Showing papers by "University of Groningen published in 1975"

Electromyography and mechanics of mastication in the albino rat.

Abstract: The masticatory apparatus in the albino rat was studied by means of electromyography and subsequent estimation of muscular forces. The activity patterns of the trigeminal and suprahyoid musculature and the mandibular movements were recorded simultaneously during feeding. The relative forces of the individual muscles in the different stages of chewing cycles and biting were estimated on the basis of their physiological cross sections and their activity levels, as measured from integrated electromyograms. Workinglines and moment arms of these muscles were determined for different jaw positions. In the anteriorly directed masticatory grinding stroke the resultants of the muscle forces at each side are identical; they direct anteriorly, dorsally and slightly lingually and pass along the lateral side of the second molar. Almost the entire muscular resultant force is transmitted to the molars while the temporo-mandibular joint remains unloaded. A small transverse force, produced by the tense symphyseal cruciate ligaments balances the couple of muscle resultant and molar reaction force in the transverse plane. After each grinding stroke the mandible is repositioned for the next stroke by the overlapping actions of three muscle groups: the pterygoids and suprahyoids produce depression and forward shift, the suprahyoids and temporal backward shift and elevation of the mandible while the subsequent co-operation of the temporal and masseter causes final closure of the mouth and starting of the forward grinding movement. All muscles act in a bilaterally symmetrical fashion. The pterygoids contract more strongly, the masseter more weakly during biting than during chewing. The wide gape shifts the resultant of the muscle forces more vertically and moreposteriorly. The joint then becomes strongly loaded because the reaction forces are applied far anteriorly on the incisors. The charateristic angle between the almost horizontal biting force and the surface of the food pellet indicates that the lower incisors produce a chisel-like action. Tooth structure reflects chewing and biting forces. The transverse molar lamellae lie about parallel to the chewing forces whereas perpendicular loading of the occlusal surfaces is achieved by their inclination in the transverse plane. The incisors are loaded approximately parallel to their longitudinal axis, placement that avoids bending forces during biting. It is suggested that a predominantly protrusive musculature favors the effective force transmission to the lower incisors, required for gnawing. By grinding food across transversely oriented molar ridges the protrusive components of the muscles would be utilized best. From the relative weights of the masticatory muscles in their topographical relations with joints, molars and incisors it may be concluded that the masticatory apparatus is a construction adapted to optimal transmission of force from muscles to teeth.

The absorption and scattering of light in bovine and human dental enamel

Abstract: The reflectance and transmission of thin slabs of dental enamel has been measured at all wavelengths between 220 and 700 nm by means of an integrating sphere. From the results the true scattering and absorption coefficients have been computed. The theoretical model used is an extended two-flux model, which is presented and discussed. The absorption spectrum of the dissolved organic component of enamel was also determined. An absorption peak at 270 nm is common to all the spectra. This peak in the bovine enamel spectrum is about three times as high as in the spectrum of human enamel. The peak of the dissolved material is about as high as the peak of the corresponding enamel. Hence it is concluded that the organic component, presumably aromatic amino acids, is responsible for most or all of the observed optical absorption.

Mandibular movements of the albino rat during feeding.

Abstract: Jaw movements of albino rats during biting and mastication of relatively hard food were recorded by means of conventional and X-ray cinematography. Mandibular kinetics have been analysed in the context of passive mechanical limits imposed by jaw morphology, particularly of the joints, and by the food itself. Movements have been described in terms of degrees of gape, condylar translation and horizontal rotation of the rami about the symphysis. During biting the condyle remains in the anterior two-thirds of the fossa, moves forward as the jaw opens and the converse. The rami usually spread well apart; the lower incisors are usually approximated. Incised food particles are transported toward the molars by means of coordinated jaw and tongue movements. The prominent palatal rugae of the diastemal region abet this process. In the power stroke of mastication, the mandible shifts forward as the lower toothrows move a little inward; the condyles occupy the posterior two-thirds of the fossa. All movements seen were bilaterally symmetrical. Simultaneous chewing occurred on both sides. It is suggested that the lingual components in the primarily anterior power stroke enhance grinding efficiency. A movable symphysis appears to be of critical importance in facilitating this type of mastication.

