Behavioural Pharmacology of Novel Kappa Opioid Compounds

<p><b>Rationale: Kappa opioid receptor (KOPr) activation by traditional agonists has been shown to produce anti-addiction behaviours. However, adverse effects such as sedation, aversion and depression have limited their clinical development. Recently, salvinorin A (Sal A), an active component of the plant Salvia divinorum was shown to be a potent and selective KOPr agonist. Sal A has a short duration of effect and quick onset of action. It also produces similar behavioural pharmacology to traditional KOPr agonists. However, little is known about the anti-addiction profile of Sal A. If Sal A and its structural analogues produce anti-addiction properties with fewer adverse effects compared to traditional KOPr agonists, they have potential to be developed into antiaddiction pharmacotherapies. Therefore, Sal A and its structural analogues (DS1, MOM Sal B, EOM Sal B, herkinorin) and Mu opioid receptor (MOPr) antagonist/partial KOPr agonist, nalmefene were tested for their behavioural anti-addiction and adverse effect profiles in rats.</b></p> <p>Methods: To test the anti-addiction profile, a within session cocaine prime induced reinstatement paradigm was used. The selectivity of KOPr agonists in attenuating cocaine seeking behaviours was tested using sucrose reinforcement (anhedonia) and cocaine induced hyperactivity in self-administering rats (sedation during reinstatement test). Furthermore, behavioural adverse effects were screened using spontaneous open field activity (motor suppression), conditioned taste aversion (aversion) and forced swim test (depression) in rats. To further quantify the anti-addiction behaviours, the effect of KOPr agonists which attenuated drug seeking selectively without producing motor suppression by themselves were tested for cocaine produced motor function (hyperactivity and behavioural sensitization) in rats. The effect of serotonin transporter blockade on KOPr agonist induced depressive behaviour was also tested. The effects of KOPr activation on in vitro serotonin transporter function were also determined. Results: Sal A, DS1 and nalmefene attenuated cocaine prime induced drug-seeking, in a selective manner, via KOPr activation. MOM Sal B, a more potent and long acting Sal A analogue attenuated cocaine seeking in a non-selective manner. Sal A, DS1 and nalmefene did not induce aversion, however nalmefene suppressed motor function, which was not seen with Sal A and DS1. Furthermore, Sal A and DS1 suppressed cocaine behavioural sensitization. All three compounds (Sal A, DS1, nalmefene) produced depression. The depressive effects produced by Sal A and DS1 were diminished by blocking the serotonin transporter. Live-cell serotonin transporter assays showed potential differences between traditional (U50488H) and novel (Sal A, DS1) KOPr agonists in their ability to modulate serotonin transporter function. Conclusion: Out of six KOPr compounds tested, Sal A, DS1, MOM Sal B and nalmefene produced anti-addiction behaviours. However, MOM Sal B exposure also suppressed natural reward seeking behaviour. Sal A and DS1 had a better adverse effect profile than nalmefene. Thus, the order of efficacy for the compounds tested were DS1 ≥ Sal A > nalmefene > MOM Sal B. However depression was noted with all three compounds tested (Sal A, DS1, nalmefene) and our study provides evidence to suggest the involvement of the serotonin system in Sal A and DS1 induced depression. Moreover, a difference in modulation of serotonin transporter function by novel and traditional KOPr agonists was observed.</p>

