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Retinal Slices (retinal + slice)
Selected AbstractsGlial cell-derived glutamate mediates autocrine cell volume regulation in the retina: activation by VEGFJOURNAL OF NEUROCHEMISTRY, Issue 2 2008Antje Wurm Abstract Astroglial cells are a source for gliotransmitters such as glutamate and ATP. We demonstrate here that gliotransmitters have autocrine functions in the regulation of cellular volume. Hypoosmotic stress in the presence of inflammatory mediators or oxidative stress, and during blockade or down-regulation of potassium channels, induces swelling of retinal glial cells. Vascular endothelial growth factor inhibits the osmotic swelling of glial cells in retinal slices or isolated cells. This effect was mediated by a kinase domain region/flk-1 receptor-evoked calcium dependent release of glutamate from glial cells, and subsequent stimulation of glial group I/II metabotropic glutamate receptors. Activation of kinase domain region/flk-1 or glutamate receptors evoked an autocrine swelling-inhibitory purinergic signaling cascade that was calcium-independent. This cascade involved the release of ATP and adenosine, and the activation of purinergic P2Y1 and adenosine A1 receptors, resulting in the opening of potassium and chloride channels and inhibition of cellular swelling. The glutamatergic-purinergic regulation of the glial cell volume may be functionally important in the homeostasis of the extracellular space volume during intense neuronal activation which is associated with a swelling of neuronal cell structures in the retina. However, glial cell-derived glutamate may also contribute to the swelling of activated neurons since metabolic poisoning of glial cells by iodoacetate inhibits the neuronal cell swelling mediated by activation of ionotropic glutamate receptors. [source] Properties of glycine receptors underlying synaptic currents in presynaptic axon terminals of rod bipolar cells in the rat retinaTHE JOURNAL OF PHYSIOLOGY, Issue 15 2009Svein Harald Mørkve The excitability of presynaptic terminals can be controlled by synaptic input that directly targets the terminals. Retinal rod bipolar axon terminals receive presynaptic input from different types of amacrine cells, some of which are glycinergic. Here, we have performed patch-clamp recordings from rod bipolar axon terminals in rat retinal slices. We used whole-cell recordings to study glycinergic inhibitory postsynaptic currents (IPSCs) under conditions of adequate local voltage clamp and outside-out patch recordings to study biophysical and pharmacological properties of the glycine receptors with ultrafast application. Glycinergic IPSCs, recorded in both intact cells and isolated terminals, were strychnine sensitive and displayed fast kinetics with a double-exponential decay. Ultrafast application of brief (,1 ms) pulses of glycine (3 mm) to patches evoked responses with fast, double-exponential deactivation kinetics, no evidence of desensitization in double-pulse experiments, relatively low apparent affinity (EC50,100 ,m), and high maximum open probability (,0.9). Longer pulses evoked slow, double-exponential desensitization and double-pulse experiments indicated slow, double-exponential recovery from desensitization. Non-stationary noise analysis of IPSCs and patch responses yielded single-channel conductances of ,41 pS and ,64 pS, respectively. Directly observed single-channel gating occurred at ,40,50 pS and ,80,90 pS in both types of responses, suggesting a mixture of heteromeric and homomeric receptors. Synaptic release of glycine leads to transient receptor activation, with about eight receptors available to bind transmitter after release of a single vesicle. With a low intracellular chloride concentration, this leads to either hyperpolarizing or shunting inhibition that will counteract passive and regenerative depolarization and depolarization-evoked transmitter release. [source] A glia,neuron alanine/ammonium shuttle is central to energy metabolism in bee retinaTHE JOURNAL OF PHYSIOLOGY, Issue 8 2008Jonathan A. Coles It has been proposed that glial cells may supply carbon fuel to neurons and also that there are fluxes of ammonium from neurons to glia. We have investigated both these proposals in Apis retinal slices, in which virtually all the mitochondria are in the photoreceptor neurons. Normally the superfusate contained no substrate of energy metabolism; addition of glucose or alanine did not increase oxygen consumption , confirming that the neurons received adequate substrate from glycogen in the glia. 1,4-Dideoxy-1,4-imino- d -arabinitol (DAB, 100 ,m), an inhibitor of glycogen phosphorylase, progressively decreased . This decrease was reversed by alanine but not glucose. Ammonium-sensitive microelectrodes did not detect significant extracellular [NH4+] ([NH4+]e) in slices superfused with normal superfusate. Removal of Cl,, necessary for cotransport of NH4+ into the glia, increased [NH4+]e so that at the end of 2 min photostimulation mean [NH4+]e was 0.442 mm (s.e.m.