Effects of CGS 10746B on hyperactivity and place preference induced by morphine

The dopamine D1 receptor antagonist SCH-23390 blocks the acquisition, but not expression of mitragynine-induced conditioned place preference in rats

Mitragynine (MG) is the primary active constituent of Mitragyna speciosa Korth (kratom), a psychoactive Southeast Asian plant with potential therapeutic use. Numerous studies support roles of dopaminergic system in drug reward. However, the involvement of the dopaminergic system in mediating MG reward and drug-seeking is poorly understood. Using conditioned place preference (CPP) paradigm, the present study aims to evaluate the roles of the dopamine (DA) D1 receptor in the acquisition and expression of MG-induced CPP in rats. The effects of SCH-23390, a selective DA D1 receptor antagonist, on the acquisition of MG-induced CPP were first investigated. Rats were pre-treated systemically with SCH-23390 (0, 0.1 and 0.3 mg/kg, i.p.) prior to MG (10 mg/kg) conditioning sessions. Next, we tested the effects of the DA D1 receptor antagonist on the expression of MG-induced CPP. Furthermore, the effects of a MG-priming dose (5 mg/kg) on the reinstatement of extinguished CPP were tested. The results showed that SCH-23390 dose-dependently suppressed the acquisition of a MG-induced CPP. In contrast, SCH-23390 had no effect on the expression of a MG-induced CPP. The findings of this study suggested a crucial role of the DA D1 receptor in the acquisition, but not the expression of the rewarding effects of MG in a CPP test. Furthermore, blockade of the D1-like receptor during conditioning did not prevent MG priming effects on CPP reinstatement test, suggesting no role for the DA D1 receptor in reinstatement sensitivity.

Decreased kynurenine pathway potentiate resilience to social defeat effect on cocaine reward

The kynurenine (KYN) pathway of tryptophan (TRP) degradation is activated by stress and inflammatory factors. It is now well established that social stress induces the activation of the immune system, with central inflammation and KYN metabolism being two of the main factors linking stress with depression. The aim of the present study was to evaluate the long-lasting changes in the KYN pathway induced by social defeat (SD) associated with the resilience or susceptibility to an increase in the conditioned rewarding effects of cocaine. Mice were exposed to repeated SD and 3 weeks later, a conditioned place preference (CPP) induced by a subthreshold dose of cocaine (1.5 mg/kg) was developed. KYN levels in plasma, cerebellum, hippocampus, striatum and limbic forebrain were studied at the end of the CPP procedure. Changes in the KYN pathway after exposure to pharmacological (oxytocin and indomethacin) and environmental interventions (environmental enrichment) were also evaluated. Our results showed that defeated susceptible (SD-S) mice had higher conditioning scores than resilient mice (SD-R). In addition, although KYN concentration was elevated in all defeated mice, SD-R mice showed smaller increases in KYN concentration in the cerebellum than SD-S mice. Oxytocin or Indomethacin treatment before SD normalized cocaine-induced CPP, although the increase in the KYN pathway was maintained. However, environmental enrichment before SD normalized cocaine-induced CPP and prevented the increase in the KYN pathway. The present study highlights the role of the KYN pathway and anti-inflammatory drugs acting on TRP metabolism as pharmacological targets to potentiate resilience to social stress effects.

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.

The role of adenosine receptor agonist and antagonist on Hippocampal MDMA detrimental effects; a structural and behavioral study

There is abundant evidence showing that repeated use of MDMA (3, 4-Methylenedioxymethamphetamine, ecstasy) has been associated with depression, anxiety and deficits in learning and memory, suggesting detrimental effects on hippocampus. Adenosine is an endogenous purine nucleoside that has a neuromodulatory role in the central nervous system. In the present study, we investigated the role of A2a adenosine receptors agonist (CGS) and antagonist (SCH) on the body temperature, learning deficits, and hippocampal cell death induced by MDMA administration. In this study, 63 adult, male, Sprague - Dawley rats were subjected to MDMA (10 and 20 mg/kg) followed by intraperitoneal CGS (0.03 mg/kg) or SCH (0.03 mg/kg) injection. The animals were tested for spatial learning in the Morris water maze (MWM) task performance, accompanied by a recording of body temperature, electron microscopy and stereological study. Our results showed that MDMA treatment increased body temperature significantly, and impaired the ability of rats to locate the hidden platform(P < 0.05). The number of hippocampal dark neurons also increased especially in CA1. These impairments were aggravated by co-administration of A2a antagonist (SCH) with MDMA. Furthermore, the administration of the A2a receptor agonist (CGS) provided partial protection against MWM deficits and hippocampal cell death(P < 0.05). This study provides for the first time evidence that, in contrast to A2a antagonist (SCH) effects, co-administration of A2a agonist (CGS) with MDMA can protect against MDMA hippocampal neurotoxic effects; providing a potential value in the prevention of learning deficits observed in MDMA users. However, the exact mechanism of these interactions requires further studies.

