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Substance abuse disorder is a chronic condition for which pharmacological treatment options remain limited. L-type calcium channels (LTCC) have been implicated in drug-related plasticity and behavior. Specifically, dopaminergic neurons in the mesocorticolimbic pathway express Ca v 1.2 and Ca v 1.3 channels, which may regulate dopaminergic activity associated with reward behavior. Therefore, this study aimed to investigate the hypothesis that pre-administration of the LTCC blocker, isradipine can mitigate the effects of cocaine by modulating central glutamatergic transmission. For that, we administered isradipine at varying concentrations (1, 7.5, and 15 μg/μL) via intracerebroventricular injection in male Swiss mice. This pretreatment was carried out prior to subjecting animals to behavioral assessments to evaluate cocaine-induced locomotor sensitization and conditioned place preference (CPP). The results revealed that isradipine administered at a concentration of 1 μg/μL effectively attenuated both the sensitization and CPP induced by cocaine (15 mg/kg, via i. p.). Moreover, mice treated with 1 μg/μL of isradipine showed decreased presynaptic levels of glutamate and calcium in the cortex and hippocampus as compared to control mice following cocaine exposure. Notably, the gene expression of ionotropic glutamate receptors, AMPA, and NMDA, remained unchanged, as did the expression of Ca v 1.2 and Ca v 1.3 channels. Importantly, these findings suggest that LTCC blockage may inhibit behavioral responses to cocaine, most likely by decreasing glutamatergic input in areas related to addiction. [Display omitted] • Isradipine reduces cocaine-induced behavioral sensitization. • Isradipine decreases cocaine-conditioned place preference. • Isradipine reduces cortical and hippocampal levels of glutamate and calcium in cocaine-treated mice. [ABSTRACT FROM AUTHOR]

Abstract Pitolisant, a selective inverse agonist for the histamine H3 receptor, is a new treatment for adults suffering from narcolepsy. Numerous studies have shown that striatal H3 receptors can modulate the activity of the dopamine mesolimbic system, a neuronal pathway that plays a crucial role in drug addiction. Therefore, it is important to guarantee that pitolisant has no abuse potential and does not potentiate the behavioral effects of psychostimulants. The present study tested the effects of pitolisant on cocaine reinforcement in C57BL/6J mice using the intravenous self-administration technique. Mice were trained to self-administer cocaine intravenously. After the acquisition of cocaine self-administration, pitolisant was tested on cocaine self-administration under different schedules of reinforcement (fixed ratio and progressive ratio). In another group of mice, cocaine was replaced with pitolisant after the acquisition of cocaine self-administration. Finally, a group of mice was trained to self-administer pitolisant intravenously and directly compared to mice trained to self-administer cocaine under the same conditions. Our results indicate that pitolisant does not influence the reinforcing effects of cocaine under any of the experimental conditions used in this study. Moreover, pitolisant has no reinforcing properties alone when tested in the self-administration paradigm. Our results offer more evidence to support the hypothesis that pitolisant is not addictive. In addition, pitolisant does not alter the reinforcing effects of cocaine. Finally, the present study provides no evidence for a significant involvement of histamine H3 receptors in cocaine dependence. [ABSTRACT FROM AUTHOR]

Abstract Sazetidine-A [6-(5(((S)-azetidine-2-yl)methoxy)pyridine-3-yl)hex-5-yn-1-ol] is a selective α4β2 nicotinic receptor desensitizing agent and partial agonist. Sazetidine-A has been shown in our previous studies to significantly reduce nicotine and alcohol self-administration in rats. The question arises whether sazetidine-A would reduce self-administration of other addictive drugs as well. Nicotinic receptors on the dopaminergic neurons in the ventral tegmental area play an important role in controlling the activity of these neurons and release of dopamine in the nucleus accumbens, which is critical mechanism for reinforcing value of drugs of abuse. Previously, we showed that the nonspecific nicotinic antagonist mecamylamine significantly reduces cocaine self-administration in rats. In this study, we acutely administered systemically sazetidine-A and two other selective α4β2 nicotinic receptor-desensitizing agents, VMY-2-95 and YL-2-203, to young adult female Sprague-Dawley rats and determined their effects on IV self-administration of cocaine and methamphetamine. Cocaine self-administration was significantly reduced by 0.3 mg/kg of sazetidine-A. In another set of rats, sazetidine-A (3 mg/kg) significantly reduced methamphetamine self-administration. VMY-2-95 significantly reduced both cocaine and methamphetamine self-administration with threshold effective doses of 3 and 0.3 mg/kg, respectively. In contrast, YL-2-203 did not significantly reduce cocaine self-administration at the same dose range and actually significantly increased cocaine self-administration at the 1 mg/kg dose. YL-2-203 (3 mg/kg) did significantly decrease methamphetamine self-administration. Sazetidine-A and VMY-2-95 are promising candidates to develop as new treatments to help addicts successfully overcome a variety of addictions including tobacco, alcohol as well as the stimulant drugs cocaine and methamphetamine. [ABSTRACT FROM AUTHOR]

Numerous studies have shown that social defeat stress induces an increase in the rewarding effects of cocaine. In this study we have investigated the role played by the main hypothalamic stress hormone, corticotropin-releasing factor (CRF), in the effects that repeated social defeat (RSD) induces in the conditioned rewarding effects and locomotor sensitization induced by cocaine. A total of 220 OF1 mice were divided into experimental groups according to the treatment received before each social defeat: saline, 5 or 10 mg/kg of the nonpeptidic corticotropin-releasing factor CRF 1 receptor antagonist CP-154,526, or 15 or 30 µg/kg of the peptidic corticotropin-releasing factor CRF 2 receptor antagonist Astressin 2 -B. Three weeks after the last defeat, conditioned place preference (CPP) induced by 1 mg/kg of cocaine was evaluated. Motor response to 10 mg/kg of cocaine was also studied after a sensitization induction. Blockade of corticotropin-releasing factor CRF 1 receptor reversed the increase in cocaine CPP induced by social defeat. Conversely, peripheral corticotropin-releasing factor CRF 2 receptor blockade produced similar effects to those observed in socially stressed animals. The effect of RSD on cocaine sensitization was again blocked by the corticotropin-releasing factor CRF 1 receptor antagonist, while peripheral CRF 2 receptor antagonist did not show effect. Acute administration of Astressin 2 -B induced an anxiogenic response. Our results confirm that CRF modulates the effects of social stress on reinforcement and sensitization induced by cocaine in contrasting ways. These findings highlight CRF receptors as potential therapeutic targets to be explored by research about stress-related addiction problems. [ABSTRACT FROM AUTHOR]

Exposure to cues previously associated with drug use and the environment can trigger intense craving and drug-seeking, often leading to relapse in individuals with substance use disorders. Several studies suggest that the decrease in the effects of the cues and the environment could help maintain abstinence from drug use in individuals abusing drugs. Mirtazapine, an antagonist of the noradrenergic (NE) α 2 receptor and the 5-HT 2A/C and 5-HT 3 receptors has demonstrated efficacy in reducing the rewarding effect of different drugs. The purpose of the present study was to investigate whether the mirtazapine, blocks the acquisition and reinstatement of cocaine-induced conditioned place preference (CPP). In this study, 120 Wistar male rats were utilized and we use the CPP as a behavioral tool to measure the context-rewarding effect of an unconditioned stimulus such as cocaine. Mirtazapine was dosed for 30 or 60 consecutive days prior to treatment with cocaine or during the extinction phase. We found that dosing with mirtazapine for 30 consecutive days caused a time-related reduction in acquisition or reinstatement of preference for the cocaine-paired chamber. When the duration of treatment is increased (60 days), reductions in preference for the cocaine-paired chamber were potentiated. These observations support its potential clinical anti-addictive properties against drugs. [ABSTRACT FROM AUTHOR]

