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Cd 2+ is one of the most widespread environmental pollutants and its accumulation in central and peripheral nervous systems leads to neurotoxicity as well as aggravation of common neurodegenerative diseases. Mechanism of the Cd 2+ toxicity is far from being resolved. Here, using microelectrode recordings of postsynaptic responses and fluorescent redox indicators we studied the effect of Cd 2+ in the submicromolar range on timing of neurotransmitter release and oxidative status in two functionally different compartments of the same frog motor nerve terminal. Cd 2+ (0.1-1 μM) acting as typical voltage-gated Ca 2+ channel (VGCC) antagonist decreased neurotransmitter release in both distal and proximal parts of the nerve terminal, but in contrast to the VGCC blockers Cd 2+ (0.1-0.5 μM) desynchronized the release selectively in the distal region. The latter action of Cd 2+ was completely prevented by inhibitor of NADPH-oxidase and antioxidants, including mitochondrial specific, as well as redox-sensitive TRPV1 channel blocker. Cd 2+ markedly increased levels of mitochondrial reactive oxygen species (ROS) in both the distal and proximal compartments of the nerve terminal, which was associated with lipid peroxidation mainly in the distal region. Zn 2+ , whose transport systems translocate Cd 2+ , markedly enhanced the effects of Cd 2+ on both the mitochondrial ROS levels and timing of neurotransmitter release. Furthermore, in the presence of Zn 2+ ions, Cd 2+ also desynchronized the neurotransmitter release in the proximal region. Thus, in synapses Cd 2+ at very low concentrations can increase mitochondrial ROS, lipid peroxidation and disturb the timing of neurotransmitter release via a ROS/TRPV-dependent mechanism. Desynchronization of neurotransmitter release and synaptic oxidative stress could be early events in Cd 2+ neurotoxicity., Competing Interests: Declaration of competing interest We declare no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Cholesterol oxidation products frequently have a high biological activity. In the present study, we have used microelectrode recording of end plate currents and FM-based optical detection of synaptic vesicle exo-endocytosis to investigate the effects of two structurally similar oxysterols, olesoxime (cholest-4-en-3-one, oxime) and 5ɑ-cholestan-3-one (5ɑCh3), on neurotransmission at the frog neuromuscular junction. Olesoxime is an exogenous, potentially neuroprotective, substance and 5ɑCh3 is an intermediate product in cholesterol metabolism, which is elevated in the case of cerebrotendinous xanthomatosis. We found that olesoxime slightly increased evoked neurotransmitter release in response to a single stimulus and significantly reduced synaptic depression during high frequency activity. The last effect was due to an increase in both the number of synaptic vesicles involved in exo-endocytosis and the rate of synaptic vesicle recycling. In contrast, 5ɑCh3 reduced evoked neurotransmitter release during the low- and high frequency synaptic activities. The depressant action of 5ɑCh3 was associated with a reduction in the number of synaptic vesicles participating in exo- and endocytosis during high frequency stimulation, without a change in rate of the synaptic vesicle recycling. Of note, olesoxime increased the staining of synaptic membranes with the B-subunit of cholera toxin and the formation of fluorescent ganglioside GM1 clusters, and decreased the fluorescence of 22-NBD-cholesterol, while 5ɑCh3 had the opposite effects, suggesting that the two oxysterols have different effects on lipid raft stability. Taken together, these data show that these two structurally similar oxysterols induce marked different changes in neuromuscular transmission which are related with the alteration in synaptic vesicle cycle., (Copyright © 2016 Elsevier B.V. All rights reserved.)