Endocrine status affects bladder size and postvoid residual urinary volume in mice Carla Mucignat-Caretta, * Michela Bondı `, and Antonio Caretta Dipartimento di Anatomia e Fisiologia Umana, Universita ` di Padova, Padova, Italy Received 2 July 2003; revised 24 November 2003; accepted 2 February 2004 Available online 4 May 2004 Abstract Urine is one of the major media for intraspecific chemical communication in mice. The urination pattern is dependent both on the mice’s hormonal and social status. The urination pattern and the morphology of the urinary tract were examined in mice following hormonal manipulations. In the first experiment, we compared pairs of intact and castrated males: intact males urinated earlier when exposed to a new environment, with a greater number of drops that were smaller than those of castrated males. In the second experiment, groups of intact males, castrated, testosterone-supplemented castrated, and isolated intact males were compared. The micturition pattern of isolated intact males consisted of numerous small droplets of urine, with a high volume of urine retained in the bladder after voiding. This also applied to grouped intact males and testosterone-treated castrated mice, while castrated mice voided a larger fraction of bladder content. Bladder weight was higher in intact males and testosterone-treated castrated males, as compared to castrated males. In the third experiment, ovary-intact and testosterone-treated intact females were compared. Testosterone-treated ovary-intact females retained a larger quantity of urine in the bladder and also had a larger bladder compared to ovary-intact females. Testosterone thus induces the morphological modifications of the urinary tract necessary for the dominant male urination pattern, which is an increase in postvoid urinary residual volume and bladder weight. As evidenced from the comparison of histological sections from intact, castrated, and testosterone-treated castrated males, the increase in bladder weight was mainly due to the bladder muscular mass. D 2004 Elsevier Inc. All rights reserved. Keywords: Testosterone; Bladder; Urination; Castration; Pheromones; Territory marking; Mice Introduction Urine is usually considered a waste product for human beings, but in many mammals, urine plays an essential role in social communication, especially among members of the same species. This implies the release of urinary chemicals that are later sensed by other animals. A familiar example is the endocrine-dependent urination pattern of dogs (Beach, 1974), which is related to territorial marking and arises peculiar social reactions in conspecifics. The role of urinary signals in social communication has been studied extensively in laboratory rodents. In mice (Mus musculus), urinary pheromones modulate aggressive reac- tions (Mugford and Nowell, 1970). Urine is used to mark territorial boundaries (Harrington, 1976; Jones and Nowell, 1973) and to signal the sex and social status of the emitter. It can also accelerate the sexual maturation of prepubertal females and affect their reproductive and social behavior (Cavaggioni and Mucignat-Caretta, 2000; Hurst et al., 2001; Keverne, 1983). The effects of urine depend on its chemical composition that is modified according to the endocrine and social condition of the emitter. For example, male mouse urine contains a variety of androgen-dependent molecules (Cavaggioni and Mucignat-Caretta, 2000; Schwende et al., 1986). Moreover, peculiar urination patterns are related to the social and hormonal status of the emitter. For example, dominant male mice mark a new territory immediately with numerous droplets of urine (Desjardins et al., 1973). There- fore, androgens appear to affect both the composition of the urine signaling the presence of a male, and the delivery pattern of the signaling molecules. There are at least three different conditions known to affect the pattern of release of urine and the morphology of 0018-506X/$ - see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2004.02.004 * Corresponding author. Dipartimento di Anatomia e Fisiologia Umana, Universita ` di Padova, Via Marzolo 3, I-35131, Padova, Italy. Fax: +39-049-8275301. E-mail address: carla.mucignat@unipd.it (C. Mucignat-Caretta). www.elsevier.com/locate/yhbeh Hormones and Behavior 46 (2004) 11 – 18