Calmodulin mediates rapid recruitment of fast-releasing synaptic vesicles at a calyx-type synapse.

In many synapses, depletion and recruitment of releasable synaptic vesicles contribute to use-dependent synaptic depression and recovery. Recently it has been shown that high- frequency presynaptic stimulation enhances recovery from depression, which may be mediated by Ca2+. We addressed this issue by measuring quantal release rates at the calyx of Held synapse and found that transmission is mediated by a heterogeneous population of vesicles, with one subset releasing rapidly and recovering slowly and another one releasing reluctantly and recovering rapidly. Ca2+ promotes refilling of the rapidly releasing synaptic vesicle pool and calmodulin inhibitors block this effect. We propose that calmodulin- dependent refilling supports recovery from synaptic depression during high-frequency trains in concert with rapid recovery of the slowly releasing vesicles

Multiple roles of calcium ions in the regulation of neurotransmitter release.

The intracellular calcium concentration ([Ca2+]) has important roles in the triggering of neurotransmitter release and the regulation of short-term plasticity (STP). Transmitter release is initiated by quite high concentrations within microdomains, while short-term facilitation is strongly influenced by the global buildup of “residual calcium.” A global rise in [Ca2+] also accelerates the recruitment of release-ready vesicles, thereby controlling the degree of short-term depression (STD) during sustained activity, as well as the recovery of the vesicle pool in periods of rest. We survey data that lead us to propose two distinct roles of [Ca2+] in vesicle recruitment: one accelerating “molecular priming” (vesicle docking and the buildup of a release machinery), the other promoting the tight coupling between releasable vesicles and Ca2+ channels. Such coupling is essential for rendering vesicles sensitive to short [Ca2+] transients, generated during action potentials

Mottainai as a Japanese Cultural Keyword： A Key Semantic Difference to the English Word Waste

認知・機能言語学研究(7

The coupling between synaptic vesicles and Ca²⁺ channels determines fast neurotransmitter release

SummaryIn order to release neurotransmitter synchronously in response to a presynaptic action potential, synaptic vesicles must be both release competent and located close to presynaptic Ca2+ channels. It has not been shown, however, which of the two is the more decisive factor. We tested this issue at the calyx of Held synapse by combining Ca2+ uncaging and electrophysiological measurements of postsynaptic responses. After depletion of the synaptic vesicles that are responsible for synchronous release during action potentials, uniform elevation of intracellular Ca2+ by Ca2+ uncaging could still elicit rapid release. The Ca2+ sensitivity of remaining vesicles was reduced no more than 2-fold, which is insufficient to explain the slow-down of the kinetics of release (10-fold) observed during a depolarizing pulse. We conclude that recruitment of synaptic vesicles to sites where Ca2+ channels cluster, rather than fusion competence, is a limiting step for rapid neurotransmitter release in response to presynaptic action potentials

Calcium dependence of exo- and endocytotic coupling at a glutamatergic synapse.

SummaryThe mechanism coupling exocytosis and endocytosis remains to be elucidated at central synapses. Here, we show that the mechanism linking these two processes is dependent on microdomain-[Ca2+]i similar to that which triggers exocytosis, as well as the exocytotic protein synaptobrevin/VAMP. Furthermore, block of endocytosis has a limited, retrograde action on exocytosis, delaying recruitment of release-ready vesicles and enhancing short-term depression. This effect sets in so rapidly that it cannot be explained by the nonavailability of recycled vesicles. Rather, we postulate that perturbation of a step linking exocytosis and endocytosis temporarily prevents new vesicles from docking at specialized sites for exocytosis

Mechanistic insights into cAMP-mediated presynaptic potentiation at hippocampal mossy fiber synapses

Presynaptic plasticity is an activity-dependent change in the neurotransmitter release and plays a key role in dynamic modulation of synaptic strength. Particularly, presynaptic potentiation mediated by cyclic adenosine monophosphate (cAMP) is widely seen across the animals and thought to contribute to learning and memory. Hippocampal mossy fiber-CA3 pyramidal cell synapses have been used as a model because of robust presynaptic potentiation in short- and long-term forms. Moreover, direct presynaptic recordings from large mossy fiber terminals allow one to dissect the potentiation mechanisms. Recently, super-resolution microscopy and flash-and-freeze electron microscopy have revealed the localizations of release site molecules and synaptic vesicles during the potentiation at a nanoscale, identifying the molecular mechanisms of the potentiation. Incorporating these growing knowledges, we try to present plausible mechanisms underlying the cAMP-mediated presynaptic potentiation

Individual and Technological Factors Affecting Undergraduates' Use of Mobile Technology in University of Ilorin, Nigeria

The proliferation and utilization of handheld mobile technology among undergraduates for mobile learning cannot be underestimated. This study was geared towards investigating individual and technological factors affecting the perceived usefulness of mobile technology by undergraduates in university of Ilorin. The study was a descriptive research of the survey type. Samples were randomly drawn from all students in the 15 faculties. A total of 100 undergraduates were sampled. Two research questions, and one hypothesis was tested. Mean was used to answer the research questions; while Pearson Product Moment Correlation (PPMC) was used to test the relationship between the technological and individual factors. Findings from the study revealed that the technological and individual factors positively affected the perceived usefulness of mobile technology among undergraduates. More so, there was a positive relationship between technological and individual factors that affected perceived usefulness of mobile technology. Based on the findings, it was concluded that both the individual and technological factors affected the perceived usefulness of mobile technology positively. It was recommended that students should be encouraged in the use of Mobile technology devices for learning