CATECHOLAMINERGIC INVOLVEMENT IN THE CONTROL OF AGGRESSION - HORMONES, THE PERIPHERAL SYMPATHETIC, AND CENTRAL NORADRENERGIC SYSTEMS

Noradrenaline is involved in many different functions, which all are k nown to affect behaviour profoundly. In the present review we argue th at noradrenaline affects aggression on three different levels: the hor monal level, the sympathetic autonomous nervous system, and the centra l nervous system (CNS), in different, but functionally synergistic way s. Part of these effects may arise in indirect ways that are by no mea ns specific to aggressive behaviour, however, they are functionally re levant to it. Other effects may affect brain mechanisms specifically i nvolved in aggression. Hormonal catecholamines (adrenaline and noradre naline) appear to be involved in metabolic preparations for the prospe ctive fight; the sympathetic system ensures appropriate cardiovascular reaction, while the CNS noradrenergic system prepares the animal for the prospective fight. Indirect CNS effects include: the shift of atte ntion towards socially relevant stimuli; the enhancement of olfaction (a major source of information in rodents); the decrease in pain sensi tivity; and the enhancement of memory (an aggressive encounter is very relevant for the future of the animal). Concerning more agression-spe cific effects one may notice that a slight activation of the central n oradrenergic system stimulates aggression, while a strong activation d ecreases fight readiness. This biphasic effect may allow the animal to engage or to avoid the conflict, depending on the strength of social challenge. A hypothesis is presented regarding the relevance of differ ent adrenoceptors in controlling aggression. It appears that neurons b earing postsynaptic alpha(2)-adrenoceptors are responsible for the sta rt and maintenance of aggression, while a situation-dependent fine-tun ing is realised through neurons equipped with beta-adrenoceptors. The latter phenomenon may be dependent on a noradrenaline-induced corticos terone secretion. It appears that by activating very different mechani sms the systems working with adrenaline and/or noradrenaline prepare t he animal in a very complex way to answer the demands imposed by, and to endure the effects caused by, fights. It is a challenge for future research to elucidate how precisely these mechanisms interact to contr ibute to functionally relevant and adaptive aggressive behaviour. (C) 1998 Elsevier Science Ltd. All rights reserved.