Gender and stimulus difference in cue-induced responses in abstinent heroin users

Disruption of positive- and negative-feature morphine interoceptive occasion setters by dopamine receptor agonism and antagonism in male and female rats

RATIONALE

Internally perceived stimuli evoked by morphine administration can form Pavlovian associations such that they can function as occasion setters (OSs) for externally perceived reward cues in rats, coming to modulate reward-seeking behaviour. Though much research has investigated mechanisms underlying opioid-related reinforcement and analgesia, neurotransmitter systems involved in the functioning of opioids as Pavlovian interoceptive discriminative stimuli remain to be disentangled despite documented differences in the development of tolerance to analgesic versus discriminative stimulus effects.

OBJECTIVES

Dopamine has been implicated in many opioid-related behaviours, so we aimed to investigate the role of this neurotransmitter in expression of morphine occasion setting.

METHODS

Male and female rats were assigned to positive- (FP) or negative-feature (FN) groups and received an injection of morphine or saline before each training session. A 15-s white noise conditioned stimulus (CS) was presented 8 times during every training session; offset of this stimulus was followed by 4-s access to liquid sucrose on morphine, but not saline, sessions for FP rats. FN rats learned the reverse contingency. Following stable discrimination, rats began generalization testing for expression of morphine-guided sucrose seeking after systemic pretreatment with different doses of the non-selective dopamine receptor antagonist, flupenthixol, and the non-selective dopamine receptor agonist, apomorphine, combined with training doses of morphine or saline in a Latin-square design.

RESULTS

The morphine discrimination was acquired under both FP and FN contingencies by males and females. Neither flupenthixol nor apomorphine at any dose substituted for morphine, but both apomorphine and flupenthixol disrupted expression of the morphine OS. This inhibition was specific to sucrose seeking during CS presentations rather than during the period before CS onset and, in the case of apomorphine more so than flupenthixol, to trials on which access to sucrose was anticipated.

CONCLUSIONS

Our findings lend support to a mechanism of occasion setting involving gating of CS-induced dopamine release rather than by direct dopaminergic modulation by the morphine stimulus.

Estrogen receptor beta signaling enhances extinction memory recall for heroin-conditioned cues in a sex- and region-specific manner

Return to use, or relapse, is a major challenge in the treatment of opioid use disorder (OUD). Relapse can be precipitated by several factors, including exposure to drug-conditioned cues. Identifying successful treatments to mitigate cue-induced relapse has been challenging, perhaps due to extinction memory recall (EMR) deficits. Previously, inhibition of estradiol (E2) signaling in the basolateral amygdala (BLA) impaired heroin-cue EMR. This effect was recapitulated by antagonism of BLA estrogen receptors (ER) in a sex-specific manner such that blocking ERα in males, but ERβ in females, impaired EMR. However, it is unclear whether increased E2 signaling, in the BLA or systemically, enhances heroin-cue EMR. We hypothesized that ERβ agonism would enhance heroin-cue EMR in a sex- and region-specific manner. To determine the capacity of E2 signaling to improve EMR, we pharmacologically manipulated ERβ across several translationally designed experiments. First, male and female rats acquired heroin or sucrose self-administration. Next, during a cued extinction session, we administered diarylpropionitrile (DPN, an ERβ agonist) and tested anxiety-like behavior on an open field. Subsequently, we assessed EMR in a cue-induced reinstatement test and, finally, measured ERβ expression in several brain regions. Across all experiments, females took more heroin and sucrose than males and had greater responses during heroin-cued extinction. Administration of DPN in the BLA enhanced EMR in females only, driven by ERβ's impacts on memory consolidation. Interestingly, however, systemic DPN administration improved EMR for heroin cues in both sexes across several different tests, but did not impact sucrose-cue EMR. Immunohistochemical analysis of ERβ expression across several different brain regions showed that females only had greater expression of ERβ in the basal nucleus of the BLA. Here, in several preclinical experiments, we demonstrated that ERβ agonism enhances heroin-cue EMR and has potential utility in combatting cue-induced relapse.

Approaches to studying emotion using physiological responses to spoken narratives: A scoping review

Narratives are effective tools for evoking emotions, and physiological measurements provide a means of objectively assessing emotional reactions - making them a potentially powerful pair of tools for studying emotional processes. However, extent research combining emotional narratives and physiological measurement varies widely in design and application, making it challenging to identify previous work, consolidate findings, and design effective experiments. Our scoping review explores the use of auditory emotional narratives and physiological measures in research, examining paradigms, study populations, and represented emotions. Following the PRISMA-ScR Checklist, we searched five databases for peer-reviewed experimental studies that used spoken narratives to induce emotion and reported autonomic physiological measures. Among 3466 titles screened and 653 articles reviewed, 110 studies were included. Our exploration revealed a variety of applications and experimental paradigms; emotional narratives paired with physiological measures have been used to study diverse topics and populations, including neurotypical and clinical groups. Although incomparable designs and sometimes contradictory results precluded general recommendations as regards which physiological measures to use when designing new studies, as a whole, the body of work suggests that these tools can be valuable to study emotions. Our review offers an overview of research employing narratives and physiological measures for emotion study, and highlights weaknesses in reporting practices and gaps in our knowledge concerning the robustness and specificity of physiological measures as indices of emotion. We discuss study design considerations and transparent reporting, to facilitate future using emotional narratives and physiological measures in studying emotions.

Pivotal role of orexin signaling in the posterior paraventricular nucleus of the thalamus during the stress-induced reinstatement of oxycodone-seeking behavior

BACKGROUND

The orexin (OX) system has received increasing interest as a potential target for treating substance use disorder. OX transmission in the posterior paraventricular nucleus of the thalamus (pPVT), an area activated by highly salient stimuli that are both reinforcing and aversive, mediates cue- and stress-induced reinstatement of reward-seeking behavior. Oral administration of suvorexant (SUV), a dual OX receptor (OXR) antagonist (DORA), selectively reduced conditioned reinstatement of oxycodone-seeking behavior and stress-induced reinstatement of alcohol-seeking behavior in dependent rats.

AIMS

This study tested whether OXR blockade in the pPVT with SUV reduces oxycodone or sweetened condensed milk (SCM) seeking elicited by conditioned cues or stress.

METHODS

Male Wistar rats were trained to self-administer oxycodone (0.15 mg/kg, i.v., 8 h/day) or SCM (0.1 ml, 2:1 dilution [v/v], 30 min/day). After extinction, we tested the ability of intra-pPVT SUV (15 µg/0.5 µl) to prevent reinstatement of oxycodone or SCM seeking elicited by conditioned cues or footshock stress.

RESULTS

The rats acquired oxycodone and SCM self-administration, and oxycodone intake correlated with signs of physical opioid withdrawal, confirming dependence. Following extinction, the presentation of conditioned cues or footshock elicited reinstatement of oxycodone- and SCM-seeking behavior. Intra-pPVT SUV blocked stress-induced reinstatement of oxycodone seeking but not conditioned reinstatement of oxycodone or SCM seeking or stress-induced reinstatement of SCM seeking.

CONCLUSIONS

The results indicate that OXR signaling in the pPVT is critical for stress-induced reinstatement of oxycodone seeking, further corroborating OXRs as treatment targets for opioid use disorder.

Mu Opioid Receptor-Positive Neurons in the Dorsal Raphe Nucleus Are Impaired by Morphine Abstinence

BACKGROUND

Chronic opioid exposure leads to hedonic deficits and enhanced vulnerability to addiction, which are observed and even strengthen after a period of abstinence, but the underlying circuit mechanisms are poorly understood. In this study, using both molecular and behavioral approaches, we tested the hypothesis that neurons expressing mu opioid receptors (MORs) in the dorsal raphe nucleus (DRN) are involved in addiction vulnerability associated with morphine abstinence.

METHODS

MOR-Cre mice were exposed to chronic morphine and then went through spontaneous withdrawal for 4 weeks, a well-established mouse model of morphine abstinence. We studied DRN-MOR neurons of abstinent mice using 1) viral translating ribosome affinity for transcriptome profiling, 2) fiber photometry to measure neuronal activity, and 3) an opto-intracranial self-stimulation paradigm applied to DRN-MOR neurons to assess responses related to addiction vulnerability including persistence to respond, motivation to obtain the stimulation, self-stimulation despite punishment, and cue-induced reinstatement.

RESULTS

DRN-MOR neurons of abstinent animals showed a downregulation of genes involved in ion conductance and MOR-mediated signaling, as well as altered responding to acute morphine. Opto-intracranial self-stimulation data showed that abstinent animals executed more impulsive-like and persistent responses during acquisition and scored higher on addiction-like criteria.

CONCLUSIONS

Our data suggest that protracted abstinence to chronic morphine leads to reduced MOR function in DRN-MOR neurons and abnormal self-stimulation of these neurons. We propose that DRN-MOR neurons have partially lost their reward-facilitating properties, which in turn may lead to increased propensity to perform addiction-related behaviors.

