Effects of dopamine antagonists with different receptor blockade profiles on morphine-induced place preference in male mice

Integrative multi-dimensional characterization of striatal projection neuron heterogeneity in adult brain

Striatal projection neurons (SPNs) are traditionally segregated into two subpopulations expressing dopamine (DA) D1-like or D2-like receptors. However, this dichotomy is challenged by recent evidence. Functional and expression studies raise important questions: do SPNs co-express different DA receptors, and do these differences reflect unique striatal spatial distributions and expression profiles? Using RNAscope in mouse striatum, we report heterogenous SPN subpopulations distributed across dorsal-ventral and rostral-caudal axes. SPN subpopulations co-express multiple DA receptors, including D1 and D2 (D1/2R) and D1 and D3. Our integrative approach using single-nuclei multi-omics analyses provides a simple consensus to describe SPNs across diverse datasets, connecting it to complementary spatial mapping. Combining RNAscope and multi-omics shows D1/2R SPNs further separate into distinct subtypes according to spatial organization and conserved marker genes. Each SPN cell type contributes uniquely to genetic risk for neuropsychiatric diseases. Our results bridge anatomy and transcriptomics to offer new understandings of striatal neuron heterogeneity.

Resilience to social defeat stress in adolescent male mice

Adverse social experiences during adolescence are associated with the appearance of mental illness in adulthood. Social defeat (SD) is an ethologically valid murine model to study the consequences of social stress. In adolescent mice, SD induces depressive-like behaviors, increased anxiety and potentiates the reinforcing effects of cocaine and alcohol. However, not all mice exposed to SD will be susceptible to these effects. Adult mice resilient to the effects of SD show a consistent phenotype being resilient to depressive-like behaviors and to the increase in cocaine and alcohol consumption. The aim of the present study was to characterize the resilient phenotype to depressive-like behaviors and increase cocaine and ethanol rewarding effects of mice socially defeated during adolescence. To that end, adolescent mice were exposed to repeated SD, and 24 h after the last encounter, they underwent a social interaction test (SIT) in order to evaluate depressive-like behaviors. Cocaine-induced reward conditioning and ethanol intake was evaluated in two different sets of mice 3 weeks after the last SD using cocaine-induced conditioned place preference (CPP) and oral ethanol self-administration (SA). The neuroinflammation response was measured at the end of the experimental procedure by measuring striatal and cortical levels of IL-6 and CX3CL1. The results confirmed that a comparable percentage of adolescent mice develop resilience to depressive-like behaviors to that observed in adult mice. However, increased anxiety was more severe in resilient mice. Likewise, an increased preference for an ineffective dose of cocaine and an increased ethanol consumption was observed in resilient mice compared to controls. The increase in IL-6 and CX3CL1 was mainly observed in the striatum of susceptible mice compared to that of control mice. Our results confirm that, contrary to prior assumptions in adults, responses to SD stress are more complex and singular in adolescents, and caution should be taken for the correct interpretation and translation of those phenotypes.

Quetiapine attenuates the acquisition of morphine-induced conditioned place preference and reduces ERK phosphorylation in the hippocampus and cerebral cortex

Background: Quetiapine is an atypical antipsychotic that antagonizes dopamine and serotonin receptors. It has been suggested that quetiapine can be used to treat substance use disorders, including opioid use disorder. Opioids modulate dopaminergic functions associated with conditioned reinforcement and these effects can be measured via the conditioned place preference (CPP) paradigm. Opioids' unconditioned effects are regulated by several proteins, including extracellular signal-regulated kinase (ERK) and cAMP-responsive element-binding (CREB).Objective: To assess the effect of quetiapine on morphine-induced CPP and motor activity levels, and on the levels of ERK and CREB proteins in the hippocampus and cerebral cortex.Methods: 42 male rats were exposed to a CPP protocol, in which they underwent a conditioning paradigm with saline, quetiapine (40 mg/kg), morphine (10 mg/kg), morphine plus quetiapine (10, 20, or 40 mg/kg), or morphine plus memantine (7.5 mg/kg, a positive control drug) (n = 6 per group). The rats were tested for CPP and exploratory activity. Levels of ERK and CREB proteins in the hippocampus and cerebral cortex were also measured.Results: Quetiapine co-administered with morphine inhibited morphine-induced CPP [F (6, 70) = 11.67, p < .001] and morphine's effects on motor activity (p < .001). Morphine enhanced ERK phosphorylation in the hippocampus (p < .001) and cerebral cortex (p < .001), an effect inhibited by quetiapine.Conclusion: Quetiapine attenuates morphine-induced CPP and locomotion and these effects are associated with a reduction of ERK phosphorylation in the hippocampus and cerebral cortex. These results suggest that quetiapine should be further explored as a potential treatment for opioid use disorder.

Prepulse inhibition can predict the motivational effects of cocaine in female mice exposed to maternal separation

The prepulse inhibition (PPI) of the startle response can identify the rodents that are more sensitive to the effects of cocaine. Mice with a lower PPI presented a higher vulnerability to the effects of cocaine and a higher susceptibility to developing a substance use disorder (SUD). Maternal separation with early weaning (MSEW) is a relevant animal model to induce motivational alterations throughout life. Nevertheless, only a few studies on females exist, even though they are more vulnerable to stress- and cocaine-related problems. Hence, the aim of the present study was to evaluate the ability of PPI to identify females with a greater vulnerability to the long-term consequences of early stress on the motivational effects of cocaine. Female mice underwent MSEW and were classified according to their high or low PPI. They were then assessed in the cocaine-induced locomotor sensitization test, the conditioned place preference paradigm or the operant self-administration paradigm. Additionally, they were also evaluated in the passive avoidance task, the tail-suspension and the splash tests. The results revealed that the females with lower PPI presented higher consequences of MSEW on the effects of cocaine and showed an increase in anhedonia-like behaviours. Our findings support that a PPI deficit could represent a biomarker of vulnerability to the effects of cocaine induced by MSEW.

Melatonin Blocks Morphine-Induced Place Preference: Involvement of GLT-1, NF-κB, BDNF, and CREB in the Nucleus Accumbens

Opioid addiction remains a widespread issue despite continuous attempts by the FDA to help maintain abstinence. Melatonin is a neurohormone considered to be involved only in the neuroendocrine and reproductive systems; however, recent reports have demonstrated its potential to attenuate drug addiction and dependence. Cumulative studies have suggested that melatonin can attenuate the rewarding effects of several drugs of abuse, including opioids. This study aimed to investigate the effect of melatonin (50 mg/kg) on morphine (5 mg/kg) to produce place preference. We also investigated the effect of melatonin and morphine on the expression of GLT-1, BDNF, NF-κB, and CREB within the nucleus accumbens. Male Wistar rats were divided into control, morphine, melatonin, and the morphine + melatonin groups. The study involved a two-phase habituation phase from day 1 to day 3 and an acquisition phase from day 5 to day 14. The conditioned place preference (CPP) score, distance traveled, resting time, ambulatory count, and total activity count were measured for all animals. Rats that received morphine showed a significant increase in CPP score compared to those in the control group. Morphine treatment reduced the mRNA expression of GLT-1, BDNF, and CREB and increased that of NF-κB. However, melatonin treatment administered 30 min before morphine treatment attenuated morphine place preference and reversed GLT-1, BDNF, NF-κB, and CREB expression levels. In conclusion, the study results indicate, for the first time, the new potential targets of melatonin in modulating morphine-induced CPP.

