Modifications in DARPP-32 phosphorylation pattern after repeated palatable food consumption undergo rapid habituation in the nucleus accumbens shell of non-food-deprived rats.

In non-food-deprived rats a palatable meal induces a transient increase in dopamine output in the prefrontal cortex and nucleus accumbens shell and core; habituation to this response develops with a second palatable meal, selectively in the shell, unless animals are food-deprived. A palatable meal also induces time-dependent modifications in the dopamine and cAMP-regulated phosphoprotein of Mr 32 000 (DARPP-32) phosphorylation pattern that are prevented when SCH 23390, a selective dopamine D(1) receptor antagonist, is administered shortly after the meal. This study investigated whether dopaminergic habituation in the shell had a counterpart in DARPP-32 phosphorylation changes. In non-food-deprived rats, two consecutive palatable meals were followed by similar sequences of modifications in DARPP-32 phosphorylation levels in the prefrontal cortex and nucleus accumbens core, while changes after the second meal were blunted in the shell. In food-deprived rats two consecutive meals also induced similar phosphorylation changes in the shell. Finally, SCH 23390 administered shortly after the first palatable meal in non-food-deprived rats inhibited DARPP-32 phosphorylation changes in response to the first meal, and prevented the habituation to a second meal in terms of dopaminergic response and DARPP-32 phosphorylation changes. Thus, dopamine D(1) receptor stimulation plays a role in the development of habituation.