The ontogeny of apomorphine-induced alterations of neostriatal dopamine release: effects on potassium-evoked release.

The effects of apomorphine (0.05, 0.1, and 1.0 mg/kg, s.c.) on K(+)-evoked dopamine release were studied through the use of in vivo microdialysis in the neostriatum of developing and adult rats. Fifteen-minute samples were collected from urethane-anesthetized rats 5, 10-11, 21-22, 35-36 days of age, and adults, and quantified by high performance liquid chromatography with electrochemical detection. Apomorphine attenuated K(+)-evoked dopamine release in all age groups, suggesting that the dopamine autoreceptor modulating release in the neostriatum is functional by 5 days of age. A dose-response effect of apomorphine was observed in all age groups except at 5 and 10 days of age. Absolute levels of extracellular dopamine were significantly lower at 5 and 10 days of age compared with the other ages, and the effectiveness of a high-K+ artificial cerebrospinal fluid to evoke dopamine release increased with age.