A possible link between morphine and alcohol preferences in rat.

Sprague-Dawley rats were intoxicated with alcohol or morphine, by ingestion in a fluid diet. Alcohol or morphine preference was studied in two-bottle choice tests. Preference increased up to a certain level with increasing time of intoxication at one dose level. Some 10% of the animals had an extremely high preference already after a short ingestion period. Another 10% showed an extremely low drug preference even after long intoxication. When rats were consecutively intoxicated with morphine and alcohol, or vice versa, followed by choice tests with the respective drug, the statistical correlation between alcohol and morphine preference was weak in the individual rats. Approximately 20% of the high morphine preference rats also had a high alcohol preference. Early postnatal morphine intoxication slightly increased morphine, but not alcohol preference in the physically dependent male adult rats. Thus, there seem to be different and specific mechanisms underlying the alcohol and opiate preference in rats, although some overlapping probably exists.