SEARCH · PubMed Health

Results for “Structural changes”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 865 records · Page 48Linked to original sources

PubMed2005

[Structural changes in the medullary nucleus ambiguus and cardiac autonomic ganglia of growing rats under influence of the immobilization stress].

The objective of this study was to evaluate the quantitative and qualitative histological changes in the medullary nucleus ambiguus (NA) and cardiac autonomic ganglia (CAG) of the growing organism under the influence of immobilization stress of different duration. The experiments were performed on 56 outbred albino rats with the initial age of 30 days. Immobilization stress was induced by placing the rats into special chambers with a controllable volume of the inner space for 3, 7, 15 and 30 days. NA and CAG were studied on paraffin sections using the neurohistological methods and a quantitative analysis. Morphological and morphometric changes have demonstrated the retardation of the growth of neurocyte cell bodies and of their nuclei both in medullary NA and CAG as compared to those in control animals, which are regarded as an indication of a disturbance of the histogenesis of the nervous tissue in postnatal development. The degree of structural changes of the components of autonomic nervous system studied was directly related to the duration of experimental exposure to immobilization stress.

Animals↗

PubMed2006

[Long-term neurotoxic effects of MDMA result in cortical and hippocampal structural changes].

3,4-Methylenedioxymethamphetamine (MDMA) is a substituted amphetamine with stimulating and hallucinogenic properties. Since MDMA induces "ecstasy" it is extensively used as a "recreational" drug. It has been well established that MDMA is neurotoxic and can result in long-term degeneration of cerebral 5-hydroxytryptamine (5-HT) nerve terminals in many species. The present study was undertaken to investigate the long-term neurotoxic effects of MDMA on cortical and hippocampal structures, by repeatedly administering MDMA in short time. Male Wistar rats were randomly assigned to control group and MDMA-treated group. MDMA (10 mg/kg) was administered to rats of MDMA-treated group, once per hour, total 40 mg/kg; rats of control group were treated with the same volume of saline. Thirty-two weeks after administering MDMA, the expression of serotonin transporter (SERT) mRNA and diazepam binding inhibitor (DBI) mRNA was detected by in situ hybridization. The expression of glial fibrillary acidic protein (GFAP) was detected by immunohistochemistry, and the degeneration of nerve terminals was demonstrated by Bielschowsky and Glee Marsland silver staining. The results showed that the expression of SERT mRNA in hippocampus decreased by 31.96%, while expression of DBI mRNA in neocortex increased by 40.51%, compared with the control group (P<0.05). The expression of GFAP in the brain tissue increased (P<0.05), while significant reduction of the nerve terminals in neocortex was demonstrated by silver staining, compared with the control group. These results suggest that the neurotoxicity of MDMA results in sustained cortical and hippocampal structural changes, which in turn result in disorder of the brain functions.

Animals↗

PubMed1989

Secondary structural changes in the intact and the disulfide bridges cleaved beta-lactoglobulin A and B in solutions of urea, guanidine hydrochloride, and sodium dodecyl sulfate.

The relative proportions of alpha-helix, beta-sheet, and unordered form in beta-lactoglobulin A and B were examined in solutions of urea, guanidine, and sodium dodecyl sulfate (SDS). In the curve-fitting method of circular dichroism (CD) spectra, the reference spectra of the corresponding structures determined by Chen et al. (1974) were modified essentially according to the secondary structure of beta-lactoglobulin B predicted by Creamer et al. (1983), i.e., that the protein has 17% alpha-helix and 41% beta-sheet. The two variants showed no appreciable difference in structural changes. The reduction of disulfide bridges in the proteins increased beta-sheet up to 48% but did not affect the alpha-helical proportion. The alpha-helical proportions of nonreduced beta-lactoglobulin A and B were not affected below 2 M guanidine or below 3 M urea, but those of the reduced proteins began to decrease in much lower concentrations of these denaturants. By contrast, the alpha-helical proportions of the nonreduced and reduced proteins increased to 40-44% in SDS. The beta-sheet proportions of both nonreduced and reduced proteins which remained unaffected even in 6 M guanidine and 9 M urea, decreased to 24-25% in SDS.

Circular Dichroism↗

PubMed1995

Effects of a structural change in collagen upon binding to conditioned dentin studied by 13C NMR.

