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 des ipramine either reduced or potentiated the locomotor response to the dopami ne D-2-like receptor agonist quinpirole, a behavioural response mediated by the mesolimbic dopamine system, depending on whether the animals were subj ected, respectively, to repeated restraint or to chronic mild stress (diffe rent stressors randomly presented). In this study, we examined the interact ion between prolonged exposure to either repeated restraint stress or chron ic mild stress with the chronic administration of the antidepressant desipr amine on two spontaneous behaviours. in which an involvement of the mesolim bic dopamine system has been suggested: novelty-induced exploratory activit y and grooming. Exploratory activity in the open field was reduced by chron ic mild stress regardless of the drug treatment, while it was not influence d by restraint stress. Desipramine reduced exploratory activity in rats sub jected to restraint stress. Restraint stress increased grooming and desipra mine reversed this effect, while increasing grooming in the chronic mild st ress 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 o bserved behavioural changes is played by the mesolimbic dopamine system. (C ) 2000 Elsevier Science B.V. All rights reserved.