Modulation of feeding-induced activation of mesolimbic dopamine transmission by appetitive stimuli and its relation to motivational state

We have previously shown in non-deprived rats that feeding of an unfamiliar palatable food (Fonzies((R))) phasically stimulates in vivo dopamine (DA) transmission in the medial nucleus accumbens (NAc) and this effect undergoe s habituation after a previous (24 h) Fonzies meal (Bassareo & Di Chiara 19 97, J. Neurosci., 17, 851-861). The present study shows that an unfamiliar food (Kinder((R))) with a taste and composition (milk chocolate) different from that of Fonzies, also induces a release of DA in the NAc subjected to one-trial habituation. Habituation was taste specific as no cross-habituati on was observed between Fonzies and Kinder. In undeprived rats, a 40-min ex posure to an intrinsic appetitive stimulus (food smell arising from a Fonzi es-filled plastic box) also prevented the increase in dialysate DA associat ed with Fonzies feeding, and this effect was partially reversed by food dep rivation. Food deprivation also prevented habituation of Fonzies-induced in crease of dialysate DA in the NAc. Predictive association of an empty plast ic box to Fonzies feeding resulted in the acquisition of appetitive propert ies by the box and in facilitation (rather than inhibition) of the phasic r esponsiveness of DA transmission to Fonzies feeding. A 10-min pre-exposure to appetitive olfactory stimuli intrinsic to Fonzies still prevented, like a 40-min pre-exposure, the NAc DA response to Fonzies feeding; however, a 5 -min pre-exposure to these appetitive stimuli did not prevent the DA respon se in the NAc. These results show that the phasic responsiveness of NAc DA transmission to an unfamiliar palatable food is under strong modulatory con trol by primary (consummatory) and secondary (appetitive) stimuli, and that the sign and extent of this control depends on the nature of the appetitiv e stimulus, delay of reward and motivational state (deprivation).