Conditioned stimuli (CSs) exert motivational effects on both adaptive and pathological reward-related behaviors, including drug taking and seeking. We developed a paradigm that allows us to investigate the neuropharmacology by which previously neutral stimuli acquire the capacity to function as CSs and elicit (intravenous) cocaine conditioned approach and used this paradigm to test the role of NMDA receptor stimulation in the acquisition of cocaine conditioned approach. Rats were injected systemically with the NMDA receptor antagonist, MK-801, before the start of 4 consecutive conditioning sessions, each of which consisted of 20 randomly presented light/tone (CS) presentations paired with cocaine infusion contingent upon nose pokes. Rats later were subjected to a CS-only test. To test the role of NMDA receptor stimulation in the already established conditioned approach, rats were injected with MK-801 prior to the CS-only test that occurred after 18 CS-cocaine conditioning sessions. Blockade of NMDA receptors significantly impaired the acquisition of cocaine-conditioned approach as indicated by the emission of significantly fewer nose pokes and significantly longer latencies to nose poke during CS presentations. When MK-801 treatment was applied after the acquisition of conditioned approach responding it had no effect on these measures. These results suggest that NMDA receptor stimulation plays an important role in the acquisition of reward-related conditioned responses driven by intravenous cocaine-associated CSs. [ABSTRACT FROM AUTHOR]

The mechanism behind the reinstament of psychostimulant, as a major obstacle in addiction treatment is not fully understood. Controversial data are available in the literature concerning the role of the endocannabinoid (eCB) system in regulating the relapse to psychostimulant addiction in preclinical studies. The current systematic review aims to evaluate eCB modulators' effect in the reinstatement of commonly abused psychostimulants, including cocaine, amphetamine, methamphetamine, and 3,4-methylenedioxymethamphetamine. By searching the PubMed, Web of Science, and Scopus databases, studies were selected. Then the studies, quality was evaluated by the SYRCLE risk of bias tool. The results have still been limited to preclinical studies. Thirty-nine articles that employed self-administration and CPP as the most prevalent animal models of addiction were selected. This data indicates that cannabinoid receptor 1 antagonists and some cannabinoid receptor 2 agonists could suppress the reinstatement of cocaine and methamphetamine addiction in a dose-dependent manner. However, only AM251 was efficient to block the reinstatement of 3,4-methylenedioxymethamphetamine. In conclusion, cannabinoid receptor 1 antagonists and some cannabinoid receptor 2 agonists may have curative potential in the relapse of psychostimulant abuse. However, time, dose, and route of administration are crucial factors in their inhibitory impacts. [ABSTRACT FROM AUTHOR]

Social stress modifies the activity of brain areas involved in the rewarding effects of psychostimulants, inducing neuroadaptations in the dopaminergic mesolimbic system and modifying the sensitivity of dopamine receptors. In the present study we evaluated the effect of the dopamine D 1 - and D 2 -like receptor antagonists (SCH23390 and raclopride, respectively) on the short-time effects of acute social defeat (ASD). Male OF1 mice were socially defeated before each conditioning session of the conditioned place preference (CPP) induced by 1 mg/kg or 25 mg/kg of cocaine plus the corresponding dopamine antagonist. A final experiment was designed to evaluate the effect of the dopamine antagonists on the CPP induced by 3 mg/kg of cocaine with or without a stress experience. Mice exposed to ASD showed an increase in reinstatement of the conditioned reinforcing effects of cocaine that was blocked by all of the dopamine receptor antagonists. Blockade of dopamine D 2 -like receptors with raclopride specifically prevented the effects of stress without affecting the rewarding properties of cocaine. However, SCH23390 inhibited cocaine-induced preference in the control groups and even induced aversion in defeated mice conditioned with the lower dose of cocaine. Moreover, the lowest dose of SCH23390 blocked the rewarding effects of 3 mg/kg of cocaine-induced CPP. Our results confirm that the dopamine D 2 receptor is involved in the short-term effects of ASD on the rewarding effects of cocaine. The dopamine D 1 receptor is clearly involved in the rewarding effects of cocaine, but its role in the effects of ASD remains to be demonstrated. [ABSTRACT FROM AUTHOR]

Cocaine- and amphetamine-regulated transcript peptide (CARTp) is an anorexigenic neuropeptide whose receptor is undisclosed. Previously, we reported the specific binding of CART(61-102) to pheochromocytoma PC12 cells, where CART(61-102) affinity and the number of binding sites per cell corresponded to ligand-receptor binding. Recently, Yosten et al. designated orphan GPR160 as the CARTp receptor, because the GPR160 antibody abolished neuropathic pain and anorexigenic effects induced by CART(55-102) and exogenous CART(55-102) coimmunoprecipitated with GPR160 in KATOIII cells. As no direct evidence that CARTp is a ligand for GPR160 has been described, we decided to verify this hypothesis by testing CARTp affinity to the GPR160 receptor. We investigated the GPR160 expression in PC12 cells since it is cell line known to specifically bind CARTp. Moreover, we examined the specific CARTp binding in THP1 cells, with high endogenous GPR160 expression and GPR160-transfected cell lines U2OS and U-251 MG. In PC12 cells, the GPR160 antibody did not compete for specific binding with 125 I-CART(61-102) or with 125 I-CART(55-102), and GPR160 mRNA expression and GPR160 immunoreactivity were not detected. Moreover, THP1 cells did not show any 125 I-CART(61-102) or 125 I-CART(55-102) specific binding despite GPR160 detection by fluorescent immunocytochemistry (ICC). Finally, no 125 I-CART(61-102) or 125 I-CART(55-102) specific binding in the GPR160-transfected cell lines U2OS and U-251 MG, selected due to their negligible endogenous expression of GPR160, was detected, despite the detection of GPR160 by fluorescent ICC. Our binding studies clearly demonstrated that GPR160 cannot be a receptor for CARTp. Further studies are needed to identify true CARTp receptors., Competing Interests: Declaration of competing interest None., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Previous studies have demonstrated that the histamine H3 receptor inverse agonist thioperamide potentiates the stimulant and rewarding effects of cocaine. However, these potentiating effects of thioperamide do not necessarily result from H3 receptor blockade since thioperamide is an imidazole-based compound capable of enhancing plasma cocaine concentrations by blocking cytochrome P450 activity. In contrast, Pitolisant is a non-imidazole H3 receptor inverse agonist that has already been tested in clinical trials but it remains to be determined whether this compound also potentiates the behavioral effects of cocaine. The present study tested the effects of Pitolisant on locomotion, on cocaine-induced hyperactivity and on the development of conditioned place preference induced by cocaine (2 and 8 mg/kg, i.p.) in male C57BL/6J mice. Pitolisant was injected 30 min before each cocaine-pairing session. Locomotion recorded on the first cocaine-pairing session was used to test the effects of Pitolisant on the locomotor effects of cocaine. Our results show that doses of Pitolisant higher than 10 mg/kg depressed locomotion. When injected alone at doses that did not affect locomotion, Pitolisant (2.5–10 mg/kg, i.p.) had no rewarding properties in the place conditioning technique. Additionally, Pitolisant did not significantly alter cocaine-induced hyperactivity and cocaine-induced conditioned place preference. Taken together, our study indicates that Pitolisant has no addictive properties alone. Moreover, this compound does not significantly affect the stimulant and rewarding effects of cocaine. These results add further evidence to support the hypothesis that a pharmacokinetic interaction is involved in the ability of thioperamide to potentiate cocaine's psychomotor effects. [ABSTRACT FROM AUTHOR]

The mechanistic target of rapamycin complex 1 (mTORC1) regulates synaptic protein synthesis and therefore synaptic function and plasticity. A role for mTORC1 has recently been demonstrated for addiction-related behaviors. For example, central or intra-accumbal injections of the mTORC1 inhibitor rapamycin attenuates several indices of cocaine-seeking including progressive ratio (PR) responding and reinstatement. These behavioral effects are associated with decreased mTORC1 activity and synaptic protein translation in the nucleus accumbens (NAC) and point to a possible therapeutic role for rapamycin in the treatment of addiction. Currently, it is unclear whether similar behavioral and biochemical effects can be achieved by administering rapamycin systemically, which represents a more clinically-appropriate route of administration. Here, we assessed the effects of repeated, systemic administration of rapamycin (10 mg/kg, i.p.) on PR responding for cocaine. We also assessed whether systemic rapamycin was associated with changes in measures of mTORC1 activity and GluA1 expression in the ventral and dorsal striatum. We report that systemic rapamycin treatment reduced PR breakpoints to levels comparable to intra-NAC rapamycin. Systemic rapamycin treatment also reduced phosphorylated p70S6K and GluA1 AMPARs within the NAC but not dorsal striatum. Thus, systemic administration of rapamycin is as effective at reducing drug seeking behavior and measures of mTORC1 activity compared to direct accumbal application and may therefore represent a possible therapeutic option in the treatment of addiction. Possible caveats of this treatment approach are discussed. [ABSTRACT FROM AUTHOR]

