Can mice be trained to discriminate urine odor of conspecifics with melanoma before clinical symptoms appear

Abstract This study sought to determine whether mice can differentiate, through urine odors, conspecifics with melanoma in early stages, when no clinical signs are detectable, from healthy animals. Forty male mice of the B57BL6 strain were urine donors before and after orthotopic inoculation with melanoma cells. Another group (35 males and 31 females), divided into two sub-groups were either tested for spontaneous preference for urine odor from donors with melanoma against urine odor of healthy conspecifics, or underwent operant conditioning training to discriminate between the two kinds of urine samples. Open-field and Y-maze tests were used initially to assess any spontaneous preference for urine of either type of donor, and subsequently a Y-maze test was used in discrimination training. During 5- minute tests, it was recorded which sample the mouse approached first, the latency to the first sniffing, the frequency of approaching, and the total duration of sniffing of each urine sample. No significant spontaneous preference for urine samples from animals with melanoma or from healthy animals were observed. However, in the open-field test, the male mice in the first trial more frequently approached the melanoma sample (P