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Characterization of a putatively vesicular binding site for [3H]MPP+ in mouse striatal membranes
M Del Zompo1, M P Piccardi, S Ruiu
1Department of Neuroscience, University of Cagliari, Italy.
Abstract:
[3H] N-Methyl-4-phenylpyridinium ion (MPP+) binds with a fully reversible, high affinity process to a population of sites mainly localized in the mouse striatum (Bmax = 168 +/- 15 fmol/mg protein, KD = 1.4 +/- 0.4 nM). The majority of specifically-bound radioactivity was localized in the synaptosomal fraction. Unilateral, striatal denervation with 6-hydroxydopamine (6-OHDA) markedly (by 65-70%) decreased the number of [3H]MPP+ sites. Besides dopamine, the vesicular markers tyramine, tetrabenazine and reserpine inhibited [3H]MPP+, while mazindol was a poor displacer. Adenosine triphosphate (ATP) and Mg(2+)-ions did not affect [3H]MPP+ binding. It is concluded that these sites may represent a marker of striatal storage vesicles for dopamine.
Insights
[3H] N-Methyl-4-phenylpyridinium ion ([3H]MPP+) binding sites in mouse striatum are primarily located in synaptosomes. These dopamine storage vesicle markers are significantly reduced by 6-hydroxydopamine (6-OHDA) denervation.
Area of Science:
- Neuroscience
- Pharmacology
- Biochemistry
Background:
- The striatum is a key brain region involved in motor control and reward.
- Dopamine is a critical neurotransmitter in the striatum, playing roles in various functions.
- Understanding dopamine storage mechanisms is crucial for neurodegenerative disease research.
Purpose of the Study:
- To characterize the binding properties of [3H] N-Methyl-4-phenylpyridinium ion ([3H]MPP+) in the mouse striatum.
- To investigate the localization and regulation of [3H]MPP+ binding sites.
- To determine if these sites serve as markers for dopamine storage vesicles.
Main Methods:
- Radioligand binding assays using [3H]MPP+ on mouse striatal tissue.
- Synaptosomal fractionation to determine subcellular localization.
- Pharmacological characterization using dopamine and other vesicular transport inhibitors.
- Assessment of [3H]MPP+ binding following 6-hydroxydopamine (6-OHDA) induced denervation.
Main Results:
- [3H]MPP+ exhibited high-affinity, reversible binding in the mouse striatum (KD = 1.4 +/- 0.4 nM).
- The majority of specifically bound [3H]MPP+ was found in the synaptosomal fraction.
- Striatal denervation with 6-OHDA reduced [3H]MPP+ binding sites by 65-70%.
- Dopamine, tyramine, tetrabenazine, and reserpine inhibited binding, while mazindol did not significantly affect it.
Conclusions:
- The characterized [3H]MPP+ binding sites are localized within striatal synaptosomes.
- These sites are associated with dopaminergic pathways and are sensitive to 6-OHDA treatment.
- The binding profile suggests these sites are reliable markers for striatal dopamine storage vesicles.