Abstract
Experimental evidence shows that neurotransmitter release, from presynaptic terminals, can be regulated by altering transmitter load per synaptic vesicle (SV) and/or through change in the probability of vesicle release. The vesicular acetylcholine transporter (VAChT) loads acetylcholine into SVs at cholinergic synapses. We investigated how the VAChT affects SV content and release frequency at central synapses in Drosophila melanogaster by using an insecticidal compound, 5Cl-CASPP, to block VAChT and by transgenic overexpression of VAChT in cholinergic interneurons. Decreasing VAChT activity produces a decrease in spontaneous SV release with no change to quantal size and no decrease in the number of vesicles at the active zone. This suggests that many vesicles are lacking in neurotransmitter. Overexpression of VAChT leads to increased frequency of SV release, but again with no change in quantal size or vesicle number. This indicates that loading of central cholinergic SVs obeys the "set-point" model, rather than the "steady-state" model that better describes loading at the vertebrate neuromuscular junction. However, we show that expression of a VAChT polymorphism lacking one glutamine residue in a COOH-terminal polyQ domain leads to increased spontaneous SV release and increased quantal size. This effect spotlights the poly-glutamine domain as potentially being important for sensing the level of neurotransmitter in cholinergic SVs.
Highlights
VESICULAR TRANSPORTERS LOAD neurotransmitter into synaptic vesicles (SVs)
Using a Drosophila central synapse, we have investigated in vivo how vesicular acetylcholine transporter (VAChT) regulates cholinergic transmission
We demonstrate that decreased VAChT activity leads to decreased spontaneous quantal release frequency
Summary
VESICULAR TRANSPORTERS LOAD neurotransmitter into synaptic vesicles (SVs). Classes of transporter include the vesicular acetylcholine transporter (VAChT), the transporters for glutamate (VGLUT), monoamines (VMAT), and GABA and glycine (Fei and Krantz 2009). The number of transporters per SV is unknown but has been estimated to be between one and three (Van der Kloot 2003) This has led to speculation that even small reductions in VAChT expression level may result in SVs devoid of transporter (Prado et al, 2013). Alteration of VAChT activity at the NMJ is seemingly sufficient to increase ACh loading into SVs, an effect that is not countered by a compensatory change in outflow. Action potential-dependent synaptic currents are not affected These changes mirror the proposed roles for VAChT in mammalian central nervous system (CNS) with respect to facilitating SV release but, importantly, provide evidence to support the set-point model for SV loading. Determination of quantal content of action potential-evoked synaptic release shows no change, indicating that this variant raises the set point of filling or alternatively switches loading to obey the steady-state model. The dVAChT poly-glutamine region is unique to some insect species and may offer an exploitable target for insecticide design
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
