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Levodopa effects on [ (11)C]raclopride binding in the resting human brain.

Black KJ, Piccirillo ML, Koller JM, Hseih T, Wang L, Mintun MA - F1000Res (2015)

Bottom Line: Levodopa did not significantly reduce striatal RAC* binding and striatal binding did not differ significantly between TS and control groups.However, levodopa's effect on DA release differed significantly in a right midbrain region (p=0.002, corrected), where levodopa displaced RAC* by 59% in control subjects but increased BP ND by 74% in TS subjects.We hypothesize that mesostriatal DA neurons fire relatively little while subjects rest, possibly explaining the non-significant effect of levodopa on striatal RAC* binding.

View Article: PubMed Central - PubMed

Affiliation: Departments of Psychiatry, Neurology, Radiology, and Anatomy & Neurobiology, Washington University School of Medicine, St. Louis, MO, 63110, USA.

ABSTRACT

Rationale: Synaptic dopamine (DA) release induced by amphetamine or other experimental manipulations can displace [ (11)C]raclopride (RAC*) from dopamine D2-like receptors. We hypothesized that exogenous levodopa might increase dopamine release at striatal synapses under some conditions but not others, allowing a more naturalistic assessment of presynaptic dopaminergic function. Presynaptic dopaminergic abnormalities have been reported in Tourette syndrome (TS).

Objective: Test whether levodopa induces measurable synaptic DA release in healthy people at rest, and gather pilot data in TS.

Methods: This double-blind crossover study used RAC* and positron emission tomography (PET) to measure synaptic dopamine release 4 times in each of 10 carbidopa-pretreated, neuroleptic-naïve adults: before and during an infusion of levodopa on one day and placebo on another (in random order). Five subjects had TS and 5 were matched controls. RAC* binding potential (BP ND) was quantified in predefined anatomical volumes of interest (VOIs). A separate analysis compared BP ND voxel by voxel over the entire brain.

Results: DA release declined between the first and second scan of each day (p=0.012), including on the placebo day. Levodopa did not significantly reduce striatal RAC* binding and striatal binding did not differ significantly between TS and control groups. However, levodopa's effect on DA release differed significantly in a right midbrain region (p=0.002, corrected), where levodopa displaced RAC* by 59% in control subjects but increased BP ND by 74% in TS subjects.

Discussion: Decreased DA release on the second scan of the day is consistent with the few previous studies with a similar design, and may indicate habituation to study procedures. We hypothesize that mesostriatal DA neurons fire relatively little while subjects rest, possibly explaining the non-significant effect of levodopa on striatal RAC* binding. The modest sample size argues for caution in interpreting the group difference in midbrain DA release with levodopa.

No MeSH data available.


Related in: MedlinePlus

Change in BPND on the placebo day.For each of thea priori VOIs, mean BPND across all 10 subjects is shown before and during the infusion on the placebo day only. Error bars show SD. Numeric labels arep values for the main effect of time in the individual region ANOVAs (putamenp=.115).
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f5: Change in BPND on the placebo day.For each of thea priori VOIs, mean BPND across all 10 subjects is shown before and during the infusion on the placebo day only. Error bars show SD. Numeric labels arep values for the main effect of time in the individual region ANOVAs (putamenp=.115).

Mentions: To our surprise, BPND increased between the 1st and 2nd scan of the day (main effect of time, F=10.605, df=1,8, p=0.012), and this change did not differ significantly between the levodopa and placebo days (time × day interaction, F=0.014, df=5,4, p=0.909). In other words, the two scans on the placebo day werenot identical. Mean BPND was 2.7% to 24.0% higher during theplacebo infusion, indicating decreased dopamine release compared to earlier on the same day. The change from the first to the second scan of each day was significant in most individual region analyses: main effect of time, thalamus p=0.002, frontal lobe p=0.032, caudate p=0.039, pallidum p=0.048, and nucleus accumbens p=0.052 (multivariate time × region interaction F=4.173, df=5,4, p=0.096).Figure 5 shows the BPND for each VOI from both scans on the placebo day only.