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.

Preclinical evidence of new opioid modulators for the treatment of addiction

IMPORTANCE OF THE FIELD

Addiction to opiates is one of the most severe forms of substance dependence, and despite a variety of pharmacological approaches to treat it, relapse is observed in a high percentage of subjects. New pharmacological compounds are necessary to improve the outcome of treatments and reduce adverse side effects. Moreover, drugs that act on the opioid system can also be of benefit in the treatment of alcohol or cocaine addiction. AREA COVERED BY THIS REVIEW: Recent preclinical studies of pharmacological agents for the treatment of opiate addiction (2008 to the present date).

WHAT THE READER WILL GAIN

The reader will be informed of the latest drugs shown in animal models to modify dependence on opiates and the reinforcing effects of these drugs. In addition, reports of the latest studies to test these compounds in models of other drug addictions are reviewed.

TAKE HOME MESSAGE

The classic clinical pharmacotherapy for opiate dependence, involving mu-opioid receptor agonists or antagonists, has not yielded a high success rate in humans. In pharmacotherapy for opioid dependence, new options are emerging and different pharmacological strategies are now being tested.

Measuring reward with the conditioned place preference (CPP) paradigm: update of the last decade

Conditioned place preference (CPP) continues to be one of the most popular models to study the motivational effects of drugs and non-drug treatments in experimental animals. This is obvious from a steady year-to-year increase in the number of publications reporting the use this model. Since the compilation of the preceding review in 1998, more than 1000 new studies using place conditioning have been published, and the aim of the present review is to provide an overview of these recent publications. There are a number of trends and developments that are obvious in the literature of the last decade. First, as more and more knockout and transgenic animals become available, place conditioning is increasingly used to assess the motivational effects of drugs or non-drug rewards in genetically modified animals. Second, there is a still small but growing literature on the use of place conditioning to study the motivational aspects of pain, a field of pre-clinical research that has so far received little attention, because of the lack of appropriate animal models. Third, place conditioning continues to be widely used to study tolerance and sensitization to the rewarding effects of drugs induced by pre-treatment regimens. Fourth, extinction/reinstatement procedures in place conditioning are becoming increasingly popular. This interesting approach is thought to model certain aspects of relapse to addictive behavior and has previously almost exclusively been studied in drug self-administration paradigms. It has now also become established in the place conditioning literature and provides an additional and technically easy approach to this important phenomenon. The enormous number of studies to be covered in this review prevented in-depth discussion of many methodological, pharmacological or neurobiological aspects; to a large extent, the presentation of data had to be limited to a short and condensed summary of the most relevant findings.

Absence of conditioned place preference or reinstatement with bivalent ligands containing mu-opioid receptor agonist and delta-opioid receptor antagonist pharmacophores

Treatment of pain with opioids is limited by their potential abuse liability. In an effort to develop analgesics without this side effect, a series of bivalent ligands containing a mu-opioid receptor agonist pharmacophore connected to a delta-opioid receptor antagonist pharmacophore through variable-length spacers (16-21 atoms) was synthesized. Members of this series [mu-opioid receptor (M)-delta-opioid receptor (D)-agonist (A)-antagonists (N): MDANs] are antinociceptive in the tail flick assay, but antinociceptive tolerance and physical dependence do not develop to ligands having spacers with 19-21 atoms. The current studies compared the rewarding properties of three bivalent ligands (MDAN-16, -19 and -21) and a mu-opioid receptor agonist (MA-19) to those of morphine in the conditioned place preference assay in mice after i.v. administration. Place preference developed to morphine and to MA-19, but not to the MDANs. The responses to MDAN-16 were highly variable, although place preference of borderline significance appeared to develop. Reinstatement was also evaluated after extinguishing morphine conditioned place preference; morphine and MA-19, but not the MDANs, reinstated morphine conditioned place preference. Taken together, these results suggest that the bivalents are less rewarding compared to morphine in opioid-naïve mice and do not induce reinstatement in previously morphine-preferring mice. The lack of a conditioned place preference response for MDAN-19 and -21, compared to the equivocal results with MDAN-16, suggests a minimum distance requirement between mu-opioid receptor and delta-opioid receptor recognition sites. This requirement may reflect the binding of MDAN-19 and -21 to mu-opioid receptor-delta-opioid receptor heterodimeric receptors that block reward but not antinociception.

