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 in the medial prefrontal cortex of rats. In our experiments we investigated the effect of anticipation and consumption of food on extracellular dopamine concentration in freely moving rats by vertical microdialysis. Rats were trained to consume their meal only two hours a day (from 11.00 A.M. to 1 P.M.). After four weeks of training, dopamine extracellular concentration was measured from 9 A.M. to 3 P.M., thus including the 2 hours before food presentation (anticipatory phase), the 2 hours during food consumption (consummatory phase), and the following 2 hours (satiety). In these rats dopamine 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. Social isolation has been widely used as an animal model of depression. In rats socially isolated at weaning for 6 weeks and trained to consume their meal in 2 hours for 4 weeks, the food restriction-induced increase in dopamine output was dramatically reduced, both in the anticipatory (+70%) and consummatory phase (+60%). This effect was almost indistinguishable from that induced by treatment with the anorectic drug SR 141716, a CB1 receptor antagonist. In fact, in rats treated with SR141716 (1mg/kg, i.p.) both acutely (60 min before food presentation) or chronically (twice a day for 21 days), the increase in dopamine output induced by food restriction was completely antagonized in the anticipatory phase and markedly reduced (+80%) in the 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 both by social isolation and CB1 receptors blockade are able to blunt the response of cortical dopaminergic neurons to pleasurable stimuli.
Social isolation, as well as treatment with the CB1 receptor antagonist SR 141716, markedly reduced the anticipatory and consummatory pleasure induced by food presentation
DAZZI, LAURA;Serra M;
2011-01-01
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 in the medial prefrontal cortex of rats. In our experiments we investigated the effect of anticipation and consumption of food on extracellular dopamine concentration in freely moving rats by vertical microdialysis. Rats were trained to consume their meal only two hours a day (from 11.00 A.M. to 1 P.M.). After four weeks of training, dopamine extracellular concentration was measured from 9 A.M. to 3 P.M., thus including the 2 hours before food presentation (anticipatory phase), the 2 hours during food consumption (consummatory phase), and the following 2 hours (satiety). In these rats dopamine 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. Social isolation has been widely used as an animal model of depression. In rats socially isolated at weaning for 6 weeks and trained to consume their meal in 2 hours for 4 weeks, the food restriction-induced increase in dopamine output was dramatically reduced, both in the anticipatory (+70%) and consummatory phase (+60%). This effect was almost indistinguishable from that induced by treatment with the anorectic drug SR 141716, a CB1 receptor antagonist. In fact, in rats treated with SR141716 (1mg/kg, i.p.) both acutely (60 min before food presentation) or chronically (twice a day for 21 days), the increase in dopamine output induced by food restriction was completely antagonized in the anticipatory phase and markedly reduced (+80%) in the 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 both by social isolation and CB1 receptors blockade are able to blunt the response of cortical dopaminergic neurons to pleasurable stimuli.
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