大眼鳜头骨形态的观察

通过对大眼鳜头骨的形态学观察表明,大眼鳜头骨由134块硬骨和3块软骨组成,其中脑颅38块,咽颅硬骨96块,软骨3块.同时将大眼鳜头骨与鲈鱼头骨进行了比较分析,两者既具有极大的相似性,又有较为显著的差异.探讨了大眼鳜头骨形态结构与其功能适应性.     

EFFECTS OF COLCEMID ON HYDRA VIRIDIS WITH MULTIPLE-PEDUNCLE GRAFTS

The effect of Colcemid on multiple-graft Hydra viridis containing three peduncles (3p) grafted in tandem is reported. At grafting, the apical member of a 3p animal is a foot-less host, the middle member, an isolated peduncle, and the proximal member, a foot-bearing peduncle. In different experimental situations all three members are treated with Colcemid, the host member alone is treated, or the host member is not treated but the others are. Control animals have only non-treated members. Head and foot regeneration on graft pieces and the formation of waists and separations at the borders between these pieces are monitored and the significance of differences between frequencies tested by Chi square. Head formation on the middle and proximal peduncles is promoted by Colcemid when all pieces are treated, but animals with treated host pieces have significantly higher frequencies of heads on their non-treated proximal pieces than other experimental and control animals. Animals with Colcemid-treated proximal peduncles do not have significantly more heads on the most proximal peduncle compared to controls. Colcemid does not alter the frequency of foot formation significantly on the host peduncles of animals in the different categories, but foot formation is increased on the middle pieces of animals with three treated pieces and on animals with middle and proximal treated pieces. The rate of waist formation and graft separation is retarded when all three or just the host piece is treated, but not when only the middle and proximal pieces are treated. The direct action of Colcemid on nerves and on dividing cells may be responsible for these effects.     

DNA synthesis in isolated HeLa cell nuclei. Evidence for in vitro initiation of synthesis of small pieces of DNA and their subsequent ligation.

Optimum conditions for a DNA synthesizing system based on isolated nuclei have been described (Krokan, H., Bjorklid, E., and Prydz, H. (1975), Biochemistry, preceding paper in this issue) [3H]TTP-labeled nascent DNA produced during very short pulses was analyzed by centrifugation in alkaline sucrose gradients. More than 80% of the radioactivity appeared in 2-4S pieces (primary DNA pieces). It would therefore seem that the synthesis of DNA is discontinuous both in the 5' leads to 3' and in the 3' leads to 5' directions. The size of the primary DNA pieces increases from 2-4 S up to 14 S with increasing pulse length. Evidence is presented that this increase is not caused by ligation between 2-4S primary pieces. Pulse-chase experiments showed that in this nuclear system primary pieces were ligated to a product generally larger than 30 S. Evidence is also given for the initiation of primary DNA pieces in vitro.     

Food stealing in cockroaches

Relationships between food stealing and exploitation of main food sources were investigated in the German cockroach,Blattella germanica (L.) (Dictyoptera: Blattellidae). The occurrence of food stealing during food exploitation was associated with the course of depletion of the main food sources and not with spatial distribution or distance from shelter. Stolen pieces of food always appeared towards the end of exploitation of a food source. Their occurrence appeared to be a consequence of the exploitation of a food source rather than a specific strategy. The proportion of animals of different developmental stages observed with stolen pieces differed significantly from that in the general population. There were proportionally more males, females and large larvae and proportionally less small larvae with stolen pieces than on the main food source. These data suggest that stolen pieces appeared when competition for access to food increased, and that larger cockroaches (adults and larger larvae) were then dominant and benefited from monopolizing stolen pieces of food.     

