Conditioning to ethanol in the fruit fly - a study using an inhibitor of ADH

To identify processes involved in the choice of ethanol by adult Drosophila , flies homozygous Adh(F), reared in the absence of alcohol were placed in contact with: a) an ethanol-free medium, b) a medium containing ethanol, c) a medium supplemented with 4-methylpyrazole (4-MP, an inhibitor of the ADH pathway), d) a medium containing ethanol and 4-MP. The choice of ethanol o ver a medium without ethanol was evaluated by measuring the duration of ext ension of the proboscis of the flies in each of the media. A slight prefere nce for the ethanol-supplemented medium was observed in the naive flies, wh ich was enhanced by previous exposure to ethanol. Exposure to ethanol and 4 -MP, however, led to an avoidance of ethanol. There was a reduction in ADH activity on treatment of the flies with 4-MP, and signs of malaise (reduced locomotor activity, loss of balance) were observed in the flies who ingest ed both ethanol and inhibitor. We concluded that the preference for ethanol stems from an associative learning related to ethanol utilization. Inhibit ion of enzymes of ADH pathway led to a conditioned aversion due to disturba nce of ethanol metabolism giving rise to malaise. (C) 1999 Elsevier Science Ltd. All rights reserved.