Effectiveness and Relationship between Biased and Unbiased Measures of Dopamine Release and Clearance

Abstract

Fast-scan cyclic voltammetry (FSCV) is an effective tool for measuring dopamine release and clearance throughout the brain, especially the striatum where dopamine terminals are abundant and signals are heavily regulated by release machinery and the dopamine transporter (DAT). Peak height measurement is perhaps the most common method for measuring dopamine release, but it is influenced by changes in clearance. Michaelis–Menten-based modeling has been a standard in measuring dopamine clearance, but it is problematic in that it requires experimenter fitted modeling subject to experimenter bias. This study presents the use of the first derivative (velocity) of evoked dopamine signals as an alternative approach for measuring and distinguishing dopamine release from clearance. Maximal upward velocity predicts reductions in dopamine peak height due to D2 and GABAB receptor stimulation and by alterations in calcium concentrations. The Michaelis–Menten maximal velocity (V max) measure, an approximation for DAT levels, predicts maximal downward velocity in slices and in vivo. Dopamine peak height and upward velocity were similar between wild-type and DAT knock-out (DATKO) mice. In contrast, downward velocity was lower and exponential decay (tau) was higher in DATKO mice, supporting the use of both measures for extreme changes in DAT activity. In slices, the competitive DAT inhibitors cocaine, PTT, and WF23 increased peak height and upward velocity differentially across increasing concentrations, with PTT and cocaine reducing these measures at high concentrations. Downward velocity and tau values decreased and increased respectively across concentrations, with greater potency and efficacy observed with WF23 and PTT. In vivo recordings demonstrated similar effects of WF23, PTT, and cocaine on measures of release and clearance. Tau was a more sensitive measure at low concentrations, supporting its use as a surrogate for the Michaelis–Menten measure of apparent affinity (K m). Together, these results inform on the use of these various measures for dopamine release and clearance.

Dopamine transmission in the tail striatum: Regional variation and contribution of dopamine clearance mechanisms

“…Additionally, peak downward velocity was determined from the first derivative of evoked dopamine release recordings, as described by Everett et al. (2022), and shown in Supplementary Figure S1. Peak downward velocity correlated with peak dopamine and therefore was normalised to peak dopamine to provide a more unbiased measure of clearance rate.…”

“…This is the first investigation of slowing diffusion with dextran on peak downward velocity of striatal dopamine clearance. The change in peak downward velocity in these regions may be exaggerated by the sensitivity of this parameter to changes in peak dopamine (to which it is directly normalised;Everett et al, 2022), as peak dopamine is more sensitive to dextran than (pre-normalisation) peak downward velocity.Slowing diffusion significantly (p < 0.05 as per Sidak's multiple comparisons) increased time to peak in the lateral and intermediate divisions, but not the medial division or dorsolateral striatum.In contrast, slowing diffusion significantly prolonged half-life in the dorsolateral striatum and medial division, but not the lateral or intermediate divisions. The unexpected disparity between the alterations in these parameters is discussed further in Section 4.4.We hypothesised that dopamine detected in the wild-type in-termediate division is contributed to by diffusion of dopamine from the neighbouring medial and/or lateral divisions.…”

Behavioral Posology: A Novel Paradigm for Modeling the Healthy Limits of Behaviors

“…Parameters were arbitrarily chosen to mimic the exponential decay of dopamine release and clearance in the brain as measured and modeled by Everett et al [ 62 ] and Chou and D'Orsogna. [ 33 ] The Hill equation was adjusted for both a‐ and b‐ processes so that the relationship between dose and effect for both processes was approximately linear for most of the plausible range of dose concentrations.…”

Kappa opioid receptor agonist U50,488 inhibits dopamine more in caudal than rostral nucleus accumbens core

“…Recording electrodes were calibrated upon termination of each experiment with known concentrations of DA (3 μM). All ex vivo FSCV data were analysed for stimulated DA release, and the uptake portion of the curve was fitted to an exponential decay model and expressed as tau or time to ~33% of the peak height (unit in seconds) 45,46 . These analyses were carried out using the peak and decay function of the Demon Voltammetry and Analysis software 45 …”