Cocaine dependence and attention switching within and between verbal and visuospatial working memory

Many studies have shown the negative effects of cocaine on neuropsychological and cognitive performance in drug-dependent individuals, but little is known about the underlying neuroanatomy of these dysfunctions. The present study addressed attention switching between items held in working memory (WM) with a task in which subjects were required to store and update two items held in verbal or visuospatial WM. Attention-switching frequency varied between trials, thereby allowing us to isolate the switching component of task performance. Behavioural data revealed that cocaine addicts performed worse than healthy controls in all tasks. On the visuospatial task addicts performed at chance levels revealing particular impairment in visuospatial WM. On the verbal task, in which controls and users could be matched for performance, we identified attenuated responses in prefrontal and cingulate cortices and in striatal regions, while other areas such as dorsolateral prefrontal cortex did not differ between healthy controls and users. The results reveal that addiction may be accompanied by specific rather than ubiquitous hypoactivation in prefrontal and subcortical areas and suggest a compromised ability in users to control their attention to their thoughts as might be particularly relevant when required to switch away from drug-related thoughts, and thus the dysfunction in attention switching may contribute to the maintenance of addiction.     

Prior Cocaine Use Alters the Normal Evolution of Information Coding in Striatal Ensembles during Value-Guided Decision-Making

Substance use disorders (SUDs) are characterized by maladaptive behavior. The ability to properly adjust behavior according to changes in environmental contingencies necessitates the interlacing of existing memories with updated information. This can be achieved by assigning learning in different contexts to compartmentalized “states.” Though not often framed this way, the maladaptive behavior observed in individuals with SUDs may result from a failure to properly encode states because of drug-induced neural alterations. Previous studies found that the dorsomedial striatum (DMS) is important for behavioral flexibility and state encoding, suggesting the DMS may be an important substrate for these effects. Here, we recorded DMS neural activity in cocaine-experienced male rats during a decision-making task where blocks of trials represented distinct states to probe whether the encoding of state and state-related information is affected by prior drug exposure. We found that DMS medium spiny neurons (MSNs) and fast-spiking interneurons (FSIs) encoded such information and that prior cocaine experience disrupted the evolution of representations both within trials and across recording sessions. Specifically, DMS MSNs and FSIs from cocaine-experienced rats demonstrated higher classification accuracy of trial-specific rules, defined by response direction and value, compared with those drawn from sucrose-experienced rats, and these overly strengthened trial-type representations were related to slower switching behavior and reaction times. These data show that prior cocaine experience paradoxically increases the encoding of state-specific information and rules in the DMS and suggest a model in which abnormally specific and persistent representation of rules throughout trials in DMS slows value-based decision-making in well trained subjects.SIGNIFICANCE STATEMENT Substance use disorders (SUDs) may result from a failure to properly encode rules guiding situationally appropriate behavior. The dorsomedial striatum (DMS) is thought to be important for such behavioral flexibility and encoding that defines the situation or “state.” This suggests that the DMS may be an important substrate for the maladaptive behavior observed in SUDs. In the current study, we show that prior cocaine experience results in over-encoding of state-specific information and rules in the DMS, which may impair normal adaptive decision-making in the task, akin to what is observed in SUDs.     

Entopeduncular Nucleus Projections to the Lateral Habenula Contribute to Cocaine Avoidance

The aversive properties associated with drugs of abuse influence both the development of addiction and relapse. Cocaine produces strong aversive effects after rewarding effects wear off, accompanied by increased firing in the lateral habenula (LHb) that contributes to downstream activation of the rostromedial tegmental nucleus (RMTg). However, the sources of this LHb activation are unknown, as the LHb receives many excitatory inputs whose contributions to cocaine aversion remain uncharacterized. Using cFos activation and in vivo electrophysiology in male rats, we demonstrated that the rostral entopeduncular nucleus (rEPN) was the most responsive region to cocaine among LHb afferents examined and that single cocaine infusions induced biphasic responses in rEPN neurons, with inhibition during cocaine''s initial rewarding phase transitioning to excitation during cocaine''s delayed aversive phase. Furthermore, rEPN lesions reduced cocaine-induced cFos activation by 2-fold in the LHb and by a smaller proportion in the RMTg, while inactivation of the rEPN or the rEPN-LHb pathway attenuated cocaine avoidance behaviors measured by an operant runway task and by conditioned place aversion (CPA). These data show an essential but not exclusive role of rEPN and its projections to the LHb in processing the aversive effects of cocaine, which could serve as a novel target for addiction vulnerability.SIGNIFICANCE STATEMENT Cocaine produces well-known rewarding effects but also strong aversive effects that influence addiction propensity, but whose mechanisms are poorly understood. We had previously reported that the lateral habenula (LHb) is activated by cocaine and contributes to cocaine''s aversive effects, and the current findings show that the rostral entopeduncular nucleus (rEPN) is a major contributor to this LHb activation and to conditioned avoidance of cocaine. These findings show a critical, though not exclusive, rEPN role in cocaine''s aversive effects, and shed light on the development of addiction.     

