Development Of Cocaine Addiction Research Articles

Oleoylethanolamide attenuates the stress-mediated potentiation of rewarding properties of cocaine associated with an increased TLR4 proinflammatory response

The lipid-derived messenger oleoylethanolamide (OEA) has been involved in multiple physiological functions including metabolism and the immune response. More recently, OEA has been observed to affect reward-related behavior. Stress is a major risk factor for drug use and a predictor of drug relapse. In the laboratory, social stress has been largely studied using the social defeat (SD) model. Here, we explored the effects of different OEA administration schedules on the increased rewarding properties of cocaine induced by SD. In addition, we evaluated the anti-inflammatory action of OEA pretreatment in TLR4 expression caused by SD in the cerebellum, a novel brain structure that has been involved in the development of cocaine addiction. Adult OF1 mice were assigned to an experimental group according to the stress condition (exploration or SD) and treatment (OEA before SD, OEA before conditioning or subchronic OEA treatment). Mice were administered with OEA i.p (10 mg/kg) 10 min previously to the corresponding event. Three weeks after the last SD encounter, conditioned place preference (CPP) was induced by a subthreshold cocaine dose (1 mg/kg). As expected, socially defeated mice presented greater vulnerability to the cocaine reinforcing effects and expressed CPP. Conversely, this effect was not observed under a non-stressed condition. Most importantly, we observed that OEA pretreatment before SD or before conditioning prevented cocaine CPP in defeated mice. Biochemical analysis showed that OEA administration before SD decreased proinflammatory TLR4 upregulation in the cerebellum caused by social stress. In summary, our results suggest that OEA may have a protective effect on stress-induced increased cocaine sensitivity by exerting an anti-inflammatory action.

Behavioral economics of cocaine self-administration in male and female rats.

There are sex differences in the development of cocaine addiction. For example, the time that it takes for women from initial use to addiction is significantly shorter than for men. Thus, understanding why females are more vulnerable to cocaine addiction will provide insights into sex differences in the mechanisms underlying cocaine addiction. This study aimed to determine how cocaine demand intensity and elasticity might differ between sexes. In addition, the impact of estrous cycle and cocaine intake on demand was investigated. Male and female rats were trained to self-administer 0.125 mg of cocaine intravenously under a chained schedule in daily 2-h sessions for 2 weeks, and then, the cocaine demand function was determined with a modified within-session threshold procedure. Following the test, the rats began to self-administer a higher dose of cocaine (0.25 mg) to increase the cocaine intake. The demand function was then similarly determined in the same rats after 2 weeks of cocaine self-administration of the higher dose. No sex differences were found in either demand intensity or elasticity. Neither did the level of cocaine intake have an impact on demand. The demand elasticity, but not intensity, was significantly lower during proestrus/estrus compared with diestrus. These data suggest that the faster transition to cocaine addiction in women cannot be explained by sex differences in the demand for cocaine and such a demand may change during different phases of estrus cycle.

KVA-D-88, a Novel Preferable Phosphodiesterase 4B Inhibitor, Decreases Cocaine-Mediated Reward Properties in Vivo.

Cocaine addiction remains a major public concern throughout the world especially in developed countries. In the last three decades, significant achievements have led to a greater understanding of the signaling pathways involved in the development of cocaine addiction; however, there are no FDA-approved treatments available to reverse or block this brain disease due to either the unsatisfactory therapeutic efficacy or severe side effects. Previous studies have demonstrated that chronic exposure to cocaine elevates levels of cyclic AMP (cAMP) as a neuroadaptative response in reward-related brain regions. Phosphodiesterase 4 (PDE4) inhibitors, which elevate cAMP levels, have been shown to block cocaine-mediated behavioral changes related to psychoactive and reinforcing properties. Unfortunately, previously studied PDE4 inhibitors induce severe side-effects, which limit their clinical usage. In this study, we identified a novel PDE4B inhibitor, KVA-D-88, with an improved selectivity profile compared to previous compounds (e.g., rolipram). Pharmacokinetic studies have shown that this compound is brain penetrant and preferably acts on PDE4B compared to PDE4D in vitro, alluding to less unwanted side effects with KVA-D-88 in vivo. Interestingly, pretreatment with KVA-D-88 significantly inhibited cocaine-induced hyperlocomotor activity. In cocaine self-administering mice with differential schedules, KVA-D-88 strikingly decreased the number of active nose-pokes and cocaine infusions and reduced the break point. Taken together, our findings demonstrate that this novel PDE4 inhibitor, KVA-D-88, could inhibit cocaine-mediated rewarding effects implying its potential clinical usage for cocaine addiction.

