Monoaminergic activities of limbic regions are elevated during aggression:Influence of sympathetic social signaling

A visual social signal inhibiting aggression is coincident with limiting se rotonergic and noradrenergic activity in subiculum, hippocampus, nucleus ac cumbens, medial amygdala, but not lateral amygdala, septum, and hypothalamu s. Darkening of postorbital skin in the lizard Anolis carolinensis is stimu lated by sympathetic activation of beta(2)-adrenergic receptors via adrenal catecholamines, and occurs more rapidly in dominant males during social in teraction. Eyespot darkening functions as a social signal limiting aggressi ve interaction. To assess the effect of this social signal on telencephalic activity of monoamines, males were painted postorbitally with green or bla ck paint, and exposed to a mirror. Serotonergic and noradrenergic turnover, as estimated by ratios of catabolite to transmitter, were elevated in the subiculum, hippocampus, nucleus accumbens, and medial amygdala of animals i n which the eyespots were masked by green paint. Conversely, dopaminergic a ctivity in these brain regions was lower in males with hidden eyespots (pai nted green). Hiding the eyespot evoked significantly increased aggressive a ctivity toward the mirror image. Furthermore, changes in monoaminergic turn over were coincident with altered aggressive behavior, suggesting a relatio nship between them. Changes of monoaminergic activity were not observed in the septum, lateral amygdala, or hypothalamus, when males with eyespots per manently marked (black) were compared with those with eyespots hidden (pain ted green). Stimulated (serotonergic and noradrenergic) or inhibited (dopam inergic) activity due to social signal and aggression are confined to regio ns of the brain similarly activated during social stress, and do not consti tute a generalized activation of monoaminergic systems. (C) 2000 Elsevier S cience B.V. All rights reserved.