Daily treatment with the dual orexin receptor antagonist DORA-12 during oxycodone abstinence decreases oxycodone conditioned reinstatement

Chronic opioid use disturbs circadian rhythm and sleep, encouraging opioid use and relapse. The orexin (OX) system is recruited by opioids and regulates physiological processes including sleep. Dual OX receptor antagonists (DORAs), developed for insomnia treatment, may relieve withdrawal-associated sleep disturbances. This study investigated whether DORA-12, a recently developed DORA, reduces physiological activity disturbances during oxycodone abstinence and consequently prevents oxycodone-seeking behavior. Male and female Wistar rats were trained to intravenously self-administer oxycodone (0.15 mg/kg, 21 sessions; 8 h/session) in the presence of a contextual/discriminative stimulus (SD). The rats were subsequently housed individually (22 h/day) to monitor activity, food and water intake. They received DORA-12 (0-30 mg/kg, p.o.) after undergoing daily 1-h extinction training (14 days). After extinction, the rats were tested for oxycodone-seeking behavior elicited by the SD. Hypothalamus sections were processed to assess oxycodone- or DORA-12-associated changes to the OX cell number. In males, oxycodone-associated increases in activity during the light-phase, reinstatement, and decreases in the number of OX cells observed in the vehicle-treated group were not observed with DORA-12-treatment. Oxycodone-associated increases in light-phase food and water intake were not observed by day 14 of 3 mg/kg DORA-12-treatment and dark-phase water intake was increased across treatment days. In females, OX cell number was unaffected by oxycodone or DORA-12. Three and 30 mg/kg DORA-12 increased females' day 7 dark-phase activity and decreased reinstatement. Thirty mg/kg DORA-12 reduced oxycodone-associated increases in light-phase food and water intake. The results suggest that DORA-12 improves oxycodone-induced disruptions to physiological activities and reduces relapse.

Morphine-context associative memory and locomotor sensitization in mice are modulated by sex and context in a dose-dependent manner

Sex differences in opioid use, development of opioid used disorder, and relapse behaviors indicate potential variations in opioid effects between men and women. The locomotor and interoceptive effects of opioids play essential roles in opioid addiction, and uncovering the neural mechanisms underlying these effects remain crucial for developing effective treatments. In this study, we examined the dose-dependent effects of morphine on locomotor sensitization and the strength and stability of morphine-context associations in the conditioned place preference (CPP) paradigm in male and female mice, as well as the relationships between these measures. We observed that while CPP is similar between sexes, the locomotor effects of repeated morphine administration and withdrawal differentially contributed to the strength and stability of morphine-context associations. Specifically, females exhibited higher morphine-induced hyperlocomotion than males regardless of the context in which morphine was experienced. Greater locomotor sensitization to morphine in females than males emerged in a dose-dependent manner only when there was sufficient context information for CPP to be established. Additionally, the relationships between the locomotor effects of morphine and the strength and stability of CPP were different in males and females. In females, positive acute and sensitizing locomotor effects of morphine were correlated with a higher CPP score, while the opposite direction of this relationship was found in males. These results suggest that different aspects of the subjective experience of morphine intoxication and withdrawal are important for morphine abuse-related behaviors and highlight the importance of sex-specific responses in the context of opioid addiction.

Increased heroin intake and relapse vulnerability in intermittent relative to continuous self-administration: Sex differences in rats

BACKGROUND AND PURPOSE

Studies using intermittent-access drug self-administration show increased motivation to take and seek cocaine and fentanyl, relative to continuous access. In this study, we examined the effects of intermittent- and continuous-access self-administration on heroin intake, patterns of self-administration and cue-induced heroin-seeking, after forced or voluntary abstinence, in male and female rats. We also modelled brain levels of heroin and its active metabolites.

EXPERIMENTAL APPROACH

Rats were trained to self-administer a palatable solution and then heroin (0.075 mg·kg^-1 per inf) either continuously (6 h·day^-1 ; 10 days) or intermittently (6 h·day^-1 ; 5-min access every 30-min; 10 days). Brain levels of heroin and its metabolites were modelled using a pharmacokinetic software. Next, heroin-seeking was assessed after 1 or 21 abstinence days. Between tests, rats underwent either forced or voluntary abstinence. The oestrous cycle was measured using a vaginal smear test.

KEY RESULTS

Intermittent access exacerbated heroin self-administration and was characterized by a burst-like intake, yielding higher brain peaks of heroin and 6-monoacetylmorphine concentrations. Moreover, intermittent access increased cue-induced heroin-seeking during early, but not late abstinence. Heroin-seeking was higher in females after intermittent, but not continuous access, and this effect was independent of the oestrous cycle.

CONCLUSIONS AND IMPLICATIONS

Intermittent heroin access in rats resembles critical features of heroin use disorder: a self-administration pattern characterized by repeated large doses of heroin and higher relapse vulnerability during early abstinence. This has significant implications for refining animal models of substance use disorder and for better understanding of the neuroadaptations responsible for this disorder.

LINKED ARTICLES

This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Opioid Withdrawal Abruptly Disrupts Amygdala Circuit Function by Reducing Peptide Actions

While the physical signs of opioid withdrawal are most readily observable, withdrawal insidiously drives relapse and contributes to compulsive drug use, by disrupting emotional learning circuits. How these circuits become disrupted during withdrawal is poorly understood. Because amygdala neurons mediate relapse, and are highly opioid sensitive, we hypothesized that opioid withdrawal would induce adaptations in these neurons, opening a window of disrupted emotional learning circuit function. Under normal physiological conditions, synaptic transmission between the basolateral amygdala (BLA) and the neighboring main island (Im) of GABAergic intercalated cells (ITCs) is strongly inhibited by endogenous opioids. Using patch-clamp electrophysiology in brain slices prepared from male rats, we reveal that opioid withdrawal abruptly reduces the ability of these peptides to inhibit neurotransmission, a direct consequence of a protein kinase A (PKA)-driven increase in the synaptic activity of peptidases. Reduced peptide control of neurotransmission in the amygdala shifts the excitatory/inhibitory balance of inputs onto accumbens-projecting amygdala cells involved in relapse. These findings provide novel insights into how peptidases control synaptic activity within the amygdala and presents restoration of endogenous peptide activity during withdrawal as a viable option to mitigate withdrawal-induced disruptions in emotional learning circuits and rescue the relapse behaviors exhibited during opioid withdrawal and beyond into abstinence.SIGNIFICANCE STATEMENT We find that opioid withdrawal dials down inhibitory neuropeptide activity in the amygdala. This disrupts both GABAergic and glutamatergic transmission through amygdala circuits, including reward-related outputs to the nucleus accumbens. This likely disrupts peptide-dependent emotional learning processes in the amygdala during withdrawal and may direct behavior toward compulsive drug use.

Estradiol Enhances the Development of Addiction-Like Features in a Female Rat Model of Opioid Use Disorder

INTRODUCTION

Women are more vulnerable than men in many aspects of opioid use disorder (OUD); a major theory of sex differences in substance use disorders is that these differences are due to ovarian hormones with estradiol enhancing vulnerability in females. However, most of this evidence is for psychostimulants and alcohol; evidence with opioids is sparse. Thus, the goal of this study was to determine the impact of estradiol on vulnerability in females in a rat model of OUD.

METHOD

Following self-administration training, ovariectomized (OVX) females with (E) or without (V) estradiol replacement were given extended (24 h/day), intermittent access (2, 5-min trials/h) to fentanyl for 10 days. Then, the development of three key features of OUD were assessed, including physical dependence, defined by the magnitude and time course of weight loss during withdrawal; an enhanced motivation for fentanyl, assessed using a progressive-ratio schedule; and relapse vulnerability, assessed using an extinction/cue-induced reinstatement procedure. These later two characteristics were examined following 14 days of withdrawal when the phenotypes are known to be highly expressed.

RESULTS

OVX+E females self-administered markedly higher levels of fentanyl under extended, intermittent-access conditions and showed a longer time course of physical dependence, a greater increase in motivation for fentanyl, and an enhanced sensitivity to the reinstating effects of fentanyl-associated cues compared to OVX+V rats. Severe health complications were also observed in OVX+E, but not OVX+V females, during withdrawal.

CONCLUSION

These results indicate that, as with findings with psychostimulants and alcohol, estradiol enhances vulnerability in females to developing opioid addiction-like features and serious opioid-related health complications.

Sex differences in neural responses to stress and drug cues predicts future drug use in individuals with substance use disorder

BACKGROUND

Substance use disorders (SUDs) are chronically recurring illnesses, where stress and drug cues significantly increase drug craving and risk of drug use recurrence. This study examined sex differences in functional magnetic resonance imaging (fMRI) brain responses to stress and drug cue exposure and assessed their prospective association with future drug use post-treatment.

