Effects of cage enrichment on territorial aggression and stress physiology in male laboratory mice

The activation of different neuroendocrine subsystems depends on the individual perception and coping with the challenging situation, the formulation of these relations by J.P. Henry represents a most useful concept also for the assessment of welfare consequences of particular caging variables. We investigated effects of cage enrichment on behaviour and neuroendocrine activations of male laboratory mice. Mice in enriched cages behaved more aggressive, lacked stable dominance hierarchies and exhibited neuroendocrine alterations depending on their individual social position. Subdominant passive mice were characterized by an augmented adrenal capacity to synthesize epinephrine despite low activities of the tyrosine hydroxylase. Dominant mice showed elevated circulating corticosterone concentrations despite high tyrosine hydroxylase-activities. Findings showed a dissociation of neurosympathetic and adrenomedullary components in subdominant passive mice and a simultaneous activation of sympathetic adrenomedullary and hypothalamo-adrenocortical components in dominant mice. Within the conceptual framework of the Henry model this would suggest different deteriorations of welfare in dominant and subdominant passive mice. In the situation of intensified aggression in the enriched cages the increased epinephrine synthesis in subdominant mice reflect their more frequent receipt of attacks and the elevated corticosterone secretion in dominant mice reflect their hindered ability to control the dominant position.