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

The effects of brain-derived neurotrophic factor (BDNF) processing by-products (proBDNF and BDNF prodomain) on the activity of mouse neuromuscular junctions (NMJs) were studied in synapses formed during the reinnervation of extensor digitorum longus muscle (m. EDL) and mature synapses of the diaphragm. The parameters of spontaneous miniature endplate potentials (MEPPs) and evoked endplate potentials (EPPs) were analyzed in presence of each of the BDNF maturation products (both - 1 nM).

Interaction between Calcium Chelators and the Activity of P2X7 Receptors in Mouse Motor Synapses.

The ability of P2X7 receptors to potentiate rhythmically evoked acetylcholine (ACh) release through Ca entry via P2X7 receptors and via L-type voltage-dependent Ca channels (VDCCs) was compared by loading Ca chelators into motor nerve terminals. Neuromuscular preparations of the diaphragms of wild-type (WT) mice and pannexin-1 knockout (Panx1) mice, in which ACh release is potentiated by the disinhibition of the L-type VDCCs upon the activation of P2X7 receptors, were used. Miniature end-plate potentials (MEPPs) and evoked end-plate potentials (EPPs) were recorded when the motor terminals were loaded with slow or fast Ca chelators (EGTA-AM or BAPTA-AM, respectively, 50 μM).

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

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.

Mechanism of P2X7 receptor-dependent enhancement of neuromuscular transmission in pannexin 1 knockout mice.

P2X7 receptors are present in presynaptic membranes of motor synapses, but their regulatory role in modulation of neurotransmitter release remains poorly understood. P2X7 receptors may interact with pannexin 1 channels to form a purinergic signaling unit. The potential mechanism of P2X7 receptor-dependent modulation of acetylcholine (ACh) release was investigated by recording miniature endplate potentials (MEPPs) and evoked endplate potentials (EPPs) in neuromuscular junctions of wild-type (WT) and pannexin 1 knockout (Panx1) mice.

Calcineurin and Its Role in Synaptic Transmission.

Calcineurin (CaN) is a serine/threonine phosphatase widely expressed in different cell types and structures including neurons and synapses. The most studied role of CaN is its involvement in the functioning of postsynaptic structures of central synapses. The role of CaN in the presynaptic structures of central and peripheral synapses is less understood, although it has generated a considerable interest and is a subject of a growing number of studies.

Ryanodine- and CaMKII-dependent release of endogenous CGRP induces an increase in acetylcholine quantal size in neuromuscular junctions of mice.

Objective: The aim of this study was to identify the mechanism responsible for an increase in miniature endplate potentials (MEPPs) amplitude, induced by ryanodine as an agonist of ryanodine receptors in mouse motor nerve terminals.

Methods: Using intracellular microelectrode recordings of MEPPs and evoked endplate potentials (EPPs), the changes in spontaneous and evoked acetylcholine release in motor synapses of mouse diaphragm neuromuscular preparations were studied.

Results: Ryanodine (0.

CaMKII Is Involved in the Choline-Induced Downregulation of Acetylcholine Release in Mouse Motor Synapses.

We investigated the involvement of calcium-dependent enzymes, protein kinase C (PKC) and calcium-calmodulin-dependent protein kinase II (CaMKII), in the signaling pathway triggered by the activation of presynaptic alpha7-type nicotinic acetylcholine receptors by exogenous choline, leading to downregulation of the evoked acetylcholine (ACh) release in mouse motor synapses. Blockade of PKC with chelerythrine neither changed the evoked release of ACh by itself nor prevented the inhibitory effect of choline. The CaMKII blocker KN-62 did not affect synaptic activity but fully prevented the choline-induced downregulation of ACh release.

Calcitonin gene-related peptide increases acetylcholine quantal size in neuromuscular junctions of mice.

