Showing papers by "Boston University published in 1981"

Central Nervous System

Abstract: It is not the intent of this chapter to provide a comprehensive documentation of all the changes that have been recorded in the cells of the central nervous system as they age. Rather, we have chosen to follow the rather narrow path of using our own studies of the pyramidal neurons and neuroglial cells in the primary auditory cortex (area 41) of the aging rat as a basis for the following account, and to refer to recent studies of our own colleagues and of other investigators as appropriate within that context. This approach is bound to result in a rather biased description of the aging of neurons and neuroglia, but we believe that sufficient information will be given in this account for the reader to use it as a means of gaining access to studies that provide additional information and other views.

Structure of the hydrophobic protein crambin determined directly from the anomalous scattering of sulphur

Abstract: The highly ordered crystal structure of crambin has been solved at 15 A resolution directly from the diffraction data of a native crystal at a wavelength remote from the sulphur absorption edge The molecule has three disulphide bridges among its 46 amino acid residues, of which 46% are in helices and 17% are in a β-sheet Crambin is shown to be an amphipathic protein, inasmuch as its six charged groups are segregated from hydrophobic surface elements Phasing methods used here will also apply elsewhere

The lithobiontic ecological niche, with special reference to microorganisms

Abstract: Revised terminology is proposed that describes the ecological niches of microorganisms within hard, mineral substrates. Organisms attached to the external surfaces of the rock are termed epiliths, while those in the interior of the rock are all termed endoliths. The latter are called chasmoendoliths if they inhabit fissures in rocks, cryptoendoliths if they dwell within structural cavities, and euendoliths if they actively penetrate calcareous substrates.

Form and distribution of neurons in rat cingulate cortex: Areas 32, 24, and 29

Abstract: The cytoarchitecture of rat cingulate cortex is described. This includes the topographical distribution and layering patterns of Brodmann's areas 25, 32, 24, and 29a, b, c, and d. Area 24 is subdivided into a ventral area 24a and a dorsal area 24b, but an area 23 could not be identified between areas 24 and 29 An analysis of Golgi impregnations in areas 32, 24, and 29 demonstrates that most neuronal types recognized in neocortical areas are also present in cingulate cortex. Besides typical and inverted pyramidal cells, there is a wide variety of nonpyramidal cells, including multipolar, bitufted, and bipolar cells. Small multipolar cells with small somata, a dendritic tree limited to one or two layers, sparse to moderately spinous dendrites and one of two varieties of short axonal trajectories are present in layers I and II of areas 32, 24, and 29d. Medium multipolar cells occur mainly in layers III and V; they have extensive dendritic trees which traverse three or more layers, moderately spinous dendrites, and an axonal plexus which either ascends or descends in the cortex. Large multipolar cells are also frequent in layers III and V; their extensive dendritic trees are essentially spine free and they have axons which form dense terminations, particularly in the layer above the one in which the cell body is located Neurons with elongated somata and a primarily vertical orientation of the dendritic tree are either bitufted or bipolar. Bitufted cells are most frequent in layers II and III of areas 32, 24, and 29d. These cells have dendritic trees which form “hourglass shaped” fields, dendrites which are moderately spinous, and axons which form either extensive horizontal and vertical projections or are “chandelier” in form. Bipolar cells, in contrast, are found in layers II–V; their sparsely spinous dendrites form narrow dendritic trees which are oriented vertically and extend across four or more layers, and their axons have the same vertical orientation as the dendritic tree It is concluded that the form of the axonal arbors of nonpyramidal cells frequently mimics the extent and shape of their dendritic trees. Thus, small multipolar cells with limited, spherical dendritic trees may have axons which arch sharply and emit short, terminal branches. In contrast, medium and large multipolar cells have more extensive dendritic and axonal arbors which traverse two, three, or more layers. Of the fusiform cells, bitufted ones with their “hourglass” dendritic trees have extensive vertical and horizontally oriented axonal branches, while bipolar cells have narrow, vertically oriented dendritic and axonal arbors The granular layers II–IV of area 29c contain the following types of neurons: small and fusiform pyramids, medium-sized pyramids, large stellate cells, and medium multipolar cells. Fusiform pyramids are the only neurons unique to cingulate cortex. They are similar to the variety of pyramidal cells, but have an oval soma and only one basal dendrite which extends from the base of the cell body to arborize in layer IV. Large stellate cells differ from large multipolar cells in that they have densely spinous dendrites and axons which enter the white matter.

