RESUMO
Principal neurons of the medial nucleus of the trapezoid body (MNTB) integrate the large, excitatory inputs from anteroventral cochlear nucleus (AVCN) bushy cells with conventional inhibitory inputs to produce an inhibitory output to the lateral and medial superior olive. This circuit is critical in the sound localization pathway of the auditory brainstem. Many ionic currents act in concert to produce the rapid phase-locked firing properties characteristic of MNTB principal neurons. We report here that MNTB neurons of the mouse possess a 2-4nS instantaneous potassium-based leak current, probably mediated by TWIK two-pore potassium leak channels. The function of the leak current was examined by modulating its magnitude with a dynamic clamp. The leak current modulates the resting voltage by 5mV/nS, reduces the input resistance of the cell by 5MOmega/nS and reduces the membrane time constant by 0.075 micros/nS. The leak current also modulates spike timing. Given leak channels are highly regulated, they are well placed to influence the firing properties, and action potential timing in principal neurons of the MNTB.
Assuntos
Potássio/metabolismo , Potenciais de Ação , Animais , Vias Auditivas/metabolismo , Eletrofisiologia , Concentração de Íons de Hidrogênio , Camundongos , Camundongos Endogâmicos CBA , Modelos Biológicos , Neurônios/metabolismo , Técnicas de Patch-Clamp , Canais de Potássio/metabolismo , Fatores de TempoRESUMO
High-throughput protein crystallography requires the automation of multiple steps used in the protein structure determination. One crucial step is to find and monitor the crystal quality on the basis of its diffraction pattern. It is often time-consuming to scan protein crystals when selecting a good candidate for exposure. The use of neural networks for this purpose is explored. A dynamic neural network algorithm to achieve a fast convergence and high-speed image recognition has been developed. On the test set a 96% success rate in identifying properly the quality of the crystal has been achieved.
Assuntos
Algoritmos , Cristalografia/métodos , Redes Neurais de Computação , Proteínas/química , Proteínas/classificação , Robótica/métodos , Difração de Raios X/métodosRESUMO
The nonlinear effects of amplitude jitter and ghost pulse generation, which are present in strongly dispersion-managed optical communication systems can be suppressed by alternation of the phase of the bits. A physical explanation for this effect is given that shows that with suitably chosen phase modulations the processes that give rise to the nonlinear effects will counteract each other.
RESUMO
We study interaction-induced timing jitter in single-channel dispersion-managed return-to-zero ttransmission systems operating at high map strengths. An equation for the frequency and timing shifts of two interacting pulses is derived by a variational approach. The interaction can be of either an attractive or a repulsive character, and we show that the resultant timing jitter can be reduced by proper design of the dispersion map.
RESUMO
We investigate the nonlinear generation and dynamics of ghost pulses in high-speed strongly dispersion-managed fiber-optic communication systems. Particular consideration is given to the importance of system parameters for the properties of the emerging ghost pulses. Conclusions are drawn about the growth rate and the temporal position of the ghost pulses in different systems.
RESUMO
Voltage-clamp and current-clamp recordings were made from bipolar cells in dark-adapted mouse retinal slices. Light-evoked responses fell into three groups corresponding to the rod bipolar cells, on-cone bipolar cells and off-cone bipolar cells. The morphology of the recorded cells confirmed this classification. Intensity-response relations were well fitted by a Michaelis saturation function with Hill coefficients of 1.15 +/- 0.11 (n = 6) for rod bipolar cells and 2.33 +/- 0.06 (n = 4) for cone inputs onto on-cone bipolar cells. In the absence of antagonists for GABA or glycine receptors, light-evoked synaptic currents for all cells displayed linear current-voltage relations that reversed near 0 mV, indicating that very little inhibition was activated under dark-adapted recording conditions. Saturating light stimuli evoked conductances of 0.81 +/- 0.56 nS (n = 4) in rod bipolar cells and 1.1 +/- 0.8 nS (n = 4) in on-cone bipolar cells. Receptive field widths were estimated by flashing a vertical light bar at various locations along the slice. Rod and on-cone bipolar cells had receptive field widths of 67 +/- 16 micrometer (n = 6) and 43 +/- 7 microm (n = 5), respectively. The maximum spatial resolution of an array of such cone bipolar cells was estimated to be 0.3 cycles deg-1, compared with a maximum resolution of 0.5 cycles deg-1 obtained from behavioural studies in mice. Our results suggest that this limit to spatial resolution could be imposed early in the visual system by the size of the bipolar cell receptive fields.
Assuntos
Retina/citologia , Retina/fisiologia , Visão Ocular/fisiologia , Animais , Adaptação à Escuridão/fisiologia , Técnicas In Vitro , Potenciais da Membrana/fisiologia , Camundongos , Técnicas de Patch-Clamp , Estimulação Luminosa , Células Fotorreceptoras Retinianas Cones/citologia , Células Fotorreceptoras Retinianas Bastonetes/citologia , Sinapses/fisiologia , Campos Visuais/fisiologiaRESUMO
We present analytical and numerical results for dispersion-managed solitons in a fiber link including guiding filters and compensating gain, both taken in the distributed approximation. Stationary propagation regimes with anomalous, zero, and normal path-average dispersion (PAD) are identified. New features, compared with those of the case without filters, are the absence of a critical strength for propagation at zero and normal PAD and, instead, the existence of a critical power for stationary propagation at any PAD.
RESUMO
Ribbon synapses of vertebrate photoreceptors constantly release glutamate in darkness. Transmitter release is maintained by a steady influx of calcium through voltage-dependent calcium channels, implying the presence of a mechanism that is able to extrude calcium at an equal rate. The two predominant mechanisms of intracellular calcium extrusion are the plasma membrane calcium ATPase (PMCA) and the Na+/Ca2+-exchanger. Immunohistochemical staining of retina sections revealed strong immunoreactivity for the PMCA in rod and cone terminals, whereas staining for the Na+/Ca2+-exchanger was very weak. The PMCA was localized to the plasma membrane along the sides of the photoreceptor terminals and was excluded from the base of the terminals where the active zones are located. The amplitude of a calcium-activated chloride current was used to monitor the intracellular calcium concentration. An upper limit for the time required to remove intracellular free calcium is obtained from two time constants measured for the calcium-activated chloride current tail currents: one of 50 msec and a second of 190 msec. Calcium extrusion was inhibited in the absence of intracellular ATP or in the presence of the PMCA inhibitor orthovanadate, but was unaffected by replacement of external Na+ with Li+. The data indicate that the PMCA, rather than the Na+/Ca2+-exchanger, is the predominant mechanism for calcium extrusion from photoreceptor synaptic terminals.
Assuntos
Cálcio/metabolismo , Células Fotorreceptoras/química , Células Fotorreceptoras/metabolismo , Animais , Transporte Biológico/fisiologia , ATPases Transportadoras de Cálcio/análise , ATPases Transportadoras de Cálcio/metabolismo , Mamíferos , Microscopia Confocal , Terminações Pré-Sinápticas/química , Terminações Pré-Sinápticas/enzimologia , Ratos , Trocador de Sódio e Cálcio/análise , Trocador de Sódio e Cálcio/metabolismo , TupaiidaeRESUMO
We determine the power dependence of dispersion-managed solitons on map strength and average dispersion, using a combination of numerical simulations and the variational approach. In particular, we investigate the behavior near zero dispersion and identify the region of existence of dispersion-managed solitons in the average normal-dispersion regime.