Drug addiction shares brain mechanisms and molecular substrates with learning and memory processes, such as the stimulation of glutamate receptors and their downstream signalling pathways. In the present work we provide an up-to-date review of studies that have demonstrated the implication of the main memory-related calcium-dependent protein kinases in opiate and cocaine addiction. The effects of these drugs of abuse in different animal models of drug reward, dependence and addiction are altered by manipulation of the mitogen-activated protein kinase (MAPK) family, particularly extracellular signal regulated kinase (ERK), calcium/calmodulin-dependent kinase II (CaMKII), the protein kinase C (PKC) family (including PKMζ), cAMP-dependent protein kinase A (PKA), cGMP-dependent protein kinase G (PKG), the phosphatidylinositol 3-kinase (PI3K) pathway and its downstream target mammalian target of Rapamycin (mTOR), cyclin-dependent kinase 5 (Cdk5), heat-shock proteins (Hsp) and other enzymes and proteins. Research suggests that drugs of abuse induce dependence and addiction by modifying the signalling pathways that involve these memory-related protein kinases, and supports the idea that drug addiction is an excessive aberrant learning disorder in which the maladaptive memory of drug-associated cues maintains compulsive drug use and contributes to relapse. Moreover, the studies we review offer new pharmacological strategies to treat opiate and cocaine dependence based on the manipulation of these protein kinases. In particular, disruption of reconsolidation of drug-related memories may have a high therapeutic value in the treatment of drug addiction. [ABSTRACT FROM AUTHOR]

Muscarinic and dopamine brain systems interact intimately, and muscarinic receptor ligands, like dopamine ligands, can modulate the reinforcing and discriminative stimulus (S D ) effects of cocaine. To enlighten the dopamine/muscarinic interactions as they pertain to the S D effects of cocaine, we evaluated whether muscarinic M 1 , M 2 or M 4 receptors are necessary for dopamine D 1 and/or D 2 antagonist mediated modulation of the S D effects of cocaine. Knockout mice lacking M 1 , M 2 , or M 4 receptors, as well as control wild-type mice and outbred Swiss-Webster mice, were trained to discriminate 10 mg/kg cocaine from saline in a food-reinforced drug discrimination procedure. Effects of pretreatments with the dopamine D 1 antagonist SCH 23390 and the dopamine D 2 antagonist eticlopride were evaluated. In intact mice, both SCH 23390 and eticlopride attenuated the cocaine discriminative stimulus effect, as expected. SCH 23390 similarly attenuated the cocaine discriminative stimulus effect in M 1 knockout mice, but not in mice lacking M 2 or M 4 receptors. The effects of eticlopride were comparable in each knockout strain. These findings demonstrate differences in the way that D 1 and D 2 antagonists modulate the S D effects of cocaine, D 1 modulation being at least partially dependent upon activity at the inhibitory M 2 /M 4 muscarinic subtypes, while D 2 modulation appeared independent of these systems. [ABSTRACT FROM AUTHOR]

Abuse of and addiction to psychostimulants remains a challenging clinical issue; yet no effective pharmacotherapy is available. Trace amine associated receptor 1 (TAAR 1) is increasingly recognized as a novel drug target that participates in the modulation of drug abuse. This review analyzed existing preclinical evidence from electrophysiological, biochemical to behavioral aspects regarding the functional interactions between TAAR 1 and dopaminergic system. TAAR 1 knockout mice demonstrate increased sensitivity to dopaminergic activation while TAAR 1 agonists reduce the neurochemical effects of cocaine and amphetamines, attenuate abuse- and addiction-related behavioral effects of cocaine and methamphetamine. It is concluded that TAAR 1 activation functionally modulates the dopaminergic activity and TAAR 1 agonists appear to be promising pharmacotherapies against psychostimulant addiction. [ABSTRACT FROM AUTHOR]

The stimulants cathinone (from Khat leaves) and methylenedioxymeth-amphetamine (MDMA) produce adrenoceptor mediated tachycardia and vasopressor actions that may be the result of direct receptor stimulation, actions on the noradrenaline transporter, and/or displacement of noradrenaline from nerve terminals. Effects of cathinone or MDMA were compared with those of the indirect sympathomimetic tyramine. Male Wistar rats were anaesthetized with pentobarbitone for blood pressure and heart rate recording. Some rats were sympathectomised by treatment with 6-hydroxydopamine. In the anaesthetised rat, cathinone, MDMA and tyramine (all 0.001–1 mg /kg) produced marked tachycardia, tyramine produced marked pressor responses and MDMA produced small pressor responses. The tachycardia to cathinone and MDMA was almost abolished by propranolol (1 mg/kg). Pretreatment with cocaine (1 mg/kg) did not significantly affect the tachycardia to cathinone or MDMA, but reduced the response to tyramine. However, in sympathectomised rats, the tachycardia to cathinone or MDMA was markedly attenuated, but the tachycardia to tyramine was only partially reduced. Blood pressure effects of tyramine and MDMA were also markedly attenuated by sympathectomy. The results demonstrate firstly that cocaine may not be the most suitable agent for assessing direct versus indirect agonism in cardiovascular studies. Secondly, the use of chemical sympathectomy achieved the desired goal of demonstrating that cardiac β-adrenoceptor mediated actions of cathinone and MDMA are probably largely indirect. [ABSTRACT FROM AUTHOR]

Neuropeptide S (NPS) is a neurotransmitter that activates the NPS receptor to modulate biological functions including anxiety-like behaviors, feeding, and drug reinforcement. RTI-118 is a novel NPS receptor antagonist that decreased cocaine self-administration in rats at doses that had little or no effect on food-maintained responding. To build on these previous findings, this study examined effects of RTI-118 on cocaine-induced facilitation of intracranial self-stimulation (ICSS) in rats. To provide a context for data interpretation, effects of RTI-118 were compared to effects of the kappa opioid receptor agonist U69,593, because the kappa opioid receptor is another peptide neurotransmitter receptor reported to modulate abuse-related cocaine effects. RTI-118 effects were also examined on ICSS facilitation produced by methylenedioxypyrovalerone (MDPV), a novel designer drug of abuse with some cocaine-like effects. Male Sprague–Dawley rats ( n =12) with electrodes targeting the medial forebrain bundle responded under a fixed-ratio 1 schedule for range of brain stimulation frequencies. Under control conditions, brain stimulation maintained a frequency-dependent increase in ICSS rates. Cocaine (1.0–10 mg/kg) and MDPV (3.2 mg/kg) facilitated ICSS. RTI-118 (3.2–32 mg/kg) alone produced little effect on ICSS but dose dependently blocked cocaine-induced ICSS facilitation. U69,593 (0.25–0.5 mg/kg) also attenuated cocaine effects, but blockade of cocaine effects was incomplete even at a U69,593 dose that alone depressed ICSS. RTI-118 (32 mg/kg) failed to block MDPV-induced ICSS facilitation. These results support further consideration of NPS receptor antagonists as candidate treatments for cocaine abuse and provide evidence for differential effects of a candidate treatment on abuse-related effects of cocaine and MDPV. [ABSTRACT FROM AUTHOR]

Abstract: Stimulants are banned in competition by the World Anti-Doping Agency, except for a small number of therapeutic agents subject to monitoring, including bupropion. We have examined the potency of bupropion in comparison with two agents banned in competition, adrafinil and modafinil, and with cocaine and desipramine as blockers of the noradrenaline re-uptake transporter in peripheral tissues of the rat. For studies in vivo, the pressor response to noradrenaline in the anaesthetized rat was studied. Cocaine, desipramine and bupropion at doses of 0.1, 0.3 and 1mg/kg, respectively, significantly increased the pressor response to noradrenaline. Overall, cocaine and desipramine were approximately 2–5 times more potent than bupropion in vivo in the rat. Adrafinil and modafinil (both 3mg/kg) did not significantly affect the pressor response. Bupropion was chosen for further study. In 1Hz paced rat right ventricular strips, bupropion (30?M) significantly increased the potency of noradrenaline at increasing the force of contraction. In rat vas deferens, bupropion and cocaine produced concentration-dependent increases in the contractile response to nerve stimulation, and cocaine was 11 times more potent than bupropion. Since bupropion is used clinically in doses of up to 300mg, it is likely that bupropion has actions at the noradrenaline transporter, and thus cardiovascular stimulant actions, in clinical doses. This may explain findings of increased exercise performance with bupropion. [Copyright &y& Elsevier]

