DOPAMINE FORMATION FROM L-DOPA ADMINISTERED EXOGENOUSLY IS INDEPENDENT OF DOPAMINERGIC NEURONAL-ACTIVITY - STUDIES WITH INVIVO MICRODIALYSIS

Extracellular dopamine (DA) levels in the steady state were not detected in the hippocampus of rats where sparse dopaminergic innervations were demonstrated. However, following L-DOPA (100 mg/kg i.p.) administration, extracellular DA was detected. Although tetrodotoxin (TTX, 1 muM) failed to prevent this phenomenon, the striatal DA peak disappeared with the addition of TTX (5 muM) into the perfusate and reappeared following L-DOPA (100 mg/kg i.p.) administration. These findings suggest that DA synthesis from L-DOPA, administered exogenously, is independent of the existence of dopaminergic neurons and that outflow of newly synthesized DA into the extracellular space is not coupled to neuronal activity.