Abstract
Publisher Summary With the inherently slower kinetics of dopamine (DA) receptor activation, DA is an ideal candidate to mediate volume transmission. Whether DA acts synaptically or extra-synaptically, of course, depends on where its receptors are located. This chapter addresses the potential for DA-mediated volume transmission in three distinct regions of the central nervous system (CNS): striatum; substantia nigra; and retina. In each region, voltammetric microelectrodes were used with fast-scan cyclic voltammetry to monitor the behavior of extracellular DA in diffusion studies or during stimulated release. These voltammetric data, taken together with known patterns of receptor and transporter localization in each region, indicate that synaptically released DA is most constrained in the striatum, but that somatodendritically release DA in the substantia nigra and DA released from amacrine cells in the retina act primarily by volume transmission. The variation in [DA]o regulation among these regions illustrates two key issues that need to be incorporated into further refinements in ones understanding of volume transmission. The second issue raised by the regional difference is the futility of trying to categorize a given substance either as a mediator of volume transmission or as a synaptic transmitter.
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