Corticosterone response to the plus-maze: High correlation with risk assessment in rats and mice

Exposure to the elevated plus-maze induces behavioural and physiological ef fects in rodents consistent with fear/anxiety. Maze-naive animals display h igh levels of risk assessment towards the open arms, and explore these area s less extensively than other parts of the maze while, immediately followin g the test, pain latencies, skin conductance levels, and plasma corticoster one titres (CORT) are significantly elevated. Although previous research ha s suggested a link between the plasma CORT response and open-arm exploratio n, significant elevations in CORT have also been found with restricted expo sure to the closed arms. The present study employed ethological measures in an attempt to further characterise the relationship between behavioural an d CORT responses to this widely used animal model of anxiety. Our results c onfirm that, relative to home-cage controls, 5-min exposure to the plus-maz e significantly increases plasma CORT levels in test-naive male Wistar rats and male Swiss-Webster mice. Furthermore, in both species, the CORT respon se was found to be highly correlated with measures of risk assessment (mice : r(s) = +0.87; rats: r(s) = +0.58), but not with measures of open-arm acti vity (entries, time), general locomotor activity, rearing, or head dipping. Findings are discussed in relation to the functional significance of risk assessment in potentially dangerous situations and the potential involvemen t of glucocorticoids in this process. (C) 1999 Elsevier Science Inc. All ri ghts reserved.