Figure 1. Schematic representation of the presynaptic receptors or ionic channels present on the striatal DA terminals. NMDA and kainate receptors are stimulated by glutamate released presynaptically from corticostriatal glutamatergic inputs, whereas nicotinic receptors are activated by acetylcholine originating from striatal interneurons. Alternatively, DA released can be elicited by activation of the voltage-operated sodium channels achieved by veratridine or the voltage-operated calcium channels stimulated by KCl. All depolarizing stimuli or natural depolarization of the nerve terminal achieved by action potential propagation lead to an increase in intracellular concentrations and subsequent DA release into the synaptic cleft. NMDA-r = N-methyl-D-aspartate receptor; kainate-r = kainate receptor; nicotinic-r = nicotinic receptor; VOSC = voltage-operated sodium channels; VOCC = voltage-operated Ca2+ channels; Ca2+i= intracellular calcium.