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Biomedical subjects

T G Smith

Publications and source records attributed to T G Smith.

At least 19 recordsLinked to original sources

beta-Cyclodextrin: 52-week toxicity studies in the rat and dog.

A 52-wk toxicity study by dietary administration was performed in Sprague-Dawley rats and in pure-bred beagle dogs with beta-cyclodextrin, a starch derivative that acts as a molecular inclusion agent. Doses of 0 (control), 12,500, 25,000 and 50,000 ppm were selected for the rat study, and 0 (control), 6200, 12,500 and 50,000 ppm were selected for the dog study. The liver and kidney were identified at the histopathological examination as target organs for toxicity in the rat at doses of 50,000 and 25,000 ppm, with the hepatic changes associated with increased plasma liver enzyme and reduced plasma triglyceride concentrations. In the dog study, there was no pathological evidence of systemic toxicity, although there were minor changes in urinalysis and biochemical parameters and a slightly higher incidence of liquid faeces. These changes were considered to be of no toxicological importance. The results in these studies, therefore, indicate that the non-toxic effect level was 12,500 ppm in the rat (equivalent to 654 or 864 mg/kg/day for males or females, respectively) and 50,000 ppm in the dog (equivalent to 1831 or 1967 mg/kg/day for males or females, respectively).

Analysis of Variance

Surface complexity of human neocortical astrocytic cells: changes with development, aging, and dementia.

Astrocytes from area 11 of the human neocortex were Golgi-impregnated. The material was taken from four human subjects, (1) a neonate without obvious CNS damage, (2) a middle-aged adult serving as control, (3) an aged individual without apparent mental disturbances, and (4) an aged patient with dementia. Camera-lucida drawings of 7 to 26 astrocytic cells from each donor were digitized into a personal computer, and analyzed for their fractal dimension D which is an objective and quantitative measure of the complexity of the cell's borders. Both radial and multipolar astrocytes from neonatal cortex showed a comparatively low fractal dimension (D approximately 1.39), that is, low surface complexity. Adult ("control") astrocytes were characterized by a high fractal dimension (D = 1.57), corresponding to their large surface complexity. Astrocytes from the aged subject showed a somewhat smaller fractal dimension (D = 1.51) and, thus, surface complexity; this difference was however not highly significant. In contrast, astrocytes from the subject with dementia showed a significant reduction in surface complexity (D = 1.47). Parallel changes were observed in the brain volume compartment occupied by the process of individual astrocytes. These data suggest that formation and maintenance of astrocytic processes and/or side branches correlate positively with the degree of information processing within their neuronal environment.

Adult

Comparative fractal analysis of cultured glia derived from optic nerve and brain demonstrate different rates of morphological differentiation.

O-2A progenitor cells derived from neonatal rat cerebral hemispheres or optic nerves, were induced to differentiate in culture into either oligodendrocytes or type 2 astrocytes. The fractal dimensions, a measure of morphological complexity, of the differentiating glial cells were measured over time. Analysis of the changes in fractal dimension (D) with respect to time revealed specific rates of growth for each glial phenotype and a specific final D. The time course of these changes is well fit by a simple mathematical model. While brain-derived oligodendrocytes matured faster than the astrocytes, they ultimately attained comparable levels of complexity, with similar maximum fractal dimensions. Oligodendrocytes from nerve also matured faster than nerve derived astrocytes, in contrast, however, they attained a greater morphological complexity than nerve astrocytes. While the brain-derived oligodendrocytes showed a faster rate of maturation than their optic nerve counterparts, astrocytes from both regions had similar rates of morphological differentiation. Self-similarity, a defining property of fractal objects was investigated, by determining the fractal dimension of cells over a range of magnifications. The calculated fractal dimension remained constant over a 10-fold range in optical magnification, illustrating that cultured glial cells exhibit this important characteristic of fractal objects. In addition, we analyzed the branching patterns of glial processes by the Sholl method and found that the results were not as interpretable or meaningful as those of fractal analysis.

Animals

The development of Hepatozoon sipedon sp. nov. (Apicomplexa: Adeleina: Hepatozoidae) in its natural host, the Northern water snake (Nerodia sipedon sipedon), in the culicine vectors Culex pipiens and C. territans, and in an intermediate host, the Northern leopard frog (Rana pipiens).

