(1/79074) Quantitative assessment of the morphology of the pig's head used as a model in surgical experimentation. Part 1: Methods of Measurements.

Thirty-two surface measurements were described for assessment of the effect of complex surgical operations on the skeleton of the face in pigs. The methods of measurements imitate those of anthropometry. The surface measurements can complement cephalometry with data about the changes in the soft tissue and thus improve the documentation of the effect of surgery. This paper can help in the evaluation of complicated osteotomy procedures using the pig as the animal model, for facial reconstruction research in humans.  (+info)

(2/79074) Investigation of the theory and mechanism of the origin of the second heart sound.

To investigate further the origin of the second heart sound we studied human subjects, dogs, and a model in vitro of the cardiovascular system. Intra-arterial sound, pressure, and, where possible, flow and high speed cine (2,000 frames/sec) were utilized. The closure sound of the semilunar valves was of higher amplitude in be ventricles than in their respective arterial cavities. The direction of inscription of the main components of intra-arterial sound were opposite in direction to the components of intraventricular sound. Notches, representative of pressure increments, were noted on the ventricular pressure tracings and were coincident with the components of sound. The amplitude of the closure sound varied with diastolic pressure, but remained unchanged with augmentation of forward and retrograde aortic flow. Cines showed second sound to begin after complete valvular closure, and average leaflet closure rate was constant regardless of pressure. Hence, the semilunar valves, when closed, act as an elastic membrane and, when set into motion, generate compression and expansion of the blood, producing transient pressure changes indicative of sound. The magnitude of the initial stretch is related to the differential pressure between the arterial and ventricular chambers. Sound transients which follow the major components of the second sound appear to be caused by the continuing stretch and recoil of the leaflets. Clinically unexplained findings such as the reduced or absent second sound in calcific aortic stenosis and its paradoxical presence in congenital aortic stenosis may be explained by those observations.  (+info)

(3/79074) Factors influencing the deposition of inhaled particles.

Because the initial deposition pattern of inhaled particles of various toxic agents determines their future clearance and insult to tissue, respiratory tract deposition is important in assessing the potential toxicity of inhaled aerosols. Factors influencing the deposition of inhaled particles can be classified into three main areas: (1) the physics of aerosols, (2) the anatomy of the respiratory tract and (3) the airflow patterns in the lung airways. In the physics of aerosols, the forces acting on a particle and its physical and chemical properties, such as particle size or size distribution, density, shape, hygroscopic or hydrophobic character, and chemical reactions of the particle will affect the deposition. With respect to the anatomy of the respiratory tract, important parameters are the diameters, the lengths, and the branching angles of airway segments, which determine the deposition. Physiological factors include airflow and breathing patterns, which influence particle deposition. Various lung models used in predicting particle deposition are reviewed and discussed. The air-way structures of various animal species are compared, showing the unique structure of the human lung compared to the animal species under study. Regional deposition data in man and dog are reviewed. Recent deposition data for small rodents are presented, showing regional difference in deposition with the right apical lobe having the highest relative deposition.  (+info)

(4/79074) Hidden genetic variability within electromorphs in finite populations.

The amount of hidden genetic variability within electromorphs in finite populations is studied by using the infinite site model and stepwise mutation model simultaneously. A formula is developed for the bivariate probability generating function for the number of codon differences and the number of electromorph state differences between two randomly chosen cistrons. Using this formula, the distribution as well as the mean and variance of the number of codon differences between two identical or nonidentical electromorphs are studied. The distribution of the number of codon differences between two randomly chosen identical electromorphs is similar to the geometric distribution but more leptokurtic. Studies are also made on the number of codon differences between two electromorphs chosen at random one from each of two populations which have been separated for an arbitrary number of generations. It is shown that the amount of hidden genetic variability is very large if the product of effective population size and mutation rate is large.  (+info)

(5/79074) The Lewontin and Krakauer test on quantitative characters.

