Objective: The objective of this study was to investigate if dopamine transporter (DAT) binding is associated with dopaminergic neurites in the putamen.

Background: Dopamine transporter binding, measured with functional brain imaging, has been considered a possible biomarker for nigrostriatal degeneration in Parkinson’s disease (PD). However, it appears that DAT binding may not correlate with nigral neuron quantity (1). It may still reflect the number of striatal axons in putamen due to axonal degeneration of the nigrostriatal neurons.

Method: Tyrosine hydroxylase positive (TH+) nerve fibers were counted from post mortem putamen sections taken from 14 parkinsonism patients who had been scanned with DAT SPECT ante mortem(PD n=10). The fiber counts were correlated with the putamen DAT binding and substantia nigra neuron counts.

Results: The putamen DAT specific binding ratio (SBR) did not correlate with the putamen TH+ axon counts (r=0.00, p=1.0; PD patients: r=0.07, p=0.86). The correlations were nonsignificant in all subregions of the putamen. No correlations were found when the time interval between the SPECT and death was used as a covariate or when the symptom duration at the time of the scan was used as a covariate. The nigra neuron counts had a positive correlation with the putamen TH+ axon counts.

Conclusion: Putamen DAT binding does not correlate with the dopaminergic axon counts of the same region. Therefore, striatal DAT imaging does not appear to be able to determine axonal nor somal loss of the nigrostriatal neurons in PD. DAT binding mayreflect dopaminergic activity or dopamine level rather than number of surviving neurons and their striatal projection axons.

References: 1. Saari L, Kivinen K, Gardberg M, Joutsa J, Noponen T, Kaasinen V. Dopamine transporter imaging does not predict the number of nigral neurons in Parkinson disease. Neurology 2017;88(15):1461-1467.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/no-link-between-striatal-dopaminergic-axons-and-dopamine-transporter-imaging-in-parkinsons-disease/