Attenuated response to nomifensine in rats during a swim test following lesion of the habenula complex.

Male Lister rats with bilateral lesions of the habenula nuclei were observed during two consecutive phases of a swim test. During the first phase of the test, when escape was not possible, lesioned animals demonstrated fewer changes of behaviour. Lesioned animals failed to utilise an introduced external cue and escape route in the second part of the test. Control rats treated with the antidepressant nomifensine showed few changes of behaviour during the inescapable phase of the test but an enhanced ability to escape. Nomifensine produced no improvement of escape behaviour in lesioned animals, suggesting that this behavioural effect of nomifensine in controls is dependent on the habenula relay. The data also suggest that more than one response in swim tests can serve as an index of depression.