Oxytocin and orexin systems bidirectionally regulate the ability of opioid cues to bias reward seeking

The central oxytocinergic system of the prairie vole

Oxytocin (OXT) is a peptide hormone and a neuropeptide that regulates various peripheral physiological processes and modulates behavioral responses in the central nervous system. While the humoral release occurs from the axons arriving at the median eminence, the neuropeptide is also released from oxytocinergic cell axons in various brain structures that contain its receptor, and from their dendrites in hypothalamic nuclei and potentially into the cerebrospinal fluid (CSF). Understanding oxytocin's complex functions requires the knowledge on patterns of oxytocinergic projections in relationship to its receptor (OXTR). This study provides the first comprehensive examination of the oxytocinergic system in the prairie vole (Microtus ochrogaster), an animal exhibiting social behaviors that mirror human social behaviors linked to oxytocinergic functioning. Using light and electron microscopy, we characterized the neuroanatomy of the oxytocinergic system in this species. OXT+ cell bodies were found primarily in the hypothalamus, and axons were densest in subcortical regions. Examination of the OXT+ fibers and their relationship to oxytocin receptor transcripts (Oxtr) revealed that except for some subcortical structures, the presence of axons was not correlated with the amount of Oxtr across the brain. Of particular interest, the cerebral cortex that had high expression of Oxtr transcripts contained little to no fibers. Electron microscopy is used to quantify dense cored vesicles (DCV) in OXT+ axons and to identify potential axonal release sites. The ependymal cells that line the ventricles were frequently permissive of DCV-containing OXT+ dendrites reaching the third ventricle. Our results highlight a mechanism in which oxytocin is released directly into the ventricles and circulates throughout the ventricular system, may serve as the primary source for oxytocin that binds to OXTR in the cerebral cortex.

Mindfulness-induced self-transcendence promotes universal love with consequent effects on opioid misuse

In addition to its health benefits, mindfulness has been theorized in classical contemplative frameworks to elicit self-transcendent experiences as a means of promoting universal love and compassion. Increasing feelings of love may be especially clinically relevant for the treatment of opioid misuse, in that addictive use of opioids dysregulates neurobiological processes implicated in the experience of love. Here we tested these hypotheses in a secondary analysis (n = 187) of data from a randomized clinical trial of Mindfulness-Oriented Recovery Enhancement (MORE) versus supportive psychotherapy for comorbid opioid misuse and chronic pain. At pre- and post-treatment, participants completed a measure of state self-transcendence immediately following a laboratory-based mindfulness task. Through 9-month follow-up, we assessed changes in universal love and opioid misuse. Participants also completed ecological momentary assessments of opioid craving during the 8-week study interventions and for the following month. Compared to supportive psychotherapy, participants in MORE reported significantly greater increases in mindfulness-induced self-transcendence, which mediated the effect of MORE on increased feelings of universal love. In turn, increases in universal love significantly predicted decreased opioid craving and lower odds opioid misuse through 1- and 9-month follow-ups, respectively. Findings suggest mindfulness-induced self-transcendence may promote feelings of universal love, with possible downstream benefits on reducing addictive behavior.

Superiority and cost-effectiveness of monthly extended-release buprenorphine versus daily standard of care medication: a pragmatic, parallel-group, open-label, multicentre, randomised, controlled, phase 3 trial

Background

Daily methadone maintenance or buprenorphine treatment is the standard-of-care (SoC) medication for opioid use disorder (OUD). Subcutaneously injected, extended-release buprenorphine (BUP-XR) may be more effective-but there has been no superiority evaluation.