Abstract: In rats, the discriminative stimulus effects of direct- and indirect-acting dopamine receptor agonists are mediated by multiple dopamine receptor subtypes and the relative contribution of dopamine D2 and D3 receptors to these effects varies as a function of feeding condition. In these studies, free-fed and food-restricted mice were trained to discriminate 10.0mg/kg cocaine using a two-lever discrimination procedure in which responding was maintained by food. Both groups of mice acquired the discrimination; however, free-fed mice responded at lower rates than food-restricted mice. Dopamine D3 receptor agonists, pramipexole and quinpirole, increased cocaine-appropriate responding (>85%) in food-restricted, but not in free-fed mice. The dopamine D2 receptor agonist, sumanirole, and the nonselective dopamine receptor agonist, apomorphine, failed to increase cocaine-appropriate responding in either group. Free-fed mice were more sensitive than food-restricted mice to the rate-decreasing effects of dopamine receptor agonists and these effects could not be overcome by increasing the magnitude of reinforcement. Because feeding condition did not alter quinpirole-induced hypothermia, it is unlikely that differences in the discriminative stimulus or rate-decreasing effects of dopamine D2-like receptor agonists were due to differences in the pharmacokinetic properties of the drugs. Although these results suggest that the discriminative stimulus effects of cocaine are mediated by both dopamine D2 and D3 receptors in food-restricted mice, the increased sensitivity of free-fed mice to the rate-decreasing effects of dopamine D2-like receptor agonists limited conclusions about the impact of feeding conditions on the relative contribution of dopamine D2 and D3 receptors to the discriminative stimulus effects of cocaine. [Copyright &y& Elsevier]

Abstract: κ Opioid receptor activation by traditional arylacetamide agonists and the novel neoclerodane diterpene κ opioid receptor agonist Salvinorin A (Sal A) results in attenuation of cocaine-seeking behavior in pre-clinical models of addiction. However, adverse effects such as sedation, depression and aversion limit their clinical utility. The Sal A analogue, 2-methoxy-methyl salvinorin B (MOM Sal B) is a longer acting Sal A analogue with high affinity for κ opioid receptors. In this study, we tested MOM Sal B for its ability to modulate cocaine-seeking behavior in rats. MOM Sal B (0.3mg/kg) successfully attenuated cocaine-seeking but also attenuated sucrose reinforcement. No change in activity was observed in either cocaine-induced hyperactivity or spontaneous open field activity tests but increased immobility and decreased swimming times in the forced swim test were observed. This study indicates that κ opioid receptor activation by more potent Sal A analogues modulates cocaine-seeking behavior non-selectively without causing sedation, suggesting an improved side effects profile. However, pro-depressive effects are seen, which may limit the therapeutic potential of this compound. Future studies with Sal A analogues having affinities at other opioid receptors are warranted as they have the potential to identify compounds having effective anti-addiction properties. [Copyright &y& Elsevier]

Abstract: Drug addiction is a chronic relapsing brain disease for which many of the underlying neuronal mechanisms are yet to be unravelled. There seems to be an interaction between the melanocortin system and drugs of abuse. For instance, infusion of the melanocortin MC4 receptor antagonist SHU9119 (Ac-Nle-cyclo(-Asp-His-d-2-Nal-Arg-Trp-Lys)-NH2) into the nucleus accumbens results in conditioned place avoidance, reduces the amount of lever presses for cocaine and blocks development of cocaine-induced locomotor sensitisation. The aim of this study is to determine whether the induction of locomotor sensitisation to repeated cocaine is inhibited by the melanocortin MC4 receptor inverse agonist Agouti Related Peptide (AgRP83–132). Rats were sensitised to daily cocaine injections for 5 consecutive days and 30min prior to every daily cocaine injection, rats received an intracerebroventricular (i.c.v.) or intra nucleus accumbens injection with AgRP(83–132) or saline, to determine whether we could inhibit cocaine-induced locomotor sensitisation. We show that i.c.v. injections of AgRP(83–132) inhibit cocaine-induced locomotor sensitisation. This effect is not regulated via the nucleus accumbens, since injecting the melanocortin receptor inverse agonist AgRP(83–132) directly into the nucleus accumbens was unable to inhibit the cocaine-induced locomotor sensitisation. This implicates that the nucleus accumbens is an unlikely site to inhibit the induction of locomotor sensitisation via the melanocortin MC4 receptor. This is in contrast to other studies that show an effect of the melanocortin MC4 receptor antagonist SHU9119 on locomotor sensitisation when injected into the nucleus accumbens. [Copyright &y& Elsevier]

Abstract: We have previously shown that orphanin FQ (also known as nociceptin; OFQ/N) attenuates the motor stimulatory effect of cocaine and blocks locomotor sensitization induced by cocaine. Furthermore, we have shown that cocaine treatment altered the level of endogenous OFQ/N, raising the possibility that endogenous OFQ/N and its receptor (NOP) may be crucial in these actions of cocaine. Accordingly, in the present study, we sought to determine the role of NOP receptors in psychomotor stimulation and locomotor sensitization induced by cocaine or amphetamine. Mice lacking the NOP receptor and their wild-type littermates were habituated to motor activity chambers for 1h, injected with cocaine (0, 15 or 30mg/kg) or amphetamine (0, 1 or 3mg/kg), and motor activity was recorded for 1h. For sensitization induced by these drugs, mice were treated with saline or the highest dose of each drug once daily for three consecutive days and tested on day 8. On this day, mice were habituated to the chambers for 1h, then received a challenge dose of cocaine (15mg/kg) or amphetamine (1mg/kg), and motor activity was recorded for 1h. Cocaine and amphetamine each induced hyperlocomotion but the extent of this response was not different between NOP receptor null mice and their controls. Sensitization developed to the motor stimulatory action of each drug, but the magnitude of cocaine-induced sensitization was only higher in null mice compared to their controls. Together, the present results suggest that the endogenous OFQ/N/NOP receptor system may modulate the development of cocaine-induced locomotor sensitization. [Copyright &y& Elsevier]

Abstract: Nociceptin (N/OFQ) has been implicated in a variety of neurological disorders, most notably in reward processes and drug abuse. N/OFQ suppresses extracellular dopamine in the nucleus accumbens (NAc) after intracerebroventricular injection. This study sought to examine the effects of retrodialyzed N/OFQ on the cocaine-induced increase in extracellular dopamine levels in the NAc, as well as locomotor activity, in freely moving rats. 1.0μM, 10μM, and 1mM N/OFQ, in the NAc shell, significantly suppressed the cocaine-induced dopamine increase in the NAc, while N/OFQ alone had no significant effect on dopamine levels. Co-delivery of the selective NOP receptor antagonist SB612111 ([(–)-cis-1-Methyl-7-[[4-(2,6-dichlorophenyl)piperidin-1-yl]methyl]-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-ol] reversed the N/OFQ suppression of cocaine-induced dopamine in the NAc, suggesting that this is an NOP receptor-mediated effect. Using a novel system to assess locomotion, we measured various motor activities of the animals with simultaneous microdialysis from the home cage. Cocaine produced an expected increase in total activity, including horizontal movement and rearing behavior. Retrodialysis of N/OFQ with cocaine administration affected all motor activities, initially showing no effect on behavior, but over time inhibiting cocaine-induced motor behaviors. These results suggest that N/OFQ can act directly in the NAc shell to block cocaine-induced increases in extracellular dopamine levels. Extracellular dopamine and locomotor activity can be dissociated within the NAc and may reflect motor output differences in shell versus core regions of the NAc. These studies confirm the widespread involvement of NOP receptors in drug addiction and further validate the utility of an NOP receptor agonist as a medication for treatment of drug addiction. [Copyright &y& Elsevier]