Proximal and distal transformation during intercalary regeneration in the planarianDugesia(S)mediterranea

Summary Studies on intercalary regeneration in several organisms have shown that a regenerate is formed when surfaces of different positional value along the proximo-distal axis are opposed. One of the main problems posed by this phenomenon is to know which piece contributes to the building of the regenerate. In the present work we have studied this problem in planarians using chimaeras made between pieces of different body levels, irradiated or not, of the sexual and asexual races ofDugesia(S)mediterranea that differ in a chromosomal marker.The results found show very clearly that intercalary regenerates in planarians are formed by cells coming from both pieces (stumps), and that irradiated pieces keep the positional values and interact with non-irradiated pieces to restore the missing parts. This means that distal and proximal transformation do actually occur at the same time during intercalary regeneration in planarians. The implications of these results as regards to the origin of cells in the regenerate and to present models of intercalary regeneration are discussed.     

The Maryland mammoth allele reduces floral stimulus activity in stem piece explants of Nicotiana tabacum (Solanaceae)

The response of axillary buds to floral stimulus activity in stem pieces was examined in two near-isogenic cultivars of tobacco that differ in the recessive maryland mammoth (mm) allele, which confers short-day behavior. All axillary buds from day-neutral plants assayed on six-internode stem pieces made few nodes (less than 20) before flowering, while axillary buds from plants homozygous for mm assayed on six-internode stem pieces either did not flower in noninductive conditions or made many nodes before flowering in inductive conditions. About 80% of day-neutral axillary buds grafted onto day-neutral stem pieces did not respond to floral stimulus in stem pieces, indicating that the floral stimulus in stem pieces is ephemeral. In other graft combinations, the proportion of axillary buds that did respond to floral stimulus in stem pieces was substantially reduced from the 20% of day-neutral buds on day-neutral stem pieces that responded. These results indicate that the mm allele probably reduces both the amount of floral stimulus activity in stem pieces and the competence of axillary buds to respond.     

Development of a new quantitative gas permeability method for dental implant-abutment connection tightness assessment

Background  

Most dental implant systems are presently made of two pieces: the implant itself and the abutment. The connection tightness between those two pieces is a key point to prevent bacterial proliferation, tissue inflammation and bone loss. The leak has been previously estimated by microbial, color tracer and endotoxin percolation.     

Music Attenuates Excessive Visual Guidance of Skilled Reaching in Advanced but Not Mild Parkinson's Disease

Parkinson''s disease (PD) results in movement and sensory impairments that can be reduced by familiar music. At present, it is unclear whether the beneficial effects of music are limited to lessening the bradykinesia of whole body movement or whether beneficial effects also extend to skilled movements of PD subjects. This question was addressed in the present study in which control and PD subjects were given a skilled reaching task that was performed with and without accompanying preferred musical pieces. Eye movements and limb use were monitored with biomechanical measures and limb movements were additionally assessed using a previously described movement element scoring system. Preferred musical pieces did not lessen limb and hand movement impairments as assessed with either the biomechanical measures or movement element scoring. Nevertheless, the PD patients with more severe motor symptoms as assessed by Hoehn and Yahr (HY) scores displayed enhanced visual engagement of the target and this impairment was reduced during trials performed in association with accompanying preferred musical pieces. The results are discussed in relation to the idea that preferred musical pieces, although not generally beneficial in lessening skilled reaching impairments, may normalize the balance between visual and proprioceptive guidance of skilled reaching.     

Mechanism of DNA chain growth: XV. RNA-linked nascent DNA pieces in Escherichia coli strains assayed with spleen exonuclease

A new method for the detection and assay of RNA-linked nascent DNA pieces has been developed. The method relies on selective degradation by spleen exonuclease of radioactive 5′-OH terminated DNA produced from the pulse-labelled nascent pieces upon alkaline hydrolysis. Analysis with this method in wild type Escherichia coli has shown relatively high proportions of the RNA-linked molecules after shorter pulses and in the smaller pieces, supporting the transient nature of the RNA attachment to the nascent pieces. The RNA-linked nascent DNA pieces are accumulated by both E. coli polAex1 (defective in 5′ → 3′ exonuclease of DNA polymerase I) and E. coli polA12 and polA1 (defective in polymerase of DNA polymerase I), suggesting the requirement of the concerted action of both 5′ → 3′ exonuclease and polymerase of DNA polymerase I for the removal of the RNA attached to the nascent pieces. Most of the nascent DNA pieces accumulated by E. coli ligts7 (defective in DNA ligase) are not linked to RNA, as expected from the direct role of DNA ligase in joining of the pieces. The analysis also has shown that a large portion of the nascent DNA pieces present in the cell under the normal steady-state conditions are not linked to RNA and that the level of the RNA-free DNA pieces is also increased in polA mutants. These findings suggest that the removal of RNA from the nascent pieces is a relatively rapid process and the joining reaction is a rate-limiting step that requires the concurrent action of DNA polymerase and DNA ligase.     