To develop a better adhesive functional monomer, it is imperative to understand the adhesion mechanisms of the resin to the dentin surface. Bond strength to the decalcified dentin surface pretreated with dentin primer, an aqueous ethanol solution of N-methacryloyl glycine, increases by increasing the water content in the primer. The aqueous primer could increase the thickness of the hybrid layer. The structural change of dentinal collagen with NM alpha A was studied by using a model compound for collagen,--(1Pro-2Pro-3Gly)10--, by 13C nuclear magnetic resonance (NMR). The model compound was aggregated in ethanol but dissociated in water. It was found that NM alpha A effectively dissociated the aggregated model compound in water. The dissociation of decalcified dentin was essential to create a thick hybrid layer that could afford a higher bond strength to dentin.

Adhesiveness↗

PubMed2004

Probing the self-assembly and the accompanying structural changes of hydrophobin SC3 on a hydrophobic surface by mass spectrometry.

The fungal class I hydrophobin SC3 self-assembles into an amphipathic membrane at hydrophilic-hydrophobic interfaces such as the water-air and water-Teflon interface. During self-assembly, the water-soluble state of SC3 proceeds via the intermediate alpha-helical state to the stable end form called the beta-sheet state. Self-assembly of the hydrophobin at the Teflon surface is arrested in the alpha-helical state. The beta-sheet state can be induced at elevated temperature in the presence of detergent. The structural changes of SC3 were monitored by various mass spectrometry techniques. We show that the so-called second loop of SC3 (C39-S72) has a high affinity for Teflon. Binding of this part of SC3 to Teflon was accompanied by the formation of alpha-helical structure and resulted in low solvent accessibility. The solvent-protected region of the second loop extended upon conversion to the beta-sheet state. In contrast, the C-terminal part of SC3 became more exposed to the solvent. The results indicate that the second loop of class I hydrophobins plays a pivotal role in self-assembly at the hydrophilic-hydrophobic interface. Of interest, this loop is much smaller in case of class II hydrophobins, which may explain the differences in their assembly.

Air↗

PubMed1997

[Long-term changes in availability of domestic nursing care based on family structure changes--a model calculation].

A central hypothesis in German family sociology is the observation of a disruption of family structures. If this disintegration prevails up to highest ages it must, among others, lead to an increasing inability to perform nursing care within families. The most important person in case of a need for nursing care is the spouse. The main topic of this paper is to determine whether demographic and familiar developments in Germany will increase or decrease the share of men and women at higher ages with a living spouse within the next decades. In spite of a slowly increasing share of the never-married and the divorced, on the average elderly men and women will be married to a greater and widowed to a much lesser proportion within the next decade. The Dutch LIPRO-model is used to calculate the exact numerical developments. The surprising result is primarily due to the fact that the actual high shares of the widowed are a consequence of distortions caused by the two World Wars. During the next few decades, these unusual developments will disappear even among the most elderly.

Aged↗

PubMed1997

Chaperone-like activity and temperature-induced structural changes of alpha-crystallin.

alpha-Crystallin is known to exhibit chaperone-like activity. We have studied its chaperone-like activity toward the aggregation of betaL-crystallin upon refolding of this protein from its unfolded state in guanidinium chloride. The chaperone-like activity of alpha-crystallin is less pronounced below 30 degrees C and is enhanced above this temperature. The plot of percentage protection as a function of temperature shows two transitions; one at 30 degrees C and another at around 55 degrees C. We have performed steady state fluorescence, fluorescence polarization, fluorescence quenching, circular dichroism, sedimentation analysis, and gel filtration chromatography to probe the temperature-induced structural changes of alpha-crystallin. Our results show that at above 50 degrees C, alpha-crystallin undergoes a transition to a multimeric molten globule-like state. Above 30 degrees C, a minor but detectable perturbation in its tertiary structure occurs that might lead to the observed exposure of its hydrophobic surfaces. These results support our earlier hypothesis that alpha-crystallin prevents the aggregation of other proteins by providing appropriately placed hydrophobic surfaces; a structural transition above 30 degrees C involving enhanced or reorganized hydrophobic surfaces of alpha-crystallin is important for its chaperone-like activity. It is possible that a structural alteration induced by temperature forms a part of the general mechanism of chaperone function, because they are required to function more effectively at nonpermissible temperatures.

Chaperonins↗

PubMed2005

Studies of the structural change during deformation in Cryptomeria japonica by time-resolved synchrotron small-angle X-ray scattering.