Abstract: The dopamine transporter removes the neurotransmitter from the synapse, regulating dopamine availability. The transporter can be internalized and its function is blocked by cocaine and other ligands. Melittin inhibits dopamine transporter function and causes internalization of the recombinant transporter in stably transfected HEK-293 cells, but the specific pathways for internalization and disposition of the transporter are unknown. Here we report that melittin treatment increased both transporter internalization and colocalization with clathrin, effects that were blocked by pretreatment with cocaine. Density gradient centrifugation revealed that melittin treatment caused the dopamine transporter to associate with a density fraction containing the early endosome marker Rab 5A. Confocal microscopy revealed that melittin treatment also increased transporter colocalization with Rab 5A and decreased colocalization with the late endosome marker Rab 7 and the recycling endosome marker Rab 11. Following 60min of melittin treatment, the transporter was trafficked back to the membrane. By comparison, phorbol ester treatment increased transporter colocalization with early endosome antigen 1 and Rab 7 in a time-dependent manner. Cocaine treatment alone does not affect transporter trafficking in these cells. Results indicate multiple dopamine transporter internalization and recycling pathways that depend on transporter-ligand interactions and post-translational modifications. [Copyright &y& Elsevier]

Abstract: We have previously shown that β-endorphin plays a functional role in the rewarding effect of acute cocaine. Considering that β-endorphin has high affinity for the μ opioid receptor, we determined the role of this receptor in the rewarding action of acute cocaine. For comparison, we assessed the role of the μ opioid receptor in the rewarding effect of acute morphine. We also examined the effect of intracerebroventricular (i.c.v.) administration of β-funaltrexamine (β-FNA), an irreversible μ opioid receptor antagonist, on the rewarding action of acute cocaine as well as that of morphine. Using the conditioned place preference (CPP) paradigm as an animal model of reward, we first assessed the rewarding action of cocaine in mice lacking β-endorphin or the μ opioid receptor and their respective wild-type littermates/controls. Mice were tested for preconditioning place preference on day 1, conditioned once daily with saline/cocaine (30mg/kg, i.p.) or cocaine/saline on days 2 and 3, and then tested for postconditioning place preference on day 4. We next studied the rewarding action of acute morphine in μ knockout mice and their wild-type controls. The CPP was induced by single alternate-day saline/morphine (10mg/kg, s.c.) or morphine/saline conditioning. We finally determined the effect of β-FNA on CPP induced by cocaine or morphine in wild-type mice, in which mice were treated with saline or β-FNA (9ug/3μl; i.c.v.) a day prior to the preconditioning test day. Our results revealed that morphine induced a robust CPP in wild-type mice but not in mice lacking the μ opioid receptor or in wild-type mice treated with β-FNA. In contrast, cocaine induced CPP in μ knockout mice as well as in wild-type mice treated with β-FNA. On the other hand, cocaine failed to induce CPP in mice lacking β-endorphin. These results illustrate that β-endorphin is essential for the rewarding action of acute cocaine, but the μ opioid receptor may not mediate the regulatory action of endogenous β-endorphin. [Copyright &y& Elsevier]

Abstract: Individuals prone to drug self-administration may be vulnerable not only to a single drug reinforcer but to a variety of drug reinforcers. It has been shown that two thirds of alcoholics regularly use drugs other than ethanol (alcohol). Up to 30% of alcohol-dependent patients report concurrent misuse of cocaine. The aim of the present study was to investigate intravenous cocaine self-administration in selectively bred, alcohol-preferring WHP (Warsaw high-preferring) and non-preferring WLP (Warsaw low-preferring) rats. It was hypothesized that WHPs could be more prone to cocaine self-administration in comparison to WLPs. Rats from both lines were allowed to nose-poke for cocaine infusions (0.33mg/kg/infusion) under the FR-1, FR-2, and FR-3 schedule of reinforcement. Dose–response curves were assessed with increasing doses of cocaine (0.03, 0.1, 0.33, 1.0mg/kg/infusion). The WHP and WLP rats did not differ in cocaine self-administration. Both groups quickly acquired nose-poke responding for cocaine, presented a similar response profile when the schedule of reinforcement was increased from FR-1 to FR-3, and similar sensitivity to cocaine in the dose–response test. The present results may indicate that the selective breeding of alcohol-preferring WHP and alcohol non-preferring WLP rats did not lead to differences in cocaine''s rewarding effects as assessed in the self-administration procedure. [Copyright &y& Elsevier]

Abstract: We examined the role of nitric oxide (NO) in the regulation of neuronal uptake of norepinephrine (uptake-1) in rats under anesthesia. The effect on systolic blood pressure of two pressor drugs that work by different mechanisms, norepinephrine and angiotensin II, was explored in anesthetized rats under control conditions and after prevention of NO synthesis with Nw-nitro-l-arginine (L-NNA). The results showed that whereas the pressor effects of increasing doses of norepinephrine were potentiated by L-NNA, those of angiotensin II were not affected, which implied that NO was selectively involved in modulating the pressor effect of norepinephrine. To explore the mechanisms involved in this potentiation, we examined the effect of L-NNA on the pressor effect of tyramine, a purely-indirectly-acting sympathomimetic amine which enters nerve terminals thorough uptake 1 and liberates norepinephrine from storage vesicles. Increasing doses of tyramine produced pressor effects which, in contrast to those of norepinephrine, were significantly attenuated by pre-treatment with L-NNA. Similarly, pretreatment with cocaine, the classical inhibitor of uptake 1, significantly decreased the pressor effect of tyramine; however, the response to tyramine was then restored when L-NNA was administered, thus reversing the effect of cocaine. We conclude that NO plays a major role in the adrenergic system by enhancing the activity of uptake 1 in sympathetic nerve terminals. Blockade of uptake 1 by cocaine is also partly dependent on NO. The stimulus for the mobilization of the NO synthase pathway in adrenergic neurons and the subsequent steps involved in modulating uptake 1 deserve further exploration. [Copyright &y& Elsevier]

Abstract: We have previously reported that selective blockade of brain dopamine D3 receptors by SB-277011A significantly attenuates cocaine self-administration and cocaine-induced reinstatement of drug-seeking behavior. In the present study, we investigated whether SB-277011A similarly inhibits methamphetamine self-administration and methamphetamine-induced reinstatement to drug-seeking behavior. Male Long–Evans rats were allowed to intravenously self-administer methamphetamine (0.05mg/kg/infusion) under fixed-ratio 2 (FR2) or progressive-ratio (PR) reinforcement conditions, and some rats were tested for methamphetamine-induced reinstatement of drug-seeking behavior after extinction of self-administration. The effects of SB-277011A on each of these methamphetamine-supported behaviors were then tested. Acute intraperitoneal (i.p.) administration of SB-277011A failed to alter methamphetamine self-administration under FR2 reinforcement, but significantly lowered the break-point for methamphetamine self-administration under PR reinforcement. SB-277011A also significantly inhibited methamphetamine-triggered reinstatement of extinguished drug-seeking behavior. Overall, these data show that blockade of dopamine D3 receptors by SB-277011A attenuates the rewarding and incentive motivational effects of methamphetamine in rats, supporting the development of selective dopamine D3 antagonists for the treatment of methamphetamine addiction. [Copyright &y& Elsevier]

Abstract: Muscarinic acetylcholine receptors in the nucleus accumbens play an important role in mediating the reinforcing effects of cocaine. However, there is a paucity of data regarding the role of accumbal muscarinic acetylcholine receptors in the reinstatement of cocaine-seeking behavior. The goal of these experiments was to assess the role of muscarinic acetylcholine receptors in the nucleus accumbens core and shell in cocaine and sucrose priming-induced reinstatement. Rats were initially trained to self-administer cocaine or sucrose on a fixed-ratio schedule of reinforcement. Lever-pressing behavior was then extinguished and followed by a subsequent reinstatement phase during which operant responding was induced by either a systemic injection of cocaine in cocaine-experienced rats or non-contingent delivery of sucrose pellets in subjects with a history of sucrose self-administration. Results indicated that systemic administration of the muscarinic acetylcholine receptor antagonist scopolamine (5.0mg/kg, i.p.) dose-dependently attenuated cocaine, but not sucrose, reinstatement. Furthermore, administration of scopolamine (36.0μg) directly into the nucleus accumbens shell or core attenuated cocaine priming-induced reinstatement. In contrast, infusion of scopolamine (36.0μg) directly into the accumbens core, but not shell, attenuated sucrose reinstatement, which suggests that muscarinic acetylcholine receptors in these two subregions of the nucleus accumbens have differential roles in sucrose seeking. Taken together, these results indicate that cocaine priming-induced reinstatement is mediated, in part, by increased signaling through muscarinic acetylcholine receptors in the shell subregion of the nucleus accumbens. Muscarinic acetylcholine receptors in the core of the accumbens, in contrast, appear to play a more general (i.e. not cocaine specific) role in motivated behaviors. [ABSTRACT FROM AUTHOR]

