| Summary: | 碩士 === 長庚大學 === 生物醫學研究所 === 98 === Dopamine (DA) plays an important role in the control of multiple brain functions including voluntary movement and a broad array of behavioral processes. Abnormal dopamine levels have been implicated in several neurological disorders, such as attention deficit hyperactivity disorder (ADHD), schizophrenia or Parkinson’s disease. DA signaling is terminated by the dopamine transporter (DAT) from the synapse as well as by presynaptic autoreceptor to keep synaptic DA in homeostasis. D3 dopamine receptors are expressed in dopamine neurons and are defined as dopamine autoreceptor in modulating the presynaptic DA neurotransmission, however the mechanisms underlying this modulation remain largely unclear. In particular, whether D3 receptors would regulate dopamine transporter in synergistically affecting synaptic neurotransmission is currently unknown. The main purpose of this study is to investigate the molecular mechanism of D3 receptors regulation of DAT function. In HEK cells co-expressing DAT and D3 receptors, the D3 –preferring agonist resulted in a rapid, concentration-dependent decrease in [3H]dopamine uptake as well as an decrease in surface DAT expression observed under immunocytochemistry. In mouse limbic forebrain, similar agonist effects were observed in DAT surface biotinylation in a synaptosomal preparation, in addition co-immunoprecipitation combined with mass spectrometry led to an identification of a 70-kDa heat shock cognate protein (Hsc70) as a DAT interacting protein, and this interaction was increased by D3 –preferring agonist treatment. Hsc70 drives the clathrin assembly–disassembly cycle during endocytosis. Overall, these results suggest that D3 receptors down-regulate DAT function via a trafficking dependent manner to affect extracellular dopamine level.
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