Journal of Neuroscience
0270-6474
1529-2401
Mỹ
Cơ quản chủ quản: Society for Neuroscience , SOC NEUROSCIENCE
Lĩnh vực:
Neuroscience (miscellaneous)
Các bài báo tiêu biểu
Pharmacological and ionic characterizations of the muscarinic receptors modulating [3H]acetylcholine release from rat cortical synaptosomes The muscarinic receptors that modulate acetylcholine release from rat cortical synaptosomes were characterized with respect to sensitivity to drugs that act selectively at M1 or M2 receptor subtypes, as well as to changes in ionic strength and membrane potential. The modulatory receptors appear to be of the M2 type, since they are activated by carbachol, acetylcholine, methacholine, oxotremorine, and bethanechol, but not by pilocarpine, and are blocked by atropine, scopolamine, and gallamine (at high concentrations), but not by pirenzepine or dicyclomine. The ED50S for carbachol, acetylcholine, and oxotremorine are less than 10 microM, suggesting that the high affinity state of the receptor is functional. High ionic strength induced by raising the NaCl concentration has no effect on agonist (oxotremorine) potency, but increases the efficacy of this compound, which disagrees with receptor- binding studies. On the other hand, depolarization with either KCl or with veratridine (20 microM) reduces agonist potencies by approximately an order of magnitude, suggesting a potential mechanism for receptor regulation.
Tập 5 Số 5 - Trang 1202-1207 - 1985
Synaptic Islands Defined by the Territory of a Single Astrocyte
Tập 27 Số 24 - Trang 6473-6477 - 2007
Trafficking and Fusion of Neuropeptide Y-Containing Dense-Core Granules in Astrocytes It is becoming clear that astrocytes are active participants in synaptic functioning and exhibit properties, such as the secretion of classical transmitters, previously thought to be exclusively neuronal. Whether these similarities extend to the release of neuropeptides, the other major class of transmitters, is less clear. Here we show that cortical astrocytes can synthesize both native and foreign neuropeptides and can secrete them in a stimulation-dependent manner. Reverse transcription-PCR and mass spectrometry indicate that cortical astrocytes contain neuropeptide Y (NPY), a widespread neuronal transmitter. Immunocytochemical studies reveal NPY-immunoreactive (IR) puncta that colocalize with markers of the regulated secretory pathway. These NPY-IR puncta are distinct from the synaptic-like vesicles that contain classical transmitters, and the two types of organelles are differentially distributed. After activation of metabotropic glutamate receptors and the release of calcium from intracellular stores, the NPY-IR puncta fuse with the cell membrane, and the peptide-containing dense cores are displayed. To determine whether peptide secretion subsequently occurred, exocytosis was monitored from astrocytes expressing NPY–red fluorescent protein (RFP). In live cells, after activation of glutamate receptors, the intensity of the NPY–RFP-labeled puncta declined in a step-like manner indicating a regulated release of the granular contents. Because NPY is a widespread and potent regulator of synaptic transmission, these results suggest that astrocytes could play a role in the peptidergic modulation of synaptic signaling in the CNS.
Tập 28 Số 51 - Trang 13815-13827 - 2008
Fast Subplasma Membrane Ca<sup>2+</sup>Transients Control Exo-Endocytosis of Synaptic-Like Microvesicles in Astrocytes Astrocytes are the most abundant glial cell type in the brain. Although not apposite for long-range rapid electrical communication, astrocytes share with neurons the capacity of chemical signaling via Ca2+ -dependent transmitter exocytosis. Despite this recent finding, little is known about the specific properties of regulated secretion and vesicle recycling in astrocytes. Important differences may exist with the neuronal exocytosis, starting from the fact that stimulus-secretion coupling in astrocytes is voltage independent, mediated by G-protein-coupled receptors and the release of Ca2+ from internal stores. Elucidating the spatiotemporal properties of astrocytic exo-endocytosis is, therefore, of primary importance for understanding the mode of communication of these cells and their role in brain signaling. We here take advantage of fluorescent tools recently developed for studying recycling of glutamatergic vesicles at synapses (Voglmaier et al., 2006; Balaji and Ryan, 2007); we combine epifluorescence and total internal reflection fluorescence imaging to investigate with unprecedented temporal and spatial resolution, the stimulus-secretion coupling underlying exo-endocytosis of glutamatergic synaptic-like microvesicles (SLMVs) in astrocytes. Our main findings indicate that (1) exo-endocytosis in astrocytes proceeds with a time course on the millisecond time scale (τexocytosis = 0.24 ± 0.017 s; τendocytosis = 0.26 ± 0.03 s) and (2) exocytosis is controlled by local Ca2+ microdomains. We identified submicrometer cytosolic compartments delimited by endoplasmic reticulum tubuli reaching beneath the plasma membrane and containing SLMVs at which fast (time-to-peak, ∼50 ms) Ca2+ events occurred in precise spatial-temporal correlation with exocytic fusion events. Overall, the above characteristics of transmitter exocytosis from astrocytes support a role of this process in fast synaptic modulation.