Colorless sulfur bacteria and their role in sulfur cycle

Abstract: The bacteria belonging to the families of the Thiobacteriaceae, Beggiatoaceae and Achromatiaceae are commonly called the colourless sulfur bacteria. While their ability to oxidize reduced inorganic sulfur compounds has clearly been established, it is still not known whether all these organisms can derive metabolically useful energy from these oxidations. During the last decades research has mainly focussed on the genus Thiobacillus. Bacteria belonging to this genus can oxidize a variety of reduced inorganic sulfur compounds and detailed information is available on the biochemistry and physiology of these energy-yielding reactions. The thiobacilli, most of which can synthesize all cell material from CO2, possess a well-regulated metabolic machinery with high biosynthetic capacities, which is essentially similar to that of other procaryotic organisms. Although the qualitative role of colourless sulfur bacteria in the sulfur cycle is well documented, quantitative data are virtually absent. Activities of colourless sulfur bacteria in nature must be related to direct and indirect parameters, such as: the rate of oxidation of (S35) sulfur compounds, the rate of C14O2-fixation, the rate of acid production and numbers and growth rates of the bacteria. However, chemical reactions and similar activities of heterotrophic organisms mask the activities of the colourless sulfur bacteria to various extents, depending on the condition of the natural environment. This interference is minimal in regions where high temperature and/or low pH allow the development of a dominant population of colourless sulfur bacteria, such as hot acid sulfur springs, sulfide ores, sulfur deposits and some acid soils. The oxidation of inorganic sulfur compounds is carried out by a spectrum of sulfur-oxidizing organisms which includes: 1) obligately chemolithotrophic organisms 2) mixotrophs 3) chemolithotrophic heterotrophs 4) heterotrophs which do not gain energy from the oxidation of sulfur compounds but benefit in other ways from this reaction, and 5) heterotrophs which do not benefit from the oxidation of sulfur compounds. The spectrum is completed by a hypothetical group of heterotrophic organisms, which may have a symbiotic relationship with thiobacilli and related bacteria. Such heterotrophs may stimulate the growth of colourless sulfur bacteria and thereby contribute to the oxidation of sulfur compounds. Future research should focus in the first place on obtaining and studying pure cultures of many of the colourless sulfur bacteria. In the second place, studies on the physiological and ecological aspects of mixed cultures of colourless sulfur bacteria and heterotrophs may add to a better understanding of the role of the colourless sulfur bacteria in the sulfur cycle.

Dopamine metabolism in depressions, psychoses, and Parkinson's disease: the problem of the specificity of biological variables in behaviour disorders.

Abstract: The probenecid technique was used in study of the central dopamine DA metabolism in patients with depressions, psychotic disorders, and Parkinson's disease. The disturbances found were neither nosologically nor syndromally specific, but appeared to be symptom-specific. Decreased DA turnover was associated with hypomotility, and increased DA turnover with hypermotility. Decreased DA turnover was probably related aetiologically to the hypomotility: the symptoms subsided after replenishment of the DA deficiency. The relation between increased DA turnover and hypermotility is still under investigation. In view of the findings obtained, a plea is made for the development of a functional psychopathology, in which psychiatric syndromes are "dissected" into their constituent psychological dysfunctions. This development is expected to stimulate human brain and behaviour research. It can be achieved only by intensive collaboration between psychiatrists and experimental psychologists.

Hpo-4(2-) content in enamel and artificial carious lesions

Abstract: The HPO 4 2− and CO 3 2− content was determined in sound enamel and in material collected from artificially produced carious lesions. The method described shows that the HPO 4 2− content can be determined from the 875 cm−1 infrared absorption band if correction for the CO 3 2− contribution are made. The I. R. spectra show that the HPO 4 2− content in sound human or bovine enamel is about 5% by weight. In artificially produced carious lesions (pH=4.0), the HPO 4 2− content is in the order of 15 wt%. Most likely, the HPO 4 2− ions in sound and carious enamel have a different environment.

Growth yields of microorganisms on methanol and methane - theoretical-study

Abstract: An attempt was made to calculate growth yields of microorganisms on methanol and methane on the basis of known biochemical pathways of C1 metabolism. Since 3‐phosphoglycerate is a key intermediate in the assimilation pathways of C1 compounds, the calculations were based on the assumption that the synthesis of cell material from C1 substrates can be regarded as a two step process. When YATP on 3‐phosphoglycerate was taken as 10.5, a maximal cell yield of organisms of the composition C4H8O2N on methanol was found to be 0.73 g cells/g substrate. For growth on methane a value of 0.91 g cells/g substrate was calculated when a mixed function oxidase was implicated in methane oxidation. These yields were calculated on the basis of the ribulose phosphate pathway of formaldehyde fixation as the major pathway of C1 assimilation. Yields calculated on the basis of the serine pathway were on an average 20% lower. The calculations disclosed that for growth on methane, at least for Methylococcus capsulatus, a reversed electron transport system is required when methane is oxidized by a mixed function oxidase. The theoretical cell yields on methanol and methane have been compared with experimentally obtained yields and the validity of the estimations of growth yields on the basis of the present calculations is discussed.

