Adaptive changes of dopamine responsiveness to palatable food: differences between accumbens shell, core and prefrontal cortex

BASSAREO, VALENTINA;DI CHIARA G.

2008-01-01

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Abstract

Drugs of abuse and highly palatable food share the property to stimulate dopamine (DA) transmission preferentially in the nucleus accumbens (NAc) shell. But while the stimulation of DA shell by non-drug reward (food) undergoes rapid habituation, that exerted by drugs of abuse does not. The lack of habituation of shell DA in response to drugs of abuse is hypothesized to abnormally strengthen stimulus-drug association and result in the attribution of excessive motivational value to discrete stimuli or contexts predictive of drug availability. Several studies reported that, in food and water deprived rats, repeated sugar consumption continuously increase DA trasmission in the NAc shell as well as drugs of abuse. The aim of our research was to study the adaptive changes in the reactivity of DA transmission in the shell and core and prefrontal cortex (PFCX) of non deprived animals to higly palatable food after long term feeding with it. Male Sprague-Dawley rats were trained to drink chocolate solution (sugar solution for control group) that was made available for two or 1 week from 8 p.m. to 8 a.m., apart from weekends. At the end of the training period, microdialysis experiments were performed for three consecutive days. Behavioral responses to chocolate infused by intraoral catheter were observed and DA modifications were monitored by chronic microdialysis probes. The main finding of our study is that no habituation was observed in the response of shell DA to intraoral infusion of chocolate in trained rats. In agreement with previous studies, no habituaton was observed in the response of DA in the NAc core and PFCX. In conclusion repeated exposure of the same palatable food abolishes the habituation of DA responsiveness in the NAc shell, and potentiates it in the NAc core and we can speculate that disturbances of feeding behavior are related to loss of adaptive regulation of food-stimulated release of DA in the NAc shell.