Showing papers by "University of Dundee published in 1986"

A family of related ATP-binding subunits coupled to many distinct biological processes in bacteria.

Abstract: Many biological processes are coupled to ATP hydrolysis We describe here a class of closely related ATP-binding proteins, from several bacterial species, which are associated with a variety of cellular functions including membrane transport, cell division, nodulation in Rhizobium and haemolysin export These proteins comprise a family of structurally and functionally related subunits which share a common evolutionary origin, bind ATP and probably serve to couple ATP hydrolysis to each of these biological processes This finding suggests a specific role for ATP in cell division, nodulation during nitrogen fixation and protein export, and allows us to assign a probable function to one of the protein components from each of these systems

The partitioning of nitrate assimilation between root and shoot of higher plants

Abstract: The partitioning of nitrate assimilation between root and shoot of higher plant species is indicated by the relative proportions of total plant nitrate reductase activity (NRA) in the two plant parts and the relative concentrations of nitrate and reduced N in the xylem sap. These have been collated here from the literature and temperate and tropical species compared. Both the distribution of NRA and xylem sap nitrate: reduced N indicate that the following four generalizations can be made. 1Temperate, perennial species growing in low external nitrate concentrations (about 1 mol m−3) carry out most of their nitrate assimilation in the root. As external nitrate concentration increases (in the range found in agricultural soils, 1–20 mol m−3), shoot nitrate assimilation becomes increasingly important. 2Temperate, annual legume species growing in low external nitrate concentrations carry out most of their nitrate assimilation in the root. Shoot nitrate assimilation increases in importance as external nitrate concentration is increased. 3Temperate, annual non-legume species vary greatly in their partitioning of nitrate assimilation between root and shoot when growing in low external nitrate concentrations. Regardless of the proportion carried out in the root at low external nitrate concentrations, nitrate assimilation in the shoot becomes increasingly important as external nitrate concentration is increased. 4Tropical and subtropical species, annual and perennial, carry out a substantial proportion of their nitrate assimilation in the shoot when growing in low external nitrate concentrations. The partitioning of nitrate assimilation between root and shoot remains constant as external nitrate concentration increases. It is proposed that a greater proportion of nitrate assimilation occurs in the shoot when an increase in the rate of nitrate uptake does not induce an increase in NR level in the root. Thus, a greater proportion of the nitrate taken up remains unassimilated and is passed into the xylem. A constant partitioning of nitrate assimilation between root and shoot is achieved by balancing NR levels in the root with rates of nitrate uptake. The advantages and disadvantages of assimilating nitrate in either the root or shoot are discussed in relation to temperate and tropical habitats.

Synaptosomes possess an exocytotic pool of glutamate

Abstract: There is increasing evidence that L-glutamate is a major excitatory neurotransmitter in the central nervous system1,2. Immunocytochemical studies indicate that glutamate within nerve terminals may be concentrated in vesicles3 and glutamate-accumulating vesicles have recently been isolated4. Exocytotic release of glutamate from synaptosomes (isolated nerve terminals) has not been convincingly demonstrated, however, and remains highly controversial5–7. In order to study the kinetics of release of endogenous L-glutamate from guinea pig cerebral cortical synaptosomes we have devised a continuous enzymatic assay. This has enabled us to identify a pool, equivalent to 15–20% of the total synaptosomal glutamate, which is capable of rapid Ca2+-dependent exocytotic release.

Ten questions to ask when planning a course or curriculum.

Abstract: This brief practical aid to course or curriculum development cannot replace educational qualifications or experience, but it does examine ten basic questions, any of which may be all too easily neglected. These are: What are the needs in relation to the product of the training programme? What are the aims and objectives? What content should be included? How should the content be organized? What educational strategies should be adopted? What teaching methods should be used? How should assessment be carried out? How should details of the curriculum be communicated? What educational environment or climate should be fostered? How should the process be managed? Each aspect is illustrated through the analogy of car manufacturing. The ten questions are relevant in all situations where a course or curriculum is being planned, including an undergraduate degree course, a short postgraduate course or a 1-hour lecture.

