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PubMed1983

Spatial distribution of acetylcholine receptors at developing chick neuromuscular junctions.

The development of high-density clusters of acetylcholine receptors (AChRs) and the relationship of these clusters to nerve contacts on embryonic chick wing muscle fibres has been studied. Fluorescent labelling of AChRs with rhodamine-conjugated alpha-bungarotoxin (R-Bgt) revealed the presence of irregularly shaped AChR clusters in wing buds at 4 1/2-5 days of incubation. This is within a day of when myotubes first appear in the wing bud, and close to the time when functional innervation becomes established. At 10 days of incubation AChR clusters present on muscle cells in anterior and posterior latissimus dorsi appear as round or oval, uniformly labelled plaques. At about the time of hatching, however, these plaques break into numerous smaller clusters. Similar changes in the morphology of AChR clusters have been observed previously in mammalian skeletal muscle during development. Using horseradish peroxidase labelled alpha-bungarotoxin (HRP-Bgt), the relationship between AChR clusters and motor nerve terminals was studied at the ultrastructural level. At all stages of development nerve-muscle contacts were labelled with HRP-Bgt. In wing buds, however, the majority (90%) of labelled clusters observed were not in contact with a motor nerve terminal. The incidence of AChR clusters with axon contacts increased sharply during development such that by 10 days more than 50% and by hatching more than 90% of all sections through labelled AChR clusters contained nerve terminal profiles. At all times studied nerve-contacted receptor clusters were longer (about 5 micron) than non-contacted clusters (about 2 micron).

Animals↗
PubMedDate not supplied

Spatial distribution of activity of the neurons of the visual cortex during stimulation with a flash of diffused light.

At different stages in the development of the response to a flash of diffused light, groupings of excited neurons in field 17 of the guinea pig continue to occur within the same cortical microzones. These zones are separated from neighboring microzones by narrow inhibition zones. The ensembles of cells participating in excitation form columns tapering with depth. The groupings of excited cells noted during a silent break indicates a grouping of inhibitory neurons. Three subgroups are distinguished within the ensembles according to the average dynamics of their impulse activity; the groups are reciprocally interrelated. One of the subgroups is in the lower layers of the cortex. This subgroup is characterized by stably localized foci of maximal activity; their dynamics, apparently reflecting groupings of corticofugal neurons, are sharply distinguished from the subgroups of the middle layers. The ensembles under investigation are considered to be one of the forms of activity of the structural-morphological units in the cortex.

Animals↗
PubMed1994

Spatial distribution of local flash electroretinogram by multi-input stimulation.

A method was developed for recording the distribution of the local flash electroretinogram with multi-input stimulation. With the use of a long flash interval, such as 100 ms, the principle and the method are useful for clinicians who know the method for recording the conventional local flash electroretinogram with single-input stimulation. This method results in a long recording time, yet it presents real local flash electroretinogram waveforms at the output.

Electroretinography↗
PubMed1985

Spatial distribution and size of acetylcholine receptor clusters determined by motor nerves in developing chick muscles.

The size and distribution of acetylcholine receptor clusters (AChR-C) on normal and aneural developing muscle fibres of the chick wing were studied by labelling AChR with fluorescent conjugates of alpha-bungarotoxin (alpha-BGT). AChR-C of a size typical of initial synaptic contacts (5 micron long) were present at 7 days incubation, shortly after the appearance of nerves, and were grouped in bands corresponding to muscle nerve branches. A regular distribution of large (approximately equal to 5 micron) AChR-C separated by 100-200 micron had developed by 10-14 days in the slow-tonic anterior latissimus dorsi and ulnimetacarpalis dorsalis muscles. The role of motor innervation in the formation of AChR-C was assessed by removing the brachial neural tube at 2 days incubation in order to prevent nerves entering the wing. Neural-tube removal prevented the appearance of the large AChR-C normally associated with the early synaptic contacts. Small AChR-C (less than 2 micron long) appeared in aneural muscles, but these were not grouped into bands characteristic of the large AChR-C in normal muscles. The results suggest that the formation of junctional AChR-C is dependent on nerves.

Animals↗
PubMed1978

Systematic experiments to establish the spatial distribution of physiologically effective stimuli of unidentified nature.

