight of the ten opioids in 2019. The highest to lowest state ratio of total opioid distribution, corrected for population, decreased from 5.25 in 2011 to 2.78 in 2019. The mean 95th/5th ratio was relatively consistent in 2011 (4.78 ± 0.70) relative to 2019 (5.64 ± 0.98). This study found a sustained decline in the distribution of ten prescription opioids during the last five years. Distribution was non-homogeneous at the state level. Analysis of state-level differences revealed a fivefold difference in the 95th:5th percentile ratio between states, which has remained unchanged over the past decade. Production quotas did not correspond with the distribution, particularly in the 2010-2016 period. Future research, focused on identifying factors contributing to the observed regional variability in opioid distribution, could prove valuable to understanding and potentially remediating the pronounced disparities in prescription opioid-related harms in the US.

Number of opiate users worldwide has doubled over the past decade, but not all of them are diagnosed with opioid use disorder. We aimed to identify the prevalence and risk factors for OUD after ten years of follow-up.
Among 8,500 chronic opiate users at Golestan Cohort Study baseline (2004-2008), we recalled a random sample of 451 subjects in 2017. We used three questionnaires: a questionnaire about current opiate use including type and route of use, the drug use disorder section of the Composite International Diagnostic Interview lifetime version, and the validated Kessler10 questionnaire. We defined opioid use disorder and its severity based on the DSM-5 criteria and used a cutoff of 12 on Kessler10 questionnaire to define psychological distress.
Mean age was 61.2 ± 6.6 years (84.7% males) and 58% were diagnosed with opioid use disorder. Starting opiate use at an early age and living in underprivileged conditions were risk factors of opioid use disorder. Individuals with opioid use disorder were twice likely to have psychological distress (OR = 2.25; 95%CI: 1.44-3.52) than the users without it. In multivariate regression, former and current opiate dose and oral use of opiates were independently associated with opioid use disorder. Each ten gram per week increase in opiate dose during the study period almost tripled the odds of opioid use disorder (OR = 3.18; 95%CI: 1.79-5.63).
Chronic opiate use led to clinical opioid use disorder in more than half of the users, and this disorder was associated with psychological distress, increasing its physical and mental burden in high-risk groups.

UNASSIGNED: Opioid withdrawal is one of the most critical complications of opioid use disorder. In this study, we aimed to examine the possible risk of ventricular arrhythmia and sudden cardiac death by calculating electrocardiography (ECG) changes, the markers of ventricular repolarization, in opioid withdrawal.
UNASSIGNED: A total of 90 patients diagnosed with opioid withdrawal who met the inclusion and exclusion criteria were included in the study. QT, QTc, TPe/QT, and TPe/QTc ratios of patients with a Clinical Opiate Withdrawal Scale (COWS) score higher than five and a Framingham heart risk score lower than 10% were measured in 12-lead ECG.
UNASSIGNED: A significant difference was found between the patients\' heart rate, QT, QTc, and TPe/QT values during withdrawal (entry-first) and after withdrawal (second) (p<0.05). Mean QT First Value (380.69±22.46) was significantly different and higher than Mean QT Second Value (372.82±19.998); Mean QTc First Value (435.41±16.22) was significantly different and higher than Mean QTc Second Value (418.03±17.79); Mean Tpe First Value (81.62±6.009) was significantly different and higher than Mean Tpe Second Value (79.93±5.524); and The Mean Tpe/QT First Value (0.221±0.005) was significantly different and higher than the Mean Tpe/QT Second Value (0.213±0.004) (p<0.05).
UNASSIGNED: The findings of our study show that electrocardiographic QT, QTc, Tpe and Tpe/QTc values, which indicate the risk of sudden cardiac death and ventricular arrhythmia, are significantly higher during opioid withdrawal. In addition to the regulation of addiction treatment during opioid withdrawal, it should be considered that individuals may be at cardiac risk, and the patient should be monitored for cardiac arrhythmia during the withdrawal period.