The life cycle of Hepatozoon sipedon sp. nov. was studied in two snake species, the Northern water snake and the Eastern garter snake, in its mosquito hosts Culex pipiens and C. territans, and in the Northern leopard frog. Gametogenesis, fertilization and sporogony occurred within fat body cells in the haemocoel of mosquitoes that had fed on infected water snakes. Mature oocysts averaging 263 microns in diameter and containing more than 500 sporocysts were observed in mosquitoes 28 days post-feeding. Each sporocyst enclosed eight sporozoites. Dizoic cysts were found in the liver of frogs that had been fed infected mosquitoes seven days previously. Two rounds of merogony in various internal organs and intraerythrocytic gamonts were observed in snakes that had been fed frogs which had been orally inoculated with infected mosquitoes. Developmental stages were not seen in snakes that were fed infected mosquitoes directly. A comparison of this life cycle with those described for other Hepatozoon species infecting snakes is presented with reference to the different modes of transmission featured by these parasites.

Animals

Morphology, ultrastructure and taxonomic status of Toddia sp. in northern water snakes (Nerodia sipedon sipedon) from Ontario, Canada.

Inclusions characteristic of an infection caused by Toddia sp. were found in the erythrocytes and erythroblasts of 15 of 26 northern water snakes (Nerodia sipedon sipedon) collected near Kingston, Ontario, Canada. Erythrocytes contained translucent inclusions, small acidophilic bodies, and square-shaped crystalloid structures. Erythrocytes infected with Toddia sp. were more rounded than uninfected erythrocytes and had pycnotic nuclei. We observed icosahedral virus particles measuring 195 to 210 nm formed from a membrane-bounded viral assembly site in the cytoplasm of the host erythrocyte. As a result of the viral identity of this parasite, we recommend that the etiologic agent of Toddia sp. infections from this and other species of North American snakes be renamed Snake Erythrocytic Virus.

Animals

Quantitative phylogenetic constancy of cerebellar Purkinje cell morphological complexity.

Golgi-stained material of cerebellar cortices from 17 species was examined by measuring the fractal dimensions of the borders of Purkinje cells, which is a quantitative, objective measure of morphological complexity. Nine species (from birds to man) were chosen for a comparison with ANOVA and no statistically significant differences were found in their fractal dimensions. In contrast, a wide range of differences was found in the membrane areas across species lines. The Sholl coefficient, a measure of branch formation and termination away from the soma, showed no consistent pattern for each cell. We interpret our results as indicating a constancy in morphological cellular complexity of Purkinje cells during late evolutionary time.

Analysis of Variance

Early dendrite development in spinal cord cell cultures: a quantitative study.

Neurons in dissociated cell culture provide a favorable system for the quantitative analysis of structural changes and the examination of structure-function relationships during development. Fragment C of tetanus toxin was used to label neurons in murine spinal cord cell cultures and dendrite outgrowth was monitored by a number of measures. The dissociated neurons increased in morphologic complexity from approximate spheres to highly branched structures during the first week in culture. Much of the structural complexity of the dendrite arbor, as quantified by fractal dimension, was established within 48 hr after plating, i.e., prior to the development of interneuronal contacts. During the first few days in culture, dendrite branching complexity increased more rapidly than dendrite size, whereas after 4 days, fractal dimension remained relatively constant while dendrites continued to grow. Fractal analysis has provided data which suggest that the early development of dendrite branching complexity is determined intrinsically. Fractal dimension, as an effective index of morphologic complexity, should be a useful tool for the further study of extrinsic signals which might modify the generation or stabilization of dendrite form.

Animals

Technical aspects of acoustic myography (AMG) of human skeletal muscle: contact pressure and force/AMG relationships.

The effect of contact pressure on acoustic myographic (AMG) recordings was examined during voluntary isometric contractions of the human quadriceps muscle in 20 normal males. A piezoelectric disk for recording muscle sounds was placed over rectus femoris at approximately mid-thigh and secured with a rubber electromyography (EMG) strap. Contact pressure was monitored by a load cell placed between the AMG device and the strap. With the subject seated, force at different percentage levels of maximum voluntary contraction (MVC) were held for 5 s each. Both AMG and EMG recordings were full-wave rectified and integrated (IAMG and IEMG) and expressed as a percentage of activity at MVC. Two contraction series were performed with 2 different contact pressures. Pressure 1 (P1), of 180 Pa was applied in all subjects. A higher pressure of either 790 Pa (P2; in 5 subjects) or 1200 Pa (P3; in 15 subjects) was also applied. No significant changes in IAMG activity (P > 0.1) occurred between P1 and P2 but P3 produced increases in IAMG at all force levels (P < 0.05 at 10, 50 and 75% MVC). Both linear and non-linear relationships between force and IAMG were observed in different subjects but the relationship also varied with the 2 contact pressures within some subjects. The force/IEMG relationship was linear in all cases. These results provide quantitative evidence that contact pressure can influence the degree of IAMG activity if the pressure is high enough. The change in the force/IAMG relationship with pressure in some subjects suggests that the different relationships observed are not determined by physiological differences between subjects but rather by technical factors.

