Summary
Rats were induced to administer morphine to themselves by drinking solutions of it in preference to water; this behaviour was found to be a valid model of morphine dependence. Previous “passive” medication with morphine was not necessary; initial aversions for the bitter morphine solutions were converted into preferences after the rats were repeatedly given only morphine solutions to drink in order to relieve thirst. The consumption of solutions of quinine which were initially equally aversive did not increase, suggesting that the repeated pairing of a bitter taste with relief of thirst did not account for the preferences for the morphine solutions. It appeared that the post-ingestional effects of morphine provided primary reinforcement for the rats; they were able to regulate their daily intake of the drug after being injected with varying doses of it and they lost weight abruptly during enforced abstinence. There was also evidence that the bitter taste of morphine had become a secondary reinforcer for rats with established preferences.
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The work was supported by a grant from the Medical Research Council and by grant MH-03313 from the U.S. Public Health Service.
One of us (R. K.) held a Beit Memorial Research Fellowship.
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Stolerman, I.P., Kumar, R. Preferences for morphine in rats: Validation of an experimental model of dependence. Psychopharmacologia 17, 137–150 (1970). https://doi.org/10.1007/BF00402704
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DOI: https://doi.org/10.1007/BF00402704