A Model of Glutamate Metabolism in Brain: A Biochemical Analysis of a Heterogeneous Structure

Abstract: Glutamate and related amino acids in brain have long attracted the attention of many scientific investigators. The suggested beneficial effects of glutamate on behavior was one of the factors stimulating research on the metabolic aspects of glutamate in brain, a research area already actively pursued in the thirties by Krebs, Weil-Malherbe, and others (Weil-Malherbe, 1950). There is no doubt that Waelsch, through his involvement in the reported beneficial effects of glutamate on epileptic patients, was stimulated to concentrate on the metabolism of glutamate in the brain.

Longitudinal growth of polymer crystals from flowing solutions .2. polyethylene crystals in poiseuille flow

Abstract: A study has been made on the longitudinal growth of fibrillar polyethylene crystals from xylene solutions subjected toPoiseuille flow. Fibrillar crystal seeds were placed at the entrance of a capillary through which a supercooled xylene solution of polyethylene was allowed to flow and the longitudinal growth in the chain direction was investigated. By winding the growing crystal on a roll with a speed equal to the growth rate, continuous fibrillar crystals could be produced. Scanning electron microscopic examinations have shown that the continuous polyethylene crystals can be regarded as assemblies of elementary fibrils of the Shish-Kebab type. Growth was found to be nucleated at the lateral surface of the seed crystals instead of at the end. Under static conditions a tapered shaped crystal develops which allows the determination of the total length of the grown fiber for a growth period of time and thereby the growth rate. The latter quantity was found to increase with flow rate, polymer concentration and degree of supercooling.

Influence of light and temperature on the photosynthetic rate of marine benthic diatoms

Abstract: The influence of light and temperature on photosynthetic rate as measured by C14O2-fixation of marine benthic diatoms was investigated, using both intact sediment samples (Marshall et al., 1973) and suspensions of diatoms harvested by a lenstissue technique (Eaton and Moss, 1966). After C14-incubation, sediment samples were filtered, burned in a sample oxidizer, and their activity determined in a liquid scintillation counter. Photosynthetic rate of mixed field populations is saturated by a light intensity of approximately 10,000 lux; at still higher light intensities no photoinhibition was found. In contrast to the mixed field populations, unialgal cultures of the benthic diatom Amphiprora alata Kutz. exhibited strong photoinhibition at higher light intensities (10,000 to 60,000 lux). Within a range of 4° to 20°C, the photosynthetic rate increased about 10%/Co. No differences in photosynthetic pattern were observed between epipelic and epipsammic species.

The central projections of the trigeminal, facial and anterior lateral line nerves in the carp (Cyprinus carpio L.).

Abstract: The central projections of the trigeminal, facial and anterior lateral line nerves were studied in the carp (Cyprinus carpio) by the Nauta and Fink-Heimer silver techniques following rhizotomy. Degenerating trigeminal fibers were found projecting on the nucleus of the descending trigeminal root and on the medial funicular nucleus. The former can be subdivided in five portions lying dorsal to the various cranial motor nuclei. The afferent facial fibers could be traced into the facial, glossopharyngeal and vagal lobes, while the anterior lateral line nerve projects on rostral, medial and caudal parts of the medial nucleus and on the eminentia granularis. The anterior lateral line nerve can be divided into a dorsal and a ventral root, each following the same course. The role trigeminal and facial nerves play in proprioception of respiratory muscles is discussed.

Microbodies in methanol-assimilating yeasts

Abstract: Cells of 3 yeast species capable of assimilating methanol have been examined by electron microscopy. When grown on methanol as the sole source of carbon and energy they contained many microbodies. Cells grown on glucose or ethanol either did not contain such bodies at all, or only to a limited extent.

