Repeated Cocaine Self-administration Research Articles

Dynamic CRMP2 Regulation of CaV2.2 in the Prefrontal Cortex Contributes to the Reinstatement of Cocaine Seeking.

Cocaine addiction remains a major health concern with limited effective treatment options. A better understanding of mechanisms underlying relapse may help inform the development of new pharmacotherapies. Emerging evidence suggests that collapsin response mediator protein 2 (CRMP2) regulates presynaptic excitatory neurotransmission and contributes to pathological changes during diseases, such as neuropathic pain and substance use disorders. We examined the role of CRMP2 and its interactions with a known binding partner, CaV2.2, in cocaine-seeking behavior. We employed the rodent self-administration model of relapse to drug seeking and focused on the prefrontal cortex (PFC) for its well-established role in reinstatement behaviors. Our results indicated that repeated cocaine self-administration resulted in a dynamic and persistent alteration in the PFC expression of CRMP2 and its binding partner, the CaV2.2 (N-type) voltage-gated calcium channel. Following cocaine self-administration and extinction training, the expression of both CRMP2 and CaV2.2 was reduced relative to yoked saline controls. By contrast, cued reinstatement potentiated CRMP2 expression and increased CaV2.2 expression above extinction levels. Lastly, we utilized the recently developed peptide myr-TAT-CBD3 to disrupt the interaction between CRMP2 and CaV2.2 in vivo. We assessed the reinstatement behavior after infusing this peptide directly into the medial PFC and found that it decreased cue-induced reinstatement of cocaine seeking. Taken together, these data suggest that neuroadaptations in the CRMP2/CaV2.2 signaling cascade in the PFC can facilitate drug-seeking behavior. Targeting such interactions has implications for the treatment of cocaine relapse behavior.

Multiple sessions of deep brain stimulation using TMS-like protocols reduce cue-induced relapse to cocaine in a rat model

s / Brain Stimulation 8 (2015) 412e427 423 University of Auckland, Clinical Neuroscience Laboratory, Department of Medicine, Auckland, New Zealand Background: External counterpulsation (ECP) enhances cerebral blood flow in patients with subacute ischemic stroke but whether it changes corticomotor excitability, which is a powerful prognostic predictor for motor recovery, remains unknown. Methods: We randomized 30 patients with subacute ischemic stroke within 4-21 days of onset (mean 6.23 days) in this sham-controlled clinical trial to either real ECP (n1⁄415) or sham ECP (n1⁄415). Treatment consisted of daily one hour sessions of ECP for ten days. Clinical measures included National Institutes of Health Stroke Scale (NIHSS); functional measures included Purdue Pegboard Test (PPT), Hand Grip (HG), Pinch Grip (PG); and cortical excitability measures included bilateral resting motor threshold (RMT) and motor evoked potential amplitude (MEP) at 130% of RMT. Measures were made at baseline, post-ECP day 1 (Post 1), and post-ECP day 30 (post 30). Results: There were no significant differences between groups at baseline. At post 30, there were significant differences between the real ECP group vs sham ECP group in normalized ipsilesional MEP amplitude (real: 2.35 vs sham: 1.08, P1⁄40.001) and ipsilesional RMT(real: 0.89 vs sham: 0.96, P1⁄40.039). The increase in HG and PPT were also significantly different between the groups at post 30 (HG: real 9.81 vs sham 4.83, P 1⁄4 0.027; PPT: real 4.73 vs sham 2.00, P 1⁄4 0.014 ), but no differences were found in the NIHSS and PG. No differences were found in the contralesional RMT or MEP amplitude. Conclusion: ECP enhances ipsilesional corticomotor excitability in subacute stroke patients. This proof-of-principle study provides a mechanism of motor recovery facilitated by ECP treatment in ischemic stroke patients. * Joint last authors 369 Multiple sessions of deep brain stimulation using TMS-like protocols reduce cue-induced relapse to cocaine in a rat model I. Goldenberg , R. Gal , S. Zibman , N. Barnea-Ygael , A. Zangen Department of Life Sciences and the Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel A major hallmark of drug (and especially cocaine-) addiction is relapse to drug use following a period of abstinence. In humans and animal models, relapse can be reliably triggered by presenting cues previously associated with drug self-administration, a phenomenon termed cue-induced relapse (CIR). It has been suggested that changes in neuronal activity in the medial prefrontal cortex (mPFC) following repeated drug use may play a key role in CIR. Here we used a chronically-implanted bilateral linear microelectrode array (14 recording electrodes + 2 stimulating electrodes) to record local field potentials (LFPs) and induce subconvulsive electrical stimulations (SCES) in the mPFC of behaving rats. Following array implantation, rats were trained to self-administer cocaine by pressing a reinforcing lever, and each reinforcement was coupled with a light+tone cues. Thereafter, abstinence from drug-taking was induced using the ‘conflict model’. Next, mPFC-SCES (50 trains of 2.5 sec at 20 Hz every 15 sec, 0.2 ms pulse duration, 400 mAmp) was applied daily (15min/day) for two weeks, simulating a typical human TMS-based treatment. The rats then entered a 30 min CIR-test, during which the cues were non-contingently presented. Cue-induced mPFC-LFP activity was recorded throughout the experiment. Whereas 80% of the rats that did not receive SCES ’relapsed’ to lever-pressing, only 33% of the rats treated with SCES ’relapsed’. Additionally, during the CIR-tests, an increased power was observed in the alpha and beta frequency ranges in response to the cues, but this was attenuated in the ICES treated group. Finally, the electrophysiological response to stimulation was altered during treatment particularly in these bands. It therefore seems that repeated cocaine self-administration is associated with increased saliency of the drug-associated cues manifested, at least, as increased cue-induced alpha/beta mPFC activity, and that SCES treatment of the mPFC reduces relapse rates following abstinence.

