Palatable food induces an appetitive behaviour in satiated rats which can be inhibited by chronic stress.

An experimental model for the study of antidepressant treatments was devised by exploiting the response maintained by vanilla pellets in rats freely fed on a standard diet. The apparatus used was a Y-maze and the rats were trained, during 10-12 consecutive sessions, to earn a vanilla pellet placed at the end of the one of the two divergent arms. Animals exposed to repeated unavoidable stressors during the training phase did not develop the appetitive behaviour. Rats previously trained on the Y-maze, however, did not modify their performance under the effect of repeated stressors. Long-term treatment with imipramine and fluoxetine, given for 2 weeks before training and during the whole of the training phase, was able to antagonize the disrupting effect of chronic stress on the acquisition of the Y-maze. Finally, vanilla pellet consumption in trained animals induced a consistent increase in extraneuronal dopamine in the nucleus accumbens, as measured by microdialysis.