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1.
Adv Exp Med Biol ; 1131: 73-91, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-31646507

RESUMO

Imaging techniques may overcome the limitations of electrode techniques to measure locally not only membrane potential changes, but also ionic currents. Here, we review a recently developed approach to image native neuronal Ca2+ currents from brain slices. The technique is based on combined fluorescence recordings using low-affinity Ca2+ indicators possibly in combination with voltage sensitive dyes. We illustrate how the kinetics of a Ca2+ current can be estimated from the Ca2+ fluorescence change and locally correlated with the change of membrane potential, calibrated on an absolute scale, from the voltage fluorescence change. We show some representative measurements from the dendrites of CA1 hippocampal pyramidal neurons, from olfactory bulb mitral cells and from cerebellar Purkinje neurons. We discuss the striking difference in data analysis and interpretation between Ca2+ current measurements obtained using classical electrode techniques and the physiological currents obtained using this novel approach. Finally, we show how important is the kinetic information on the native Ca2+ current to explore the potential molecular targets of the Ca2+ flux from each individual Ca2+ channel.


Assuntos
Canais de Cálcio , Neuroimagem , Animais , Cálcio/metabolismo , Canais de Cálcio/fisiologia , Dendritos/fisiologia , Humanos , Potenciais da Membrana/fisiologia , Imagem Óptica , Células Piramidais/fisiologia
2.
J Neurosci ; 39(11): 1969-1981, 2019 Mar 13.
Artigo em Inglês | MEDLINE | ID: mdl-30630881

RESUMO

In cerebellar Purkinje neuron dendrites, the transient depolarization associated with a climbing fiber (CF) EPSP activates voltage-gated Ca2+ channels (VGCCs), voltage-gated K+ channels (VGKCs), and Ca2+-activated SK and BK K+ channels. The resulting membrane potential (V m) and Ca2+ transients play a fundamental role in dendritic integration and synaptic plasticity of parallel fiber inputs. Here we report a detailed investigation of the kinetics of dendritic Ca2+ and K+ channels activated by CF-EPSPs, based on optical measurements of V m and Ca2+ transients and on a single-compartment NEURON model reproducing experimental data. We first measured V m and Ca2+ transients associated with CF-EPSPs at different initial V m, and we analyzed the changes in the Ca2+ transients produced by the block of each individual VGCCs, of A-type VGKCs and of SK and BK channels. Then, we constructed a model that includes six active ion channels to accurately match experimental signals and extract the physiological kinetics of each channel. We found that two different sets of channels are selectively activated. When the dendrite is hyperpolarized, CF-EPSPs mainly activate T-type VGCCs, SK channels, and A-type VGKCs that limit the transient V m ∼ <0 mV. In contrast, when the dendrite is depolarized, T-type VGCCs and A-type VGKCs are inactivated and CF-EPSPs activate P/Q-type VGCCs, high-voltage activated VGKCs, and BK channels, leading to Ca2+ spikes. Thus, the potentially activity-dependent regulation of A-type VGKCs, controlling the activation of this second set of channels, is likely to play a crucial role in signal integration and plasticity in Purkinje neuron dendrites.SIGNIFICANCE STATEMENT The climbing fiber synaptic input transiently depolarizes the dendrite of cerebellar Purkinje neurons generating a signal that plays a fundamental role in dendritic integration. This signal is mediated by two types of Ca2+ channels and four types of K+ channels. Thus, understanding the kinetics of all of these channels is crucial for understanding PN function. To obtain this information, we used an innovative strategy that merges ultrafast optical membrane potential and Ca2+ measurements, pharmacological analysis, and computational modeling. We found that, according to the initial membrane potential, the climbing fiber depolarizing transient activates two distinct sets of channels. Moreover, A-type K+ channels limit the activation of P/Q-type Ca2+ channels and associated K+ channels, thus preventing the generation of Ca2+ spikes.

3.
Eur J Neurosci ; 2018 Nov 02.
Artigo em Inglês | MEDLINE | ID: mdl-30387216

RESUMO

Optogenetics is based on the selective expression of exogenous opsins by neurons allowing experimental control of their electrical activity using visible light. The interpretation of the results of optogenetic experiments is based on the assumption that light stimulation selectively acts on those neurons expressing the exogenous opsins without perturbing the activity of naive ones. Here, we report that light stimulation, of wavelengths and power in the range of those normally used in optogenetic experiments, consistently reduces the firing activity of naive Mitral Cells (MCs) and Tufted Neurons in the olfactory bulb as well as in Medium Spiny Neurons (MSNs) in the striatum. No such effect was observed for cerebellar Purkinje and hippocampal CA1 neurons. The effects on MC firing appear to be mainly due to a light-induced increase in tissue temperature, between 0.1 and 0.4°C, associated with the generation of a hyperpolarizing current and a modification of action potential (AP) shape. Therefore, light in the visible range can affect neuronal physiology in a cell-specific manner. Beside the implications for optogenetic studies, our results pave the way to investigating the use of visible light for therapeutic purposes in pathologies associated with neuronal hyperexcitability.