METHODS

Inpatient, treatment engaged men (N = 46) and women (N = 26) with SUDs, including alcohol, cocaine and/or cannabis use disorders, participated in an fMRI scan that assessed subjective (anxiety, drug craving), heart rate and neural responses to brief individualized script-driven imagery of stress, drug, and neutral-relaxing trials. Prospective follow-up interviews post-treatment assessed future drug use recurrence over 90 days.

RESULTS

During fMRI, stress and drug versus neutral cue exposure led to increased anxiety, heart rate and craving responses (p's < 0.004) in both men and women, but greater drug cue-induced anxiety (p < .017) and higher drug use days during follow-up (p < .006) in women relative to men. In whole brain analyses of stress and drug cues (p < .05 FWE corrected), and in whole brain correlation (p < .05, FWE corrected) with drug use days, significant sex differences revealed drug cue-related striatal hyperactivation (caudate, putamen) in men, but drug cue-related cortico-limbic (insula and dorsolateral prefrontal cortex) hypoactivation and stress-related hypoactivation in the ventromedial prefrontal cortex (VmPFC) in women; and these were significantly associated with higher future drug use days.

CONCLUSIONS

Findings indicate sex-specific pathophysiology of SUD recurrence and support the need for differential treatment development for men and women with SUD to improve drug use outcomes.

Suvorexant, an FDA-approved dual orexin receptor antagonist, reduces oxycodone self-administration and conditioned reinstatement in male and female rats

Background: The Department of Health and Human Services reports that prescription pain reliever (e.g., oxycodone) misuse was initiated by 4,400 Americans each day in 2019. Amid the opioid crisis, effective strategies to prevent and treat prescription opioid use disorder (OUD) are pressing. In preclinical models, the orexin system is recruited by drugs of abuse, and blockade of orexin receptors (OX receptors) prevents drug-seeking behavior. The present study sought to determine whether repurposing suvorexant (SUV), a dual OX receptor antagonist marketed for the treatment of insomnia, can treat two features of prescription OUD: exaggerated consumption and relapse. Methods: Male and female Wistar rats were trained to self-administer oxycodone (0.15 mg/kg, i. v., 8 h/day) in the presence of a contextual/discriminative stimulus (S^D) and the ability of SUV (0-20 mg/kg, p. o.) to decrease oxycodone self-administration was tested. After self-administration testing, the rats underwent extinction training, after which we tested the ability of SUV (0 and 20 mg/kg, p. o.) to prevent reinstatement of oxycodone seeking elicited by the S^D. Results: The rats acquired oxycodone self-administration and intake was correlated with the signs of physical opioid withdrawal. Additionally, females self-administered approximately twice as much oxycodone as males. Although SUV had no overall effect on oxycodone self-administration, scrutiny of the 8-h time-course revealed that 20 mg/kg SUV decreased oxycodone self-administration during the first hour in males and females. The oxycodone S^D elicited strong reinstatement of oxycodone-seeking behavior that was significantly more robust in females. Suvorexant blocked oxycodone seeking in males and reduced it in females. Conclusions: These results support the targeting of OX receptors for the treatment for prescription OUD and repurposing SUV as pharmacotherapy for OUD.

Sex- and Dose-Dependent Differences in the Development of an Addiction-Like Phenotype Following Extended-Access Fentanyl Self-Administration

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

Opioid and Sucrose Craving Are Accompanied by Unique Behavioral and Affective Profiles after Extended Abstinence in Male and Female Rats

Incubation of craving refers to the intensification of drug-seeking behavior in response to reward-paired cues over the course of abstinence. In rodents, craving and drug-seeking behaviors have been measured by an increase in lever pressing in the absence of reinforcer availability in response to cue presentations. However, craving in rodents is difficult to define and little is known about the behavioral signatures that accompany increased drug-seeking behavior measured by lever pressing. The affective components of relapse are also important, but understudied in rodents. Hormonal fluctuations influence craving for psychostimulants, but little is known about the impact of the estrous cycle on opioid-seeking behavior. This study sought to delineate the behavioral and affective signatures associated with craving, and to examine the influence of the female estrous cycle on craving. Male and female rats underwent 10 d of intravenous opioid self-administration. Separate cohorts of control rats self-administered oral sucrose, a natural nondrug reward. Cue-induced seeking tests were conducted after 1 or 30d of forced abstinence. These sessions were recorded and scored for overall locomotion, instances of sniffing, grooming, or hyperactivity. Ultrasonic vocalizations (USVs) were also recorded to determine affective profiles that accompany opioid seeking. Although active lever presses and overall locomotion increased unanimously over extended abstinence from heroin and sucrose, a sex- and reinforcer-specific behavioral and affective signature of craving emerged. Furthermore, although the female estrous cycle did not affect taking or seeking, it appears to influence more granular behaviors.

Sex differences in opioid receptor mediated effects: Role of androgens

An abundance of data indicates there are sex differences in endogenous opioid peptides and opioid receptors, leading to functional differences in sensitivity to opioid receptor mediated behaviors between males and females. Many of these sex differences are mediated by the effects of gonadal hormones on the endogenous opioid system. Whereas much research has examined the role of ovarian hormones on opioid receptor mediated endpoints, comparatively less research has examined the role of androgens. This review describes what is currently known regarding the influence of androgens on opioid receptor mediated endpoints and how androgens may contribute to sex differences in these effects. The review also addresses the clinical implications of androgenic modulation of opioid receptor mediated behaviors and suggests future lines of research for preclinical and clinical investigators. We conclude that further investigation into androgenic modulation of opioid receptor mediated effects may lead to new options for addressing conditions such as chronic pain and substance use disorders.

Sex Differences in Opioid and Psychostimulant Craving and Relapse: A Critical Review

A widely held dogma in the preclinical addiction field is that females are more vulnerable than males to drug craving and relapse. Here, we first review clinical studies on sex differences in psychostimulant and opioid craving and relapse. Next, we review preclinical studies on sex differences in psychostimulant and opioid reinstatement of drug seeking after extinction of drug self-administration, and incubation of drug craving (time-dependent increase in drug seeking during abstinence). We also discuss ovarian hormones' role in relapse and craving in humans and animal models and speculate on brain mechanisms underlying their role in cocaine craving and relapse in rodent models. Finally, we discuss imaging studies on brain responses to cocaine cues and stress in men and women.The results of the clinical studies reviewed do not appear to support the notion that women are more vulnerable to psychostimulant and opioid craving and relapse. However, this conclusion is tentative because most of the studies reviewed were correlational, not sufficiently powered, and not a priori designed to detect sex differences. Additionally, imaging studies suggest sex differences in brain responses to cocaine cues and stress. The results of the preclinical studies reviewed provide evidence for sex differences in stress-induced reinstatement and incubation of cocaine craving but not cue- or cocaine-induced reinstatement of cocaine seeking. These sex differences are modulated in part by ovarian hormones. In contrast, the available data do not support the notion of sex differences in craving and relapse/reinstatement for methamphetamine or opioids in rodent models. SIGNIFICANCE STATEMENT: This systematic review summarizes clinical and preclinical studies on sex differences in psychostimulant and opioid craving and relapse. Results of the clinical studies reviewed do not appear to support the notion that women are more vulnerable to psychostimulant and opioid craving and relapse. Results of preclinical studies reviewed provide evidence for sex differences in reinstatement and incubation of cocaine seeking but not for reinstatement or incubation of methamphetamine or opioid seeking.

Factors modulating the incubation of drug and non-drug craving and their clinical implications

It was suggested in 1986 that cue-induced cocaine craving increases progressively during early abstinence and remains high during extended periods of time. Clinical evidence now supports this hypothesis and that this increase is not specific to cocaine but rather generalize across several drugs of abuse. Investigators have identified an analogous incubation phenomenon in rodents, in which time-dependent increases in cue-induced drug seeking are observed after abstinence from intravenous drug or palatable food self-administration. Incubation of craving is susceptible to variation in magnitude as a function of biological and/or the environmental circumstances surrounding the individual. During the last decade, the neurobiological correlates of the modulatory role of biological (sex, age, genetic factors) and environmental factors (environmental enrichment and physical exercise, sleep architecture, acute and chronic stress, abstinence reinforcement procedures) on incubation of drug craving has been investigated. In this review, we summarized the behavioral procedures adopted, the key underlying neurobiological correlates and clinical implications of these studies.

