Vomeronasal mechanisms of mate recognition in mice.

The ability of animals to distinguish individual con-specifics influences many aspects of their behaviour, including choice of mate, territorial marking and mother-offspring interactions. In rodents, information about individuality is conveyed by chemical cues in their urine and body secretions. Hence, mice can be trained to discriminate the urine odour of congenic mice that differ only in genes of their major histocompatibility complex (MHC). This ability is likely to be based on MHC-related differences in the profile of urinary volatiles (Singer et al., 1997), which are sensed by the main olfactory system and generate statistically different patterns of activity across large populations of neurons in the main olfactory bulb (Schaefer et al., 2002). In contrast, individual recognition underlying urine countermarking behaviour of male mice depends on the profile of major urinary proteins rather than MHC type (Hurst et al., 2001), suggesting that mice use different chemosignals for signalling individual identity in different behavioural contexts. Furthermore, information about the individual identity of mice can be conveyed by both the main olfactory and vomeronasal systems. Whereas the main olfactory system is adapted to learn and discriminate small differences in the profile of airborne volatiles, the vomeronasal system responds to a more limited range of non-volatile stimuli taken up following direct contact. Moreover, the representation of individual identity in vomeronasal system appears to differ from that in the main olfactory system, as individual neurons in the accessory olfactory bulb (AOB), respond highly selectively to the strain identity of anaesthetized conspecifics (Luo et al., 2003).