Abstract: The association between cocaine administration and induction of oxidative stress in different brain regions suggests that oxidative damage is an important factor participating in cocaine disruption of normal central nervous system functions. In order to deal with this topic, brain penetrating exogenous antioxidants were suggested as a tool to prevent cocaine-induced oxidative damage and behavioral changes. Lately, we have shown that Tempol, a stable nitroxide radical reduced oxidative damage and attenuated the development and expression of cocaine psychomotor sensitization. To examine whether nitroxides, represented by Tempol, can exhibit protective effects against cocaine-induced cell death and to elucidate the molecular mechanism of cocaine-induced oxidative damage, we used the well established PC12 cell line model. The results showed that (1) cocaine induced cell death in a dose-dependent manner (2) and that it was reduced significantly by the stable nitroxide radical Tempol. Furthermore, (3) Tempol significantly inhibited oxidative damage induced by cocaine as reflected by mitochondrial superoxide radical and peroxide enhancement. Finally, (4) Tempol restored the total scavenging capacity which was reduced by cocaine in PC12 cells. Cumulatively, these results suggest that nitroxides such as Tempol can attenuate oxidative damage and cell death induced by cocaine and that PC12 cells can be used as an in vitro model to further investigate the precise molecular mechanism of these compounds. [ABSTRACT FROM AUTHOR]

Abstract: A successful replacement pharmacotherapy for treating cocaine dependency would likely reduce cocaine''s abuse, support a low abuse liability, overlap cocaine''s subjective effects, and have a long duration of action. Inhibitors with varying selectivity at the dopamine transporter (DAT) have approximated these properties. The objective of the present study was to characterize the behavioural effects of an extremely selective DAT inhibitor, (+) trans-4-(2-Benzhydryloxyethyl)-1-(4-fluorobenzyl) piperadin-3-ol (D-84), a 3-hydroxy substituted piperidine derivative of GBR-12935, for its cocaine-like discriminative stimulus effects, its effects on cocaine self-administration, and for its own self-administration. During cocaine discrimination tests, cocaine occasioned the 10mg/kg cocaine training stimulus with an ED50 value of 3.13 (1.54–6.34)mg/kg, and reduced response rates with an ED50 value of 20.39 (7.24–57.44)mg/kg. D-84 incompletely generalized to the cocaine stimulus occasioning a maximal 76% cocaine-lever responding, while reducing response rates with lower potency than cocaine (ED50 =30.94 (12.34–77.60)mg/kg). Pretreatment with D-84 (9.6–30.4mg/kg) significantly (P< 0.05) reduced cocaine intake at 17.1mg/kg D-84 when cocaine was self-administered at 0.5mg/kg/infusion, and at 30.4mg/kg D-84 when cocaine was self-administered at 0.1, 0.5 .and 1.0mg/kg/infusion. During self-administration tests with D-84 (0.1–1mg/kg/infusion), numbers of infusions significantly exceeded vehicle levels at 0.3mg/kg/infusion. These results show that D-84 pretreatment can decrease cocaine intake especially when high doses of cocaine are being self-administered. This observation, combined with its incomplete generalization to the cocaine discriminative stimulus and its reported long duration of action, provides a profile consistent with a potential replacement therapy for treating cocaine-abusing patients. [Copyright &y& Elsevier]

Abstract: Cocaine and amphetamine regulated transcript (CART) has been implicated in the regulation of the stress response. Although the forced swimming test (FST), in which rats are forced to swim for 15min (pretest swim) and then again for 5min (test swim) 24h later, has been used to study the effects of antidepressants, there have been few studies examining the effects of antidepressants on FST-induced changes in CART mRNA levels in the brain. To answer this question, we injected reboxetine and citalopram into male Sprague-Dawley rats 1, 5, and 23.5h before the test swim and then sacrificed rats 2h after the test swim, at the peak of the FST-induced increase in CART expression. The FST significantly increased CART mRNA levels in the nucleus accumbens, central nucleus of the amygdala, and locus ceruleus 2h after the test session. Both reboxetine and citalopram pretreatment blocked FST-induced increases in CART mRNA levels in the nucleus accumbens, central nucleus of the amygdala, and locus ceruleus, despite the fact these antidepressants exert their therapeutic effect by different mechanisms. In addition, the FST significantly increased plasma corticosterone levels, and this effect was also blocked by reboxetine and citalopram pretreatment. These results suggest that inhibition of FST-induced increases in CART expression in the nucleus accumbens, central nucleus of the amygdala, and locus ceruleus may be a common mechanism of antidepressant effects during the FST. [ABSTRACT FROM AUTHOR]

Abstract: Cocaine dependence continues to be a worldwide public health concern. Although the majority of individuals reporting cocaine use do so via the intranasal route, relatively few laboratory experiments have examined the reinforcing effects of cocaine administered intranasally. The purpose of this experiment was to measure the reinforcing effects of intranasal cocaine using a progressive ratio schedule in which eight cocaine-using subjects chose between doses of cocaine (4 [placebo], 15, 30 and 45mg) and an alternative reinforcer ($0.25). During each session, subjects first sampled the dose of cocaine available that day and then made six choices between that dose and money, which were available on concurrent progressive ratio schedules of responding. Break points for active cocaine doses were higher than those for placebo but no statistically significant active versus placebo dose effects were observed on subject-rated or physiological measures. These data demonstrate that intranasal cocaine functions as a reinforcer under a progressive ratio schedule in humans. Future research should test higher cocaine doses and larger values of the alternative reinforcer. These procedures may be useful for examining the influence of putative pharmacological and behavioral interventions on intranasal cocaine self-administration. [ABSTRACT FROM AUTHOR]

Abstract: The long lasting addiction-related abnormal memory is one of the most important foundations for relapse. DNA methylation may be a possible mechanism for persistence of such memory. Here we injected the DNA methyltransferases (DNMTs) inhibitor, 5-aza-2-deoxycytidine (5-aza) into hippocampus CA1 area and prelimbic cortex during the stages of acquisition and expression of cocaine-induced place preference in C57BL/6 mice. Results showed that in CA1 DNA methylation inhibitors could restrain acquisition but had no impact on expression of the cocaine-induced conditioned place preference (CPP). On the contrary, in prelimbic cortex, 5-aza had no effect on acquisition but blocked expression. Our results indicated that DNA methylation in hippocampus is required for learning; while DNA methylation in prelimbic cortex is necessary for memory retrieval. The present finding is consistent with the role of the hippocampus as a structure contributing to cocaine-induced memory acqu i sition, and prelimbic cortex, a part of prefrontal cortex as an area responsible for cocaine-induced memory retrieval. In conclusion, DNA methylation does play an important role in drug-induced learning and memory although the detailed effect still calls for further research. [Copyright &y& Elsevier]

Abstract: GM1 pretreatment enhanced the rewarding properties of cocaine as assessed in the conditioned place preference paradigm. This effect was shown by the lower dosage of cocaine necessary to induce conditioning compared with rats receiving cocaine alone, as well as by the fewer number of sessions necessary to induce place preference. GM1 pretreatment did not modify the plasma level of cocaine, but it induced a significant increase in the brain cocaine level compared with animals receiving cocaine alone. In order to evaluate the possibility that GM1 pretreatment may alter the pharmacokinetic parameters of cocaine, the brain and plasma esterase activities, the plasma bound/free cocaine ratio and the brain blood barrier permeability to i.v. Evans Blue administration were assessed. None of these parameters was modified by the GM1 administration. In addition, GM1 (100µM) did not alter the dopamine transporter inhibition induced by cocaine (10−7–10−5 M), as determined by the uptake of [3−H]-dopamine in the microsacs of nucleus accumbens. In conclusion, GM1 pretreatment, which did not have any effect per se, increased the rewarding effect of cocaine, a phenomenon correlated with a significant increase in the brain cocaine levels. The different pharmacokinetic parameters evaluated, as well as the inhibitory effect of cocaine on the dopamine transporter, were not modified by GM1, but it modifies the brain cocaine disposition. Thus, the mechanisms by which GM1 enhanced the rewarding effects of cocaine merit further study. [Copyright &y& Elsevier]

