Pollen-based quantitative reconstructions of Holocene regional vegetation cover (plant-functional types and land-cover types) in Europe suitable for climate modelling.

We present quantitative reconstructions of regional vegetation cover in north-western Europe, western Europe north of the Alps, and eastern Europe for five time windows in the Holocene [around 6k, 3k, 0.5k, 0.2k, and 0.05k calendar years before present (bp)] at a 1° × 1° spatial scale with the objective of producing vegetation descriptions suitable for climate modelling. The REVEALS model was applied on 636 pollen records from lakes and bogs to reconstruct the past cover of 25 plant taxa grouped into 10 plant-functional types and three land-cover types [evergreen trees, summer-green (deciduous) trees, and open land]. The model corrects for some of the biases in pollen percentages by using pollen productivity estimates and fall speeds of pollen, and by applying simple but robust models of pollen dispersal and deposition. The emerging patterns of tree migration and deforestation between 6k bp and modern time in the REVEALS estimates agree with our general understanding of the vegetation history of Europe based on pollen percentages. However, the degree of anthropogenic deforestation (i.e. cover of cultivated and grazing land) at 3k, 0.5k, and 0.2k bp is significantly higher than deduced from pollen percentages. This is also the case at 6k in some parts of Europe, in particular Britain and Ireland. Furthermore, the relationship between summer-green and evergreen trees, and between individual tree taxa, differs significantly when expressed as pollen percentages or as REVEALS estimates of tree cover. For instance, when Pinus is dominant over Picea as pollen percentages, Picea is dominant over Pinus as REVEALS estimates. These differences play a major role in the reconstruction of European landscapes and for the study of land cover-climate interactions, biodiversity and human resources.

Low-noise current amplifier based on mesoscopic Josephson junction.

We used the band structure of a mesoscopic Josephson junction to construct low-noise amplifiers. By taking advantage of the quantum dynamics of a Josephson junction, i.e., the interplay of interlevel transitions and the Coulomb blockade of Cooper pairs, we created transistor-like devices, Bloch oscillating transistors, with considerable current gain and high-input impedance. In these transistors, the correlated supercurrent of Cooper pairs is controlled by a small base current made up of single electrons. Our devices reached current and power gains on the order of 30 and 5, respectively. The noise temperature was estimated to be around 1 kelvin, but noise temperatures of less than 0.1 kelvin can be realistically achieved. These devices provide quantum-electronic building blocks that will be useful at low temperatures in low-noise circuit applications with an intermediate impedance level.

Prospective randomized comparison of endonasal endoscopic dacryocystorhinostomy and external dacryocystorhinostomy.

OBJECTIVES AND STUDY DESIGN: The advent of the rigid endonasal endoscope and the development of functional endoscopic sinus surgery (FESS) technique have awakened interest in an endonasal endoscopic dacryocystorhinostomy (EESC-DCR) in treating nasolacrimal obstruction. This prospective, randomized study compares EESC-DCR with traditional external dacryocystorhinostomy (EXT-DCR) for their success rates, surgical duration, and postoperative symptoms. PATIENTS AND METHODS: Sixty-four cases in 60 patients with primary acquired nasolacrimal sac or duct obstruction were divided into two subgroups by symptoms (simple epiphora/chronic dacryocystitis). These patients were randomized within both subgroups into two operation groups. Altogether 32 EESC-DCRs and 32 EXT-DCRs were performed. The final follow-up visit was at 1 year. The patency of the lacrimal passage was investigated by irrigation and patients were questioned about their symptoms. RESULTS: The success rate at 1 year after surgery was 75% for EESC-DCR and 91% for EXT-DCR after primary surgery. The difference was not statistically significant (P = .18). The success rate after secondary surgery with a follow-up time of 1 year was 97% in both study groups. The average duration for EESC-DCR was 38 minutes, and 78 minutes for EXT-DCR, (P < .001). CONCLUSIONS: EXT-DCR, when compared with EESC-DCR, appears to give a higher, although not statistically significant, primary success rate, but the secondary success rates are equal, indicating that these two different DCR techniques are acceptable alternatives.

Prospective randomized comparison of external dacryocystorhinostomy and endonasal laser dacryocystorhinostomy.