Oxidative Stress Biomarkers in Some Rat Brain Structures and Peripheral Organs Underwent Cocaine

Oxidative stress (OS) generates or intensifies cocaine-evoked toxicity in the brain and peripheral organs. The aim of this study was to examine superoxide dismutase (SOD) activity and lipid peroxidation [measured by malondialdehyde (MDA) levels] in rats during maintenance of cocaine self-administration and after withdrawal by a yoked-triad procedure. Our results indicate that repeated cocaine self-administration provoked an elevation of SOD activity in the hippocampus, frontal cortex, dorsal striatum, and liver. MDA levels were reduced in the brain, increased in the liver, kidney, and heart during maintenance of self-administration, and increased in the kidney in cocaine-yoked rats. In addition, following extinction training, we found enhanced MDA levels and SOD activity in the rat hippocampus, while changes in the activity of OS biomarkers in other brain structures and peripheral tissues were reminiscent of the changes seen during cocaine self-administration. These findings highlight the association between OS biomarkers in motivational processes related to voluntary cocaine intake in rats. OS participates in memory and learning impairments that could be involved in drug toxicity and addiction mechanisms. Therefore, further studies are necessary to address protective mechanisms against cocaine-induced brain and peripheral tissue damage.

Essential Role of the Histone Methyltransferase G9a in Cocaine-Induced Plasticity

Cocaine-induced alterations in gene expression cause changes in neuronal morphology and behavior that may underlie cocaine addiction. In mice, we identified an essential role for histone 3 lysine 9 (H3K9) dimethylation and the lysine dimethyltransferase G9a in cocaine-induced structural and behavioral plasticity. Repeated cocaine administration reduced global levels of H3K9 dimethylation in the nucleus accumbens. This reduction in histone methylation was mediated through the repression of G9a in this brain region, which was regulated by the cocaine-induced transcription factor DeltaFosB. Using conditional mutagenesis and viral-mediated gene transfer, we found that G9a down-regulation increased the dendritic spine plasticity of nucleus accumbens neurons and enhanced the preference for cocaine, thereby establishing a crucial role for histone methylation in the long-term actions of cocaine.

Inhibition of kappa opioid receptors attenuated increased cocaine intake in rats with extended access to cocaine

Previous studies demonstrated that the dynorphin/kappa opioid system was up-regulated upon repeated cocaine self-administration. In the present study, we tested the hypothesis that increased cocaine self-administration with extended access was associated with increased activity of the kappa opioid system in rats. Rats self-administered 0.5 mg/kg per injection of cocaine on a fixed-ratio (FR) schedule in either 1-h (short access, ShA) or 6-h (long access, LgA) sessions. After cocaine intake in the LgA rats increased to a maximum, the effects of kappa opioid receptor antagonists and a partial agonist were tested on cocaine intake in ShA and LgA rats. Cocaine self-administration increased under FR and progressive-ratio (PR) schedules in LgA rats. Nor-BNI (15-30 mg/kg), a kappa receptor antagonist, decreased cocaine intake in LgA rats under a PR schedule (ShA, +1.7%; LgA, -27.4% from baseline), whereas naltrexone (0.3-10 mg/kg) and SG-II-49 (0.025-0.1 mg/kg), a nonspecific opioid receptor antagonist and a partial agonist, respectively, decreased cocaine intake in both groups (PR data: SG-II-49, ShA -28.6%, LgA -19.8%; naltrexone, ShA -34.6%, LgA -11.8% compared with vehicle data). The present study demonstrated that the antagonism of kappa opioid receptors attenuated only the increased cocaine intake in LgA rats under a PR schedule, whereas the antagonism of micro and kappa receptors decreased cocaine intake in both ShA and LgA groups. The data suggest that increased motivation for cocaine in rats with extended access may be related to increased kappa opioid activity and may contribute to compulsive use.

