Cocaine Self-administration Research Articles

Long- vs short-access cocaine alters behavioral inhibition for cocaine in male rats

Impulsivity and behavioral inhibition are measures commonly associated with substance misuse, particularly cocaine use disorder. However, patterns of impulsive behaviors have been shown to differ based on cocaine use history and level of cocaine dependence. Extended cocaine access, which more closely models neural and behavioral changes that take place during the development of problematic cocaine use, has been shown to decrease behavioral inhibition in comparison to limited cocaine access. However, previous preclinical studies investigating these relationships have been mostly correlational and only utilize non-drug rewards. This study aims to utilize a differential rates of low reinforcement (DRL) schedule to investigate the impact of extended access to cocaine on behavioral inhibition toward a cocaine reinforcer. Male Sprague Dawley rats first self-administered intravenous cocaine infusions on a DRL schedule of reinforcement before being split into two groups: one given 6-h extended cocaine access (LgA) and one given 1-h short cocaine access (ShA) for 10 daily sessions. Following a washout period, the rats were placed back on DRL cocaine self-administration sessions. Results revealed that LgA rats showed impaired performance on the behavioral inhibition measure during the DRL self-administration sessions compared to baseline DRL performance and compared to ShA post-access behavioral inhibition measures. These results indicate that extended cocaine access impairs an organism's behavioral inhibition toward future cocaine use, indicating that those individuals with a history of heavy cocaine use will have impaired behavioral inhibition toward future cocaine use.

The function of the ZFP189 transcription factor in the nucleus accumbens facilitates cocaine-specific transcriptional and behavioral adaptations.

Distinguishing the brain mechanisms affected by distinct addictive drugs may inform targeted therapies against specific substance use disorders (SUDs). Here, we explore the function of a drug-associated, transcriptionally repressive transcription factor (TF), ZFP189, whose expression in the nucleus accumbens (NAc) facilitates cocaine-induced molecular and behavioral adaptations. To uncover the necessity of ZFP189-mediated transcriptional control in driving cocaine-induced behaviors, we created synthetic ZFP189 TFs of distinct transcriptional function, including ZFP189VPR, which activates the expression of target genes and exerts opposite transcriptional control to the endogenously repressive ZFP189. By virally delivering synthetic ZFP189 TFs to the NAc of mice, we discover that the transcriptional control exerted by synthetic or endogenous ZFP189 solely alters behavioral adaptations to cocaine but not morphine, saline, or sucrose. Further, these synthetic ZFP189 TFs are only capable of producing gene-expression changes in rodents exposed to cocaine, but not morphine or saline. In these cocaine exposed mice, the gene-expression profile produced by ZFP189VPR is inversely related to the cocaine-induced transcriptional response, as characterized by Upstream Regulator Analysis in Ingenuity Pathway Analysis. Lastly, we demonstrate that NAc ZFP189WT increases vulnerability to cocaine reinforcement through selective sensitization to the reinforcing effects of small cocaine doses. In contrast, ZFP189VPR treated mice do not experience changes in cocaine sensitivity and had lower rates of cocaine self-administration. Collectively, this research describes the brain mechanisms by which a TF specifically coordinates the molecular adaptations that produce increased cocaine addiction-like behaviors. The use of synthetic ZFP189VPR uncovers novel strategies for therapeutic interventions to potentially halt these cocaine-induced transcriptional processes.

Contrasting the reinforcing effects of the novel dopamine transport inhibitors JJC8-088 and JJC8-091 in monkeys: Potential translation to medication assisted treatment