= 0.082 mm, n= 16). In 0 Cl,, [NH4+]e was reduced by 2-(methylamino)isobutyrate (MeAIB) an inhibitor of alanine transport. MeAIB also blocked oxidation of alanine in the presence of DAB, but did not decrease in normal superfusate. Lactate (l and d) and pyruvate (but not glucose) increased in DAB and decreased [NH4+]e in 0 Cl,. These results strengthen the evidence that in superfused retinal slices, glucose is metabolized exclusively in the glia, which supply alanine to the neurons, and that ammonium returns to the glia. They also show that another fuel (perhaps lactate) can be supplied by the glia to the neurons. [source] Spontaneous IPSCs and glycine receptors with slow kinetics in wide-field amacrine cells in the mature rat retinaTHE JOURNAL OF PHYSIOLOGY, Issue 1 2007Margaret Lin Veruki The functional properties of glycine receptors were analysed in different types of wide-field amacrine cells, narrowly stratifying cells considered to play a role in larger-scale integration across the retina. The patch-clamp technique was used to record spontaneous IPSCs (spIPSCs) and glycine-evoked patch responses from mature rat retinal slices (4,7 weeks postnatal). Glycinergic spIPSCs were blocked reversibly by strychnine (300 nm). Compared to previously described spIPSCs in AII amacrine cells, the spIPSCs in wide-field amacrine cells displayed a very slow decay time course (,fast, 15 ms; ,slow, 57 ms). The kinetic properties of spIPSCs in whole-cell recordings were paralleled by even slower deactivation kinetics of responses evoked by brief pulses of glycine (3 mm) to outside-out patches from wide-field amacrine cells (,fast, 45 ms; ,slow, 350 ms). Non-stationary noise analysis of patch responses and spIPSCs yielded similar average single-channel conductances (,31 and ,34 pS, respectively). Similar, as well as both lower- and higher-conductance levels could be identified from directly observed single-channel gating during the decay phase of spIPSCs and patch responses. These results suggest that the slow glycinergic spIPSCs in wide-field amacrine cells involve ,2, heteromeric receptors. Taken together with previous work, the kinetic properties of glycine receptors in different types of amacrine cells display a considerable range that is probably a direct consequence of differential expression of receptor subunits. Unique kinetic properties are likely to differentially shape the glycinergic input to different types of amacrine cells and thereby contribute to distinct integrative properties among these cells. [source] Functional segregation of synaptic GABAA and GABAC receptors in goldfish bipolar cell terminalsTHE JOURNAL OF PHYSIOLOGY, Issue 1 2006Mary J. Palmer The transmission of light responses to retinal ganglion cells is regulated by inhibitory input from amacrine cells to bipolar cell (BC) synaptic terminals. GABAA and GABAC receptors in BC terminals mediate currents with different kinetics and are likely to have distinct functions in limiting BC output; however, the synaptic properties and localization of the receptors are currently poorly understood. By recording endogenous GABA receptor currents directly from BC terminals in goldfish retinal slices, I show that spontaneous GABA release activates rapid GABAA receptor miniature inhibitory postsynaptic currents (mIPSCs) (predominant decay time constant (,decay), 1.0 ms) in addition to a tonic GABAC receptor current. The GABAC receptor antagonist (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) has no effect on the amplitude or kinetics of the rapid GABAA mIPSCs. In addition, inhibition of the GAT-1 GABA transporter, which strongly regulates GABAC receptor currents in BC terminals, fails to reveal a GABAC component in the mIPSCs. These data suggest that GABAA and GABAC receptors are highly unlikely to be synaptically colocalized. Using non-stationary noise analysis of the mIPSCs, I estimate that GABAA receptors in BC terminals have a single-channel conductance (,) of 17 pS and that an average of just seven receptors mediates a quantal event. From noise analysis of the tonic current, GABAC receptor , is estimated to be 4 pS. Identified GABAC receptor mIPSCs exhibit a slow decay (,decay, 54 ms) and are mediated by approximately 42 receptors. The distinct properties and localization of synaptic GABAA and GABAC receptors in BC terminals are likely to facilitate their specific roles in regulating the transmission of light responses in the retina. [source] Physiological properties of rod photoreceptor electrical coupling in the tiger salamander retinaTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Jian Zhang Using dual whole-cell voltage and current clamp recording techniques, we investigated the gap junctional conductance and the coupling coefficient between neighbouring rods in live salamander retinal slices. The application of sinusoidal stimuli over a wide range of temporal frequencies allowed us to characterize the band-pass filtering properties of the rod network. We found that the electrical coupling of all neighbouring rods exhibited reciprocal and symmetrical conductivities. On average, the junctional conductance between paired rods was 500 pS and the coupling coefficient (the ratio of voltage responses of the follower cell to those of the driver cell), or K -value, was 0.07. Our experimental results also demonstrated that the rod network behaved like a band-pass filter with a peak frequency of about 2,5 Hz. However, the gap junctions between adjacent rods exhibited linearity and voltage independency within the physiological range of rods. These gap junctions did not contribute to the filtering mechanisms of the rod network. Combined with the computational modelling, our data suggest that the filtering of higher frequency rod signals by the network is largely mediated by the passive resistive and capacitive (RC) properties of rod plasma membranes. Furthermore, we found several attributes of rod electrical coupling resembling the physiological properties of gene-encoded Cx35/36 gap junctions examined in other in vitro studies. This indicates that the previously found Cx35/36 expression in the salamander rod network may be functionally involved in rod,rod electrical coupling. [source] | ||||||||||