Social and hormonal status influence the emission of urinary molecules in the mouse

In male mice, several behavioural traits and physiological characteristics were in the past attributed to social and/or hormonal status. Analysis of the literature showed that most of these reported associations were obtained in studies that compared male mice with castrated mice, assuming the latter as a model for non-dominant, submissive mice. We aimed at obtaining a more precise correlation, by analyzing in adult male mice (Mus musculus) their dominance behaviour, hormonal levels and quantity of molecules emitted with urine, potentially involved in pheromonal communication. Mice were kept either isolated (n=6) or 6 per cage (n=18) since weaning. At 2 months of age, the grouped mice were tested for dominance within each cage. The day after, all mice were put singly in a small cage. Their first micturition was collected, the number of urine drops and fecal pellet released were counted. Immediately afterwards, mice were sacrificed, their blood and urine residual volume collected and frozen. The internal organs were weighed. GC/MS and GC/FID were performed on urine to identify and quantify volatile molecules. Major Urinary Protein (MUP) and creatinine were quantified spectrophotometrically in urine. In plasma, testosterone, dehydroepiandrosterone and corticosterone were detected by radioimmunoassay. Isolated mice voided a lower volume of urine, with a higher number of urine droplets. The spleen and adrenal glands were smaller in isolated mice, that also had a larger thymus. No difference was present in the other organs, in the corticosterone levels and in creatinine. Testosterone levels tended to be higher in isolated and were positively correlated with MUP, 2-sec-butyl-4,5-dihydrothiazole and brevicomin excreted in urine. 2-sec-butyl-4,5-dihydrothiazole and 4-ethylphenol were significantly more in the urine of isolated males. Isolated mice showed a peculiar micturition pattern, with a great number of small drops, possibly intended to mark the territory, while grouped mice voided a larger volume in a single spot. While behavioural data on dominance were variably related to hormonal levels, several molecules involved in pheromonal communication showed a positive correlation with testosterone levels. This work was supported by the University of Padova