Enhanced heroin self-administration and distinct dopamine adaptations in female rats

Increasing evidence suggests that females are more vulnerable to the harmful effects of drugs of abuse, including opioids. Additionally, rates of heroin-related deaths substantially increased in females from 1999 to 2017 [1], underscoring the need to evaluate sex differences in heroin vulnerability. Moreover, the neurobiological substrates underlying sexually dimorphic responding to heroin are not fully defined. Thus, we evaluated male and female Long Evans rats on acquisition, dose-responsiveness, and seeking for heroin self-administration (SA) as well as using a long access model to assess escalation of intake at low and high doses of heroin, 0.025 and 0.1 mg/kg/inf, respectively. We paired this with ex vivo fast-scan cyclic voltammetry (FSCV) in the medial nucleus accumbens (NAc) shell and quantification of mu-opioid receptor (MOR) protein in the ventral tegmental area (VTA) and NAc. While males and females had similar heroin SA acquisition rates, females displayed increased responding and intake across doses, seeking for heroin, and escalation on long access. However, we found that males and females had similar expression levels of MORs in the VTA and NAc, regardless of heroin exposure. FSCV results revealed that heroin exposure did not change single-pulse elicited dopamine release, but caused an increase in dopamine transporter activity in both males and females compared to their naïve counterparts. Phasic-like stimulations elicited robust increases in dopamine release in heroin-exposed females compared to heroin-naïve females, with no differences seen in males. Together, our results suggest that differential adaptations of dopamine terminals may underlie the increased heroin SA behaviors seen in females.

Behavioral sex differences in cocaine and opioid use disorders: The role of gonadal hormones

Females are more vulnerable than males to many aspects of cocaine use disorder. This vulnerability also translates to opioid use disorder, with females exhibiting stronger behavioral responses than males to drugs such as heroin and morphine. While there is evidence for many overlapping neural mechanisms underlying cocaine and opioid abuse, there is also a breadth of evidence indicating divergent effects of the drugs on synaptic plasticity. This makes it unclear whether the behavioral sex differences seen in substance use disorder across different drugs of abuse rely on the same mechanisms. Ovarian hormones have consistently been implicated as drivers of the behavioral sex differences in cocaine taking and seeking. While there are far fewer studies on the role of ovarian hormones in opioid use disorder, the existing data suggest that ovarian hormones may not drive these behavioral effects in the same manner as in cocaine use disorder. This review highlights evidence that behavioral sex differences in substance use disorder might be driven by different mechanisms depending on drug class.

A buprenorphine-validated rat model of opioid use disorder optimized to study sex differences in vulnerability to relapse

RATIONALE

Opioid use disorder (OUD) is a major epidemic in the USA. Despite evidence indicating that OUD may be particularly severe for women, preclinical models have yet to establish sex as a major factor in OUD.

OBJECTIVES

Here, we examined sex differences in vulnerability to relapse following intermittent access fentanyl self-administration and protracted abstinence and used buprenorphine, the FDA-approved treatment for OUD, to test the validity of our model.

METHODS

Following acquisition of fentanyl self-administration under one of two training conditions, male and female rats were given extended, 24-h/day access to fentanyl (0.25 μg/kg/infusion, 10 days) using an intermittent access procedure. Vulnerability to relapse was assessed using an extinction/cue-induced reinstatement procedure following 14 days of abstinence; buprenorphine (0 or 3 mg/kg/day) was administered throughout abstinence.

RESULTS

Levels of drug-seeking were high following extended-access fentanyl self-administration and abstinence; buprenorphine markedly decreased drug-seeking supporting the validity of our relapse model. Females self-administered more fentanyl and responded at higher levels during subsequent extinction testing. Buprenorphine was effective in both sexes and eliminated sex and estrous phase differences in drug-seeking. Interestingly, the inclusion of a time-out during training had a major impact on later fentanyl self-administration in females, but not males, indicating that the initial exposure conditions can persistently impact vulnerability in females.

CONCLUSIONS

These findings demonstrate the utility of this rat model for determining sex and hormonal influences on the development and treatment of OUD.

Cues conditioned to withdrawal and negative reinforcement: Neglected but key motivational elements driving opioid addiction

Opioid use disorder (OUD) is a debilitating disorder that affects millions of people. Neutral cues can acquire motivational properties when paired with the positive emotional effects of drug intoxication to stimulate relapse. However, much less research has been devoted to cues that become conditioned to the aversive effects of opioid withdrawal. We argue that environmental stimuli promote motivation for opioids when cues are paired with withdrawal (conditioned withdrawal) and generate opioid consumption to terminate conditioned withdrawal (conditioned negative reinforcement). We review evidence that cues associated with pain drive opioid consumption, as patients with chronic pain may misuse opioids to escape physical and emotional pain. We highlight sex differences in withdrawal-induced stress reactivity and withdrawal cue processing and discuss neurocircuitry that may underlie withdrawal cue processing in dependent individuals. These studies highlight the importance of studying cues associated with withdrawal in dependent individuals and point to areas for exploration in OUD research.

Female rats express heroin-induced and -conditioned suppression of peripheral nitric oxide production in response to endotoxin challenge

Opioids and opioid-conditioned stimuli (CS) negatively alter host immunity, impairing the response to pathogens during opioid use and following drug cessation. Using male rats, our laboratory has determined that heroin or heroin-CS exposure preceding a lipopolysaccharide (LPS) challenge markedly suppresses normal induction of peripheral pro-inflammatory biomarkers. Presently, it is unknown if these heroin-induced and -conditioned effects extend to the female immune response. To begin this venture, the current study tested the direct effects of heroin and heroin-CS on LPS-induced peripheral nitric oxide (NO) production in female rats. We focused investigations on peripheral NO as it is a critical pro-inflammatory molecule necessary for pathogen resistance. In Experiment 1, male and female Lewis rats were administered 0 (Saline), 1, or 3 mg/kg heroin subcutaneously (s.c). Sixty minutes later, animals were injected with LPS (1 mg/kg, s.c.). Spleen and plasma samples were collected 6 h later to examine NO production through inducible NO synthase (iNOS) expression and nitrate/nitrite concentration, respectively. In Experiment 2, female Lewis rats underwent five, 60-minute context conditioning sessions with heroin (1 mg/kg, s.c.) or saline. On test day, CS-exposed and control (home cage) animals were injected with LPS (1 mg/kg, s.c.). Tissue was collected 6 h later to examine splenic iNOS expression and plasma nitrate/nitrite concentration. Both heroin administration alone and exposure to heroin-CS suppressed LPS-induced indices of NO production in spleen and plasma. Our results are the first to indicate that, similar to males, female rats express heroin-induced and -conditioned immunomodulation to a LPS challenge.

The Impact of Co-occurring Post-traumatic Stress Disorder and Substance Use Disorders on Craving: A Systematic Review of the Literature

The frequent co-occurrence of post-traumatic stress disorder (PTSD) and substance use disorders (SUDs) leads to manifestations of both conditions that are more severe and more resistance to treatment than single disorders. One hypothesis to explain this synergy is the impact of intrusive memories on craving which, in turn, increases the risk of relapse among patients with substance use disorders. The aim of this systematic review is to examine this possibility by assessing the impact of PTSD and its symptoms on craving among dual disorder patients. Using PRISMA criteria, four databases were comprehensively searched up to June, 2021, in order to identify all candidate studies based on broad key words. Resulting studies were then selected if they examined the impact of PTSD or PTSD symptoms on craving, and if they used standardized assessments of PTSD, SUD, and craving. Twenty-seven articles matched the selection criteria and were included in this review. PTSD was found to be significantly associated with increased craving levels among patients with alcohol, cannabis, cocaine, tobacco, and other substance use disorders. Exposition to traumatic cues among dual disorder patients was also shown to trigger craving, with an additive effect on craving intensity when exposure to substance-related cues occurred. In addition, certain studies observed a correlation between PTSD symptom severity and craving intensity. Concerning mechanisms underlying these associations, some findings suggest that negative emotional states or emotion dysregulation may play a role in eliciting craving after traumatic exposure. Moreover, these studies suggest that PTSD symptoms may, independently of emotions, act as powerful cues that trigger craving. These findings argue for the need of dual disorder treatment programs that integrate PTSD-focused approaches and emotion regulation strategies, in addition to more traditional interventions for craving management.

Reduced response inhibition after exposure to drug-related cues in male heroin abstainers

RATIONALE

Deficits in response inhibition associated with heroin use could last several months after abstinence in heroin users, and their response inhibition can also be interfered with task-irrelevant drug-related cues. However, it is unclear whether exposure to drug-related cues affects subsequent response inhibition in heroin users following abstinence.

OBJECTIVES

The present study aimed to investigate how drug-related cues with different durations between stimulus presentations, referred to as stimulus onset asynchronies (SOAs), affect subsequent response inhibition in heroin abstainers (HAs) with different length of abstinence.

METHODS

Sixty-seven male HAs performed a modified Go/NoGo task in which a motor response to frequent Go targets and no response to rare NoGo targets were required and a Go or NoGo target was displayed after either a heroin-related or a neutral picture presented for the 200 ms and 600 ms SOAs.

RESULTS

The HAs responded significantly faster to Go targets following the neutral pictures for the 600 ms SOA compared to other conditions. They also made more commission errors following heroin-related pictures compared to neutral pictures regardless of the SOAs. The shorter-term HAs made more commission errors compared to the longer-term HAs following the 200 ms SOA, and it was only a trend when the SOA was 600 ms. Additionally, negative correlations between the duration of current abstinence and commission errors were observed following cues with the 200 ms SOA.