Cocaine increases ryanodine receptors via dopamine D1 receptors

For review there are little available data on regulatory mechanisms of ryanodine receptor (RyR) expression with cocaine treatment, though methamphetamine was reported to up-regulate RyRs in mouse brain. This study attempted to investigate regulatory mechanisms of RyR expression using the cerebral cortical neurons in primary culture intermittently exposed to a psychostimulant, cocaine. Intermittent exposure to cocaine (10 μM) significantly enhanced RyR 1 and 2 proteins and their mRNA, but not RyR 3 expression in the neurons. These cocaine-induced increases of RyR proteins and their mRNA were dose-dependently blocked by a dopamine D1 receptor antagonist (SCH23390), but not by a dopamine D2 receptor antagonist (sulpiride). These results indicate a regulatory role of dopamine D1 receptors in RyR expression bycocaine.     

Association of the trace amine associated receptor 6 (TAAR6) gene with schizophrenia and bipolar disorder in a Korean case control sample

Trace amines and their receptors may be implicated in the pathogenesis of psychiatric disorders. Previous studies have reported association of the trace amine associated receptor 6 (TAAR6) gene with susceptibility to schizophrenia and bipolar disorder but results have not been consistent. The purpose of this study was to examine these associations in Korean patients and also to test for association of TAAR6 with susceptibility to major depressive disorder (MDD). A case control sample consisting of 281 patients with schizophrenia, 190 patients with bipolar disorder, 187 patients with MDD and 288 psychiatrically healthy control subjects, was examined. Patients with schizoaffective disorder were not included in any of the psychiatric samples. Five single nucleotide polymorphisms (SNPs: rs4305745; rs8192625; rs7452939; rs6903874 and rs6937506) were genotyped in the TAAR6 gene and in the 3' regulatory region, using pyrosequencing. SNP rs6903874 was significantly associated with schizophrenia (p = 0.012) and bipolar disorder (p = 0.004). A three SNP haplotype consisting of alleles GCT from SNPs rs7452939, rs6903874 and rs6937506, respectively, was significantly over-represented in patients with schizophrenia (p = 0.0003) and bipolar disorder (p = 0.00002). A second three SNP haplotype (GTT) derived from the same SNPs was significantly under-represented in patients with bipolar disorder (p = 0.001). The GTT haplotype associations withstand the most rigorous corrections for multiple testing. These findings strongly support association of the TAAR6 gene with susceptibility to both schizophrenia and bipolar disorder in Korean patients. Further studies are needed to confirm these findings in this and other populations and to identify functional variants in TAAR6 that may be implicated in pathogenesis.     

