The mesocortical dopaminergic system is involved in the coping response to environmental stimuli. Accordingly, both stressful and pleasurable stimuli can induce an increase in the extracellular concentration of dopamine (DA) in the medial prefrontal cortex of rats. Social isolation (SI), a widely used animal model of depression, is able to induce anhedonia in rats, reducing the consume of sucrose. In our experiments we investigated, by vertical microdialysis, whether SI can modify the changes in DA extracellular concentration induced by anticipation and consumption of food in rats trained to consume their daily meal in two hours. In control, group housed (GH), rats DA extracellular concentration showed a marked increase (+180% over basal values) 80 min before food presentation, reached a maximum during food consumption (+350%), and returned to basal values when food was taken away. In SI rats the food restriction-induced increase in DA output was almost completely abolished with respect to GH animals, both in the anticipatory and consummatory phase. In order to restore the response of mesocortical DAergic neurons to food, we administered the antidepressant drug imipramine (IMI, 20 mg/kg/day for 21 days) in a chocolate (CH) pellet that was presented to the animals one hour before food. This way of administration was chosen to avoid to handle the animals as handling has been shown to abolish the effect of SI on several paradigms. Control animals received only the CH pellet. Our results showed that in SI rats neither CH or IMI administered in CH were able to restore the food-induced increase in DA extracellular concentration. In GH rats the anticipatory increase in DA output was shifted before CH presentation, while food consumption still induced an increase in DA output similar to that observed in control rats. IMI administered with CH was able to enhance the increase in DA output observed both in the anticipatory and consummatory phase. Our data confirm the crucial role of mesocortical dopaminergic neurons in the regulation of emotion and suggest that the alterations in mood state induced by SI are able to blunt the response of cortical dopaminergic neurons to pleasurable stimuli.
Social isolation stress markedly reduces the response of cortical dopaminergic neurons to pleasurable stimuli
DAZZI, LAURA;LALLAI, VALERIA;
2013-01-01
Abstract
The mesocortical dopaminergic system is involved in the coping response to environmental stimuli. Accordingly, both stressful and pleasurable stimuli can induce an increase in the extracellular concentration of dopamine (DA) in the medial prefrontal cortex of rats. Social isolation (SI), a widely used animal model of depression, is able to induce anhedonia in rats, reducing the consume of sucrose. In our experiments we investigated, by vertical microdialysis, whether SI can modify the changes in DA extracellular concentration induced by anticipation and consumption of food in rats trained to consume their daily meal in two hours. In control, group housed (GH), rats DA extracellular concentration showed a marked increase (+180% over basal values) 80 min before food presentation, reached a maximum during food consumption (+350%), and returned to basal values when food was taken away. In SI rats the food restriction-induced increase in DA output was almost completely abolished with respect to GH animals, both in the anticipatory and consummatory phase. In order to restore the response of mesocortical DAergic neurons to food, we administered the antidepressant drug imipramine (IMI, 20 mg/kg/day for 21 days) in a chocolate (CH) pellet that was presented to the animals one hour before food. This way of administration was chosen to avoid to handle the animals as handling has been shown to abolish the effect of SI on several paradigms. Control animals received only the CH pellet. Our results showed that in SI rats neither CH or IMI administered in CH were able to restore the food-induced increase in DA extracellular concentration. In GH rats the anticipatory increase in DA output was shifted before CH presentation, while food consumption still induced an increase in DA output similar to that observed in control rats. IMI administered with CH was able to enhance the increase in DA output observed both in the anticipatory and consummatory phase. Our data confirm the crucial role of mesocortical dopaminergic neurons in the regulation of emotion and suggest that the alterations in mood state induced by SI are able to blunt the response of cortical dopaminergic neurons to pleasurable stimuli.
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