CONCLUSIONS

Impaired response inhibition in HAs can be improved through protracted drug abstinence. However, that effect can be reduced by exposure to drug-related cues, which may increase the risk of relapse.

Divergent behavioral responses in protracted opioid withdrawal in male and female C57BL/6J mice

Persons suffering from opioid use disorder (OUD) experience long-lasting dysphoric symptoms well into extended periods of withdrawal. This protracted withdrawal syndrome is notably characterized by heightened anxiety and hyperkatifeia. Here, we investigated if an exacerbated withdrawal model of acute morphine dependence results in lasting behavioral adaptation 6 weeks into forced abstinence in C57BL/6J mice. We found that our exacerbated morphine withdrawal paradigm produced distinct alterations in behavior in elevated plus maze (EPM), open field, and social interaction tests in male and female mice. Following protracted withdrawal male mice showed enhanced exploration of the open arms of the EPM, reduced latency to enter the corner of the OF, and a social interaction deficit. In contrast, female mice showed enhanced thigmotaxis in the OF. In both sexes, protracted withdrawal enhanced locomotor behavior in response to subsequent morphine challenge, albeit at different doses. These findings will be relevant for future investigation examining the neural mechanisms underlying these behaviors and will aid in uncovering physiological sex differences in response to opioid withdrawal.

Age- and sex-related changes in the severity of physical and psychological dependence in morphine-dependent rats

Gender- and age-dependent effects on the severity of morphine dependence are still controversial. The aim of this study was to investigate the effects of age and sex on the severity of physical and psychological dependence in morphine-dependent rats. The adult/aged male and female Wistar rats were chronically treated with bi-daily doses (10 mg/kg, at 12 h intervals) of morphine for 14 days. Then, rats were tested for the severity of physical dependence on morphine (spontaneous withdrawal signs), anxiety-like (the elevated plus maze), depressive-like (sucrose preference test) and grooming behaviors after spontaneous morphine withdrawal. We found that the morphine withdrawal signs decreased after 3 and 7 days of withdrawal in female and male rats respectively, while there was no significant difference in overall dependence severity between the two sexes or ages. Also, we found that the withdrawal of morphine led to increased anxiety, depression and obsessive-compulsive behavior in the D (dependent)/Adult male and female rats. Also, the D/aged female and male rats exhibited a reduction in depressive-like behavior than the D/Adult rats. Moreover, the D/female rats exhibited a decreased obsessive-compulsive behavior in both age groups than male rats. We conclude that age has no effect on the duration of withdrawal from morphine and overall dependence severity. While, the duration of withdrawal from morphine was lower in female than male rats. Our results showed a sex difference on the duration of morphine withdrawal and an age difference in the expression of psychological dependence on morphine. Thus, therapeutic strategies may be different for opiate-dependent individuals in physical and psychological dimensions.

Forging Neuroimaging Targets for Recovery in Opioid Use Disorder

The United States is in the midst of an opioid epidemic and lacks a range of successful interventions to reduce this public health burden. Many individuals with opioid use disorder (OUD) consume drugs to relieve physical and/or emotional pain, a pattern that may increasingly result in death. The field of addiction research lacks a comprehensive understanding of physiological and neural mechanisms instantiating this cycle of Negative Reinforcement in OUD, resulting in limited interventions that successfully promote abstinence and recovery. Given the urgency of the opioid crisis, the present review highlights faulty brain circuitry and processes associated with OUD within the context of the Three-Stage Model of Addiction (1). This model underscores Negative Reinforcement processes as crucial to the maintenance and exacerbation of chronic substance use together with Binge/Intoxication and Preoccupation/Anticipation processes. This review focuses on cross-sectional as well as longitudinal studies of relapse and treatment outcome that employ magnetic resonance imaging (MRI), functional near-infrared spectroscopy (fNIRs), brain stimulation methods, and/or electroencephalography (EEG) explored in frequency and time domains (the latter measured by event-related potentials, or ERPs). We discuss strengths and limitations of this neuroimaging work with respect to study design and individual differences that may influence interpretation of findings (e.g., opioid use chronicity/recency, comorbid symptoms, and biological sex). Lastly, we translate gaps in the OUD literature, particularly with respect to Negative Reinforcement processes, into future research directions involving operant and classical conditioning involving aversion/stress. Overall, opioid-related stimuli may lessen their hold on frontocingulate mechanisms implicated in Preoccupation/Anticipation as a function of prolonged abstinence and that degree of frontocingulate impairment may predict treatment outcome. In addition, longitudinal studies suggest that brain stimulation/drug treatments and prolonged abstinence can change brain responses during Negative Reinforcement and Preoccupation/Anticipation to reduce salience of drug cues, which may attenuate further craving and relapse. Incorporating this neuroscience-derived knowledge with the Three-Stage Model of Addiction may offer a useful plan for delineating specific neurobiological targets for OUD treatment.

Prelimbic cortex is a common brain area activated during cue-induced reinstatement of cocaine and heroin seeking in a polydrug self-administration rat model

Many preclinical studies examined cue-induced relapse to heroin and cocaine seeking in animal models, but most of these studies examined only one drug at a time. In human addicts, however, polydrug use of cocaine and heroin is common. We used a polydrug self-administration relapse model in rats to determine similarities and differences in brain areas activated during cue-induced reinstatement of heroin and cocaine seeking. We trained rats to lever press for cocaine (1.0 mg/kg per infusion, 3-hr/day, 18 day) or heroin (0.03 mg/kg per infusion) on alternating days (9 day for each drug); drug infusions were paired with either intermittent or continuous light cue. Next, the rats underwent extinction training followed by tests for cue-induced reinstatement where they were exposed to either heroin- or cocaine-associated cues. We observed cue-selective reinstatement of drug seeking: the heroin cue selectively reinstated heroin seeking and the cocaine cue selectively reinstated cocaine seeking. We used Fos immunohistochemistry to assess cue-induced neuronal activation in different subregions of the medial prefrontal cortex, dorsal striatum, nucleus accumbens, and amygdala. Fos expression results indicated that only the prelimbic cortex (PL) was activated by both heroin and cocaine cues; in contrast, no significant cue-induced neuronal activation was observed in other brain areas. RNA in situ hybridization indicated that the proportion of glutamatergic and GABAergic markers in PL Fos-expressing cells was similar for the heroin and cocaine cue-activated neurons. Overall, the results indicate that PL may be a common brain area involved in both heroin and cocaine seeking during polydrug use.

Sex differences in daily life stress and craving in opioid-dependent patients

BACKGROUND

Responses to stress and drug craving differ between men and women. Differences in the momentary experience of stress in relation to craving are less well-understood.

OBJECTIVES

Using ecological momentary assessment (EMA), we examined sex differences in real-time in two areas: (1) causes and contexts associated with stress, and (2) the extent to which stress and drug cues are associated with craving.

METHODS

Outpatients on opioid-agonist treatment (135 males, 47 females) reported stress, craving, and behavior on smartphones for 16 weeks. They initiated an entry each time they felt more stressed than usual (stress event) and made randomly prompted entries 3 times/day. In stress-event entries, they identified the causes and context (location, activity, companions), and rated stress and craving severity.

RESULTS

The causes reported for stress events did not differ significantly by sex. Women reported arguing and being in a store more often during stress events, and men reported working more often during stress events, compared to base rates (assessed via random prompts). Women showed a greater increase in opioid craving as a function of stress (p < 0.0001) and had higher stress ratings in the presence of both stress and drug cues relative to men (p < 0.01). Similar effects were found for cocaine craving in men (p < 0.0001).

CONCLUSION

EMA methods provide evidence based on real-time activities and moods that opioid-dependent men and women experience similar contexts and causes for stress but differ in stress- and cue-induced craving. These findings support sex-based tailoring of treatment, but because not all participants conformed to the overall pattern of sex differences, any such tailoring should also consider person-level differences.

Sex as a biological variable: Drug use and abuse

The study of sex as a biological variable is a necessary emphasis across a wide array of endpoints, including basic neuroscience, medicine, mental health, physiology and behavior. The present review summarizes work from clinical and preclinical populations on sex differences in drug use and abuse, ranging from initiation to escalation/dysregulation and from drug cessation/abstinence to relapse. These differences are analyzed in the context of the addiction cycle conceptualization of Koob and his colleagues and address patterns of drug use (binge/intoxication), motivation underlying its use (withdrawal/negative affect) and likelihood and causes of craving and relapse of drug taking (preoccupation/anticipation). Following this overview, an assessment of the basis for the reported sex differences is discussed in the context of the affective (rewarding and aversive) properties of drugs of abuse and how such properties and their balance vary with sex and contribute to drug intake. Finally, the interaction of sex with several experiential (drug history) and subject (age) factors and how these interactions affect reward and aversion are discussed to highlight the importance of understanding such interactions in predicting drug use and abuse. We note that sex as a biological variable remains one of critical evaluation and that such investigations of sex differences in drug use and abuse continue and be expanded to assess all facets of their mediation, including these affective properties, how their balance may be impacted by the multiple conditions under which drugs are taken and how this overall balance affects drug use and addiction vulnerability.

