Behavioral validation of the elevated T-maze, a new animal model of anxiety

The elevated T-maze test of anxiety has been used to separate in the same rat conditioned from unconditioned responses of fear/anxiety. The test apparatus consists of three elevated arms-one enclosed and two open. Inhibitory avoidance--representing learned fear--is measured by recording the time taken to leave the enclosed arm in three consecutive trials. Unconditioned fear is evaluated by recording the time to escape from the open arm. In this study we investigated procedural questions raised by the use of the elevated T-maze. Experiment 1 showed that restraining the animals at the end of the enclosed arm for 30 s did not change the first (baseline) latency to leave this arm, indicating that aversion for the hands of the experimenter is not a key motivation for this response. The results of Experiment 2 indicated that open-arm experience, but not handling stress is the main cause for inhibitory avoidance acquisition, because rats trained in a T-maze with the three arms enclosed did not show the usual increase in withdrawal latency along the three consecutive trials. The same experiment also showed that the latency to leave the open arm did not undergo habituation over five consecutive trials, evidencing an aversive motivation for this response. The importance of open-arm experience for inhibitory avoidance acquisition was further suggested by the results of Experiment 3, as the removal of a shield that prevents perception of openness tended to increase avoidance latency in the elevated T-maze from the first trial.