Water structure of a hydrophobic protein at atomic resolution: Pentagon rings of water molecules in crystals of crambin.

Abstract: The water structure has been analyzed for a model of the protein crambin refined against 0.945-A x-ray diffraction data. Crystals contain 32% solvent by volume, and 77% of the solvent molecules have been located—i.e., 2 ethanol molecules and 64 water molecules with 10-14 alternate positions. Many water oxygen atoms found form chains between polar groups on the surface of the protein. However, a cluster of pentagonal arrays made up of 16 water molecules sits at a hydrophobic, intermolecular cleft and forms a cap around the methyl group of leucine-18. Several waters in the cluster are hydrogen-bonded directly to the protein. Additional closed circular arrays, which include both protein atoms and other water oxygen atoms, form next to the central cluster. This water array stretches in the b lattice direction between groups of three ionic side chains.

Cancer Incidence by Levels of Cholesterol

Abstract: In 5,209 subjects studied for 24 years in Framingham, Mass, 691 cases of cancer were documented, with histological confirmation for 94%. Predetermined personal characteristics were tested for associations with subsequent occurrence of cancer at specific sites using multiple logistic regression. Significant associations of various cancer sites with cigarette smoking, alcohol use, education, height, weight, and parity agreed with other studies. Serum cholesterol level was inversely associated with incidence of colon cancer and with other sites only in men; these inverse associations were statistically significant after adjustment for age, alcohol consumption, cigarette smoking, education, systolic blood pressure, and relative weight. Associations may reflect effects of competing lethal diseases, underlying pathophysiological mechanisms that promote or inhibit development of cancer in men, biologic or social response to early and undiagnosed states of cancer. ( JAMA 1981;245:247-252)

Symbiosis in cell evolution: Life and its environment on the early earth

Abstract: The book treats cell evolution from the viewpoint of the serial endosymbiosis theory of the origin of organelles Following a brief outline of the symbiotic theory, which holds that eukaryotes evolved by the association of free-living bacteria with a host prokaryote, the diversity of life is considered, and five kingdoms of organisms are distinguished: the prokaryotic Monera and the eukaryotic Protoctista, Animalia, Fungi and Plantae Symbiotic and traditional direct filiation theories of cell evolution are compared Recent observations of cell structure and biochemistry are reviewed in relation to early cell evolution, with attention given to the geological context for the origin of eukaryotic cells, the origin of major bacterial anaerobic pathways, the relationship between aerobic metabolism and atmospheric oxygen, criteria for distinguishing symbiotic organelles from those that originated by differentiation, and the major classes of eukaryotic organelles: mitochondria, cilia, microtubules, the mitotic and meiotic apparatuses, and pastids Cell evolution during the Phanerozoic is also discussed with emphasis on the effects of life on the biosphere

Thermal Phase Transition of the Dilute s -State Potts and n -Vector Models at the Percolation Threshold

Abstract: A general theory is given for the quenched dilute $s$-state Potts and $n$-vector models in any dimension $d$. It is shown that for $T\ensuremath{\rightarrow}0$ at the percolation threshold the Potts thermal exponent ${\ensuremath{ u}}_{T}$ equals the percolation exponent ${\ensuremath{ u}}_{p}$, implying a crossover exponent $\ensuremath{\varphi}=1$, for any $s$ and $d$. For the $n$-vector model ($ng1$), ${\ensuremath{ u}}_{T}=\frac{{\ensuremath{ u}}_{p}}{{\ensuremath{\zeta}}_{R}}$, where ${\ensuremath{\zeta}}_{R}$ is a resistivity critical exponent. Agreement with recent experiments for two-dimensional dilute Ising and Heisenberg systems is excellent.

