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M S Jacobs

Publications and source records attributed to M S Jacobs.

At least 19 recordsLinked to original sources
PubMed1991

An investigation of dental luting cement solubility as a function of the marginal gap.

The purpose of this study was to investigate the rate of type I zinc phosphate cement solubility as it relates to the degree of marginal opening. Standardized test samples were constructed that would simulate clinically relevant marginal gaps of 25, 50, 75, and 150 microns and their subsequent cement lines. The study was divided into two phases. Phase 1 evaluated the effects of simple diffusion on cement solubility in a static environment, whereas phase 2 investigated the effects of convective forces on cement dissolution in a dynamic environment. Both the phase 1 and phase 2 studies demonstrated no significant difference in the rate of cement dissolution for the 25-, 50-, and 75-micron test groups. The 150-micron test groups for both studies, however, demonstrated an increase in the rate of cement dissolution. The results of the phase 1 and phase 2 studies should not be compared because different methodologies were used.

Analysis of Variance↗
PubMed1989

Rates of protein synthesis--a review.

The rates of protein synthesis can be measured by a variety of methods including pulse labeling, massive precursor administration, Scornik method, continuous feeding of labeled precursor, infusion, and pellet implantation. Each technique has some advantages and disadvantages. Massive precursor administration and infusion are the most widely used. The advantage of massive precursor administration is its simplicity, however, the amino acid concentration used is much higher than physiological levels. Infusion, however, is much more complicated as a technique and requires complicated calculations. The synthesis rates can also be calculated from degradation curves. Some of the above techniques can be used both in vivo and in vitro, and also for different organs (Shahbazian et al. (1987), Int. J. Dev. Neurosci., 5: 39-42). The brain has rapid rates of protein synthesis both in vivo and in vitro, the latter being much lower for adults.

Animals↗
PubMed1988

Visual cortex of the dolphin: an image analysis study.

On cytoarchitectonic grounds we have identified two distinct types of cortical formations composing the lateral gyrus (visual cortex) of the dolphin and have termed these heterolaminar cortex and homolaminar cortex. The heterolaminar cortex occupies the medial and lateral banks of the entolateral sulcus whereas the homolaminar cortex occupies the remainder of the lateral gyrus both lateral and medial to the entolateral sulcus. Each of these cortices exhibits special cytoarchitectonic features, a major difference being that heterolaminar cortex contains an incipient layer IV whereas layer IV is clearly absent in homolaminar cortex. Quantitative imaging procedures reveal that there is greater laminar differentiation in heterolaminar than in homolaminar cortex. Golgi analysis of neuronal forms and dendritic architecture confirms this distinction between the two types of cortex composing the lateral gyrus. Computer-assisted morphometric methods have been applied to both types of cortex and indicate by a variety of parameters several quantitative differences in the cellular numbers, types, and organization in each type of cortex. Both types of cortex, homolaminar and heterolaminar, exhibit a markedly higher cellular density in the posterior sector of the lateral gyrus than in the anterior sector. We have also for the first time been able to identify a columnar type of organization of the cetacean visual cortex and have described two types of cytoarchitectonic columns, major and minor, in each of these types of cortex. Comparisons in organization of these basic columnar units between the bat, representing a prototypic brain, and the dolphin reveal many similarities but also major quantitative differences in type of organization between the visual cortices in these species. Marked differences are also seen between the cytoarchitectonic columnar organization of the visual cortices in the dolphin and columnar organization of striate cortex in the human brain, the number of columns per unit of cortex in the human being almost twice that seen in the dolphin brain. Some phylogenetic implications of these findings are discussed in relation to the so-called "initial" type of cortical organization reconstructed largely by retrospective inference.

Aging↗
PubMed1987

Ultrastructure of the blood-brain barrier in the dolphin (Stenella coeruleoalba).