Despite considerable efforts, there remains no Food and Drug Administration-approved medications for cocaine use disorder. One strategy to mitigate cocaine craving and relapse is to elevate dopamine. The dopamine transport inhibitor and releaser d-amphetamine has been shown to decrease cocaine self-administration (SA), although it has abuse liability. Recently, several modafinil analogs reduced cocaine SA in rats and monkeys, including JJC8-088, characterized as “cocaine-like” in rats, and JJC8-091, characterized as “atypical” and not SA by rats. The present study evaluated the reinforcing effects of both compounds in monkeys under several conditions. For experiment 1, 4 male cocaine-experienced rhesus monkeys self-administered cocaine (0.001–0.3 mg/kg per injection), JJC8-088 (0.001–0.3 mg/kg per injection), and JJC8-091 (0.1–3.0 mg/kg per injection) under a progressive-ratio schedule of reinforcement. Both JJC compounds functioned as reinforcers with equal reinforcing strength to cocaine. Although JJC8-091 was less potent than cocaine, JJC8-088 and cocaine had similar potencies. For experiment 2, 1 male and 2 female drug-naïve cynomolgus monkeys responded on a fixed-ratio schedule of food reinforcement. JJC8-091 was self-administered at rates higher than saline in all 3 monkeys. In experiment 3, monkeys from experiment 2 responded under a concurrent drug versus food choice paradigm and given access to cocaine or JJC8-091 under these conditions. At doses equal to or one-half log-units higher than doses used in experiment 2, cocaine, but not JJC8-091, was chosen over food. Together, these results demonstrate that although JJC8-091 may be reinforcing under some conditions, its reinforcing strength, in the presence of an alternative reinforcer, is substantially less than cocaine. Significance StatementJJC8-088 and JJC8-091 have shown efficacy is reducing cocaine self-administration (SA) in rats and in nonhuman primates. This study found that both compounds maintained SA in monkeys responding under several conditions. However, when given access to an alternative reinforcer during the SA session, JJC8-091 was not reinforcing, suggesting that JJC8-091 may have lower abuse liability than cocaine and may be a viable candidate for cocaine use disorder because, in the human population, alternatives to drug use are often available.

RDS04-010: A novel atypical DAT inhibitor that inhibits cocaine taking and seeking and itself has low abuse potential in experimental animals.

Cocaine use disorder (CUD) is a severe public health problem, and currently, there is no FDA-approved medication for its treatment. Atypical dopamine (DA) transporter (DAT) inhibitors display low addictive liability by themselves and may have therapeutic potential for treatment of psychostimulant use disorders. Here, we report that RDS04-010, a novel atypical DAT inhibitor that binds to an inward-facing conformation of DAT due to its sulfoxide moiety, displayed distinct pharmacological profiles in animal models of addiction from its sulfide analog, RDS03-094, a DAT inhibitor that binds to a more outward-facing conformation. Systemic administration of RDS04-010 dose-dependently inhibited cocaine self-administration (SA), shifted the cocaine SA dose-response curve downward, decreased motivation for cocaine seeking under progressive ratio reinforcement conditions, and inhibited cocaine-primed reinstatement of drug-seeking behavior. RDS04-010 alone neither altered optical brain-stimulation reward nor evoked reinstatement of drug-seeking behavior. RDS04-010 substitution for cocaine was not able to maintain self-administration in rats trained to self-administer cocaine. In contrast, RDS03-094 displayed more cocaine-like reinforcing effects. Its pretreatment upward-shifted both the cocaine self-administration dose-response and optical brain-stimulation reward curves. RDS03-094 alone was able to reinstate extinguished cocaine-seeking behavior and sustain self-administration during a substitution test. Collectively, these findings suggest that RDS04-010 is a novel atypical DAT inhibitor with favorable therapeutic potential in reducing cocaine-taking and -seeking behavior with low addictive liability. Moreover, this extensive behavioral evaluation further confirms the role DAT binding conformation plays in the distinctive profiles of atypical DAT inhibitors that prefer the inward facing conformation.

Delineating anticipatory arousal from reward consumption: evaluating fixed-intervals in cocaine seeking-taking response chains.

Anticipation is a critical antecedent to drug use, in which the prospect of imminent drug availability can potently motivate instrumental actions directed to procure it. Models that capture the behavioral dynamics that precede drug access may allow for the dissociation of key neural mechanisms underlying appetitive or consummatory processes in drug self-administration. We aimed to isolate measurements attributed to the procurement and consumption of a reward by defining distinct actions for each using a chain-schedule of reinforcement. Male Long-Evans rats were trained to self-administer cocaine or saccharin under a chained schedule of reinforcement (FI-FR) in order to dissociate appetitive ('seeking') from consummatory ('taking') behaviors. Completion of a fixed-interval (5min) was followed by 5min of continuously reinforced responding (FR1) on another lever. The FI-FR chain procedure appears to provide sensitive and dissociable dimensions of cocaine self-administration within a single experimental session. Importantly, we demonstrate that responding during the FI (i.e., seeking) link tracks with the incentive value of anticipated reward access - whereby response rates corresponded to expected reward magnitude, degree of reward-specific satiety, and general motivational state. The FI component is a sensitive and reliable index of motivational changes induced by either the extrinsic incentive value of reinforcement (i.e., anticipated dose) or intrinsic motive states (i.e., satiety or deprivation). This procedure provides a valuable tool for interrogating the neural dynamics of drug-seeking and -taking behavior, in isolation.