Gene profiling the response to repeated cocaine self-administration in dorsal striatum: A focus on circadian genes

Alterations in gene expression in the dorsal striatum caused by chronic cocaine exposure have been implicated in the long-term behavioral changes associated with cocaine addiction. To gain further insight into the molecular alterations that occur as a result of cocaine self-administration, we conducted a microarray analysis of gene expression followed by bioinformatic gene network analysis that allowed us to identify adaptations at the level of gene expression as well as into interconnected networks. Changes in gene expression were examined in the dorsal striatum of rats 1 day after they had self-administered cocaine for 7 days under a 24-h access, discrete trial paradigm (averaging 98 mg/kg/day). Here we report the regulation of the circadian genes Clock, Bmal1, Cryptochrome1, Period2, as well as several genes that are regulated by/associated with the circadian system (i.e., early growth response 1, dynorphin). We also observed regulation of other relevant genes (i.e., Nur77, beta catenin). These changes were then linked to curated pathways and formulated networks which identified circadian rhythm processes as affected by cocaine self-administration. These data strongly suggest involvement of circadian-associated genes in the brain's response to cocaine and may contribute to an understanding of addictive behavior including disruptions in sleep and circadian rhythmicity.

Dysregulation of Dopamine Transporter Trafficking and Function after Abstinence from Cocaine Self-Administration in Rats: Evidence for Differential Regulation in Caudate Putamen and Nucleus Accumbens

The profound alterations produced by cocaine on dopamine (DA) neurotransmission raise the possibility that dopamine transporter (DAT)-expressing neurons may modify DA transport in response to repeated cocaine exposure to maintain the appropriate efficiency of DA clearance. In this study, we determined the changes in molecular mechanisms of DAT regulation in rats with a history of repeated cocaine self-administration followed by 3 weeks of abstinence. Using ex vivo caudate putamen (CPu) and nucleus accumbens (NAcc) synaptosomal preparations, we found that DA uptake was significantly higher in the CPu and NAcc of cocaine-experienced animals compared with yoked saline animals. Surface distribution, p-Ser phosphorylation, and protein phosphatase 2A catalytic subunit (PP2Ac) interaction of DAT were all altered in the CPu. Maximal velocity (V(max)) values were elevated both in the CPu and NAcc of cocaine-experienced rats compared with saline controls. Although there was no change in the apparent affinity for DA in the CPu, increased DA affinity was evident in the NAcc. Consistent with elevated DAT activity in cocaine-experienced animals, a higher level of surface DAT, DAT-PP2Ac association, and decreased serine phosphorylation of DAT were observed in the CPu, but not in the NAcc. These results, for the first time, suggest that chronic cocaine self-administration followed by abstinence leads to persisting alterations in normal DAT trafficking and catalytic regulatory cascades in the CPu and NAcc in a brain region-specific manner.

Accumbal Neurons that are Activated during Cocaine Self-Administration are Spared from Inhibitory Effects of Repeated Cocaine Self-Administration

Hypoactivity of the accumbens is induced by repeated cocaine exposure and is hypothesized to play a role in cocaine addiction. However, it is difficult to understand how a general hypoactivity of the accumbens, which facilitates multiple types of motivated behaviors, could contribute to the selective increase in drug-directed behavior that defines addiction. Electrophysiological recordings, made during sessions in which rats self-administer cocaine, show that most accumbal neurons that encode events related to drug-directed behavior achieve and maintain higher firing rates during the period of cocaine exposure (Task-Activated neurons) than do other accumbal neurons (Task-Non-Activated neurons). We have hypothesized that this difference in activity makes the neurons that facilitate drug-directed behavior less susceptible than other neurons to the chronic inhibitory effects of cocaine. A sparing of neurons that facilitate drug-directed behavior from chronic hypoactivity might lead to a relative increase in the transmission of neuronal signals that facilitate drug-directed behavior through accumbal circuits and thereby contribute to changes in behavior that characterize addiction (ie differential inhibition hypothesis). A prediction of the hypothesis is that neurons that are activated in relation to task events during cocaine self-administration sessions will show less of a decrease in firing across repeated self-administration sessions than will other neurons. To test this prediction, rats were exposed to 30 daily (6 h/day) cocaine self-administration sessions. Chronic extracellular recordings of single accumbal neurons were made during the second to third session and the 30th session. Between-session comparisons showed that decreases in firing were exhibited by Task-Non-Activated, but not by Task-Activated, neurons. During the day 30 session, the magnitude of the difference in firing rate between the two groups of neurons was positively related to the propensity of animals to seek and take cocaine. The findings of the present study are consistent with a basic prediction of the differential inhibition hypothesis and may be relevant to understanding cocaine addiction.

