Brain monoaminergic activity in rainbow trout selected for high and low stress responsiveness

This paper investigates whether two lines of rainbow trout displaying genet ically determined variation in stress responsiveness and behavior also show differences in brain monoaminergic activity. In several brain regions, str ains of rainbow trout selected for consistently high or low post-stress cor tisol levels displayed differences in tissue concentrations of monoamines a nd/or monoamine metabolites, or in metabolite/monoamine ratios. High-respon sive trout reacted to stress by an increase in the concentrations of both s erotonin (brain stem), dopamine (brain stem), and norepinephrine (optic tec tum, telencephalon), whereas low-responsive fish did not. Brain stem and op tic tectum concentrations of monoamine metabolites were also elevated after stress in high responders, but not in low-responsive fish. The simultaneou s increase in the concentration of monoamines and their metabolites suggest s that both synthesis and metabolism of these transmitters were elevated af ter stress in high-responsive trout. A divergent pattern was seen in the hy pothalamus, where low-responsive fish displayed elevated levels of 5-hydrox yindoleacetic acid (a serotonin metabolite) and 3-methoxy-4-hydroxyphenylgl ycol (a norepinephrine metabolite). In the telencephalon, both populations had elevated concentrations of these metabolites after stress. These result s clearly suggest that selection for stress responsiveness in rainbow trout is also associated with changes in the function of brain monoaminergic sys tems. The possible functional significance of these observations is discuss ed with respect to the physiological and behavioral profile of these strain s of fish. Literature is reviewed showing that several factors affecting br ain monoaminergic activity might be altered by selection for stress respons iveness, or alternatively be under direct influence of circulating glucocor ticoids. Copyright (C) 2001 S. Karger AG, Basel.