Cocaine occupancy of sigma1 receptors and dopamine transporters in mice

Activation of sigma₁ (σ₁) receptors contributes to the behavioral and toxic effects of (?)‐cocaine. We studied a key step, the ability of (?)‐cocaine to occupy σ₁ receptors in vivo, using CD‐1^® mice and the novel radioligand [¹²⁵I]E‐N?1‐(3′‐iodoallyl)‐N′‐4‐(3″,4″‐dimethoxyphenethyl)‐piperazine ([¹²⁵I]E‐IA‐DM‐PE‐PIPZE). (?)‐Cocaine displayed an ED₅₀ of 68 μmol/kg for inhibition of specific radioligand binding in whole brain, with values between 73 and 80 μmol/kg for heart, lung, and spleen. For comparison, an ED₅₀ of 26 μmol/kg for (?)‐cocaine occupancy of striatal dopamine transporters (DAT) was determined by inhibition of [¹²⁵I]3β‐(4‐iodophenyl)tropan‐2β‐carboxylic acid isopropyl ester ([¹²⁵I]RTI‐121) binding. A chief finding is the relatively small potency difference between (?)‐cocaine occupancy of σ₁ receptors and the DAT, although the DAT occupancy is likely underestimated. Interactions of (?)‐cocaine with σ₁ receptors were assessed further using [¹²⁵I]E‐IA‐DM‐PE‐PIPZE for regional cerebral biodistribution studies and quantitative ex vivo autoradiography of brain sections. (?)‐Cocaine binding to cerebral σ₁ receptors proved directly proportional to the relative site densities known for the brain regions. Nonradioactive E‐IA‐DM‐PE‐PIPZE gave an ED₅₀ of 0.23 μmol/kg for occupancy of cerebral σ₁ receptors, and a 3.16 μmol/kg (i.p.) dose attenuated (?)‐cocaine‐induced locomotor hyperactivity by 30%. This effect did not reach statistical significance, but suggests that E‐IA‐DM‐PE‐PIPZE is a probable σ₁ receptor antagonist. As groundwork for the in vivo studies, we used standard techniques in vitro to determine ligand affinities, site densities, and pharmacological profiles for the σ₁ and σ₂ receptors expressed in CD‐1^® mouse brain. Synapse 70:98–111, 2016. © 2016 Wiley Periodicals, Inc.     

Cocaine withdrawal reduces GABABR transmission at entopeduncular nucleus – lateral habenula synapses

Lateral habenula (LHb) hyperactivity plays a pivotal role in the emergence of negative emotional states, including those occurring during withdrawal from addictive drugs. We have previously implicated cocaine‐driven adaptations at synapses from the entopeduncular nucleus (EPN) to the LHb in this process. Specifically, ionotropic GABA_A receptor (R)‐mediated neurotransmission at EPN‐to‐LHb synapses is reduced during cocaine withdrawal, due to impaired vesicle filling. Recent studies have shown that metabotropic GABA_BR signaling also controls LHb activity, although its role at EPN‐to‐LHb synapses during drug withdrawal is unknown. Here, we predicted that cocaine treatment would reduce GABA_BR‐mediated neurotransmission at EPN‐to‐LHb synapses. We chronically treated mice with saline or cocaine, prepared brain slices after two days of withdrawal and performed voltage‐clamp recordings from LHb neurons whilst optogenetically stimulating EPN terminals. Compared with controls, mice in cocaine withdrawal exhibited reduced GABA_AR‐mediated input to LHb neurons, and a reduced occurrence of GABA_BR‐signaling at EPN‐to‐LHb synapses. We then assessed the underlying mechanism of this decrease. Application of GABA_BR agonist baclofen evoked similar postsynaptic responses in EPN‐innervated LHb neurons in saline‐ and cocaine‐treated mice. Release probability at EPN‐to‐LHb GABAergic synapses was also comparable between groups. However, incubating brain slices in glutamine to facilitate GABA vesicle filling, normalized GABA_BR‐currents at EPN‐to‐LHb synapses in cocaine‐treated mice. Overall, we show that during cocaine withdrawal, together with reduced GABA_AR transmission, also GABA_BR‐mediated inhibitory signaling is diminished at EPN‐to‐LHb synapses, likely via the same presynaptic deficit. In concert, these alterations are predicted to contribute to the emergence of drug withdrawal symptoms, facilitating drug relapse.     

c‐Fos expression associated with reinstatement of cocaine‐seeking behavior by response‐contingent conditioned cues