Light and electron microscopic methods were used for investigation of angioarchitectonics, glioarchitectonics and the structural basis of the blood-brain barrier in the dolphin Stenella coeruleoalba. It was shown that the cortical plate of the dolphin brain is extremely rich in capillaries and small arteries that are organized into a complicated net of continuous loops surrounding neuronal groups. The density of the capillary loops is related to the cytoarchitectural density of the cortex. It was also found that the neuronal microenvironment in the dolphin cortex is characterized by the presence of a large number of the astroglia-like cells that make a multi-layered investment surrounding capillaries and small arteries. These glial cells, unlike typical astrocytes of terrestrial mammals, have a large number of different organelles and their nuclei are similar to those of the oligocytes. The ultrastructure of the blood-brain barrier in the dolphin is characterized by the presence of extremely long tight junctions between endothelial cells and by specialized junctions between pericapillary astroglia-like cells. A belt of the glial end-feet interlocked with different types of junctions such as zonulae adherentes, maculae adherentes and gap junctions was found around all investigated capillaries. This system of specialized interendothelial and glio-glial junctions is tentatively hypothesized to be a feature of adaptation of the dolphin to the aquatic environment.

Animals↗
PubMed1985

Conservative features of neocortical evolution in dolphin brain.

A Golgi survey of the convexity cortex in the brain of the dolphin, Tursiops truncatus, has revealed many cellular characteristics which may be indicative of conservative cortical evolution. These include a high degree of pyramidalization, and an accentuation of layer II. The presence of an accentuated layer II in convexity cortex is a protoneocortical characteristic found in more 'primitive' cortical arrangements. The growth ring concepts of cortical development outward in concentric waves from archicortical and paleocortical origins are discussed. In that context we have not been able to identify cores of hyperspecialization in the dolphin cortex corresponding to koniocortex and gigantopyramidal areas. This leads us to suggest that the cortex of the dolphin reflects a condition of the paralimbic-parinsular stage of evolutionary development. Thus, the dolphin brain may serve as a model of the theoretical mammalian archetype brain and its study may shed light on the organization of the brains of the initial ancestors of modern mammals.

Animals↗
PubMed1984

The insular formations of the dolphin brain: quantitative cytoarchitectonic studies of the insular component of the limbic lobe.

The large insula of the bottlenose dolphin consists of radial gyri arising, in fanlike fashion, from the transverse insular gyrus, and is covered completely by the frontal, parietal, and temporal opercula . On cytoarchitectonic grounds, the dolphin insula is divided into anterior, middle, and posterior sectors that may be the equivalent of the three similar sectors present in the primate insula. Rostrocaudally, these sectors become increasingly more homogeneous and less laminated. Within each sector progressive differentiation occurs in the direction of the circular sulcus. A transitional cortex, the peripaleocortex in the transverse insular gyrus, is interposed between the prepiriform and the periamygdalar cortex and the proisocortex of the insula proper. This peripaleocortex consists of outer and inner cellular strata separated by a hypocellular lamina dissecans. The outer cell stratum is continuous with layers II and III of the insular proisocortex ; the more prominent inner stratum is continuous with proisocortical layers V and VI; the intervening lamina dissecans becomes partially filled, mostly with modified pyramidal cells of medium size that may constitute an incipient layer IV. A band of myelinated fibers corresponding to the external band of Baillarger is found within the lamina dissecans. The anterior insular sector is characterized by distinct lamination and a well-defined, ribbonlike layer Va. In the middle sector, the cortex is internodense and lamination is less clear. The posterior sector is even less laminated and tends to be externodense . Within each sector, lamination becomes clearer in the direction of the circular sulcus. Furthermore, the rostrocaudal architectonic changes suggest a possible transition from a motor-type to a sensory-type cortex. Beyond the insula, the architecture of the opercular cortices reflect, in turn, the influences of the insular sectors.

Animals↗
PubMed1982

The limbic lobe of the dolphin brain: a quantitative cytoarchitectonic study.

