What Can A Rat's "Behavioral Despair" Tell You?

If someone tells you that they researched your antidepressant by performing a "TST" you might be impressed, but you shouldn't be. You should just know that the researchers who tested it were skilled at dodging rat teeth.

A "tail suspension test" is exactly what its title implies. Researchers lift a rat by the tail for a few minutes at a time, just to see what it does. The test is meant to discovers what animals do under "stress." It's also meant to test antidepressants. Under normal circumstances, a rat suspended by its tail for about six minutes will spend a certain amount of time try to climb up nearby walls or up its own tail to get out of the situation. After a while, it will just hang there, having given up.

Antidepressants have been found to increase the "try to escape" to "given up," ratio, so a common early test for antidepressants is holding rats by tails, stuffing them with antidepressants, and then holding them by their tails again. That's an unpleasant picture, but even worse are the "forced swim tests." Put a rat in a smooth-walled cylinder partially filled with water and it will scrabble to escape, or at least swim. After a while it will become "immobile." The rats are taken out of the cylinder after about 15 minutes, and given a 24-hour break before they're chucked back in for another test. Just to give a picture of what the forced swim test was measuring, it used to be called the "behavioral despair test." On antidepressants, rats generally swim more and despairingly float less.

Some people question whether this is actually a decent test of antidepressants. Many argue that what the swim and suspension tests are testing isn't despair but the ability to learn and assess a given situation — even if what the rats are learning is helplessness. A rat might opt to conserve its energy until the giant gets there, rather than desperately swimming and scrabbling at blank walls. If antidepressants change that behavior, might it be a sign that they block learning behavior, or increase restlessness, rather than stop despair?

Image: Janet Stephens.

[Via Rodent models for depression, The tail suspension test]