Abstract
Exocytosis is one of the essential steps for chemical signal transmission between neurons. In this process, vesicles dock and fuse with the plasma membrane and release the stored neurotransmitters through fusion pores into the extracellular space, and all of these steps are governed with various molecules, such as proteins, ions, and even lipids. Quantitatively monitoring vesicular neurotransmitter release in exocytosis and initial neurotransmitter storage in individual vesicles is significant for the study of chemical signal transmission of the central nervous system (CNS) and neurological diseases. Electrochemistry with micro/nanoelectrodes exhibits great spatial–temporal resolution and high sensitivity. It can be used to examine the exocytotic kinetics from the aspect of neurotransmitters and quantify the neurotransmitter storage in individual vesicles. In this review, we first introduce the recent advances of single-cell amperometry (SCA) and the nanoscale interface between two immiscible electrolyte solutions (nanoITIES), which can monitor the quantity and release the kinetics of electrochemically and non-electrochemically active neurotransmitters, respectively. Then, the development and application of the vesicle impact electrochemical cytometry (VIEC) and intracellular vesicle impact electrochemical cytometry (IVIEC) and their combination with other advanced techniques can further explain the mechanism of neurotransmitter storage in vesicles before exocytosis. It has been proved that these electrochemical techniques have great potential in the field of neuroscience.
Highlights
The neuron is an important structural and functional unit of the central nervous system (CNS), which controls higher mental functions
A 2-h treatment of PC12 cells with 100 μM L-3,4-dihydroxyphenylalanine (L-DOPA), a direct biochemical precursor to DA, increased the vesicular catecholamine content to 323,100 ± 29,000 molecules as determined in intracellular vesicle impact electrochemical cytometry (IVIEC). Both results suggested that the current transients measured in IVIEC were from the oxidation of catecholamine stored in single vesicles, and the mechanism for vesicle impact electrochemical cytometry (VIEC) is applicable for IVIEC
Electrochemistry assembled with micro/nano electrodes provides a powerful tool for quantitative monitoring of neurotransmitter released from or stored in single vesicles
Summary
The neuron is an important structural and functional unit of the central nervous system (CNS), which controls higher mental functions. Reprinted from Wigstrom et al (2016), with permission from American Chemical Society In another elegant study, a brand new conical carbon fiber nanoelectrode (CFNE) fabricated by flame-etching the cylindrical carbon fiber microelectrode was placed into a single trained synapse formed between cultured superior cervical ganglion (SCG) and sympathetic neurons to monitor catecholamine release during exocytosis, as displayed in Figure 3 (Li et al, 2014). Ewing’s group developed a novel method to record the neurotransmitter release from exocytosis at single varicosities in the Drosophila larval system with SCA (Figure 2) (Majdi et al, 2015) When they placed a regular carbon fiber microelectrode in close proximity to Type II varicosities which were stimulated with blue light, a train of current transients representing the oxidation of octopamine released were recorded at a potential of + 900 mV (vs Ag/AgCl). Once analyzing each current transient in detail, various shapes of exocytotic events, including simple and complicated ones, reveal that partial release is prevalent in this condition
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