Systemic administration of N-acetylcysteine during the extinction period and on the reinstatement day decreased the maintenance of morphine rewarding properties in the rats

Many animal studies and early clinical trials suggested that N-acetylcysteine (NAC) may benefit addiction treatment. The present study tried to evaluate whether chronic administration of systemic NAC during the extinction period and acute administration of systemic NAC on the reinstatement day could reduce the maintenance of the morphine rewarding properties in the conditioned place preference (CPP) paradigm in the rats. Ninety-six adult male Wistar rats (190-220 g) were examined with morphine (7 mg/kg; sc) and saline (1 mL/kg; sc) during the 3-day conditioning phase in the CPP paradigm. After the acquisition of morphine CPP, different doses of NAC were daily administered during the extinction period (5, 10, 25, and 50 mg/kg; ip), or 30 min before the CPP test on the reinstatement day (2, 5, 10, 25, and 50 mg/kg; ip). Conditioning score and locomotor activity were recorded by the video tracking system and Ethovision software after acquisition on the post-conditioning day, the extinction period, and reinstatement day. Daily NAC administration in high doses (25 and 50 mg/kg; ip) reduced extinction-responding compared with the vehicle-control group during the extinction period. Although a single injection of NAC in doses 10, 25, 50 mg/kg decreased the reinstatement of morphine-induced CPP, two lower doses (2 and 5 mg/kg) could not significantly reduce the CPP scores. These are the first data suggesting that NAC's application during the extinction period could attenuate the morphine reward-associated behaviors in the rats. Moreover, NAC could inhibit the reinstatement of morphine CPP, which adds to the growing appreciation that the NAC may have potential therapeutic use in combating morphine dependence. It can be consistent with the hypothesis of the involvement of the glutamatergic system in the pathophysiology of addiction.

Low-dose polypharmacology targeting dopamine D1 and D3 receptors reduces cue-induced relapse to heroin seeking in rats

Chemical compounds that target dopamine (DA) D1 or D3 receptors have shown promise as potential interventions in animal models of cue-induced relapse. However, undesirable side effects or pharmacodynamic profiles have limited the advancement of new compounds in preclinical studies when administered as independent treatments. In this series of experiments, we explored the effects of coadministration of a D1-receptor partial agonist (SKF 77434) and a D3-receptor antagonist (NGB 2904) in heroin-seeking rats within a "conflict" model of abstinence and cue-induced relapse. Rats were first trained to press a lever to self-administer heroin, and drug delivery was paired contingently with cues (e.g., light and pump noise). Self-initiated abstinence was facilitated by applying electrical current to the flooring in front of the levers. Lastly, a relapse response was provoked by noncontingent presentation of conditioned cues. Prior to provocation, rats received a systemic injection of SKF 77434, NGB 2904, or a combination of both compounds to assess treatment effects on lever pressing. Results indicated that the coadministration of low (i.e., independently ineffective) doses of both compounds was more effective in reducing cue-induced relapse to heroin seeking than either compound alone, with some evidence of drug synergism. Follow-up studies indicated that this reduction was not due to motoric impairment nor enhanced sensitivity to the electrified flooring and that this treatment did not significantly affect motivation for food. Implications for the treatment of opiate use disorder and recommendations for further research are discussed.

The effects of Berberis vulgaris L. root extract on the opiate withdrawal syndrome and psychological factors: a randomized double-blind clinical trial

OBJECTIVES

In this clinical trial, the effect of aqueous extract of Berberis vulgaris L. was investigated on opiate withdrawal syndrome, depression, anxiety, stress, and sleep quality in opioid addicts which were under methadone maintenance therapy.

METHODS

For this purpose, 52 opiate addicts were randomly selected of whom 28 received 500 mg capsules of B. vulgaris extract (treatment) and the rest received 500 mg of starch capsules (placebo), twice daily for 4 weeks. Signs and symptoms of opiate withdrawal syndrome, depression, anxiety, stress, and sleep quality were assessed through Clinical Opiate Withdrawal Scale (COWS), Pittsburgh Sleep Quality Inventory (PSQI) and Depression Anxiety Stress Scales-21 (DASS-21) questionnaires at baseline and after 7, 14, and 28 days of receiving intervention.

RESULTS

Signs and symptoms of opiate withdrawal syndrome were significantly improved in those who received the extract for 1 month compared to the placebo group. However, there were no significant differences in depression, anxiety, stress, and sleep quality scores in the treatment group compared to those in the placebo group.

CONCLUSIONS

The extract of B. vulgaris root as a traditional herbal product in combination with methadone could improve the symptoms and signs of opiate withdrawal.

Adaptive changes in local field potential oscillation associated with morphine conditioned place preference in mice

Neural adaptation associated with formation of morphine conditioned place preference remained largely unexplored. This study monitored longitudinal changes in neural signaling during pre-conditioning, conditioning and post-conditioning periods of morphine conditioned place preference (CPP) paradigm for investigation of adaptive mechanisms of opiate addiction. Male Swiss albino mice implanted with intracranial electrodes into the nucleus accumbens (NAc), striatum (STr) and hippocampus (HC) were used for recording of local field potentials (LFPs). Animals received a 10-day schedule for associative learning to pair the specific compartment of the chamber with morphine effects. Exploratory behavior and LFP signals were recorded during pre-conditioning (baseline level), conditioning (day 1, 5 and 10) and post-conditioning (day 1, 4 and 7) periods. Repeated measures one-way ANOVA followed by Tukey test revealed significant increases in number of visit and time spent in morphine compartment during post-conditioning days. Frequency analysis of LFP highlighted the increases in alpha activity (12 - 18 Hz) in the NAc from post-conditioning day 1 until day 7. Moreover, significantly increased coherent activities between the pair of NAc-HC were developed within gamma frequency range (35 - 42 Hz) on morphine conditioning day 10 and disappeared during post-conditioning days. Taken together, these findings emphasized NAc LFP signaling and neural connectivities between the NAc and HC associated with morphine CPP. These adaptive changes might underlie the formation of morphine conditioned place preference and behavioral consequences such as craving and relapse.

Neuroinflammatory and behavioral susceptibility profile of mice exposed to social stress towards cocaine effects

Using the social defeat (SD) model, numerous studies have shown that stressed mice display an enhanced response to the motivational effects of cocaine in the self-administration (SA) and conditioned-place preference (CPP) paradigms. However, not all subjects exposed to stress express its harmful effects. Some are particularly susceptible to the deleterious effects of repeated SD, while resilient mice successfully cope with stressful experiences and display adjusted psychological functioning after stress. Vulnerability to develop stress-related disorders, such as depression, has been linked to coping strategies and more recently to individual differences in the immune system. However, no studies have evaluated if coping strategies and immune system reactivity to social stress experiences can also predict susceptibility to stress-induced enhancement of the cocaine response. We evaluated cocaine response in socially defeated mice in the CPP and SA paradigms. To evaluate neuroimmune reactivity to stress the pro-inflammatory cytokine IL-6 and the chemokine CX3CL1 were measured in the striatum and hippocampus. Behavioral phenotype during and after SD episodes was also evaluated. Our results showed that susceptible mice to the depressive-like behaviors effects of stress showed increased conditioned rewarding effects of cocaine in the CPP. In addition, susceptible mice displayed passive-reactive coping behavior during social stress episodes and more pronounced changes in neuroinflammatory markers after the last SD episode, which lasted for one month. Although the complex mechanisms underlying susceptibility or resilience to social stress are still unclear, our results point to multiple adaptive stress responses expressed at different phenotypic levels.

Effects of Isoniazid on Tolerance and Sensitization to the Rewarding Properties of Morphine: A Conditioned Place Preference Procedure Investigation in Mice

Introduction:

The GABAergic system of the brain plays a key role in morphine tolerance and sensitization. As isoniazid is a modulator of the GABAergic system, the present study aims to understand whether isoniazid can influence the induction of tolerance and sensitization to the rewarding effects of morphine.

