Dopamine D2 receptor dimers in human and rat brain

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Dopamine D2 receptors are crucial for neurotransmission.
• The oligomeric state of dopamine D2 receptors is not fully understood.
• Existing radioligands may exhibit differential binding to receptor complexes.

Purpose of the Study:

• To investigate the existence of dopamine D2 receptor dimers and oligomers in mammalian brain.
• To compare the binding characteristics of two selective photoaffinity ligands for dopamine D2 receptors.
• To explore potential reasons for discrepancies in dopamine D2 receptor density measurements.

Main Methods:

• Photolabeling of rat and human brain striatal membranes with [125I]azidophenethylspiperone and [125I]-4-azido-5-iodonemonapride.
• Western blotting of human cloned D2 receptors using a D2-specific antibody.

Main Results:

• [125I]azidophenethylspiperone labeled only D2 monomers.
• [125I]-4-azido-5-iodonemonapride labeled both D2 monomers and dimers.
• Antibody probing revealed trimers, tetramers, and pentamers of D2 receptors.

Conclusions:

• Dopamine D2 receptors exist as monomers, dimers, and higher-order oligomers in mammalian brain.
• Spiperone and benzamide ligands exhibit distinct binding patterns to D2 receptor complexes.
• Differences in ligand binding to D2 receptor oligomers may explain variable receptor density findings in positron tomography studies.