Effects of chronic forced swimming and exposure to alarm substance: physiological and behavioral consequences.

Rats tested for 7 consecutive days in the forced swim test in fresh water were more immobile than those tested in soiled water on all days. Animals in both water conditions increased their immobility times slightly over days, but animals tested in soiled water, which presumably contained an alarm substance, never attained the immobility times of those tested in fresh water. When animals were switched between fresh and soiled water, they behaved exactly like animals in the water condition to which they were switched. Prior inescapable forced swimming in either water condition affected subsequent escape in a Morris water maze, but more so for animals tested only in fresh water. A second study corroborated the escape results. Serum corticosterone and relative adrenal weights were increased as a result of forced swimming but escape performance differences could not be attributed to differences in the stress-provoking consequences of the two water conditions.