Dopamine accumulation may impair impulse control in Parkinson’s disease
medwireNews: Patients with Parkinson’s disease who have impulse control disorders (ICDs) appear to have reduced striatal dopamine transporter (DAT) density relative to those without such disorders, research shows.
Previous studies have shown increased striatal dopamine release among Parkinson’s disease patients when presented with cues related to their ICD, say lead researcher Valerie Voon (University of Cambridge, UK) and team.
“Our findings suggest that one possible explanation for the enhanced dopaminergic activity is that impaired clearance of dopamine may play a role in extending the physiological effect of dopamine at the synaptic terminal,” they write in the Journal of Neurology, Neurosurgery & Psychiatry.
Their finding builds on a previous small study that reported reduced striatal DAT expression in Parkinson’s disease patients with gambling problems, they say, and is consistent with research in substance use disorders.
In the current study, binding of [123I]2β-carbomethoxy-3β-(4-iodophenyl)tropane, measured on single photon emission computed tomography in the absence of any ICD-related cues, was significantly decreased in the left and right striatum of 15 patients with ICDs relative to that in 15 age- and gender-matched patients without ICDs.
The researchers note that the decreased binding “may reflect either lower DAT levels or greater dopaminergic nerve terminal degeneration.” But in the absence of clinical evidence indicative of exacerbated nerve terminal degeneration in the presence of ICDs, they suggest that “lower binding levels might either reflect greater sensitivity to medication-related DAT downregulation or baseline trait differences and hence higher dopaminergic activity.”
Patients with ICDs had significantly reduced binding in the left and right putamen and the right caudate, with a trend (p=0.06) toward reduced binding in the left caudate. After accounting for age and duration of Parkinson’s disease, the reduced binding in the right striatum remained significant, while a trend (p=0.07) for reduced binding persisted in the left striatum.
Of note, when analyzed separately, the combined group of patients with compulsive shopping, hypersexuality, or pathologic gambling had significantly reduced striatal binding, whereas patients with punding or hobbyism did not.
This is consistent with suggestions that the underlying mechanisms of punding relate to levodopa rather than dopamine, say the researchers.
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By Eleanor McDermid, Senior medwireNews Reporter