A definite proportional limit which has been observed typically in metallic materials during the transition from elastic deformation into plastic one was also detected in the load-displacement curve of the compression wood with the water content about 100% from Cryptomeria japonica D. Don. Time-resolved small-angle X-ray scattering studies demonstrated a large structural change, that is, a strong decrease in the microfibril angle in the cell wall occurring with increasing the displacement beyond the proportional limit for the compression wood loaded in uniaxial tension. Correspondingly, the mechanical properties are changed and high elongations begin to be seen. For the dried normal wood, on the other hand, only a weak decrease in the microfibril angle was observed with increasing the elongation until the fracture is initiated, where the elastic behavior was maintained.

Cryptomeria↗

PubMed1987

[Structural changes of the chromatin DNA in situ in partial deproteinization of DNP by a 0.6 M NaCl solution. A polarization-fluorescence microscopic study].

By means of polarization fluorescence microscopy changes in polarization degree of fluorescence of DNA-bound of Acridine orange in situ were observed. A marked decrease in polarization degree of chromatin fluorescence was found after the treatment of cell nuclei with 0.6 M NaCl. It shows that the removal of histone H1 from the chromatin results in destabilization of its structure. The data obtained show that the measurements of polarization degree of fluorescence allow to obtain relevant information about structural changes in DNA chromatin.

Acridine Orange↗

PubMed1983

A temperature-dependent structural change of mitochondrial ATPase.

The temperature dependence of the intrinsic tryptophan fluorescence in either bovine heart submitochondrial particles or oligomycin-sensitive ATPase isolated therefrom shows a discontinuity at near 25 degrees C, which coincides with the temperature where a break in the Arrhenius plot of ATPase activity is found. Addition of n-butanol to submitochondrial particles induces a decrease of tryptophan fluorescence in the whole temperature range. The discontinuity is interpreted as a temperature-dependent structural change and related to a viscosity-induced phase separation of the intrinsic mitochondrial proteins.

1-Butanol↗

PubMed1999

Myb-DNA recognition: role of tryptophan residues and structural changes of the minimal DNA binding domain of c-Myb.

The Myb oncoprotein specifically binds DNA by a domain composed of three imperfect repeats, R1, R2, and R3, each containing 3 tryptophans. The tryptophan fluorescence of the minimal binding domain, R2R3, of c-Myb was used to monitor structural flexibility changes occurring upon DNA binding to R2R3. The quenching of the Trp fluorescence by DNA titration shows that four out of the six tryptophans are involved in the formation of the specific R2R3-DNA complex and the environment of the tryptophan residues becomes more hydrophobic in the complex. The fluorescence intensity quenching of the tryptophans by binding of R2R3 to DNA is consistent with the decrease of the decay time: 1.46 ns for free R2R3 to 0.71 ns for the complexed protein. In the free R2R3, the six tryptophans are equally accessible to the iodide and acrylamide quenchers with a high collisional rate constant (4 x 10(9) and 3 x 10(9) M-1 s-1, respectively), indicating that R2R3 in solution is very flexible. In the R2R3-DNA complex, no Trp fluorescence quenching is observed with iodide whereas all tryptophan residues remain accessible to acrylamide with a collisional rate constant slightly slower than that in the free state. These results indicate that (i) a protein structural change occurs and (ii) the R2R3 molecule keeps a high mobility in the complex. The complex formation presents a two-step kinetics: a fast step corresponding to the R2R3-DNA association (7 x 10(5) M-1 s-1) and a slower one (0.004 s-1), which should correspond to a structural reorganization of the protein including a reordering of the water molecules at the protein-DNA interface.

Animals↗

PubMed1982

Distal tubular segments of the rabbit kidney after adaptation to altered Na- and K-intake. I. Structural changes.

The baso-lateral cell-membrane area in kidney tubules appears to be associated with the capacity for electrolyte transport; in the rabbit, it decreases from the distal convoluted tubule (DCT-cells) over the connecting tubule (CNT-cells) to the cortical collecting duct (principal cells). Adaptation to low Na-, high K-intake changes this pattern: CNT-cells at the beginning of the connecting tubule have the highest membrane area, which decreases along the segment, but remains two-fold higher than in controls. Principal cells have a four-fold higher membrane area than in controls. Simultaneous treatment with the antimineralocorticoid canrenoate-K inhibits the structural changes in CNT-cells only in end-portions of the connecting tubule and in principal cells. After prolonged high Na-, low K-intake DCT-cells display a two-fold higher membrane area than controls, while CNT-cells and principal cells are not affected. Simultaneous treatment with DOCA does not affect the DCT-cells but provokes a moderate increase in membrane area in CNT-cells, and a 5.5-fold increase in principal cells. The data provide evidence that DCT-, CNT- and principal cells are functionally different cell types. The baso-lateral cell-membrane area, associated with electrolyte-transport capacity, appears to be influenced in DCT-cells mainly by Na-intake, in CNT-cells mainly by K-intake and in part also by mineralocorticoids, and in principal cells mainly by mineralocorticoids.

