Resistance of baseline activity in the elevated plus-maze to exogenous influences

Factors which may influence the exploratory behaviour of male Sprague-Dawley rats in the elevated plus-maze were investigated in two series of experiments. The first dealt with factors related to the test apparatus: light level, spatial configuration and height of the maze. The second dealt with factors intended to modify the internal state of the animals by an acute stressful treatment: partial immersion in water, forced immobilization for 10 or 20min, electric shock or 20min preexposure to open or closed arms. Chlordiazepoxide, 5mg/kg i.p., was administered as the reference drug and significantly increased the exploration of the open arms in all but one of the experiments. In saline-treated animals, no effects of the environmental or behavioural treatments were detected. This resistance to exogenous manipulations suggests that "plus-maze-anxiety" should be considered as a situational-bound response, i.e. characteristic of rodents placed in this particular situation.