Gradient of alarm substance in the forced swimming test.

Three studies were conducted with rats to study the effects of a proposed alarm substance released during the forced swimming test. In the first study, rats were retested in water previously swum in but which had been subsequently diluted to varying degrees. When water was diluted by more than 25% the proposed alarm substance could no longer be detected. In the second study, rats were retested at various times after initial testing. This study showed that the alarm substance was still active by eight days after it had been initially released. The final study tested animals to see if the alarm substance could be depleted by repeated testing. Testing animals for more than an hour did not result in depletion of the alarm substance. These three studies suggest that the proposed alarm substance secreted by rats during the forced swimming test has considerable biological significance.