Acoustics

Prospective survey of the use of the laryngeal mask airway in 2359 patients.

Patients undergoing anaesthesia in which the laryngeal mask airway was used were prospectively audited over a 6-month period. A simple record sheet was completed at the time of anaesthetic administration and 2359 completed forms were analysed to assess problems encountered with its use. It was used successfully in 2350 patients (99.61%); of these, 1399 patients (59%) breathed spontaneously through the airway and 960 patients (41%) underwent intermittent positive pressure ventilation of the lungs. Two patients (0.08%) were reported to have regurgitated during the use of the laryngeal mask airway, but no serious sequelae associated with its use were encountered.

Adolescent

Amitriptyline prevents N-methyl-D-aspartate (NMDA)-induced toxicity, does not prevent NMDA-induced elevations of extracellular glutamate, but augments kainate-induced elevations of glutamate.

The effect of amitriptyline on kainate- and N-methyl-D-aspartate (NMDA)-induced toxicity and release of amino acids from cerebellar granule neurons was studied. The ED50 for amitriptyline, imipramine, and nortriptyline protection against NMDA-induced toxicity was 6.9, 6.5, and 1.3 microM, respectively. None of these compounds protected against kainate-induced toxicity. Even though amitriptyline was protective against NMDA-induced toxicity, it had no effect on the NMDA-induced increase in extracellular levels of glutamate or aspartate from these cells, indicating a dissociation between NMDA receptor activation (as indicated by glutamate content elevations) and NMDA-induced toxicity. However, kainate and quisqualate treatment resulted in elevations of glutamate and taurine levels that were further augmented in the presence of 25 microM amitriptyline. These findings confirm the reports of others that tricyclic antidepressants have neuroprotective effects related to the NMDA receptor and expand on these reports by showing that even though there is protection against toxicity, the NMDA receptor is nevertheless activated, suggesting an involvement of these compounds at sites removed from the receptor. Furthermore, this is the first report showing an interaction of tricyclic antidepressants with the function of non-NMDA receptors.

Amitriptyline

A fractal analysis of pyramidal neurons in mammalian motor cortex.

Pyramidal neurons in the mammalian cerebral cortex can be described by a fractal dimension (Mandelbrot, 1982), which is an objective, quantitative measure of the complexity of their soma/dendritic borders. In the cat, the fractal dimensions of lamina V cells, which include pyramidal tract neurons (PTN), indicate that these cells are more complex than other pyramidal neurons (PN) in the same region of motor cortex. The lamina V cells of the cat are also more complex than those in motor cortex of the monkey. Moreover, lamina III neurons in the monkey are more complex than monkey lamina V neurons. The fractal dimension of the intracortical axon collateral arborizations of the same pyramidal neurons indicated, in all cases, that the branching of these terminals is less complex than the branching of the dendrites of the same cells. In line with the observation that the fractal dimensions of some homologous cellular populations are different in different species, it is suggested that the fractal dimension and the degree of morphological complexity may relate to the requirement for the number of separable functions to be accommodated within one neuron. For example, as the size of the cortex and the number of neurons in a region increase, the opportunity exists within a given cortical zone, for individual functions to be segregated and for functional specialization to be accommodated with less morphological complexity of the individual neurons performing each of these functions.

Animals

Comparative morphometry of Bergmann glial (Golgi epithelial) cells. A Golgi study.

Bergmann glial (Golgi epithelial) cells were Golgi-impregnated in the cerebella of species with great differences in the thickness of the molecular layer, in small African native mouse, rat, rhesus monkey, and man. The thickness of the molecular layer determines the length of the radial Bergmann cell processes. Whereas the overall morphology of the cells was found to be strikingly similar in all species studied, there were great quantitative differences in length and diameter of the stem processes. Species with thick molecular layers (man, monkey) have thicker stem processes than species with short distances between Bergmann glial cell soma and pial surface (rat, mouse). This could mean that larger animals with longer gestation periods allow for prolonged growth of cell volumes. On the other hand, an increase in the diameter of long processes should reduce the cytoplasmic resistance against ionic currents; this would be important when Bergmann glial cells--like retinal Müller cells--would act as "cables" for spatial buffering of potassium ions released by electrically active neurons. By contrast, the fractal dimension--i.e., a quantitative measure of the complexity of the cell's border--of the cell processes was lower in species with long processes. In an age series of rat cells, the fractal dimension is shown to increase slightly up to a very old age.

