Chronic Perturbation Research Articles

LONG-TERM RESPONSES OF THE KUPARUK RIVER ECOSYSTEM TO PHOSPHORUS FERTILIZATION

A long-term stream fertilization experiment was performed to evaluate the potential eutrophication of an arctic stream ecosystem. During 16 years of summer phosphorus (H3PO4) fertilization, we observed a dramatic change in the community structure of the Kuparuk River on the North Slope of Alaska. A positive response to fertilization was observed at all trophic levels with increases in epilithic algal stocks, some insect densities, and fish growth rates. After approximately eight years of P fertilization, bryophytes (mosses) replaced epilithic diatoms as the dominant primary producers in the Kuparuk River. The moss impacted NH4+ uptake rates, benthic gross primary production, habitat structure, and insect abundance and species composition. This study documents the long-term changes in an arctic tundra stream in response to nutrient enrichment. Predicting stream ecosystem responses to chronic perturbation requires long-term observation and experiments.

Endothelial cell activation in thrombotic thrombocytopenic purpura (TTP): a prospective analysis

It is generally assumed that endothelial cell injury is the primary event in the pathogenesis of thrombotic thrombocytopenic purpura (TTP). In this study, we have determined the extent of vascular perturbation during acute episodes of the disease. We performed a prospective, serial study of nine patients with relapsing TTP during hospitalization and treatment, and assessed the degree of endothelial cell involvement at admission, exacerbation and remission by measurement of von Willebrand factor (VWF) and VWF-propeptide levels. Measurement of both VWF and its propeptide enabled discrimination between acute and chronic perturbation of the endothelium. Elevated levels of both VWF and propeptide were found at admission. These levels decreased immediately upon plasma exchange therapy. However, plasma VWF and propeptide concentrations did not change, even at the time of acute exacerbation. These observations suggest that endothelial cell activation is not the primary event leading to TTP. Vascular perturbation seems to be a consequence, rather than a cause, of the disease.

A putative role for intramolecular regulatory mechanisms in the adaptor function of amphiphysin in endocytosis

Amphiphysin 1 is a brain-specific protein enriched at the synapse and a major binding partner of several components of the clathrin-mediated endocytic machinery (Proc Natl Acad Sci USA 93 (1996) 331). It interacts with clathrin-coat proteins, dynamin, and membranes (Nat Cell Biol 1 (1999) 33; JBC). A role of amphiphysin in synaptic vesicle recycling is supported by both acute and chronic perturbation studies (Science 276 (1997) 259; Neuron 33 (2002) 789). Here we show that amphiphysin directly stimulates clathrin recruitment onto liposomes in an in vitro assay. Amphiphysin-dependent clathrin-coat recruitment is enhanced by the interaction of amphiphysin with dynamin. We also show that the amphiphysin SH3 domain binds full-length amphiphysin, likely via an internal poly-proline region, and that clathrin recruitment onto liposomes by amphiphysin is enhanced in the presence of the isolated amphiphysin SH3 domain. Expression of a mutant amphiphysin harboring two amino acid substitutions in the SH3 domain, and therefore unable to bind proline-containing motifs, induces an accumulation of large intracellular aggregates including amphiphysin, clathrin, AP-2, and other endocytic proteins, as well as a concomitant block of transferrin endocytosis. Thus, putative intramolecular interactions between the amphiphysin COOH-terminal SH3 domain and its internal poly-proline region may regulate clathrin recruitment onto membranes.

Hippocampal serotonin responses in short and long attack latency mice.