Behavioural Pharmacology of Novel Kappa Opioid Compounds

<p><b>Rationale: Kappa opioid receptor (KOPr) activation by traditional agonists has been shown to produce anti-addiction behaviours. However, adverse effects such as sedation, aversion and depression have limited their clinical development. Recently, salvinorin A (Sal A), an active component of the plant Salvia divinorum was shown to be a potent and selective KOPr agonist. Sal A has a short duration of effect and quick onset of action. It also produces similar behavioural pharmacology to traditional KOPr agonists. However, little is known about the anti-addiction profile of Sal A. If Sal A and its structural analogues produce anti-addiction properties with fewer adverse effects compared to traditional KOPr agonists, they have potential to be developed into antiaddiction pharmacotherapies. Therefore, Sal A and its structural analogues (DS1, MOM Sal B, EOM Sal B, herkinorin) and Mu opioid receptor (MOPr) antagonist/partial KOPr agonist, nalmefene were tested for their behavioural anti-addiction and adverse effect profiles in rats.</b></p> <p>Methods: To test the anti-addiction profile, a within session cocaine prime induced reinstatement paradigm was used. The selectivity of KOPr agonists in attenuating cocaine seeking behaviours was tested using sucrose reinforcement (anhedonia) and cocaine induced hyperactivity in self-administering rats (sedation during reinstatement test). Furthermore, behavioural adverse effects were screened using spontaneous open field activity (motor suppression), conditioned taste aversion (aversion) and forced swim test (depression) in rats. To further quantify the anti-addiction behaviours, the effect of KOPr agonists which attenuated drug seeking selectively without producing motor suppression by themselves were tested for cocaine produced motor function (hyperactivity and behavioural sensitization) in rats. The effect of serotonin transporter blockade on KOPr agonist induced depressive behaviour was also tested. The effects of KOPr activation on in vitro serotonin transporter function were also determined. Results: Sal A, DS1 and nalmefene attenuated cocaine prime induced drug-seeking, in a selective manner, via KOPr activation. MOM Sal B, a more potent and long acting Sal A analogue attenuated cocaine seeking in a non-selective manner. Sal A, DS1 and nalmefene did not induce aversion, however nalmefene suppressed motor function, which was not seen with Sal A and DS1. Furthermore, Sal A and DS1 suppressed cocaine behavioural sensitization. All three compounds (Sal A, DS1, nalmefene) produced depression. The depressive effects produced by Sal A and DS1 were diminished by blocking the serotonin transporter. Live-cell serotonin transporter assays showed potential differences between traditional (U50488H) and novel (Sal A, DS1) KOPr agonists in their ability to modulate serotonin transporter function. Conclusion: Out of six KOPr compounds tested, Sal A, DS1, MOM Sal B and nalmefene produced anti-addiction behaviours. However, MOM Sal B exposure also suppressed natural reward seeking behaviour. Sal A and DS1 had a better adverse effect profile than nalmefene. Thus, the order of efficacy for the compounds tested were DS1 ≥ Sal A > nalmefene > MOM Sal B. However depression was noted with all three compounds tested (Sal A, DS1, nalmefene) and our study provides evidence to suggest the involvement of the serotonin system in Sal A and DS1 induced depression. Moreover, a difference in modulation of serotonin transporter function by novel and traditional KOPr agonists was observed.</p>

Behavioral Sensitization Induced by Methamphetamine Causes Differential Alterations in Gene Expression and Histone Acetylationin of Prefrontal Cortex in the Rat

BACKGROUND: Methamphetamine (METH) is one of the most widely abused illicit substances around the world, unfortunately its addiction mechanism remains unclear. Increasing evidences indicate that the change of gene expression and the involvement of chromatin modifications might be related with the lasting effects of METH on the brain. In the study, we took advantage of METH-induced behavioral sensitization as the animal model that reflects some aspects of drug addiction, and examined the transcription and histone acetylation changes in gene expression in prefrontal cortex (PFC) of adult rats. METHODS: We conducted the mRNA microarray and chromatin immunoprecipitation (ChIP) coupled to DNA microarrays (ChIP-chip) analysis to test and screen the transcriptional changes and histone acetylation modifications. The functional-enrichment analysis including Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) were performed to analyze the differential expression genes. We then further identified the alterations of ANP32A (Acidic leucine-rich nuclear phosphoprotein-32A) and POU3F2 (The POU domain, class 3, transcription factor 2) by real-time PCR and ChIP-PCR assay. RESULTS: In the rat model of METH-induced behavioral sensitization, challenge of METH caused 275 differentially expressed genes and a number of hyperacetylations (821 genes in H3 acetylation and 10 genes in H4 acetylation). We further tested the alteration of ANP32A and POU3F2 in transcription and histone acetylation at the different periods of this model, and revealed that histone acetylation modifications contributed to mRNA change of the genes expression caused by METH induced-behavioural sensitization while not by METH acute treatment. CONCLUSIONS: the present results revealed an amount of alteration in transcription and histone acetylation in rat PFC by the exposure of METH, and provided the evidence that the modifications of histone acetylation is contributed to the alteration of the genes expression caused by METH-induced behavioural sensitization.