OBJECTIVE AND DESIGN: The introduction of endonasal laser dacryocystorhinostomy (ENL-DCR) in the early 1990s showed great promise of changing dacryocystorhinostomy into an elegant, minimally invasive procedure from the traditional external dacryocystorhinostomy (EXT-DCR). This prospective, randomized study compares these two operations, their success rates, surgical durations, and postoperative symptoms. PARTICIPANTS: A total of 64 cases in 61 patients with primary acquired nasolacrimal sac or duct obstruction were divided into 2 subgroups by symptoms (simple epiphora and chronic dacryocystitis). These patients were randomized within both subgroups into 2 operation groups with 32 cases in each group. INTERVENTION: Altogether, 32 EXT-DCRs and 32 ENL-DCRs were performed. The silicone tube was removed at 6 months after surgery. The final follow-up visit was at 1 year after surgery. The patency of the lacrimal passage was investigated by irrigation, and patients were questioned about their symptoms. MAIN OUTCOME MEASURES: The patency of the lacrimal passage to irrigation and the duration of surgery were measured. RESULTS: The success rate at 1 year after surgery was 91% for EXT-DCR and 63% for ENL-DCR after primary surgery. The difference was statistically significant (P = 0.016). The surgical duration for ENL-DCR was three times shorter than for EXT-DCR, the average duration being 23 minutes and 78 minutes, respectively (P < 0.0001). CONCLUSIONS: The EXT-DCR, when compared with ENL-DCR, seems to provide superior operation results in primary acquired nasolacrimal duct obstruction.

Lacrimal bone thickness at the lacrimal sac fossa.

BACKGROUND AND OBJECTIVE: Because laser dacryocystorhinostomy techniques have become more popular during the past few years, interest has grown concerning the anatomic structures that need to be penetrated in these procedures. The authors therefore studied the thickness and the histologic type of the lacrimal bone at the lacrimal sac fossa. PATIENTS AND METHODS: The thickness of 69 lacrimal bones at the lacrimal sac fossa from 48 patients was measured. RESULTS: The mean thickness was 106 microns. In 67% of the patients the mean thickness of individual lacrimal bone was less than 100 microns and in 4% it was more than 300 microns. The thinnest measured cross section of the lacrimal bone sample was 11 microns and the thickest was 722 microns. The lacrimal bone was composed of a thin plate of lamellar bone. CONCLUSION: In most cases the lacrimal bone at the lacrimal sac fossa is so thin that it can be easily penetrated with most surgical instruments.

Endonasal CO2-Nd:YAG laser dacryocystorhinostomy.

A preliminary series of endonasal dacryocystorhinostomy was carried out on 12 patients with nasolacrimal obstruction using a recently developed combined CO2-Nd:YAG laser that was guided by a fiberoptic light pipe inserted into the lacrimal sac through lacrimal canaliculi. The lacrimal passages were stented using silicone tubing that was kept in place for 6 months postoperatively. At an average follow-up time of 14.3 months the success rate was 83%. The advantages of the operation include a relatively short operation time, quick rehabilitation, absence of a skin wound, good hemostasis, and preservation of canthal anatomy.

A study of the mechanism of ocular irritation following YAG laser capsulotomy in rabbits.

The irritative response to Nd:YAG laser capsulotomy was studied in unanaesthetized rabbits. Posterior lens capsulotomy with a total energy of 100 mJ had no effect on the pupil size but increased the intraocular pressure by 5-10 mmHg and caused a breakdown of the blood-aqueous barrier. Anterior lens capsulotomy with a total energy of 20, 60 or 100 mJ caused constriction of the pupil, and an increase in intraocular pressure in a dose-dependent manner, and a breakdown of the blood-aqueous barrier. Indomethacin attenuated all the component parts of the irritative response and (D-arg1, D-pro2, D-trp7,9, leu11)-SP attenuated the miotic response. A combination of indomethacin and the substance P antagonist almost completely abolished the irritative response. This indicates that the acute YAG-laser-induced irritation in the rabbit eye is dependent both on a release of prostaglandins and on substance P, the former probably releasing the latter from sensory nerves.

A low-Mr chemoattractant for vascular endothelial cells.