Short and long attack latency mice, which are selected based on their offensive behaviour in a resident-intruder model, differ in their neuroendocrine regulation as well as in aspects of their brain serotonin system. Previous studies showed that the binding capacity and expression of serotonin-1A receptors in the hippocampal CA1 field of long attack latency mice are significantly lower than that found in short attack latency mice. We tested whether the functional responses of CA1 hippocampal cells to serotonin are also reduced in long attack latency mice. To this end, serotonin-induced changes in the membrane potential and input resistance were recorded in vitro with microelectrodes in CA1 pyramidal neurones of long and short attack latency mice. The data show that in long attack latency mice, along with a reduction of the serotonin-1A receptor mRNA expression, the serotonin-induced membrane hyperpolarization and decrease in resistance are attenuated. Basal membrane properties of CA1 neurones in the two.mice lines were comparable. Plasma corticosterone levels in response to a novelty stress were elevated in long compared to short attack latency mice and inversely related to the serotonin-induced responses. We tentatively conclude that long attack latency mice show attenuated functional responses to serotonin in the hippocampus, possibly linked to a chronic perturbation of hormonal levels.

Sarcomere Number Regulation Maintained After Immobilization In Desmin-Null Mouse Skeletal Muscle

The serial sarcomere number of skeletal muscle changes in response to chronic length perturbation. The role of the intermediate filament desmin in regulating these changes was investigated by comparing the architectural adaptations of the tibialis anterior, extensor digitorum longus (EDL) and soleus from wild-type mice with those of homozygous desmin knockout mice after hindlimb immobilization. After 28 days, serial sarcomere number increased significantly in the lengthened wild-type tibialis anterior (by approximately 9%) and EDL (by approximately 17%). Surprisingly, muscles from desmin knockout mice also experienced significant serial remodeling, with the serial sarcomere number of the tibialis anterior increasing by approximately 10% and that of the EDL by approximately 27%. A consistent result was observed in the shortened soleus: a significant decrease in sarcomere number was observed in the muscles from both wild-type (approximately 26%) and knockout (approximately 12%) mice. Thus, although desmin is not essential for sarcomerogenesis or sarcomere subtraction in mouse hindlimb muscles, the results do suggest subtle differences in the nature of sarcomere number adaptation. We speculate that desmin may play a role in regulating the optimal arrangement of sarcomeres within the muscle or in sensing the magnitude of the immobilization effect itself.

Abnormalities of the soleus H-reflex in lumbar spondylolisthesis: a possible early sign of bilateral S1 root dysfunction.

Using routine electrodiagnostic procedures, the authors searched for physiologic evidence of nerve root compromise in patients with chronic mechanical perturbation to the lumbar spine. They examined 37 patients with spondylolisthesis and various degrees of degenerative changes in the lumbar canal. Clinical and neurophysiologic findings were compared with data obtained from 36 healthy persons. The soleus H-reflex appeared to be a sensitive indicator of sensory fiber compromise at the S1 root level, because changes correlated well with the focal sensory signs and preceded clinical and electromyographic signs of motor root involvement. When these occurred, the clinical findings were consistent with a more severe nerve root deficit and with radiographic evidence of neural compression. The greater sensitivity of the soleus H-reflex may be related to the pathophysiologic events that occur at the lesion site.

Seasonal variations of thyroid hormone levels in wild fish

Variations in plasma thyroxine (T4) and triiodothyronine (T3) contents of pike, pikeperch, perch, bream and chub from a large reservoir (Pareloup, South of France) were investigated before and during the progressive emptying of the reservoir. Fish were caught by gill nets, except at the last time of emptying when controls were collected with landing nets. Both iodothyronine levels showed desynchronized seasonal cycles resulting in higher T3/T4 ratios in fish stressed by gill-netting in early summer. The aforementioned results principally emphasized the prevailing influence of the technique of catching on eliciting stress responses and subsequent thyroidal impairment in all five species. However, the much higher amounts of T4 and/or T3 observed in specimens caught in the later stages of draining gave evidence to suggest that the progressive alteration in habitat might also have indirectly affected the thyroidal status of these fish, this latter result leading to the consideration of fish plasma thyroid hormones as possible endocrine biomarkers of chronic perturbation.