Methods

This pragmatic, parallel-group, open-label, multi-centre, effectiveness superiority randomised, controlled, phase 3 trial was conducted at five National Health Service community-based treatment clinics in England and Scotland. Participants (adults aged ≥ 18 years; all meeting DSM-5 diagnostic criteria for moderate or severe OUD at admission to their current maintenance treatment episode) were randomly assigned (1:1) to receive continued daily SoC (liquid methadone (usual dose range: 60-120 mg) or sublingual/transmucosal buprenorphine (usual dose range: 8-24 mg) for 24 weeks; or monthly BUP-XR (Sublocade;® two injections of 300 mg, then four maintenance injections of 100 mg or 300 mg, with maintenance dose selected by response and preference) for 24 weeks. In the intent-to-treat population (senior statistician blinded to blinded to treatment group allocation), and with a seven-day grace period after randomisation, the primary endpoint was the count of days abstinent from non-medical opioids between days 8-168 (i.e., weeks 2-24; range: 0-161 days). Safety was reported for the intention-to- treat population. Adopting a broad societal perspective inclusive of criminal justice, NHS and personal social service costs, a trial-based cost-utility analysis estimated the Incremental Cost-effectiveness Ratio (ICER) per quality-adjusted life year (QALY) of BUP-XR versus SoC at the National Institute for Health and Care Excellence threshold. The study was registered EudraCT (2018-004460-63) and ClinicalTrials.gov (NCT05164549), and is completed.

Findings

Between Aug 9, 2019 and Nov 2, 2021, 314 participants were randomly allocated to receive SoC (n = 156) or BUP-XR (n = 158). Participants were abstinent from opioids for an adjusted mean of 104.37 days (standard error [SE] 9.89; range: 0-161 days) in the SoC group and an adjusted mean of 123.43 days (SE 4.76; range: 24-161 days) in the BUP-XR group (adjusted incident rate ratio [IRR] 1.18, 95% confidence interval [CI] 1.05-1.33; p-value 0.004). The incidence of any adverse event was higher in the BUP-XR group than the SoC group (128 [81.0%] of 158 participants versus 67 [42.9%] of 156 participants, respectively-most commonly rapidly-resolving (mild-moderate range) pain from drug administration in the BUP-XR group (121 [26.9%] of 450 adverse events). There were 11 serious adverse events (7.0%) in the 158 participants in the BUP-XR group, and 18 serious adverse events (11.5%) in the 156 participants in the SoC group-none judged to be related to study treatment. The BUP-XR treatment group had a mean incremental cost of £1033 (95% central range [CR] -1189 to 3225) and was associated with a mean incremental QALY of 0.02 (95% CR 0.00-0.05), and an ICER of £47,540 (0.37 probability of being cost-effective at the £30,000/QALY gained willingness-to-pay threshold). However, BUP-XR dominated the SoC among participants who were rated more severe at study baseline, and among participants in maintenance treatment for more that 28 days at study enrolment.

Interpretation

Evaluated against the daily oral SoC, monthly BUP-XR is clinically superior, delivering greater abstinence from opioids, and with a comparable safety profile. BUP-XR was not cost-effective in a base case cost-utility analysis using the societal perspective, but it was more effective and less costly (dominant) among participants with more severe OUD, or those whose current treatment episode was longer than 28 days. Further trials are needed to evaluate if BUP-XR is associated with better clinical and health economic outcomes over the longer term.

Funding

Indivior.

Endogenous opiates and behavior: 2022

This paper is the forty-fifth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2022 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Lateral hypothalamus hypocretin/orexin glucose-inhibited neurons promote food seeking after calorie restriction

OBJECTIVE

The present study tests the hypothesis that changes in the glucose sensitivity of lateral hypothalamus (LH) hypocretin/orexin glucose-inhibited (GI) neurons following weight loss leads to glutamate plasticity on ventral tegmental area (VTA) dopamine neurons and drives food seeking behavior.

METHODS

C57BL/6J mice were calorie restricted to a 15% body weight loss and maintained at that body weight for 1 week. The glucose sensitivity of LH hypocretin/orexin GI and VTA dopamine neurons was measured using whole cell patch clamp recordings in brain slices. Food seeking behavior was assessed using conditioned place preference (CPP).

RESULTS

1-week maintenance of calorie restricted 15% body weight loss reduced glucose inhibition of hypocretin/orexin GI neurons resulting in increased neuronal activation with reduced glycemia. The effect of decreased glucose on hypocretin/orexin GI neuronal activation was blocked by pertussis toxin (inhibitor of G-protein coupled receptor subunit Gαi/o) and Rp-cAMP (inhibitor of protein kinase A, PKA). This suggests that glucose sensitivity is mediated by the Gαi/o-adenylyl cyclase-cAMP-PKA signaling pathway. The excitatory effect of the hunger hormone, ghrelin, on hcrt/ox neurons was also blocked by Rp-cAMP suggesting that hormonal signals of metabolic status may converge on the glucose sensing pathway. Food restriction and weight loss increased glutamate synaptic strength (indexed by increased AMPA/NMDA receptor current ratio) on VTA dopamine neurons and the motivation to seek food (indexed by CPP). Chemogenetic inhibition of hypocretin/orexin neurons during caloric restriction and weight loss prevented these changes in glutamate plasticity and food seeking behavior.