Tập 28 Số 37 - Trang 9122-9132 - 2008
Rapid Astrocyte Calcium Signals Correlate with Neuronal Activity and Onset of the Hemodynamic Response In Vivo
Tập 27 Số 23 - Trang 6268-6272 - 2007
Elevation of intracellular Ca2+ in astrocytes can influence cerebral microcirculation and modulate synaptic transmission. Recently, in vivo imaging studies identified delayed, sensory-driven Ca2+ oscillations in cortical astrocytes; however, the long latencies of these Ca2+ signals raises questions in regards to their suitability for a role in short-latency modulation of cerebral microcirculation or rapid astrocyte-to-neuron communication. Here, using in vivo two-photon Ca2+ imaging, we demonstrate that ∼5% of sulforhodamine 101-labeled astrocytes in the hindlimb area of the mouse primary somatosensory cortex exhibit short-latency (peak amplitude ∼0.5 s after stimulus onset), contralateral hindlimb-selective sensory-evoked Ca2+ signals that operate on a time scale similar to neuronal activity and correlate with the onset of the hemodynamic response as measured by intrinsic signal imaging. The kinetics of astrocyte Ca2+ transients were similar in rise and decay times to postsynaptic neuronal transients, but decayed more slowly than neuropil Ca2+ transients that presumably reflect presynaptic transients. These in vivo findings suggest that astrocytes can respond to sensory activity in a selective manner and process information on a subsecond time scale, enabling them to potentially form an active partnership with neurons for rapid regulation of microvascular tone and neuron–astrocyte network properties.
On the Role of Voltage-Dependent Calcium Channels in Calcium Signaling of Astrocytes<i>In Situ</i>
Tập 18 Số 12 - Trang 4637-4645 - 1998
“Kiss-and-Run” Glutamate Secretion in Cultured and Freshly Isolated Rat Hippocampal Astrocytes Under physiological conditions, astrocytes not only passively support and nourish adjacent neurons, but also actively modulate neuronal transmission by releasing “glial transmitters,” such as glutamate, ATP, andd -serine. Unlike the case for neurons, the mechanisms by which glia release transmitters are essentially unknown. Here, by using electrochemical amperometry and frequency-modulated single-vesicle imaging, we discovered that hippocampal astrocytes exhibit two modes of exocytosis of glutamate in response to various stimuli. After physiological stimulation, a glial vesicle releases a quantal content that is only 10% of that induced by nonphysiological, mechanical stimulation. The small release event arises from a brief (∼2 ms) opening of the fusion pore. We conclude that, after physiological stimulation, astrocytes release glutamate via a vesicular “kiss-and-run” mechanism.
