PT  - JOURNAL ARTICLE
AU  - Karmen K. Yoder
AU  - Chunzhi Wang
AU  - Evan D. Morris
TI  - Change in Binding Potential as a Quantitative Index of Neurotransmitter Release Is Highly Sensitive to Relative Timing and Kinetics of the Tracer and the Endogenous Ligand
DP  - 2004 May 01
TA  - Journal of Nuclear Medicine
PG  - 903--911
VI  - 45
IP  - 5
4099  - http://jnm.snmjournals.org/content/45/5/903.short
4100  - http://jnm.snmjournals.org/content/45/5/903.full
SO  - J Nucl Med2004 May 01; 45
AB  - Change in binding potential (ΔBP) is often used to indicate alterations in neurotransmitter concentration in response to stimuli. Increasingly, it is being used in bolus studies as a quantitative index of dopamine (DA) release. In bolus studies, however, BP is an average quantity over time that is influenced by the dynamics of both the tracer and the neurotransmitter. We sought to characterize the sensitivity of ΔBP to changes in endogenous DA concentration and to elucidate possible biases in ΔBP with respect to timing of task-induced or drug-induced increases in DA. Methods: Noiseless simulations of 11C-raclopride PET curves were performed in a specific binding region with concomitant increases in endogenous DA. DA changes were modeled as δ-functions, γ-variates, or as realistic drug-induced increases in DA over time, based on published results. Graphical estimation of BP with a reference region as the input function was used, with a multilinear formulation of the operational equation. Results: Simulations demonstrated that ΔBP (a) is linear over a narrow range of integrated DA release, (b) has an inherent sensitivity to timing of DA perturbations, and (c) could incorrectly infer the relative amounts of DA released between subject populations or experimental conditions. These results are explained by what we term the effective weighted availability, which describes the interaction of a DA function and free raclopride concentration over time and follows directly from earlier work. Conclusion: We illustrate how, under quite plausible circumstances, ΔBP may lead to erroneous conclusions about relative amounts of DA released after dopaminergic perturbations. Our findings caution against using ΔBP as a quantitative or rank index of DA release when comparing different dopaminergic stimuli.