CONCLUSIONS

We hypothesize that this change in the glucose sensitivity of hypocretin/orexin GI neurons may drive, in part, food seeking behavior following caloric restriction.

Tabernanthalog Reduces Motivation for Heroin and Alcohol in a Polydrug Use Model

Background

The potential use of psychedelic drugs as therapeutics for neuropsychiatric disorders has been limited by their hallucinogenic properties. To overcome this limitation, we developed and characterized tabernanthalog (TBG), a novel analogue of the indole alkaloids ibogaine and 5-methoxy-N,N-dimethyltryptamine with reduced cardiac arrhythmogenic risk and a lack of classical psychedelic drugs-induced sensory alterations. We previously demonstrated that TBG has therapeutic efficacy in a preclinical model of opioid use disorder (OUD) in rats and in a binge model of alcohol drinking in mice. Alcohol is commonly co-used in ∼35-50% of individuals with OUD, and yet, preclinical models that recapitulate this comorbidity are lacking.

Methodology

Here we employed a polydrug model of heroin and alcohol couse to screen the therapeutic efficacy of TBG on metrics of both opioid and alcohol seeking. We first exposed rats to alcohol (or control sucrose-fade solution) in the home-cage (HC), using a two-bottle binge protocol, over a period of 1 month. Rats were then split into two groups that underwent self-administration training for either intravenous heroin or oral alcohol, so that we could assess the impact of HC alcohol exposure on the self-administration of each substance separately. Thereafter, rats began self-administering both heroin and alcohol in the same sessions. Finally, we tested the effects of TBG on break points for heroin and alcohol in a progressive ratio test, where the number of lever presses required to obtain a single reward increased exponentially.

Results and Conclusion

TBG effectively reduced motivation for heroin and alcohol in this test, indicating its efficacy is preserved in animals with a history of heroin and alcohol polydrug use.

Binge eating, overeating and food addiction: Approaches for examining food overconsumption in laboratory rodents

Overeating ranges in severity from casual overindulgence to an overwhelming drive to consume certain foods. At its most extreme, overeating can manifest as clinical diagnoses such as binge eating disorder or bulimia nervosa, yet subclinical forms of overeating such as emotional eating or uncontrolled eating can still have a profoundly negative impact on health and wellbeing. Although rodent models cannot possibly capture the full spectrum of disordered overeating, studies in laboratory rodents have substantially progressed our understanding of the neurobiology of overconsumption. These experimental approaches range from simple food-exposure protocols that promote binge-like eating and the development of obesity, to more complex operant procedures designed to examine distinct 'addiction-like' endophenotypes for food. This review provides an overview of these experimental approaches, with the view to providing a comprehensive resource for preclinical investigators seeking to utilize behavioural models for studying the neural systems involved in food overconsumption.

Comparison of binge-eating disorder and food addiction

In the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, binge-eating disorder (BED) is classified as episodes of binge eating while not being hungry, eating too fast until feeling uncomfortably full, or eating in solitude with feelings of shame and disgust after eating, without compensatory mechanisms. The controversial disorder food addiction (FA) is characterized by overconsumption, cravings, failure to cut down on amounts of food, and withdrawal and tolerance to overeating. In this narrative review, we aimed to comprehensively characterize and compare BED and FA. We searched PubMed using the keywords "binge-eating disorder" and "food addiction." We finally included 51 publications according to topic specificity, credibility, the authors' reputation, and non-bias criteria. BED is characterized by concerns about dietary issues, body shape, and weight as well as depressive symptoms and brooding rumination. FA can be divided into substance addiction and behavioral addiction, which can be differentiated using a list of criteria including hunger, taste, pleasure, function of food, loss of social connections, weight concerns, and awareness about the disorder. Further research is needed to further characterize and distinguish BED and FA.