Large-scale characterization of cocaine addiction-like behaviors reveals that escalation of intake, aversion-resistant responding, and breaking-points are highly correlated measures of the same construct.

Addiction is commonly characterized by escalation of drug intake, compulsive drug seeking, and continued use despite harmful consequences. However, the factors contributing to the transition from moderate drug use to these problematic patterns remain unclear, particularly regarding the role of sex. Many preclinical studies have been limited by small sample sizes, low genetic diversity, and restricted drug access, making it challenging to model significant levels of intoxication or dependence and translate findings to humans. To address these limitations, we characterized addiction-like behaviors in a large sample of >500 outbred heterogeneous stock (HS) rats using an extended cocaine self-administration paradigm (6 hr/daily). We analyzed individual differences in escalation of intake, progressive ratio (PR) responding, continued use despite adverse consequences (contingent foot shocks), and irritability-like behavior during withdrawal. Principal component analysis showed that escalation of intake, progressive ratio responding, and continued use despite adverse consequences loaded onto a single factor that was distinct from irritability-like behaviors. Categorizing rats into resilient, mild, moderate, and severe addiction-like phenotypes showed that females exhibited higher addiction-like behaviors, with a lower proportion of resilient individuals compared to males. These findings suggest that, in genetically diverse rats with extended drug access, escalation of intake, continued use despite adverse consequences, and PR responding are highly correlated measures of a shared underlying construct. Furthermore, our results highlight sex differences in resilience to addiction-like behaviors.

The Mechanism of the Nucleus Accumbens-Ventral Pallidum Pathway Mediated by Drug Withdrawal-Induced High-Seeking Motivation in Cocaine Addiction.

The reinforcement of drug-seeking motivation following drug withdrawal is recognized as a significant factor contributing to relapse. The ventral pallidum (VP) plays a crucial role in encoding and translating motivational aspects of reward. However, current research lacks a clear understanding of how the VP mediates drug-seeking motivation and the feedback modulation between the VP and the nucleus accumbens (NAc) following drug withdrawal. Therefore, utilizing a rat model of cocaine self-administration, we investigated the circuitry mechanisms underlying drug-seeking behavior post-drug withdrawal involving the NAc-VP pathway. Initially, we observed a significant enhancement in drug-seeking behavior 14 days after cocaine withdrawal. Subsequently, we identified the feedback mechanism through which the NAc-VP regulates this behavior. Immunofluorescence results indicated an increase in c-Fos expression levels in the ventral pallidum ventromedial (VPvm) and ventrolateral ventral pallidum (VPvl) following drug withdrawal. Calcium fiber photometry further elucidated that during the expression of high motivational drug-seeking behavior, there was a specific enhancement in VPvm neuronal activity, and retrograde tracing techniques suggested a weakened transmission function in the NAc-VPm pathway. Additionally, chemical genetic techniques demonstrated that inhibiting the activity of the NAc-VP pathway could increase the motivational level of drug-seeking behavior. These findings indicate that the reduced inhibitory function of the NAc-VP pathway following prolonged cocaine withdrawal forms the basis for heightened reactivity in VPvm neurons, thus regulating the expression of high motivational behavior triggered by drug-related cues. Our study results suggest that maintaining normal NAc-VP pathway functionality may decrease drug-seeking motivation post long-term drug withdrawal, offering new insights for interventions targeting relapse.

Vilazodone,aNovel SSRI Antidepressant with 5-HT1A Partial Agonist Properties: Diminished Potentiation of Chronic Oral Methylphenidate-Induced Dynorphin Expression in the Striatum in Adolescent Male Rats.