Spatial correlation of regional pulmonary perfusion.

Despite the heterogeneous distribution of pulmonary blood flow, perfusion appears to be spatially ordered, with neighboring regions of lung having similar magnitudes of flow. This premise was tested by determining the spatial correlation of regional flow [rho(d)] as a function of distance (d) between regions. Regional pulmonary perfusion was measured in both supine and prone positions in seven anesthetized mechanically ventilated dogs with radiolabeled microspheres. After excision and drying, the lungs were cubed into pieces 1.2 cm on a side, with a three-dimensional coordinate assigned to each piece. The microsphere-determined flow to each piece was measured by radioactive counts, and rho(d) was calculated for all paired pieces within the same lobe. rho(d) was greatest for adjacent pieces (d = 1.2 cm) and decreased with increasing d, becoming negative at large distances in all dogs and positions. The spatial correlation of flow between adjacent pieces, rho(1.2 cm), was greater in the supine than in the prone position (0.66 vs. 0.72, P less than 0.05). The observations for each dog and position were fit to the equation rho(d) = d(a)+b.d+c, and the coefficients were used to compare rho(d) in the supine and prone positions. rho(d) differed in the two positions (P less than 0.05), with rho(d) falling off more rapidly with distance in the supine position. When trends in flow due to gravity were mathematically removed, differences between supine and prone positions were no longer observed. The spatial correlation of regional pulmonary perfusion was anisotropic in both supine and prone positions. The observation that regional pulmonary perfusion is highly correlated over large spatial distances has important implications for models of flow distribution.     

Scyphozoan jellyfish's mesoglea supports attachment, spreading and migration of anthozoans' cells in vitro

Mechanically and enzymatically dissociated cells from five anthozoan species were laid on seven substrates in vitro. Cells were taken from two sea anemones (Aiptasia sp. and Anemonia sulcata), a scleractinian coral (Stylophora pistillata) and two alcyonacean corals (Heteroxenia fuscescence and Nephthea sp). Substrates tested: glass (coverslips), plastic (uncoated tissue culture plates), type IV collagen, gelatin, fibronectin, mesoglea pieces from the scyphozoan jellyfish Rhopilema nomadica and acetic acid extract of jellyfish mesoglea. Except for the mesoglea pieces, cells did not respond to any one of the other substrates, retaining their rounded shape. Following contact with mesoglea pieces, cells attached and spread. Subsequently they migrated into the mesogleal matrix at a rate of 5-10 microm/h during the first 2-5 h. No difference was found between the behavior of cells from the five different cnidarian species.     

Differentiation of the interstitial cell line in hydrozoan planulae

Repopulation of epithelial (colchicine-treated) planular tissue by interstitial cells, nematoblasts/nematocytes, and ganglionic cells was examined via grafting. Seventy-two-hour epithelial planular head pieces were grafted to 72-hour control labelled planular tail pieces, left in contact for 24 h, separated, and the head pieces were analyzed for interstitial cells and their derivatives. The reciprocal experiment of grafting 72-hour epithelial planular tails to 72-hour control labelled planular heads was also done and the tail pieces were examined. Repopulated planular head pieces contained interstitial cells, ganglionic cells and a reforming neural plexus but few nematoblasts/nematocytes. Reconstituted planular tail pieces contained interstitial cells and nematoblasts/nematocytes but no ganglionic cells. Results possibly suggest that the migrating interstitial cell population of 72-hour planulae is rich in committed precursors.     

