ON THE INVOLVEMENT OF A TONIC DOPAMINE D2-AUTOINHIBITION IN THE REGULATION OF PULSE-TO-PULSE-EVOKED DOPAMINE RELEASE IN THE RAT STRIATUM IN-VIVO

The dopamine overflow evoked by trains of electrical stimulation pulse s applied to the ascending dopaminergic pathway was measured with cont inuous amperometry in the striatum of anesthetised rats. As previously observed in in vitro studies, a pulse by pulse analysis showed a fall in dopamine overflow evoked by pulses 2 to 6, compared to the respons e evoked by pulse 1. However, in contrast with in vitro findings, the present in vivo data showed that the dopamine receptor antagonist halo peridol i) completely reverses the fall in dopamine overflow between p ulse 1 and subsequent pulses, ii) enhances the dopamine overflow elici ted by pulse 1. These results suggest that in vivo, both basal and pul se evoked dopamine overflow results in stimulation of dopamine D2-type autoreceptors and therefore in regulation of dopamine release.