Behavioural and pharmacological characterisation of the canopy stretched attend posture test as a model of anxiety in mice and rats

The behavioural element, stretched attend posture (SAP), is an important component of the “risk-assessment” repertoire of defensive behaviour in rodents. The present experimental paradigm was devised as a novel and simple method of eliciting high levels of SAP in mice and rats. The SAP test apparatus comprised an elevated black Perspex circular platform. A smaller clear red Perspex circular “Canopy” was supported directly above the platform by a central pillar, thus dividing the platform into an inner, dimly lit covered zone and an outer, brightly lit exposed zone. In both the rat and mouse version of this model, vehicle-treated animals exhibited a marked preference for exploring the covered zone and also exhibited high baseline levels of SAP, particularly at the covered zone boundary whilst they investigated the exposed zone. In the mouse SAP test, the benzodiazepine receptor agonists, diazepam (0.5 mg/kg SC) and chlordiazepoxide (2 mg/kg SC), and the 5-HT1A receptor agonists, buspirone (1 and 3 mg/kg SC), ipsapirone (3 mg/kg SC) and 8-OH-DPAT (0.2 mg/kg SC), all significantly decreased the frequency of SAP without impairing motor activity. In the rat SAP test, diazepam (0.5 mg/kg SC) significantly decreased, whilst the anxiogenic 5-HT2C/1B receptor agonist, mCPP (0.25 and 0.5 mg/kg SC), significantly increased, the frequency of SAP. Ipsapirone (3 mg/kg SC) induced a non-specific behavioural inhibition. These data suggest that the “Canopy” SAP test is a useful paradigm to investigate risk assessment behaviour in both rats and mice, and may provide a sensitive novel rodent model of anxiety.