Assay of RNA-linked nascent DNA pieces with polynucleotide kinase.

The 5′-OH end of DNA created upon alkaline hydrolysis of the RNA-linked nascent DNA pieces can be labeled with [γ-³²P]ATP using T4 polynucleotide kinase. However, it is difficult to use this method for the assay of these molecules in the presence of RNA-free DNA pieces because of the exchange reaction between the γ-phosphate of ATP and the 5′-phosphate of DNA catalyzed by the kinase. This difficulty can be circumvented by performing the polynucleotide kinase reaction at 0°C, where little exchange reaction occurs. Using these conditions, $\text{E. coli pol}$Aexl, a mutant defective in the 5′ → 3′ exonuclease activity of DNA polymerase I, is shown to contain several times as many RNA-linked DNA pieces as the wild type.     

Large wood and fluvial processes

1. Large wood forms an important component of woodland river ecosystems. The relationship between large wood and the physical characteristics of river systems varies greatly with changes in the tree species of the marginal woodland, the climatic and hydrological regime, the fluvial geomorphological setting and the river and woodland management context. 2. Research on large wood and fluvial processes over the last 25 years has focussed on three main themes: the effects of wood on flow hydraulics; on the transfer of mineral and organic sediment; and on the geomorphology of river channels. 3. Analogies between wood and mineral sediment transfer processes (supply, mobility and river characteristics that affect retention) are found useful as a framework for synthesising current knowledge on large wood in rivers. 4. An important property of wood is its size when scaled to the size of the river channel. ′Small′ channels are defined as those whose width is less than the majority of wood pieces (e.g. width < median wood piece length). `Medium' channels have widths greater than the size of most wood pieces (e.g. width < upper quartile wood piece length), and `Large' channels are wider than the length of all of the wood pieces delivered to them. 5. A conceptual framework defined here for evaluating the storage and dynamics of wood in rivers ranks the relative importance of hydrological characteristics (flow regime, sediment transport regime), wood characteristics (piece size, buoyancy, morphological complexity) and geomorphological characteristics (channel width, geomorphological style) in `Small', `Medium' and `Large' rivers. 6. Wood pieces are large in comparison with river size in `small' rivers, therefore they tend to remain close to where they are delivered to the river and provide important structures in the stream, controlling rather than responding to the hydrological and sediment transfer characteristics of the river. 7. For `Medium' rivers, the combination of wood length and form becomes critical to the stability of wood within the channel. Wood accumulations form as a result of smaller or more mobile wood pieces accumulating behind key pieces. Wood transport is governed mainly by the flow regime and the buoyancy of the wood. Even quite large wood pieces may require partial burial to give them stability, so enhancing the importance of the sediment transport regime. 8. Wood dynamics in `Large' rivers vary with the geometry of the channel (slope and channel pattern), which controls the delivery, mobility and breakage of wood, and also the characteristics of the riparian zone, from where the greatest volume of wood is introduced. Wood retention depends on the channel pattern and the distribution of flow velocity. A large amount is stored at the channel margins. The greater the contact between the active channel and the forested floodplain and islands, the greater the quantity of wood that is stored.     

Problem solving and functional design features: experiments on cotton-top tamarins, Saguinus oedipus oedipus

