Biomedical subjects

Thomas Euler

Publications and source records attributed to Thomas Euler.

7 recordsLinked to original sources

PubMed2006

Two-photon imaging reveals somatodendritic chloride gradient in retinal ON-type bipolar cells expressing the biosensor Clomeleon.

A somatodendritic gradient of Cl(-) concentration ([Cl(-)](i)) has been postulated to generate GABA-evoked responses of different polarity in retinal bipolar cells, hyperpolarizing in OFF cells with low dendritic [Cl(-)](i), and depolarizing in ON cells with high dendritic [Cl(-)](i). As glutamate released by the photoreceptors depolarizes OFF cells and hyperpolarizes ON cells, the bipolars' antagonistic receptive field (RF) could be computed by simply integrating glutamatergic inputs from the RF center and GABAergic inputs from horizontal cells in the RF surround. Using ratiometric two-photon imaging of Clomeleon, a Cl(-) indicator transgenically expressed in ON bipolar cells, we found that dendritic [Cl(-)](i) exceeds somatic [Cl(-)](i) by up to 20 mM and that GABA application can lead to Cl(-) efflux (depolarization) in these dendrites. Blockers of Cl(-) transporters reduced the somatodendritic [Cl(-)](i) gradient. Hence, our results support the idea that ON bipolar cells employ a somatodendritic [Cl(-)](i) gradient to invert GABAergic horizontal cell input.

Animals↗

PubMed2005

Direction-selective dendritic action potentials in rabbit retina.

Dendritic spikes that propagate toward the soma are well documented, but their physiological role remains uncertain. Our in vitro patch-clamp recordings and two-photon calcium imaging show that direction-selective retinal ganglion cells (DSGCs) utilize orthograde dendritic spikes during physiological activity. DSGCs signal the direction of image motion. Excitatory subthreshold postsynaptic potentials are observed in DSGCs for motion in all directions and provide a weakly tuned directional signal. However, spikes are generated over only a narrow range of motion angles, indicating that spike generation greatly enhances directional tuning. Our results indicate that spikes are initiated at multiple sites within the dendritic arbors of DSGCs and that each dendritic spike initiates a somatic spike. We propose that dendritic spike failure, produced by local inhibitory inputs, might be a critical factor that enhances directional tuning of somatic spikes.

Action Potentials↗

PubMed2005

The primordial, blue-cone color system of the mouse retina.

Humans and old world primates have trichromatic color vision based on three spectral types of cone [long-wavelength (L-), middle-wavelength (M-), and short-wavelength (S-) cones]. All other placental mammals are dichromats, and their color vision depends on the comparison of L- and S-cone signals; however, their cone-selective retinal circuitry is still unknown. Here, we identified the S-cone-selective (blue cone) bipolar cells of the mouse retina. They were labeled in a transgenic mouse expressing Clomeleon, a chloride-sensitive fluorescent protein, under the control of the thy1 promoter. Blue-cone bipolar cells comprise only 1-2% of the bipolar cell population, and their dendrites selectively contact S-opsin-expressing cones. In the dorsal half of the mouse retina, only 3-5% of the cones express S-opsin, and they are all contacted by blue-cone bipolar cells, whereas all L-opsin-expressing cones (approximately 95%) are avoided. In the ventral mouse retina, the great majority of cones express both S- and L-opsin. They are not contacted by blue-cone bipolar cells. A minority of ventral cones express S-opsin only, and they are selectively contacted by blue-cone bipolar cells. We suggest that these are genuine S-cones. In contrast to the other cones, their pedicles contain only low amounts of cone arrestin. The blue-cone bipolar cells of the mouse retina and their cone selectivity are closely similar to primate blue-cone bipolars, and we suggest that they both represent the phylogenetically ancient color system of the mammalian retina.

Animals↗

PubMed2004

In vivo validation of the historical in vitro thermocycling temperature range for dental materials testing.

