Characteristics of coping behavior of rats exposed to a long-term hardly escapable aversive stimulus: a possible...

The purpose of the present study was to induce a state of depression including both the elements of behavioral despair and chronic stress. Therefore, this study was performed under the hypothesis that a long-term exposure of rats to the experimental situation of difficult to escape from foot-shock in a Skinner box might produce animals with a state of depression containing both the elements. Male Wistar strain rats were trained to press a lever to escape from foot-shock under a fixed ratio (FR) schedule. After the training, rats were exposed daily to a schedule consisting of 20 trials (the early 10 trials, FR 5; the later 10 trials, FR 20) once a day. The exposure resulted in reduction of the number of lever presses and successful escape in FR 20. Only the animals whose number of escapes, reduced to under 20% in FR 20 were treated with psychotropic drugs once a day for 4 days. The results showed that the reduced number of escapes was most improved by antidepressants (imipramine or mianserin), but not by haloperidol and methamphetamine. Although subchronic treatment with chlordiazepoxide partially recovered the reduced escape, the efficiency of lever pressing to escape from foot-shock was lower than that with the antidepressants. The results of the present study suggest that the behavioral suppression observed in this study might include characteristics similar to a state of depression.