Drug-induced dysphoria is enhanced following prolonged cocaine abstinence and dynamically tracked by nucleus accumbens neurons

Randomized, placebo-controlled trial of injectable extended-release naltrexone and injectable extended-release buprenorphine for cocaine use disorder (CURB-2): Study rationale and design

BACKGROUND

Cocaine remains the most abused stimulant, causing considerable morbidity and mortality. Despite decades of research, there is no FDA-approved medication to treat cocaine use disorder (CUD). In individuals with cocaine and opioid dependence/abuse, extended-release injectable naltrexone (XR-NTX) and sublingual buprenorphine (BUP; 16 mg with naloxone; Suboxone) reduced cocaine use compared to placebo and XR-NTX in the 'Cocaine Use Reduction with Buprenorphine' (CURB; CTN-0048) study.

OBJECTIVES

The CURB-2 (CTN-0109) study aims to examine whether administering XR-NTX in combination with extended-release injectable buprenorphine (XR-BUP), thus creating a "kappa antagonist," is an effective pharmacotherapy compared to placebo for the treatment of CUD.

STUDY DESIGN

CURB-2 is a fully powered, phase IIb, randomized, placebo-controlled trial. Approximately 426 participants will be randomized across 12 study sites in the United States. There will be a 1-week medication induction phase, an 8-week active medication phase, and a 4-week follow-up phase. XR-NTX (Day 1, Week 3, Week 6) will be administered before XR-BUP (Day 4, Week 4). With naltrexone blocking the mu-opioid receptors, the reinforcing effects of buprenorphine will be blocked while leaving the kappa antagonist effects.

DISCUSSION

If this kappa antagonist approach demonstrates efficacy in reducing urine-verified cocaine use compared to placebo, XR-NTX and XR-BUP combination therapy would be an important tool in addressing cocaine use disorder.

CLINICAL TRIALS REGISTRATION

https://clinicaltrials.gov/ct2/show/NCT05262270.

The amygdala-ventral pallidum pathway contributes to a hypodopaminergic state in the ventral tegmental area during protracted abstinence from chronic cocaine

BACKGROUND AND PURPOSE

Incubation of craving, the progressive increase in drug seeking over the first weeks of abstinence, is associated with temporal changes during abstinence in the activity of several structures involved in drug-seeking behaviour. Decreases of dopamine (DA) release and DA neuronal activity (hypodopaminergic state) have been reported in the ventral tegmental area (VTA) during cocaine abstinence, but the mechanisms underlying these neuroadaptations are not well understood. We investigated the potential involvement of a VTA inhibiting circuit (basolateral amygdala [BLA]-ventral pallidum [VP] pathway) in the hypodopaminergic state associated with abstinence from chronic cocaine.

EXPERIMENTAL APPROACH

In a model of cocaine self-administration, we performed in vivo electrophysiological recordings of DA VTA neurons and BLA neurons from anaesthetised rats during early and protracted abstinence and evaluated the involvement of the BLA-VP pathway using a pharmacological approach.

KEY RESULTS

We found significant decreases in VTA DA population activity and significant increases in BLA activity after protracted but not after short-term abstinence from chronic cocaine. The decrease in VTA DA activity was restored by pharmacological inhibition of the activity of either the BLA or the VP, suggesting that these regions exert a negative influence on DA activity.

CONCLUSION AND IMPLICATIONS

Our study sheds new lights on neuroadaptations occurring during incubation of craving leading to relapse. In particular, we describe the involvement of the BLA-VP pathway in cocaine-induced decreases of DA activity in the VTA. This study adds important information about the specific brain network dysfunctions underlying hypodopaminergic activity during abstinence.

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.

Noninvasive Brain Stimulation Rescues Cocaine-Induced Prefrontal Hypoactivity and Restores Flexible Behavior

BACKGROUND

To obtain desirable goals, individuals must predict the outcome of specific choices, use that information to direct appropriate actions, and adjust behavior accordingly in changing environments (behavioral flexibility). Substance use disorders are marked by impairments in behavioral flexibility along with decreased prefrontal cortical function that limits the efficacy of treatment strategies. Restoring prefrontal hypoactivity, ideally in a noninvasive manner, is an intriguing target for improving flexible behavior and treatment outcomes.

METHODS

A behavioral flexibility task was used in Long-Evans male rats (n = 97) in conjunction with electrophysiology, optogenetics, and a novel rat model of transcranial alternating current stimulation (tACS) to examine the prelimbic cortex (PrL) to nucleus accumbens (NAc) core circuit in behavioral flexibility and determine whether tACS can restore cocaine-induced neural and cognitive dysfunction.

