Alcohol and Alcoholism Vol. 36, No. 4, pp. 286-291, 2001
© 2001 Medical Council on Alcoholism
Effects of repeated morphine treatment on metabolism of cerebral dopamine and serotonin in alcohol-preferring AA and alcohol-avoiding ANA rats
Department of Pharmacy, Division of Pharmacology and Toxicology, University of Helsinki, P.O. Box 56, FIN-00014 and
1 Department of Mental Health and Alcohol Research, National Public Health Institute, P.O. Box 719, FIN-00300, Helsinki, Finland
Received 12 July 2000; in revised form 21 December 2000; accepted 22 January 2001
The alcohol-preferring AA (Alko Alcohol) rats are more rapidly sensitized to the locomotor activity-stimulating effects of small doses of morphine than the alcohol-avoiding ANA (Alko Non-Alcohol) rats. To study the involvement of dopaminergic and serotonergic transmission in this behaviour, the effects of acute morphine (1 mg/kg) challenge on the concentrations of dopamine (DA), 5-hydroxytryptamine (5-HT, serotonin) and their metabolites were estimated in three dopaminergic areas in AA and ANA rats on the fourth day after a 3-day morphine or saline treatment. Acute administration of morphine enhanced DA metabolism in the caudate-putamen in the AA, but not in the ANA, rats; in the nucleus accumbens and in the olfactory tubercle the acute effect of morphine was similar in rats of both lines. Morphine pretreatment did not significantly enhance acute morphine's effects on DA metabolites in any of the brain areas studied in rats of either line. Acute administration of morphine enhanced brain 5-HT metabolism in the AA rats but not in the ANA rats, but after repeated treatment it induced no enhancement of 5-HT metabolism. With the methods used, no significant differences were found between the AA and ANA rats in the effects of repeated morphine on cerebral dopaminergic or serotonergic mechanisms which could account for the different behavioural sensitization found previously in rats of these lines. However, both monoamines studied might be involved in the acute locomotor stimulatory effects of morphine.