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The microtubule‐associated protein tau participates in neurotransmission regulation via its interaction with synaptic vesicles (SVs). The precise nature and mechanics of tau's engagement with SVs, especially regarding alterations in vesicle dynamics, remain a matter of discussion. We report an electrochemical method using a synapse‐mimicking nanopipette to monitor vesicle dynamics induced by tau. A model vesicle of ~30 nm is confined within a lipid‐modified nanopipette orifice with a comparable diameter to mimic the synaptic lipid environment. Both tau and phosphorylated tau (p‐tau) present two‐state dynamic behavior in this biomimetic system, showing typical ionic current oscillation, induced by lipid‐tau interaction. The results indicate that p‐tau has a stronger affinity to the lipid vesicles in the confined environment, blocking the vesicle movement to a higher degree. Taken together, this method bridges a gap for sensing synaptic vesicle dynamics in a confined lipid environment, mimicking vesicle movement near the synaptic membrane. These findings contribute to understanding how different types of tau protein regulate synaptic vesicle motility and to underlying its functional and pathological behaviours in disease. [ABSTRACT FROM AUTHOR]

The nerve terminals found in the body wall of Drosophila melanogaster larvae are readily accessible to experimental manipulation. We used the light-activated ion channel, channelrhodopsin-2, which is expressed by genetic manipulation in Type II varicosities to study octopamine release in Drosophila. We report the development of a method to measure neurotransmitter release from exocytosis events at individual varicosities in the Drosophila larval system by amperometry. A microelectrode was placed in a region of the muscle containing a varicosity and held at a potential sufficient to oxidize octopamine and the terminal stimulated by blue light. Optical stimulation of Type II boutons evokes exocytosis of octopamine, which is detected through oxidization at the electrode surface. We observe 22700±4200 molecules of octopamine released per vesicle. This system provides a genetically accessible platform to study the regulation of amine release at an intact synapse.

Resolution of synaptic vesicle neurotransmitter content has mostly been limited to the study of stimulated release in cultured cell systems, and it has been controversial as to whether synaptic vesicle transmitter levels are saturated in vivo. We use electrochemical cytometry to count dopamine molecules in individual synaptic vesicles in populations directly sampled from brain tissue. Vesicles from the striatum yield an average of 33,000 dopamine molecules per vesicle, an amount considerably greater than typically measured during quantal release at cultured neurons. Vesicular content was markedly increased by L-DOPA or decreased by reserpine in a time-dependent manner in response to in vivo administration of drugs known to alter dopamine release. We investigated the effects of the psychostimulant amphetamine on vesicle content, finding that vesicular transmitter is rapidly depleted by 50% following in vivo administration, supporting the "weak base hypothesis" that amphetamine reduces synaptic vesicle transmitter and quantal size.

We used correlative transmission electron microscopy (TEM) and nanoscale secondary ion mass spectrometry (NanoSIMS) imaging to quantify the contents of subvesicular compartments, and to measure the partial release fraction of 13C‐dopamine in cellular nanovesicles as a function of size. Three modes of exocytosis comprise full release, kiss‐and‐run, and partial release. The latter has been subject to scientific debate, despite a growing amount of supporting literature. We tailored culturing procedures to alter vesicle size and definitively show no size correlation with the fraction of partial release. In NanoSIMS images, vesicle content was indicated by the presence of isotopic dopamine, while vesicles which underwent partial release were identified by the presence of an 127I‐labelled drug, to which they were exposed during exocytosis allowing entry into the open vesicle prior to its closing again. Demonstration of similar partial release fractions indicates that this mode of exocytosis is predominant across a wide range of vesicle sizes. [ABSTRACT FROM AUTHOR]

A recent article in Angewandte Chemie discusses a new method for monitoring vesicle dynamics using a synapse-mimicking nanopipette. The researchers developed a modified lipid layer within the nanopipette to mimic the lipid environment in synapses. By recording characteristic ionic current oscillations, they were able to evaluate the binding affinity of tau protein and found that phosphorylated tau inhibits vesicle dynamics through strong interactions with synaptic vesicles. This research provides valuable insights into the role of tau protein in synaptic function. [Extracted from the article]

A recent article in Angewandte Chemie International Edition discusses a new method for monitoring vesicle dynamics using a synapse-mimicking nanopipette. The researchers developed a modified lipid layer within the nanopipette to mimic the lipid environment in synapses. By recording characteristic ionic current oscillations, they were able to evaluate the binding affinity of tau protein and found that phosphorylated tau inhibits vesicle dynamics through strong interactions with synaptic vesicles. This research provides valuable insights into the role of tau protein in synaptic function. [Extracted from the article]