Abstract: The serotonin transporter (SERT) terminates serotonergic neurotransmission by the rapid removal of serotonin (5-hydroxytryptamine, 5-HT) from the extracellular space back into serotonergic neurons. SERT therefore controls the concentration of extracellular 5-HT, and thus one mechanism to regulate the efficacy of serotonergic neurotransmission is via modulation of the density of SERT molecules on the cell membrane. We have studied the effects of prolonged exposure to various selective serotonin re-uptake inhibitors (SSRIs), as well as cocaine and the transport substrates 5-HT and 3,4-methylenedioxy-methamphetamine (MDMA), on SERT cell surface expression in cultured serotonergic neurons. This was achieved via quantification of the amount of cell surface-expressed SERT molecules using antibody detection combined with confocal laser scanning microscopy. Our results show that exposure to the SSRIs citalopram, fluoxetine, sertraline and paroxetine all induced SERT internalization, but with different efficacies. The substrates 5-HT and MDMA also induced SERT internalization, while cocaine elevated SERT cell surface expression. [Copyright &y& Elsevier]

Abstract: We tested if discontinuation of cocaine self-administration can lead to the development of depressive-like symptoms in the forced swim test expressed as changes in immobility, swimming and climbing behaviors in rats. A “yoked” procedure in which rats were run simultaneously in groups of three, with two rats received the passive injection of cocaine or saline, was employed. Later, we examined whether acute treatment with the classical antidepressant imipramine or GABAB receptor ligands could alter the increases in immobility recorded after discontinuation of self-administered cocaine. We found a significant increase (44%) in the immobility time 3days following discontinuation of cocaine (0.5mg/kg/infusion/2h daily) self-administration for 14days; such enhancement resembled that observed in rats following the chronic mild stress. Acute administration with imipramine (15 or 30mg/kg), the GABAB receptor agonists baclofen (0.125mg/kg) and SKF 97541 (0.005mg/kg), the positive allosteric modulator CGP 7930 (0.3mg/kg) or the antagonist SCH 50911 (0.3mg/kg) counteracted the cocaine discontinuation-induced enhancement in the immobility time. The enhanced immobility time in rats that self-administered cocaine (but not given cocaine passively) may reflect the motivated or cognitive processes of reinforced responding of cocaine and could be a potential driver of the addiction process per se. Moreover, either blockade or stimulation of GABAB receptors by their ligands in very low doses attenuated the enhanced immobility time in rats after discontinuation of cocaine self-administration and these findings extend preclinical studies demonstrating the potential involvement of GABAB receptor ligands to reduce cocaine craving. [Copyright &y& Elsevier]

Abstract: We have recently reported that the endogenous mGlu2/3 agonist N-acetylaspartylglutamate (NAAG) and the N-acetylated-α-linked-acidic dipeptidase (NAALADase, a NAAG degradation enzyme) inhibitor 2-PMPA significantly inhibit cocaine self-administration and cocaine-induced reinstatement of drug-seeking behavior by attenuating cocaine-enhanced extracellular dopamine and glutamate in the nucleus accumbens. However, the poor oral bioavailability of NAAG and 2-PMPA limits their practical use in humans. In the present study, we investigated the effects of the orally active NAALADase inhibitor GPI-5693 and its enantiomers on cocaine-taking and cocaine-seeking behaviours. We found that oral administration of GPI-5693 (15, 30, 60mg/kg, p.o.) did not significantly alter intravenous cocaine self-administration under fixed-ratio (FR2) reinforcement, but significantly inhibited cocaine-induced reinstatement of the extinguished drug-seeking behavior. This inhibition was blocked by pretreatment with LY341495, a selective mGlu2/3 receptor antagonist. Pretreatment with the same doses (15, 30, 60mg/kg, p.o.) of GPI-16476 or GPI-16477, two enantiomers of GPI-5693, also inhibited cocaine-induced reinstatement similar to GPI-5693. In contrast, GPI-5693 altered neither oral sucrose self-administration nor sucrose-triggered reinstatement of sucrose-seeking behavior. These data suggest that orally effective NAAG peptidase inhibitors deserve further study as potential agents for the treatment of cocaine addiction. [Copyright &y& Elsevier]

Abstract: Many studies have observed relevant executive alterations in polysubstance users but no data have been generated in terms of prevalence of these alterations. Studies of the prevalence of neuropsychological impairment can be useful in the design and implementations of interventional programs for substance abusers. The present study was conducted to estimate the prevalence of neuropsychological impairment in different components of executive functions in polysubstance users enrolled in therapeutic communities. Moreover, we estimated the effect size of the differences in the executive performance between polysubstance users and non substance users in order to know which neuropsychological tasks can be useful to detect alterations in the executive functions. Study results showed a high prevalence of executive function impairment in polysubstance users. Working memory was the component with the highest impairment proportion, followed by fluency, shifting, planning, multi-tasking and interference. Comparisons between user groups showed very similar executive impairment prevalence for all the analyzed executive components. The best discriminating task between users and controls was Arithmetic (Wechsler Adult Intelligence Scale, WAIS-III). Moreover FAS and Ruff Figural Fluency Test was discriminating for fluency, Category Test for shifting, Stroop Colour–Word Interference Test for interference, Zoo Map (Behavioural Assessment of the Dysexecutive Syndrome, BADS) for planning and Six Elements (BADS) for multi-tasking. The existence of significant prevalence of executive impairment in polysubstance users reveals the need to redirect the actuation policies in the field of drug-dependency towards the creation of treatments addressed at the executive deficits of the participants, which in turn would facilitate the individuals'' compliance and final rehabilitation. [Copyright &y& Elsevier]

Abstract: The dopamine transporter (DAT) plays an important role in substance abuse, schizophrenia, and dopaminergic toxicity associated with the Parkinsonian animal model toxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Accordingly, the DAT serves as a critical component in regulating dopaminergic function in health and disease states. We have been working with a novel cage compound, 8-phenylethyl-pentacycloundecane (1), and found that this compound can inhibit dopamine uptake and serve as a neuroprotectant against MPTP-induced dopaminergic toxicity. The current study was aimed at investigating additional mechanistic features of DAT function that interact with our compound (1). Extracellular dopamine levels were analyzed from superfused striatal tissue in response to various conditions of compound 1 infusion. The results showed that compound 1 : (1) significantly increased spontaneous dopamine; (2) significantly decreased methamphetamine-stimulated dopamine; (3) significantly increased dopamine when co-infused with 30mM potassium chloride; (4) lost the stimulatory effect of potassium chloride-evoked dopamine when calcium-free buffer was used and (5) exhibited moderate voltage-gated calcium channel blocking activity with an IC50 of 22μM. These data demonstrate that compound 1 modulates dopaminergic function as determined by effects upon extracellular dopamine responses. It appears that compound 1 exerts these effects primarily through interaction with the DAT by blocking dopamine uptake via a calcium-dependent mechanism, and does not lead to extracellular efflux via the DAT. In conclusion, the findings suggest that compound 1 may have the potential to serve as a lead candidate for therapeutics designed to treat drug abuse and possibly disorders like Parkinson''s disease. [Copyright &y& Elsevier]

Abstract: In previous work we have shown that rats running a straight alley for intravenous (i.v.) or intracerebroventricular (i.c.v.) injections of cocaine develop an ambivalence about entering the goal box that results from cocaine''s mixed reinforcing and anxiogenic properties. What remains unclear is whether or not cocaine''s opposing properties stem from actions on a common neuronal system or from dual actions on separate systems — one related to reward and another to anxiogenic responses. One way to address this question is to deliver cocaine into discrete brain areas as a means of assessing whether or not the positive and negative effects of the drug can be spatially dissociated. Given the putative role of mesocorticolimbic dopamine pathways in the mediation of cocaine-reinforced behavior, the current study examined the cocaine-seeking behavior of rats permitted to run an alley once each day for bilateral medial prefrontal cortex microinjections of cocaine (0.0, 12.5, 25 or 50 µg/0.5 µl per side) delivered upon goal-box entry. The results demonstrated that undrugged animals are highly motivated to seek medial prefrontal cortex cocaine without any evidence of negative or anxiogenic effects at any dose. These results are therefore consistent with suggestions of a medial prefrontal cortex involvement in the reinforcing actions of cocaine, and indicate that the dual and opposing actions of the drug can be dissociated and hence may be mediated by the drug''s actions on separate neuronal systems. [Copyright &y& Elsevier]