Beginning reading without phonology

Abstract: The reading development of the individual members of a class of new entrants to primary school (aged 4 1/2–5 1/2 years) was studied over a period of a year. The teaching they received emphasised the formation of a “sight vocabulary”. Instruction in letter-sound associations was restricted to spelling and writing. The children appeared to “read without phonology”, that is without the application of letter-sound (grapheme-phoneme) associations. Words could be read only after they had been taught. Errors involved visual confusions and occasional semantic, visual-then-semantic, derivational, and functor substitution paralexias. Error responses were generally selected from the set of words the child had been taught and this set was represented in episodic memory. In many cases spatial distortions which were destructive of word shape were not effective in abolishing reading. The results are discussed in terms of the formation of a rudimentary word recognition system, termed a “logographic lexicon”.

Effects of sodium chloride and polyethylene glycol on root-hair infection and nodulation of Vicia faba L. plants by Rhizobium leguminosarum

Abstract: The effects of sodium chloride and polyethylene glycol (PEG) on the interaction between Rhizobium leguminosarum strain 29d and root hairs of field bean (Vicia faba L. cv. Maris Bead) plants were investigated. Two levels each of NaCl (50 and 100 mol·m−3) and PEG (100 and 200 mol·m−3) were given at the time of root-hair formation. Scanning electron microscopy showed rhizobial attachment and colonization on root-hair tips. Adhesion of rhizobia in both lateral and polar orientation, sometimes associated with microfibrils, occurred mainly in crooks at the root-hair tips; most of the infections also occurred here. Bacterial colonization and root-hair curling were both reduced by stress treatments. Polyethylene glycol but not NaCl significantly reduced root-hair diameter. The proportion of root hairs containing infection threads was reduced by 30% under NaCl and by 52% under PEG. The structure of some of the root hairs, epidermal and hypodermal cells, as seen by light microscopy in ultrasections, was distorted as a result of NaCl and PEG treatments; cells showed plasmolysis and folded membranes. After three weeks of treatment, both NaCl and PEG inhibited nodule number by about 50% and nodule weight by more than 60%. It is concluded that the root-hair infection process in Vicia faba is impaired by NaCl and PEG treatments and this in turn results in fewer nodules being produced.

Organic solute accumulation in osmotically stressed cyanobacteria

Abstract: Three groups of cyanobacteria are recognized on the basis of their organic osmotica and upper salinity limit for growth. In general, the least halotolerant forms accumulate disaccharides, while cyanobacteria of intermediate halotolerance synthesize the heteroside glucosylglycerol and the most halotolerant isolates accumulate betaines in response to salt stress. However, certain strains also accumulate additional organic solutes, depending upon the growth temperature, the ambient salinity and the duration of salt stress.

Peptide chemotaxis in E. coli involves the Tap signal transducer and the dipeptide permease.

Abstract: Bacterial chemotaxis provides a simple model system for the more complex sensory responses of multicellular eukaryotic organisms1. In Escherichia coli, methylation and demethylation of four related membrane proteins, the methyl-accepting chemotaxis proteins (or MCPs), is central to chemotactic sensing and signal transduction2. Three of these proteins, Tar, Tsr and Trg, have been assigned specific roles in chemotaxis. However, the role of the fourth MCP, Tap, has remained obscure3. We demonstrate here that Tap functions as a conventional signal transducer, enabling the cell to respond chemotactically to dipeptides. This provides the first evidence of specific bacterial chemotaxis towards peptides. Peptide taxis requires the function of a periplasmic component of the dipeptide permease. This protein represents the first example of a periplasmic chemoreceptor that does not have a sugar substrate.

