Scent marking behavior as an odorant communication in mice

Abstract

In rodents, where chemical signals play a particularly important role in determining intraspecies interactions including social dominance and intersexual relationships, various studies have shown that behavior is sensitive to conspecific odor cues. Mice use urinary scent marks for communication with individual conspecifics in many social contexts. Urinary scent involves genetic information about individuals such as species, sex, and individual identity as well as metabolic information such as social dominance, and reproductive and health status, which are mediated by chemical proteins in scent marks including the major histocompatibility complex and the major urinary proteins. The odor of the predator which can be considered to be a threatening signal for the prey also modulate mouse behavior in which scent marking is suppressed in response to the cat odor exposure in mice. These odorant chemicals are detected and recognized through two olfactory bulbs, the role of which in detection of chemosignals with biological relevant appears to be differential, but partly overlapped. Mice deposit scent marks toward conspecifics to maintain their social relationships, and inhibit scent marking in a context where natural predator, cat odor is contained. This suppression of scent marking is long-lasting (for at least 7 days) and context-dependent, while the odorant signaling to conspecifics tends to appear frequently (over 24h but less than 7 days intervals) depending on the familiarity of each signal-recipient. It has been discussed that scent marking is a communicative behavior associated with territoriality toward conspecifics, indicating that the social signaling within species are sensitive to predator odor cues in terms of vulnerability to predation risk.

Fig. 1

Scent marks of C57 male mice fixed and colored by ninhydrin spray. A C57 male was introduced into a rectangular cage which was placed upside-down on a rough newsprint paper for 20 minute. Following removal of the mouse, the ethanol with ninhydrin was sprayed on the paper sheet and the sheet was left to be dried for 24 hours in room temperature. A large round shaped urine spot on an upper left portion of the sheet was counted as a urine pool.

Fig. 2

Number of squares with scent marks of C57 males which were confronted with the same, initially novel, CD-1 male during the first 4 trials, and then on 5^th trial, exposed to the same CD-1 male (same male) or a different, novel CD-1 male (different male). The inter-trial interval was 24 hrs on the first 4 trials, and on 5^th trial 24 hrs (upper panel) or 7 days (bottom panel). Data are expressed as mean ± S.E.M. Significant post hoc differences between groups; *p<.05, and between trials compared to trial 4, #p<.05..

Fig. 3

Number of squares with scent marks of male C57 mice. On day 1, they were placed into the test chamber with a wire mesh partition, on the opposite side of which a towel block without odor (CONTROL), or with cat fur/skin odor (TEST ODOR) was placed. A third group was exposed to cat odor in their home cage prior to the test (HOMECAGE ODOR). Twenty-four hours (D2) and 7 days later (D8), they were replaced into the identical chamber and confronted with a towel block without cat odor. On day 9 they were placed into a differently shaped (triangular) chamber with a towel block without cat odor on the opposite side of a wire mesh partition. Data are expressed as mean ± S.E.M. Significant post hoc differences between groups compared to CONTROL; *p<.05

Fig. 4

Behaviors of C57 males in the test chamber on D1 when confronted with a towel block containing cat fur/skin odor (TEST ODOR) or no odor (CONTROL), or exposed to cat odor in their home cage prior to the test (HOMECAGE ODOR). a) Location: Time in each location (Contact; contacted with wire mesh; near; or far from the towel block side). b) Locomotion: Number of crossings of the lines on the chamber floor. c) Behaviors: Sniffing or poking at the wire mesh; climbing on the wire mesh; grooming; or risk assessment ratio -- duration of sniffing or nose poking per contact period with the wire mesh. Data are expressed as mean ± S.E.M. Significant post hoc differences between groups compared to CONTROL; *p<.05.