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A Peters

Publications and source records attributed to A Peters.

At least 307 records · Page 17Linked to original sources
PubMed1977

The projection of the lateral geniculate nucleus to area 17 of the rat cerebral cortex. IV. Terminations upon spiny dendrites.

The forms of the spiny dendrites in layer IV receiving degenerating thalamocortical axon terminals have been examined in serial thin sections. Reconstructions of segments of these dendrites show that the axon terminals synapse with both the dendritic spines and the dendritic shafts. No main shafts of apical dendrites of pyramidal neurons were found to synapse with the thalamic afferents, which are received mainly by spiny dendrites 1-2 micron in diameter, at least some of which appear to be the oblique branches of apical dendrites. The forms of these postsynaptic dendrites are so variable that is concluded they arise from more than one morphological type of neuron. The conclusion based on this and previous articles in the series is that most neuronal elements in layer IV which form asymmetric synaptic junctions are potential recipients of the thalamocortical afferents.

Animals↗
PubMed1976

The projection of the lateral geniculate nucleus to area 17 of the rat cerebral cortex. I. General description.

Lesions were made in the lateral geniculate nucleus of the rat and the consequent degeneration in area 17 of the cerebral cortex was studied by light and electron microscopy. These lesions produced prominent degeneration of axon terminals in layer IV extending into layer III and a much lesser amount in layers I and VI. The darkened degenerating axon terminals forming asymmetric synaptic junctions and were frequently surrounded by hypertrophied astrocytic processes. These terminals appeared to be disposed randomly, forming no discernible patterns. In layer IV 83% of the synapsing, degenerating terminals formed junctions with dendritic spines, 15% with dendritic shafts, and 2% with neuronal perikarya. The dendritic shafts and neuronal perikarya appeared to belong to spine-free stellate cells. The dendrites giving rise to the spines receiving degenerating axon terminals could not be identified, for most of the spines appeared as isolated profiles that could not be traced back to their dendritic shafts. One example of a degenerating axon terminal synapsing with an axon initial segment was encountered. Small, degenerating myelinated axons were prevalent in layers VI, V and IV, but were only infrequent in the supragranular layers. These results are compared with those obtained in other studies of thalamocortical projections.

Animals↗
PubMed1976

The projection of the lateral geniculate nucleus to area 17 of the rat cerebral cortex. II. Terminations upon neuronal perikarya and dendritic shafts.

The forms of dendrites in layer IV receiving degenerating thalamocortical axon terminals directly on their shafts were examined in serial thin sections. Reconstructions showed these dendrites varied in thickness between 2.5 and 0.5 mum. They had essentially smooth contours and rarely showed evidence of protrusions or spines. They were further characterized by the presence of many synapses along their shafts. Only about one in 12 of these synapses was formed by degenerating thalamocortical axon terminals. These smooth dendrites emerged from neuronal perikarya that also received degenerating axon terminals which formed asymmetric synaptic junctions. Such cell bodies bore both symmetric and asymmetric synaptic junctions, and not all of the latter were caused to degenerated after a thalamic lesion. These postsynaptic neurons appeared to be of two kinds, ones with thin dendrites that often contained closely packed microtubules, and others with thicker dendrites that emerged from the poles of oval perikarya.

Animals↗
PubMed1975

An autoradiographic study of the projections from the lateral geniculate body of the rat.

The projections from the lateral geniculate body of the rat were followed using the technique of autoradiography after injections of [3H] proline into the dorsal and/or ventral nuclei of this diencephalic structure. Autoradiographs were prepared from either frozen or paraffin coronal sections through the rat brain. The dorsal nucleus of the lateral geniculate projected via the optic radiation to area 17 of the cerebral cortex. There was also a slight extension of label into the zones of transition between areas 17, 18 and 18a. The distribution of silver grains in the various layers of the cerebral cortex was analyzed quantitatively and showed a major peak of labeling in layer IV with minor peaks in outer layer I and the upper half and lowest part of layer VI. The significance of these peaks is discussed in respect to the distribution of geniculocortical terminals in other mammalian species. The ventral nucleus of the lateral geniculate body had 5 major projections to brain stem structures both ipsilateral and contralateral to the injected nucleus. There were two dorsomedial projections: (1) a projection to the superior colliculus which terminated mainly in the medial third of the stratum opticum, and (2) a large projection via the superior thalamic radiation which terminated in the ipsilateral pretectal area; a continuation of this projection passed through the posterior commissure to attain the contralateral pretectal area. The three ventromedial projections involved: (1) a geniculopontine tract which coursed through the basis pedunculi and the lateral lemniscus to terminate in the dorsomedial and dorsolateral parts of the pons after giving terminals to the lateral terminal nucleus of the accessory optic tract, (2) a projection via Meynert's commissure to the suprachiasmatic nuclei of both sides of the brain stem as well as to the contralateral ventral lateral geniculate nucleus and lateral terminal nucleus of the accessory optic tract, and (3) a medial projection to the ipsilateral zona incerta. The results obtained in these experiments are contrasted with other data on the rat's central visual connections to illustrate the importance of these connections in many subcortical visual functions.

