SYMPATHETIC MEDIATION OF STRESS AND AGGRESSIVE COMPETITION - PLASMA-CATECHOLAMINES IN FREE-LIVING MALE TREE LIZARDS

The sympathetic nervous system and adrenal catecholaminergic tissue ac t to prepare an animal for ''fight or flight'' by release of catechola mines into synapses and plasma. However, few studies have measured pla sma catecholamines in nonmammalian vertebrates and none have measured them in free-living animals. We report plasma levels of norepinephrine (NE), epinephrine (EPI) and dopamine (DA) in free-living tree Lizards (Urosaurus ornatus) bled in the field: 1) immediately after capture, 2) after 10 minutes of restraint, 3) immediately after a staged territ orial encounter and 4) four minutes after the end of a staged territor ial encounter. Time to capture and time to bleed after capture were al so recorded for each sample. Time to capture had little effect on plas ma catecholamines suggesting that plasma catecholamines do not rise du ring the brief pursuit by the investigator necessary to capture the li zards in the field. In contrast, plasma NE and EPI increased during bl ood collection. However, this response was very consistent allowing co mparisons to be made using analysis of covariance to control for time to bleed. Results indicate that restraint stress caused a large increa se in plasma levels of NE, E and DA. Plasma levers of NE and E, but no t plasma DA, were also significantly elevated both immediately and 4 m inutes after aggressive encounters, although less so than following re straint stress. These studies show that stress and aggression activate the sympatho-adrenal system. This activation could be involved in beh avioral changes during aggression, meeting metabolic demands of the en counter, or both. (C) 1997 Elsevier Science Inc.