Regulation of Acetylcholine Quantal Release by Coupled Thrombin/BDNF Signaling in Mouse Motor Synapses

Abstract

The aim of this study was to compare the acute effects of thrombin and brain-derived neurotrophic factor (BDNF) on spontaneous miniature endplate potentials (MEPPs) and multiquantal evoked endplate potentials (EPPs) in mouse neuromuscular junctions (NMJs) of m. diaphragma and m. EDL. Intracellular microelectrode recordings of MEPPs and EPPs were used to evaluate the changes in acetylcholine (ACh) release in mature and newly-formed mouse NMJs. Thrombin (1 nM) increased the amplitude of MEPPs and EPPs by 25–30% in mature and newly-formed NMJs. This effect was due to an enhanced loading of synaptic vesicles with ACh and increase of ACh quantal size, since it was fully prevented by blocking of vesicular ACh transporter. It was also prevented by tropomyosin-related kinase B (TrkB) receptors inhibitor ANA12. Exogenous BDNF (1 nM) mimicked thrombin effect and increased the amplitude of MEPPs and EPPs by 25–30%. It required involvement of protein kinase A (PKA) and mitogen-activated protein kinase (MEK1/2)-mediated pathway, but not phospholipase C (PLC). Blocking A2A adenosine receptors by ZM241385 abolished the effect of BDNF, whereas additional stimulation of A2A receptors by CGS21680 increased MEPP amplitudes, which was prevented by MEK1/2 inhibitor U0126. At mature NMJs, BDNF enhanced MEPPs frequency by 30–40%. This effect was selectively prevented by inhibition of PLC, but not PKA or MEK1/2. It is suggested that interrelated effects of thrombin/BDNF in mature and newly-formed NMJs are realized via enhancement of vesicular ACh transport and quantal size increase. BDNF-induced potentiation of synaptic transmission involves the functional coupling between A2A receptor-dependent active PKA and neurotrophin-triggered MAPK pathway, as well as PLC-dependent increase in frequency of MEPPs.

ProBDNF and Brain-Derived Neurotrophic Factor Prodomain Differently Modulate Acetylcholine Release in Regenerating and Mature Mouse Motor Synapses

“…In contrast to that, we have previously shown that mature BDNF potentiates ACh release both in newly formed and mature motor synapses ( Gaydukov et al, 2018 , 2019 ).…”

“…Amplitude distribution of MEPPs is also altered and does not fit to normal curve due to the appearance of both low-amplitude events and so-called “giant miniature” events ( McArdle and Albuquerque, 1973 ). Evoked endplate potentials (EPPs) are also altered and demonstrated lower amplitude and quantal content, prolonged time course, and longer synaptic delay compared to mature NMJs ( Argentieri et al, 1992 ; Gaydukov et al, 2019 ). During short repetitive nerve stimulation (50 Hz, 1 s) no depression of EPPs amplitude or quantal content is observed, but instead a facilitation that is sustained at a higher level than a first EPP in train ( Balezina et al, 2007 ; Bogatcheva and Balezina, 2013 ).…”

“…The presence of both BDNF and its receptors has been shown in all three compartments of neuromuscular junctions (NMJs) – axon terminals, perisynaptic Schwann cells, and muscle fibers ( Garcia et al, 2010b ). Moreover, nowadays BDNF is considered a myokine as it can be released from the muscle and act on nerve terminals as a retrograde messenger ( Hurtado et al, 2017 ; Gaydukov et al, 2019 ). Recently, it became obvious that the numerous synaptic effects of BDNF cannot be unambiguously interpreted without taking into account the possible simultaneous action of its maturation by-products.…”

Delayed increase of acetylcholine quantal size induced by the activity‐dependent release of endogenous CGRP but not ATP in neuromuscular junctions

“…But growing bulk of evidence demonstrates the acute contraction‐induced secretion of myokines (such as BDNF, ATP, H 2 S etc.) that are described to control presynaptic enzymatic and secretory activity of motor synapses (Gaydukov et al., 2019; Gerasimova et al., 2015; Hurtado et al, 2017; Mantilla, Zhan, & Sieck, 2004; Obis et al., 2015; Zhan, Mantilla, & Sieck, 2003). Whether muscle contractions and myokines can also control CGRP release/activity in motor synapses and be involved in the phenomenon of posttetanic potentiation of MEPP amplitude remains to be further investigated.…”

Sarcopenia: What Is the Origin of This Aging-Induced Disorder?

“…Conversely, the target muscle produces trophic factors (e.g., CNTF, GDNF, NGF, BDNF, and more, reviewed in Kawabuchi et al, 2011;Mrówczyński, 2019;Stanga et al, 2020) that are taken up and retrogradely transported to the MN cell body. These neurotrophins are non-redundant for MN survival during development (Hollyday and Hamburger, 1976) but are continuously expressed throughout life and, as suggested by experimental data, may then serve different functions such as potentiation of transmission and frequency of mEPPs (Gaydukov et al, 2019) (BDNF), maintenance and re-innervation (Stanga et al, 2020) (GDNF), and MN maintenance (BDNF, GDNF; idem). Assessment in aged MNs (and sensory neurons) of the expression of target-derived neurotrophic factor receptors of the NGF family and the expression level of these neurotrophic factors in the target tissue points toward decreased trophic support in old age (Edström et al, 2007).…”