The Effects of Cocaine on the Expression of Brain‐Derived Neurotrophic Factor in Female Rat Reward Circuits

Cocaine is a highly addictive psychostimulant drug with a high relapse rate. Studies have shown that women have greater subjective responses to cocaine depending on the hormonal phase they are in, making them more susceptible to addiction. Literature shows that sex hormones can modulate the activities of Brain‐Derived Neurotrophic Factor (BDNF). BDNF modulates the growth and survival of neurons in areas such as the nucleus accumbens (NAc) and prefrontal cortex, specifically the pre‐limbic cortex (PL). However, it is still unknown how hormonal stages influence the expression of BDNF in the different phases of cocaine addiction development: self‐administration, extinction and reinstatement. We hypothesized that the expression of BDNF in the NAc and PL varies depending on the hormonal stage, as well as the stage in the development of cocaine addiction. To determine this, female adult rats were subjected to 12 sessions of short‐access self‐administration of cocaine, 16 sessions of extinction and a session of cue‐primed reinstatement. Tissue from the PL and NAc were extracted to compare the expression of BDNF after each phase of cocaine addiction. Preliminary data suggests that BDNF decreases in the NAc during low‐hormonal phases (Diestrus and Metestrus), while it increases during high‐hormonal phases (Estrus and Proestrus). In addition, BDNF protein levels seem to be elevated in the prelimbic cortex after cue‐primed reinstatement, but further analysis is required to confirm this observation. These findings suggest that BDNF expression depends on the phase of cocaine addiction and the estrous cycle in female rats.Support or Funding InformationFunding was received from the following sources: UPR PRISE Program: #R25GM096955; Start up funds from Ponce Research Institute; Rise Program: NIH‐NIGMS #2R25GM082406; B.R.A.I.N. and M.A.G.I.C. Core: NIM‐HD MD007579.

Acute Cocaine Reduces Excitatory Synaptic Transmission in Pyramidal Neurons of the Mouse Medial Prefrontal Cortex.

The medial prefrontal cortex (mPFC) plays critical roles in the development of cocaine addiction. Numerous studies have reported about the effects of cocaine on neuronal and synaptic activities in the nucleus accumbens and ventral tegmental area, which are brain regions associated with cocaine addiction; however, a limited number of studies have reported the effect of cocaine on mPFC neuronal activity. In this study, using whole-cell patch-clamp recordings in brain slices, we present that under the condition where synaptic transmission is enhanced by increasing extracellular K+ concentration, cocaine significantly reduced the frequency but not amplitude of spontaneous excitatory postsynaptic currents. These findings suggest that cocaine exposure could be a trigger to induce hypofrontality, which is related to the compulsive craving for cocaine use.

Cocaine-mediated downregulation of microglial miR-124 expression involves promoter DNA methylation

ABSTRACTNeuroinflammation plays a critical role in the development of reward-related behavior in cocaine self-administration rodents. Cocaine, one of most commonly abused drugs, has been shown to activate microglia both in vitro and in vivo. Detailed molecular mechanisms underlying cocaine-mediated microglial activation remain poorly understood. microRNAs (miRs) belonging to a class of small noncoding RNA superfamily have been shown to modulate the activation status of microglia. miR-124, one of the microglia-enriched miRs, functions as an anti-inflammatory regulator that maintains microglia in a quiescent state. To date, the possible effects of cocaine on microglial miR-124 levels and the associated underlying mechanisms have not been explored. In the current study, we demonstrated that cocaine exposure decreased miR-124 levels in both BV-2 cells and rat primary microglia. These findings were further validated in vivo, wherein we demonstrated decreased abundance of miR-124 in purified microglia isolated from cocaine-administered mice brains compared with cells from saline administered animals. Molecular mechanisms underlying these effects involved cocaine-mediated increased mRNA and protein expression of DNMTs in microglia. Consistently, cocaine substantially increased promoter DNA methylation levels of miR-124 precursors (pri-miR-124-1 and −2), but not that of pri-miR-124-3, both in vitro and in vivo. In summary, our findings demonstrated that cocaine exposure increased DNA methylation of miR-124 promoter resulting into its downregulation, which, in turn, led to microglial activation. Our results thus implicate that epigenetic modulation of miR-124 could be considered as a potential therapeutic approach to ameliorate microglial activation and, possibly, the development of cocaine addiction.