In dental research, restorative materials have been regularly subjected to alternating in vitro thermal stress in investigations since the 1950s, in order to simulate in vivo alternating temperature stress and to artificially stress them in vitro. The provocation temperature is mostly 5 degrees C for cold provocation, and 55 degrees C for hot provocation. These temperatures are determined quite arbitrarily based on very few examinations in vivo. Extensive temperature data for the approximal space of teeth, which is decisive for the success of fillings adhesively attached to dentin, has so far not been addressed. The objective of this study was to examine the interproximal temperature characteristics created in the space of all teeth in vivo with thermal alternating stress, and therefore to validate the in vitro standardized thermal alternating stress of 5-55 degrees C. Fifteen study participants with healthy teeth were used to determine the temperature in each inter-dental space, resulting from hot/cold provocation in the upper and lower jaw, from the central incisor to the second molars. This was performed by a thermal element (cable sensor GTF 300, Greisinger Electronic GmbH, Regenstauf, Germany). The temperature sensor was attached with dental floss into the interproximal space and the temperature was recorded by the computer. The participants in the pilot test had to state when they were able to sip an 85 degrees C hot drink. That particular temperature value was taken for hot provocation as maximum temperature reference. Cold ice water (0 degrees C) was used for cold provocation as minimum temperature reference. The respective recordings with a total of 14 measurements for each individual were performed simultaneously in the upper and lower jaw. The study participants were to start with hot provocation, followed by cold provocation. This cycle was repeated at least once with an individual dwell time. The highest recorded approximal space temperature was 52.8 degrees C in the lower jaw, between the first and the second premolar. The lowest temperature of 13.7 degrees C was recorded in two participants in the upper jaw, between the 1st and 2nd incisor, and between the two central incisors. The mean of the maximum temperatures was 43.8+/-3.7 degrees C, and the mean of the minimum temperatures 24.2+/-4.6 degrees C. The mean initial temperature was 35.2+/-1.3 degrees C. None of the recordings reached either the upper threshold (55 degrees C) or the lower threshold (5 degrees C). This study showed that the actual thermal stress in the interproximal space of teeth is slightly lower than the one used in in vitro examinations. For class II cavities, most of the alternating temperature stress limits selected at 5-55 degrees C cover the actually occurring temperature interval quite well.

Adolescent↗

PubMed2004

Functional fluorescent Ca2+ indicator proteins in transgenic mice under TET control.

Genetically encoded fluorescent calcium indicator proteins (FCIPs) are promising tools to study calcium dynamics in many activity-dependent molecular and cellular processes. Great hopes-for the measurement of population activity, in particular-have therefore been placed on calcium indicators derived from the green fluorescent protein and their expression in (selected) neuronal populations. Calcium transients can rise within milliseconds, making them suitable as reporters of fast neuronal activity. We here report the production of stable transgenic mouse lines with two different functional calcium indicators, inverse pericam and camgaroo-2, under the control of the tetracycline-inducible promoter. Using a variety of in vitro and in vivo assays, we find that stimuli known to increase intracellular calcium concentration (somatically triggered action potentials (APs) and synaptic and sensory stimulation) can cause substantial and rapid changes in FCIP fluorescence of inverse pericam and camgaroo-2.

Animals↗

PubMed2003

G protein subunit G gamma 13 is coexpressed with G alpha o, G beta 3, and G beta 4 in retinal ON bipolar cells.

We investigated the expression of Ggamma13, a recently discovered G protein subunit, and a selection of Gbeta subunits in retinal bipolar cells, by using a transgenic mouse strain in which green fluorescent protein is strongly expressed in a single type of cone bipolar cell. The cells have ON morphology, and patch-clamp recordings in slices confirmed that they are of the physiological ON type. Immunohistochemistry showed that Ggamma13 is expressed in rod bipolar cells and ON cone bipolar cells, where it is colocalized in the dendrites with Galphaomicron. ON and OFF cone bipolar cells and rod bipolar cells were identified among dissociated cells by their green fluorescence and/or distinct morphology. Hybridization of single-cell polymerase chain reaction products with cDNA probes for G protein subunits Gbeta1 to 5 showed that Gbeta3, Gbeta4, and Ggamma13 are coexpressed in ON bipolar cells but not present in OFF bipolar cells. Gbeta1, 2, and 5 are expressed in partially overlapping subpopulations of cone bipolar cells. Ggamma13 and Gbeta3 and/or Gbeta4, thus, seem selectively to participate in signal transduction by ON bipolar cells.

Animals↗

PubMed2002

Directionally selective calcium signals in dendrites of starburst amacrine cells.

The detection of image motion is fundamental to vision. In many species, unique classes of retinal ganglion cells selectively respond to visual stimuli that move in specific directions. It is not known which retinal cell first performs the neural computations that give rise to directional selectivity in the ganglion cell. A prominent candidate has been an interneuron called the 'starburst amacrine cell'. Using two-photon optical recordings of intracellular calcium concentration, here we find that individual dendritic branches of starburst cells act as independent computation modules. Dendritic calcium signals, but not somatic membrane voltage, are directionally selective for stimuli that move centrifugally from the cell soma. This demonstrates that direction selectivity is computed locally in dendritic branches at a stage before ganglion cells.

Amacrine Cells↗