R. O. Uusitalo

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To characterize the transfer of graded potentials and the properties of the associated noise in the photoreceptor-interneuron synapse of the blowfly (Calliphora vicina) compound eye, we recorded voltage responses of photoreceptors (R1-6) and large monopolar cells (LMC) evoked by: (a) steps of light presented in the dark; (b) contrast steps; and (c)(More)
Many neurons use graded membrane-potential changes, instead of action potentials, to transmit information. Traditional synaptic models feature discontinuous transmitter release by presynaptic action potentials, but this is not true for synapses between graded-potential neurons. In addition to graded and continuous transmitter release, they have multiple(More)
1. Randomly modulated light stimuli were used to characterize the nonlinear dynamic properties of the synapse between photoreceptors and large monopolar neurons (LMC) in the fly retina. Membrane potential fluctuations produced by constant variance contrast stimuli were recorded at eight different levels of background light intensity. 2. Representation of(More)
1. We studied the graded and spiking properties of the "non-spiking" first-order visual interneurons of the fly compound eye in situ with the use of intracellular recordings. Iontophoretical QX-314 injections, Lucifer yellow marking, and (discontinuous) current-clamp method together with transfer function analysis were used to characterize the neural signal(More)
1. We studied graded synaptic transmission in the fly photoreceptor-interneuron synapse by using intracellular in situ recordings from pre- and postsynaptic cells. 2. A large presynaptic hyperpolarization after light adaptation, caused by the activation of the electrogenic Na+/K+ pump, drastically reduced the conspicuous postsynaptic dark noise. At the same(More)
In the first visual synapse of the insect compound eye, both the presynaptic and postsynaptic signals are graded, nonspiking changes in membrane voltage. The synapse exhibits tonic transmitter release (even in dark) and strong adaptation to long-lasting light backgrounds, leading to changes also in the dynamics of signal transmission. We have studied these(More)
Light-adapted fly photoreceptor cells were stimulated with brief positive and negative contrast flashes (contrast=ΔI/I, I=intensity). Membrane potential responses to a wide range of flash intensities were well-fitted by a static nonlinearity followed by a compartmental model represented by a gamma function. However, the agreement improved if one parameter(More)
1. We have used intracellular recordings and ionophoretic injections in vivo to investigate the ion exchange mechanisms responsible for the maintenance of the ion gradients in the large monopolar cells (LMCs) of the first optic ganglion of the blowfly, Calliphora vicinia. 2. Ionophoretic chloride injections caused a rapid approximately 20-mV depolarization(More)
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