RESULTS

Optogenetic inactivation revealed that the PrL-NAc core circuit is necessary for the ability to learn strategies to flexibly shift behavior. Cocaine self-administration history caused aberrant PrL-NAc core neural encoding and deficits in flexibility. Optogenetics that selectively activated the PrL-NAc core pathway prior to learning rescued cocaine-induced cognitive flexibility deficits. Remarkably, tACS prior to learning the task reestablished adaptive signaling in the PrL-NAc circuit and restored flexible behavior in a relatively noninvasive and frequency-specific manner.

CONCLUSIONS

We establish a role of NAc core-projecting PrL neurons in behavioral flexibility and provide a novel noninvasive brain stimulation method in rats to rescue cocaine-induced frontal hypofunction and restore flexible behavior, supporting a role of tACS as a therapeutic to treat cognitive deficits in substance use disorders.

Corticosterone in the ventral hippocampus differentially alters accumbal dopamine output in drug-naïve and amphetamine-withdrawn rats

Dysregulation in glucocorticoid stress and accumbal dopamine reward systems can alter reward salience to increase motivational drive in control conditions while contributing to relapse during drug withdrawal. Amphetamine withdrawal is associated with dysphoria and stress hypersensitivity that may be mediated, in part, by enhanced stress-induced corticosterone observed in the ventral hippocampus. Electrical stimulation of the ventral hippocampus enhances accumbal shell dopamine release, establishing a functional connection between these two regions. However, the effects of ventral hippocampal corticosterone on this system are unknown. To address this, a stress-relevant concentration of corticosterone (0.24ng/0.5 μL) or vehicle were infused into the ventral hippocampus of urethane-anesthetized adult male rats in control and amphetamine withdrawn conditions. Accumbal dopamine output was assessed with in vivo chronoamperometry. Corticosterone infused into the ventral hippocampus rapidly enhanced accumbal dopamine output in control conditions, but produced a biphasic reduction of accumbal dopamine output in amphetamine withdrawal. Selectively blocking glucocorticoid-, mineralocorticoid-, or cytosolic receptors prevented the effects of corticosterone. Overall, these results suggest that the ability of corticosterone to alter accumbal dopamine output requires cooperative activation of mineralocorticoid and glucocorticoid receptors in the cytosol, which is dysregulated during amphetamine withdrawal. These findings implicate ventral hippocampal corticosterone in playing an important role in driving neural systems involved in positive stress coping mechanisms in healthy conditions, whereas dysregulation of this system may contribute to relapse during withdrawal.

A Neuronal Ensemble in the Rostral Agranular Insula Tracks Cocaine-Induced Devaluation of Natural Reward and Predicts Cocaine Seeking

In substance use disorders, negative affect associated with drug withdrawal can elicit strong drug craving and promote relapse. One brain region implicated in those processes is the rostral agranular insular cortex (RAIC), although precisely how this region encodes negative affect associated with drug seeking is unknown. Here, a preclinical model was used where RAIC activity was examined in male Sprague Dawley rats during intraoral infusions of a sweet (saccharin) paired with impending but delayed access to cocaine self-administration, and for comparative purposes, during the sweet predicting saline self-administration or injection of lithium chloride (LiCl), or during intraoral infusions of a bitter taste (quinine). Consistent with previous work, cocaine-paired saccharin, LiCl-paired saccharin, and quinine all elicited aversive taste reactivity. However, the aversive taste reactivity elicited by the cocaine-paired tastant was qualitatively different from that evoked by the other two agents. Furthermore, differences in taste reactivity were reflected in RAIC cell firing, where distinct shifts in neural signaling were observed specifically after cocaine but not LiCl conditioning. Notably, low motivation for cocaine (indicated by low loading and slower latencies to lever press) was correlated with this shift in RAIC signaling, but aversive (gaping) responses were not. Collectively, these findings indicate that cocaine-paired tastants elicit unique aspects of aversive behaviors that differ from traditional conditioned taste aversion (LiCl) or quinine and that the RAIC plays a role in modulating drug-seeking behaviors driven by drug-induced dysphoria (craving), but not negative affect per se.SIGNIFICANCE STATEMENT In substance use disorders, negative affect associated with drug cues can elicit craving and promote relapse; however, the underlying neurocircuitry of this phenomenon is unknown. Here, we investigated the role of the rostral agranular insula cortex (RAIC) in these processes using a preclinical model wherein intraoral delivery of a sweet is paired with delayed access to cocaine self-administration. The taste comes to elicit negative affect that predicts heightened drug seeking. Here, we found that a population of RAIC neurons became inhibited during presentation of the cocaine-paired tastant (when negative affect is high) and that this inhibitory neural profile predicted lower drug seeking. These findings suggest that the RAIC may function to oppose cue-induced cocaine craving and help reduce motivation for the drug.