Wideband ratiometric measurement of tonic and phasic dopamine release in the striatum

Reward learning, cognition, and motivation are supported by changes in neurotransmitter levels across multiple timescales. Current measurement technologies for various neuromodulators (such as dopamine and serotonin) do not bridge timescales of fluctuations, limiting the ability to define the behavioral significance, regulation, and relationship between fast (phasic) and slow (tonic) dynamics. To help resolve longstanding debates about the behavioral significance of dopamine across timescales, we developed a novel quantification strategy, augmenting extensively used carbon-fiber Fast Scan Cyclic Voltammetry (FSCV). We iteratively engineered the FSCV scan sequence to rapidly modify electrode sensitivity within a sampling window and applied ratiometric analysis for wideband dopamine measurement. This allowed us to selectively eliminate artifacts unrelated to electrochemical detection (i.e., baseline drift), overcoming previous limitations that precluded wideband dopamine detection from milliseconds to hours. After extensive characterization and validation in vitro and in vivo with simultaneous microdialysis, pharmacological, reward, and optogenetic manipulations, we demonstrate the utility of ratiometric FSCV to resolve key questions about how phasic DA transients contribute to setting striatal DA tone. We identify specific DA frequency bands that correlate with canonical microdialysis-defined “tonic” DA levels while also uncovering a paradoxical constraint on the accumulation of phasic DA into tonic levels. Our approach can extend to additional analytes, including serotonin, empowering the emperical testing of contrasting predictions from theories about neuromodulator circuit and computaional mechanisms that support behavioral flexibility.