ROLES OF BRAIN MONOAMINE NEUROTRANSMITTERS IN AGONISTIC BEHAVIOR AND STRESS REACTIONS, WITH PARTICULAR REFERENCE TO FISH

1. Experimental results on the involvement of brain monoamines in agonistic behaviour and stress in fish are reviewed and discussed in relation to available data from other vertebrates. 2. In fish as well as mammals, stress induces increased brain serotonergic activity, and a similar increase in serotonergic activity is seen in subordinate individuals in a dominance hierarchy. 3. The brain serotonergic system appears to inhibit aggression and spontaneous locomotor activity in both fish and mammals. 4. Subordinate fish show several behavioural characteristics, notably inhibition of aggressive behaviour, low spontaneous locomotor activity and decreased food intake, that are likely to be related to their increased brain serotonergic activity. 5. By contrast, the brain dopaminergic system appears to stimulate aggressive behaviour in both fish and mammals, and dominant fish show signs of elevated dopaminergic activity in telencephalon. 6. The similarities between fish and mammalian monoaminergic functions suggest that these are phylogenetically very old mechanisms that have been conserved during the last 400 million years of vertebrate evolution.