Selective serotonin reuptake inhibitor (SSRI) antidepressants such as fluoxetine are used in combination with the medical psychostimulant methylphenidate (Ritalin) in a variety of treatments in children and adults. Unintended co-exposure to these psychotropic medications also occurs in patients on SSRIs who abuse methylphenidate as a "cognitive enhancer" or recreational drug. Preclinical research shows that SSRIs such as fluoxetine when given in conjunction with methylphenidate potentiate addiction-related gene regulation by methylphenidate in the striatum, consistent with the known facilitatory role for serotonin in psychostimulant-induced neuronal and behavioral changes. Moreover, fluoxetine combined with methylphenidate also facilitated subsequent acquisition of cocaine self-administration in adolescent rats, suggesting an increased addiction liability for methylphenidate. In the present study, we investigated the impact of a novel SSRI, vilazodone, on methylphenidate-induced gene regulation in adolescent male rats. In contrast to prototypical SSRIs such as fluoxetine, vilazodone also acts as a partial 5-HT1A serotonin receptor agonist and is thus proposed to temper serotonin input to the striatum. We compared the effects of chronic treatment (4 weeks) with vilazodone (10mg/kg, twice daily) with those of fluoxetine (5mg/kg, twice daily) on striatal dynorphin expression induced by oral methylphenidate treatment (30/60mg/kg/day in drinking water, 8h access daily). Our results demonstrate that, in contrast to fluoxetine, vilazodone had minimal or no potentiating effects on methylphenidate-induced dynorphin expression. This diminished impact on gene regulation was seen throughout the striatum, including the nucleus accumbens, where increased dynorphin expression has previously been associated with various aspects of addiction. Our findings suggest that vilazodone may serve as a better adjunct SSRI with reduced addiction-facilitating properties.

Dopamine D1-Like Receptor-Mediated Insurmountable Blockade of the Reinforcing Effects of Cocaine in Rats.

Previous studies indicated differing effects of dopamine D1-like and D2-like receptor (D1R and D2R, respectively) agonists on cocaine self-administration. Leftward shifts by D2R agonists in the cocaine self-administration dose-effect function contrast with decreases by D1R agonists in maximal cocaine self-administration without rightward or leftward displacement. Whether the effects of the D1R agonists are due to actions at D1Rs has not been determined possibly due to the difficulty in separating the blockade by a D1R antagonist of the effects of the D1R agonists and those of cocaine. In the present study, pretreatment with the D1R agonists R(+)-SKF-81297 (0.1-1.0 mg/kg) and ({plus minus})-SKF-82958 (0.032-0.32 mg/kg) dose-dependently decreased maximal cocaine self-administration at doses below those affecting food-reinforced responding. In contrast, pretreatment with the D2R agonists R(-)-NPA (0.001-0.01 mg/kg) and (-)-quinpirole (0.01-0.1 mg/kg) dose-dependently left shifted the cocaine self-administration dose-effect function. The decreases by D1R agonists in maximal cocaine self-administration were dose-dependently antagonized by the D1R antagonist SCH-39166 at doses that alone had no effects on cocaine self-administration. Doses of SCH-39166 that blocked the effects of the D1R agonists on cocaine self-administration were like those that shifted self-administration of D1R agonists to the right but had no effects on self-administration of D2R agonists. Self-administration of the D2R agonists was dose-dependently shifted to the right by the preferential D2R antagonist, L-741,626, but not by SCH-39166. These results demonstrate that the decreases by the D1R agonists in cocaine self-administration are selectively D1R-mediated, and support findings suggesting fundamentally distinct roles of the D1Rs and D2Rs in cocaine reinforcement. Significance Statement Dopamine D1-like (D1R) agonists decrease maximal cocaine self-administration, whereas D2-like (D2R) agonists shift the cocaine self-administration dose-effect function leftward with mechanisms for those different effects unclear. The present study demonstrates blockade by the selective D1R antagonist SCH-39166 of decreases in maximal cocaine self-administration at doses that blocked other D1R-mediated effects but not effects of cocaine, suggesting fundamentally distinct roles of the dopamine D1-like and D2-like receptors in cocaine reinforcement and development of D1R agonists as potential treatments for cocaine-use disorder.

Astrocytic HIV-1 Nef expression decreases glutamate transporter expression in the nucleus accumbens and increases cocaine-seeking behavior in rats.