Repeated Cocaine Self-Administration Alters Processing of Cocaine-Related Information in Rat Prefrontal Cortex

One of the core symptoms of cocaine addiction is compulsive drug-seeking behavior. Although the precise neural substrates are unknown, it has been hypothesized that this behavior involves cocaine-induced hypofunction of the prefrontal cortex (PFC) or "hypofrontality." To test this hypothesis, PFC neuronal activity was monitored in rats during approximately 3 weeks of cocaine self-administration (SA). Rats were trained to press a lever to self-administer cocaine in daily 2 h sessions. Responding was reinforced contingent on a modified fixed-ratio 5 schedule of reinforcement. In the first SA session, the overall firing rate and burst rate were significantly decreased after cocaine infusions relative to the period immediately before the session. These effects disappeared after > or = 10 d of drug SA and were replaced by a significant increase in burst duration and firing rate within a burst. Notably, however, the level of basal activity before the first drug infusion of each SA session decreased significantly after multiple weeks of cocaine exposure. Collectively, these data support the view that although repeated sessions of cocaine SA decrease basal PFC activity, increased burst-related firing in response to cocaine infusions suggests that processing of cocaine-related information is enhanced and may contribute to increased control by cocaine over cocaine-seeking behavior.

Repeated cocaine self-administration causes multiple changes in rat frontal cortex gene expression.

Repeated cocaine administration produces changes in gene expression that are thought to contribute to the behavioral alterations observed with cocaine abuse. This study focuses on gene expression changes in the frontal cortex, a component of reinforcement, sensory, associative, and executive circuitries. Changes in frontal cortex gene expression after repeated cocaine self-administration may lead to changes in the behaviors associated with this brain region. Rats self-administered cocaine for 10 days in a continuous access, discrete trial paradigm (averaging 100 mg/kg/day) and were examined for changes in relative frontal cortex mRNA abundance by cDNA hybridization arrays. Among the changes observed following array analysis, increased nerve-growth-factor-induced B (NGFI-B), adenylyl cyclase type VIII (AC VIII), and reduced cysteine-rich protein 2 (CRP2) mRNA were confirmed by quantitative RT-PCR. These changes share commonalities and exhibit differences with previous reports of gene expression changes in the frontal cortex after noncontingent cocaine administration.

Neuroendocrine effects of d-fenfluramine and bromocriptine following repeated smoked cocaine in humans

To study the consequences of repeated smoked cocaine use on central serotonergic and dopaminergic function, the effects of d-fenfluramine ( d-FEN) and bromocriptine on plasma hormones were determined at three time-points following repeated cocaine self-administration under carefully controlled conditions. In a 20-day inpatient study, male cocaine abusers ( d-FEN: n=10; bromocriptine: n=8) self-administered smoked cocaine (12–50 mg) for 3 days followed by 2 weeks of abstinence. The acute effects of d-FEN (0 or 30 mg po) or bromocriptine (0 or 1.25 mg po) on plasma neuroendocrine levels were determined 1–2, 7–8, and 13–14 days after the last cocaine dose. Blood was drawn before and then every 30–60 min for 4 h after capsule administration. The effects of d-FEN and bromocriptine were also determined in healthy, outpatient controls; d-FEN was removed from medical use in the US midway through the study due to complications associated with chronic administration, so all of the control participants were tested in Italy. Cocaine users had a blunted prolactin and cortisol response to d-FEN that lasted for at least 2 weeks of cocaine abstinence, but had a normal response to bromocriptine, which suppressed prolactin by 50% of baseline. The long-lasting and selective disruptions in serotonin pathways following chronic cocaine use may provide a neurochemical basis for changes in mood commonly reported during cocaine withdrawal.

Changes in cigarette smoking not observed following repeated cocaine self-administration.

