Age and isolation influence steroids release and chemical signaling in male mice.

Social interactions in mice involve olfactory signals, which convey information about the emitter. In turn, the mouse social and physiological status may modify the release of chemical cues. In this study, the influences of age and social isolation on the endocrine response and the release of chemical signals were investigated in male CD1 mice, allocated into four groups: Young Isolated (from weaning till 60 days; N = 6), Adult Isolated (till 180 days; N = 6), Young Grouped (6 mice/cage; till 60 days; N = 18), Adult Grouped (6 mice/cage; till 180 days; N = 18). Mice were transferred in a clean cage to observe the micturition pattern and then sacrificed. Body and organs weights, serum testosterone, dehydroepiandros- terone, corticosterone and the ratio Major Urinary Protein/creatinine were measured. Urinary volatile molecules potentially involved in pheromonal communication were identified. Androgen secretion was greater in isolated mice (P < 0.05), suggesting a greater reactivity of the Hypothalamic–Pituitary–Gonadal axis. Grouped mice presented a higher degree of adrenal activity, and young mice showed a higher serum corticosterone (P < 0.05) suggesting a greater stimulation of the Hypothalamic–Pituitary–Adrenal axis. The micturition pattern typical of dominant male, consisting in voiding numerous droplets, was observed in Young Isolated mice only, which showed a higher protein/creatinine ratio (P < 0.05). Urinary 2-s-butyl- thiazoline was higher in both Young and Adult Isolated mice (P < 0.005). Young Isolated mice showed the most prominent difference in both micturition pattern and potentially active substance emission, while long term isolation resulted in a less extreme phenotype; therefore social isolation had a higher impact on young mice hormone and pheromone release.