It is shown that LEWONTIN and KRAKAUER's test could also be applied to quantitative characters that do not show important dominance and epistatic genetic variances. The design of experiments for this purpose and the error of the estimation of F are discussed.  (+info)

(6/79074) Testing for selective neutrality of electrophoretically detectable protein polymorphisms.

The statistical assessment of gene-frequency data on protein polymorphisms in natural populations remains a contentious issue. Here we formulate a test of whether polymorphisms detected by electrophoresis are in accordance with the stepwise, or charge-state, model of mutation in finite populations in the absence of selection. First, estimates of the model parameters are derived by minimizing chi-square deviations of the observed frequencies of genotypes with alleles (0,1,2...) units apart from their theoretical expected values. Then the remaining deviation is tested under the null hypothesis of neutrality. The procedure was found to be conservative for false rejections in simulation data. We applied the test to Ayala and Tracey 's data on 27 allozymic loci in six populations of Drosophila willistoni . About one-quarter of polymorphic loci showed significant departure from the neutral theory predictions in virtually all populations. A further quarter showed significant departure in some populations. The remaining data showed an acceptable fit to the charge state model. A predominating mode of selection was selection against alleles associated with extreme electrophoretic mobilities. The advantageous properties and the difficulties of the procedure are discussed.  (+info)

(7/79074) Stromal cells mediate retinoid-dependent functions essential for renal development.

The essential role of vitamin A and its metabolites, retinoids, in kidney development has been demonstrated in vitamin A deficiency and gene targeting studies. Retinoids signal via nuclear transcription factors belonging to the retinoic acid receptor (RAR) and retinoid X receptor (RXR) families. Inactivation of RARaplpha and RARbeta2 receptors together, but not singly, resulted in renal malformations, suggesting that within a given renal cell type, their concerted function is required for renal morphogenesis. At birth, RARalpha beta2(-) mutants displayed small kidneys, containing few ureteric bud branches, reduced numbers of nephrons and lacking the nephrogenic zone where new nephrons are continuously added. These observations have prompted us to investigate the role of RARalpha and RARbeta2 in renal development in detail. We have found that within the embryonic kidney, RARalpha and RARbeta2 are colocalized in stromal cells, but not in other renal cell types, suggesting that stromal cells mediate retinoid-dependent functions essential for renal development. Analysis of RARalpha beta2(-) mutant kidneys at embryonic stages revealed that nephrons were formed and revealed no changes in the intensity or distribution of molecular markers specific for different metanephric mesenchymal cell types. In contrast the development of the collecting duct system was greatly impaired in RARalpha beta2(-) mutant kidneys. Fewer ureteric bud branches were present, and ureteric bud ends were positioned abnormally, at a distance from the renal capsule. Analysis of genes important for ureteric bud morphogenesis revealed that the proto-oncogene c-ret was downregulated. Our results suggest that RARalpha and RARbeta2 are required for generating stromal cell signals that maintain c-ret expression in the embryonic kidney. Since c-ret signaling is required for ureteric bud morphogenesis, loss of c-ret expression is a likely cause of impaired ureteric bud branching in RARalpha beta2(-) mutants.  (+info)

(8/79074) Regulation of body length and male tail ray pattern formation of Caenorhabditis elegans by a member of TGF-beta family.

We have identified a new member of the TGF-beta superfamily, CET-1, from Caenorhabditis elegans, which is expressed in the ventral nerve cord and other neurons. cet-1 null mutants have shortened bodies and male tail abnormal phenotype resembling sma mutants, suggesting cet-1, sma-2, sma-3 and sma-4 share a common pathway. Overexpression experiments demonstrated that cet-1 function requires wild-type sma genes. Interestingly, CET-1 appears to affect body length in a dose-dependent manner. Heterozygotes for cet-1 displayed body lengths ranging between null mutant and wild type, and overexpression of CET-1 in wild-type worms elongated body length close to lon mutants. In male sensory ray patterning, lack of cet-1 function results in ray fusions. Epistasis analysis revealed that mab-21 lies downstream and is negatively regulated by the cet-1/sma pathway in the male tail. Our results show that cet-1 controls diverse biological processes during C. elegans development probably through different target genes.  (+info)