Methods:

The rewarding effects of morphine and isoniazid were assessed using a Conditioned Place Preference (CPP) procedure in female mice. Tolerance to the rewarding effects of morphine was induced with high-dose morphine (25 mg/kg, SC), twice a day, for four days. Also, the sensitization was induced with an effective dose of morphine (5 mg/kg, SC), once a day, for three days. During the induction of tolerance or sensitization, the different groups of mice received saline or isoniazid (25, 50, and 75 mg/kg, IP) one hour before each morphine injection.

Results:

Morphine (0.5–10 mg/kg, SC) produced a significant CPP, but isoniazid (25, 50, and 75 mg/kg, IP) did not induce place preference or place aversion in mice. Although an effective dose of morphine (5 mg/kg, SC) did not induce CPP in morphine tolerated mice, an ineffective dose (0.5 mg/kg, SC) could produce a significant CPP in morphine-sensitized animals. The administration of isoniazid before morphine (on the days of tolerance or sensitization induction) inhibited the development of tolerance or sensitization to the rewarding effect of morphine in the CPP paradigm.

Conclusion:

Isoniazid can be a useful drug for the prevention of tolerance and sensitization to the rewarding effects of morphine.

Potential for Kappa-Opioid Receptor Agonists to Engineer Nonaddictive Analgesics: A Narrative Review

A serious adverse effect of prescription opioid analgesics is addiction, both to these analgesics and to illicit drugs like heroin that also activate the µ-opioid receptor (MOR). Opioid use disorder (OUD) and opioid overdose deaths represent a current American health crisis, and the prescription of opioid analgesics has contributed significantly to this crisis. While prescription opioids are highly effective analgesics, there currently exists no facile way to use them for extended periods without the risk of addiction. If addiction caused by MOR-targeting analgesics could be blocked by blending in a new "antiaddiction" ingredient that does not diminish analgesia and does not introduce its own therapeutically limiting side effects, then continued clinical use of prescription opioids for treating pain could be maintained (or even enhanced) instead of curtailed. In this narrative review, we contextualize this hypothesis, first with a brief overview of the current American opioid addiction crisis. The neurobiology of 2 key receptors in OUD development, MOR and the κ-opioid receptor (KOR), is then discussed to highlight the neuroanatomical features and circuitry in which signal transduction from these receptors lie in opposition-creating opportunities for pharmacological intervention in curtailing the addictive potential of MOR agonism. Prior findings with mixed MOR/KOR agonists are considered before exploring new potential avenues such as biased KOR agonists. New preclinical data are highlighted, demonstrating that the G protein-biased KOR agonist nalfurafine reduces the rewarding properties of MOR-targeting analgesics and enhances MOR-targeting analgesic-induced antinociception. Finally, we discuss the recent discovery that a regulator of G protein signaling (namely, RGS12) is a key component of signaling bias at KOR, presenting another drug discovery target toward identifying a single agent or adjuvant to be added to traditional opioid analgesics that could reduce or eliminate the addictive potential of the latter drug.

Critical role of TLR4 in uncovering the increased rewarding effects of cocaine and ethanol induced by social defeat in male mice

BACKGROUND

Substance use disorders and social stress are currently associated with changes in the immune system response by which they induce a proinflammatory state in neurons and glial cells that eventually modulates the reward system.

AIMS

The aim of the present work was to assess the role of the immune TLR4 (Toll-like receptors 4) and its signaling response in the increased contextual reinforcing effects of cocaine and reinforcing effects of ethanol (EtOH) induced by social defeat (SD) stress.

METHODS

Adult male C57BL/6 J wild-type (WT) mice and mice deficient in TLR4 (TLR4-KO) were assigned to experimental groups according to stress condition (exploration or SD). Three weeks after the last SD, conditioned place preference (CPP) was induced by a subthreshold cocaine dose (1 mg/kg), while another set underwent EtOH 6% operant self-administration (SA). Several inflammatory molecules were analyzed in the hippocampus and the striatum.

RESULTS

SD induced higher vulnerability to the conditioned rewarding effects of cocaine only in defeated WT mice. Similarly, defeated WT mice exhibited higher 6% EtOH consumption, an effect that was not observed in the defeated TLR4-KO group. However, the motivation to obtain the drug was observed in both genotypes of defeated animals. Notably, a significant upregulation of the protein proinflammatory markers NFkBp-p65, IL-1β, IL-17 A and COX-2 were observed only in the defeated WT mice, but not in their defeated TLR4-KO counterparts.

CONCLUSIONS

These results suggest that TLR4 receptors mediate the neuroinflammatory response underlying the increase in the rewarding effects of cocaine and EtOH induced by social stress.

Chronic risperidone administration leads to greater amphetamine-induced conditioned place preference

Risperidone is an atypical antipsychotic drug used increasingly in children to manage symptoms of ADHD and conduct disorder. In rats, developmental risperidone administration is accompanied by increased locomotor activity during adulthood, as well as heightened sensitivity to the locomotor stimulating effects of amphetamine. This study compared sensitivity to the rewarding effects of amphetamine, as measured by conditioned place preference (CPP), between groups of rats administered chronic risperidone (3.0 mg/kg, s.c.) during development (postnatal days 14-42) or adulthood (postnatal days 77-105). Locomotor activity in a novel test cage and amphetamine-induced CPP were measured beginning three and four weeks, respectively, after the final risperidone injection. Female rats administered risperidone early in life were more active than any other group tested. Previous risperidone administration enhanced amphetamine CPP regardless of sex, and this effect appeared more prominent in the developmentally treated group. The density of forebrain dopamine transporters, a primary target of amphetamine, was also quantified in rats administered risperidone early in life and found to be reduced in the medial anterior, posterior, and ventral caudate nucleus. These results suggest that chronic risperidone treatment modifies later locomotor activity and sensitivity to the reinforcing effects of amphetamine, perhaps via a mechanism related to decreased forebrain dopamine transporter density.

Opposite regulation of conditioned place preference and intravenous drug self-administration in rodent models: Motivational and non-motivational examples

Although developed from a common antecedent, conditioned place preference (CPP) and intravenous drug self-administration (SA) represent different behavioral paradigms, each with strong face validity. The field has treated results from these studies largely interchangeably; however, there is considerable evidence of opposite modulation of CPP vs. SA. This review outlines four manipulations that differentially affect CPP and SA based on alterations of motivation. These examples are contrasted with one example of differential CPP and SA results that can be explained by simple parallel shifts in dose-response functions. The final two examples have yet to be classified as motivation-based or parallel shifts. Important aspects, including motivation, volitional control of drug administration, reward, and the role of cues are discussed. One major conclusion of this paper is that explanations for apparent discrepancies between CPP and SA require full dose effect functions and assessment of PR breakpoints. Overall, this manuscript offers a more nuanced insight into how CPP and SA can be used to study different aspects of substance use disorders.

Effect of Topiramate on Morphine-induced Conditioned Place Preference (CPP) in Rats: Role of ERK and CREB Proteins in Hippocampus and Cerebral Cortex

In this study, the effect of topiramate, as an antiepileptic drug, was evaluated on morphine craving in rats. The conditioned place preference (CPP) test was used for this purpose. Repeated administration of morphine (10 mg/kg, i.p. for 4 days) induced significant CPP. Administration of topiramate (50 and 100 mg/kg, i.p. for 4 days) with each morphine administration decreased the acquisition of morphine-induced CPP. At the next step, the levels of extracellular signal-regulated kinase (ERK), p-ERK, cAMP responsive element binding (CREB), and p-CREB proteins were evaluated in hippocampus and cerebral cortex using western blot analysis. Following the repeated administration of morphine, the level of p-ERK protein markedly enhanced in both tissues, while topiramate could significantly reduce the phosphorylation of ERK in these brain regions. Additionally, the level of CREB and p-CREB proteins did not change in different groups. Memantine as a positive control reduced the acquisition of morphine-induced CPP. Also, memantine significantly decreased the level of p-ERK protein in hippocampus and cerebral cortex. These results demonstrated that topiramate can attenuate the acquisition of morphine-induced CPP in rats. This effect in part can be mediated through down regulation of p-ERK protein in hippocampus and cerebral cortex.