Purification and properties of membrane‐bound hydrogenase isoenzyme 1 from anaerobically grown Escherichia coli K12

Abstract: Hydrogenase isoenzyme 1 from the membrane fraction of anaerobically grown Escherichia coli has been purified to near homogeneity. The preparation involved dispersion of the membrane fraction with deoxycholate followed by ammonium sulphate precipitation, ion-exchange, hydroxyapatite and gel filtration chromatography steps. The enzyme was assayed by quantification of the H2:benzyl viologen oxidoreductase activity immunoprecipitated by a non-inhibitory antiserum specific for the enzyme. The enzyme constituted about 8% of the hydrogenase activity found in the detergent-dispersed membranes, the remainder being attributable to hydrogenase isoenzyme 2. Isoenzyme 1 was purified 130-fold and the specific activity of the final preparation was 10.6 mumol benzyl viologen reduced min-1 (mg protein)-1 (H2:benzyl viologen oxidoreductase). The final preparation contained polypeptides of apparent Mr 64,000, 31,000 and 29,000. Antibodies were raised both to the final preparation and to immunoprecipitation arcs containing hydrogenase isoenzyme 1, excised from crossed immunoelectrophoresis plates. The former cross-reacted with all three polypeptides in the enzyme preparation but the latter recognised only the Mr-64,000 polypeptide. Immunological analysis revealed that the polypeptides of apparent Mr 31,000 and 29,000 are fragments of a single polypeptide of Mr 35,000 which is present in the detergent-dispersed membranes. The fragmentation of the Mr-35,000 polypeptide during the preparation correlates with a change in the electrophoretic mobility of the enzyme. A similar electrophoretic mobility change was observed, accompanied by cleavage of the Mr-35,000 polypeptide to one of 32,000 when the enzyme was analysed after exposure of detergent-dispersed membranes to trypsin. The enzyme in the detergent-dispersed membranes consists minimally of two subunits of Mr 64,000 and two subunits of Mr 35,000. It contained 12.2 mol Fe and 9.1 mol acid-labile S2-/200,000 g enzyme. The enzyme, purified from bacteria grown in the presence of 63Ni, was found to contain 0.64 (+/- 0.20) mol Ni/200,000 g enzyme. A constant ratio of 63Ni immunoprecipitated to hydrogenase isoenzyme 1 activity immunoprecipitated by antiserum specific for the enzyme was observed during the preparation, consistent with Ni being part of the enzyme. The enzyme has a low Km for H2 (2.0 microM) in the H2:benzyl viologen oxidoreductase assay. It catalyses H2 evolution employing reduced methyl viologen as electron donor. It is inhibited reversibly by CO and irreversibly by N-bromosuccinimide.

Cognitive analysis of dyslexia

Abstract: The author adopts a cognitive approach to developmental dyslexia and argues that the mental system underlying reading competence can be represented as a set of information processors.

The Biology of Pentastomids

Abstract: Publisher Summary This chapter describes the biology of pentastomids and several of the most important deficiencies are outlined. Pentastomids, otherwise known as linguatulids or tongueworms, are a relatively neglected and poorly understood class of endoparasites, which occupy a unique position among invertebrates in that, as adults, they are entirely restricted to the respiratory tract of vertebrates: the majority of species grow to maturity in the lungs. About 90% of species infect reptiles, and it is probable that they have been associated with these hosts since the Mesozoic. Despite this long period for potential adaptive radiation, the basic body design is remarkably conservative, and pentastomids comprise a homogeneous and distinctive systematic assemblage of about 100 species. All possess a vermiform, often conspicuously annulated abdomen, usually strongly united with a rounded cephalothorax, which bears, on its ventral surface, a small sucking mouth flanked by two pairs of hooks. Pentastomids, in common with other parasites, are regulators of host populations and many of the species recovered from zoo autopsies. In some cases, host death is directly or indirectly attributable to a pentastomid infection.

Biochemical disposal of excess H+ in growing plants?

