The Origin of Physiological Local mGluR1 Supralinear Ca2+ Signals in Cerebellar Purkinje Neurons.

In mouse cerebellar Purkinje neurons (PNs), the climbing fiber (CF) input provides a signal to parallel fiber (PF) synapses, triggering PF synaptic plasticity. This signal is given by supralinear Ca2+ transients, associated with the CF synaptic potential and colocalized with the PF Ca2+ influx, occurring only when PF activity precedes the CF input. Here, we unravel the biophysical determinants of supralinear Ca2+ signals associated with paired PF-CF synaptic activity. We used membrane potential (Vm) and Ca2+ imaging to investigate the local CF-associated Ca2+ influx following a train of PF synaptic potentials in two cases: (1) when the dendritic Vm is hyperpolarized below the resting Vm, and (2) when the dendritic Vm is at rest. We found that supralinear Ca2+ signals are mediated by type-1 metabotropic glutamate receptors (mGluR1s) when the CF input is delayed by 100-150 ms from the first PF input in both cases. When the dendrite is hyperpolarized only, however, mGluR1s boost neighboring T-type channels, providing a mechanism for local coincident detection of PF-CF activity. The resulting Ca2+ elevation is locally amplified by saturation of endogenous Ca2+ buffers produced by the PF-associated Ca2+ influx via the mGluR1-mediated nonselective cation conductance. In contrast, when the dendritic Vm is at rest, mGluR1s increase dendritic excitability by inactivating A-type K+ channels, but this phenomenon is not restricted to the activated PF synapses. Thus, Vm is likely a crucial parameter in determining PF synaptic plasticity, and the occurrence of hyperpolarization episodes is expected to play an important role in motor learning.SIGNIFICANCE STATEMENT In Purkinje neurons, parallel fiber synaptic plasticity, determined by coincident activation of the climbing fiber input, underlies cerebellar learning. We unravel the biophysical mechanisms allowing the CF input to produce a local Ca2+ signal exclusively at the sites of activated parallel fibers. We show that when the membrane potential is hyperpolarized with respect to the resting membrane potential, type-1 metabotropic glutamate receptors locally enhance Ca2+ influx mediated by T-type Ca2+ channels, and that this signal is amplified by saturation of endogenous buffer also mediated by the same receptors. The combination of these two mechanisms is therefore capable of producing a Ca2+ signal at the activated parallel fiber sites, suggesting a role of Purkinje neuron membrane potential in cerebellar learning.

Laboratory method of microbial induced solidification/stabilization for municipal solid waste incineration fly ash.

This paper presents a method to solidify/stabilize the municipal solid waste incineration (MSWI) fly ash by originally employing the microbial induced carbonate precipitation (MICP) technique. In this method, the rich endogenous calcium in the MSWI fly ash was utilized to induce calcite precipitation, which is different from the operation of adding extra calcium source in previous researches. The fly ash sample had a CaO content of 44.5%, and its leaching concentrations of Zn, Cr and Pb exceed the limits of the identification standard for hazardous wastes in China. The optical density at 600 nm (OD600) of the bacterial solution was about 1.0 after the processes of bacterial activation and reproduction. The prepared fly ash sample was well mixed with bacterial solution at an ash-liquid ratio of 1 kg: 0.3 L and cured at a temperature of 20 °C and a humidity of ≥95% for 7 days. After treatment, the heavy metal leachability significantly reduced to meet the standard for pollution control of landfill site, and the unconfined compressive strength increased approximately 40%. The precipitated carbonates were verified by SEM-EDS analysis and quantified by measurement of carbonate content via acid-dissolving method. The results shone a light on the possibility of using MICP technique as a useful and efficient tool to stabilize the MSWI fly ash before being reused or properly stored in landfills. •The MICP method is efficient to reduce the heavy metal leachability and increase the compressive strength of MSWI fly ash.•The endogenous calcium in MSWI fly ash was utilized to induce calcite precipitation.•The heavy metals in MSWI fly ash were well immobilized by the formation of carbonates.

Estimation of presynaptic calcium currents and endogenous calcium buffers at the frog neuromuscular junction with two different calcium fluorescent dyes.

At the frog neuromuscular junction, under physiological conditions, the direct measurement of calcium currents and of the concentration of intracellular calcium buffers-which determine the kinetics of calcium concentration and neurotransmitter release from the nerve terminal-has hitherto been technically impossible. With the aim of quantifying both Ca(2+) currents and the intracellular calcium buffers, we measured fluorescence signals from nerve terminals loaded with the low-affinity calcium dye Magnesium Green or the high-affinity dye Oregon Green BAPTA-1, simultaneously with microelectrode recordings of nerve-action potentials and end-plate currents. The action-potential-induced fluorescence signals in the nerve terminals developed much more slowly than the postsynaptic response. To clarify the reasons for this observation and to define a spatiotemporal profile of intracellular calcium and of the concentration of mobile and fixed calcium buffers, mathematical modeling was employed. The best approximations of the experimental calcium transients for both calcium dyes were obtained when the calcium current had an amplitude of 1.6 ± 0.08 pA and a half-decay time of 1.2 ± 0.06 ms, and when the concentrations of mobile and fixed calcium buffers were 250 ± 13 µM and 8 ± 0.4 mM, respectively. High concentrations of endogenous buffers define the time course of calcium transients after an action potential in the axoplasm, and may modify synaptic plasticity.