Metabotropic glutamate type 5 receptor binding availability during dextroamphetamine sensitization in mice and humans

Background: Glutamate transmission is implicated in drug-induced behavioural sensitization and the associated long-lasting increases in mesolimbic output. Metabotropic glutamate type 5 (mGlu5) receptors might be particularly important, but most details are poorly understood. Methods: We first assessed in mice (n = 51, all male) the effects of repeated dextroamphetamine administration (2.0 mg/kg, i.p.) on locomotor activity and binding of the mGlu5 ligand [3H]ABP688. In a parallel study, in 19 stimulant-drug-naïve healthy human volunteers (14 female) we administered 3 doses of dextroamphetamine (0.3 mg/kg, p.o.) or placebo, followed by a fourth dose 2 weeks later. We measured [11C]ABP688 binding using positron emission tomography before and after the induction phase. We assessed psychomotor and behavioural sensitization using speech rate, eye blink rate and self-report. We measured the localization of mGlu5 relative to synaptic markers in mouse striatum using immunofluorescence. Results: We observed amphetamine-induced psychomotor sensitization in mice and humans. We did not see group differences in mGlu5 availability following 3 pre-challenge amphetamine doses, but group differences did develop in mice administered 5 doses. In mice and humans, individual differences in mGlu5 binding after repeated amphetamine administration were negatively correlated with the extent of behavioural sensitization. In drug-naïve mice, mGlu5 was expressed at 67% of excitatory synapses on dendrites of striatal medium spiny neurons. Limitations: Correlational results should be interpreted as suggestive because of the limited sample size. We did not assess sex differences. Conclusion: Together, these results suggest that changes in mGlu5 availability are not part of the earliest neural adaptations in stimulant-induced behavioural sensitization, but low mGlu5 binding might identify a higher propensity for sensitization.

Effect of chronic variable stress on sensitization to amphetamine in high and low sucrose-consuming rats

Background:Individual vulnerability to stress manifests in the interaction of innate properties and environment. There is a growing interest in the individual variability in vulnerability to stress and how it contributes to the development of psychiatric disorders. Intake of palatable substances is often measured in animal models. We have previously demonstrated that the consumption of sucrose solution is a stable trait in rats.Aims:The present study aimed to compare the sensitivity of rats with high vs low liquid sucrose consumption to chronic variable stress and the stress effect on behavioural sensitization to amphetamine.Methods:Male Wistar rats were subjected to a chronic stress regimen and subsequent repeated treatment with amphetamine (1 mg/kg, intraperitoneally). Fifty-kHz ultrasonic vocalizations, locomotor activity and stereotypies were measured.Results:In no-stress baseline conditions, the behavioural response to acute amphetamine was similar in rats with high vs low sucrose consumption. Prior chronic stress potentiated the effect of amphetamine only in rats with high sucrose consumption. Behavioural sensitization to repeated administration of amphetamine was observed in non-stressed rats with lower sucrose preference, but not in the respective stressed group that had increased monoamine turnover in the nucleus accumbens. In contrast, in rats with high sucrose preference the amphetamine sensitization effect was prevalent in stressed rats, but not in non-stressed animals.Interpretation:Chronic stress can change the psychostimulant effect but this depends on the inherent reward sensitivity of the animal. Trait-wise, sucrose intake reflects vulnerability to chronic stress and may interact with the development of addiction.