A neuropeptide FF agonist blocks the acquisition of conditioned place preference to morphine in C57Bl/6J mice

Neuropeptide FF behaves as an opioid-modulating peptide that seems to be involved in morphine tolerance and physical dependence. Nevertheless, the effects of neuropeptide FF agonists on the rewarding properties of morphine remain unknown. C57BL6 mice were conditioned in an unbiased balanced paradigm of conditioned place preference to study the effect of i.c.v. injections of 1DMe (D-Tyr1(NMe)Phe3]NPFF), a stable agonist of the neuropeptide FF system, on the acquisition of place conditioning by morphine or alcohol (ethanol). Morphine (10 mg/kg, i.p.) or ethanol (2 g/kg, i.p.) induced a significant place preference. Injection of 1DMe (1-20 nmol), given 10 min before the i.p. injection of the reinforcing drug during conditioning, inhibited the rewarding effect of morphine but had no effect on the rewarding effect of ethanol. However, a single injection of 1DMe given just before place preference testing was unable to inhibit the rewarding effects of morphine. By itself, 1DMe was inactive but an aversive effect of this agonist could be evidenced if the experimental procedure was biased. These results suggest that neuropeptide FF, injected during conditioning, should influence the development of rewarding effects of morphine and reinforce the hypothesis of strong inhibitory interactions between neuropeptide FF and opioids.

Cross-reinstatement by cocaine and amphetamine of morphine-induced place preference in mice

The cross-reinstatement by psychostimulants of a conditioned place preference (CPP) induced by morphine was evaluated in mice. In Experiment 1, we examined the effects of a single dose of cocaine and amphetamine on a previously extinguished morphine CPP. After acquisition of CPP induced by morphine (40 mg/kg), animals underwent daily extinction sessions of 15 min duration until the CPP was extinguished. Subsequently, animals received a non-contingent injection of cocaine (25 mg/kg) or amphetamine (4 mg/kg), which produced the reinstatement of the extinguished morphine-induced CPP. In Experiment 2, we evaluated the reinstating effects of several priming doses of cocaine (Experiment 2A) or amphetamine (Experiment 2B). As in the first experiment, after conditioning with morphine (40 mg/kg), mice underwent daily 15 min extinction sessions. When the preference was no longer evident, we tested the effects of cocaine (0, 6.25, 12.5, 25 and 50 mg/kg) and amphetamine (0, 0.5, 1, 2 and 4 mg/kg) on the reinstatement of CPP. Doses from 12.5 mg/kg of cocaine upward and doses from 1 mg/kg of amphetamine upward effectively reinstated CPP. Our results demonstrate cross-reinstatement with psychostimulants and opiates, suggesting that in abstinent individuals, drug exposure can produce craving for the previously abused drug and relapse.

Long-lasting rewarding effects of morphine induced by drug primings

To evaluate the persistence of the rewarding effects of morphine, the acquisition, maintenance, extinction and reinstatement of a conditioned place preference (CPP) was assessed in OF1 mice. In Experiment 1, the persistence of morphine-induced CPP was evaluated weekly. Mice showed CPP after four sessions of conditioning with 5, 10, 20 and 40 mg/kg of morphine, which lasted 0, 1, 2 and 4 weeks, respectively. In Experiment 2, after four sessions of conditioning with 40 mg/kg of morphine, the effects of four schedules of extinction differing in the time interval (2, 4, 6 or 8 weeks) between sessions were evaluated. CPP was no longer evident after 8 weeks for the groups examined each 2 or 8 weeks and after 12 weeks for the groups examined each 4 and 6 weeks. After extinction, the reinstating effects of a priming dose of 20 mg/kg of morphine were demonstrated. This procedure of extinction/reinstatement was repeated with a decreasing priming dose of morphine (10, 5, 2.5 and 1.25 mg/kg) until a noneffective dose was found. These results show that morphine-induced CPP is very persistent over time, suggesting that drug exposure induces long-lasting changes in the brain, which supports the idea that drug addiction must be considered as a chronic, lifelong disorder.