Effects of sex and remifentanil dose on rats' acquisition of responding for a remifentanil-conditioned reinforcer

Opioid-conditioned reinforcement is thought to exacerbate opioid abuse and dependence. Sex/gender can influence opioid abuse behaviors, but the effects of sex/gender on opioid-conditioned reinforcement, specifically, are unclear. In this study, we compared new-response acquisition with opioid-conditioned reinforcement in male and female rats. First, separate groups received response-independent remifentanil injections (0.0-32.0 μg/kg, intravenous) and presentations of a light-noise stimulus. In the experimental groups, injections and stimulus presentations always co-occurred [paired Pavlovian conditioning (PAV)]; in the control groups, the two occurred independently of each other (random PAV). Next, in the instrumental acquisition (ACQ) sessions, two novel nose-poke manipulanda were introduced. All animals (regardless of sex, dose, and PAV type) could respond in the active nose-poke, which produced the stimulus alone, or in the inactive nose-poke. Both males and females dose-dependently acquired nose-poke responding (active>inactive) after paired PAV, but not after random PAV. Therefore, the stimulus was a conditioned reinforcer. We identified three sex differences. First, only females acquired responding after paired PAV with 32.0 μg/kg remifentanil. Second, using a progressive ratio schedule for ACQ, both sexes acquired responding, but females made significantly more active responses. Third, when a single session of PAV was conducted, only males acquired responding. Thus, rats' sex interacts with pharmacological and environmental factors to determine opioid-conditioned reinforcement.

Behavioral sensitization of the reinforcing value of food: What food and drugs have in common

Sensitization is a basic property of the nervous system whereby repeated exposure to a stimulus results in an increase in responding to that stimulus. This increase in responding contributes to difficulty with treatment of drug abuse, as stimuli associated with substance use become signals or triggers for drug craving and relapse. Our work over the past decade has applied the theoretical framework of incentive sensitization to overeating. We have shown, in several studies, that lean adults do not commonly demonstrate behavioral sensitization after repeated exposure to snack food, but a subset of obese adults reliably does. This review will discuss this change in behavioral response to repeated consumption of snack food in obese individuals and apply the theoretical framework of incentive sensitization to drugs of abuse to high fat/high sugar snack foods. We will also show data that suggest that behavioral sensitization to repeated administration of snack food is predictive of weight gain, which may enhance its utility as a diagnostic tool for identifying at-risk individuals for obesity. Finally, we will discuss the future directions of this line of research, including studying the phenomenon in children and adolescents and determining if similar principles can be used to increase motivation to eat healthier food. A combination of reductions in unhealthy food intake and increases and healthy food intake is necessary to reduce obesity rates and improve health.

Magnitude and duration of cue-induced craving for marijuana in volunteers with cannabis use disorder

AIMS

Evaluate magnitude and duration of subjective and physiologic responses to neutral and marijuana (MJ)-related cues in cannabis dependent volunteers.

METHODS

33 volunteers (17 male) who met DSM-IV criteria for Cannabis Abuse or Dependence were exposed to neutral (first) then MJ-related visual, auditory, olfactory and tactile cues. Mood, drug craving and physiology were assessed at baseline, post-neutral, post-MJ and 15-min post MJ cue exposure to determine magnitude of cue- responses. For a subset of participants (n=15; 9 male), measures of craving and physiology were collected also at 30-, 90-, and 150-min post-MJ cue to examine duration of cue-effects.

RESULTS

In cue-response magnitude analyses, visual analog scale (VAS) items craving for, urge to use, and desire to smoke MJ, Total and Compulsivity subscale scores of the Marijuana Craving Questionnaire, anxiety ratings, and diastolic blood pressure (BP) were significantly elevated following MJ vs. neutral cue exposure. In cue-response duration analyses, desire and urge to use MJ remained significantly elevated at 30-, 90- and 150-min post MJ-cue exposure, relative to baseline and neutral cues.

CONCLUSIONS

Presentation of polysensory MJ cues increased MJ craving, anxiety and diastolic BP relative to baseline and neutral cues. MJ craving remained elevated up to 150-min after MJ cue presentation. This finding confirms that carry-over effects from drug cue presentation must be considered in cue reactivity studies.

Contributions of mobile technologies to addiction research

Mobile technologies are revolutionizing the field of mental health, and particular progress has been made in their application to addiction research and treatment. The use of smartphones and other mobile devices has been shown to be feasible with individuals addicted to any of a wide range of substances, with few biases being observed concerning the repeated monitoring of daily life experiences, craving, or substance use. From a methodological point of view, the use of mobile technologies overcomes longstanding limitations of traditional clinical research protocols, including the more accurate assessment of temporal relationships among variables, as well as the reduction in both contextual constraints and discipline-specific methodological isolation. The present article presents a conceptual review of these advances while using illustrations of research applications that are capable of overcoming specific methodological barriers. Finally, a brief review of both the benefits and risks of mobile technology use for the treatment of patients will be addressed.

Heart Rate Variability and the Efficacy of Biofeedback in Heroin Users with Depressive Symptoms

Objective

Low heart rate variability (HRV) has been confirmed in heroin users, but the effects of heart-rate-variability–biofeedback in heroin users remain unknown. This study examined (1) correlations between depression and HRV indices; (2) group differences in HRV indices among a heroin-user group, a group with major depressive disorder but no heroin use, and healthy controls; and (3) the effects of heart-rate-variability–biofeedback on depressive symptoms, HRV indices, and respiratory rates within the heroin group.

Methods

All participants completed a depression questionnaire and underwent electrocardiogram measurements, and group differences in baseline HRV indices were examined. The heroin group underwent electrocardiogram and respiration rate measurements at baseline, during a depressive condition, and during a happiness condition, before and after which they took part in the heart-rate-variability–biofeedback program. The effects of heart-rate-variability–biofeedback on depressive symptoms, HRV indices, and respiration rates were examined.

Results

There was a negative correlation between depression and high frequency of HRV, and a positive correlation between depression and low frequency to high frequency ratio of HRV. The heroin group had a lower overall and high frequency of HRV, and a higher low frequency/high frequency ratio than healthy controls. The heart-rate-variability–biofeedback intervention increased HRV indices and decreased respiratory rates from pre-intervention to post-intervention.

Conclusion

Reduced parasympathetic and increased sympathetic activations were found in heroin users. Heart-rate-variability–biofeedback was an effective non-pharmacological intervention to restore autonomic balance.

Cue-induced craving to paraphernalia and drug images in opioid dependence

BACKGROUND AND OBJECTIVES

Stimuli that are repeatedly paired with substance use, such as drug paraphernalia, can themselves elicit drug craving. The aim of this study was to examine whether particular cue types elicit greater craving responses than others among individuals with opioid dependence.

METHODS

Participants seeking inpatient treatment for opioid dependence were recruited for a study of cue-induced craving. This sample (N = 50), included 25 primary heroin users, 20 primary prescription opioid users, and 5 users of heroin and prescription opioids equally. Participants completed a cue reactivity task, in which images of drug-related stimuli were presented on a computer screen, each followed by a question assessing state drug craving.

RESULTS

Overall, participants reported higher craving following paraphernalia stimuli relative to drug stimuli. However, this was moderated by opioid type; there was significantly higher craving in response to images of paraphernalia cues in the heroin group, and higher craving in response to drug cues in the prescription opioid group.

DISCUSSION AND CONCLUSIONS

These findings highlight potential differences in cue reactivity to opioid paraphernalia and drug cues, which appears to be moderated by drug type.

SCIENTIFIC SIGNIFICANCE

Cue-induced craving is an important factor in relapse. This study adds further to the literature on cue-induced craving in opioid dependence, suggesting that craving may vary based on both cue type and opioid type. Future studies designed to discriminate the impact of substance of abuse, route of administration, and cue type will help to further clarify cue-induced craving in this population.

Craving and substance use among patients with alcohol, tobacco, cannabis or heroin addiction: a comparison of substance- and person-specific cues

BACKGROUND AND AIMS

It is well established that craving increases following exposure to substance-related 'cues', but the role of life-styles or substance use habits that are unique to each person remains poorly understood. This study examines the association of substance-specific and personal cues with craving and substance use in daily life.

DESIGN

Ecological momentary assessment was used during a 2-week period.

SETTING

Data were collected in a French out-patient addiction treatment centre.

PARTICIPANTS

A total of 132 out-patients beginning treatment for alcohol, tobacco, cannabis or opiate addiction were included.

MEASUREMENTS

Using mobile technologies, participants were questioned four times per day relative to craving, substance use and exposure to either substance-specific cues (e.g. seeing a syringe) or personal cues unique to that individual (e.g. seeing the specific person with whom the substance is used).