The formation of new blood vessels occurs by sprouting from previously existing microvasculature. The process involved directed migration of the vascular endothelial cells towards chemical signals released from the target tissue. We have used the Boyden chemotaxis chamber method to identify chemotactic signals for fetal bovine vascular endothelial cells. Human placenta organ cultures produce a high-Mr chemoattractant for the endothelial cells from which a low-Mr factor can be liberated with trichloroacetic acid treatment and ethanol extraction. This activity was isolated from extracts of human placenta using Sephadex LH-20, Amberlite XAD-2, and silica gel thin-layer chromatography. The Mr of the factor is less than 400, it is lipophilic and resistant to proteolytic enzymes. The factor induces chemotactic migration of both aortic endothelial cells and capillary endothelial cells from the retina, but has no effect on fibroblasts or leukocytes suggesting a specific function of the compound for the vascular endothelial cells.

Components of subendothelial aorta basement membrane. Immunohistochemical localization and role in cell attachment.

Cryosections of fetal and adult bovine aorta were stained with purified, cross-absorbed antibodies against various connective tissue components. The antibodies to the basement membrane components, laminin, heparan sulfate proteoglycan, and type IV collagen, gave a sharp reaction in the subendothelial layer. Antibodies against type III procollagen showed a broad endothelial staining, and staining was also seen in the media layer. A similar staining reaction was seen with antibodies against fibronectin. Bovine fetal aortic endothelial (BAE) cells were isolated and cultured in vitro. The cells became stained by the indirect immunofluorescence method with antibodies against laminin and heparan sulfate proteoglycan and also with antibodies against types III and IV collagen and type I procollagen, as in previously reported experiments. The attachment properties of endothelial cells to the same extracellular matrix components were also studied. BAE cells became attached most readily to surfaces coated with fibronectin or type III or type IV collagen. Laminin and collagen types I and V served as less effective substrates. Attachment to heparan sulfate proteoglycan was slowest of the tested components. The results of the study demonstrate that the BAE cells are associated with basement membranes in vivo. The BAE cells in culture produced interstitial connective tissue components in addition to basement membrane components and showed no clear specific preference in their attachment to any of these.

Cultured tumor cells produce chemotactic factors specific for endothelial cells: a possible mechanism for tumor-induced angiogenesis.

The production of stimulants of endothelial cell motility by cultured tumor cells was studied. Spontaneously transformed murine fibroblasts in culture produced activity that stimulated migration of endothelial cells, while this kind of activity was not detected in media from cultures of the normal counterparts of the transformed cells. Furthermore, a line of murine tumor cells (HB4), known to induce vasoformative sarcomas in vivo, was found to produce in culture a strong chemoattractant specific for endothelial cells. Since the tumor-derived material also caused vessel ingrowth when implanted in the rabbit eye, these results suggest that the angiogenesis observed during tumor growth may involve chemoattractants for endothelial cells produced by tumor cells.

Platelet-derived growth factor is a chemoattractant for vascular smooth muscle cells.

In previous experiments (Grotendorst et al, 1981), we showed that platelet-derived growth factor promotes the migration of smooth muscle cells in vitro. Using a "checkerboard" analysis, we now establish that platelet-derived growth factor (PDGF) acts as a true chemoattractant for cultured aortic smooth muscle cells. Other growth factors such as epidermal growth factor, fibroblast growth factor, and insulin are not chemoattractants. The chemotactic response occurs before the initiation of DNA synthesis and is not affected by inhibition of DNA synthesis. Chemotaxis occurs at levels of PDGF lower than required for mitogenesis. RNA and protein synthesis are required for the chemotactic response. As found previously in bacteria and leucocytes, we find that methylation reactions are required for the chemotactic response. The possibility is discussed that PDGF acts in vivo at sites of vascular injury to attract smooth muscle cells from the medial layer to the luminal surface, and is involved in the early stages of the formation of atherosclerotic plaques.

Fibronectin promotes rat Schwann cell growth and motility.

