The possibility of the presence of inter-individual emotional differences and the memory performance of rats was examined in the elevated T-maze. Two kinds of aversively motivated behaviors, inhibitory avoidance and escape learning, were measured. Based on the number of trials to achieve a learning criterion, rats were divided into two subgroups with either low or high avoidance reactivity (LAR or HAR, respectively). Retention test avoidance latencies showed that HAR animals had better avoidance memory (Mann-Whitney rank sum test, P = 0.0035). No such differences were found for the escape component of this test. These data suggest that individual emotional differences affect inhibitory avoidance performance, which may help to explain the dispersion of the data observed in other studies using this paradigm.
Key words· Elevated T-maze · High and low avoidance rats · Anxiety · Emotional reactivity A large number of studies have described strains of rats selected on the basis of their emotional reactivity and conditionability. In general, these strains are the outcome of bidirectional selection for emotionality differences determined by open-field defecation and ambulation scores, as well as the speed of acquisition and retention of a conditioned avoidance response measured in an escapeavoidance conditioning apparatus. Examples are the Maudsley rats (1), Roman rats (2), Naples rats (3), Syracuse and Australian rats (4), and some selections of Sprague-Dawley rats (5).Recently, Graeff and co-workers (6-8) described the elevated T-maze test as a new method for investigating emotionally related behaviors and processes underlying learning. The apparatus is composed of two open arms arranged at right angles to one enclosed arm, elevated above the ground. The maze permits the measurement of two kinds of aversively motivated behaviors, namely, inhibitory avoidance (time the animal takes to leave the enclosed arm) and one-way escape (time taken to leave the open arm). This experimental model allows the parallel measurement of responses related to both innate and learned fear in the same subject, and permits the simultaneous assessment of memory for these behaviors. The elevated Tmaze has been shown to be sensitive to the effects of anxiolytic and memory-modulating drugs such as diazepam, the 5-HT 1A ligand ipsapirone (6,7,9) and the 5-HT 3 receptor antagonist BRL 46470A (10). Moreover, the results of these studies suggest that the two tasks measured in the T-maze test (inhibitory avoidance -conditioned component, and oneway escape -unconditioned component) generate distinct types of fear and memory that could be related to different kinds of psychiatric disorders and thus be differently affected by distinct drugs. Although the results of these studies are promising, an examination of the data for the conditioned component indicates a wide dispersion of measured values. This dispersion is not likely to be due to animal manipulation by the experimenter. In a recent study we observed a similar dispersion in rats teste...