Cocaine use disorder is an intersecting issue in populations with HIV-1, further exacerbating the clinical course of the disease, contributing to neurotoxicity and neuroinflammation. Cocaine and HIV neurotoxins play roles in neuronal damage during neuroHIV progression by disrupting glutamate homeostasis in the brain. Even with cART, HIV-1 Nef, an early viral protein expressed in approximately 1% of infected astrocytes, remains a key neurotoxin. This study investigates the relationship that exists between Nef, glutamate homeostasis, and cocaine in the NAc, a critical brain region associated with drug motivation and reward. Using a rat model, we compared the effects of astrocytic Nef and cocaine by molecular analysis of glutamate transporters in the NAc. We further conducted behavioral assessments for cocaine self-administration to evaluate cocaine-seeking behavior. Our findings indicate that both cocaine and Nef independently decrease the expression of the glutamate transporter GLT-1 in the NAc. Additionally, rats with astrocytic Nef expression exhibited increased cocaine-seeking behavior but demonstrated sex dependent molecular differences after behavioral paradigm. In conclusion, our results suggest the expression of Nef intensifies cocaine-induced alterations in glutamate homeostasis in the NAc, potentially underlying increased cocaine-seeking. Understanding these interactions better may inform therapeutic strategies for managing cocaine use disorder in HIV-infected individuals.

Replication and extension of the subregion selectivity of glutamate-related changes within the nucleus accumbens associated with the incubation of cocaine-craving

Cue-elicited drug-seeking behavior intensifies with the passage of time during withdrawal from drug taking and this “incubation of cocaine-craving” involves alterations in nucleus accumbens (NA) glutamate transmission. Here, we employed a combination of in vivo microdialysis and immunoblotting approaches to further examine changes in biochemical indices of glutamate transmission within NA subregions that accompany the incubation of cocaine-craving exhibited by male rats with a 10-day history of 6-h access to intravenous cocaine (0.25 mg/infusion). Immunoblotting on whole cell lysates from the core subregion (NAc core) revealed interactions between cocaine self-administration history, withdrawal and drug cue re-exposure for Homer2a/b, mGlu1, and GluN2b expression, as well as indices of Akt and ERK activity. With the exception of PKCε phosphorylation, most protein changes within the shell subregion (NAc shell) depended on drug cue re-exposure and cocaine history rather than varying in a consistent time-dependent manner. Reduced basal extracellular glutamate content was apparent only in the NAc core of cocaine-experienced rats during protracted (30 days) withdrawal and this was accompanied by a markedly blunted capacity of the mGlu1/5 agonist DHPG to elevate glutamate levels within this subregion. Finally, over-expressing neither Homer1c nor Homer2b within the NAc core during protracted cocaine withdrawal altered the magnitude of cue-elicited responding, its extinction or cocaine-primed reinstatement of drug-seeking behavior. The present findings are consistent with the extant literature implicating changes in Group 1 mGlu receptor function within the NAc core subregion as central to incubated cocaine-craving and provide further evidence against a major role for Homer proteins in gating incubated cocaine-craving. Further, our results provide novel correlational evidence implicating elevated Akt and blunted ERK activity within the NAc core as potential contributors to the expression of incubated cocaine-craving, worthy of future investigation.

Cognitive effort increases the intensity of rewards.

An important body of literature suggests that exerting intense cognitive effort causes mental fatigue and can lead to unhealthy behaviors such as indulging in high-calorie food and taking drugs. Whereas this effect has been mostly explained in terms of weakening cognitive control, cognitive effort may also bias behavioral choices by amplifying the hedonic and emotional impact of rewards. We report parallel findings with animals and humans supporting this hypothesis. In rats, exerting cognitive effort immediately before access to cocaine self-administration significantly increased drug intake. In addition, exerting cognitive effort increased the psychostimulant effect of cocaine. The effects of cognitive effort on addiction-related behaviors were eliminated and even reversed when animals could rest in their home-cage for 2-4 h before access to cocaine self-administration. Among humans, we found that expending cognitive effort increased consumption of tasty (but unhealthy) food by increasing the hedonic enjoyment of consuming the food. In addition, the effects were specific for emotionally relevant stimuli (i.e. food rewards) and did not generalize to judgment about neutral objects. Altogether these data suggest that intense cognitive effort can increase the perceived intensity of rewards and lead to their overconsumption. This effect may contribute to bad decision making induced by excessive cognitive effort and make people more vulnerable to indulge in unhealthy behaviors such as use of addictive drugs.