The capability of cocaine cues to generate craving in cocaine‐dependent humans, even after extended abstinence, is modeled in rats using cue reinstatement of extinguished cocaine‐seeking behavior. We investigated neural activity associated with incentive motivational effects of cocaine cues using c‐fos mRNA and Fos protein expression as markers. Unlike preceding studies, we used response‐contingent presentation of discrete cues to elicit cocaine seeking. Rats were first trained to press a lever, resulting in cocaine reinforcement and light and tone cues. Rats then underwent extinction training, during which lever presses decreased. On the test day, rats either received response‐contingent cocaine cues or received no cues. The cues reinstated extinguished cocaine‐seeking behavior on the test day. In general, cue‐elicited c‐fos mRNA and protein expression were similar and both were enhanced in the prefrontal cortex, ventral tegmental area (VTA), dorsal striatum, and nucleus accumbens. Cues elicited more widespread Fos protein expression relative to our previous research in which cues were presented noncontingently without prior extinction training, including increases in the VTA, substantia nigra, ventral subiculum, and lateral entorhinal cortex. We also observed a correlation between cocaine‐seeking behavior and Fos in the agranular insula (AgI) and basolateral amygdala (BLA). The findings suggest that connections between BLA and AgI play a role in cue‐elicited incentive motivation for cocaine and that reinstatement of cocaine seeking by response‐contingent cues activates a similar corticolimbic circuit as that observed with other modes of cue presentation; however, activation of midbrain and ventral hippocampal regions may be unique to reinstatement by response‐contingent cues. Synapse 63:823–835, 2009. © 2009 Wiley‐Liss, Inc.     

Disruption of dopamine D1 receptor phosphorylation at serine 421 attenuates cocaine-induced behaviors in mice

Dopamine D1 receptors（D1Rs） play a key role in cocaine addiction, and multiple protein kinases such as GRKs, PKA, and PKC are involved in their phosphorylation. Recently, we reported that protein kinase D1 phosphorylates the D1 R at S421 and promotes its membrane localization. Moreover, this phosphorylation of S421 is required for cocaineinduced behaviors in rats. In the present study, we generated transgenic mice over-expressing S421A-D1 R in the forebrain. These transgenic mice showed reduced phospho-D1R（S421） and its membrane localization, and reduced downstream ERK1/2 activation in the striatum. Importantly, acute and chronic cocaine-induced locomotor hyperactivity and conditioned place preference were significantly attenuated in these mice. These findings provide in vivo evidence for the critical role of S421 phosphorylation of the D1 R in its membrane localization and in cocaine-induced behaviors. Thus, S421 on the D1 R represents a potential pharmacotherapeutic target for cocaine addiction and other drug-abuse disorders.     

CB1 Receptor Signaling Modulates Amygdalar Plasticity during Context-Cocaine Memory Reconsolidation to Promote Subsequent Cocaine Seeking

Contextual drug-associated memories precipitate craving and relapse in cocaine users. Such associative memories can be weakened through interference with memory reconsolidation, a process by which memories are maintained following memory retrieval-induced destabilization. We hypothesized that cocaine-memory reconsolidation requires cannabinoid type 1 receptor (CB1R) signaling based on the fundamental role of the endocannabinoid system in synaptic plasticity and emotional memory processing. Using an instrumental model of cocaine relapse, we evaluated whether systemic CB1R antagonism (AM251; 3 mg/kg, i.p.) during memory reconsolidation altered (1) subsequent drug context-induced cocaine-seeking behavior as well as (2) cellular adaptations and (3) excitatory synaptic physiology in the basolateral amygdala (BLA) in male Sprague Dawley rats. Systemic CB1R antagonism, during, but not after, cocaine-memory reconsolidation reduced drug context-induced cocaine-seeking behavior 3 d, but not three weeks, later. CB1R antagonism also inhibited memory retrieval-associated increases in BLA zinc finger 268 (zif268) and activity regulated cytoskeletal-associated protein (Arc) immediate-early gene (IEG) expression and changes in BLA AMPA receptor (AMPAR) and NMDA receptor (NMDAR) subunit phosphorylation that likely contribute to increased receptor membrane trafficking and synaptic plasticity during memory reconsolidation. Furthermore, CB1R antagonism increased memory reconsolidation-associated spontaneous EPSC (sEPSC) frequency in BLA principal neurons during memory reconsolidation. Together, these findings suggest that CB1R signaling modulates cellular and synaptic mechanisms in the BLA that may facilitate cocaine-memory strength by enhancing reconsolidation or synaptic reentry reinforcement, or by inhibiting extinction-memory consolidation. These findings identify the CB1R as a potential therapeutic target for relapse prevention.SIGNIFICANCE STATEMENT Drug relapse can be triggered by the retrieval of context-drug memories on re-exposure to a drug-associated environment. Context-drug associative memories become destabilized on retrieval and must be reconsolidated into long-term memory stores to persist. Hence, targeted interference with memory reconsolidation can weaken maladaptive context-drug memories and reduce the propensity for drug relapse. Our findings indicate that cannabinoid type 1 receptor (CB1R) signaling is critical for context-cocaine memory reconsolidation and subsequent drug context-induced reinstatement of cocaine-seeking behavior. Furthermore, cocaine-memory reconsolidation is associated with CB1R-dependent immediate-early gene (IEG) expression and changes in excitatory synaptic proteins and physiology in the basolateral amygdala (BLA). Together, our findings provide initial support for CB1R as a potential therapeutic target for relapse prevention.     