Techniques are now available for culturing well characterized and purified Schwann cells. Therefore, we investigated the role of fibronectin in the adhesion, growth, and migration of cultured rat Schwann cells. Double-immunolabeling shows that, in primary cultures of rat sciatic nerve, Schwann cells (90%) rarely express fibronectin, whereas fibroblasts (10%) exhibit a granular cytoplasmic and fibrillar surface-associated fibronectin. Secondary cultures of purified Schwann cells do not express fibronectin. Exogenous fibronectin has a small effect on promoting the adhesion of Schwann cells to the substrate and does not significantly affect cell morphology, but it produced a surface fibrillar network on fibronectin on the secondary Schwann cells. Tritiated thymidine autoradiography revealed that addition of fibronectin to the medium, even at low concentrations, markedly stimulates Schwann cell proliferation, in both primary and secondary cultures. In addition, when cell migration was measured in a Boyden chamber assay, fibronectin was found to moderately, but clearly, stimulate directed migration or chemotaxis.

Platelet-derived growth factor in chemotactic for fibroblasts.

Chemotaxis assays in modified Boyden chambers were used to detect fibroblast chemoattractants in materials released from early-stage inflammatory cells, namely, mast cells, platelets, and neutrophils. Strong attractant activity was found in substances released from platelets. This activity was accounted for mainly by the platelet-derived growth factor (PDGF), which is released from the platelets and which was active as a chemoattractant at 0.5-1.0 mitogenic units/ml. The mitogenic activity of purified PDGF, measured by [3H]thymidine incorporation, occurs at a similar concentration range. By varying the gradient of PDGF, we demonstrated that PDGF stimulates chemotaxis rather than random motility. Preincubation of suspensions of fibroblasts in the presence of PDGF decreased the subsequent migration of cells to a gradient of PDGF as well as to a gradient of fibronectin, which is also in attractant for fibroblasts. The chemotactic response of fibroblasts to PDGF was not inhibited by hydroxyurea or azidocytidine but was inhibited by actinomycin D and cycloheximide, suggesting that synthesis of RNA and proteins but not of DNA is required for the chemotactic response to occur. Fibroblast growth factor, epidermal growth factor, nerve growth factor, and insulin were not chemotactic for human skin fibroblasts, suggesting that the chemoattractant activity of PDGF for fibroblasts is not a general property of growth factors and mitogens. These results suggest that PDGF could have two functions in wound healing: to attract fibroblasts to migrate into the clot and then to induce their proliferation.

The cell binding fragment of fibronectin is chemotactic for fibroblasts.

The fibroblast chemoattractant property of fibronectin is retained in the proteolytically produced 160 kilodalton peptide that contains the heparin binding and cell binding domains of the molecule, while the 40 kilodalton collagen binding peptide is inactive. Further degradation of the 160 kilodalton peptide leads to destruction of chemoattractant activity. An analysis of the migration of fibroblasts in varied gradients of the 160 K peptide shows that the effect is chemotactic, i.e. directed migration of cells towards a higher concentration of the peptide.

Attachment of smooth muscle cells to collagen and their migration toward platelet-derived growth factor.

Smooth muscle cells use fibronectin to bind to type I and type III collagens but bind to type V collagen by a trypsin-resistant intrinsic glycoconjugate. The binding site on type V collagen is located in the alpha A chain. By using collagen-coated filters in a modified Boyden chamber assay for chemotaxis, it was observed that the platelet-derived growth factor was chemotactic for smooth muscle cells but that several other growth factors were inactive. We suggest that the migration of smooth muscle cells from the media to the intima of a blood vessel, which leads to the formation of an atherosclerotic plaque, may be the result of a chemotactic migration of cells responsive to the platelet-derived growth factor.

Adult tissues contain chemoattractants for vascular endothelial cells.

New blood vessel formation, or angiogenesis, occurs through the migration of endothelial cells in elongated sprouts. These sprouts are directed preferentially towards the inciting stimulus. Several studies have demonstrated that certain chemical substances can stimulate angiogenesis. In these cases, endothelial cell migration towards the chemical stimulus may be due to a preferential migration of cells from lower to higher concentrations of the mediator. Such concentration gradient-dependent cellular migration has been termed chemotaxis. Using a modification of the Boyden chamber technique to measure chemotaxis in vitro, we have now found that extracts of various adult bovine tissues have potent chemotactic activity for vascular endothelial cells. Adult bovine serum lacks similar chemotactic activity.