Social defeat-induced increase in the conditioned rewarding effects of cocaine: Role of CX3CL1

Social stress is associated with higher vulnerability to drug use, as it enhances the reinforcing effects of psychostimulants in rodents. Furthermore, continued or severe stress induces a proinflammatory state of microglial activation and augmented cytokine production. The aim of the present work was to evaluate the role of fractalkine [C-X3-C motif ligand 1 (CX3CL1)], an inflammatory chemokine, in the increased conditioned rewarding effects of cocaine in animals exposed to social defeat stress. In addition, we measured the signaling cascade pathway of CX3CL1 in the hippocampus (HPC) (including p-ERK/ERK, p-p38/p38 MAPK, p-p65/p65 NFκB and p-CREB/CREB ratios). The glutamate receptor subunits NR1, NR2B and GluA1 were also assessed. A total of 102 adult male C57BL/6 J wild-type (WT) and Cx3cr1 knockout (KO) mice were divided into different experimental groups according to stress condition (exploration or social defeat). Three weeks after the last social defeat, conditioned place preference (CPP) was induced by a subthreshold dose of cocaine (1 mg/kg). Brain tissue samples were taken 24 h after the CPP procedure to determine the levels of the proteins and transcription factors. Our results showed that, in WT animals, repeated social defeat (RSD) decreased CX3CL1 striatal levels without producing changes in the HPC. In addition, RSD induced an increase in the conditioned rewarding effects of cocaine, regardless of the genotype. After CPP induced by cocaine, defeated Cx3cr1-deficient mice showed a decrease in the p-p65/p65 NFκB and pCREB/CREB ratio in the HPC, and an increase in the hippocampal levels of CX3CL1 and p-p38/p38 MAPK relation. In all defeated mice, there was a decrease in the ionotropic glutamate receptor subunit NR1. In conclusion, these results suggest that the lack of CX3CL1/Cx3cr1 signaling under stress conditions induces changes in protein and transcription factors, indicating that CX3CL1 is needed to shield the response to social defeat.

Comparative Evaluation of A Partial Dopamine Agonist with A Preferential D2 and D3 Receptor Antagonist on Ethanol Induced Conditioned Place Preference in Mice

Background:

The role of dopamine receptor sub-families in the rewarding and reinforcing effects of drugs of abuse has been established in numerous studies. </P><P> Objectives: In view of the extensive role of mesolimbic dopaminergic transmission in rewarding and reinforcing effect of abused drugs including ethanol, the present study evaluated three mechanistically different drugs viz a partial dopaminergic agonist (PDA, aripiprazole), preferential D3 (mixed D2/D3) receptor antagonist (nafadotride), and a preferential D2 antagonist (haloperidol), on ethanol-induced conditioned place preference (CPP) in mice. </P><P> Method: The study was carried out in Swiss strain albino mice. Ethanol (20%, 2g/kg) was used to induce CPP in mice. After the acquisition of CPP, behavioral tests (elevated plus maze and locomotor activity) were conducted and effect of drugs on expression and on reinstatement (after extinction) was studied.

Results:

We found that aripiprazole (1 and 2 mg/kg but not 0.5mg/kg), haloperidol (0.2 mg/kg), and nafadotride (4.5 mg/kg) administered for 1 week during the conditioning phase prevented acquisition, expression and reinstatement of ethanol-induced CPP. All the three drugs reduced the ethanol-induced locomotor stimulation and produced antianxiety effects in elevated plus maze following the acquisition of ethanol CPP.

Conclusion:

Partial dopaminergic agonism by aripiprazole was found to be a better strategy for normalizing dopaminergic neurotransmission in alcoholics as seen in rodents.

CB1 positive allosteric modulation attenuates Δ9-THC withdrawal and NSAID-induced gastric inflammation

Recently, multiple compounds have been synthesized that target the allosteric binding site(s) of CB1. These CB1 positive allosteric modulators may capture the benefits of cannabinoid receptor activation without unwanted psychoactive effects, such as sedation. For example, ZCZ011 blocks neuropathic pain, absent the catalepsy, sedation, and hypothermia caused by CB1 orthosteric modulators, including Δ9-tetrahydrocannabinol (THC). The primary goal of the present study was to evaluate the potential of ZCZ011 to attenuate somatic signs of cannabinoid withdrawal in mice. Mice were repeatedly administered THC (10 mg/kg, s.c.) or vehicle, and withdrawal was either precipitated using the CB1 antagonist rimonabant (3 mg/kg, i.p.) or elicited spontaneously via THC abstinence. ZCZ011 (≥10 mg/kg, i.p.) significantly attenuated somatic signs of withdrawal, including head twitches and paw tremors, but had no effect on locomotor activity or conditioned place preference. We next tested the antiulcerogenic properties of CB1 positive allosteric modulation. Mice were fasted for 22 h, administered ZCZ011, and gastric hemorrhages were induced with the nonsteroidal anti-inflammatory drug diclofenac sodium (100 mg/kg, p.o.). ZCZ011 alone had no effect on gastric ulceration, but ZCZ011 (≥10 mg/kg) blocked ulcer formation when combined with a subthreshold MAGL inhibitor (JZL184; 1 mg/kg, i.p.). Thus, CB1 positive allosteric modulation is a novel approach to treat cannabinoid dependence and gastric inflammation.

Baseline prepulse inhibition of the startle reflex predicts the sensitivity to the conditioned rewarding effects of cocaine in male and female mice

RATIONALE

Prepulse inhibition (PPI) of the startle reflex is a model of pre-attentional inhibitory function. The dopamine baseline in the nucleus accumbens plays a key role in PPI regulation as well as in the rewarding effects of cocaine.

OBJECTIVES

The aim of this study was to evaluate the predictive ability of PPI to identify the more vulnerable mice of both sexes to the conditioned rewarding effects of cocaine.

METHODS

Male and female OF1 mice were first tested in the PPI paradigm to classify them as high or low PPI. Afterwards, they were evaluated in the conditioned place preference (CPP) paradigm induced by cocaine (1, 6 and 12 mg/kg). Moreover, the D1R and D2R protein expressions in the striatum of high and low PPI animals were analysed by Western blot.

RESULTS

Only high-PPI mice acquired CPP induced by low doses of cocaine (1 and 6 mg/kg), while the low-PPI mice needed a higher dose of cocaine (12 mg/kg) to acquire the CPP, but once mice were conditioned, males did not extinguish the conditioned preference and females reinstated the preference with lower doses of cocaine than their control counterparts. Low-PPI animals, especially females, showed higher basal levels of D2R than those with a higher PPI.

CONCLUSIONS

Low-PPI mice presented a lower sensitivity to the conditioned rewarding effects of cocaine, but once they were conditioned with a higher dose, they displayed a stronger, perseverant conditioned preference. The predictive capacity of PPI to detect the more vulnerable mice to the conditioned effects of cocaine is discussed.

Effects of Clavulanic Acid on the Acquisition and Reinstatement Following Morphine-induced Conditioned Place Preference in Mice

Introduction:

β-Lactam antibiotics like Clavulanic Acid (CA) enhances cellular glutamate uptake through activation of Glutamate Transporter subtype 1 (GLT-1) and decreases the level of glutamate in the nervous system. Based on studies, blocking the glutamate activity inhibits morphine-induced Conditioned Place Preference (CPP) in animals. Therefore, the effects of CA on the acquisition of morphine craving were evaluated using the CPP model in the current study.