Effect of optogenetic manipulation of accumbal medium spiny neurons expressing dopamine D2 receptors in cocaine‐induced behavioral sensitization

Repetitive exposure to addictive drugs causes synaptic modification in the mesocorticolimbic dopamine (DA) system. Dopamine D1 receptors (D1R) or D2 receptors (D2R) expressed in the medium spiny neurons (MSNs) of the nucleus accumbens (NAc) play critical roles in the control of addictive behaviors. Optogenetic activation of D2R‐expressing MSNs (D2R‐MSNs) in the NAc previously demonstrated that these neurons play a key role in withdrawal‐induced plasticity. Here, we examined the effect of optogenetic inhibition of D2R‐MSNs in the NAc on cocaine‐induced behavioral sensitization. Adeno‐associated viral vectors encoding archaerhodopsin (ArchT) were delivered into the NAc of D2‐Cre transgenic mice. Activation of ArchT produced photoinhibition of D2R‐MSNs and caused disinhibition of neighboring MSNs in the NAc. However, such optogenetic silencing of D2R‐MSNs in the NAc in vivo affected neither the initiation nor the expression of cocaine‐induced behavioral sensitization. Similarly, photoinhibition of NAc D2R‐MSNs in the NAc during the drug withdrawal period did not affect the expression of cocaine‐induced behavioral sensitization. More detailed analysis of the effects of optogenetic activation of D2R‐MSNs suggests that D2R‐MSNs in the NAc exert important modulatory effects on neighboring MSN neurons, which may control the balanced output of NAc MSNs to control addictive behaviors.     

Cocaine withdrawal reduces group I mGluR-mediated long-term potentiation via decreased GABAergic transmission in the amygdala

Cocaine relapse can occur when cocaine-associated environmental cues induce craving. Conditioned place preference (CPP) is a behavioral paradigm modeling the association between cocaine exposure and environmental cues. The amygdala is involved in cocaine cue associations with the basolateral amygdala (BLA) and central amygdala (CeA) acting differentially in cue-induced relapse. Activation of metabotropic glutamate receptors induces synaptic plasticity, the mechanism of which is thought to underlie learning, memory and drug-cue associations. The goal of this study was to examine the neural alterations in responses to group I metabotropic glutamate receptor (mGluR) agonists in the BLA to lateral capsula of CeA (BLA-CeLc) pathway in slices from rats exposed to cocaine-CPP conditioning and withdrawn for 14 days. mGluR1, but not mGluR5, agonist-induced long-term potentiation (mGluR1-LTP) in the BLA-CeLc pathway was reduced in rats withdrawal from cocaine for 2 and 14 days, and exhibited an altered concentration response to picrotoxin. Cocaine withdrawal also reduced γ-aminobutyric acid (GABA)ergic synaptic inhibition in CeLc neurons. Blocking cannabinoid receptor 1 (CB(1) ) reduced mGluR1-LTP in the saline-treated but not cocaine-withdrawn group. Response to CB(1) but not CB(2) agonist was altered after cocaine. Additionally, increasing endocannabinoid (eCB) levels abolished mGluR1-LTP in the saline but not cocaine-withdrawn group. However, CB(1) and CB(2) protein levels were increased in the amygdala of cocaine-withdrawn rats while mGluR1 and mGluR5 remained unchanged. These data suggested that the mechanisms underlying the diminished mGluR1-LTP in cocaine-withdrawn rats involve an altered GABAergic synaptic inhibition mediated by modulation of downstream eCB signaling. These changes may ultimately result in potentiated responses to environmental cues that would bias behavior toward drug-seeking.