Neurogenesis in the 3-month-old rat visual cortex.

Abstract: Newly formed neurons in the adult mammalian neocortex have been reported by several investigators using light microscopic radioautography, but these reports have not been confirmed by electron microscopy--probably because their rarity precludes any reasonable chance of observing these cells with electron microscopic radioautography. To overcome this problem I have used a recently developed method that allows serial thin sectioning and subsequent electron microscopic examination of plastic-embedded sections previously prepared for light microscopic radioautography. Ninety-day-old rats were injected with 4.3 microCi per gm body weight of [H3] thymidine and allowed to survive for 30 days. In the light radioautographs, labeled cells were found in layer IV of the visual cortex, and analysis of electron micrographs of selected examples of these labeled cells clearly demonstrated their neuronal nature wit synapses along their cell bodies and dendrites. In order to quantify the relative frequency of labeled neurons, the number of labeled cells seen in the light microscopic sections was expressed as a percentage of the total number of neurons found in sections through the entire thickness of the visual cortex; the percentage was 0.011%, or about 1 in 10,000. The results of this study are in agreement with evidence of neurogenesis of granular neurons in the adult rat olfactory bulb and dentate gyrus (Kaplan and Hinds, '77). Thus, it has now been confirmed that relatively small labeled neurons and their synapses are found in at least 3 brain regions (olfactory bulb, dentate gyrus, and visual cortex) in a normal adult rodent.

Maturation of rat visual cortex. II. A combined Golgi-electron microscope study of pyramidal neurons.

Abstract: Tissue removed from 3, 6, 9, 12, 15, and 21-day-old rats has been prepared for correlative light and electron microscopy to examine the maturation of cell bodies, dendrites, and axons of pyramidal neurons in layer V of rat visual cortex. As the size of the cell body increases steadily during the first 3 postnatal weeks there is an equivalent growth in nuclear volume. By day 15, there are infoldings in the nuclear envelope which may be induced by eye opening on day 14. Nucleoli increase in size until day 9, after which they appear to condense. Within the perikarya, the most conspicuous change is the amount and organization of the rough endoplasmic reticulum. Symmetric axosomatic synapses are evident by day 6. The ultrastructure of dendrites does not change substantially with age. Dendrites form synapses with symmetric densities as early as day 3 and asymmetric ones by day 9. It seems that dendritic spines begin as low, broad protrusions having symmetric junctions with smaller diameter axonal processes. With time they become taller stumps, before acquiring their mature lollipop shape and participating in asymmetric synapses with axonal varicosities. Other dendritic appendages, filopodia, and growth cones are transient structures, being conspicuous only between days 3 and 12. "Terminal" growth cones are essential for extension of dendritic processes, whereas "en passant" growth cones and filopodia seem important for dendritic branching. Boutons of mature pyramidal cell axons form asymmetric synapses with dendritic shafts and spines, but the developing synapses formed by these axons have more symmetric junctions. The maturation of pyramidal cell features progresses in concert with such extrinsic determinants as afferent input and is probably influenced by the competency of synaptic connections.

Night roosting and the nocturnal time budget of the little brown bat, Myotis lucifugus: Effects of reproductive status, prey density, and environmental conditions.

Abstract: The insectivorous bat Myotis lucifugus typically apportions the night into two foraging periods separated by an interval of night roosting. During this interval, many bats occupy roosts that are used exclusively at night and are spatially separate from maternity roosts. The proportion of the night which bats spend roosting, and thus the proportion spent foraging, vary both daily and seasonally in relation to the reproductive condition of the bats, prey density, and ambient temperature. A single, continuous night roosting period is observed during pregnancy. During lactation, females return to maternity roosts between foraging bouts, and night roosts are used only briefly and sporadically. Maximum use of night roosts occurs in late summer after young become volant. Superimposed upon these seasonal trends is day-to-day variation in the bats' nightly time budget. Long night roosting periods and short foraging periods are associated with cool nights and low prey density. This behavioral response may minimize energetic losses during periods of food scarcity.