NMDA glutamate but not dopamine antagonists blocks drug-induced reinstatement of morphine place preference

The effects of dopaminergic and glutamatergic antagonists on the drug-induced reinstatement of a previously extinguished morphine conditioned place preference (CPP) in mice were evaluated. Following extinction of a place preference induced by morphine (40 mg/kg), a non-contingent injection of the dopaminergic antagonists SCH 23390 (0.125, 0.5 mg/kg), raclopride (0.3, 1.2 mg/kg), haloperidol (0.1, 0.2 mg/kg) and the dopamine (DA) release inhibitor CGS 10746B (1, 10 mg/kg) or glutamatergic NMDA antagonists memantine (10, 20, 40 mg/kg) and MK-801 (0.1, 0.2, 0.3 mg/kg) alone or with 10 mg/kg morphine was given. Neither the dopaminergic nor the glutamatergic antagonists alone reinstated the place preference. Dopamine antagonists failed to block the morphine-induced reinstatement of place preference while memantine and MK-801 blocked it with intermediate and high doses. These results suggest that drug-induced reinstatement of place preference may be largely independent of dopamine and more closely related to glutamatergic neurotransmission.

GHB ameliorates naloxone-induced conditioned place aversion and physical aspects of morphine withdrawal in mice

RATIONALE

Gamma-hydroxybutyric acid (GHB) is a naturally occurring substance in the brain, the administration of which has proved useful in the treatment of the opiate withdrawal symptoms in humans.

OBJECTIVES

The aim of the present work was to validate this beneficial effect on the physical and motivational aspects of morphine withdrawal in mice.

METHODS

In a first experiment, animals rendered morphine-dependent were conditioned to develop a place aversion (CPA) to the compartment paired with naloxone administration in a two-chamber apparatus. The conditioning phase consisted of three pairings of either naloxone (0.250 mg/kg) or vehicle in one compartment, both with similar time allotments during the preconditioning test. During the testing phase, mice were again allowed to explore the entire apparatus. GHB (6, 12.5, 25, and 50 mg/kg) was administered during either the acquisition or expression phase of this conditioning. In a second experiment, the capacity of GHB to ameliorate the intensity of physical signs of morphine withdrawal was evaluated.

RESULTS

GHB blocked CPA in both phases: administered during acquisition (from 12.5 mg/kg and higher) as well as in the expression phase (from 6 mg/kg, except for 25 mg/kg). It also decreased the intensity of physical signs of morphine withdrawal to near control levels measured by the modified Gellert-Holtzman scale (25 mg/kg and higher). Decreases in jumping, body shakes, and paw tremor were also observed.

CONCLUSIONS

Our results support the idea that GHB ameliorates both aspects of morphine withdrawal, physical as well as motivational signs.

Effects of NMDA receptor antagonists (MK-801 and memantine) on the acquisition of morphine-induced conditioned place preference in mice

Several studies have shown that the systemic administration of a variety of N-methyl-D-aspartate (NMDA) receptor antagonists can block the development or expression of conditioned place preference (CPP) induced by rewarding drugs such as morphine. In the present study, we examined the effects of different doses of two non-competitive NMDA receptor antagonists, MK-801 (0.1, 0.2 and 0.3 mg/kg) and memantine (2.5, 5, 10, 20 and 40 mg/kg), in CPP induced by 40 mg/kg of morphine in male mice. The CPP was carried out with an unbiased procedure in terms of initial spontaneous preference. Animals received the different doses of drugs in the conditioning sessions. MK-801 and memantine, at all doses used, produced neither place preference nor place aversion, but the higher doses of memantine (20 and 40 mg/kg) were able to completely block morphine-induced CPP. The present data show that the NMDA receptor antagonists MK-801 and memantine have no reinforcing properties but memantine is capable of preventing the acquisition of morphine-induced CPP. These results suggest that the development of morphine-induced CPP may be closely related to NMDA receptors and that the glutamatergic system can modulate opiate reward.