Many persons react to a kind of external agent by unconscious muscular reactions if they move across a place where this agent is supposed to be particularly active. Such places normally coincide with geological discontinuities, such as water veins, mineral ores. Practitioners of this art of detecting claim that the reaction patterns on different levels above ground are identical as vertical projections of the source pattern, this without perceptible attenuation. In some cases the supposed source was believed to have been found up to several hundred meters below ground surface. The statement of perpendicular propagation, which is the subject of this paper, is of prime importance for an approach towards understanding and all kinds of prospecting.

Biophysical Phenomena↗
PubMed2001

Applicability of the single equivalent point dipole model to represent a spatially distributed bio-electrical source.

Although the single equivalent point dipole model has been used to represent well-localised bio-electrical sources, in realistic situations the source is distributed. Consequently, position estimates of point dipoles determined by inverse algorithms suffer from systematic error due to the non-exact applicability of the inverse model. In realistic situations, this systematic error cannot be avoided, a limitation that is independent of the complexity of the torso model used. This study quantitatively investigates the intrinsic limitations in the assignment of a location to the equivalent dipole due to distributed electrical source. To simulate arrhythmic activity in the heart, a model of a wave of depolarisation spreading from a focal source over the surface of a spherical shell is used. The activity is represented by a sequence of concentric belt sources (obtained by slicing the shell with a sequence of parallel plane pairs), with constant dipole moment per unit length (circumferentially) directed parallel to the propagation direction. The distributed source is represented by N dipoles at equal arc lengths along the belt. The sum of the dipole potentials is calculated at predefined electrode locations. The inverse problem involves finding a single equivalent point dipole that best reproduces the electrode potentials due to the distributed source. The inverse problem is implemented by minimising the chi2 per degree of freedom. It is found that the trajectory traced by the equivalent dipole is sensitive to the location of the spherical shell relative to the fixed electrodes. It is shown that this trajectory does not coincide with the sequence of geometrical centres of the consecutive belt sources. For distributed sources within a bounded spherical medium, displaced from the sphere's centre by 40% of the sphere's radius, it is found that the error in the equivalent dipole location varies from 3 to 20% for sources with size between 5 and 50% of the sphere's radius. Finally, a method is devised to obtain the size of the distributed source during the cardiac cycle.

Computer Simulation↗
PubMed1990

Mathematical models of the spatial distribution of retinal oxygen tension and consumption, including changes upon illumination.

To better understand oxygen utilization by the retina, a mathematical model of oxygen diffusion and consumption in the cat outer, avascular retina was developed by analyzing previously recorded profiles of oxygen tension (PO2) as a function of retinal depth. Simple diffusion modelling of the oxygen distribution through the outer retina is possible because the PO2 depends only on diffusion from the choroidal and retinal circulations and on consumption within the tissue. Several different models were evaluated in order to determine the best one from the standpoints of their ability to represent the data and to agree with physiological reality. For the steady state one-dimensional diffusion model adopted (the special three-layer diffusion model), oxygen consumption was constant through the middle layer and zero in the layers near the choroid and near the inner retina. On the average, the oxygen consuming layer, as found by nonlinear regression for each profile, extended from about 75% to 85% of the retinal depth from the vitreous. This is a narrow band through the mid-region of the photoreceptors. Oxygen consumption of the entire avascular retina, determined from fitting eight PO2 profiles measured in light-adapted retinas, averaged 2.7 ml O2(STP)/(100 g tissue.min), while the value determined from fitting thirty-two PO2 profiles measured in dark-adapted retinas averaged 4.4 ml O2(STP)/(100 g tissue.min). Consumption in the light was thus only 60% of that in the dark. This suggests that the outer retina is at greater risk of hypoxic injury in the dark than in the light, a finding of considerable clinical significance.

Animals↗
PubMed1993

Estimation of the extent of the cutoff region from the spatial distribution of labelling and mitotic indices of intestinal crypts of a fixed length.

Current understanding of the pattern of proliferation within intestinal crypts involves the notion of a cutoff region introduced by Cairnie et al. (Exp. Cell. Res. 39, 539-553, 1965b). (Cells produced above the cutoff are non-cycling, whereas cells produced below the cutoff are cycling.) They contrasted the predicted distribution of proliferation in the extreme cases of a cutoff of width 0 (a sharp cutoff) with one eight cells wide (a slow cutoff) and concluded that the data were better explained by the latter. We have shown that crypt size variation artificially broadens the apparent distribution of proliferating cells in the crypt (Totafurno et al., Biophys. J. 54, 845-858, 1988). Here we show that the measurement and analysis of crypts of a specified height reduces this artifact. This work introduces the use of distance from the crypt base (in microns) to specify the location of cells within the crypt as an improvement over the cell position ordering traditionally used in the determination of the distribution of proliferating cells. We also show how to explicitly correct for several artifacts in the measurement of the labelling index. We conclude that cell proliferation within the crypt is more localized than previously realized; in fact, a cutoff as slow as eight cells wide is rejected.