Methods:

CA (1, 50 and 150 mg/kg, ip) was co-administered with morphine (40 mg/kg) for 4 days in the conditioning phase. On day 8, the effects of CA on morphine preference was assessed. In another experiment, the effect of CA on reinstatement of morphine preference by a single morphine injection (10 mg/kg) was evaluated after an extinction period.

Results:

In the first method, the morphine-induced place preference was markedly reduced following administration of CA (50 and 150 mg/kg). In the second experiment, a single administration of CA (50 and 150 mg/kg) markedly inhibited the reinstatement of morphine preference on day 16. The results indicated that CA (50, 150 mg/kg) can block both morphine-induced CPP and the reinstatement of place preference following priming dose of morphine. Also memantine (as a positive control) (10 mg/kg) significantly inhibited both acquisition and reinstatement of morphine CPP.

Conclusion:

Considering the important role of glutamate neurotransmission in morphine dependence, the effects of CA may be partly due to decrease in glutamate level in synaptic space and blockade of N-Methyl-D-aspartate Acid (NMDA) receptors. Although, we need further studies to determine exact cellular mechanism.

Reinstatement of Drug-seeking in Mice Using the Conditioned Place Preference Paradigm

The present protocol describes the Conditioned Place Preference (CPP) as a model of relapse in drug addiction. In this model, animals are first trained to acquire a conditioned place preference in a drug-paired compartment, and after the post-conditioning test, they perform several sessions to extinguish the established preference. The CPP permits the evaluation of the conditioned rewarding effects of drugs related to environmental cues. Then, the extinguished CPP can be robustly reinstated by the non-contingent administration of a priming dose of the drug, and by exposure to stressful stimuli. Both methods will be explained here. When the animal reinitiates the behavioral response, a reinstatement of the conditioned reward is considered to have taken place. The main advantages of this protocol are that it is non-invasive, inexpensive, and simple with good validity criteria. In addition, it allows the study of different environmental manipulations, such as stress or diet, which can modulate relapse into drug seeking behaviors. However, one limitation is that if the researcher aims to explore the motivation and primary reinforcing effects of the drug, it should be complemented with self-administration procedures, as they involve operant responses of animals.

Brain nicotinic acetylcholine receptors are involved in stress-induced potentiation of nicotine reward in rats

The aim of the present study was to examine the possible role of nicotinic acetylcholine receptors of the dorsal hippocampus (CA1 regions), the medial prefrontal cortex or the basolateral amygdala in the effect of acute or sub-chronic stress on nicotine-induced conditioned place preference. Our results indicated that subcutaneous administration of nicotine (0.2 mg/kg) induced significant conditioned place preference. Exposure to acute or sub-chronic elevated platform stress potentiated the response of an ineffective dose of nicotine. Pre-conditioning intra-CA1 (0.5-4 µg/rat) or intra-medial prefrontal cortex (0.2-0.3 µg/rat) microinjection of mecamylamine (a non-selective nicotinic acetylcholine receptor antagonist) reversed acute stress-induced potentiation of nicotine reward as measured in the conditioned place preference paradigm. By contrast, pre-conditioning intra-basolateral amygdala microinjection of mecamylamine (4 µg/rat) potentiated the effects of acute stress on nicotine reward. Our findings also showed that intra-CA1 or intra-medial prefrontal cortex, but not intra-basolateral amygdala, microinjection of mecamylamine (4 µg/rat) prevented the effect of sub-chronic stress on nicotine reward. These findings suggest that exposure to elevated platform stress potentiates the rewarding effect of nicotine which may be associated with the involvement of nicotinic acetylcholine receptors. It seems that there is a different contribution of the basolateral amygdala, the medial prefrontal cortex or the CA1 nicotinic acetylcholine receptors in stress-induced potentiation of nicotine-induced conditioned place preference.

Dopamine D2 receptors mediate the increase in reinstatement of the conditioned rewarding effects of cocaine induced by acute social defeat

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 D₁- and D₂-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 1mg/kg or 25mg/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 3mg/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 D₂-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 3mg/kg of cocaine-induced CPP. Our results confirm that the dopamine D₂ receptor is involved in the short-term effects of ASD on the rewarding effects of cocaine. The dopamine D₁ receptor is clearly involved in the rewarding effects of cocaine, but its role in the effects of ASD remains to be demonstrated.

Topiramate increases the rewarding properties of cocaine in young-adult mice limiting its clinical usefulness

RATIONALE

Topiramate is an anticonvulsant drug which has been evaluated as a therapeutic option for the treatment of cocaine addiction during the last decade.

OBJECTIVES

The purpose of this study was to evaluate the effects of topiramate on the reinforcing actions of cocaine. To this aim, the topiramate-mediated regulation of acquisition and extinction phases of the cocaine conditioned place preference (CPP) was assessed in young-adult mice using three experimental designs.

METHODS

Topiramate (50 mg/kg, p.o.) was given as follows: (1) during cocaine (1 and 25 mg/kg, i.p.) conditioning sessions (4 days) and cocaine (25 mg/kg) post-conditioning session; (2) 2 weeks before and during cocaine conditioning (25 mg/kg); and (3) during extinction of CPP induced by cocaine (25 mg/kg). In the first experimental design, changes in tyrosine hydroxylase (TH) and dopamine transporter (DAT) gene expressions were measured in the ventral tegmental area (VTA).

RESULTS

Topiramate significantly increased cocaine-induced CPP and delayed or failed to produce extinction after the first cocaine reinstatement extinction in the first and second experiments. Furthermore, treatment with topiramate after place conditioning blocked the extinction of cocaine-induced CPP. TH and DAT gene expression in the VTA was significantly lower both with topiramate alone and in combination with cocaine compared with animals receiving only cocaine.

CONCLUSIONS

These findings suggest that topiramate increases the rewarding properties of cocaine, at least in part, by regulating dopaminergic signaling in the mesolimbic circuit. Consequently, the results of this study do not support the use of topiramate for the treatment of problems related to cocaine dependence.

HIGHLIGHTS

• Topiramate increases the rewarding properties of cocaine in CPP • Topiramate alters dopaminergic signaling in the mesolimbic circuit • Topiramate delays the extinction of cocaine-induced CPP • TH and DAT gene expression in the VTA decreases with topiramate and/or with cocaine • Results show that it should limit the use of topiramate in cocaine-dependent subjects.

Role of dopamine neurotransmission in the long-term effects of repeated social defeat on the conditioned rewarding effects of cocaine

Numerous studies report that social defeat stress alters dopamine (DA) neurotransmission in several areas of the brain. Alterations of the mesolimbic dopaminergic pathway are believed to be responsible for the increased vulnerability to drug use observed as a result of social stress. In the present study, we evaluated the influence of DA receptors on the long-term effect of repeated social defeat (RSD) on the conditioned rewarding and reinstating effects of cocaine. For this purpose, the D1R antagonist SCH 23390 and the D1R antagonist raclopride were administered 30min before each social defeat and a cocaine-induced CPP procedure was initiated three weeks later. The expression of the D1R and D2R was also measured in the cortex and hippocampus throughout the entire procedure. Mice exposed to RSD showed an increase in the conditioned rewarding effects of cocaine that was blocked by both DA receptors antagonists when a subthreshold dose of cocaine was employed. However, while the vulnerability to reinstatement of the preference induced by 25mg/kg cocaine-induced CPP was abolished by the D1R antagonist, it was practically unaffected by raclopride. Increases in D2R receptor levels were observed in the cortex of defeated animals after the first and fourth social defeats and in the hippocampus 3weeks later. Nevertheless, D1R receptor levels in the hippocampus decreased only after the last social defeat. Our results confirm that RSD enhances the conditioned rewarding effects of cocaine and that both DA receptors are involved in this enduring effect of social stress.

