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U Eysel

Publications and source records attributed to U Eysel.

11 recordsLinked to original sources
PubMed2007

[Signal reception and processing by the retina].

Phototransduction occurs in the retina, which, as an outsourced part of the brain, fulfills important tasks in neuronal processing for image analysis relevant to perception. Interlinked biochemical cycles with immense amplification factors transform the electromagnetic waves of light into neuronal activity, and photochemical adaptation allows adjustment to light intensities of over more than 10 logarithmic units. Beginning with its dual system of photoreceptors with highly sensible rods and a color sensitive cone system, the retina, with between 50 and 100 main cell types, is characterized by complex neuronal circuits. The resulting center-surround antagonism of the receptive fields serves, amongst other things, to amplify intensity and color contrasts. Specialized ganglion cell types give rise to parallel signaling pathways into the higher visual centers of the brain.

Humans↗
PubMed2001

Changes of contrast gain in cat dorsal lateral geniculate nucleus by dopamine receptor agonists.

The modulatory effects of dopamine (DA) on the contrast gain of retino-geniculate transmission were tested with local micro-iontophoretical application of DA and the DA receptor agonists SKF38393 (SKF, D1/D5) and quinpirole (QUIN, D2/D3/D4) while recording visually induced spike activity of relay cells of the dorsal aspect of cat lateral geniculate nucleus (dLGN) in the anesthetised and paralyzed preparation. DA and QUIN could either facilitate or inhibit visual activity in a dose-dependent fashion: small amounts caused a facilitation while larger quantities resulted in a more (DA) or less (QUIN) strong inhibition. The effect of SKF was almost always suppressive and increased with the amount of drug applied. The absolute change in activity was depending on stimulus contrast and the strength of the elicited response: facilitation and inhibition of activity was proportional to stimulus contrast and response strength and thus resulted in a changed contrast gain. The results indicate that the visual deficits found in Parkinson's disease patients my be not solely related to retinal dysfunctions.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed2000

Selective heating of vibrissal follicles in seals (Phoca vitulina) and dolphins (Sotalia fluviatilis guianensis).

The thermal characteristics of the mystacial vibrissae of harbour seals (Phoca vitulina) and of the follicle crypts on the rostrum of the dolphin Sotalia fluviatilis guianensis were measured using an infrared imaging system. Thermograms demonstrate that, in both species, single vibrissal follicles are clearly defined units of high thermal radiation, indicating a separate blood supply to these cutaneous structures. It is suggested that the high surface temperatures measured in the area of the mouth of the follicles is a function of the sinus system. In seals and dolphins, surface temperature gradually decreased with increasing distance from the centre of a follicle, indicating heat conduction from the sinus system via the follicle capsule to adjacent tissues. It is suggested that the follicular sinus system is a thermoregulatory structure responsible for the maintenance of high tactile sensitivity at the extremely low ambient temperatures demonstrated for the vibrissal system of seals. The vibrissal follicles of odontocetes have been described as vestigial structures, but the thermograms obtained in the present study provide the first evidence that, in Sotalia fluviatilis, the follicles possess a well-developed sinus system, suggesting that they are part of a functional mechanosensory system.

Animals↗
PubMed1996

Utilizing latency for object recognition in real and artificial neural networks.

A consistent analysis of a visual scene requires the recognition of different objects. In vertebrate brains this could be achieved by synchronization of the activity of disjunct nerve cell assemblies. During such a process cross-talk between spatially adjacent image parts occurs, preventing efficient synchronization. Temporal differences, naturally introduced by stimulus latencies in every sensory system, were utilized in this study to counteract this effect and strongly improve network performance. To this end in our model the image is 'spread out' in time as a function of contrast-dependent visual latencies, and synchronization of cell assemblies occurs without mutual disturbance. The network model requires a direct link between visual latencies and the onset of synchronous oscillations in cortical cells. This was confirmed experimentally.

Cognition↗
PubMed1990

Corticofugal feedback influences the responses of geniculate neurons to moving stimuli.

Geniculate cell responses to moving bars and moving texture were compared in normal cats and in cats in which the corticofugal feedback was removed by cortical ablation. In experimental animals the response strength and the velocity upper cutoff assessed with a moving bar was reduced compared to control animals. The strength of response to texture decreased even more after cortical ablation, which also changed the response pattern of X cells to moving texture. These data suggest that corticofugal feedback contributes to the geniculate responses to moving stimuli and in particular to moving texture.

Animals↗
PubMed1989

[Degenerative, regenerative and adaptive reactions to local damage of the retina].