Abstract: SUMMARY Many data support the view that, when NH4+ [or N2, NH3, or CO(NH2)2] is the N source for plant cell growth, the excess H+ generated in the synthesis of core metabolites is excreted to the bathing medium (biophysical pH-stat). This paper explores the possibility that a ‘biochemical’ disposal of these excess H+ could occur, thus allowing net NHJ assimilation to take place in the shoot of land plants. A‘biochemical’ H+-neutralizing pH-stat requires that a non-toxic resource be taken into the plant in a form in which metabolism can convert into a non-toxic product with H+ consumption or OH− production. This possibility was explored for reductive metabolism of B(OH)3, Si (OH)4, H2PO4−, H2AsO4−, O2, SO42, SeO42− and HVO42; and for oxidative metabolism of Cr, Br−, I−, Fe2+ and Mn2+. For B(OH)3 and Si(OH)4, reductive metabolism (even if it were thermo-dynamically possible, granted the reductants available to plants) does not involve significant 11+ removal. H2PO4− reduction may be thermodynamically possible, but is quantitatively insignificant as an H+ sink in plants. H2AsO4− reduction is probably a detoxification mechanism, and it is not a significant H+ sink in plants for which quantitative data are available. O2 assimilation (reduction) into -OH, and thence ≡O+, occurs in anthocyanin synthesis, but not to an extent which disposes of much of the excess H+ produced in growth with NHJ as N source. SO42− reduction in excess of that required by primary, core metabolism (i.e. that leading to amino acids, thylakoid sulpholipid and cell wall esters) can generate OH−, but such ‘secondary’ SO42− metabolism is related to osmoregulation and to chemical defence rather than to H+ disposal per se. The quantity of S metabolism which is ‘negotiable’ is not, apparently, adequate to neutralize a substantial fraction of excess H+ formed during growth. SeO4−2 reduction and assimilation performs largely a detoxification and/or chemical defence role, and the quantities involved (even in Se-accumulators) do not generate enough OH− to offset much of the excess H+ formed during growth. Vanadate reduction is quantitatively insignificant as an H+ sink. Oxidation of Cl−, Br− and I− in incorporation into C-halide groups is, in land plants, a quantitatively insignificant process. H+ disposal via HCl volatalization from an aqueous phase of low pH which contains Cl− does not seem to be an important sink for H+ in terrestrial plants. Oxidation of F− to form ≡C-F usually produces CH2F.COO− with no net H+ consumption. Oxidation of Fe2+ and Mn2+ is H+-consuming as long as oxides or hydroxides of Fe3 and Mn4+ are not formed. However, the oxides and hydroxides are often formed so that the oxidation processes consume OH− rather than H+. These quantitative considerations, together with those of the availability of starting materials and the toxicity of end products suggest that the H+-consuming processes, even in combination, probably cannot dispose of all of the H+ generated in growth with NHJ as N source. In general, these H+-consuming reactions seem to be related to synthesis of osmoregulatory and chemical defence compounds, and to detoxification; the products appropriate to these functions generally have high molecular masses per mol H+ consumed in their synthesis, a feature which does not make them ideal parts of a ‘biochemical pH-stat’.

Chloride uptake in freshwater teleosts and its relationship to nitrite uptake and toxicity

Abstract: 1. The relationship between rate of chloride uptake and external chloride concentration was investigated in Rainbow trout,Salmo gairdneri, and Perch,Perca fluviatilis. The relationship between nitrite uptake and external nitrite and the inhibition of chloride uptake by nitrite was also investigated. Nitrite tolerance tests were performed on a variety of freshwater animals, including Carp,Cyprinus carpio, Tench,Tinca tinca, Pike,Esox lucius, Eel,Anguilla anguilla, and tadpoles,Rana temporaria. 2. The chloride uptake mechanism is saturable, with maximum uptake rates of 368 μMh−1kg−1 and 429 μMh−1kg−1 for the trout and perch, respectively. The half saturation value (Km, the affinity constant) is 159 μMl−1 for trout and 333 μMl−1 for perch. 3. Net nitrite transport was determined in trout, net movement being into the fish against a concentration gradient, with a maximum uptake rate of 281 μMh−1kg−1; theKm is 198 μMl−1. This suggests that nitrite enters the fish via an active uptake process. 4. The data suggest that nitrite is a simple competitive inhibitor of active chloride uptake in both trout and perch. Trout are less tolerant of nitrite than perch (24-h LC50 values are 0.7 mMl−1 for trout and 1.2 mM l−1 for perch) and also have a greater affinity for nitrite. 5. The spectrum of nitrite sensitivity seen in freshwater animals is discussed in relation to chloride uptake kinetics. These data support the hypothesis that nitrite uptake is an active process and furthermore uptake is linked quantitatively with chloride uptake, suggesting that chloride and nitrite enter the fish via the same route.