4.
J Biophotonics ; 11(3)2018 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29165917

RESUMO

In brain slices, resolving fast Ca2+ fluorescence signals from submicron structures is typically achieved using 2-photon or confocal scanning microscopy, an approach that limits the number of scanned points. The novel multiplexing confocal system presented here overcomes this limitation. This system is based on a fast spinning disk, a multimode diode laser and a novel high-resolution CMOS camera. The spinning disk, running at 20 000 rpm, has custom-designed spiral pattern that maximises light collection, while rejecting out-of-focus fluorescence to resolve signals from small neuronal compartments. Using a 60× objective, the camera permits acquisitions of tens of thousands of pixels at resolutions of ~250 nm per pixel in the kHz range with 14 bits of digital depth. The system can resolve physiological Ca2+ transients from submicron structures at 20 to 40 µm below the slice surface, using the low-affinity Ca2+ indicator Oregon Green BAPTA-5N. In particular, signals at 0.25 to 1.25 kHz were resolved in single trials, or through averages of a few recordings, from dendritic spines and small parent dendrites in cerebellar Purkinje neurons. Thanks to an unprecedented combination of temporal and spatial resolution with relatively simple implementation, it is expected that this system will be widely adopted for multisite monitoring of Ca2+ signals.

5.
J Neurosci Methods ; 268: 66-77, 2016 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-27163479

RESUMO

BACKGROUND: Fast Ca(2+) imaging using low-affinity fluorescent indicators allows tracking Ca(2+) neuronal influx at high temporal resolution. In some systems, where the Ca(2+)-bound indicator is linear with Ca(2+) entering the cell, the Ca(2+) current has same kinetics of the fluorescence time derivative. In other systems, like cerebellar Purkinje neuron dendrites, the time derivative strategy fails since fluorescence kinetics is affected by Ca(2+) binding proteins sequestering Ca(2+) from the indicator. NEW METHOD: Our novel method estimates the kinetics of the Ca(2+) current in cells where the time course of fluorescence is not linear with Ca(2+) influx. The method is based on a two-buffer and two-indicator model, with three free parameters, where Ca(2+) sequestration from the indicator is mimicked by Ca(2+)-binding to the slower buffer. We developed a semi-automatic protocol to optimise the free parameters and the kinetics of the input current to match the experimental fluorescence change with the simulated curve of the Ca(2+)-bound indicator. RESULTS: We show that the optimised input current is a good estimate of the real Ca(2+) current by validating the method both using computer simulations and data from real neurons. We report the first estimates of Ca(2+) currents associated with climbing fibre excitatory postsynaptic potentials in Purkinje neurons. COMPARISON WITH EXISTING METHODS: The present method extends the possibility of studying Ca(2+) currents in systems where the existing time derivative approach fails. CONCLUSIONS: The information available from our technique allows investigating the physiological behaviour of Ca(2+) channels under all possible conditions.


Assuntos
Canais de Cálcio/metabolismo , Cálcio/metabolismo , Potenciais da Membrana/fisiologia , Neurônios/metabolismo , Processamento de Sinais Assistido por Computador , Imagens com Corantes Sensíveis à Voltagem/métodos , Animais , Cerebelo/citologia , Cerebelo/metabolismo , Simulação por Computador , Hipocampo/citologia , Hipocampo/metabolismo , Cinética , Camundongos Endogâmicos C57BL , Modelos Neurológicos , Neurônios/citologia , Dinâmica não Linear , Reconhecimento Automatizado de Padrão/métodos , Técnicas de Cultura de Tecidos
6.
Proc Natl Acad Sci U S A ; 112(2): E204-13, 2015 Jan 13.
Artigo em Inglês | MEDLINE | ID: mdl-25550512

RESUMO

NMDA receptors (NMDARs) require the coagonists D-serine or glycine for their activation, but whether the identity of the coagonist could be synapse specific and developmentally regulated remains elusive. We therefore investigated the contribution of D-serine and glycine by recording NMDAR-mediated responses at hippocampal Schaffer collaterals (SC)-CA1 and medial perforant path-dentate gyrus (mPP-DG) synapses in juvenile and adult rats. Selective depletion of endogenous coagonists with enzymatic scavengers as well as pharmacological inhibition of endogenous D-amino acid oxidase activity revealed that D-serine is the preferred coagonist at SC-CA1 mature synapses, whereas, unexpectedly, glycine is mainly involved at mPP-DG synapses. Nevertheless, both coagonist functions are driven by the levels of synaptic activity as inferred by recording long-term potentiation generated at both connections. This regional compartmentalization in the coagonist identity is associated to different GluN1/GluN2A to GluN1/GluN2B subunit composition of synaptic NMDARs. During postnatal development, the replacement of GluN2B- by GluN2A-containing NMDARs at SC-CA1 synapses parallels a change in the identity of the coagonist from glycine to D-serine. In contrast, NMDARs subunit composition at mPP-DG synapses is not altered and glycine remains the main coagonist throughout postnatal development. Altogether, our observations disclose an unprecedented relationship in the identity of the coagonist not only with the GluN2 subunit composition at synaptic NMDARs but also with astrocyte activity in the developing and mature hippocampus that reconciles the complementary functions of D-serine And Glycine In Modulating Nmdars During The Maturation Of Tripartite Glutamatergic Synapses.


Assuntos
Hipocampo/crescimento & desenvolvimento , Hipocampo/metabolismo , Receptores de N-Metil-D-Aspartato/agonistas , Receptores de N-Metil-D-Aspartato/metabolismo , Sinapses/metabolismo , Animais , Animais Recém-Nascidos , Astrócitos/metabolismo , Região CA1 Hipocampal/crescimento & desenvolvimento , Região CA1 Hipocampal/metabolismo , Giro Denteado/crescimento & desenvolvimento , Giro Denteado/metabolismo , Glicina/metabolismo , Potenciação de Longa Duração , Masculino , Neurônios/metabolismo , Ratos , Serina/metabolismo
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