Animal models of compulsion alcohol drinking: Why we love quinine-resistant intake and what we learned from it

Alcohol Use Disorder (AUD) ranks among the most prevalent mental disorders, extracting ~$250 billion/year in the US alone and producing myriad medical and social harms. Also, the number of deaths related to problem drinking has been increasing dramatically. Compulsive alcohol drinking, characterized by intake that persists despite negative consequences, can be particularly important and a major obstacle to treatment. With the number of people suffering from AUD increasing during the past years, there is a critical need to understand the neurobiology related to compulsive drives for alcohol, as well as the development of novel AUD pharmacological therapies. Here we discuss rodent compulsion-like alcohol drinking (CLAD) models, focusing on the two most widely used adverse stimuli to model rodent compulsion-like responding, quinine adulteration of alcohol and footshook-resistant alcohol intake. For both cases, the goal is to uncover behavior patterns and brain circuits that underlie drive for alcohol even in the face of negative consequences. We discuss caveats, benefits, and potential brain mechanisms, of models for consequence-resistant responding for alcohol more generally, and especially highlight some advantages of quinine-resistance over footshook-resistance. Further, since this review contributes to a Special issue focused on Molecular Aspects of Compulsive Drug Use, we discuss our new findings showing how the noradrenergic system is related to CLAD responding. In particular, we comment on the importance of α1 and β adrenergic receptors (ARs) as potential targets for treating AUD.

Neural circuits controlling choice behavior in opioid addiction

As the opioid epidemic presents an ever-expanding public health threat, there is a growing need to identify effective new treatments for opioid use disorder (OUD). OUD is characterized by a behavioral misallocation in choice behavior between opioids and other rewards, as opioid use leads to negative consequences, such as job loss, family neglect, and potential overdose. Preclinical models of addiction that incorporate choice behavior, as opposed to self-administration of a single drug reward, are needed to understand the neural circuits governing opioid choice. These choice models recapitulate scenarios that humans suffering from OUD encounter in their daily lives. Indeed, patients with substance use disorders (SUDs) exhibit a propensity to choose drug under certain conditions. While most preclinical addiction models have focused on relapse as the outcome measure, our data suggest that choice is an independent metric of addiction severity, perhaps relating to loss of cognitive control over choice, as opposed to excessive motivational drive to seek drugs during relapse. In this review, we examine both preclinical and clinical literature on choice behavior for drugs, with a focus on opioids, and the neural circuits that mediate drug choice versus relapse. We argue that preclinical models of opioid choice are needed to identify promising new avenues for OUD therapy that are translationally relevant. Both forward and reverse translation will be necessary to identify novel treatment interventions. This article is part of the Special Issue on "Opioid-induced changes in addiction and pain circuits".

Paraventricular Nucleus of the Hypothalamus Oxytocin and Incubation of Heroin Seeking

INTRODUCTION

There are numerous pharmacologic treatments for opioid use disorder (OUD), but none that directly target the underlying addictive effects of opioids. Oxytocin, a peptide hormone produced in the paraventricular nucleus (PVN) of the hypothalamus, has been investigated as a potential therapeutic for OUD. Promising preclinical and clinical results have been reported, but the brain region(s) and mechanism(s) by which oxytocin impacts reward processes remain undetermined.

METHODS

Here, we assess peripherally administered oxytocin's impacts on cued reinstatement of heroin seeking following forced abstinence and its effects on neuronal activation in the PVN and key projection regions. We also examine how designer receptors exclusively activated by designer drug (DREADD)-mediated activation or inhibition of oxytocinergic PVN neurons alters cued heroin seeking and social interaction.

RESULTS

As predicted, peripheral oxytocin administration successfully decreased cued heroin seeking on days 1 and 30 of abstinence. Oxytocin administration also led to increased neuronal activity within the PVN and the central amygdala (CeA). Activation of oxytocinergic PVN neurons with an excitatory (Gq) DREADD did not impact cued reinstatement or social interaction. In contrast, suppression with an inhibitory (Gi) DREADD reduced heroin seeking on abstinence day 30 and decreased time spent interacting with a novel conspecific.

DISCUSSION

These findings reinforce oxytocin's therapeutic potential for OUD, the basis for which may be driven in part by increased PVN-CeA circuit activity. Our results also suggest that oxytocin has distinct signaling and/or other mechanisms of action to produce these effects, as inhibition, but not activation, of oxytocinergic PVN neurons did not recapitulate the suppression in heroin seeking.