Von Willebrand Factor Propeptide in Vascular Disorders: A Tool to Distinguish Between Acute and Chronic Endothelial Cell Perturbation

Before de novo synthesized von Willebrand factor (vWF) leaves the endothelial cell, it undergoes endoproteolytic cleavage of its propeptide (vW antigen II). The processed vWF and propeptide are either released constitutively or, following activation of the endothelium, released through the regulated pathway. In a recent study (Borchiellini et al, Blood 88:2951, 1996), we showed that the half-life of mature vWF and of its propeptide differ fourfold to fivefold. We postulated that the molar ratio of the propeptide to mature vWF could serve as a tool to assess the extent of endothelial cell activation under physiologic and clinical conditions. To test this hypothesis, we measured mature vWF and propeptide in patients with documented acute and chronic vascular disease, including patients with thrombotic thrombocytopenic purpura (TTP), acute septicemia, and diabetes mellitus. These data were compared with experimental conditions in healthy subjects in which perturbation of the endothelium was simulated by physical exercise or by administration of 1-deamino-8-D-arginine vasopressin (DDAVP) or endotoxin. In all individuals of the latter study group, both vWF and propeptide levels were elevated during the acute phase of the experimentally induced vascular perturbation; at later time points after stimulation, only vWF levels remained elevated. In patients with sepsis and TTP, both vWF and propeptide were elevated several-fold. Thus, this pattern can readily be explained in terms of acute perturbation of the endothelium. In contrast, in patients with diabetes mellitus propeptide levels were only slightly elevated, whereas vWF levels were elevated twofold to threefold. This pattern is a typical feature of chronic, low-grade activation of the endothelium. These observations support our hypothesis that measurement of both propeptide and vWF levels allows to discriminate between chronic and acute phases of endothelial cell activation in vivo. Measurement of only vWF is less indicative in this respect.

Non-parametric statistical formulas for factors of safety of plant stems

A previously proposed statistical approach for computing factors of safety (i.e. numerical measures of mechanical reliability) for any load bearing structure, like a vertical plant stem, is here extended to cope with organic structures whose morphological or mechanical properties have Weibull frequency distributions. This approach is illustrated using the actual length L and critical buckling length Lerof flower stalks (peduncles) collected from isogenic garlic (Allium sativum) populations grown under windy field and protected glasshouse conditions. Our analyses of the data indicate that L and Lerof peduncles harvested from both populations have Weibull frequency distributions, that the factor of safety for glasshouse grown peduncles is very near unity (i.e. S=1.03), and that the factor of safety of field grown peduncles is 73% higher than that of glasshouse grown plants (i.e. S=1.73). Comparisons between the S -values computed on the basis of our formulas and on the basis of the quotient of the mean values of Lerand L for each of the two populations indicate that the statistical method gives biologically realistic S -values and that the difference in the S -values for stems grown under protected and unprotected environmental conditions likely reflects the effects of chronic mechanical perturbation (due to wind-induced drag) on normal stem growth and development. Copyright 1999 Academic Press.

Effects of Vibration on Mechanical Properties and Biomass Allocation Pattern ofCapsella bursa-pastoris(Cruciferae)

The herbaceous dicot speciesCapsella bursa-pastoris(Cruciferae) was used to determine the influence of chronic mechanical perturbation on the biomass allocation pattern (i.e. dry weight distribution among roots, stems and reproductive structures) and the mechanical properties of roots and stems (i.e. tensile breaking stress and Young's modulus). It was hypothesized that mechanically stimulated plants would allocate more of their total biomass to root systems and less to shoots compared to control plants and that the breaking stress (a measure of strength) and Young's modulus (a measure of material stiffness) would increase for roots and decrease for stems because these responses would adaptively reduce the bending moment at the base of shoots and increase the anchorage strength of root systems. It was also hypothesized that mechanical perturbation would maladaptively reduce the relative fitness of individuals by reducing biomass allocation to their reproductive organs and the ability to broadcast seeds by means of elastic stem flexure. These hypotheses were tested by vibrating cultivated plants for 60 s every day during the course of growth to maturity and comparing their dry weight distributions and the mechanical properties of their body parts (measured in tension) to those of undisturbed control plants. Based on a total of 51 experimentally manipulated and 44 control plants for which mechanical properties were successfully tested, chronic organ flexure resulted in more massive root systems and less massive vegetative shoots, increased the magnitudes of root breaking stress and Young's modulus and had the reverse effect on stems, reduced the dry weight of reproductive structures at maturity, delayed the formation of the first mature flower and fruit, and accelerated the on-set of plant senescence compared to control plants. These responses to chronic organ flexure are interpreted to be vegetatively adaptive, since they reduce the probability of stem and root failure as a consequence of wind-pressure or foraging, and to be reproductively maladaptive, since they reduce reproductive effort and the ability to mechanically discharge seeds.