In these cytoarchitectonic studies of the cortical limbic formations of the bottlenose dolphin and other whale brains we have carried out quantitative analyses of the entire limbic lobe, including all of its sectors: supracallosal, retrosplenial and temporal. The limbic lobe proper has been examined as well as transitional areas between the limbic lobe and the archicortical and paleocortical formations and the extralimbic neocortices, including the entorhinal area and presubiculum. Analyses include total cortical thickness, thickness of individual cortical layers, overall cortical cell densities and glia/neuron ratios, individual laminar counts and glia/neuron ratios and neuron size. Comparisons have been made between these parameters in the brains of the dolphin (Tursiops truncatus), beluga whale (Delphinapterus leucas) and humpback whale (Megaptera novaeangliae). Cortical neuron density values (cells per mm3) in these three species of whales and in the human brain have been compared with similar data given in the literature for elephant, fin whale (Balaenoptera physalus) and human brains. Our values reflect the inverse relationship between brain size and neuron density. Thus, the dolphin shows approximately 13,000 neurons/mm3 in its limbic cortex, compared to 12,000 in the beluga whale and 8,000 in the humpback whale. Further, the data provide the first quantitative accounts on a layer by layer basis of the limbic cortices in the whale brain. In the dolphin, the anterior limbic cortices have a much lower cell density than the posterior limbic area. However, in the humpback whale these two cortices have similar neuron densities. In the temporal region, the entorhinal area is well differentiated into many architectonic subdivisions in the dolphin though not to the extent described in the primate brains. Our findings in the three whale species are discussed in terms of their possible significance and provide quantitative data for future comparative studies with other mammalian species.

Animals↗
PubMed1981

Separate mechanisms of deformability loss in ATP-depleted and Ca-loaded erythrocytes.

Membrane rigidity has been widely accepted as the dominant cause of reduced deformability both of ATP-depleted erythrocytes and erythrocytes containing excess calcium (Ca). However, recent studies have shown normal membrane deformability in ATP-depleted erythrocytes. In addition, Ca accumulation causes massive ion and water loss, and it has been shown that extensive dehydration causes an increase in intracellular viscosity with attendant loss of whole cell deformability. To obtain a detailed understanding of the processes accompanying ATP depletion and/or Ca accumulation that limit cell deformability, we have used a viscodiffractometric method to identify the cellular factors contributing to reduced whole cell deformability. Analysis of the influence of the suspending medium osmolality on deformability showed the presence of two independent processes. One was a Ca-independent reduction in cell surface area/volume ratio, resulting from the spheroechinocyte formation that follows total ATP consumption. The other was a Ca-dependent increase in intracellular viscosity resulting from a Ca-induced loss of intracellular potassium and water. This deformability loss due to increased intracellular viscosity was found for cells depleted of ATP in the presence of Ca and in cells treated with Ca and A23187 without prior depletion. Ionophore-treated cells at high Ca concentration (>500 muM) formed spheroechinocytes with reduced surface area and a further loss of whole cell deformability. The rate of deformability loss associated with Ca-induced spheroechinocytosis was much more rapid than that associated with ATP-depletion-induced spheroechinocytosis, suggesting different mechanisms for the morphologic changes. No major effects of altered membrane elasticity on the reduced deformability of either ATP-depleted or Ca-loaded cells were observed.

Adenosine Triphosphate↗
PubMed1981

Reservoir hosts of human babesiosis on Nantucket Island.

The host range of Babesia microti was studied on Nantucket Island in order to identify the enzootic reservoir of this human pathogen. White-footed mice (Peromyscus leucopus) were more frequently parasitized than were other indigenous animals. Infection was ubiquitous in locations where deer were abundant. Mice were most frequently parasitemic during spring and summer and adults more frequently than juveniles. Parasitemia, which was rarely intense, was sustained for as long as 4 months. Mice lived as long as 10 months, and juveniles were most abundant during early summer. Prevalence of zoonotic infection, in certain locations, appeared to be inversely correlated with abundance of mice. B. microti was present solely in regions harboring deer.

Animal Population Groups↗
PubMed1981

Factors that limit whole cell deformability in erythrocytes after calcium loading and ATP depletion.

Whole cell deformability of ATP-depleted and Ca-loaded red cells has been measured at various osmolalities to determine those cellular factors responsible for the reduce deformability of these cells. For cells depleted of ATP in Ca-free medium, a progressive loss of hypotonic deformability identified membrane loss with reduced surface area-to-volume ratio as the dominant mechanism of deformability loss. For cells treated with Ca and the ionophore A23187 without prior depletion, a rapid loss of isotonic deformability, reversible in hypotonic medium, identified dehydration with increased internal viscosity as the dominant mechanism of deformability loss. In contrast to previously held concepts, increased membrane rigidity was not found to have a major influence.

Adenosine Triphosphate↗
PubMed1980

Analysis of factors regulating erythrocyte deformability.

