Long-term stress-induced changes in brain monoamines of the gray snapper, Lutjanus griseus. Neurotransmitters as indicators of physiological stress

It is well established that altered neurotransmitter levels have long been associated with stress in many mammals. The purpose of this study was to determine if changes in the brain tissue concentration and/or turnover rates of the monoamine neurotransmitters could be used as an early indicator of physiological stress for fish in different aquatic ecosystems. Gray snapper, Lutjanus griseus, were collected from two sites, a pristine (control) and a polluted (experimental) site, classification based upon the hydrocarbon content of their sediment. The brains were quickly removed and dissected into three regions: frontal lobes, hypothalamus, and brain stem which were later analyzed for using high performance liquid chromatography. A decrease in brain tissue norepinephrine and dopamine concentration in the frontal lobes and hypothalamus was observed in individuals collected from the polluted site. No significant difference in either norepinephrine or dopamine concentration was present in the brain stem. Despite a decrease in dopamine levels, there was no significant change in dopamine turnover. There was a significant decrease in serotonin concentration in the hypothalamus at the polluted site. There was an increase in serotonergic activity in the hypothalamus and brain stem at the polluted site. A significant decrease in the weight of the hypothalamus in fish from the polluted site was also observed. These results suggest that a change in brain monoamines can be used as a early indicators of chronic environmental stress.