S.03.04 Functional changes in limbic and sensorimotor circuits in the development of cocaine addiction: results from human PET studies

S.03.04 Functional changes in limbic and sensorimotor circuits in the development of cocaine addiction: results from human PET studies

Carrier-mediated cocaine transport at the blood-brain barrier as a putative mechanism in addiction liability.

Background:The rate of entry of cocaine into the brain is a critical factor that influences neuronal plasticity and the development of cocaine addiction. Until now, passive diffusion has been considered the unique mechanism known by which cocaine crosses the blood-brain barrier.Methods:We reassessed mechanisms of transport of cocaine at the blood-brain barrier using a human cerebral capillary endothelial cell line (hCMEC/D3) and in situ mouse carotid perfusion.Results:Both in vivo and in vitro cocaine transport studies demonstrated the coexistence of a carrier-mediated process with passive diffusion. At pharmacological exposure level, passive diffusion of cocaine accounted for only 22.5% of the total cocaine influx in mice and 5.9% in hCMEC/D3 cells, whereas the carrier-mediated influx rate was 3.4 times greater than its passive diffusion rate in vivo. The functional identification of this carrier-mediated transport demonstrated the involvement of a proton antiporter that shared the properties of the previously characterized clonidine and nicotine transporter. The functionnal characterization suggests that the solute carrier (SLC) transporters Oct (Slc22a1-3), Mate (Slc47a1) and Octn (Slc22a4-5) are not involved in the cocaine transport in vivo and in vitro. Diphenhydramine, heroin, tramadol, cocaethylene, and norcocaine all strongly inhibited cocaine transport, unlike benzoylecgonine. Trans-stimulation studies indicated that diphenhydramine, nicotine, 3,4-methylenedioxyamphetamine (ecstasy) and the cathinone compound 3,4-methylenedioxypyrovalerone (MDPV) were also substrates of the cocaine transporter.Conclusions:Cocaine transport at the BBB involves a proton-antiporter flux that is quantitatively much more important than its passive diffusion. The molecular identification and characterization of this transporter will provide new tools to understand its role in addictive mechanisms.

Selective action of an atypical neuroleptic on the mechanisms related to the development of cocaine addiction: a pre-clinical behavioural study

An increased function in the mesolimbic dopaminergic system has been extensively associated with the rewarding effects of both natural stimuli and drugs of abuse. Thus, dopamine receptor blockers, such as neuroleptic drugs, can be proposed as candidates for potential therapeutic approaches to treat drug dependence. Notwithstanding, this therapeutic potential of neuroleptics critically depends on a selective action on the specific mechanisms related to the development of addiction. We compared the effects of different doses of haloperidol, ziprasidone and aripiprazole (first-, second- and third-generation neuroleptics, respectively) on spontaneous locomotor activity of mice in a novel environment, hyperlocomotion induced by acute cocaine administration and cocaine-induced locomotor sensitization by a two-injection protocol. Whereas high doses of haloperidol abolished the three behavioural paradigms without selectivity, low doses of ziprasidone selectively abolished the development of the behavioural sensitization phenomenon. Finally, low doses of aripiprazole inhibited acute cocaine-induced hyperlocomotion and behavioural sensitization without modifying spontaneous locomotor activity. Thus, aripiprazole at lower doses was the most selective antipsychotic drug concerning the inhibition of the development of behavioural sensitization to cocaine. Because locomotor sensitization in rodents has been proposed to share plastic mechanisms with drug addiction in humans, our data provide relevant suggestions to the clinical practice.

