Estimation of striatal dopamine spillover and metabolism in vivo

A microdialysis probe with an attached microinjection cannula was inserted into rat striatum. [H-3]dopamine (or [C-14]sucrose as a reference substance for diffusion) was infused via the cannula, with microdialysate sampled fo r concentrations of endogenous and [H-3]-labeled dopamine and its metabolit es. The calculated specific activities of the [H-3]-labeled metabolites led to the conclusions that striatal extracellular dopamine undergoes inactiva tion mainly by extraneuronal but also by neuronal uptake and intracellular metabolism. Some of the dopamine taken up into nerve terminals slowly re-en ters (spillover) the extracellular fluid unchanged. This spillover was calc ulated to be about 5 pmol/min. Destruction of dopaminergic terminals increa ses the turnover of vesicular stores in the surviving terminals, both by in creased vesicular leakage and by increased release into the extracellular f luid. NeuroReport 11:3367-3373 (C) 2000 Lippincott Williams & Wilkins.