Synaptosomal bioenergetics. The role of glycolysis, pyruvate oxidation and responses to hypoglycaemia.

Abstract: The bioenergetic interaction between glycolysis and oxidative phosphorylation in isolated nerve terminals (synaptosomes) from guinea-pig cerebral cortex is characterized. 1 Essentially all synaptosomes contain functioning mitochondria. 2 There is a tight coupling between glycolytic rate and respiration: uncoupler causes a tenfold increase in glycolysis and a sixfold increase in respiration. 3 Synaptosomes contain little endogenous glycolytic substrate and glycolysis is dependent on external glucose. 4 In glucose-free media, or following addition of iodoacetate, synaptosomes continue to respire and to maintain high ATP/ADP ratios. 5 In contrast to glucose, the endogenous substrate can neither maintain high respiration in the presence of uncoupler nor generate ATP in the presence of cyanide. 6 Pyruvate, but not succinate, is an excellent substrate for intact synaptosomes. 7 The in-situ mitochondrial membrane potential (ΔΨm) is highly dependent upon the availability of glycolytic or exogenous pyruvate; glucose deprivation causes a 20-mV depolarization, while added pyruvate causes a 6-mV hyperpolarization even in the presence of glucose. 8 Inhibition of pyruvate dehydrogenase by arsenite or pyruvate transport by α-cyano-4-hydroxycinnamate has little effect on ATP/ADP ratios; however respiratory capacity is severely restricted. 9 It is concluded that synaptosomes are valuable models for studying the control of mitochondrial substrate supply in situ.

