PubMed Health⌕ Search

Biomedical subjects

E Wieniawa-Narkiewicz

Publications and source records attributed to E Wieniawa-Narkiewicz.

8 recordsLinked to original sources
PubMed1992

The superficial plexiform layer: a third retinal association area.

Electron microscopy enables the identification of a new association area in the mammalian retina. It is a region whose processes and synaptic junctions form a diffuse and intermittent layer bridging the boundary between the optic nerve fibre layer and ganglion cell layer. It involves displaced amacrine cells, retinal ganglion cells and probably interplexiform cell processes. Because it is close to the vitreal surface of the retina and has several properties of a plexiform layer, it has been named the superficial plexiform layer. It is much more sparse than the outer or inner plexiform layers in the rabbit, but contains a significant and substantial density of 6,100 synapses/mm2 near the visual streak. Morphological criteria distinguish two classes of synapses in the new association area. One has features of Colonnier's symmetric type and is formed by amacrine-like processes or their terminals, onto other amacrine-like processes or the cell bodies, dendrites and axon hillocks of some large ganglion cells. It makes up 79% of the population at a density of 4,800 synapses/mm2 in the examined sample. The second class arises from large processes of the fibre layer, which resemble axons rather than amacrine cell branches, has Colonnier's asymmetric form, and synapses onto a variety of other neuronal processes and cells. At a local density of 1,300/mm2 this type forms 21% of the population. A series of experiments including Wallerian degeneration, retrograde degeneration, electron microscopy and horseradish peroxidase (HRP) transport was employed to determine the nature of the large synapse-forming processes of the fibre layer that were the most amenable to investigation. It is concluded that the processes project into the optic nerve because they can be filled with HRP by retrograde transport from the end of the transected optic nerve. Although this result is based on limited evidence, it is complemented by the observation that the majority of the fibres undergo retrograde degeneration within 25 days of optic nerve section. It is concluded that the processes are either centrifugal fibres or the axons of retinal ganglion cells. The persistence of a relatively normal density of synapse-forming large fibres for seven days after optic nerve section, without Wallerian degeneration, argues that they are not the terminals of centrifugal axons. This conclusion is complemented by a separate class of profiles that did degenerate in this short period and are concluded to represent the centrifugal fibres. The large synapsing processes of the fibre layer are concluded to be the axons of some large ganglion cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Area 21a in the cat and the detection of binocular orientation disparity.

Visual response properties were examined in 115 cells, recorded in area 21a of the cerebral cortex of anaesthetized and paralysed adult cats. Cells were binocular and had receptive fields consisting of a single uniform discharge region which fired with composite ON/OFF responses to stationary flashing stimuli. Most cells were sharply tuned for orientation, but this was unaffected by changes in stimulus length. This result is consistent with a model in which the cells of area 21a receive their input from C cells of the striate cortex. Evidence for this was obtained by studying the decline in the responsiveness in area 21a that accompanied the cooling of areas 17 and 18. There was little indication that the cells of area 21a were effective detectors of spatial disparity, but their sharp monocular orientation tuning and differences in the preferred orientation of ipsilateral and contralateral eyes hinted at a role in the detection of binocular orientation disparity. Our results, however, showed that the recorded binocular disparity curves could be accounted for by summing the two monocular contributions and there was no apparent novel binocular component.

Animals↗
PubMed1987

Differences in the amplitude of X-cell responses as a function of depth in layer A of lateral geniculate nucleus in cat.

1. Extracellular recordings were made from 131 X-like cells (hereafter called X cells) at different depths in layer A of the lateral geniculate nucleus (l.g.n.) in the cat. The depths of the cells were measured accurately by orienting the electrodes parallel to the borders of the layer and reconstructing the electrode tracks from histological sections. 2. Each cell was stimulated with a standardized stimulus; a 500 ms, low-contrast (10%) spot of light, matched in size to the centres of the receptive fields. The responses were later compared with the depths of the cells in the layer. 3. The amplitudes of the responses, which ranged between peak values of 20 and 400 spikes/s in different cells, were related to the depths of the cells in the layer. On average, the response amplitudes of the X-on cells near the borders of the layer were small compared to those in the middle. The responses of the X-off cells were reciprocal; large near the borders of the layer and small in the middle. 4. The results reveal a sublaminar organization in layer A based on the signs and amplitudes of X-cell responses. It is suggested that the pattern reflects differences in signalling within the X-on and X-off channels that are preserved in the relay to the visual cortex.

Action Potentials↗
PubMed1987

Ultrastructural evidence related to presynaptic inhibition of primary muscle afferents in Clarke's column of the cat.

As part of an investigation on excitatory synaptic transmission in the mammalian CNS, we have examined ultrastructural details of the synaptic connection between primary afferent fibers and dorsal spinocerebellar tract (DSCT) neurons in Clarke's column of the cat spinal cord. Single primary muscle afferents (group Ia and Ib) and DSCT neurons were identified and stained intracellularly with HRP. The terminations of these afferent fibers were examined in serial sections under the EM. Five of 6 Ib boutons and 1 of 14 Ia boutons were contacted by small presynaptic boutons. An example was illustrated in which only 1 out of 7 boutons arising from the same Ia fiber and contacting the same postsynaptic DSCT neuron was contacted by a presynaptic bouton. It is likely that the presynaptic contacts are responsible for presynaptic inhibition of synaptic transmission between primary afferents and DSCT neurons. We have proposed that the observed differences in presynaptic contacts from bouton to bouton may be one of the causes of a nonuniformity in the probability of transmitter release between release sites at this connection.

