L’isolamento sociale riduce marcatamente la risposta dei neuroni dopaminergici mesocorticali agli stimoli piacevoli.

The mesolimbic dopaminergic pathway plays an important role in the genesis of emotional arousal and behavioral activation in response to stimuli that provide a reward. This neural circuitry is also active in the early stages of learning and stabilization of addictive behavior due to substances abuse. Isolated animals have a different sensitivity to natural or artificial reinforcers. Accordingly, experimental evidences suggest that exposure to stress can deeply modify eating behavior. In light of these evidences the aim of this study was to investigate the influence of a chronic stress, like social isolation at weaning, on the sensitivity of mesocorticolimbic dopaminergic neurons to anticipation and consumption of food. Rats have been food restricted using a protocol that consists in training the animals to consume their meal for only two hours for day. Using vertical microdialysis, extracellular concentrations of dopamine in response to anticipation and consumption of food were measured both in the mPFC and the NAC. In PFC of GH rats extracellular DA increased (+180%) 80 minutes before food presentation showing the maximal increase (+350%) during food intake. On the contrary, in the NAc of GH rats no significant changes were observed. In SI animals trained to food restriction the increase in mPFC DA output observed in GH animals was completely blunted, while, in the NAc, 40 min before the presentation of the food, a significant increase in extracellular concentrations of DA was observed. Our results show that exposure to chronic stress modified the response of mesocortico-limbic dopaminergic neurons to an enjoyable stimulus and suggest that these changes might be important to explain the greater sensitivity to abuse that is observed in individuals subjected to stressful stimuli. This underlying alteration in brain function might be a crucial mechanism that predisposes individuals to impulsive behavior and increases the risk of developing addiction.