FINDINGS

Craving intensity was associated with the number of concurrently assessed substance-specific cues (t = 4.418, P < 0.001) and person-specific cues (t = 4.006, P < 0.001) when analysed jointly within the same model. However, only person-specific cues were associated with increases in craving over subsequent hours of the day (t = 2.598, P < 0.05). Craving intensity, in turn, predicted increases in later substance use (t = 4.076, P < 0.001). Causal mediation analyses demonstrated that the association of cues with later substance use was mediated by craving intensity (mediated effect = 0.007, 95% confidence interval = 0.004-0.011).

CONCLUSIONS

Unique person-specific cues appear to have a robust effect on craving addictive substances, and the duration of this association may persist longer than for more general substance-specific cues. Mobile technologies provide new opportunities for understanding these person-specific risk factors and for providing individually tailored interventions.

Effect of oral THC pretreatment on marijuana cue-induced responses in cannabis dependent volunteers

BACKGROUND

The current study tested whether oral Δ(9)-tetrahydrocannabinol (THC: 0-, 10-, and 20-mg) pretreatment would attenuate polysensory cue-induced craving for marijuana.

METHODS

Cannabis dependent participants (7 males and 7 females, who smoked on average 5.4 ± 1.1 blunts daily) completed 3 experimental sessions (oral THC pretreatment dose; counterbalanced order) using a placebo-controlled within-subject crossover design. During each session, participants completed a baseline evaluation and were first exposed to neutral cues then marijuana cues while physiological measures and subjective ratings of mood, craving, and drug effect were recorded.

RESULTS

Following placebo oral THC pretreatment, marijuana (vs. neutral) cues significantly increased ratings of marijuana craving (desire and urge to use, Marijuana Craving Questionnaire (MCQ)-Compulsivity scale), anxious mood and feeling hungry. Males also reported feeling more "Down" during marijuana cues relative to females. Pretreatment with oral THC (10-mg and/or 20-mg vs. placebo) significantly attenuated marijuana cue-induced increases in craving and anxiety but not hunger. Oral THC attenuation of the cue-induced increase in MCQ-Compulsivity ratings was observed in females only. Oral THC produced statistically (but not clinically) significant increases in heart rate and decreases in diastolic blood pressure, independent of cues.

CONCLUSIONS

These marijuana-cue findings replicate earlier results and further demonstrate that oral THC can attenuate selected effects during marijuana multi-cue exposure, and that some of these effects may be sex-related. Results of this study suggest oral THC may be effective for reducing marijuana cue-elicited (conditioned) effects. Further study is needed to determine whether females may selectively benefit from oral THC for this purpose.

Ecological momentary assessment in the investigation of craving and substance use in daily life: a systematic review

BACKGROUND

Craving is viewed as a major determinant of relapse in persons with substance addiction, but this association remains poorly understood due to its time-limited nature and the biases associated with retrospective reporting. Ecological momentary assessment (EMA) offers new opportunities to examine both craving and substance use with strong ecological validity by collecting real-time data in daily life. This review examined all published studies using EMA to: (1) assess the link between craving and substance use; and (2) identify relevant moderators of craving among substance users.

METHODS

We searched PubMed and PsycInfo databases up to October 31, 2013.

RESULTS

Ninety-one studies were selected, involving mostly tobacco smokers (73%). A majority of studies (92%) reported a positive relationship between craving and substance use, concurrently and prospectively, and among users with different levels of use for both legal and illegal substances. Results suggest that craving is a stronger predictor of relapse episodes when assessed in close temporal proximity to substance use. EMA data also confirmed the influence of diverse within-person and between-person sources of variation in daily life craving reports.

CONCLUSIONS

This review provides strong support for the link between craving and substance use, and underscores the importance of the timing of assessments.

Brain-derived neurotrophic factor and addiction: Pathological versus therapeutic effects on drug seeking

Many abused drugs lead to changes in endogenous brain-derived neurotrophic factor (BDNF) expression in neural circuits responsible for addictive behaviors. BDNF is a known molecular mediator of memory consolidation processes, evident at both behavioral and neurophysiological levels. Specific neural circuits are responsible for storing and executing drug-procuring motor programs, whereas other neural circuits are responsible for the active suppression of these "seeking" systems. These seeking-circuits are established as associations are formed between drug-associated cues and the conditioned responses they elicit. Such conditioned responses (e.g. drug seeking) can be diminished either through a passive weakening of seeking- circuits or an active suppression of those circuits through extinction. Extinction learning occurs when the association between cues and drug are violated, for example, by cue exposure without the drug present. Cue exposure therapy has been proposed as a therapeutic avenue for the treatment of addictions. Here we explore the role of BDNF in extinction circuits, compared to seeking-circuits that "incubate" over prolonged withdrawal periods. We begin by discussing the role of BDNF in extinction memory for fear and cocaine-seeking behaviors, where extinction circuits overlap in infralimbic prefrontal cortex (PFC). We highlight the ability of estrogen to promote BDNF-like effects in hippocampal-prefrontal circuits and consider the role of sex differences in extinction and incubation of drug-seeking behaviors. Finally, we examine how opiates and alcohol "break the mold" in terms of BDNF function in extinction circuits.

Laboratory-induced cue reactivity among individuals with prescription opioid dependence

Prescription opioid (PO) dependence is a critical health problem. Although examination of drug cue reactivity paradigms has advanced the understanding of risk factors for relapse for a variety of substances (e.g., cocaine, alcohol, nicotine), no PO specific drug cue paradigm has been developed. The current study addressed this gap in the literature and evaluated the ability of a newly developed PO drug cue paradigm to elicit subjective, physiological, and neuroendocrine changes among PO-dependent participants (n = 20) as compared to controls (n = 17). The drug cue paradigm included an induction script, viewing and handling paraphernalia (e.g., bottle of oxycontin pills, pill crusher) and watching a video depicting people using POs as well as places related to POs (e.g., pharmacies). Consistent with hypotheses, the PO group demonstrated significant pre- to post-cue increases on subjective ratings of craving, difficulty resisting POs, stress, and anger. The control group did not demonstrate significant changes on any of the subjective measures. Both the PO group and the control group evidenced significant pre- to post-cue increases in physiological responses (e.g., blood pressure, skin conductance), as expected given the arousing nature of the drug cue stimuli. The PO group, but not the control group, evidenced a significant pre- to post-cue increase in heart rate and salivary cortisol levels. The development and validation of a drug cue paradigm for POs may help inform future research and treatment development efforts for patients with PO dependence.

Cue-induced craving in dependence upon prescription opioids and heroin

BACKGROUND AND OBJECTIVES

Cues associated with heroin use (eg, needles, powder) elicit robust craving responses in individuals dependent upon heroin. Elevated cue-induced craving may be a risk factor for relapse and can persist after periods of drug abstinence. Despite the growing prevalence of opioid dependence involving prescription opioids, published studies have yet to examine whether cue-induced craving is also present in prescription opioid dependence.

METHODS

A sample of 50 adults diagnosed with opioid dependence (20 prescription opioid users, 25 heroin users, and 5 mixed opioid users) completed a cue reactivity assessment. Participants were administered a series of 90 pictures, including heroin-specific, prescription opioid-specific, and neutral images, and were asked to rate craving and cue salience after each image.

RESULTS

Both the prescription opioid and heroin groups experienced significantly more craving to drug than to neutral stimuli. The prescription opioid group reported significantly less craving to prescription opioid stimuli than the heroin group to heroin stimuli; however, this effect was smaller and non-significant when controlling for group differences in cue salience.

DISCUSSION AND CONCLUSIONS

This study found evidence for cue-induced craving in individuals dependent upon prescription opioids. Further research is needed to better understand the role of cue reactivity in the course and treatment of opioid dependence involving prescription opioid use.

SCIENTIFIC SIGNIFICANCE

As elevated craving reactivity to drug cues may reflect a risk factor for relapse, understanding the nature of cue-induced craving in individuals with opioid dependence is important to improving treatments for this population.

Sustained incentive value of heroin-related cues in short- and long-term abstinent heroin users

Models of addiction and addiction memory propose that drug-associated cues elicit incentive effects in drug users, which play an important role in maintenance of drug use and relapse. Incentive effects have been demonstrated for smoking and alcohol-related cues but evidence for heroin-related cues has been inconclusive. Furthermore, it is unknown whether appetitive effects of heroin-related cues persist after prolonged abstinence, although heroin addiction is known to have high relapse rates. Therefore, we investigated implicit and explicit valence of heroin-related cues in dependent users at different stages of abstinence using affective startle modulation. In Study I, 15 current heroin users were measured before and after detoxification. Correspondingly, 15 healthy control participants were tested twice at an interval of 14 days. In Study II, 14 long-term abstinent heroin users were additionally measured in a single session. Implicit processing of drug-related stimuli was assessed using affective startle modulation by pictures of heroin and smoking scenes. Explicit reactions were measured using ratings of valence and craving. In contrast to controls, heroin-dependent participants showed a clear reduction of startle response during heroin-related pictures (p<0.05). Detoxification did not significantly change their startle responses to heroin-cues. No difference between non-detoxified current and long-term abstinent heroin users was found in implicit reactions to heroin-cues, whereas explicit measures differed between both groups (all p<0.05). After detoxification and even after prolonged abstinence, heroin cues still exert implicit appetitive effects in heroin users. This implies that drug-induced adaptations of reward circuits are long-lasting, resulting in a highly stable addiction memory.