Animals↗
PubMed1986

The distribution of on- and off-centre X- and Y-like cells in the A layers of the cat's lateral geniculate nucleus.

Responses to light were recorded extracellularly from single cells in the A laminae of the dorsal lateral geniculate nucleus (d.l.g.n.) in the cat. Micro-electrodes were passed through the nucleus parallel to the laminar borders allowing the depths of the cells to be measured accurately and the depth distributions of the different cell types to be determined. 1200 cells were recorded in thirty cats along ninety-nine tracks through layers A and A1. The cells were identified physiologically as on- or off-centre cells (hereafter called on or off cells) and most (n = 960) were classified as X- or Y-like cells (hereafter called X or Y cells). Both on and off cells were found throughout layers A and A1 but their proportions changed in a graded fashion with depth. On cells were the predominant type at the tops of the layers, the on and off cells were in balance in the centres, and off cells were the predominant type at the bottoms. The steepest gradient and the maximum differences in proportions occurred in layer A while in A1 the same pattern appeared to be present but was weak and not statistically significant in the present sample. X and Y cells were also distributed differently through the depths of the layers but in patterns that differed from those of the on and off cells. The Y cells were concentrated at the borders and there was a complementary increase of X cells toward the centres of the layers. Again, the pattern was strong in A but weak and not statistically significant in A1. The distribution of X-on cells peaked near the top of layer A while the distribution of X-off cells peaked near the bottom. This was not so in A1 where the distributions of X-on and X-off cells were nearly uniform and similar to one another except for a slight predominance (56%) of X-on over X-off cells that was not related to depth. The Y-on and Y-off cells showed similar patterns of distribution in both layers A and A1 with Y-on cells predominant at the tops of the layers and Y-off cells predominant at the bottoms. The differences in the distributions of the four cell types (X-on, X-off, Y-on, Y-off) through the depths of the layers result in unique combinations of cells at different depths. It is suggested in the Discussion that the changing balance between the cells may have functional consequences.

Action Potentials↗
PubMed1985

The ultrastructural basis for synaptic transmission between primary muscle afferents and neurons in Clarke's column of the cat.

The synaptic connection between primary muscle afferents and dorsal spinocerebellar tract (DSCT) neurons has been studied in an attempt to reveal some of the mechanisms underlying excitatory transmission in the mammalian central nervous system. Previous electrophysiological experiments have shown that the excitatory postsynaptic potentials (EPSPs) evoked DSCT neurons by impulses in a single muscle afferent fluctuate in amplitude. These fluctuations occur between discrete amplitudes which are separated by quantal increments. Two alternative hypotheses relate such a quantal increment to all-or-nothing transmitter release from either (1) an entire synaptic bouton or (2) an individual transmitter release site, given that a bouton may contain multiple release sites. The present study was undertaken primarily to gain ultrastructural evidence on these proposals. Electrodes filled with horseradish peroxidase (HRP) were used to label single identified group Ia afferent fibers and DSCT neurons in the lumbar spinal cord of anesthetized cats. HRP-labeled Ia synaptic boutons, and the contacts formed between HRP-labeled Ia boutons and the dendrites of a DSCT neuron labeled intracellularly with HRP, were examined in serial sections under the electron microscope. Group Ia boutons were found to contain multiple synaptic specializations, as evidenced by pre- and postsynaptic thickenings and presynaptic clusters of vesicles. Careful examination of a bouton in serial sections revealed each specialization as a separate structure. These observations support the proposal that synaptic transmission between group I muscle afferents and DSCT neurons occurs with discrete all-or-nothing EPSPs associated with transmitter release sites, rather than boutons per se.

Animals↗
PubMed1980

A newly identified population of presumptive microneurones in the cat retinal ganglion cell layer.

A large population of microneurones has recently been discovered in the rabbit retinal ganglion cell layer. These 'coronate' cells may represent a class of displaced amacrine cells. Like conventional amacrine cells they are swiftly and selectively destroyed by low concentrations of kainic acid, a neurotoxin. No similar cell has been described in the cat retina, which is reported to contain 217-260,000 neurones of classical appearance. These outnumber the 128-180,000 optic nerve fibres but it has been suggested that the excess comprise Nissl-staining glial cells. We report here that, using the neurotoxic effects of kainic acid to test and confirm the neuronal nature of the classic neurone excess, a large additional population of at least 730,000 presumptive microneurones was revealed. They resemble rabbit coronate cells, do not project into the optic nerve and have been previously identified as presumed glia. Various lines of evidence for the neuronal nature of these cells is presented below, but synapses have not been demonstrated; subsequent reference to microneurones must therefore be regarded as presumptive.

Animals↗