Abstract
Barnard, C. J., J. M. Behnke, A. R. Gage, H. Brown and P. R. Smithurst. Modulation of behaviour and testosterone concentration in immunodepressed male laboratory mice (Mus musculus). Physiol Behav 61(6) 907–917, 1997.—Recent ideas suggest that current immunocompetence may act as a constraint on behavioural and physiological decisions, where these risk imposing an additional burden on immune function. We tested this in the context of time budgeting and the secretion of the potentially immunodepressive hormones testosterone and corticosterone, by treating adult male CFLP laboratory mice with antithymocyte serum (ATS) to depress thymus-mediated immune function. In comparison with males given a naive rabbit serum (NRS) vehicle control, ATS-treated mice showed a reduction in serum testosterone concentration, aggressive behaviour, and general activity, and maintained time spent sleeping, relative to pretreatment levels. Behaviours that differed between treatments correlated with measures of immunodepression (reduction in relative thymus weight or serum total IgG concentration), but relationships with behavioural changes were independent of those with testosterone. There was little evidence that changes were affected by social status. The results are discussed in the context of the adaptive modulation of immune function and physiological and behavioural decision-making.
Highlights
RECENT discussions have suggested that immune function has an important influence on physiological and behavioural decision-making [e.g., (6,14,26,32,35)]
In a series of experiments with male laboratory mice of the CFLP strain, we have shown that aggressive behaviour and serum hormone and total IgG [a bystander measure of immunocompetence (4–6)] concentrations covary in ways that are consistent with the adaptive modulation hypothesis and influence resistance to an experimental infection of the piroplasmid protozoan Babesia microti (3– 6,32)
All analyses relating to social status were based on high- and lowrank categories and data for those of low rank were averaged within cages to control for potential problems of nonindependence (4,5)
Summary
RECENT discussions have suggested that immune function has an important influence on physiological and behavioural decision-making [e.g., (6,14,26,32,35)]. A consistent finding in our previous work has been that, increased aggressive behaviour and testosterone concentration were both associated with reduced immunocompetence and resistance to B. microti, they were not themselves significantly correlated (5,6,32) This suggests that hormonal and behavioural changes may provide independent avenues of response to variation in immune status, rather than behaviour reflecting changes in underlying hormonal causal mechanisms [e.g., (36)]. In potentially lowering all circulating T cells in the host, ATS treatment was preferred to treatment with monoclonal antibodies that would have required the administration of 2 reagents (antiCD4 and antiCD8) and suitable controls to achieve the same end In this experiment, we compared changes in behaviour and serum testosterone and corticosterone concentrations in mice treated with rabbit (Oryctolagus cuniculus ) antimouse thymocyte serum with that of mice treated with serum from naive rabbits (NRS). We might expect an increase in social investigation, because a reduction in aggression may destabilize aggressive social relationships and lead to an increase in information-seeking [e.g., (17,18)]
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