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The regulation of extracellular dopamine (DA) concentrations was examined and compared in vivo in four projection fields of mesotelencephalic dopaminergic neurons with fast-scan cyclic voltammetry at carbon-fiber microelectrodes. Transient electrical stimulation of ascending DA fibers in a near physiological range of frequencies (10-20 Hz) elicited similar levels of extracellular DA in the medial prefrontal cortex (MPFC), basal lateral amygdaloid nucleus (BAN), caudate-putamen (CP), and nucleus accumbens (NAc) despite the documented 90-fold disparity in DA tissue levels and terminal density. However, marked differences were observed in the dynamics and overall frequency dependence of the evoked synaptic overflow of DA. These differences are due to the significantly different rates of release and uptake found in each of the four regions. For example, rate constants for the release of the four regions. For example, rate constants for the release and uptake of DA were similar in the MPFC and BAN but approximately 8 and 50 times less, respectively, than that in the CP and NAc. When the parameters were normalized to endogenous DA tissue content, a unique picture emerged: compared to all other regions, relative release was 10-fold greater in the MPFC while relative uptake was at least 10 times less in the BAN. The results further differentiate the functional characteristics of mesotelencephalic dopaminergic systems and demonstrate the regiospecific nature of DA neural transmission in the brain. In addition, the regulation of extracellular DA levels in the MPFC and BAN is suitable for the "long-range" transfer of chemical information in the brain and is consistent with a hypothesis of extrasynaptic neurotransmission.
Garris et al. (Sat,) studied this question.