Using a laser diffraction technique, we have studied factors that influence the deformability of erythrocytes. Variations in suspending medium osmolality and applied shear stress were employed to isolate the individual contributions to whole cell deformability of internal viscosity, surface area-to-volume ratio, and viscoelastic properties of the membrane. An experimental system was devised in which normal cells were modified in vitro to induce specific alterations in each factor. Measurements of deformability as a function of medium osmolality showed characteristic behavior of the modified cells. Reduced surface area-to-volume ratio was detected by an exaggeration of the normal decrease in deformability as medium osmolality was decreased. In contrast, increased internal viscosity was detected by an increase in deformability as osmolality was decreased. Finally, decreased membrane flexibility was detected by reduced deformation at low shear stress. These methods of analysis were applied to cells from patients with hereditary spherocytosis, hereditary pyropoikilocytosis, and hemoglobin CC disease to define the basis of reduced deformability. Hereditary spherocytes showed the combined effects of reduced surface area and increased internal viscosity. Hereditary pyropoikilocytes revealed the effects of severely reduced surface area-to-volume ratio. Hemoglobin CC cells showed only the effects of high internal viscosity. An increase in the membrane shear modulus (decreased membrane deformability) was not evident in these disorders.

Anemia, Hemolytic, Congenital↗
PubMed1980

Ektacytometric analysis of factors regulating red cell deformability.

Photometric analysis of laser diffraction patterns has been used to obtain quantitative measurements of deformability of specifically modified normal red cells. Variation of deformability with suspending medium osmolality and with applied shear stress was used to distinguish between changes in internal viscosity, surface area-to-volume ratio, and viscoelastic properties of the membrane in their influence on whole cell deformability.

Dextrans↗
PubMed1979

The anatomy of the brain of the bottlenose dolphin (Tursiops truncatus). Rhinic lobe (Rhinencephalon): The archicortex.

The hippocampal formation or archicortical division of the rhinecephalon of the bottlenose dolphin, Tursiops truncatus, is described from the standpoint of its gross topographic relations and cytoarchitecture. A feature of the dolphin brain, which lacks olfactory bulbs and peduncles, is the striking reduction of the archicortical relative to the paleocortical formations. The small, poorly developed archicortex covered by massive epihippocampal portions of the hemispheres (parietal and temporal lobes), appears greatly reduced relative to the large, well developed olfactory lobes which are covered by small epistriatal portions of the hemispheres (orbital lobes). The archicortex exhibits three junctional zones with the paleocortex, two laterally in the unci and one anteriorly in the septal area. Despite the small size of the hippocampal formations, the general topographic disposition of its cytoarchitectonic areas and their cellular organization in Tursiops have many features that are similar to those in other placental mammals. The archicortex is subdivisible into four major sectors: temporal, retrosplenial, supracallosal and subcallosal. With the exception of the temporal sector, cytoarchitectonic areas of the other sectors are variously attenuated and poorly differentiated, particularly the dentate area and the hippocampal areas H5 and H4. Here, the dentate area and hippocampal areas H5 and H4 which are present along the paradentate bank of the hippocampal sulcus, extend to the level of the oblique sulcus of the parahippocampal gyrus and then disappear. Hippocampal areas H3, H2 and H1 are also clear in the floor and along the parahippocampal bank of the hippocampal sulcus in the temporal sector. These areas are less definable as they extend beyond the oblique sulcus into the retrosplenial sector and are difficult to recognize as distinct areas in the supracallosal and subcallosal sectors of the archicortex. The archicortex is demarcated bilaterally from limbic formations in the border of the hemisphere by segments of the rhinic cleft which are very clear. Equally clear is the cytoarchitectonic demarcation of the archicortex from the neocortex in the border (limbus) of each hemisphere, i.e., where the subiculum abuts against the presubiculum. The subicular area, best expressed in the temporal sector, extends anteriorly over the corpus callosum to the subcallosal gyrus and, throughout its extent from the uncal to the septal junction, is clearly demarcated from limbic neocortex by a transition zone characterized by archicortical cells merging with cells in the deep layer of the bordering neocortex. Overall, the archicortical formations of the dolphin and other whale brains we have examined exhibit many regional peculiarities that we have described, both grossly and architectonically, with emphasis on the comparative anatomical approach.

Animals↗