Biomedical subjects

Sunmee Wee

Publications and source records attributed to Sunmee Wee.

7 recordsLinked to original sources

PubMed2007

Effects of dose and session duration on cocaine self-administration in rats.

Previous studies showed that an extended 6-h session duration produced an increasing rate of cocaine self-administration in rats. The present study further investigated the effect of dose and session duration on cocaine self-administration. Eight groups of rats (4 doses x 2 session durations) self-administered one of four cocaine doses (0.25, 0.5, 1, and 2 mg/kg/injection) in either 1- or 6-h sessions under a fixed-ratio schedule. In another experiment, two other groups of rats self-administered 0.5 mg/kg/injection of cocaine in either 3- or 12-h sessions. Cocaine self-administration increased at all doses in 6-h sessions but not in 1-h sessions. Cocaine intake (milligram/kilogram) reached an asymptote earlier at a higher dose, but the rate of responding increased faster when the dose was lower. In ShA rats, the cocaine dose-response function was higher in rats at the two higher unit doses than at the lower doses. Cocaine self-administration increased in 6- and 12-h sessions, but not in 1- and 3-h sessions. The increase in self-administration was faster and greater in 12-h sessions than 6-h sessions. The data suggest that cocaine self-administration increases at various doses with prolonged access and that an increase in the rate of responding is positively and inversely associated with session duration and unit dose, respectively. Results also imply that cocaine intake reaches a ceiling faster at high doses even under short session duration. Therefore, high doses or prolonged access to cocaine are more likely to result in a pattern of cocaine intake that reflects compulsive use.

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PubMed2006

Self-administration of mixtures of fenfluramine and amphetamine by rhesus monkeys.

Previous research with psychostimulants has suggested a negative relationship between both potency and efficacy as a reinforcer and serotonergic potency, particularly relative to dopaminergic potency. The present experiment was designed to examine the relationship between the serotonergic activity and efficacy as a reinforcer by allowing rhesus monkeys (n=5) to self-administer amphetamine mixed with a serotonin releaser, fenfluramine. Additionally, the role of 5-HT2 receptors in the interaction between amphetamine and fenfluramine was investigated using ketanserin, a selective 5-HT2 receptor antagonist. Amphetamine and fenfluramine were combined in ratios of, respectively, 1:1 to 1:10 on a mg/kg basis and made available for self-administration under a progressive-ratio schedule of reinforcement. Amphetamine (0.0056-0.1 mg/kg/injection) functioned as a positive reinforcer with sigmoidal or biphasic dose-response functions. The addition of fenfluramine to amphetamine decreased the maximum responding, at least at the highest dose ratio (1:10, amphetamine/fenfluramine), in all monkeys. When measured after the pretreatment of ketanserin (1.0-3.0 mg/kg, i.m.), the self-administration of the mixture of amphetamine and fenfluramine at a ratio of 1:10 decreased in three monkeys and was unaffected in the fourth. These results support the notion of a negative influence of increased serotonergic neurotransmission on reinforcing efficacy of drugs that act via monoamine systems. However, the involvement of 5-HT2 receptors in the interaction between the serotonergic system and the reinforcing efficacy still remains equivocal.

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PubMed2006

Escalation of methamphetamine self-administration in rats: a dose-effect function.

RATIONALE: The transition from stable to escalated drug intake has been demonstrated in rats self-administrating cocaine and heroin using a single dose of drug. OBJECTIVES: To investigate the prolonged exposure to methamphetamine self-administration and the effect of various training doses of methamphetamine on the changes of methamphetamine intake over a 21-day period. METHODS: Two groups of rats were trained in 1-h daily sessions of methamphetamine self-administration [0.033 mg/infusion (inf); approximately 0.066 mg/kg/inf]. Methamphetamine access was increased to 6 h in one group [Long Access (LgA)] or maintained at 1 h in another [Short Access (ShA)]. The same procedure was repeated in rats exposed to different training doses of methamphetamine (0.05, 0.1, and 0.2 mg/kg/inf). RESULTS: In LgA rats, total and first hour intake of methamphetamine significantly increased compared to ShA rats at various methamphetamine doses. LgA animals, at all doses in the second study, escalated intake to 8-9 mg/kg per 6-h session, with the most rapid escalation occurring at 3-5 days at a methamphetamine dose of 0.1 mg/kg/inf. CONCLUSIONS: The escalation of drug intake observed with extended access is produced at multiple doses of methamphetamine. The rapidity of escalation depends on the dose. Ultimately, all doses in the dose-response study engendered self-administration of the same amount of total drug in a 6-h session in the extended-access group. Results suggest that the rapidity of escalation is dependent on dose and has an upper limit of intake over a period of 21 days.

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PubMed2006

A reduced rate of in vivo dopamine transporter binding is associated with lower relative reinforcing efficacy of stimulants.