Animals↗
PubMed1997

Transient global brain ischemia in the rat: spatial distribution, extension, and evolution of lesions evaluated by magnetic resonance imaging.

A newly developed model of transient global ischemia in the rat was evaluated by magnetic resonance imaging (MRI) in terms of localization of brain lesions, their extent and severity, and temporal evolution. Such a model, consisting of bilateral occlusion of common carotid arteries for 10 minutes and mild hypoxia (15% O2) for 20 minutes induces delayed neuronal degeneration, necrosis, and gliosis (detected histologically and immunohistochemically). Ischemia was assessed by full suppression of spontaneous electroencephalographic activity. A "hybrid" T2-/diffusion-weighted MR sequence enhancing more effectively the contrast between injured and intact tissues as compared to T2-weighted MRI was used at 24, 48, 72, and 96 hours and at 7 days postischemia. Twenty hypoxic-ischemic rats showed a considerable variability in brain damage. In 8, there were no MRI-detectable lesions at any interval. In the other 12 rats, the severity and extension of neuronal damage varied markedly, but the lesions were always localized (monolaterally in 8 and bilaterally in 4 rats) in the occipital, temporal, or parietal cerebral cortex. Mainly, they were of intermediate severity or were severe (as assessed by MRI hyperintensity) and were accompanied by usually less severe lesions in the thalamus and/or caudate putamen. The hippocampus was affected moderately or severely in 4 of 12 rats. In most cases, there was at 48 hours a considerable growth in severity and/or extension of lesions, which usually remained stable at later intervals. In conclusion, MRI allowed us to follow brain lesions during the first week in this relatively simple and noninvasive model of transient global ischemia.

Animals↗
PubMed1986

Spatial distribution of Langerhans' cells and T-lymphocyte subpopulations in human tympanic membrane and aural cholesteatoma.

Immunohistochemical analysis of human cholesteatoma matrices revealed the presence of Langerhans' cells and T-lymphocytes. Through cell-to-cell interaction, Langerhans' cells probably play a key role in skin-related disorders, including cholesteatomas. They probably originate from a mobile cell population of monocyte origin and migrate into and out of the body's lining. Their custodial function is often carried out in close relation with T-lymphocytes. Monoclonal antibodies against Langerhans' cells and T-lymphocyte membrane receptors reveal the presence of these cell populations in cholesteatoma matrices but not in the tympanic membrane. Langerhans' cells and T-cell "traffic" through cholesteatomas are discussed in relation to the pathogenesis, natural course and recurrence of cholesteatomas. Through immunopathologic evaluation the clinical aggressiveness of a cholesteatoma may become predictable. It may even have consequences for the future handling of cholesteatomas.

Antibodies, Monoclonal↗
PubMed2000

Identification and spatial distribution of the mRNA encoding an egg envelope component of the Cyprinid zebrafish, Danio rerio, homologous to the mammalian ZP3 (ZPC).

Using degenerate reverse transcription polymerase chain reaction (RT-PCR) techniques we have isolated a cDNA encoding a putative component of the zebrafish Danio rerio egg chorion, homologous to the mammalian ZP3 (ZPC). The predicted protein (zfZPC) has a calculated molecular mass of 58.4 kDa and contains a signal peptide (located in the N-terminal region) composed of 11 hydrophobic amino acid residues followed by a signal peptide cleavage site. The zfZPC contains the ZP domain, a characteristic amino acid sequence shared by all ZP proteins of the mammalian zona pellucida and of both amphibian and bird egg envelope components. The zfZPC also exhibits certain unique features including five N-terminal Q-rich tandem repeats presumably involved in the hardening of the chorion after the fertilization of the egg and a long C-terminal tail containing two potential sites of N-linked type glycosylation. RT-PCR and in situ hybridization revealed a restricted pattern of tissue distribution: the gene encoding zfZPC is transcribed only in the growing oocyte of sexually mature female fish.

Amino Acid Sequence↗