To the Editor: Dr Marek and colleagues1 reported that patients with Parkinson disease (PD)
who were treated with pramipexole for 22 to 46 months had evidence of less
dopamine neuron degeneration (as assessed by single-photon computed tomography
[SPECT]) than did patients who were treated with levodopa for a similar period.
It is unclear whether these results simply reflect the pharmacological
effects of pramipexole on dopamine transporter (DAT) expression, or the ability
of DAT to sequester the radiologic marker 2β-carboxymethoxy-3β(4-iodophenyl)tropane
(β-CIT). If pramipexole simply increased DAT expression in surviving
nerve terminals, imaging could falsely indicate more surviving neurons. Pramipexole
alteration of DAT function might have a similar influence. Drugs that bind
to dopaminergic receptors have significant effects on DAT phosphorylation,
functions, expression, and turnover.2 Dopamine
agonists and levodopa can influence DAT synthesis and degradation, with D1-
and D2-linked second messenger systems often affecting DAT expression in opposite
ways.2 Dopamine generated from levodopa
stimulates both classes of receptors, while pramipexole spares D1 receptors.3
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Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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