Light absorption by plants and its implications for photosynthesis

Abstract: Summary The preceding account has attempted to examine the interactions between light absorption and photosynthesis, with reference to both unicellular and multicellular terrestrial and aquatic plants. There are, however, some notable plant groups to which no direct reference has been made, e.g. mosses, liverworts and lichens. Although many have similar optical properties to terrestrial vascular plants (Gates, 1980) and apparently similar photosynthetic responses (see Green & Snelgar, 1982; Kershaw, 1984) they may possess subtle, as yet unknown differences. For instance, the lichen thallus has a high surface reflectance although the transmittance is virtually zero (Gates, 1980; Osborne, unpublished results). It is envisaged, however, that differences in optical properties between species will reflect differences in degree not kind. Although not all variation in photosynthesis is due to differences in light absorption a number of accounts suggest that this is a contributing factor. Variations in leaf absorptance have been found to account for most of the variation in leaf photosynthesis at low Jis (see Ehleringer & Bjorkman, 1978a; Osborne & Garrett, 1983). There is, however, little direct experimental evidence on light absorption and photosynthesis in either microalgal species or aquatic macrophytes. We also do not know over what range of incident photon flux densities photosynthesis is determined largely by changes in light absorption. Plants growing under natural conditions also experience large diurnal and seasonal fluctuations in Ji, unlike species grown under laboratory conditions. The occurrence of transitory peaks in Ji tends to overshadow the fact that the average Ji is often lower than the J1 required to saturate photosynthesis, i.e. 1500–2000 μmol m-2 s-1, depending on the growth treatment. Using the data of Monteith (1977) and I W m2= 5 μmol m-2 s-1, and with photosynthetically active radiation 50% of total solar radiation, the daily mean value for Britain is approximately 450 μmol m-2 s-1, with a maximum in June of 1000μmol m-2 s-1 and a minimum during the winter of 75 μmol m-2 s-1. Such values could be even lower on shaded understory leaves and considerably lower for aquatic species. Based on average values of net photosynthesis for a terrestrial plant leaf, light saturation would only be expected in June while for most of the year the average values would lie largely on the light-limited portion of the photosynthesis light response curve. Although the daily average values in tropical climates may be higher during the winter months, they are remarkably similar throughout the world for the respective summers in the northern and southern hemispheres, because the increased daylength at high latitudes compensates for the lower Jis. The expected lower dark respiration rates during the winter may also partially offset the effects of a lower light level. There is therefore a trade-off between high Jis for a short period of time against a lower Ji for a longer period of time. We might expect different photosynthetic responses to these two very different conditions. Importantly, a low Ji with a long daylength may enable a plant to photosynthesize at or near its maximum photon efficiency for most of the day. Although the response of the plant to fluctuations in Ji is complicated because it is affected by the previous environmental conditions, this may indicate that light absorption has a much greater significance under natural conditions, particularly for perennial species. The bias in many laboratories towards research on terrestrial vascular plants also tends to ignore the fact that a number of multicellular and unicellular aquatic species survive in very low light environments. Furthermore, the direct extrapolation of photosynthetic responses from measurements on single leaves to those of whole plants is clearly erroneous. Although this is obvious, many physiological ecologists have attributed all manner of things to the photosynthetic responses of ‘primary’ leaves. Most researchers have ignored problems associated with composite plant tissues and internal light gradients. Clearly caution is required in interpreting the photosynthesis light-response curve of multicellular tissues based on biochemical features alone. Also, the importance of cell structure on light absorption and photosynthesis has generally been ignored and attributed solely to the effects of structural features on CO2 diffusion. In doing so the work of two or three generations of plant physiologists has been ignored. Haberlandt (1914) at the turn of the century probably first implicated the role of cell structure in leaf optics, and Heath (1970) stressed that in order to completely understand the role of light in photosynthesis we need to know the flux incident on the chloroplast itself. Even this suggestion may need modification because of the capacity of the internal chloroplast membranes for scattering light. It is worth emphasizing the importance of light gradients within tissues and their role in regulating photosynthesis, particularly at light saturation. Measurements of light gradients are fraught with problems because of experimental difficulties and the majority (few) are based on reflectance and transmittance measurements. Seyfried & Fukshansky (1983) have shown that light incident on the lower surface of a Cucurbita cotyledon produced a larger light gradient than light incident from above, indicating the importance of the spatial arrangement of the tissues with respect to the light source. Also, light incident on the lower surface of leaves of Picea sitchensis was less ‘effective’ in photosynthesis than light from above (Leverenz & Jarvis, 1979). Clearly, two tissues could have the same gross absorptance but different photosynthetic rates because of differences in the internal light environment. Fisher & Fisher (1983) have recently found asymmetries in the light distribution within leaves, which they related to asymmetries in photosynthetic products due to differences in solar elevation. Such modifications in light distribution could be important for a number of solar-tracking species. Changes in light absorption are brought about by a whole gamut of physiological, morphological and behavioural responses which serve to optimize the amount of light absorbed. Perhaps the simplest way of regulating the amount of light absorbed is by restricting growth either to particular times of the year or to conditions when the light climate is favourable. We are still largely ignorant of many details of these modifications. In particular, differences in tissue structure such as the size and number of vacuoles or the effects of organelles on the scattering component of the internal light environment of photosynthetic tissues are not understood. A better understanding of the interaction of light with plants in aquatic systems is also required. It is unfortunate that light-absorptance measurements are not routinely made in photosynthetic studies, and this is quite clearly a neglected area of study. That these measurements are not made is even more surprising, since techniques have been available for over sixty years (Ulbricht, 1920). Absorptance measurements are of particular importance in the photosynthetic adaptation of microalgae, where only a small proportion of the incident photon flux density is absorbed. For multicellular species more detailed information is required on internal light gradients and their variability. Light-absorptance measurements are also important in any study relating kinetic data on CO2 fixation to in vivo photosynthesis, especially when there are large variations in the morphology and structure of the photosynthetic organ.

