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Non-stationary Noise Analysis (non-stationary + noise_analysis)
Selected AbstractsProperties 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] 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] Diversity of GABAA receptor synaptic currents on individual pyramidal cortical neuronsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2007Timothy Ing Abstract Miniature GABAA receptor-mediated inhibitory postsynaptic currents (mIPSCs) in cortical pyramidal neurons have previously been categorized into two types: small amplitude mIPSCs with a mono-exponential deactivation (mono-mIPSCs) and relatively larger mIPSCs with bi-exponential deactivation (bi-mIPSCs). The aim of this study was to determine if the GABAA channels that underlie these mIPSCSs are molecularly distinct. We found, using non-stationary noise analysis, that the difference in their amplitude could be not accounted for by their single channel conductance (both were 40 pS). Next, using , subunit selective GABAA receptor modulators, we examined the identity of the , subunits that may be expressed in the synapses that give rise to these mIPSCs. Zolpidem (100 and 500 nm, ,1 selective) affected the deactivation of a subset of the mono-mIPSCs, indicating that ,1 subunits are not highly expressed in these synapses. However, zolpidem (100 nm) prolonged the deactivation of all bi-mIPSCs, indicating a high abundance of ,1 subunits in these synapses. SB-205384 (,3 selective) had no effect on the mono-mIPSCs but the bi-mIPSCs were prolonged. Furosemide (,4 selective) reduced the amplitude of only the mono-mIPSCs. L655,708 (,5 selective) reduced the amplitude of both populations and shortened the duration of the mono-mIPSCs. Finally, we found that the neuroactive steroid pregesterone sulphate reduced the amplitude of both mIPSC types. These results provide pharmacological evidence that synapses on cortical pyramidal neurons are molecularly distinct. The purpose of these different types of synapses may be to provide different inhibitory timing patterns on 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] | ||||||||||