Levodopa effects on [ (11)C]raclopride binding in the resting human brain.

Black KJ, Piccirillo ML, Koller JM, Hseih T, Wang L, Mintun MA - F1000Res (2015)

Change in BPND on the placebo day.For each of thea priori VOIs, mean BPND across all 10 subjects is shown before and during the infusion on the placebo day only. Error bars show SD. Numeric labels arep values for the main effect of time in the individual region ANOVAs (putamenp=.115).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4490799&req=5

f5: Change in BPND on the placebo day.For each of thea priori VOIs, mean BPND across all 10 subjects is shown before and during the infusion on the placebo day only. Error bars show SD. Numeric labels arep values for the main effect of time in the individual region ANOVAs (putamenp=.115).
Mentions: To our surprise, BPND increased between the 1st and 2nd scan of the day (main effect of time, F=10.605, df=1,8, p=0.012), and this change did not differ significantly between the levodopa and placebo days (time × day interaction, F=0.014, df=5,4, p=0.909). In other words, the two scans on the placebo day werenot identical. Mean BPND was 2.7% to 24.0% higher during theplacebo infusion, indicating decreased dopamine release compared to earlier on the same day. The change from the first to the second scan of each day was significant in most individual region analyses: main effect of time, thalamus p=0.002, frontal lobe p=0.032, caudate p=0.039, pallidum p=0.048, and nucleus accumbens p=0.052 (multivariate time × region interaction F=4.173, df=5,4, p=0.096).Figure 5 shows the BPND for each VOI from both scans on the placebo day only.

Bottom Line: Levodopa did not significantly reduce striatal RAC* binding and striatal binding did not differ significantly between TS and control groups.However, levodopa's effect on DA release differed significantly in a right midbrain region (p=0.002, corrected), where levodopa displaced RAC* by 59% in control subjects but increased BP ND by 74% in TS subjects.We hypothesize that mesostriatal DA neurons fire relatively little while subjects rest, possibly explaining the non-significant effect of levodopa on striatal RAC* binding.

View Article: PubMed Central - PubMed

Affiliation: Departments of Psychiatry, Neurology, Radiology, and Anatomy & Neurobiology, Washington University School of Medicine, St. Louis, MO, 63110, USA.

ABSTRACT

Rationale: Synaptic dopamine (DA) release induced by amphetamine or other experimental manipulations can displace [ (11)C]raclopride (RAC*) from dopamine D2-like receptors. We hypothesized that exogenous levodopa might increase dopamine release at striatal synapses under some conditions but not others, allowing a more naturalistic assessment of presynaptic dopaminergic function. Presynaptic dopaminergic abnormalities have been reported in Tourette syndrome (TS).

Objective: Test whether levodopa induces measurable synaptic DA release in healthy people at rest, and gather pilot data in TS.

Methods: This double-blind crossover study used RAC* and positron emission tomography (PET) to measure synaptic dopamine release 4 times in each of 10 carbidopa-pretreated, neuroleptic-naïve adults: before and during an infusion of levodopa on one day and placebo on another (in random order). Five subjects had TS and 5 were matched controls. RAC* binding potential (BP ND) was quantified in predefined anatomical volumes of interest (VOIs). A separate analysis compared BP ND voxel by voxel over the entire brain.

Results: DA release declined between the first and second scan of each day (p=0.012), including on the placebo day. Levodopa did not significantly reduce striatal RAC* binding and striatal binding did not differ significantly between TS and control groups. However, levodopa's effect on DA release differed significantly in a right midbrain region (p=0.002, corrected), where levodopa displaced RAC* by 59% in control subjects but increased BP ND by 74% in TS subjects.

Discussion: Decreased DA release on the second scan of the day is consistent with the few previous studies with a similar design, and may indicate habituation to study procedures. We hypothesize that mesostriatal DA neurons fire relatively little while subjects rest, possibly explaining the non-significant effect of levodopa on striatal RAC* binding. The modest sample size argues for caution in interpreting the group difference in midbrain DA release with levodopa.

No MeSH data available.


Related in: MedlinePlus