Inhibition of Reinforcing, Hyperalgesic, and Motor Effects of Morphine by Buspirone in Rats

Morphine and other opioids are among the most effective prescription medications for the treatment of pain. Addiction and hyperalgesia associated with their long-term use limits the clinical utility of these drugs. In view of a role of somatodendritic serotonin-1A receptors in addiction and analgesic effects of morphine, the present study concerns effects of co-use of buspirone, a partial agonist at the serotonin-1A receptor, on reinforcing, hyperalgesic, and motor effects of morphine in rats. A dose of morphine (7.5 mg/kg) producing moderate effects on motor activity and analgesia, and buspirone (doses of 0, 1.0, and 2.0 mg/kg) were injected intraperitoneally. Reinforcing effects were monitored in a conditioned place preference (CPP) paradigm and associated changes in motor activity were monitored during a drug conditioning phase. The hot plate test was used to monitor nociceptive response. Acute administration of morphine decreased motor activity and reduced pain perception. Repeated administration was reinforcing in the CPP paradigm and was associated with hyperalgesia and tolerance in motor depressant effects of morphine. These effects of repeated morphine administration were blocked in rats cotreated with buspirone. Pain perception was also slightly reduced in rats repeatedly treated with higher doses of buspirone. The findings are important for improving and extending therapeutic medications for pain.

PERSPECTIVE

The present study shows an important role of serotonin-1A receptors in morphine-induced hyperalgesia and addiction. It shows that buspirone, a prescription medicine for anxiety and depression can block addictive and hyperalgesic effects of morphine. Clinicians should consider buspirone as adjunctive therapy with morphine to improve therapeutic medications in pain.

`Up-regulation of histone acetylation induced by social defeat mediates the conditioned rewarding effects of cocaine

Social defeat (SD) induces a long-lasting increase in the rewarding effects of psychostimulants measured using the self-administration and conditioned place procedures (CPP). However, little is known about the epigenetic changes induced by social stress and about their role in the increased response to the rewarding effects of psychostimulants. Considering that histone acetylation regulates transcriptional activity and contributes to drug-induced behavioral changes, we addressed the hypothesis that SD induces transcriptional changes by histone modifications associated with the acquisition of place conditioning. After a fourth defeat, H3(K9) acetylation was decreased in the hippocampus, while there was an increase of HAT and a decrease of HDAC levels in the cortex. Three weeks after the last defeat, mice displayed an increase in histone H4(K12) acetylation and an upregulation of histone acetyl transferase (HAT) activity in the hippocampus. In addition, H3(K4)me3, which is closely associated with transcriptional initiation, was also augmented in the hippocampus three weeks after the last defeat. Inhibition of HAT by curcumin (100mg/kg) before each SD blocked the increase in the conditioned reinforcing effects of 1mg/kg of cocaine, while inhibition of HDAC by valproic acid (500mg/kg) before social stress potentiated cocaine-induced CPP. Preference was reinstated when animals received a priming dose of 0.5mg/kg of cocaine, an effect that was absent in untreated defeated mice. These results suggest that the experience of SD induces chromatin remodeling, alters histone acetylation and methylation, and modifies the effects of cocaine on place conditioning. They also point to epigenetic mechanisms as potential avenues leading to new treatments for the long-term effects of social stress on drug addiction.

CART peptide and opioid addiction: Expression changes in male rat brain

Previous studies have shown the prominence of cocaine- and amphetamine-regulated transcript (CART) peptide in rewarding and reinforcing effects of drugs of abuse specially psychostimulants. The data regarding the effects of different stages of opioid addiction on CART expression and the interconnection between CART and opioids are not much available. Here we have studied the changes in the expression level of CART mRNA and protein in various parts of the brain reward pathway in different stages of opioid addiction. Groups of male rats received acute low-dose (10mg/kg), acute high-dose (80mg/kg) and chronic escalating doses of morphine. In addition, withdrawal and abstinence states were evaluated after injection of naloxone (1mg/kg) and long-term maintenance of addicted animals, respectively. Expression of CART mRNA in the brain was measured by real-time PCR method. Western blotting was used to quantify the protein level. CART mRNA and protein were both up-regulated in high-dose morphine-administered animals and also in the withdrawal group in the nucleus accumbens (NAc), striatum and prefrontal cortex (PFC). In the addicted group, CART mRNA and protein were both down-regulated in NAc and striatum. In the abstinent group, CART mRNA was down-regulated in NAc. In the hippocampus, the only observed change was the up-regulation of CART mRNA in the withdrawal group. We suggest that the modulatory role of CART peptide in rewarding and reinforcing effects of opioids weakens when opioids are used for a long time and is stimulated when acute stress such as naloxone-induced withdrawal syndrome or acute high-dose administration of morphine occurs to the animal.

A selective D3 receptor antagonist YQA14 attenuates methamphetamine-induced behavioral sensitization and conditioned place preference in mice

AIM

We have reported that a selective dopamine D3 receptor antagonist YQA14 attenuates cocaine reward and relapse to drug-seeking in mice. In the present study, we investigated whether YQA14 could inhibit methamphetamine (METH)-induced locomotor sensitization and conditioned place preference (CPP) in mice.

METHODS

Locomotor activity was monitored in mice treated with METH (1 mg/kg, ip) daily on d 4-13, followed by a challenge with METH (0.5 mg/kg) on d 21. CPP was examined in mice that were administered METH (1 mg/kg) or saline alternately on each other day for 8 days (METH conditioning). YQA14 was injected intraperitoneally 20 min prior to METH or saline.

RESULTS

Both repetitive (daily on d 4-13) and a single injection (on the day of challenge) of YQA14 (6.25, 12.5 and 25 mg/kg) dose-dependently inhibited the acquisition and expression of METH-induced locomotor sensitization. However, repetitive injection of YQA14 (daily during the METH conditioning) did not alter the acquisition of METH-induced CPP, whereas a single injection of YQA14 (prior to CPP test) dose-dependently attenuated the expression of METH-induced CPP. In addition, the repetitive injection of YQA14 dose-dependently facilitated the extinction and decreased the reinstatement of METH-induced CPP.

CONCLUSION

Brain D3 receptors are critically involved in the reward and psychomotor-stimulating effects of METH. Thus, YQA14 deserves further study as a potential medication for METH addiction.

Severe dopaminergic neuron loss in rhesus monkey brain impairs morphine-induced conditioned place preference

It is well known that dopamine (DA) is critical for reward, but the precise role of DA in reward remains uncertain. The aim of this study was to determine what percentage of dopaminergic neurons in the primate brain is required for the expression of conditioned reward by measuring the performance of DA-deficient rhesus monkeys in a morphine-induced conditioned place preference (CPP) paradigm. Animals with mild Parkinsonian symptoms successfully developed and retained a morphine preference that was equivalent to control monkeys. However, these monkeys could not maintain the preference as well as controls when they retained severe Parkinsonian symptoms. On the other hand, monkeys initially in a severe Parkinsonian state developed a preference for morphine, but this preference was weaker than that of the controls. Histological results showed that the loss of dopaminergic neurons in monkeys that had severe Parkinsonian symptoms was about 80% in comparison to the control monkeys. All these data suggest that a severely impaired DA system alters rewarding-seeking behavior in non-human primates.

Sex differences in the long-lasting consequences of adolescent ethanol exposure for the rewarding effects of cocaine in mice

RATIONALE

The practice of binge drinking is very common among adolescents of both sexes. It can have long-term consequences with respect to drug consumption during adulthood, but knowledge on these effects in females is limited.

OBJECTIVES

The long-lasting effects of intermittent exposure to ethanol (EtOH) during adolescence on different cocaine-elicited behaviours, including locomotor reactivity, conditioned place preference (CPP) and intravenous self-administration, were evaluated in male and female adult mice. It was hypothesized that an EtOH binge during adolescence would increase sensitivity to the effects of a sub-threshold dose of cocaine and has a differential impact on the drug's effects in males and females.

