The novel mu-opioid antagonist, GSK1521498, reduces ethanol consumption in C57BL/6J mice.

RATIONALE Using the drinking-in-the-dark (DID) model, we compared the effects of a novel mu-opioid receptor antagonist, GSK1521498, with naltrexone, a licensed treatment of alcohol dependence, on ethanol consumption in mice. OBJECTIVE We test the ability of GSK1521498 to reduce alcohol consumption and compare its intrinsic efficacy to that of naltrexone by comparing the two drugs at doses matched for equivalent receptor occupancy. METHODS Thirty-six C57BL/6J mice were tested in a DID procedure. In 2-day cycles, animals experienced one baseline, injection-free session, and one test session when they received two injections, one of test drug and one placebo. All animals received GSK1521498 (0, 0.1, 1 and 3 mg/kg, i.p., 30 min pre-treatment) and naltrexone (0, 0.1, 1 and 3 mg/kg, s.c. 10 min pre-treatment) in a cross-over design. Receptor occupancies following the same doses were determined ex vivo in separate groups by autoradiography, using [3H]DAMGO. Binding in the region of interest was measured integrally by computer-assisted microdensitometry and corrected for non-specific binding. RESULTS Both GSK1521498 and naltrexone dose-dependently decreased ethanol consumption. When drug doses were matched for 70-75 % receptor occupancy, GSK1521498 3 mg/kg, i.p., caused a 2.5-fold greater reduction in alcohol consumption than naltrexone 0.1 mg/kg, s.c. Both GSK1521498 and naltrexone significantly reduced sucrose consumption at a dose of 1 mg/kg but not 0.1 mg/kg. In a test of conditioned taste aversion, GSK1521498 (3 mg/kg) reduced sucrose consumption 24 h following exposure to a conditioning injection. CONCLUSIONS Both opioid receptor antagonists reduced alcohol consumption but GK1521498 has higher intrinsic efficacy than naltrexone

Performance deficits of NK1 receptor knockout mice in the 5 choice serial reaction time task: effects of d Amphetamine, stress and time of day.

Background The neurochemical status and hyperactivity of mice lacking functional substance P-preferring NK1 receptors (NK1R-/-) resemble abnormalities in Attention Deficit Hyperactivity Disorder (ADHD). Here we tested whether NK1R-/- mice express other core features of ADHD (impulsivity and inattentiveness) and, if so, whether they are diminished by d-amphetamine, as in ADHD. Prompted by evidence that circadian rhythms are disrupted in ADHD, we also compared the performance of mice that were trained and tested in the morning or afternoon. Methods and Results The 5-Choice Serial Reaction-Time Task (5-CSRTT) was used to evaluate the cognitive performance of NK1R-/- mice and their wildtypes. After training, animals were tested using a long (LITI) and a variable (VITI) inter-trial interval: these tests were carried out with, and without, d-amphetamine pretreatment (0.3 or 1 mg/kg i.p.). NK1R-/- mice expressed greater omissions (inattentiveness), perseveration and premature responses (impulsivity) in the 5-CSRTT. In NK1R-/- mice, perseveration in the LITI was increased by injection-stress but reduced by d-amphetamine. Omissions by NK1R-/- mice in the VITI were unaffected by d-amphetamine, but premature responses were exacerbated by this psychostimulant. Omissions in the VITI were higher, overall, in the morning than the afternoon but, in the LITI, premature responses of NK1R-/- mice were higher in the afternoon than the morning. Conclusion In addition to locomotor hyperactivity, NK1R-/- mice express inattentiveness, perseveration and impulsivity in the 5-CSRTT, thereby matching core criteria for a model of ADHD. Because d-amphetamine reduced perseveration in NK1R-/- mice, this action does not require functional NK1R. However, the lack of any improvement of omissions and premature responses in NK1R-/- mice given d-amphetamine suggests that beneficial effects of this psychostimulant in other rodent models, and ADHD patients, need functional NK1R. Finally, our results reveal experimental variables (stimulus parameters, stress and time of day) that could influence translational studies

The contribution of genetically manipulated animals to the study of stimulant and alcohol addiction

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Uniform Microarray Hybridisation: A Comparative Study

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Repeated withdrawal from ethanol impairs acquisition but not expression of conditioned fear.