Abstract: The melanin-concentrating hormone MCH1 receptor has been proposed to exert an inhibitory control on monoaminergic (especially dopaminergic) activity within the mesolimbic system, which underpins drug seeking and reward. That hypothesis predicts that an inactivation of these receptors should enhance the sensitivity to drug rewarding effects. To test that prediction, we examined the propensity of mice lacking the melanin-concentrating receptor (MCH1 KO) and their intact counterparts (WT) to form cocaine- and amphetamine-induced conditioned place preference. The conditioned rewarding effects induced by 0.375, 0.75, 1.5 and 3 mg/kg amphetamine were assessed in two sub-experiments and those induced by 1, 2, 4 and 8 mg/kg cocaine in two other sub-experiments. All mice were tested under saline for place preference 24 h following four every-other-day conditioning trials and an initial pre-conditioning session under saline. Most of the cocaine and amphetamine doses induced place preference, but without any genotype difference being revealed. Also, none of the cocaine doses induced psychomotor sensitization during conditioning, whereas amphetamine generated clear-cut dose-dependent sensitization in both genotypes. Albeit MCH1 KO mice exhibited higher levels of psychomotor activation, the rates of sensitization were comparable across genotypes at 1.5 and 3 mg/kg amphetamine. Moreover, 0.375 and especially 0.75 mg/kg amphetamine produced a slight but yet significant sensitization in MCH1 KO but not in their WT counterparts. Despite such an effect, the results cannot be considered as unambiguously supportive of the tested prediction. [Copyright &y& Elsevier]

Abstract: We examined neuroadaptive changes in γ-aminobutyric acid (GABA)B receptor binding following cocaine self-administration and its withdrawal in several rat brain structures using a “yoked” procedure and a quantitative autoradiographic analysis. In order to estimate the distribution of GABAB receptors in several brain areas, we used ([S-(R⁎,R⁎)]-[3-[[1-(3,4-diclorophenyl)ethyl]amino]-2-hydroxypropyl]([3,4-3H]-cyclohexylmethyl) phosphinic acid) ([3H]CGP 54626), a GABAB receptor antagonist. The binding of [3H]CGP 54626 in the nucleus accumbens subareas and the amygdala was decreased by ca. 20% in rats that actively self-administered cocaine. Similar decreases in the nucleus accumbens were seen in the animals passively receiving cocaine. These animals also showed a reduction in GABAB receptor binding in the prefrontal and frontal cortices, septum and dorsal striatum. The [3H]CGP 54626 binding in several rat brain areas was decreased after 10-day withdrawal from self-administered cocaine. In summary, the decreases in the GABAB receptor binding seem to reflect the effects of chronic administration of cocaine per se and not the motivated process of reinforced responding. Furthermore, withdrawal from cocaine self-administration evoked changes in the GABAB receptor binding in several rat brain areas that may indicate neurobiological adaptations. [Copyright &y& Elsevier]

Abstract: Pleiotrophin is a cytokine involved in differentiation, survival and repair processes in the central nervous system. Pleiotrophin is upregulated in the brain after administration of different drugs of abuse, thus suggesting a protective role of this cytokine on drug-induced toxicity. We have tested this hypothesis in vitro using NG108-15 cells, a line widely used for neurotoxicity studies. It was found that pleiotrophin (3 and 6 μM) significantly prevents cocaine (5 mM)-induced cytotoxicity as measured by the neutral red test. Similar results were obtained in PC12 cells, which were found to endogenously express both pleiotrophin and its main target, receptor protein tyrosine phosphatase (RPTP) β/ζ. Blockade of pleiotrophin signaling using anti-pleiotrophin antibodies (2 μg/ml) did not potentiate cocaine-induced toxicity; interestingly, incubation of PC12 cells only with anti-pleiotrophin antibodies significantly reduced cellular viability, thus suggesting an important role of endogenous pleiotrophin signaling in cell survival. The data suggest that pleiotrophin overexpression in response to drugs of abuse may be relevant to prevent drug-induced toxicity. [Copyright &y& Elsevier]

Abstract: The poly-drug pattern is the most common among MDMA users, with cocaine being a frequently associated drug. The aim of the present work was to evaluate the behavioural and neurotoxic long-term effects of exposure during adolescence to MDMA alone or plus cocaine. Mice of 28 to 30 days of age received a treatment of two daily injections of an identical dose of MDMA (5, 10 or 20 mg/kg), alone or plus cocaine (25 mg/kg), for 3 days (6 administrations). Three weeks after receiving MDMA, an increase in the time dedicated by the animals to social contacts with their conspecifics was observed, whilst their behaviour in the elevated plus maze showed no differences from that of non-treated mice. After being exposed to MDMA plus cocaine, mice spent more time in social contacts during the interaction test, as well as exhibiting an anxiolytic profile in the elevated plus maze, with an increase in the time and number of entries in the open arms. The activity of mice treated with cocaine alone or plus MDMA remained constant; the decrease observed among the rest of the animals after the second hour was absent in their case. The level of dopamine in the striatum was diminished in mice treated with 20 mg/kg of MDMA, but this neurotransmitter was not affected in animals exposed to the same dose plus cocaine. The present results highlight pronounced alterations in the behaviour of adult mice after exposure to MDMA and cocaine during adolescence, and demonstrate that these long-term effects can occur without the dopaminergic system becoming affected. [Copyright &y& Elsevier]

Abstract: This study was conducted to determine the phosphorylation state of N-methyl-d-aspartate (NMDA) NR1 subunit on serine residues 896 (Ser896) and 897 (Ser897), the extracellular signal-regulated kinase 1/2 (ERK1/2), and the cyclic AMP response element-binding protein (CREB) after repeated exposure to cocaine (20 mg/kg, once daily for 9 days) in the dorsal striatum of rats. The real-time changes of glutamate concentration evoked by repeated cocaine injections were examined using a glutamate biosensor in order to evaluate the correlation between glutamate concentration and the change in these phosphoproteins. The results of this study showed that the immunoreactivity of phosphorylated (p)NMDA NR1 subunit at Ser896 and Ser897 as well as pERK1/2, but not pCREB, in the dorsal striatum was increased at 30 min and then returned to basal levels 4 h after repeated cocaine injections. Similarly, glutamate responses evoked by repeated cocaine injections were also increased 30 min after repeated cocaine injections for 3 days and were prolonged by the 9th day of treatment. However, the glutamate responses were not detected at 4 h after repeated cocaine injections for 5 days. In addition, the elevated immunoreactivity of the phosphoproteins 2 h after repeated cocaine injections was attenuated by the blockade of dopamine D1 receptors and NMDA receptors with the SCH23390 or MK801 antagonists, respectively. These findings suggest that glutamate release and dopamine D1 and NMDA receptor stimulation after repeated exposure to cocaine are associated with NMDA NR1 subunit, ERK1/2 and CREB phosphorylation in the dorsal striatum. [Copyright &y& Elsevier]

Abstract: Glycyrrhizae radix (licorice) comprises a variety of flavonoids as major constituents including isoliquiritigenin, liquiritin, liquiritigenin, and glycyrrihizin. It has shown various biological activities such as anti-inflammatory, anti-carcinogenic and antihistamic. As very little is known in regard to drug addiction, we carried out a study on the effect of G. radix and its active component, isoliquiritigenin, on acute cocaine-induced extracellular dopamine release in moving rats. Male Sprague–Dawley rats were orally administered with methanolic extracts of G. radix or isoliquiritigenin 1 h prior to an injection of cocaine (20 mg/kg, intraperitoneal (i.p.)). Extracellular dopamine was measured by in vivo microdialysis. Extract of G. radix and isoliquiritigenin inhibited cocaine-induced extracellular dopamine level in the nucleus accumbens by dose-dependent manner. Inhibition of dopamine release by isoliquiritigenin resulted in attenuation of the expression of c-Fos, an immediately early gene induced by cocaine. Effect of isoliquiritigenin was completely prevented by a GABAB receptor antagonist. Thus, these results showed that G. radix and isoliquiritigenin inhibit cocaine-induced dopamine release by modulating GABAB receptor, suggesting that isoliquiritigenin might be effective in blocking the reinforcing effects of cocaine. [Copyright &y& Elsevier]