A slow onset of action has been hypothesized to weaken the reinforcing effects of drugs. The present study evaluated this hypothesis with slow-onset cocaine analogs, WIN 35428, RTI 31, and RTI 51. When cocaine or a cocaine analog was made available to rhesus monkeys (n = 4 or 5) for self-administration under a progressive-ratio (PR) schedule with a 1-h time-out between injections, all the drugs functioned as positive reinforcers. The maximum number of injections was in the order of cocaine > WIN 35428 > RTI 31 > RTI 51. In in vivo binding in rat striatum, equipotent doses of cocaine, WIN 35428, RTI 31, and RTI 51 were estimated to displace 25% of [(3)H]WIN 35428 binding at the dopamine transporters (DAT), respectively, 5.8, 22.4, 30.8, and 44.1 min after the intravenous injection. Further, relative reinforcing efficacy was correlated with rate of DAT binding such that slower displacement of [(3)H]WIN 35428 was associated with a weaker reinforcing effect. In in vitro binding in monkey brain tissue, the cocaine analogs had higher affinity for monoamine transporter sites, but similar affinity ratios of 5-HTT/DAT, compared to cocaine. Lastly, RTI 31 was shown to function as a positive reinforcer in drug-naïve rhesus monkeys under a fixed-ratio 1 schedule. Collectively, the data support the hypothesis that a slow onset at the DAT is associated with reduced reinforcing efficacy of DAT ligands. The data under both the PR and FR schedules, however, suggest that a slow onset at the DAT influence reinforcing effect only to a limited extent.

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PubMed2005

Role of the increased noradrenergic neurotransmission in drug self-administration.

Psychostimulants increase extracellular monoamine concentrations in the CNS. While the contributions of dopamine (DA) and serotonin (5-HT) to the reinforcing effect of psychostimulants have been examined, less is known about the involvement of norepinephrine (NE). In the present study, cocaine, desipramine (DMI) and JZ-III-84 were made available to rhesus monkeys (n=4) responding under a progressive-ratio (PR) schedule. These compounds vary in their in vitro selectivities for blocking NE uptake relative to DA from high (DMI) to modest (JZ-III-84) to non-selective (cocaine). Additionally, cocaine mixed with DMI in mg/kg dose-ratios of 1:1 to 1:3 was made available for self-administration. NE uptake inhibition by the mixture of cocaine and DMI at a ratio of 1:3 was evaluated in an ex vivo uptake assay. Cocaine (0.01-0.1 mg/(kg injection)) and JZ-III-84 (0.001-0.1 mg/(kg injection)) functioned as positive reinforcers with sigmoidal or biphasic dose-response functions, whereas DMI failed to do so. The addition of DMI to cocaine did not systemically alter self-administration of cocaine. In the ex vivo uptake assay, the addition of DMI to cocaine significantly increased the NE uptake inhibition compared to cocaine. These results support the conclusion that CNS NE is not involved in the reinforcing mechanism of psychostimulants.

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PubMed2004

Evaluation of the reinforcing effects of atomoxetine in monkeys: comparison to methylphenidate and desipramine.

Atomoxetine is a selective norepinephrine (NE) reuptake blocker that has recently been marketed for the treatment of attention deficit hyperactivity disorder. The purpose of the present study was to evaluate the self-administration of atomoxetine in an animal model predictive of abuse liability in humans. Rhesus monkeys (N = 5) were prepared with chronic intravenous catheters and allowed to self-administer cocaine or saline during alternating baseline sessions. When behavior was stable, atomoxetine (0.03-3.0 mg/kg per injection), desipramine (0.1-3.0 mg/kg per injection), methylphenidate (0.001-0.1 mg/kg per injection), or their vehicles were substituted for baseline conditions. Methylphenidate consistently maintained responding above the levels maintained by its vehicle. Atomoxetine and desipramine failed to reliably maintain self-administration above vehicle levels in four of five individual monkeys. These results predict that atomoxetine, in contrast to methylphenidate but like desipramine, will lack reinforcing effects and abuse potential in humans.

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PubMed2004

Reinforcing effect of pseudoephedrine isomers and the mechanism of action.

It has been proposed that ephedrine and its isomers may have abuse potential. When made available to rhesus monkeys (n = 4) for self-administration, +-pseudoephedrine functioned as a positive reinforcer in all monkeys, as did (-)-pseudoephedrine in two of three monkeys. Pseudoephedrine isomers were 10- to 33-fold less potent than cocaine. In in vitro binding in monkey brain tissue, both isomers had low affinity for dopamine and serotonin transporters by at least 200-fold relative to cocaine, but comparable affinity for norepinephrine transporters. +-Pseudoephedrine also blocked dopamine uptake in 293 hDAT cells with low potency relative to cocaine. When given in vivo +-pseudoephedrine significantly displaced radioligand binding to dopamine transporters with a potency comparable to that in self-administration. Therefore, pseudoephedrine isomers can function as reinforcers and the mechanism at dopamine transporters may underlie this effect. However, pseudoephedrine appears to be a weak reinforcer and may have relatively low abuse potential.

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