THE ELEVATED T-MAZE - A NEW ANIMAL-MODEL OF ANXIETY AND MEMORY

In an attempt to analyze different types of anxiety, and at the same time assess memory, a new experimental model was developed. The apparatus, named the elevated T-maze, consisted of three arms of equal dimensions (50 x 10 cm) elevated 50 cm from the ground. One arm, enclosed by 40-cm high walls, was perpendicular to two open arms. The first experimental session was conducted 25 min after IP injection of either drug or saline. To assess inhibitory (passive) avoidance, the rat was placed at the end of the enclosed arm and the time taken to withdraw from this arm was recorded three times in succession. Soon afterwards, the rat was placed at the end of one of the open arms and the time taken to withdraw from this arm was measured, thus estimating one-way escape. To assess memory, inhibitory avoidance and escape were measured again 3 days later, without drug. Dose-response curves were determined for the benzodiazepine anxiolytic and amnestic agent diazepam (DZP, 0.5-4 mg/kg), as well as for ipsapirone (IPS, 0.25-2 mg/kg), an azapirone anxiolytic that is devoid of clinically significant amnestic effects. The doses of 1, 2, and 4 mg/kg DZP and of 1 and 2 mg/kg IPS impaired inhibitory avoidance, an effect that may be viewed as anxiolytic. Inhibitory avoidance remained impaired 3 days later in the rats treated with 1-4 mg/kg DZP, indicating anterograde amnesia. This effect was not due to state-dependent learning, because rats injected both at pretraining and pretesting with 2 mg/kg DZP still showed complete amnesia. In contrast, the doses of 1 and 2 mg/kg IPS did not significantly affect memory, indicating a dissociation between the drug effects on anxiety and memory. Neither the performance of escape nor its memory was affected by DZP or IPS. Therefore, the two aversive tasks studied are likely to generate distinct types of fear/anxiety and memory, which may correlate with different classes of psychiatric disorders. The present results also warrant further exploration of the elevated T-maze as a potential model for the combined study of anxiety and memory.