Latent aggression-promoting properties of mouse bladder urine activated by heat

The aggression-promoting property of bladder urine in adult male mice was investigated. Under a newly developed stimulus application procedure (i.e., camel hairbrush applicator). Experiment 1 determined the minimal volume at which bladder and voided urine educed agonistic behavior in agressors. It was found that at least 0.05 ml of bladder urine and 0.03 ml of voided urine, both from intact males, were needed to induce significantly more attacks and uro-anal sniffs than respective urine types from castrated males. Also, bladder urine educed significantly less agonistic behavior than voided urine, both from intact males. Hence, the presence of a weak bladder urine chemosignal was confirmed. From these and previous findings, it was hypothesized that the chemocommunicative property of the weak bladder urine chemosignal could be accentuated by releasing the prochemosignal(s). Using 0.03 ml as the urine volume in Experiment 2, it was shown that heating bladder urine at 37 degrees C educed significantly more agonistic behavior than freezing bladder urine. The heating of bladder urine, however, effected significantly fewer attacks than the freezing of voided urine. It was concluded that bladder urine contains a latent and a free chemosignal, both of which are weak relative to voided urine chemosignal activity.