Sex differences in cocaine/heroin users: drug-use triggers and craving in daily life

BACKGROUND

Studies of sex differences have shown that men and women with drug-use disorders differ in course and outcome and in cue-induced activation of putative brain "control network" areas. We evaluated sex differences in daily functioning and subjective events related to drug use with ecological momentary assessment (EMA).

METHODS

EMA data were collected from cocaine- and heroin-using outpatients (72 men; 42 women) in methadone maintenance in 2-5 randomly prompted (RP) entries per day and in participant-initiated entries for heroin or cocaine use or craving, for up to 25 weeks. Urine drug screens were conducted three times weekly. Data were analyzed via repeated-measures logistic regression, using sex as a predictor of responses.

RESULTS

In RP reports, women and men reported significantly different patterns of drug-cue exposure, with women significantly more likely to report having seen cocaine or been tempted to use in the past hour. Women also had higher craving after past-hour exposure to drug cues. In reports of drug use, women, compared to men, were more likely to report that they had used more cocaine than they had meant to, tended to feel guilty more often after drug use, and to have used despite trying not to use.

CONCLUSIONS

These findings provide real-time behavioral evidence that women respond differently than men to exposure to drug cues and to drug use, consistent with laboratory and brain-imaging findings. This information may be useful for development of sex-specific treatment strategies.

Disrupted integrity of white matter in heroin-addicted subjects at different abstinent time

PURPOSE

To investigate and compare the integrity of white matter in heroin-addicted and healthy control subjects at different abstinent time using diffusion tensor imaging.

MATERIALS AND METHODS

We performed voxelwise analysis of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in 35 currently abstinent heroin abusers who were divided into long-term group (n = 17) and short-term group (n = 18) and 17 healthy volunteers. Measurements of FA and ADC of the identified regions (genu and splenium of corpus callosum, bilateral frontal lobe) were obtained from all subjects.

RESULTS

The FA at callosal splenium was higher in the long-term group than in the short-term group (P < 0.05). The FA at left prefrontal cortex was higher in the short-term group than in the long-term group (P < 0.05). No significant difference in ADC was found among the 3 groups. The education history had a positive correlation with the FA value on the gena of corpus callosum (r = 0.402, P = 0.017). Months of abstinence had a negative correlation with left frontal FA (r = -0.366, P = 0.03) and a positive correlation with splenium FA (r = 0.348, P = 0.04).

CONCLUSIONS

Heroin abuse seems to alter white matter microstructure differentially in long-term and short-term heroin addicts. This study will contribute to the current literature by examining the quality of white matter fiber structure in heroin abstinence.

Gender differences in craving and cue reactivity to smoking and negative affect/stress cues

There is evidence that women may be less successful when attempting to quit smoking than men. One potential contributory cause of this gender difference is differential craving and stress reactivity to smoking- and negative affect/stress-related cues. The present human laboratory study investigated the effects of gender on reactivity to smoking and negative affect/stress cues by exposing nicotine dependent women (n = 37) and men (n = 53) smokers to two active cue types, each with an associated control cue: (1) in vivo smoking cues and in vivo neutral control cues, and (2) imagery-based negative affect/stress script and a neutral/relaxing control script. Both before and after each cue/script, participants provided subjective reports of smoking-related craving and affective reactions. Heart rate (HR) and skin conductance (SC) responses were also measured. Results indicated that participants reported greater craving and SC in response to smoking versus neutral cues and greater subjective stress in response to the negative affect/stress versus neutral/relaxing script. With respect to gender differences, women evidenced greater craving, stress and arousal ratings and lower valence ratings (greater negative emotion) in response to the negative affect/stressful script. While there were no gender differences in responses to smoking cues, women trended towards higher arousal ratings. Implications of the findings for treatment and tobacco-related morbidity and mortality are discussed.

Depot naltrexone decreases rewarding properties of sugar in patients with opioid dependence

BACKGROUND

Opioid neurotransmission mediates hedonic value of sweet tastants; their intake may be exaggerated by the consumption of exogenous opioids (e.g., opioid dependence). Sweet Taste Test (STT) is a validated quantitative instrument assessing taste perception and hedonic features of sugar (sucrose) using a randomized and double-blind administration at five different sucrose concentrations ranging from 0.05 to 0.83 M.

METHODS

The STT and cue-induced craving procedure were administered to opioid-dependent patients (n = 15) before and 1 week after the injection of a long-acting depot naltrexone (XRNT) preparation.

RESULTS

Analyses of covariance, employing sucrose concentration and its perceived taste as covariates, showed that XRNT therapy significantly reduced the self-reported hedonic and motivational characteristics of sucrose. Greater reductions in both these characteristics were associated with more diminution in the cue-induced opioid craving.

CONCLUSIONS

Opioid antagonism in opioid-dependent subjects leads to a smaller sweet taste reward, which, in turn, may be proportional to decreased opioid craving. These pilot results support the heuristic value of the STT as a potential marker of the XRNT treatment response and call for further inquiry into potential clinical applications of the test.

Cue-induced reactivity, cortisol response and substance use outcome in treated heroin dependent individuals

BACKGROUND

Environmental stimuli associated with drug taking have been known to elicit drug craving and physiologic arousal, as well as hypothalamic-pituitary-adrenal axis activation. However, the relationship between these responses and substance use outcomes in heroin-dependent subjects has not been previously studied. We investigated the relationship among subjective and physiologic reactivity, biological stress response evoked in the laboratory, and relapse to substance use in treated opiate-dependent individuals.

METHODS

Eighteen opiate-abstinent methadone- or buprenorphine-treated patients and 13 control subjects were exposed to neutral- and drug-cue exposure laboratory sessions with a 3-month follow-up period. Exposure to cues involved both videotapes and handling during a 100-min session. Subjective craving, agonistic effects, withdrawal feelings, galvanic skin resistance, and salivary cortisol were assessed. Substance use outcome among patients was examined during the follow-up phase. Differences between relapsers, nonrelapsers, and controls were analyzed with respect to the data on drug-cue responsivity and on cortisol responses using repeated-measures analysis of variance. The association with substance use outcome was assessed using a nominal logistic model.

RESULTS

Relapsers experienced greater drug-cue induced subjective responses and an increased cortisol response compared with both nonrelapsers and control subjects. After adjusting on covariates, cue-induced cortisol response was associated with the relapser group and was highly correlated with self-reports of "high."

CONCLUSIONS

Subjects defined as relapsers presented a higher cue-induced reactivity during the drug-cue exposure as well as an increased cortisol response to drug cues. Higher cortisol response to drug cues may increase relapse vulnerability in stable-dose buprenorphine or methadone-maintained subjects.

Pharmacological enhancement of drug cue extinction learning: translational challenges

Augmentation of cue exposure (extinction) therapy with cognitive-enhancing pharmacotherapy may constitute a rational strategy for the clinical management of drug relapse. While certain success has been reported for this form of therapy in anxiety disorders, in this paper we highlight several obstacles that may undermine the efficacy of exposure therapy for substance use disorders. We also review translational studies that have evaluated the facilitative effects of the cognitive enhancer D-cycloserine on extinction targeting drug-related cues. Finally, important considerations for the design and implementation of future studies evaluating exposure therapy combined with pharmacotherapy for substance use disorders are discussed.

Is there a gender difference in associates of adolescents' lifetime illicit drug use in Tehran, Iran?

INTRODUCTION

Information regarding gender differences in drug use of adolescents is essential for designing gender-specific drug prevention policies. This study was conducted in high school students in Tehran, Iran, in 2007. Here, we report the gender differences in lifetime prevalence as well as psychosocial associates of drug use.

MATERIAL AND METHODS

This was a gender analysis of the data collected in a drug use survey conducted in a random sample of high school adolescents (573 boys and 551 girls) in Tehran, Iran, 2007. Demographic characteristics, parental and peers' substance use, school performance, religious beliefs, attachment, self-esteem and emotional intelligence (EI) were entered in logistic regression analyses to predict the lifetime illicit drug use in boy and girls, separately.

RESULTS

Boys were more likely to report lifetime illicit drug use than girls (10.1% vs. 6.4%, p = 0.023). Differences in the risk profile associated with lifetime illicit drug use by gender included history of substance use in the family, higher score of attachment, and having an employed mother as predictors of substance use in boys, but not girls.

CONCLUSIONS

Understanding this gender difference in predictors of lifetime use of illicit drugs in high school adolescents facilitates the design of gender-sensitive drug use preventive programmes. It seems that family variables may have more value in prevention of illicit drug use in male adolescents.