Allidal Control of Substantia Nigra Dopaminergic Euron Firing Pattern and Its Relation to Extracellular Eostriatal Dopamine Levels

bstract—The firing patterns of dopaminergic neurons in vivo re strongly modulated by afferent input. The principal GABAeric inputs to the dopaminergic neurons of the substantia nigra riginate from neurons of the neostriatum, globus pallidus and ubstantia nigra pars reticulata. It has previously been shown hat the firing pattern of nigral dopaminergic neurons can be anipulated by pharmacologically induced excitation or inhibiion of the globus pallidus with relatively little effect on firing ate. We used this technique to explore the relation between the ring pattern of dopaminergic neurons and extracellular dopaine levels in the neostriatum in vivo. Specifically, we tested hether an increase in burst firing in dopaminergic neurons roduced by increased pallidal activity led to increased extraellular dopamine levels in the neostriatum. Single unit extraellular recording combined with simultaneous microdialysis as used to measure the firing rates and patterns of dopamiergic neurons and extracellular striatal dopamine levels, repectively, during bicuculline-induced excitation of the globus allidus. Pallidal excitation resulted in a marked increase in urst firing in dopaminergic neurons along with only a slight ncrease in firing rate, but produced a significant elevation (aproximately 45%) in neostriatal dopamine levels. These data uggest that afferent-induced burst firing in dopaminergic neuons leads to an increase in extracellular dopamine levels in the eostriatum when compared with less bursty patterns with simlar overall firing rates. © 2004 IBRO. Published by Elsevier Ltd. ll rights reserved.