Animals↗
PubMed1975

Solvation of oxygen in lecithin bilayers.

The solubility of oxygen in dipalmitoyllecithin (DPL) and paraffinc C19 has been investigated by measurement of the enhanced proton relaxation rates under the influence of oxygen pressure. The paraffin shows a noticeable effect in the rotator phase, but not so in the crystalline phase. tin contrast to paraffins, both phases of DPL-bilayers dissolve oxygen, but the solubility in the liquid-crystalline phase is greater than in the crystalline state by a factor approximately equal to 3. Furthermore, the experiments indicate a distribution of electron relaxation times in the crystalline phase in contrast to the liquid-crystalline phase. A possible explanation of this behaviour is a multiphase structure of the "crystalline' lamellae. The biological relevance of thbse results could be a triggering of the gas-transport by the alveolar lining of lungs, if cyclic phase transitions occur during the breathing-cycle.

Binding Sites↗
PubMed1975

[Application of free flow preparative methods for the separation of blood cells].

Human blood cells can be separated using an apparatus described by Hanning and co-workers (Model FF4 Desaga Heidelberg). The method of free flow preparative electrophoresis uses a specific property of blood cells when subjected to an electric field: their electrophoretic mobility. Three regions of migration can be defined: --a high mobility region (HMR); --a low mobility region (LMR) and --an intermediate mobility region (IMR). After the electrophoretic migration, the various cell fractions are identified. If human leucocytes are subjected to an electric field (40 volts/cm) it is possible to isolate several populations which differ by their membranes electric charge. The repartition of the neutrophiles granulocytes is twofold: --one fraction of high mobility (HMR) and --one fraction of low mobility (LMR). The meaning of these two populations is being discussed. Between these teo fractions is located the lymphocyte fraction which is represented by a single peak of intermediate mobility (IMR). Eosinophiles and monocytes are concentrated in low mobility fraction (LMR). With appropriate migration parameters (80 volts/cm, various component buffers) it is possible to obtain from lymphocytes, purified by density gradient, an electrophoretic separation of T and B lymphocytes population. Histograms obtained from quantitative measures (on collected cell fractions) show an unimodal distribution. When separated cells are characterized by three membranes markers (E. Rosettes, EAC Rosettes and surface immunoglobulins) the electrophoretic heterogeneity of B and T cells is then demonstrated. With E Rosettes (T cells) the majority of T lymphocytes is distributed in HMR and IMR. With EAC Rosettes and membrane immunofluorescence (B cells markers) the majority of B lymphocytes is found in the LMR. Thus an important enrichment of T and B sub-population is obtained, but contamination from one another still remains too important. More selective methods should lead to an improvement of this cell separation.

B-Lymphocytes↗
PubMed1974

Ultrastructure of a large ventro-lateral dendritic bundle in the rat ventral horn.

There is an extensive bundle of dendrites with a rostro-caudal axis in the ventro-lateral lamina of the sixth lumbar segment in each side of the rat spinal cord. Such a bundle has a diameter of about 250 mum and contains over 1400 parallel dendrites, each with a diameter of less than 8 mum, interspersed between neuronal somata. The volume fraction of dendrites in the bundle neuropil is about 55%, the remainder being equally distributed between astrocytes, synaptic boutons, and axons, most of which are unmyelinated. An analysis of the median percentage covering of dendrites by contiguous elements of the neuropil reveals that as the dendrite diameter decreases from 4 to 0.2 mum (mean equals 2 mum), astrocytes increase from 43 to 75%, axons decrease from 21% to zero, boutons decrease from 28% to zero, and dendrites decrease from 10% to zero. There is a mean of 18 synaptic boutons per 100 mum-2 of the overall dendritic surface, but larger boutons tend to be more frequent on larger dendritic profiles. Apposed dendrites and their somata may have either puncta adhaerentia or confronting subsurface cisternae. Synaptic types in the rat are similar to those reported for the cat. The morphological findings are discussed with respect to previously proposed interaction between neural elements.

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