Repeated withdrawal from ethanol impairs acquisition of conditioned fear [Stephens, D.N., Brown, G., Duka, T. & Ripley, T.L. (2001) Eur. J. Neurosci., 14, 2023¿2031]. This study further examined the effect of repeated withdrawal from ethanol on the expression and acquisition of fear conditioning. Following training, presentation of a cue associated with footshock (CS+) resulted in a suppression of operant responding for food reinforcement. In different groups, shock thresholds were manipulated to give weak or severe behavioural suppression. Rats were subsequently chronically treated with ethanol-containing liquid diet either continuously (single withdrawal) or with three withdrawal periods (repeated withdrawal). Ethanol treatment and withdrawal had no effect on conditioned suppression of responding tested 2 weeks after the final withdrawal, at either shock intensity. Nevertheless, extinction of conditioned fear was impaired in the repeated withdrawal group exposed to the higher shock intensity. In the high intensity group, the stimulus¿shock association was then reversed, so that the previously neutral conditioned stimulus (CS¿) became the CS+. Acquisition of suppression to the new CS+ was significantly less in the animals previously given repeated experience of withdrawal, confirming our previous finding. Thus, repeated withdrawal from ethanol lead to disruption in the acquisition of fear conditioning but had no effect on retrieval of an association formed prior to the ethanol-withdrawal experiences

Ethanol effects on impulsivity in two mouse strains: similarities to diazepam and ketamine

Rationale: The effects of ethanol on attention and impulsivity have been contradictory. Objectives: The aim of the present investigation is to study the effects of acute ethanol administration in measures of attention and response control in the five-choice serial reaction time task (5-CSRTT) in two strains of mice, C57BL/6JOlaHsd and CD1.Materials and methods: Mice were trained in the 5-CSRTT and then were injected intraperitoneally (i.p.) with 0, 0.5, 1 and 2 g/kg ethanol before testing under standard parameters and in a long inter-trial interval (ITI) session, which promotes the emergence of premature responses, a measure of poor inhibitory control. To examine if the effects of ethanol in the 5-CSRTT were due to its actions at GABAA receptors or at NMDA receptors, the GABAA receptor agonist diazepam (1 and 2 mg/kg, i.p.) and the non-competitive NMDA antagonist ketamine (10 and 20 mg/kg, i.p.) were tested in long ITI sessions.Results: Ethanol did not affect attention or impulsivity in the standard procedure, but increased premature responding in long ITI sessions. The effects of ethanol were mimicked by diazepam in both strains of mice, whereas ketamine increased premature responding only in the CD1 strain.Conclusions: Ethanol's ability to increase impulsivity in the 5-CSRTT is mediated by both common and different neurotransmitter systems in the two strains of mice and is dependent on the task's parameters. Furthermore, ethanol did not decrease response accuracy, suggesting that attentional mechanisms are preserved after acute ethanol in mice and that the increases in impulsive behaviour are independent of attentional performance

Alleviating waiting impulsivity and perseverative responding by μ-opioid receptor antagonism in two inbred mouse strains

Rationale Recent evidence has implicated the opioid system in exaggerated ethanol consumption and impulsivity deficits. The opioid receptor antagonist naltrexone (NTX) has proven efficient in reducing alcohol consumption; however, its role on impulsive behaviour is not fully characterised. Objective The aim of this study was to investigate the effects of NTX on two measures of impulsive behaviour in two inbred mouse strains that differ in ethanol preference and impulsive phenotype. Methods Two separate groups of C57BL/6J (B6, n=24) and DBA2/J (D2, n=24) male mice were exposed to intermittent ethanol (IEE; 2 g/kg) during early (PND 30–45, IEE_Early) or late (PND 45–60, IEE_Late adolescence or the respective saline control. The ability of NTX (10 mg/kg) alone, or coadministered with ethanol (0.5 g/kg), to diminish waiting impulsivity in the five-choice serial reaction time task (5-CSRTT), or improve decision-making in a mouse version of the Iowa Gambling Task (mIGT), was examined in adulthood. Results In the 5-CSRTT, NTX diminished impulsivity in both strains of mice, irrespective of previous ethanol experience. In the mIGT, NTX failed to alter risky decision-making but decreased perseverative responding. Conclusions Blocking the actions of endogenous opioidsmay attenuate waiting impulsivity, in addition to alleviating perseverative responding. In a broader context, μ-opiate antagonism may be of potential interest for impulse-control disorders

Evidence for disrupted NMDA-receptor function in tissue plasminogen activator knockout mice