Dissociable dorsal medial prefrontal cortex ensembles are necessary for cocaine seeking and fear conditioning in mice

The dorsal medial prefrontal cortex (dmPFC) plays a dual role in modulating drug seeking and fear-related behaviors. Learned associations between cues and drug seeking are encoded by a specific ensemble of neurons. This study explored the stability of a dmPFC cocaine seeking ensemble over 2 weeks and its influence on persistent cocaine seeking and fear memory retrieval. In the first series of experiments, we trained TetTag c-fos-driven-EGFP mice in cocaine self-administration and tagged strongly activated neurons with EGFP during the initial day 7 cocaine seeking session. Subsequently, a follow-up seeking test was conducted 2 weeks later to examine ensemble reactivation between two seeking sessions via c-Fos immunostaining. In the second series of experiments, we co-injected viruses expressing TRE-cre and a cre-dependent inhibitory PSAM-GlyR into the dmPFC of male and female c-fos-tTA mice to enable “tagging” of cocaine seeking ensemble or cued fear ensemble neurons with inhibitory chemogenetic receptors. These c-fos-tTA mice have the c-fos promoter that drives expression of the tetracycline transactivator (tTA). The tTA can bind to the tetracycline response element (TRE) site on the viral construct, resulting in the expression of cre-recombinase, which enables the expression of cre-dependent inhibitory chemogenetic receptors and fluorescent reporters. Then we investigated ensemble contribution to subsequent cocaine seeking and fear recall during inhibition of the tagged ensemble by administering uPSEM792s (0.3 mg/kg), a selective ligand for PSAM-GlyR. In both sexes, there was a positive association between the persistence of cocaine seeking and the proportion of reactivated EGFP+ neurons within the dmPFC. More importantly, inhibition of the cocaine seeking ensemble suppressed cocaine seeking, but not recall of fear memory, while inhibition of the fear ensemble reduced conditioned freezing but not cocaine seeking. The results demonstrate that cocaine and fear recall ensembles in the dmPFC are stable, but largely exclusive from one another.

Abstinence from cocaine self-administration promotes microglia pruning of astrocytes which drives cocaine-seeking behavior.

Rodent drug self-administration leads to compromised ability of astrocytes to maintain glutamate homeostasis within the brain's reward circuitry, as well as reductions in surface area, volume, and synaptic colocalization of astrocyte membranes. However, the mechanisms driving astrocyte responses to cocaine are unknown. Here, we report that long-access cocaine self-administration followed by prolonged home cage abstinence results in decreased branching complexity of nucleus accumbens astrocytes, characterized by the loss of peripheral processes. Using a combination of confocal fluorescence microcopy and immuno-gold electron microscopy, we show that alterations in astrocyte structural features are driven by microglia phagocytosis, as labeled astrocyte membranes are found within microglia phagolysosomes. Inhibition of complement C3-mediated phagocytosis using the neutrophil inhibitory peptide (NIF) rescued astrocyte structure and decreased cocaine seeking behavior following cocaine self-administration and abstinence. Collectively, these results provide evidence for microglia pruning of accumbens astrocytes across cocaine abstinence which mediates cocaine craving.

Histone deacetylase 5 in prelimbic prefrontal cortex limits context-associated cocaine seeking.

