Short-term effects of fights for social dominance and the establishment ofdominant-subordinate relationships on brain monoamines and cortisol in rainbow trout

We report changes in brain serotonergic, noradrenergic and dopaminergic act ivity, along with plasma cortisol concentrations, occurring during the init ial 24-h period following the establishment of dominant-subordinate relatio nships in pairs of rainbow trout. Immediately (within 5 min) after the term ination of staged fights for social dominance, a large increase in blood pl asma cortisol was observed in both fight losers (future subordinate fish) a nd winners (future dominant fish), In dominant fish, cortisol decreased rap idly (within 3 h) to the level of unstressed controls, while continuing to increase in subordinate fish. At 3 h following fights, the brain serotonerg ic system was activated in both dominant fish and subordinate fish, at leas t in some brain regions (telencephalon), This effect was reversed in domina nt individuals within 24 h of social interaction, whereas in subordinate fi sh a substantial activation of the serotonergic system was manifest in all brain regions by 24 h. Similarly, a strong increase in brain catecholaminer gic activation was indicated after 24 h of social interaction in subordinat e fish, but not in dominant fish. Relationships between plasma cortisol and brain serotonergic and noradrenergic activity in the various experimental groups suggest that these systems influence cortisol secretion under normal conditions and during moderate or shortterm stress. Copyright (C) 2000 S. Karger AG, Basel.