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  • 1
    ISSN: 1432-2072
    Keywords: Heroin ; Schedule-induced behaviour ; Activity ; Food-contingent operant responding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The present study demonstrates a method which enables separation of the “direct’ pharmacological effects of heroin on activity and operant responding from the ‘indirect’ reinforcing effects of heroin. Experiment I was carried out at 0.1 mg/kg heroin with naive male albino Wistar rats (N=21) from a La Trobe University (Bundoora, Australia) colony. Experiments II and III were carried out at 0.05 mg/kg (N=21) and 0.2 mg/kg (N=21) heroin doses with Wistar rats from a Monash University (Clayton, Australia) colony. Each experiment consisted of a 5-day pre-training period and a 10-day experimental period. Food-contingent operant behaviour was shaped in 14 animals during the first 4 days of the pre-training period. On day 5, baseline data was taken. Pairs of animals were then randomly yoked to one of seven naive ‘executive’ animals and the executive animals were allowed to self-inject heroin. Each self-injection of heroin by an executive animal led to a simultaneous injection of heroin to a yoked-heroin animal, and a simultaneous injection of saline to a yoked-saline animal. Results of 1-h data showed a significant decrement in food-contingent operant behaviour only for the yoked-heroin animals in the 0.2 mg/kg and 0.05 mg/kg groups. A significant decrement in both food-contingent operant behaviour and activity was found for the yoked-heroin animals at all three doses studied when data from the first half of 1-h sessions only was examined. It was concluded that the rate of self-injection demonstrated by executive animals was limited by the direct pharmacological effects of heroin on activity, and that the impairment of responding for food reflected this direct pharmacological effect of heroin. A theoretical model of reinforcement strength was subsequently proposed.
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  • 2
    ISSN: 1432-2072
    Keywords: DRL ; Chlordiazepoxide ; Naloxone ; Benzodiazepines ; Opiates ; Learning ; Nonreward ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The opiate antagonist naloxone can completely or partially reverse the effects of the benzodiazepines on appetitive behaviours and conflict tasks involving electric shook. If naloxone changes the anxiolytic action of the benzodiazepines it should, theoretically, be effective in tasks employing nonreward as well as those employing shock. We tested naloxone and chlordiazepoxide on acquisition and performance of a nonreward task, DRL. With both continuous administration during acquisition of DRL, and intermittent administration during stable performance, chlordiazepoxide (5 mg/kg IP) increased burst responding and shifted the peak of the inter-response time (IRT) distribution curve to shorter IRTs. Naloxone (3 mg/kg IP) blocked the effects of chlordiazepoxide on acquisition of DRL. Naloxone (3 mg/kg and 10 mg/kg IP) did not change the effects of chlordiazepoxide on well-learned performance of the DRL schedule. These results show that endogenous opiates could mediate some but not all of the actions of the benzodiazepines. They also suggest that state-dependent and “truly anxiolytic” effects of the benzodiazepines (McNaughton 1985) may have different pharmacological substrates.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Psychopharmacology 42 (1975), S. 255-261 
    ISSN: 1432-2072
    Keywords: Methadone ; Mode of Withdrawal ; Body Weight ; Relapse ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Physical dependence on methadone was induced in rats by an initial “forced drinking” procedure and subsequently by i.p. administration of the drug. In a subsequent Experimental Phase of the study the physical dependence of one group was sustained by a “methadone maintenance” treatment, while two other groups were withdrawn from the drug, one gradually and one abruptly. When relapse trials were carried out during a Readdiction Phase it was found that the maintained group voluntarily consumed significantly greater amounts of methadone than did the two withdrawal groups. These groups did not differ between themselves but did in turn ingest significantly more methadone than a control group with no prior exposure to the drug. The characteristic loss of body weight reliably found during withdrawal from morphine was not demonstrated. This may have been due to the unexpected weight loss which occurred during the last stage of the initial Addiction Phase. The dependent variables of amount of methadone solution and the percentage of fluid consumed as methadone solution correlated highly. However the amount of methadone solution ingested was a better indicator of addiction liability as it was not influenced by fluctuations in the amount of water consumed by the animals.
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  • 4
    ISSN: 1432-2072
    Keywords: Heroin ; Methadone ; Self-administration ; Schedule ; Nutrition ; Body weight ; Corticosterone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Experiment 1 reported the effects of the interaction of a fixed 1 min delivery schedule and body weight, using schedule-induced self-injection paradigm, in the rate of acquisition of methadone and heroin. Eighty-one rats were assigned to 100% and 80% reduced body weight conditions with and without a schedule. The findings show that: (a) voluntary heroin and methadone intake was enhanced when a schedule was introduced to animals at 80% but not at 100% body weight; (b) high intake of heroin and methadone was accompanied by increased levels of plasma 11-OHCS. Experiment 2 showed that the high rate of self-injection was due to the interaction of pharmacological properties of opiates and environmetal variables rather than to a general increase in activity arising from the deprivation state or the effects of the schedule. The results are discussed in terms of a stress factor arising from an interaction between environmental and pharmacological factors.
    Type of Medium: Electronic Resource
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