Anxiogenic properties of cocaine in the rat evaluated with the elevated plus-maze.

In previous work, we reported that cocaine (5, 10, and 20 mg/kg) failed to induce significant responses in naive rats in the elevated plus-maze test of anxiety. This study investigates the putative anxiogenic properties of cocaine in rats selected as "anxious" or "nonanxious" on the basis of their behavior in the plus-maze prior to drug treatment. In nonanxious rats, cocaine (10 mg/kg) increased the latency to the first entry into the open arms and reduced the number of entries into and time spent on the open arms. All these measures are indicative of an anxiogenic action of cocaine. In contrast, cocaine failed to modify the behavior of anxious rats. These findings demonstrate that rats with high exploratory activity in the plus-maze and regarded as nonanxious are more sensitive to cocaine's anxiogenic effects. Further, the present manipulation provides a useful procedure for investigating the anxiogenic effects of cocaine in rats.