Repeated cocaine use produces neuroadaptations that support drug craving and relapse in substance use disorders (SUDs). Powerful associations formed with drug-use environments can promote a return to active drug use in SUD patients, but the molecular mechanisms that control the formation of these prepotent drug-context associations remain unclear. In the rat intravenous cocaine self-administration (SA) model, we examined the role and regulation of histone deacetylase 5 (HDAC5) in the prelimbic (PrL) and infralimbic (IL) cortices in context-associated drug seeking. To this end, we employed viral molecular tools, chemogenetics, RNA-sequencing, electrophysiology, and immunohistochemistry. In the PrL, reduction of endogenous HDAC5 augmented context-associated, but not cue-or drug prime-reinstated cocaine seeking, whereas overexpression of HDAC5 in PrL, but not IL, reduced context-associated cocaine seeking, but it had no effects on sucrose seeking. In contrast, PrL HDAC5 overexpression following acquisition of cocaine SA had no effects on future cocaine seeking. We found that HDAC5 and cocaine SA altered the expression of numerous PrL genes, including many synapse-associated genes. HDAC5 significantly increased inhibitory synaptic transmission onto PrL deep-layer pyramidal neurons, and it reduced the induction of FOS-positive neurons in the cocaine SA environment. Our findings reveal an essential and selective role for PrL HDAC5 to limit associations formed in cocaine, but not sucrose, SA environments, and that it alters the PrL excitatory/inhibitory balance, possibly through epigenetic regulation of synaptic genes. These results further position HDAC5 as a key factor regulating reward-circuit neuroadaptations that underlie common relapse triggers in SUD.

Dopamine transmission at D1 and D2 receptors in the nucleus accumbens contributes to the expression of incubation of cocaine craving.

Relapse represents a consistent clinical problem for individuals with substance use disorder. In the incubation of craving model of persistent craving and relapse, cue-induced drug seeking progressively intensifies or "incubates" during the first weeks of abstinence from drug self-administration and then remains high for months. Previously, we and others have demonstrated that expression of incubated cocaine craving requires strengthening of excitatory synaptic transmission in the nucleus accumbens core (NAcc). However, despite the importance of dopaminergic signaling in the NAcc for motivated behavior, little is known about the role that dopamine (DA) plays in the incubation of cocaine craving. Here we used fiber photometry to measure DA transients in the NAcc of male and female rats during cue-induced seeking tests conducted in early abstinence from cocaine self-administration, prior to incubation, and late abstinence, after incubation of craving has plateaued. We observed DA transients time-locked to cue-induced responding but their magnitude did not differ significantly when measured during early versus late abstinence seeking tests. Next, we tested for a functional role of these DA transients by injecting DA receptor antagonists into the NAcc just before the cue-induced seeking test. Blockade of either D1 or D2 DA receptors reduced cue-induced cocaine seeking after but not before incubation. We found no main effect of sex or significant interaction of sex with other factors in our experiments. These results suggest that DA contributes to incubated cocaine seeking but the emergence of this role reflects changes in postsynaptic responsiveness to DA rather than presynaptic alterations.

Artificial intelligence-based analysis of behavior and brain images in cocaine-self-administered marmosets

BackgroundThe sophisticated behavioral and cognitive repertoires of non-human primates (NHPs) make them suitable subjects for studies involving cocaine self-administration (SA) schedules. However, ethical considerations, adherence to the 3Rs principle (replacement, reduction and refinement), and other factors make it challenging to obtain NHPs individuals for research. Consequently, there is a need for methods that can comprehensively analyze small datasets using artificial intelligence (AI). New methodsWe employed AI to identify cocaine dependence patterns from collected data. First, we collected behavioral data from cocaine SA marmosets (Callithrix jacchus) to develop a dependence prediction model. SHapley Additive exPlanations (SHAP) values were used to demonstrate the importance of various variables. Additionally, we collected positron emission tomographic (PET) images showing dopamine transporter (DAT) binding potential and developed an algorithm for PET image segmentation. ResultsThe prediction model indicated that the Random Forest (RF) algorithm performed best, with an area under the curve (AUC) of 0.92. The top five variables influencing the model were identified using SHAP values. The PET image segmentation model achieved an accuracy of 0.97, a mean squared error of 0.02, an intersection over union (IoU) of 0.845, and a Dice coefficient of 0.913. Comparison with existing methods and conclusionUtilizing data from the marmoset SA experiment, we developed an ML-based dependence prediction model and analyzed variable importance rankings using SHAP. AI-based imaging segmentation methods offer a valuable tool for evaluating DAT availability in NHPs following chronic cocaine administration.