In any problem-solving situation, there are features associated with the problem that are relevant from a functional perspective and other features that are irrelevant. To determine whether animals are sensitive to the distinction between functionally relevant and irrelvant features of a problem, we conducted two main experiments with a New World monkey, the cotton-top tamarin. In the first condition of both experiments, subjects were required to pull a piece of cloth to gain access to a piece of food. The first experiment involved choosing between food that was on the cloth and food that was off the cloth. The second experiment involved choosing between food that was on a connected piece of cloth and food that was on two pieces of cloth separated by a horizontal gap. Having learned to solve either of these two problems, we conducted a series of probe conditions to determine whether the tamarins would generalize to changes in the shape, size, colour, and texture of the cloth and food, the position of the food relative to the cloth, and the type of connection between two pieces of cloth. For most of the probe conditions, the tamarins readily generalized, showing no decrement in performance, even on the first trial. For other conditions, involving apparently more subtle discrimination (e.g. a narrow vertical gap between the two pieces of cloth), explicit training was required. These results indicate that tamarins solve means-end relationships, and that their ability depends on a discrimination between properties that are functionally relevant as opposed to irrelevant. Copyright 1999 The Association for the Study of Animal Behaviour.     

Alfalfa stem tissues: Impact of lignification and cell length on ruminal degradation of large particles

A series of experiments were conducted with alfalfa to determine how extensively rumen microorganisms can degrade various tissues within large stem pieces. The seventh internode from the base of the stem was collected from alfalfa clone 718 after 4 weeks of regrowth. Internode length and diameter were measured, and approximately 2 cm stem pieces were excised from the internodes. Stem pieces were incubated with rumen fluid in vitro for 24 h. Bee's wax was used to coat the stem pieces to prevent microbial access other than at one end of the stem pieces. After exposure to the rumen microorganisms, stem pieces were serially cross-sectioned starting at the exposed surface. Sections were examined by light microscopy to determine which tissues had been degraded and to what depth into the stem piece degradation had occurred. Non-lignified alfalfa stem tissues (chlorenchyma, collenchyma, cambium, and primary xylem parenchyma) were degraded to great depth (3700–8200 μm) in stem pieces, but degradation of lignified tissues (phloem fibres and xylem fibres) was much more limited (150–1360 μm). Depth of degradation was greater in stem pieces derived from long internodes compared to short internodes. Using longitudinal sections and isolated cells of stem tissues, it was found that mean cell length increased by approximately 50% with a doubling of internode length for all tissues examined. Many cell layers of non-lignified tissues were degraded whereas only the exposed cell layer of lignified tissues exposed at the cut end of the internode pieces was susceptible to degradation. Depth of degradation for non-lignified tissues was attributed to a combination of cell wall degradability, cell length, and the presence of intercellular spaces in chlorenchyma tissue. The lignified wall established a complete barrier to degradation of cells below those mechanically ruptured.     

Endo R DpnI restriction of Escherichia coli DNA synthesized in vitro. Evidence that the ends of Okazaki pieces are determined by template deoxynucleotide sequence.

A restriction enzyme from Diplococcus pneumoniae, Endo R DpnI, cuts methylated DNA on cellophane discs into pieces which are about the same size as Okazaki pieces.DNA was synthesized in vitro on cellophane discs in the presence of β-nicotinamide mononucleotide to prevent joining of Okazaki pieces. This DNA was methylated by the addition of S-adenosyl methionine to the reaction mixture. When Endo R DpnI was used to cut methylated DNA made in vitro in the presence of S-adenosyl methionine and β-nicotinamide mononucleotide, no decrease in sedimentation of the Okazaki pieces was observed. Control experiments demonstrated that Okazaki pieces were methylated in vitro and that Endo R DpnI was capable of cutting double-stranded DNA containing methylated Okazaki pieces, that is, synthesized in β-nicotinamide mononucleotide and S-adenosyl methionine.These results are interpreted to mean that the ends of Okazaki pieces are non-randomly distributed with respect to 6-methyl adenine residues.     