Isolation and characterisation of a soluble active fragment of hydrogenase isoenzyme 2 from the membranes of anaerobically grown Escherichia coli

Abstract: An active tryptic fragment of membrane-bound hydrogenase isoenzyme 2 from anaerobically grown Escherichia coli has been purified. The soluble enzyme derivative was released from the membrane fraction by trypsin cleavage. The purification procedure involved ion-exchange, hydroxyapatite and gel permeation chromatography. The enzyme derivative was purified 100-fold from the membrane fraction and the specific activity of the final preparation was 320 mumol benzyl viologen reduced min-1 mg protein-1 (H2:benzyl viologen oxidoreductase). The native enzyme derivative had an Mr of 180,000 and was composed of equimolar amounts of polypeptides of Mr 61,000 and 30,000. It possessed 12.5 mol Fe, 12.8 mol acid-labile S2- and 3.1 mol Ni/180,000 g enzyme. Antibodies were raised to the purified preparation which cross-reacted with hydrogenase isoenzyme 2 but not with isoenzyme 1 in detergent-dispersed preparations. Western immunoblot analysis revealed that isoenzyme 2 which had not been exposed to trypsin contained cross-reacting polypeptides of Mr 61,000 and 35,000. Trypsin treatment of the membrane-bound enzyme to form the soluble derivative of isoenzyme 2, therefore, cleaves a polypeptide of Mr 35,000 to produce the 30,000-Mr fragment. Trypsin treatment of the detergent-dispersed isoenzyme 2 produces the same fragmentation of the enzyme. Neither of the subunits of the enzyme revealed any immunological identity with those of hydrogenase isoenzyme 1.

Metastable defects in amorphous-silicon thin-film transistors.

Abstract: When a positive gate voltage is applied to an amorphous-silicon thin-film transistor, electrons become trapped in states close to the silicon-dielectric interface. This is studied by a new technique involving the transient discharge current produced under illumination. It is suggested that the behavior may involve metastable dangling bonds generated within the amorphous silicon as a consequence of the field-effect-induced increase in electron concentration. This constitutes an important new instability mechanism for amorphous-silicon thin-film transistors.

Whisker growth induced by implantation of cultured vibrissa dermal papilla cells in the adult rat.

Abstract: Retention of the capacity to induce the growth of hair by cultured adult rat vibrissa dermal papilla cells has been investigated. Small pellets of serially cultured papilla cells were implanted into the bases of the exposed follicular epidermis of amputated adult rat vibrissa follicles. Amputated follicles that received no cell implants or implants of cultured dorsal skin fibroblasts were used as controls. Over 50% of follicles implanted with cultured papilla cells in the passage range 1-3 grew hairs. In contrast none of the follicles that received late passage cells (range 6-15) produced hairs; and spontaneous regeneration of hair occurred in only 3% of the control follicles. These results demonstrate that cultured papilla cells of early passage numbers retain their ability to induce hair growth. Histological examination confirmed that the implanted papilla cells interacted with follicular epidermis to organize the development of new, hair-producing bulbs, each containing a discrete dermal papilla. An important observation was that aggregative behaviour leading to papilla formation was only manifested by early passage papilla cell implants. This persisting embryonic characteristic appears to be an essential functional component of papilla cell activity which operates to regulate the profound morphogenetic changes that occur during the hair growth cycle.

What is medical education here really like? Suggestions for action research studies of climates of medical education environments.