The ventral tegmental area dopamine to basolateral amygdala projection supports acquisition of cocaine self-administration

Dopamine signaling in the amygdala is known to play a role in associative learning and memory, including the process of learning to associate environmental cues with the reinforcing properties of drugs like cocaine. Evidence suggests that the ventral tegmental area (VTA) dopamine (DA) projection specifically to the basolateral amygdala (BLA) participates in establishing cocaine-cue associations that can promote later craving- and relapse-like responses to the cue alone. In order to further investigate the specific role of VTA-BLA projections in cocaine-reinforced learning, we used chemogenetics to manipulate VTA DA inputs to the BLA during cocaine self-administration, cue- and cocaine-primed reinstatement, and conditioned place preference. We found inhibiting DA input to the BLA during cocaine self-administration inhibited acquisition and weakened the ability of the previously cocaine-paired cue to elicit cocaine-seeking, while acutely inhibiting the pathway on the day of cue-induced reinstatement testing had no effect. Conversely, exciting the projection during self-administration boosted the salience of the cocaine-paired cue as indicated by enhanced responding during cue-induced reinstatement. Importantly, interfering with DA input to the BLA had no impact on the ability of cocaine to elicit a place preference or induce reinstatement in response to a priming cocaine injection. Overall, we show that manipulation of projections underlying DA signaling in the BLA may be useful for developing therapeutic interventions for substance use disorders.

Changes in nucleus accumbens core translatome accompanying incubation of cocaine craving.

In the 'incubation of cocaine craving' model of relapse, rats exhibit progressive intensification (incubation) of cue-induced craving over several weeks of forced abstinence from cocaine self-administration. The expression of incubated craving depends on plasticity of excitatory synaptic transmission in nucleus accumbens core (NAcC) medium spiny neurons (MSN). Previously, we found that the maintenance of this plasticity and the expression of incubation depends on ongoing protein translation, and the regulation of translation is altered after incubation of cocaine craving. Here we used male and female rats that express Cre recombinase in either dopamine D1 receptor- or adenosine 2a (A2a) receptor-expressing MSN to express a GFP-tagged ribosomal protein in a cell-type specific manner, enabling us to use Translating Ribosome Affinity Purification (TRAP) to isolate actively translating mRNAs from both MSN subtypes for analysis by RNA-seq. We compared rats that self-administered saline or cocaine. Saline rats were assessed on abstinence day (AD) 1, while cocaine rats were assessed on AD1 or AD40-50. For both D1-MSN and A2a-MSN, there were few differentially translated genes between saline and cocaine AD1 groups. In contrast, pronounced differences in the translatome were observed between cocaine rats on AD1 and AD40-50, and this was far more robust in D1-MSN. Notably, all comparisons revealed sex differences in translating mRNAs. Sequencing results were validated by qRT-PCR for several genes of interest. This study, the first to combine TRAP-seq, transgenic rats, and a cocaine self-administration paradigm, identifies translating mRNAs linked to incubation of cocaine craving in D1-MSN and A2a-MSN of the NAcC.

Psilocybin administered following extinction sessions does not affect subsequent cocaine cue reinstatement in male and female rats and mice

There are currently no pharmacological treatments for cocaine use disorder. Recently there has been a great deal of interest in the potential of psychedelic drugs such as psilocybin to treat psychiatric disorders. Human studies have indicated that a single administration of psilocybin can have long-lasting effects. Few preclinical studies have examined a role for psilocybin in addiction models. The goal of the current study was to determine whether psilocybin would enhance extinction following cocaine self-administration in male and female mice and rats and thus result in an attenuation of cue-induced drug-seeking. In experiments in mice, 16 female and 19 male mice underwent 8d of cocaine self-administration (0.5 mg/kg/infusion) and extinction training. Immediately following extinction trials, mice were injected with vehicle or 1.0 mg/kg psilocybin. Following the conclusion of extinction training, mice were tested for cue-induced reinstatement. In experiments in rats, 24 female and 23 male rats underwent 15d of cocaine self-administration (0.8 mg/kg/infusion) and extinction training. Immediately following extinction trials, rats were injected with vehicle, 1.0 mg/kg psilocybin, or 2.5 mg/kg psilocybin. Following the conclusion of extinction training, rats were tested for cue-induced reinstatement. Psilocybin administered following extinction trials had no effect, as both female and male mice and rats demonstrated significant cue-induced reinstatement. These data suggest that psilocybin is ineffective at altering cocaine-seeking behavior in the paradigm and doses used in the current study. It remains to be seen whether treatment with psilocybin under different conditions may be useful in the long-standing goal of finding pharmacotherapies to treat CUD.