METHODS

Adolescent OF1 mice (postnatal day (PND) 26) underwent a 2-week pre-treatment schedule consisting of 16 doses of EtOH (2.5 g/kg) or saline (twice daily administrations separated by a 4-h interval i.p.) administered on two consecutive days separated by an interval of 2 days. Three weeks later (PND > 60), we assessed locomotor activity responses induced by an acute injection of different doses of cocaine in experiment 1 and the rewarding effects of cocaine on the CPP (1 mg/kg) and intravenous self-administration (1 mg/kg/infusion) paradigms in experiment 2.

RESULTS

Pre-exposure to EtOH during adolescence altered motor reactivity to cocaine in a dose- and sex-dependent manner, increased sensitivity to cocaine in CPP and enhanced self-administration in adult mice.

CONCLUSIONS

The effects of intermittent exposure to ethanol during adolescence are evident in adulthood, during which greater sensitivity and intake of cocaine is observed and differ in each sex.

Inhibition of phosphodiesterase10A attenuates morphine-induced conditioned place preference

Background

Phosphodiesterase (PDE) 10A is selectively expressed in medium spiny neurons of the striatum. Nucleus accumbens (NAc) is a key region that mediates drug reward and addiction-related behaviors. To investigate the potential role of PDE10A in the reinforcement properties of morphine, we tested the effect of MP-10, a selective inhibitor of PDE10A, on acquisition, expression, and extinction of morphine-induced conditioned place preference (CPP).

Results

The results show that 2.5 mg/kg MP-10, administered subcutaneously, significantly inhibited the acquisition of morphine-induced CPP. The same dose of MP-10 alone did not result in the CPP. Moreover, MP-10 did not alter the expression of morphine-induced CPP, but did accelerate the extinction of morphine-induced CPP. Additionally, chronic treatment with 2.5 mg/kg MP-10 decreased expression of phosphorylated CREB (pCREB), activated cAMP response element binding protein, in dorsomedial striatum, in shell of NAc, and in anterior cingulate cortex (ACC) as well as decreased expression of ΔFosB in the shell of NAc and ACC.

Conclusion

The results suggest that inhibition of PDE10A may have therapeutic potential in the treatment of opioid addiction.

Inhibition of apomorphine-induced conditioned place preference in rats co-injected with buspirone: relationship with serotonin and dopamine in the striatum

Apomorphine is a non-narcotic derivative of morphine, which acts as a dopamine agonist to produce psychostimulant like effects. Currently, apomorphine is used in patients with advanced Parkinson׳s disease, for the treatment of persistent and disabling motor fluctuations, but a constellation of addictive syndromes such as excessive over use of medication, compulsive behaviors, and disturbances of impulse control are noticed in certain patients. Research on rodent models using conditioned place preference (CPP) paradigm also shows that the drug is rewarding. Previously we have shown that repeated administration of apomorphine produces behavioral sensitization which is prevented in rats co-injected with a low (1.0mg/kg) but not higher (2.0mg/kg) dose of buspirone. The present study shows that rewarding effects of apomorphine (1.0mg/kg) in a CPP paradigm are also blocked in rats co-injected with a low (1.0mg/kg) but not higher (2.0mg/kg) dose of buspirone. The levels of serotonin and its metabolite are decreased in the caudate as well as nucleus accumbens of rats exhibiting CPP and the decreases do not occur in animals co-injected with low or higher dose of buspirone. The levels of dopamine and its metabolites are not affected in animals exhibiting CPP; administration as well as co-administration of higher dose of buspirone decreased dopamine metabolism in the caudate as well as nucleus accumbens. The findings suggest a critical role of serotonin in the rewarding effects of apomorphine and imply that co-use of buspirone at low doses can help to control addictive syndromes in Parkinson׳s disease patients on apomorphine therapy.

Inhibitory Effect of Berberis vulgaris Aqueous Extract on Acquisition and Reinstatement Effects of Morphine in Conditioned Place Preferences (CPP) in Mice

Background:

It has been elucidated that Berberis vulgaris (barberry) can alleviate morphine withdrawal syndrome. Also it has been reported that aqueous extract of barberry possibly have inhibitory effect on NMDA receptors.

Objectives:

In this study, we decided to evaluate the effects of aqueous extract of B. vulgaris fruit on morphine tendency in mice using conditioned place preference (CPP) method.

Materials and Methods:

In experiment 1 (acquisition phase), mice underwent morphine-induced conditioned place preference (CPP) training with injections of morphine (40 mg/kg). In experiment 2 (extinction and reinstatement phases), mice underwent the same CPP training as in experiment 1 and subsequent extinction training on day 16th a reinstatement by CPP was done by injection of reminding 10 mg/kg morphine.

Results:

The administration of morphine (40 mg/kg for four days) produced place preference. In the first method, the aqueous extract of barberry (200 mg/kg) prevented morphine tendency to white cell in CPP method. In the second method, after inter-peritoneal injection of aqueous extracts of barberry at 100 and 200 mg/kg, the animals tendency toward the white cells of CPP chamber on the sixteenth day (after a reminder injection of morphine 10 mg/kg) was significantly reduced.

Conclusions:

These results show that aqueous extract of barberry can reduce the acquisition and reinstatement of morphine-induced conditioned place preference.

Effects of dopamine receptor antagonists on the acquisition of ethanol-induced conditioned place preference in mice

RATIONALE

Studies support differential roles of dopamine receptor subfamilies in the rewarding and reinforcing properties of drugs of abuse, including ethanol. However, the roles these receptor subfamilies play in ethanol reward are not fully delineated.

OBJECTIVE

To examine the roles of dopamine receptor subfamilies in the acquisition of ethanol-induced conditioned place preference (CPP), we pretreated animals systemically with antagonist drugs selective for dopamine D1-like (SCH-23390) and D2-like (raclopride) receptors prior to ethanol conditioning trials.

METHODS

Effects of raclopride (0-1.2 mg/kg) and SCH-23390 (0-0.3 mg/kg) on the acquisition of ethanol-induced CPP were examined in DBA/2J mice (experiments 1 and 2). Based on significant effects of SCH-23390, we then determined if SCH-23390 (0.3 mg/kg) produced a place preference on its own (experiment 3). To evaluate whether SCH-23390 impaired learning, we used a conditioned place aversion (CPA) paradigm and pretreated animals with SCH-23390 (0-0.3 mg/kg) before conditioning sessions with LiCl (experiment 4).

RESULTS

Whereas raclopride (0-1.2 mg/kg) did not affect acquisition, SCH-23390 (0.1-0.3 mg/kg) impaired the development of ethanol-induced CPP. SCH-23390 (0.3 mg/kg) did not produce place preference when tested alone and SCH-23390 (0.1-0.3 mg/kg) did not perturb the acquisition of LiCl-induced CPA.

CONCLUSIONS

Our results support a role for dopamine D1-like but not D2-like receptors in ethanol's unconditioned rewarding effect as indexed by CPP. Blockade of D1-like receptors did not affect aversive learning in this procedure.

The dopamine D3 receptor antagonist YQA14 that inhibits the expression and drug-primed reactivation of morphine-induced conditioned place preference in rats

Increasing evidence suggests that the mesolimbic dopamine system plays a critical role in opioid addiction. However, there is currently no standard drug treatment for opioid addiction. Growing preclinical evidence indicates that the dopamine D3 receptor antagonists are the potential anti-addiction pharmacotherapeutic agents based on in animal models of multiple drug addiction. In this study, we investigated the inhibitory effects of YQA14, a novel dopamine D3 receptor antagonist with a high affinity and selectivity for dopamine D3 receptor, using morphine-induced conditioned place preference (CPP) in rats. The results suggested that YQA14 (6.25-25mg/kg; intraperitoneal, i.p.) decreased the expression of morphine (10mg/kg, s.c.)-induced CPP in a dose-related manner but did not influence the acquisition of morphine-induced CPP. At a 25mg/kg dose of YQA14, it also notably inhibited the reactivation of morphine-priming CPP. These findings suggest that YQA14 is a potential agent for anti-opioid addiction which warrants further study and development.