Novel variants of amphiphysin I expressed in the retina

Amphiphysin 1 is a brain-specific protein enriched at the synapse and a major binding partner of several components of the clathrin-mediated endocytic machinery (Proc Natl Acad Sci USA 93 (1996) 331). It interacts with clathrin-coat proteins, dynamin, and membranes (Nat Cell Biol 1 (1999) 33; JBC). A role of amphiphysin in synaptic vesicle recycling is supported by both acute and chronic perturbation studies (Science 276 (1997) 259; Neuron 33 (2002) 789). Here we show that amphiphysin directly stimulates clathrin recruitment onto liposomes in an in vitro assay. Amphiphysin-dependent clathrin-coat recruitment is enhanced by the interaction of amphiphysin with dynamin. We also show that the amphiphysin SH3 domain binds full-length amphiphysin, likely via an internal poly-proline region, and that clathrin recruitment onto liposomes by amphiphysin is enhanced in the presence of the isolated amphiphysin SH3 domain. Expression of a mutant amphiphysin harboring two amino acid substitutions in the SH3 domain, and therefore unable to bind proline-containing motifs, induces an accumulation of large intracellular aggregates including amphiphysin, clathrin, AP-2, and other endocytic proteins, as well as a concomitant block of transferrin endocytosis. Thus, putative intramolecular interactions between the amphiphysin COOH-terminal SH3 domain and its internal poly-proline region may regulate clathrin recruitment onto membranes.

DNA mismatch repair in lymphoblastoid cells from hereditary non-polyposis colorectal cancer (HNPCC) patients is normal under conditions of rapid cell division and increased mutational load

Patients with hereditary non-polyposis colorectal cancer (HNPCC) have germ-line mutations in one of four DNA mismatch repair genes (hMSH2, hMLH1, hPMS1 and hPMS2). It is supposed that a single functional copy of these genes is sufficient for normal mismatch repair, but it is not certain that this is the case under abnormal conditions such as rapid cell division or an increased tendency to DNA replication errors (RERs). We have analysed mismatch repair by examining replication errors in immortalised lymphoblastoid cells derived from two HNPCC patients heterozygous for mismatch repair defects (one hMSH2 mutant and one hMLH1 mutant), and from control individuals. Three conditions of cell culture have been used: (i) relatively slow cell growth and division; (ii) relatively fast growth and division; and (iii) chronic perturbation of the intracellular dNTP pool to promote a increased frequency of replication errors. No significant differences in microsatellite instability were found between HNPCC patients and controls in any of these environments. Lymphoblastoid cells from hMSH2 and hMLH1 mutant/wild-type heterozygotes appear, therefore, to have normal levels of mismatch repair, even under conditions that increase the requirement for repair. The pool bias cultures from the HNPCC patients and controls did, however, show similar, increased frequencies of RERs, suggesting that the mismatch repair capacity of the cells had been overloaded, but that the number of normal HNPCC alleles was not the limiting factor.

Localization of epidermal sphingolipid synthesis and serine palmitoyl transferase activity: alterations imposed by permeability barrier requirements.

