Exploratory behaviour and grooming after repeated restraint and chronic mild stress: effect of desipramine

In a previous study, we have recently shown that chronic treatment with desipramine either reduced or potentiated the locomotor response to the dopamine D(2)-like receptor agonist quinpirole, a behavioural response mediated by the mesolimbic dopamine system, depending on whether the animals were subjected, respectively, to repeated restraint or to chronic mild stress (different stressors randomly presented). In this study, we examined the interaction between prolonged exposure to either repeated restraint stress or chronic mild stress with the chronic administration of the antidepressant desipramine on two spontaneous behaviours, in which an involvement of the mesolimbic dopamine system has been suggested: novelty-induced exploratory activity and grooming. Exploratory activity in the open field was reduced by chronic mild stress regardless of the drug treatment, while it was not influenced by restraint stress. Desipramine reduced exploratory activity in rats subjected to restraint stress. Restraint stress increased grooming and desipramine reversed this effect, while increasing grooming in the chronic mild stress group. These findings suggest that antidepressants exert their effect by opposing the modifications induced by stress. The available experimental evidence is consistent with the hypothesis that an important role in the observed behavioural changes is played by the mesolimbic dopamine system.