Brain stress system response after morphine-conditioned place preference

This study examined the involvement of the brain stress system in the reinforcing effects of morphine. One group of mice was conditioned to morphine using the conditioned place preference (CPP) paradigm and the other group received morphine in a home-cage (non-conditioned). Adrenocorticotropic hormone and corticosterone levels were measured by radioimmunoassay; phospho (p) CREB expression and the number of corticotropin-releasing factor (CRF) neurons and fibres were measured by immunohistochemistry in different brain areas. We observed that the number of CRF neurons in the paraventricular nucleus (PVN) was increased after morphine-induced CPP, which was paralleled with enhanced CRF-immunoreactivity fibres in the nucleus tractus solitarius (NTS) and ventral tegmental area (VTA) vs. home-cage group injected with morphine. Morphine exposure induced an increase in CREB phosphorylated at Ser133 in the PVN and central amygdale (CeA), whereas mice exhibiting morphine CPP had higher levels of pCREB in the PVN, CeA and bed nucleus of the stria terminalis (BNST). We also found that most of the CRF-positive neurons in the PVN, CeA and BNST co-express pCREB after morphine CPP expression, suggesting that the drug-associated environmental contexts can elicit neuronal activity in the brain stress system. From the present results it is clear that exposure to a drug-associated context remains a potent activator of signalling pathways leading to CRF activation in the brain stress system.

A Methanol Extract of Brugmansia arborea Affects the Reinforcing and Motor Effects of Morphine and Cocaine in Mice

Previous reports have shown that several of the effects of morphine, including the development of tolerance and physical withdrawal symptoms, are reduced by extracts of Brugmansia arborea (L.) Lagerheim (Solanaceae) (B. arborea). In the present study we evaluate the action of the methanol extract of B. arborea (7.5–60 mg/kg) on the motor and reinforcing effects of morphine (20 and 40 mg/kg) and cocaine (25 mg/kg) using the conditioned place preference (CPP) procedure. At the doses employed, B. arborea did not affect motor activity or induce any effect on CPP. The extract partially counteracted morphine-induced motor activity and completely blocked the CPP induced by 20 mg/kg morphine. On the other hand, B. arborea blocked cocaine-induced hyperactivity but did not block cocaine-induced CPP. Reinstatement of extinguished preference with a priming dose of morphine or cocaine was also inhibited by B. arborea. The complex mechanism of action of B. arborea, which affects the dopaminergic and the cholinergic systems, seems to provide a neurobiological substrate for the effects observed. Considered as a whole, these results point to B. arborea as a useful tool for the treatment of morphine or cocaine abuse.

Effect of saikosaponin A on maintenance of intravenous morphine self-administration

In this study, we investigated the effects of saikosaponin A (SSA), a major compound of Bupleurum falcatum L., on morphine self-administration behavior. Male Sprague-Dawley rats were trained to self-administer intravenous morphine (0.1mg/kg per injection over 5s) during daily 1-h sessions under a fixed-ratio 1 schedule. Rats were pretreated with SSA (0.25, 0.5, 1.0mg/kg) by intraperitoneal injection 30 min prior to the start of the test session. Results demonstrated that pretreatment with SSA reduced morphine-maintained responding dose-dependently. Additionally, SSA inhibition of morphine-reinforced behavior was blocked by the selective GABA(B) receptor antagonist (2S)(+)-5,5-dimethyl-2-morpholineacetic acid (SCH 50911), but not the selective GABA(A) receptor antagonist bicuculline. Together, these results suggest that SSA may effectively suppress morphine-reinforced behavior by activating GABA(B) receptors.

Role of the dopaminergic system in the acquisition, expression and reinstatement of MDMA-induced conditioned place preference in adolescent mice

Background

The rewarding effects of 3,4-methylenedioxy-metamphetamine (MDMA) have been demonstrated in conditioned place preference (CPP) procedures, but the involvement of the dopaminergic system in MDMA-induced CPP and reinstatement is poorly understood.

Methodology/Principal Findings

In this study, the effects of the DA D1 antagonist SCH 23390 (0.125 and 0.250 mg/kg), the DA D2 antagonist Haloperidol (0.1 and 0.2 mg/kg), the D2 antagonist Raclopride (0.3 and 0.6 mg/kg) and the dopamine release inhibitor CGS 10746B (3 and 10 mg/kg) on the acquisition, expression and reinstatement of a CPP induced by 10 mg/kg of MDMA were evaluated in adolescent mice. As expected, MDMA significantly increased the time spent in the drug-paired compartment during the post-conditioning (Post-C) test, and a priming dose of 5 mg/kg reinstated the extinguished preference. The higher doses of Haloperidol, Raclopride and CGS 10746B and both doses of SCH 23390 blocked acquisition of the MDMA-induced CPP. However, only Haloperidol blocked expression of the CPP. Reinstatement of the extinguished preference was not affected by any of the drugs studied. Analysis of brain monoamines revealed that the blockade of CPP acquisition was accompanied by an increase in DA concentration in the striatum, with a concomitant decrease in DOPAC and HVA levels. Administration of haloperidol during the Post-C test produced increases in striatal serotonin, DOPAC and HVA concentrations. In mice treated with the higher doses of haloperidol and CGS an increase in SERT concentration in the striatum was detected during acquisition of the CPP, but no changes in DAT were observed.

Conclusions/Significance

These results demonstrate that, in adolescent mice, the dopaminergic system is involved in the acquisition and expression of MDMA-induced CPP, but not in its reinstatement.

Pre-treatment with high doses of cocaine decreases the reinforcing effects of cocaine in the conditioned place preference paradigm

The aim of the present study was to determine if pre-exposure to high doses of cocaine can subsequently alter the rewarding effects of this drug. Adult male mice received a pretreatment of physiological saline, or 12.5 or 25 mg/kg of cocaine (one injection a day for five days). After an interval of six days without injections, the rewarding effects of low doses of cocaine (0.5, 1 or 1.5 mg/kg) were evaluated in the conditioned place preference (CPP) paradigm. Doses of 1 and 1.5 mg/kg induced a clear CPP in animals pre-treated with saline but were ineffective in those pre-treated with 25 mg/kg of cocaine. Only the dose of 1.5 mg/kg induced CPP in mice pre-treated with 12.5 mg/kg of cocaine. Our results, which reveal a decrease in the conditioned rewarding effects of threshold doses of cocaine, demonstrate that exposure to high doses of this drug can alter the reward system.

Electroacupuncture of 2 hz has a rewarding effect: evidence from a conditioned place preference study in rats

Electroacupuncture (EA) has been used to suppress heroin craving in addicts and the conditioned place preference (CPP) for morphine in the rat. The question remained whether EA by itself will produce some rewarding effect. This was investigated using the CPP procedure in the present study. The results indicated that rats showed a significant preference to the 2 Hz EA-paired compartment. This rewarding effect of EA was prevented by pre-treatment with the opioid receptor antagonist naloxone [2 mg kg⁻¹, intraperitoneally (i.p.)], CB1 cannabinoid antagonist AM251 (3 μg per rat, intracerebroventricularly) or D1 dopamine receptor antagonist SCH23390 (0.1 mg kg⁻¹, i.p.), respectively. TempspacetempspaceIt is concluded that 2 Hz EA is capable of inducing CPP in the rat via the activation of the endogenous opioid-, cannabinoid- and dopamine-systems.