Retinal ganglion cells can respond to local lesions due to mechanical trauma or photocoagulation with degeneration, adaptation or regeneration. Animal experiments show that under natural conditions the kind of reaction is dependent on the age at onset and on the degree of destruction caused by the lesion. In early postnatal life directly severed cells undergo fast degeneration while indirectly affected cells show adaptive changes (dendritic reorganization in the neighborhood of retrogradely degenerated retinal areas). This kind of reaction is not observed in adulthood. In contrast, in the adult retina there is a greater resistance to lesion effects and surviving cells show signs of axonal regeneration. Such attempts at regeneration, however, do not lead to successful reentry of axons into the optic nerve. In addition, at the very borders of photocoagulator lesions we observe both in early postnatal and adult animals signs of dendritic plasticity (redistribution of dendrites away from the lesion and towards the normal retina). The dendritic changes are aimed at retaining function and at reducing lesion size. They are characterized by a redistribution of dendritic volume towards the intact retina. While spontaneous intraretinal axonal regeneration does not appear to be beneficial for the system, the dendritic phenomena can be interpreted as attempts to limit the actual damage.

Adaptation, Ocular↗
PubMed1987

A quantitative study of morphological reorganization following chronic optic deafferentation in the adult cat dorsal lateral geniculate nucleus.

Neuronal and synaptic reorganization in the lateral geniculate nucleus (dLGN) of adult cats following chronic visual deafferentation has been investigated with the aid of GABA immunocytochemistry and quantitative electron microscopy. The main purpose of this study was to establish the morphological counterpart of the functional plasticity of dLGN relay cells after total visual deafferentation (Eysel: Brain Res. 166:259-271, '79). The results provide evidence that the regained excitability of relay cells is not the result of disinhibition (caused hypothetically by the selective loss of GABAergic cells) since the proportion of GABA-positive and GABA-negative cells as well as the inhibitory synaptic density did not change. The alternative suggestion that the enhanced excitability could be the result of compensatory axonal sprouting by corticothalamic fibers had also to be dropped: the absolute number of corticothalamic axons to the deafferented dLGN remains unchanged. Because of shrinkage of the dendritic trees of dLGN neurons, however, the density of cortical synaptic input at dLGN cells becomes elevated by almost 60%. It is suggested that the regained excitability of relay neurons is the consequence of the combined effects of adaptive (structural) reduction in size ("atrophy") of retinally denervated nerve cells, and, as a consequence, increase of input resistance, reduced shunting effects, and relative increase in density of the excitatory cortical input per neuron.

Animals↗
PubMed1982

Studies of retinal representations within the cat's optic tract.

The manner in which each retina can be mapped onto a single cross section of the optic tract of the cat has been defined by neuroanatomical methods. It has been found that the contralateral nasal hemi-retina and both temporal hemi-retinae are represented in each tract by multiple, rough maps which partially overlap one another. All maps show the same general orientation, with area centralis represented dorsomedially, lower retina represented dorsolaterally, and upper retina represented ventromedially. The peripheral part of the horizontal meridian is represented ventrolaterally. Labeling all of the fibers from one eye by axonal degeneration or autoradiographic methods shows that the crossed map is displaced dorsally and medially relative to the uncrossed map, leaving a dorsomedial crescent of pure crossed fibers. Localized retinal lesions or injections of 3H-amino acid show the general orientation of the maps. Lesions within the dorsomedial pure crossed crescent show that fibers in this crescent arise from retinal areas close to the optic disc, near the site of the early fetal fissure. Localized injections of horseradish peroxidase into the optic tract show the relationships of the several maps in terms of the retinal distribution of retrogradely labeled retinal ganglion cells. They show that axons of large and small cells map ventrolaterally in the tract while intermediate sizes map dorsomedially. They confirm that the crossed map is displaced relative to the uncrossed maps. It is suggested that the optic tract develops by fibers taking a position in the tract in accordance with their time of arrival at the chiasm. The several maps are displaced because they develop sequentially and the optic tract can be read as a developmental record, the most dorsomedial axons being the oldest.

Animals↗
PubMed1980

[Changes in the cat's visual system following retinal lesions. A functional reorganization in the mature central nervous system (author's transl)].

Layers of the lateral geniculate nucleus (LGN) of mature cats were completely or partially deafferentated by precisely defined photocoagulation of the retina. Single neuron recordings were performed with microelectrodes from an experimentally modified layer and compared with neurons from a normally innervated layer in the same animal. The spontaneous activity of cells after monocular deafferentation was severely reduced in the beginning and increased subsequently without reaching normal values within ten weeks. At this time the pattern of excitation and inhibition after light stimulation of the nondominant unsevered eye had completely changed. Twenty-seven days and later after coagulation of a part of the nasal retina light-excitable cells with displaced receptive fields were found in the LGN in the border region of the partial visual deafferentation. This indicated a lesion-induced lateral expansion of excitation by up to 200 microns within the LGN. Small, round retinal lesions initially caused a complete visual deafferentation of a certain region in the LGN. After 30 days and later visual excitation from the normally innervated surrounding was observed in cells which were not light-excitable during the first days after coagulation. Thus, while the retinal lesion itself did not substantially change, its representation within the LGN was distinctly reduced. The results indicate lesion-induced reorganization in the subcortical visual system of the adult cat. This might enable the system to a certain degree of compensation after loss of visual inputs. The transferability of these results to human pathophysiology has to be critically considered.

Animals↗