The impact of chronic disease

Abstract: A large number of individuals with rheumatoid arthritis have been studied in order to better delineate the sociomedical problems experienced by patients with this chronic disease. Two hundred forty-five respondents were surveyed by use of a detailed questionnaire and interview, and the results indicate that major losses in the areas of work, finances, and family structure are extremely common. The majority of workers were totally disabled as a result of their disease. On the average, subjects in the group were earning only 50% of the income predicted for them had they not had arthritis. Sixty-three percent experienced a major change in their psychosocial status as a result of their disease. Work disability appears to be the most important sociomedical impact of rheumatoid arthritis since it is associated with significantly greater income and psychosocial losses. This evidence of numerous and serious sociomedical problems in persons with rheumatoid arthritis raises questions of emphasis and approach for physicians involved in the clinical care of chronic rheumatic disease patients.

Aging in the rat olfactory system: Correlation of changes in the olfactory epithelium and olfactory bulb

Abstract: Two regions closely linked synaptically (olfactory epithelium and olfactory bulb) have been compared in an age-graded series of rats. Previous findings of growth and atrophy of constituent elements in Sprague-Dawley Wisconsin (SD) rats have now been confirmed in Charles River (Crl) rats. In the olfactory bulbs of Charles River (Crl) rats, the volume of layers, the number of olfactory axodendritic synapses in the glomeruli, the total volume of glomerular dendrites, and the size of mitral cell bodies all approximately double between 3 and 24--27 months, and then all decrease by 36 months. Unlike SD rats, however, no loss in the number of mitral cells occurs in Crl rats, and the increase in volume of the olfactory bulbs from 3 to 24 months is approximately double that of SD rats. In the olfactory epithelium the total number of septal olfactory receptors more than doubles between 3 and 18--24 months and then declines markedly, as does the volume of olfactory axons in olfactory bulb glomeruli. Comparison of the regression lines for change in number of septal receptors with that of the size of mitral cell bodies discloses that the decline in number of receptors begins several months earlier than the decline in mitral cell size. This suggests that the atrophic changes in the olfactory bulb may in part be secondary to changes in the receptors of the olfactory epithelium. Numbers of synapses in the glomeruli appear to decline less markedly with age than the number of receptors, and a significant increase in number of synapses per receptor occurs in the oldest group studied (33 months), suggesting a compensatory increase in the relative number of synapses per receptor in the surviving receptors.

Maturation of rat visual cortex. I. A quantitative study of Golgi-impregnated pyramidal neurons.

Abstract: The early postnatal maturation of pyramidal neurons in layers II/III and V of the rat visual cortex has been examined in an attempt to elucidate some determinants of their mature morphology. Three indices have been quantified using Golgi-impregnated pyramidal cells: densities of spines along apical dendrites, numbers of primary basal dendrites and volumes of cell bodies. The mean density of spines on the apical dendrites of all pyramidal neurons increases in a stepwise fashion. The first significant increase occurs between days 6 and 9 and the second, between days 12 and 15; these increases may correlate with the arrival of geniculate afferents and with the opening of the eyes, respectively. In younger animals, the distribution of spines along the apical shafts is relatively even, whereas in older animals, spine density increases significantly over the proximal 125 μm portion and is relatively constant over the remaining distal portion. By day 21, layer V pyramidal cells have acquired more primary basal dendrites and larger somatic volumes than layer II/III cells. Furthermore, as the cells mature the rates of change in these characteristics are significantly different for neurons in layer II/III and in layer V. For both cell populations, the mean number of primary basal dendrites increases to a maximum before falling to a steady level, but for neurons in layer V, the maximum is higher and attained three days earlier than for layer II/III cells. Moreover, the increase in volume of cell bodies of layer V neurons begins three days before that of layer II/III cells. This three day phase difference in maturation may reflect the cell birth dates, since autoradiographic evidence indicates that layer V pyramidal neurons reach the cortical plate about three days prior to those which occupy layer II/III in the adult visual cortex.