Cytochemical Localization of Catalase Activity in Methanol-Grown Hansenula polymorpha

Abstract: The localization of peroxidase activity in methanol-grown cells of the yeast Hansenula polymorpha has been studied by a method based on cytochemical staining with diaminobenzidine (DAB). The oxidation product of DAB occurred in microbodies, which characteristically develop during growth on methanol, and in the intracristate space of the mitochondria. The staining of microbodies was H2O2 dependent, appeared to be optimal at pH 10.5, diminished below pH 10 and was inhibited by 20 mM 3-amino 1,2,4 triazole (AT). In contrast to these observations, the reaction in the mitochondria was not H2O2 dependent and not notably affected by differences in pH in the range of 8.5 to 10.5. Microbodies and mitochondria were also stained when H2O2 was replaced by methanol. Appropriate control experiments indicated that in this case methanol oxidase generated the H2O2 for the peroxidative conversion of DAB by catalase. These results suggest that catalase is located in the microbodies of methanol-grown yeasts. A model for a possible physiological function of the microbodies during growth on methanol is put forward.

Metal-nonmetal transition in vo2 - x-ray photoemission and resistivity measurements

Abstract: The semiconductor-metal transition in VO2 has been investigated by means of XPS measurements. The band gap in the semiconducting region is found to be temperature-dependent with a room temperature value of Eg=0.3 eV, in agreement with resistivity measurements. The core lines, which are asymmetric below Tnu broaden and become symmetric above Tt. A model is discussed to explain the broadening in the metallic region, which requires that the core hole-valence electron interaction is comparable to the bandwidth. The relative shift of the O 1s and V 2p peak positions below and above Tt indicates that the charges on the ions are highest in the metallic phase, suggesting a more ionic bond in this region.

Chemical analysis of cell wall regeneration and reversion of protoplasts from Schizophyllum commune.

Abstract: In the presence of MgSO4 as osmotic stabilizer, nucleated protoplasts of Schizophyllum commune developed a large vacuole and could be isolated on the basis of their low buoyant density. All these protoplasts were capable of wall regeneration and about 50 percent reverted to the hyphal mode of growth in liquid medium. The kinetics of the formation of three main cell-wall components, S-glucan (α-1,3-glucan), R-glucan (β-1,3, β-1,6-glucan) and chitin were studied from the onset of regeneration. S-glucan and chitin accumulation as well as RNA and protein synthesis started simultaneously after a short lag, but R-glucan formation was delayed. The reversion to hyphal tubes only began after several hours of rapid R-glucan synthesis. Cycloheximide (0.5 μg/ml), inhibiting protein synthesis by 98% inhibited the formation of R-glucan and the reversion to hyphal growth but the formation of chitin and S-glucan did start and continued seemingly unimpaired for several hours. This indicates that the enzymes responsible for the synthesis of S-glucan and chitin remained intact during protoplast preparation. Polyoxin D inhibited both the synthesis of chitin and R-glucan and also the reversion to hyphal growth. However, the synthesis of S-glucan was not suppressed. These inhibitor studies as well as the kinetics of R-glucan formation during normal regeneration suggest that the synthesis of R-glucan is required for the initiation of hyphal morphogenesis.

Selection at the alcoholdehydrogenase locus in Drosophila melanogaster.

Abstract: Des populations deDrosophila melanogaster, elevees avec une nourriture contenant differents alcools, montrent une augmentation de la frequence de l'allele «fast» du locus alcool deshydrogenase. Ce phenomene est interprete comme etant le resultat d'une selection et ne correspond pas a l'hypothese de la neutralite des variants d'isoenzymes.

Production and characterization of the agarase of Cytoplaga flevensis.

Abstract: Cytophaga flevensis produced an inducible agarase which was extracellular under most conditions tested. The effect of cultural conditions on the production of enzyme was studied in batch and continuous culture. In batch culture, production was optimal when Cytophaga flevensis was incubated at 20 C in a mineral medium with agar as the sole carbon source and ammonium nitrate as the nitrogen source at an initial pH of 6.6-7.0. The enzyme appeared to be subject to catabolite repression, since its synthesis was repressed when glucose was added to the medium in batch culture. Furthermore, in continuous culture, enzyme production decreased with increasing growth rate. Extracellular agarase was partially purified and the enzyme preparation obtained was very stable. The enzyme has a molecular weight of 26 000 daltons. It is a beta-agarase which is highly specific for polysaccharides containing neoagarobiose units. The final products of hydrolysis of agarose by the endo-acting enzyme were neoagarotetraose and neoagarobiose. Optimal conditions for its activity were pH 6.3 and 30C. When agarose was used as a substrate, an apparent temperature optimum of 35C was found, due to gelling of the substrate during the assay procedure.