After a single cocaine dose, the enzyme that makes tyramine becomes more active in normal flies.

ECONOMIST: Flying high

In the circadian-gene mutants, however, the enzyme's activity stays steady after a dose of the drug, so tyramine levels remain low.

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The absence of the circadian genes, which seem to regulate the release of tyramine, prevents flies from becoming more responsive to cocaine.

ECONOMIST: Flying high

In fruit flies, a biochemical called tyramine seems to be responsible for such drug responses, and Dr Hirsh thinks that tyramine regulation is the chemical link between these two very different processes.

ECONOMIST: Flying high

But if the propensity to addiction is also genetically controlled in humans, it could provide a mechanism to address the problem at the cellular level, by regulating tyramine or its vertebrate equivalent.

ECONOMIST: Flying high