Animals

A fractal analysis of cultured rat optic nerve glial growth and differentiation.

Fractal dimension can be used as a quantitative measure of morphological complexity. Separate, enriched populations of oligodendrocytes or type 2 astrocytes derived from neonatal rat optic nerves were allowed to differentiate in vitro. Fractal dimensions of differentiating glial cells were measured over time. The fractal dimension correlated with perceived complexity and increased in value as the glial cells matured. Analysis of the changes in fractal dimension with time revealed unique rates of growth and differentiation for each glial phenotype.

Animals

Low calcium-induced release of glutamate results in autotoxicity of cerebellar granule cells.

Primary cultures of cerebellar rat granule neurons were grown for 18-22 days in vitro in the absence of antibiotics. When the cultures were placed in a low calcium (no EGTA) balanced salt solution at room temperature, rapid cell death occurred usually within 30 min of placing cells in the buffer. Changes in the cells were evident within 10 min and included an apparent cellular granulation with a partial loss of cell body birefringence at 10 x magnification which was complete by 30 min. This rapid death was prevented by (1) replacing chloride in the buffer with acetate; (2) increasing the osmolarity of the buffer by 30% with sucrose; (3) the addition of the selective excitatory amino acid (EAA) antagonist, 2-amino-7-phosphonoheptanoic acid (APH, 200 microM) but not by the selective kainate-quisqualate antagonist, glutamylaminomethylsulfonic acid (GAMS, 400 microM); or (4) the addition of one of the following calcium channel antagonists, verapamil (400 microM) diltiazem (150 microM) or lanthanum (5 microM). Placing cells in low calcium buffer resulted in a 3.7- and 3.2-fold increase in the non-selective secretion of aspartate and glutamate (as well as other amino acids) over baseline secretion (same buffer except containing 2.5 mM calcium). This increase was partially prevented by verapamil, but not by APH or chloride deletion. Verapamil only partially prevented the efflux of glutamate in buffer containing 1 mM EGTA. These results indicate that placing cells in low calcium buffer results in neurotoxicity secondary to both the influx of chloride and water in conjunction with the efflux of amino acids, some of which stimulate an excitatory amino acid receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals

A fractal analysis of cell images.

Methods of digital image analysis have been adapted to measure the fractal dimension of cellular profiles. The fractal dimension is suggested as a useful measure of the complexity of a contour. Three methods produce similar results when applied to constructed, near-ideal fractal figures. Comparison of the measurements for a variety of image types indicates the measurement accuracy in each case and may help in interpreting the results when applied to real, non-ideal cell images of unknown fractal dimension. Two of the methods are currently adopted as appropriate for use on neuronal contours. A correlation exists between the complexity of these contours and the magnitude of the estimated fractal dimension.

Animals

Quisqualate, high calcium concentration and zero-chloride prevent kainate-induced toxicity of cerebellar granule cells.

Kainic acid (KA; 100 microM), results in the death of all cultured rat cerebellar granule cells (18-22 days in vitro) within 30 min. Changes in the cells are evident within 2 min of applying the excitatory amino acid (EAA) and include an apparent cellular granulation with a loss of cell body birefringence at 10 X magnification. Quisqualic acid (QA; 25 microM) completely prevents this KA-induced neurotoxicity. In addition, cells are protected from toxicity by increasing calcium concentrations to 10 mM. Moreover, following a 30 min exposure and after washing the cells free of these compounds, cells placed in culture media remain alive 24 h later. Interestingly, neurons die when placed in a balanced salt solution which lacks calcium even when no KA is present. This death is also dependent on the presence of chloride and is prevented with the non-selective EAA antagonist, kynurenic acid, but is not prevented by QA. Collectively, these data suggest that the activation of the EAA receptor by KA in cerebellar granule cells is at least partially regulated by calcium and chloride and is suppressed by QA. Furthermore, placing granule cells in zero-calcium results in neuronal death which appears to be mediated by EAA mechanisms.

Animals