Proteomic profile of differentially expressed proteins in the medial prefrontal cortex after repeated cocaine exposure

Medial prefrontal cortex (mPFC) has been implicated in the reward process and the development of cocaine addiction. In the current study, we used a proteomics-based approach, combining two-dimensional gel electrophoresis (2-DE) with mass spectrometry (MS), to analyze protein expression profiles of rat mPFC after repeated cocaine exposure. Conditioned place preference (CPP) assay was used here to evaluate cocaine-induced reward effect in rats. We detected about 3100 protein spots in rat mPFC. After repeated cocaine exposure, 125 spots were changed by more than 1.1-fold of control levels. Among them, 71 spots with 1.5-fold or greater changes in protein expression over control levels have been identified, including 50 spots that were up-regulated and 21 spots that were down-regulated by repeated cocaine exposure. These identified proteins that showed significant changes in expression in mPFC after repeated cocaine exposure may be useful biomarkers for assessing cocaine abuse and potential new targets for investigating the mechanism of cocaine abuse.

Sex differences in basal and cocaine-induced alterations in PKA and CREB proteins in the nucleus accumbens

Alterations in protein kinase (PKA) protein levels have been implicated in the regulation of responses to and development of cocaine addiction. However, the contribution of differences in PKA intracellular cascade to the known sex differences in responses to cocaine is not well understood. This study examined whether there are intrinsic or cocaine-induced alterations in PKA-mediated responses, such as phosphorylation of cyclic AMP response element binding protein, in male and female rats. To this end, protein levels of PKA and phosphorylated CREB (pCREB) in the caudate putamen (CPu) and nucleus accumbens (NAc) of male and female rats were measured basally or after acute (one 30-mg/kg intraperitoneal injection) or chronic (twice-daily 15-mg/kg injections for 14 days) cocaine administration. Behavioral responses to both cocaine administration paradigms were also studied. Similar to previous findings, ambulatory, rearing, and stereotypic activities were higher in female rats after acute cocaine administration. Sex differences in cocaine-induced responses were also observed after chronic cocaine administration: While males developed a robust sensitization in ambulatory activities to cocaine, females developed tolerance in cocaine-induced rearing and stereotypic activities. In the basal group, females had significantly higher PKA protein levels in the NAc. Regardless of the cocaine administration paradigm, PKA protein levels in the NAc were higher overall in females than in males. Furthermore, after cocaine administration, while pCREB protein levels in male rats were induced for a longer amount of time than in female rats, the magnitude of change on pCREB levels were higher in female than male rats. However, in the CPu, no sex differences in PKA or pCREB protein levels were observed either in the basal group or after acute or chronic cocaine administration. Taken together, these findings suggest that sex differences in basal and cocaine-induced alterations in the PKA signaling regulation in the NAc may contribute to sex differences in the psychomotor responses to cocaine.

Dopamine-beta hydroxylase polymorphism and cocaine addiction

Cocaine addiction involves a number of medical, psychological and social problems. Understanding the genetic aetiology of this disorder will be essential for design of effective treatments. Dopamine-beta hydroxylase (DbH) catalyzes the conversion of dopamine to norepinephrine and could, therefore, have an influence on both cocaine action and the basal sensitivity of neurotransmitter systems to cocaine. Recently, the -1021C>T polymorphism have been found to strongly correlated with individual variation in plasma DbH activity. To test the influence of this polymorphism on the susceptibility of cocaine addiction, we decided to genotype it in a sample of 689 cocaine addicts and 832 healthy individuals. Genotypic and allelic analyses did not show any evidence of association with cocaine addiction, even after correcting for the effect of population stratification and other possible confounders. Our results do not support a major role of the -1021C>T polymorphism or the gene itself in the development of cocaine addiction but further examination of other variants within this gene will be necessary to completely rule out an effect.

