Induction of social dominance by L-dopa treatment in Arctic charr.

The effect of L-dopa on social dominance was studied in the juvenile Arctic charr (Salvelinus alpinus). L-dopa is the immediate precursor of dopamine, a neurotransmitter that has been connected with aggressive behaviour in fish as well as mammals. Arctic charr were placed in pairs. One individual in each pair was given L-dopa orally, while the other was given vehicle. The results showed that 18 out of 22 fish given 10 mg L-dopa kg-1 became dominant (p = 0.004, binomial test). A higher dose of L-dopa (200 mg kg-1) induced dyskinesia. L-dopa was found to cause a dose-dependent increase in the brain levels of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC, a major dopamine metabolite), as well as an increase in the DOPAC/dopamine ratio (an index of dopaminergic activity).