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The Journal of Neuroscience, July 1, 1998, 18(13):5068–5077 Striatal Extracellular Dopamine Levels in Rats with Haloperidol- Induced Depolarization Block of Substantia Nigra Dopamine Neurons Holly Moore, Christopher L. Todd, and Anthony A. Grace Departments of Neuroscience and Psychiatry, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 Correlations between substantia nigra (SN) dopamine (DA) cell more, although basal striatal DA efflux was independent of SN activity and striatal extracellular DA were examined using si- DA cell burst-firing activity in control rats, these variables were multaneous extracellular single-unit recordings and in vivo mi- significantly correlated in rats with HAL-induced DA cell DB. crodialysis performed in drug-naive rats and in rats treated Therefore, HAL-induced DB of SN DA neurons is disrupted by repeatedly with haloperidol (HAL). Intact rats treated with HAL implantation of a microdialysis probe into the striatum using for 21–28 d exhibited significantly fewer active DA cells, indi- standard procedures. However, a modified microdialysis cating the presence of depolarization block (DB) in these cells. method that allowed reinstatement of DA neuron DB revealed However, in rats that received surgical implantation of the mi- that the HAL-induced inactivation of SN DA neurons was as- crodialysis probe followed by a 24 hr recovery period, HAL- sociated with significantly lower extracellular DA levels in the induced DA cell DB was reversed, as evidenced by a number of striatum. Moreover, the residual extracellular DA maintained in active DA neurons