Obesity, very low density lipoproteins, and glucose intolerance over fourteen years the framingham study

Abstract: A total of 5082 men and women in the Framingham Heart Study population who were free of any glucose abnormality and aged 33 to 67 years were followed prospectively over 14 years for the occurrence of glucose intolerance. The diagnosis of glucose intolerance was defined as developing documented hyperglycemia or being placed on justified treatment by a physician. The 14-year incidence was 6.7% in men and 5.5% in women. Multivariate analysis was used and future glucose intolerance in men and women was highly associated with casual blood glucose, Metropolitan Relative Weight and very low density lipoproteins at the baseline exam. Other factors showed only sex-specific or univariate associations. Obesity and lipoprotein abnormalities were shown to be independent markers in the prediction of future glucose intolerance.

A reassessment of the forms of nonpyramidal neurons in area 17 of cat visual cortex

Abstract: The nonpyramidal neurons in area 17 of cat visual cortex have been examined in Golgi preparations. From their dendritic patterns, neurons are classified as being multipolar, bitufted, or bipolar, and on the basis of the abundance of dendritic spines as spinous, sparsely spinous, or smooth. When neurons are so classified seven different types of nonpyramidal neurons are encountered in layers II through V. Three of the types of multipolar neurons in layers II through V have spherical dendritic trees. The small multipolar cells have smooth dendrites and are the smallest neurons in the cortex. They have short dendrites and dense local axonal plexuses and occur throughout layers II to V The sparsely spinous stellate cells have longer dendrites, are confined to layer II/III, and have local axonal arborizations, whereas the spinous stellate cells are limited to layer IV. A fourth type of multipolar neuron in layers II through V is the basket cell. Such neurons have elongate dendritic trees and either smooth or sparsely spinous dendrites. Depending upon the orientation of the neurons in the sections, their axons appear to form arcades or long, horizontally extended branches, or a mixture of these two axonal patterns. The terminal portions of the axons of these basket cells pass around the cell bodies of adjacent neurons. The two types of bitufted neurons in layers II through V have vertically oriented dendritic trees. One type, the chandelier cell, has smooth dendrites and a characteristic axon forming vertical strings of terminals. The other sparsely spinous bitufted neurons have axons producing vertically oriented plexuses. The remaining type of neuron encountered in layers II through V is a bipolar cell. The bipolar cell has a single major dendritic trunk arising from each pole of the cell body, and each of these gives rise to a very narrow, long, and vertically oriented dendritic tree. The axon usually takes origin from one of the primary dendrites. In layer I are horizontally oriented, bitufted cells with smooth dendrites. The axons of these horizontal cells of layer I arise from one of the primary dendritic trunks and appear to form a plexus confined to layer I. Horizontally oriented neurons are also present in deep layer VI, but the horizontal cells of layer VI are bipolar. The other two neuronal types in layer VI are multipolar cells with sparsely spinous dendrites. The larger of these two types resembles the basket cells in layers II through V, the only important difference between them being that in addition to the long horizontal branches, the axons of the basket cells of layer VI have a long ascending branch which reaches at least as far as layer IV. The other sparsely spinous cells of layer VI are medium sized. Their axons take a descending and oblique course before elaborating a locally distributed plexus. The various types of neurons defined in this study are compared with neurons described by previous authors who have examined the populations of nonpyramidal cells in area 17 of cat visual cortex and in other visual and nonvisual cortical areas of cats, monkeys, and rodents. In some cases it has been possible to postulate the functional roles that particular types of neurons might play within cat visual cortex.

Strategic Planning for Regulated Companies

Abstract: SUMMARY The need for strategic planning by firms to achieve an alignment vvith their environment is widely recognized. Various studie.'^ have analysed the structures and strategic processes utilized b> t'lrms in their altetnpts to eslahlish domains and attain goals. Yet the problems faced by firms in regulated environments by and large have been ignored. This paper examines the c.-itical differences found in regulated environments that aflect strategic planning. Propositions which can serve as the hasis of future empirical research arc offered and a theoretical .'"ranfiework in which to view the regulated industry situation is developed.