Tissue plasminogen activator (tPA), a serine protease immediate-early gene product expressed in brain areas important in learning and memory, has been shown to cleave the NR1 subunit of the NMDA receptor leading to a potentiated Ca2+ influx. Mice lacking tPA (tPA−/− mice) have disrupted late phase-LTP in the hippocampus, possibly as a consequence of reduced Ca2+ flux through NMDA receptors. In the present experiments, we investigated whether the NMDA antagonist dizocilpine might alter performance in tPA−/− mice in behavioural tasks shown to be sensitive to hippocampal lesions. tPA−/− mice and wild-type controls (WT) showed similar rates of acquisition and performance of a spatial working memory task (eight-arm radial maze). Dizocilpine (0.03–0.3 mg/kg, i.p.), given acutely, disrupted performance by increasing the number of errors equally across both genotypes. At asymptotic performance of a differential reinforcement of low response rate operant task (DRL), acute dizocilpine (0.03–0.3 mg/kg) impaired performance, but no differences between genotypes were observed. However, dizocilpine (0.1 mg/kg), given repeatedly during acquisition of a signalled-DRL15′′ task, retarded acquisition in tPA−/− but not WT mice. This treatment regime had no effect on locomotor activity in either genotype. tPA−/− mice showed no spatial learning deficits, but were more sensitive to dizocilpine during acquisition (though not expression) of a DRL task. This supports a role for tPA in modification of the NMDA receptor, although absence of tPA does not have consequences for all forms of NMDA-dependent mediated learning

Effect of CGP39551 administration on the kindling of ethanol-withdrawal seizures

Rationale: It has previously been shown that drugs, such as benzodiazepines, that inhibit seizure activity during ethanol withdrawal, fail to alleviate the potentiated withdrawal seen following repeated episodes of withdrawal when administered during each withdrawal episode. Acute administration of the N-methyl-D-aspartate (NMDA) receptor competitive antagonist, CGP39551, has been shown to inhibit seizure activity during ethanol withdrawal, and, when administered during the periods of repeated diazepam withdrawal, it blocked the reduction in pentylenetetrazol (PTZ) seizure threshold seen following a final, untreated withdrawal. Objectives: The aim of the current study was to determine if CGP39551 could alter final ethanol-withdrawal symptoms when administered during the acute intermittent withdrawal periods. Methods: Mice were chronically treated with ethanol-containing liquid diet for either 30 days continuously (single withdrawal) or with 8-h withdrawal periods on day 16 and day 23 of treatment (repeated withdrawal). Control animals received a control diet for the same period of time. On the final withdrawal animals were tested for behavioural signs of withdrawal. The effect of CGP39551 administered acutely on withdrawal [up to 5 mg/kg, intraperitoneally (i.p.)] or during the intermittent withdrawal periods (10 mg/kg, i.p.) was examined. Results: Acute administration of CGP39551 failed to inhibit handling-induced convulsions in the single-withdrawal or repeated-withdrawal group and had no effect on either decreased exploration or increased sensitivity to PTZ seen in withdrawal. Surprisingly, when CGP39551 was administered during periods of repeated ethanol withdrawal a potentiation of seizure activity was seen in the final, untreated withdrawal. This potentiation of seizure activity, compared with vehicle-treated animals, was not seen when CGP39551 was given whilst animals had access to ethanol (single-withdrawal group and repeated-withdrawal group where CGP39551 treatment was non-contingent with withdrawal episodes). However, the decrease in exploration seen during withdrawal was potentiated in repeated-withdrawal animals treated with CGP39551 irrespective of the time at which the CGP39551 was administered. Conclusions: Treatment with an NMDA receptor-competitive antagonist potentiated the ethanol-withdrawal syndrome in animals with previous experience of ethanol withdrawal

Studying the neurobiology of stimulant and alcohol abuse and dependence in genetically manipulated mice

The ability to manipulate the genetic makeup of organisms by specific targeting of selected genes has provided a novel means of investigating the neurobiological mechanisms underlying drug abuse and dependence. However, as with other techniques, there are a number of potential pitfalls in the use of genetically manipulated animals (usually mice) in behavioural experiments. This review discusses the techniques involved in creating genetically manipulated mice, and points to opportunities and insights into addictive processes provided by the new science, while illustrating some of the potential problems encountered in interpretation of data obtained from such animals. The use of the mouse as an experimental animal also raises some specific problems which limit the usefulness of the technique at present. Examples taken from research into alcohol and psychostimulant abuse and dependence are used to illustrate the usefulness of genetically manipulated animals in addiction research, the problems of interpretation which sometimes arise, and how techniques are being developed to overcome present limitations to this exciting area of research