A within-subject dose-response analysis was conducted by locally perfusing increasing concentrations (0.1, 1, 10 and 100 microM) of the selective D2 agonist quinpirole via a microdialysis probe into the neostriatum of urethane-anesthetized rat pups 5, 10-11, 15-16 and 21-22 days of age and adult rats. In Expt. 1, K(+)-evoked dopamine release was significantly decreased by quinpirole relative to the vehicle control group for each age in a dose-dependent manner. The maximum effect of quinpirole was not influenced by acute tolerance or the length of the experiment (Expt. 2). Finally, the effect of quinpirole (10 microM) was blocked by the addition of the selective D2 antagonist (-)-sulpiride (100 microM) to the perfusion solution (Expt. 3). These results support and extend previous research that suggests that presynaptic D2 autoreceptors in the neostriatum are able to modulate K(+)-evoked dopamine release in vivo by postnatal day 5 in the rat.