Stress-induced changes in brain serotonergic activity, plasma cortisol andaggressive behavior in Arctic charr (Salvelinus alpinus) is counteracted by L-DOPA

Arctic charr (Salvelinus alpinus) were tested for aggressive behavior using intruder tests, before and after 2 days of dyadic social interaction. Foll owing social interaction, half of the dominant and half of the subordinate fish were given L-DOPA (10 mg/kg, orally), whereas the remaining dominant a nd subordinate fish were given vehicle. One hour following drug treatment, the fish were tested for aggressive behavior again in a third and final int ruder test, after which blood plasma and brain tissue were sampled for anal ysis of plasma cortisol concentrations and brain levels of monoamines and m onoamine metabolites. Subordinate fish showed a reduction in the number of attacks launched against the intruder, as well as an increase in attack lat ency, as compared to prior to dyadic social interactions. Social subordinat ion also resulted in an elevation of brain serotonergic activity. Fish rece iving L-DOPA prior to the final intruder test showed shorter attack latency than vehicle controls. Drug treatment was a stressful experience and vehic le controls showed elevated plasma cortisol levels and longer attack latenc y as compared to before treatment. L-DOPA-treated fish showed lower plasma levels of cortisol and lower serotonergic activity in certain brain areas t han vehicle controls. These results suggest that L-DOPA counteracts the str ess-induced inhibition of aggressive behavior, and at the same time inhibit s stress-induced effects on brain serotonergic activity and plasma cortisol concentrations. (C) 2001 Elsevier Science Inc. All rights reserved.