An exploration of the postural, location- and social contact- related sub-characteristics of inactive but awake behaviour as a depression-like indicator in mice.

Inactive behaviour is essential to life. However, specific forms of inactivity may be indicative of compromised welfare in certain captive conditions. Inactive but awake behaviour (IBA - spontaneous, motionless awake behaviour without interacting with the surroundings) has been documented in some species and may be associated with poor welfare and negatively valenced affective states. In our previous work in laboratory mice, we have identified environmental risk factors (non-enriched housing) and curative factors (antidepressant drug Venlafaxine) for IBA and we hypothesise that greater levels of IBA may represent a depression-like state in this species. Here we aimed to identify which specific sub-characteristics of IBA would show construct validity as a depression-like state by exploring the posture (i.e. lying, curled lying or sitting), social contact position (i.e. in physical contact with a cage mate or not) and location of mice while performing the behaviour during two experiments (respectively investigating the aetiology and the curative factors of IBA). In both experiments we expected that more IBA would be displayed in standard (non-enriched) laboratory cages, compared with large highly-enriched cages and that a move from a highly-enriched to a non-enriched cage would increase IBA, while the opposite treatment would result in a decrease. In our second experiment (curative factors investigation), we predicted that less IBA would be displayed by mice that voluntarily ingested an antidepressant (Venlafaxine)