We used an intracellular microelectrode technique to study the mechanisms of action of two isoforms (human and rat) of calcitonin gene-related peptide (CGRP) on the evoked and spontaneous quantal secretion of acetylcholine (ACh) in mouse diaphragm motor synapses. Recordings of miniature endplate potentials (MEPPs) and evoked multiquantal endplate potentials (EPPs) in a cut neuromuscular preparation showed that CGRP increased the amplitude of EPPs without influencing their quantal content. Both isoforms of CGRP in a wide range of concentrations (1nM-1μM) provoked a similar considerable increase in MEPPs amplitude in a dose-dependent manner (up to 150-160% compared to control) without changing their frequency, rise-time, and decay.

The mechanism of choline-mediated inhibition of acetylcholine release in mouse motor synapses.

The mechanism of action of tonically applied choline, the agonist of α7 nicotinic acetylcholine receptors (nAChRs), to the spontaneous and evoked release of a neurotransmitter in mouse motor synapses in diaphragm neuromuscular preparations using intracellular microelectrode recordings of miniature endplate potentials (MEPPs) and evoked endplate potentials (EPPs) was studied. Exogenous choline was shown to exhibit a presynaptic inhibitory effect on the amplitude and quantal content of EPPs for the activity of neuromuscular junction evoked by single and rhythmic stimuli. This effect was inhibited either by antagonists of α7-nAChRs, such as methyllycaconitine and α-cobratoxin, or by blocking SK-type calcium-activated potassium (KCa) channels with apamin or blocking intraterminal ryanodine receptors with ryanodine.

Involvement of basal and calcium-activated protein kinase C in neurotransmitter secretion in mouse motor synapses.

Blocker of presynaptic protein kinase C isoforms, GF109203X, reduced quantal content of single and rhythmic evoked end-plate potentials. The increase in quantal content of single potentials under the effect of 4- aminopyridine was neutralized by 75% under the effect of L-type Ca(2+)-channel blocker nitrendipine and completely returned to the control level after protein kinase C inhibition with chelerythrine. Neither nitrendipine, nor GF109203X affected the potentiating effect of tetraethylammonium on quantal content of end-plate potentials.

Facilitation of neurotransmitter release in mouse motor synapses in different modes of protein kinase C activation.

Protein kinase C blocker chelerythrine prevented the increase in quantal content of single and rhythmic evoked end-plate potentials after disinhibition of L-type Ca(2+)-channels with paxillin. Phorbol ester increased quantal content of single end-plate potentials and changed rhythmic activity of mouse motor synapses. The effects of phorbol ester were to a great extent neutralized by L-type Ca(2+)-channel blocker nitrendipine and were completely abolished by K(+)-channel blocker 4-aminopyridine.

Facilitation of acetylcholine secretion in mouse motor synapses caused by calcium release from depots upon activation of L-type calcium channels.

Pharmacological disinhibition of L-type Ca(2+) channels by two ways (with agonist S(-) BAY K 8644 and iberiotoxin, a Ca(2+)-activated BK-type K(+)-channel blocker) increases quantal content of evoked end-plate potentials, which was completely prevented by ryanodine (2 microM) blockade of ryanodine receptors. We conclude that increased quantal secretion of the transmitter induced by L-type Ca(2+) channel functioning requires activation of ryanodine receptors and calcium release from depots in motor terminals in mice.

The neuromuscular junctions of the slow and the fast excitatory axon in the closer of the crab Eriphia spinifrons are endowed with different Ca2+ channel types and allow neuron-specific modulation of transmitter release by two neuropeptides.

Most crustacean muscle fibers receive double excitatory innervation by functionally different motor neurons termed slow and fast. By using specific omega-toxins we show that the terminals of the slow closer excitor (SCE) and the fast closer excitor (FCE) at a crab muscle are endowed with different sets of presynaptic Ca(2+) channel types. omega-Agatoxin, a blocker of vertebrate P/Q-type channels, reduced the amplitude of EPSCs by decreasing the mean quantal content of transmitter release in both neurons by 70-85%, depending on the concentration.