EFFECTS OF CAGE ENRICHMENT ON TERRITORIAL AGGRESSION AND STRESS PHYSIOLOGY IN MALE LABORATORY MICE

The activation of different neuroendocrine subsystems depends on the i ndividual perception and coping with the challenging situation. the fo rmulation of these relations by J.P. Henry represents a most useful co ncept also for the assessment of welfare consequences of particular ca ging variables. We investigated effects of cage enrichment on behaviou r and neuroendocrine activations of male laboratory mice. Mice in enri ched cages behaved more aggresive, lacked stable dominance hierarchies and exhibited neuroendocrine alterations depending on their individua l social position. Subdominant passive mice were characterized by an a ugmented adrenal capacity to synthesize epinephrine despite low activi ties of the tyrosine hydroxylase. Dominant mice showed elevated circul ating corticosterone concentrations despite high tyrosine hydroxylase- activities. Findings showed a dissociation of neurosympathetic and adr enomedullary components in subdominant passive mice and a simultaneous activation of sympathetic adrenomedullary and hypothalamo-adrenocorit cal components in dominant mice. Within the conceptual framework of th e Henry model this would suggest different deteriorations of welfare i n dominant and subdominant passive mice. In the situation of intensifi ed aggression in the enriched cages the increased epinephrine synthesi s in subdominant mice relfect their more frequent receipt of attacks a nd the elevated corticosterone secretion in dominant mice reflect thei r hindered ability to control the dominant position.