NONLINEAR RELATIONSHIP BETWEEN IMPULSE FLOW, DOPAMINE RELEASE AND DOPAMINE ELIMINATION IN THE RAT-BRAIN IN-VIVO

Central dopaminergic neurons exhibit two kinds of discharge activity: single spikes and bursts of two to six action potentials.(2,4-6,8) Sin ce these neurons can switch from one discharge pattern to the other wh ereas the mean discharge rate remains little affected, bursts may be m ore potent in triggering the release of their neurotransmitter, dopami ne.(4,6,8) Electrical stimulations mimicking the bursting pattern were actually twice as potent as regularly spaced stimulations to enhance the dopamine extracellular concentration.(3,12) This suggested that do pamine release might be facilitated by increasing the impulse flow fre quency.(3) The high extracellular overflow evoked by a burst might als o be due to accumulation of the released dopamine whereas, at lower fr equencies, dopamine might be readily eliminated between every action p otential.(10,19) In the present study the dopamine overflow evoked by electrical stimulation of the dopaminergic pathway was measured in viv o by carbon fibre electrodes combined with continuous amperometry.(1) We observed a small facilitation of the release per pulse during stimu lations mimicking a burst but only in mesolimbic areas. The high extra cellular dopamine level evoked by a burst was mainly due to accumulati on of the released dopamine.