Sphingolipids, the predominant lipid species in mammalian stratum corneum play, a central role in permeability barrier homeostatis. Prior studies have shown that the epidermis synthesizes abundant sphingolipids, a process regulated by barrier requirements, and that inhibition of sphingolipid synthesis interferes with barrier homeostasis. To investigate further the relationship between epidermal sphingolipid metabolism and barrier function, we localized sphingolipid synthetic activity in murine epidermis under basal conditions, and following acute (acetone treatment) or chronic (essential fatty acid deficiency, EFAD) barrier perturbation, using dithiothreitol and/or the staphylococcal epidermolytic toxin to isolate the lower from the outer epidermis. Under basal conditions, both the activity of serine palmitoyl transferase (SPT), the rate-limiting enzyme of sphingolipid synthesis, and the rates of 3H-H2O incorporation into sphingolipids were nearly equivalent in the lower and the outer epidermis. Following acute barrier perturbation, SPT activity increased significantly in both the lower (35%; P < 0.05) and the outer epidermal layers (60%; P < 0.01). The rates of 3H-H2O incorporation into each major sphingolipid family, including ceramides, glucosylceramides and sphingomyelin, increased significantly in both the lower and the outer epidermis of treated flanks after acute barrier disruption. Finally, SPT activity was modestly elevated (20%; P < 0.01) in the lower but not in the outer epidermis of EFAD animals. These studies demonstrate the ability of both lower and outer epidermal cells to generate sphingolipids, and that permeability barrier homeostatic mechanisms appear to differentially regulate SPT activity and sphingolipid synthesis in the lower and the outer epidermis in response to acute and chronic barrier perturbation.(ABSTRACT TRUNCATED AT 250 WORDS)

Biologic aspects of human immunodeficiency virus-related lymphoma.

A high frequency of lymphoma in human immunodeficiency virus-infected individuals has been reported since the outbreak of the acquired immunodeficiency syndrome (AIDS) epidemic in 1982. In the vast majority of cases, these lymphomas are highly aggressive B-cell, non-Hodgkin's lymphoma of intermediate or high grade of malignancy. AIDS-associated non-Hodgkin's lymphoma are histologically classified as small noncleaved cell lymphoma, large cell immunoblastic plasmacytoid lymphoma, or large noncleaved cell lymphoma. Host factors predisposing to lymphoma development in AIDS patients include decreased immunosurveillance as well as human immunodeficiency virus-induced chronic perturbation of the immune system leading to cytokine overproduction and increased B-cell stimulation. These alterations are associated with the development of multiple oligoclonal B-cell expansions, which are characterized by persistent generalized lymphadenopathy. The presence of Epstein-Barr virus within a persistent generalized lymphadenopathy clone further increases the risk of its neoplastic transformation. The appearance of non-Hodgkin's lymphoma is characterized by the presence of a monoclonal B-cell population displaying several genetic lesions, including monoclonal Epstein-Barr virus infection, c-myc rearrangements, Ras mutations, and p53 inactivation. The number and type of lesions varies among the different types of AIDS-non-Hodgkin's lymphoma, defining multiple alternative molecular pathways in AIDS-associated lymphomagenesis.

Trypsin activable renin in rat plasma. Effects of acute and chronic perturbation of the renin system.

Plasma levels of active and inactive renin were measured in the rat following manipulation of renin release. In the anesthetized rat intravenous captopril or sodium nitroprusside resulted in elevation of active renin only. Neither active nor inactive renin were altered following ether anesthesia of 2 hour bilaterally nephrectomized animals. Elevated levels of active and total renin were observed in anesthetized Wistar rats that had received oral captopril for a 6 week period. Renin substrate was decreased suggesting that blood angiotensin II exerts a tonic influence on renin substrate. In sodium deplete SHR, sacrificed by decapitation, chronic captopril resulted in a significant increase of both the active and inactive form of the enzyme concomitant with blood pressure reduction. The present data further confirm the independent control of active and inactive renin in the rat.