Region‐specific tolerance to cocaine‐regulated cAMP‐dependent protein phosphorylation following chronic self‐administration

Chronic cocaine self-administration can produce either tolerance or sensitization to certain cocaine-regulated behaviours, but whether differential alterations develop in the biochemical response to cocaine is less clear. We measured cocaine-induced phosphorylation of multiple cAMP-dependent and -independent protein substrates in mesolimbic dopamine terminal regions following chronic self-administration. Changes in self-administering rats were compared to changes produced by passive yoked injection to identify reinforcement-related regulation, whereas acute and chronic yoked groups were compared to identify the development tolerance or sensitization in the biochemical response to cocaine. Microwave-fixed brain tissue was collected immediately following 4 h of intravenous cocaine administration, and subjected to Western blot analysis of phosphorylated and total protein substrates. Chronic cocaine produced region- and substrate-specific tolerance to cAMP-dependent protein phosphorylation, including GluR1(S845) phosphorylation in striatal and amygdala subregions and NR1(S897) phosphorylation in the CA1 subregion of the hippocampus. Tolerance also developed to cAMP-independent GluR1(S831) phosphorylation in the prefrontal cortex. In contrast, sensitization to presynaptic regulation of synapsin(S9) phosphorylation developed in the hippocampal CA3 subregion while cAMP-dependent tyrosine hydroxylase(S40) phosphorylation decreased in striatal dopamine terminals. Cocaine-induced ERK and CREB(S133) phosphorylation were dissociated in many brain regions and failed to develop either tolerance or sensitization with chronic administration. Positive reinforcement-related correlations between cocaine intake and protein phosphorylation were found only in self-administering animals, while negative dose-related correlations were found primarily with yoked administration. These regional- and substrate-specific adaptations in cocaine-induced protein phosphorylation are discussed in view of their potential impact on the development of cocaine addiction.

Sex differences in brain activation during stress imagery in abstinent cocaine users: A functional magnetic resonance imaging study

Because stress mediates drug seeking and relapse, and sex differences have been observed in stress and in the development of cocaine addiction, in this study we used functional neuroimaging to examine the effect of sex on stress responses in abstinent cocaine users. In a functional magnetic resonance imaging session, 17 male and 10 female cocaine-dependent subjects participated in script-guided imagery of neutral or stress situations. Subjects rated imagery vividness, anxiety, and cocaine craving for each trial. Brain activation during the stress and neutral imagery periods relative to their own baseline was examined in individual subjects. Sex contrast was obtained in second-level group analysis. Female subjects demonstrated more activation, compared with male subjects, in left middle frontal, anterior cingulate, and inferior frontal cortices and insula, and right cingulate cortex during stress imagery. Region of interest analysis showed that the change of activity in left anterior cingulate and right posterior cingulate cortices both correlated inversely with the change of craving rating during stress imagery. The greater left frontolimbic activity in women suggests that women might use more verbal coping strategies than do men while experiencing stress. The results also suggest a distinct role of the cingulate cortices in modulating stress-induced cocaine craving.

Neurobiology of stress and cocaine addiction. Studies on corticotropin-releasing factor in rats, monkeys, and humans.

Stress may contribute to the increased vulnerability to and the development of cocaine addiction. Corticotropin-releasing factor (CRF) activates the hypothalamic-pituitary-adrenal (HPA) axis as well as behavioral and immune processes in response to different environmental and pharmacologic stressors. We hypothesized that CRF might mediate some of the effects of cocaine and as such it may be a link between stressful events and increased vulnerability to cocaine addiction. We demonstrated that blockade of endogenous CRF by a CRF antiserum or a receptor antagonist prevented the cocaine-induced corticosterone response in rats. In male rhesus monkeys and in humans, cocaine selectively increased the amplitude-related, CRF-dependent, elements of pulsatile ACTH release. Cocaine-induced locomotor hyperactivity was antagonized by intracerebroventricular (i.c.v.) administration of a CRF antiserum and a CRF receptor antagonist in rats. In rhesus monkeys, strong correlations were found between behavioral hyperactivity and CRF-dependent elements of pulsatile activity of the HPA axis. Acute cocaine administration induced dose- and time-dependent alterations in hypothalamic and extrahypothalamic/limbic CRF concentrations in rats. Cocaine withdrawal elicited anxiety-like behavior and alterations of CRF concentration in the hypothalamus, amygdala, and basal forebrain. CRF antiserum (i.c.v.) antagonized anxiety-like behavior related to cocaine withdrawal. These data strongly suggest that the HPA axis, brain CRF in particular, may mediate some of the neuroendocrine and behavioral effects of cocaine. The potential involvement of CRF and HPA axis in cocaine-induced psychopathology is hypothesized.