Acute administration of some psychoactive drugs (e.g., cocaine, heroin, methadone d-amphetamine) has been found to increase spontaneous cigarette smoking for 1-3 hr, but the effects of chronic drug administration have not been systematically studied. Computerized cigarette dispensers were used to study the effects of multiple daily cocaine administrations on cigarette smoking. Participants were 8 (5 male) cocaine-dependent cigarette smokers who resided on a closed clinical research ward and smoked an average of 16.7 cigarettes per day during the week prior to starting the study. During test sessions on Monday, Wednesday, and Friday of each week, participants could obtain either cocaine (25 mg i.v.) on 2 days or saline (1 ml i.v.) on the other day, 3 times per day at 2-hr intervals under double-blind conditions. The number of cigarettes dispensed during study days was analyzed in 2-hr increments. No significant cocaine effect was found. These findings fail to show a change in the number of cigarettes smoked after chronic cocaine self-administration over time intervals longer than 1-3 hr.

Inhibitory effects of dopamine and methylenedioxymethamphetamine (MDMA) on glutamate-evoked firing of nucleus accumbens and caudate/putamen cells are enchanced following cocaine self-administration

Rats were allowed to self-administer cocaine during a 3-h session for 15 days. One to 11 days after the last cocaine exposure, rats were anesthetized with urethane and effects of microiontophoretically-applied dopamine on glutamate-evoked firing of neurons in the nucleaus accumbens and in the caudate/putamen were tested. Dopamine produced a dose-dependent inhibition of glutamate-evoked firing in both the nucleus accumbens and the caudate/putamen of rats that had been repeatedly exposed to self-admisnistered cocaine and in control rats. However, the DA-induced inhibition was significantly greater in the group that had self-administered cocaine. The cocaine self-administration group was significantly sensitized to the inhibitory effects of dopamine in both early (1–3 day) and later (9–11 days) periods of cocaine abstinence. Following cessation of repeated cocaine self-administration sessions, nucleus accumbens cells were also sensitized to the inhibitory effects of methylenedioxymethamphetamine (MDMA), a drug that increases extracellular levels of DA and serotonin in the nucleus accumbens. This sensitization to DA- and MDMA-induced inhibition in the nucleus accumbens and in the striatum indicates that long-term neuroadaptations occur in these regions of the nervous system following repeated exposure to self-administered cocaine.

The influence of cocaine self-administration on in vivo dopamine and acetylcholine neurotransmission in rat caudate-putamen

Presynaptic dopamine and acetylcholine transmission in the anteroventral (limbic) caudate-putamen were studied by microdialysis in freely moving rats during cocaine self-administration sessions. Acute cocaine exposure elevated dopamine (DA) overflow in drug-naive animals. However, during repeated cocaine administration, the drug-induced elevation of DA was attenuated in animals previously exposed (during the prior 9 days) to cocaine. The diminished dopamine response in repeatedly treated animals while self-administering cocaine was speculated to be due to increased activity of DA transport carrier and/or supersensitive receptors modulating DA release. During repeated cocaine administration, extracellular acetylcholine levels in animals previously exposed to cocaine were found to be significantly decreased compared with controls. The findings of the study may suggest a functional development of supersensitive DA receptors postsynaptic to the DA terminal (located on cholinergic neurons) as a consequence of previous cocaine exposure. Such supersensitivity would allow for a reduced DA signal to be amplified at the postsynaptic level during repeated cocaine self-administration.

New perspectives on cocaine addiction: recent findings from animal research.

Research with laboratory animals has provided several insights into the nature of cocaine abuse and addiction. First, the nature of drug addiction has been reevaluated and the emphasis has shifted from physical dependence to compulsive drug-taking behavior. Second, animal studies suggest that cocaine is at least as addictive as heroin and possibly even more addictive. Third, cocaine is potentially more dangerous than heroin as evidenced by the higher fatality rate seen in laboratory animals given unlimited access to these drugs. Fourth, the neural basis of cocaine reinforcement has been identified and involves an enhancement of dopaminergic neurotransmission in the ventral tegmental dopamine system. Other addictive drugs (e.g., opiates) may also derive at least part of their reinforcing impact by pharmacologically activating this reward system. Fifth, although the biological consequences of repeated cocaine self-administration on central nervous system functioning are poorly understood, preliminary findings suggest that intravenous cocaine self-administration may decrease neural functioning in this brain reward system. This has important clinical implications because diminished functioning of an important brain reward system may significantly contribute to relapse into cocaine addiction. These and other findings from experimentation with laboratory animals suggest new considerations for the etiology and treatment of drug addiction.