BRAIN MONOAMINE LEVELS AND ENERGY STATUS IN COMMON CARP (CYPRINUS-CARPIO) AFTER EXPOSURE TO SUBLETHAL LEVELS OF COPPER

Serotonin (5-hydroxytryptamine, 5-HT) and dopamine (DA) are two major monoamine neurotransmitters with a multitude of functions in the vertebrate brain. In fish, the 5-HT system has been shown to be sensitive to various forms of stress, but very few studies have examined the effects of toxic metals on these monoamine systems. Juvenile common carp were exposed to copper levels of 0.22, 0.34 and 0.84 mu M during 1 week. In telencephalon, dose-dependent falls in 5-HT and DA levels were observed, with approximately 50% losses of these neurotransmitters at the highest copper concentration. Although less dramatic, falls were also seen in 5-HT and DA levels in hypothalamus and brain stem. No changes in 5-hydroxyindoleacetic acid (5-HIAA, the main 5-HT metabolite), AMP, ADP, ATP, adenylate energy charge or lactate levels were observed in brain. However, lactate levels in blood plasma increased with copper concentration. A significant copper accumulation only occurred in the liver, while no changes in brain or muscle were seen. It is concluded that copper exposure of common carp causes decreased brain 5-HT and DA levels, two neurotransmitters involved in, for example, feeding behaviour and locomotor control in fish. In fact, in telencephalon a fall in 5-HT levels was seen already at a copper concentration below that where food intake and movement were impaired.