Abstract: The climate or overall ambience of medical education environments is a concept that is of relevance to medical teachers It includes for example, the extent to which the environment fosters scholarly or intellectual activities and the extent to which it encourages friendliness, co-operation and supportiveness This paper reviews how medical teachers can assess the climate of the medical education environment It reviews climate research studies that medical teachers might undertake and some methodologies they might employ in such studies The focus of the paper is on the notion of the medical teacher as an action researcher using climate instrumentation and research strategies, to understand the nature, and improve the quality, of the educational experience that students gain in medical schools, and their constituent departments, classrooms and other settings

Gyrus formation in the cerebral cortex of the ferret. II: Description of the internal histological changes

Abstract: The internal changes within a developing gyrus of the ferret cerebral cortex were studied by recording (i) the changing length and direction of the radial tissue lines and (ii) the emergence of the tangential banding of the classical six cortical layers. Together these lines provided a coordinate net whose deformations during development gave an indication of the differential growth occurring within a gyrus. The changes in these features suggested that a gyrus was initiated by an area of local growth appearing in the subplate and then in the suprajacent segment of cortical plate. During subsequent growth there was tangential spreading of the more mature tissue at the gyral crown while at the site of the future sulci the cortical plate remained immature and growth was retarded. During later stages the majority of tangential growth occurred in the parasulcal area. At this site a very much thinner cortex was generated from a segment of cortical plate of the same depth and degree of nuclear crowding as elsewhere, implying that growth here was resolved into tangential spreading. The cells and fibres of the deeper cortical layers of the sulcal cortex eventually became tangentially orientated suggesting that they subserved a commissural function between the columnar systems of adjacent gyri. At the scale prevailing in the ferret, gyrus formation was seen as a configuration which tended to conserve both the total length of the cortical columns and the depth of the individual cortical layers.

Gyrus formation in the cerebral cortex in the ferret. I. Description of the external changes.

Abstract: The external features of gyrus formation in the postnatal ferret cerebral cortex are described and correlated with certain internal changes. The observations indicate that gyri are formed by longitudinal and radial expansion of the cortical compartment occurring between relatively fixed areas which form the sulcal floors. The gyri were initially rounded with open sulci and the cerebrum had a rectangular outline when seen in lateral and dorsal view. By adult life the hemisphere had been subjected to considerable moulding by the growing skull, so that the frontal pole of the cerebrum became pointed while the sulcal walls became closely opposed and the gyral crowns flattened.

11 Muscle Glycogen Synthase

Abstract: Publisher Summary This chapter discusses the structure and activity of muscle glycogen synthase. Glycogen synthase is regulated by a phosphorylation–dephosphorylation mechanism. Following the discovery that glycogen phosphorylase and phosphorylase kinase were activated by phosphorylation, Larner and co-workers found that glycogen synthase could exist in two forms in mammalian skeletal muscle. One possessed little activity without glucose 6-phosphate (G6P), whereas the other was almost fully active in the absence of this allosteric activator. The conversion of glycogen synthase from a G6P-independent to a G6P-dependent form is shown to require MgATP and a further protein and to be stimulated by cyclic adenosine 3′,5′-monophosphate (cAMP). The basis for these effects became clearer following the purification of glycogen synthase to homogeneity, when the enzyme is phosphorylated by cAMP-dependent protein kinase. It was reported in an earlier study that the G6P-dependent form contained ≃6 mol phosphate/86 kDa subunit, and with the subsequent identification of additional glycogen synthase kinases it became clear that glycogen synthase is regulated by multisite phosphorylation.

Evaluation of a self-help manual for media-recruited problem drinkers: six-month follow-up results.

Abstract: A total of 785 individuals responded to a newspaper advertisement offering free help to cut down drinking and were sent alternately either a self-help manual based on behavioural principles or a general information and advice booklet. Of these, 247 (31.3 per cent) returned assessment questionnaires or agreed to be interviewed by telephone and 132 of these respondents (53.4 per cent) were successfully contacted at six-month follow-up. Those lost to follow-up were more ‘ socially stable’ on initial measures than those successfully contacted. Results showed a greater reduction in previous week's consumption in the group receiving the manual than in the control group. In addition, respondents interviewed by telephone showed a greater reduction on a measure of alcohol-related problems and a higher proportion reducing drinking than those contacted only by post. There was no evidence that reductions in consumption were confined to relatively low consumers or to those showing only early signs of dependence on alcohol, irrespective of which type of material was received.