Effect of milk on dopamine release in the newborn rat: an in vivo microdialysis study.

Newborn rats exhibit a rich behavioral repertoire to access the nipple and obtain milk. In older pups, catecholamines including dopamine (DA) mediate the behavioral effects of milk. In the present study, pups were delivered at term by caesarean section and instrumented with the microdialysis probe. Microdialysis samples were collected at 15 min intervals and K(+)-evoked levels of DA were measured with HPLC-ED. Pups received either no infusion, single or multiple intraoral infusions of saline or milk during subsequent samples. A decrease in K(+)-evoked DA release was evident after the first infusion in all subjects. Repeated milk infusions continued to reduce levels of extracellular DA, which remained evident 30 min after the last milk infusion. The rat neonate's first exposure to milk exerts lasting effects on neostriatal DA activity in the absence of prior suckling experience.