Tập 25 Số 40 - Trang 9236-9243 - 2005
Vesicular Glutamate Transporter-Dependent Glutamate Release from Astrocytes Astrocytes exhibit excitability based on variations of their intracellular Ca2+ concentrations, which leads to glutamate release, that in turn can signal to adjacent neurons. This glutamate-mediated astrocyte–neuron signaling occurs at physiological intracellular Ca2+ levels in astrocytes and includes modulation of synaptic transmission. The mechanism underlying Ca2+ -dependent glutamate release from astrocytes is most likely exocytosis, because astrocytes express the protein components of the solubleN -ethyl maleimide-sensitive fusion protein attachment protein receptors complex, including synaptobrevin 2, syntaxin, and synaptosome-associated protein of 23 kDa. Although these proteins mediate Ca2+ -dependent glutamate release from astrocytes, it is not well understood whether astrocytes express functional vesicular glutamate transporters (VGLUTs) that are critical for vesicle refilling. Here, we find in cultured and freshly isolated astrocytes the presence of brain-specific Na+ -dependent inorganic phosphate cotransporter and differentiation-associated Na+ -dependent inorganic phosphate cotransporter that have recently been identified as VGLUTs 1 and 2. Indirect immunocytochemistry showed a punctate pattern of VGLUT immunoreactivity throughout the entire cell body and processes, whereas pharmacological inhibition of VGLUTs abolished mechanically and agonist-evoked Ca2+ -dependent glutamate release from astrocytes. Taken together, these data indicate that VGLUTs play a functional role in exocytotic glutamate release from astrocytes.
Tập 24 Số 11 - Trang 2633-2642 - 2004
Glutamate Released from Glial Cells Synchronizes Neuronal Activity in the Hippocampus Glial cells of the nervous system directly influence neuronal and synaptic activities by releasing transmitters. However, the physiological consequences of this glial transmitter release on brain information processing remain poorly understood. We demonstrate here in hippocampal slices of 2- to 5-week-old rats that glutamate released from glial cells generates slow transient currents (STCs) mediated by the activation of NMDA receptors in pyramidal cells. STCs persist in the absence of neuronal and synaptic activity, indicating a nonsynaptic origin of the source of glutamate. Indeed, STCs occur spontaneously but can also be induced by pharmacological tools known to activate astrocytes and by the selective mechanical stimulation of single nearby glial cells. Bath application of the inhibitor of the glutamate uptakedl -threo-β-benzyloxyaspartate increases both the frequency of STCs and the amplitude of a tonic conductance mediated by NMDA receptors and probably also originated from glial glutamate release. By using dual recordings, we observed synchronized STCs in pyramidal cells having their soma distant by <100 μm. The degree of precision (<100 msec) of this synchronization rules out the involvement of calcium waves spreading through the glial network. It also indicates that single glial cells release glutamate onto adjacent neuronal processes, thereby controlling simultaneously the excitability of several neighboring pyramidal cells. In conclusion, our results show that the glial glutamate release occurs spontaneously and synchronizes the neuronal activity in the hippocampus.
Tập 24 Số 31 - Trang 6920-6927 - 2004
Key Role of the Postsynaptic Density Scaffold Proteins Shank and Homer in the Functional Architecture of Ca<sup>2+</sup>Homeostasis at Dendritic Spines in Hippocampal Neurons A key aspect of postsynaptic function, also important for plasticity, is the segregation within dendritic spines of Ca2+ rises attributable to release from intracellular stores. Previous studies have shown that overexpression in hippocampal neurons of two postsynaptic density (PSD) scaffold proteins, Shank1B and Homer1b, induces spine maturation, including translocation of the intracellular Ca2+ channel inositol trisphosphate receptor (IP3 R). The structural and functional significance of these processes remained undefined. Here, we show that in its relocation, IP3 R is accompanied by other endoplasmic reticulum (ER) proteins: the Ca2+ pump sarcoendoplasmic reticulum calcium ATPase, the lumenal Ca2+ -binding protein calreticulin, the ER lumen-addressed green fluorescent protein, and, to a lesser extent, the membrane chaperone calbindin. The specificity of these translocations was demonstrated by their inhibition by both a Shank1 fragment and the dominant-negative Homer1a. Activation in Shank1B-transfected neurons of the metabotropic glutamatergic receptors 1/5 (mGluRs1/5), which induce IP3 generation with ensuing Ca2+ release from the stores, triggered considerable increases in Ca2+ -dependent responses: activation of the big K+ channel, which was revealed by patch clamping, and extracellular signal-regulated protein kinase (ERK) phosphorylation. The interaction of Shank1B and Homer1b appears as the molecular mechanism linking mGluRs1/5, strategically located in the spines, to IP3 R with the integration of entire ER cisternas in the PSD and with consequences on both local Ca2+ homeostasis and overall neuronal signaling.
Tập 25 Số 18 - Trang 4587-4592 - 2005