7-Nitroindazole blocks conditioned place preference but not hyperactivity induced by morphine

The effects of 7-nitroindazole (7-NI), a neural nitric oxide synthase (nNOS) inhibitor, on spontaneous locomotor activity, morphine-induced hyperactivity, acquisition of place conditioning and morphine-induced conditioned place preference (CPP) were evaluated in male mice. In experiment 1, animals treated with 7-NI (25, 50 and 100mg/kg), morphine (40 mg/kg) or morphine (40 mg/kg) plus 7-NI (25, 50 or 100mg/kg) were placed in an actimeter for 3h. In experiment 2, animals treated with the same drugs and doses were conditioned following an unbiased procedure. 7-NI did not affect the spontaneous locomotor activity or hyperactivity induced by morphine. However, the moderate and high doses of 7-NI produced conditioned place aversion (CPA) and the lowest dose blocked morphine-induced CPP. Our results suggest that nitric oxide is involved in the rewarding properties of morphine but not in its motor effects.

β-Phenylethylamines and the isoquinoline alkaloids

This review covers beta-phenylethylamines and isoquinoline alkaloids derived from them, including further products of oxidation. condensation with formaldehyde and rearrangement, some of which do not contain an isoquinoline system, together with naphthylisoquinoline alkaloids, which have a different biogenetic origin. The occurrence of the alkaloids, with the structures of new bases, together with their reactions, syntheses and biological activities are reported. The literature from July 2002 to June 2003 is reviewed, with 568 references cited.

Morphine conditioned place preference is attenuated by perinatal lead exposure

The purpose of this investigation was to determine if perinatal lead exposure alters the conditioned reinforcing properties of morphine when offspring were tested as adults. Dams were gavaged daily with 0- (sodium acetate) or 16-mg lead (as lead acetate) for 30 days prior to breeding with nonexposed males. Administration continued through gestation and lactation and was discontinued at weaning (postnatal day [PND] 21). At PND 70 animals were tested in a conditioned place preference (CPP) preparation using 0.00, 0.60, 1.25, 2.50, or 5.00 mg/kg i.p. morphine as the unconditioned stimulus (US). Relative to controls, attenuation of CPP was evident in animals exposed to 16-mg lead at 1.25 and 2.50 mg/kg morphine. Analysis of blood lead concentration revealed that by the end of testing residue levels in metal-exposed animals had returned to control levels. However, data from littermates sacrificed well beyond the current testing period revealed that brain lead residues remained elevated in animals exposed to lead, even though the metal had gained clearance from blood. The present data suggest that early lead exposure may have an enduring impact on the reinforcing properties of morphine.

Endogenous opiates and behavior: 2001

This paper is the twenty-fourth installment of the annual review of research concerning the opiate system. It summarizes papers published during 2001 that studied the behavioral effects of the opiate peptides and antagonists. The particular topics covered this year include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology(Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Effects of DA D1 and D2 antagonists on the sensitisation to the motor effects of morphine in mice

Acute morphine administration produces hyperactivity in mice and repeated treatment induces an enhancement of this effect. In this experiment, we study the sensitisation to the hyperactivity induced by intermittent morphine administration (40 mg/kg) and the effects of dopamine (DA) antagonists on this phenomenon. Animals received three injections, separated by 48 h, and after each injection, their activity was registered between 30 and 60 min. In Experiment 1, animals were divided into two groups, which received saline and morphine (S-S-M) or only morphine (M-M-M). In Experiment 2, animals were divided into 12 groups. Half, which was designed to study the effects of DA antagonists on the acquisition of morphine sensitisation, received morphine plus 0.125, 0.25, or 0.5 mg/kg SCH 23390 or raclopride in the two first administrations and only morphine in the third (M+SCH-M+SCH-M; M+R-M+R-M). The other groups, designed to study the effects of DA antagonists on the expression of morphine sensitisation, received morphine in the two first administrations and morphine plus DA antagonists in the last injection (M-M-M+SCH; M-M-M+R). Intermittent morphine administration produces greater hyperactivity than acute morphine. DA D1 antagonists reduce acquisition and block expression of sensitisation, while DA D2 antagonists only affect expression with the intermediate and high dose. These results support the implication of DA in the behavioural sensitisation of morphine in mice.