Cryopreservation of human ovarian tissue: comparison of rapid and conventional freezing

Cryopreservation, which is the most important procedure in ovarian tissue banking, can be divided into two methods: conventional freezing and rapid freezing. In previous study, the higher effectiveness of rapid freezing in comparison with the conventional freezing for human oocytes and embryos was shown. Data on comparison of these two methods for human ovarian tissue are limited. The aim of this study was to compare conventional freezing and rapid freezing for human ovarian tissue. Ovarian tissue fragments from 14 patients were transported to the laboratory within 22–25 h in a special, isolated transport box, which can maintain a stable temperature of between 5 and 8 °C for 36 h. Small pieces of ovarian tissue (1 × 1–1.5 × 0.7–1 mm) were randomly distributed into four groups: Group 1: control, fresh pieces immediately after receiving transport box, Groups 2 and 3: experimental pieces after rapid freezing/warming, and Group 4: experimental pieces after conventional freezing/thawing. All pieces were cultured in vitro for 14 days. The viability of the tissue by in vitro production of hormones and development of follicles after culture was evaluated. The level of estradiol 17-β and progesterone was measured using heterogeneous competitive magnetic separation immunoassay. For histological analysis, the number of viable and damaged follicles was counted. After culture of fresh tissue pieces (Group 1), rapidly frozen/warmed pieces (Groups 2 and 3), and conventionally frozen/thawed pieces (Group 4), the supernatants showed estradiol 17-β concentrations of 358, 275, 331, and 345 pg/ml, respectively, and progesterone concentrations of 3.02, 1.77, 1.99, and 2.01 ng/ml, respectively. It was detected that 96%, 36%, 39%, and 84% follicles for Groups 1, 2, 3, and 4, respectively, were normal. For cryopreservation of human ovarian tissue, conventional freezing is more promising than rapid freezing.     

A finite element comparison between the mechanical behaviour of rigid and resilient oral implants with respect to immediate loading

In this paper, a qualitative comparison between two types of dental implants with respect to their behaviour under immediate loading is presented. This analysis has been carried out using the finite element method. Since micromotions (and not the load) are responsible of the appearance of a fibrous interface avoiding osseointegration, the relative displacement between the bone surface and the implant has been the main variable analyzed at different loading states and for the two implant types here considered. The implants analyzed differ in their mechanical behavior: rigid or resilient. Their main difference lies in the joining between the different pieces that make up the dental system. While in the rigid implant all the pieces are screwed, in the resilient implant a relative displacement between the pieces is allowed, with the additional introduction of a silicone gasket that acts like the periodontal ligament. Both implants were considered with a similar geometry and under two different loading scenarios, one equivalent to the force of chewing applied to a molar and another which corresponds to a premolar. For the resilient implant, a hyperelastic behaviour for the silicone and contact conditions between the different mobile parts of the implant are considered. The displacements of the emerging-body in both designs are also compared with the values obtained by several authors. However, the results show that both implants fulfill the constraint of the immediate loading protocol. The micromotions of the resilient implant are lower to those of the rigid one, favouring therefore a good osseointegration process while keeping the stresses in the implant under admissible maximum values.     

Dynamics of large wood at the watershed scale: a perspective on current research limits and future directions

Recent research has elucidated the positive ecological roles of large wood (LW) in fish-bearing channels. However, where logjams increase local flooding and bank erosion, LW has negative impacts on public safety and property protection. Although our understanding of reach-scale processes and patterns has increased dramatically in recent years, only a few studies have integrated this knowledge at the watershed scale. Here we review variations in LW dynamics along a gradient of watershed sizes. In small watersheds, a massive amount of LW, resulting from forest dynamics and hillslope processes, remains on the valley floor. These pieces may persist for several decades and are eventually transported during debris flows. In intermediate watersheds, LW is dominantly recruited by bank erosion from adjacent riparian areas. These pieces are continuously transported downstream with LW pieces that are supplied from the upstream watershed by floods because these channels have a greater width and depth than the length and diameter of the pieces, as well as a high stream power. This leads to fragmentation of the LW pieces, which increases their transportability. In large watersheds, LW pieces are frequently recruited at locations where the channel is adjacent to riparian forests. Floated LW pieces can accumulate along channels with wide floodplains. Storage in floodplains can lead to more rapid decay than in an anaerobic environment, resulting in the subsequent removal of LW pieces from the system. Our review presents a generalized view of LW processing at the watershed scale, and is relevant to ecosystem management, disaster prevention and the identification of knowledge gaps.