Abstract
Prior studies using mice have shown that scent marks are an important source of information and can cause behavioural changes in other individuals. Studies have also shown that scent marks in the environment can affect the outcome of social interactions between mice. We used conditioned place preference tests to investigate whether CD-1 male mice ( Mus musculus) are reinforced by olfactory cues from the home cage. Soiled bedding from the home cage was presented in the initially less preferred chamber of the apparatus to determine whether this association would reduce the unconditioned preference for one chamber over the other. We tested the effects of social rank and housing condition by comparing the performance of dyads that were polarised into dominant and subordinate relationships, both when paired and when separated, with mice that were isolated throughout. The development of conditioned place preference (CPP) supported by home cage odours was influenced by social rank but not by housing condition. Only subordinate mice showed CPP to home cage odours, and this effect was seen irrespective of whether they were housed with a dominant cage mate or alone. Neither dominant (paired or separated) nor isolated mice showed any change in their preference for the chamber associated with home cage odours. This suggests that the smell of home is a more powerful reinforcer for subordinate mice in that it can produce contextual conditioning to the environment in which it is experienced.
Highlights
Laboratory rodents spend a large amount of time in their home cage environment
For the number of defensive behaviours, there was no effect of social status or housing condition and no interaction between these factors (maximum F(1,20) = 1.957)
The development of conditioned place preference (CPP) supported by home cage odours was influenced by social rank but not by housing condition
Summary
Laboratory rodents spend a large amount of time in their home cage environment. How do they like it? It is known that the home cage can act as an effective reinforcer for mice tested in a radial maze procedure [45]. Intruder males are less likely to attack a male whose odours match the surrounding substrate odours, and more likely to attack males whose odours do not match those on the surrounding substrate [16,18] This has implications for best husbandry practice: laboratory cage cleaning can cause an increase in aggression between group-housed mice, presumably because it disrupts the odour cues within the cage [20,64]. The conditioned place preference (CPP) paradigm provides a convenient test of how cues can come to support contextual conditioning This was originally developed to investigate the rewarding or aversive nature of drugs: the context in which the drug is experienced becomes secondarily rewarding or aversive and the animal chooses to spend time there or elsewhere. Comparison between dominant and subordinate males that have been separated and re-housed as singletons with those that remain paired will tell us how long lasting any effects of social status may be [13]
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