Adaptation, Physiological↗

PubMed1998

Reduction of cardiovascular structural changes by nifedipine GITS in essential hypertensive patients.

The aim of this study was to evaluate the effect of the calcium antagonist Nifedipine GITS in a double-blind, randomized comparison with the diuretic hydrochlorothiazide (HCTZ) on reduction of left ventricular (LV) mass and minimal vascular resistance in a group of essential hypertensives with left ventricular hypertrophy (LVH). The effects on blood pressure and on echocardiographic LV functional parameters were also analysed. After two months of randomized treatment with Nifedipine GITS or HCTZ, if diastolic blood pressure was > 90 mmHg, a combination of the two drugs was given and was continued for 24 weeks. M-mode, 2D-guided echocardiography was used to measure LV mass index (LVMI) according to the "Penn convention". Minimal vascular resistance was measured in the forearm, from arterial pressure and maximal blood flow, using a strain gauge plethysmography. All examinations were performed before and after 8 and 24 weeks of treatment. Changes in LVMI were analysed at 8 weeks and at 24 weeks in patients receiving monotherapy ("according to protocol" analysis), and also at the end of treatment in patients taking Nifedipine or HCTZ monotherapy or the combination of the two drugs ("intention to treat" analysis). Both Nifedipine and HCTZ significantly reduced systolic and diastolic blood pressure (p < 0.001), without any significant difference between the two drug treatments. Heart rate was not significantly modified by either treatment. A progressive decrease in LVMI was observed after 8 and 24 weeks of treatment with Nifedipine monotherapy (ANOVA, p = 0.03), while the decrease in LVMI during HCTZ treatment did not progress further at 24 weeks (ANOVA, p = 0.49). A significant reduction of minimal vascular resistance was observed in patients treated with Nifedipine GITS monotherapy (ANOVA, p = 0.001), but not in the HCTZ group (ANOVA, p = 0.06). Comparison of changes of forearm minimal vascular resistance, considering baseline values, could demonstrate a greater effect during Nifedipine monotherapy as compared to HCTZ monotherapy. In conclusion, in a group of hypertensive patients with LVH, treatment for 24 weeks with Nifedipine GITS alone or in combination with HCTZ induced a significant reduction in LVMI and of forearm vascular structural changes, as evaluated by minimal vascular resistance. The decrease of minimal vascular resistance was significantly greater in patients treated with Nifedipine monotherapy, as compared to those given HCTZ.

Adult↗

PubMed1991

Inhibitor binding induces structural changes in porcine pepsin.

The refined structures of two isomorphous pepsin/inhibitor complexes demonstrate that significant conformational changes take place upon ligand binding for a mammalian representative of the aspartic proteinase family. These differences can be attributed mostly to the concerted rigid body movements of two separate clusters of residues relative to a central core. One cluster in the amino domain comprises the flap, the adjacent beta strand (sheet IV) and helices, as well as the interconnecting loops. The other, larger cluster is in the carboxy end and corresponds approximately to the flexible subdomain described previously. Similar conformational changes are proposed to occur in renin and cathepsin D.

Animals↗

PubMed1997

The effects of maternal protein deprivation on the fetal rat pancreas: major structural changes and their recuperation.

There is evidence that low birth weight and poor growth in early life cause a long-term predisposition to non-insulin-dependent diabetes. Morphological changes were assessed in fetal rat pancreas subjected to both pre- and post-natal maternal protein deprivation (LP). Further groups were subjected to purely prenatal maternal protein deprivation (preLP) and purely postnatal maternal protein deprivation (postLP), as well as a control group. The results show that the LP and postLP groups had fewer but larger islets than the control group, while the preLP group had more numerous, smaller islets. All three low protein groups had more irregularly shaped islets than the control group. There was a reduction in the amount of beta cells within each islet in all three protein-deprived groups. The LP and postLP groups showed a reduction in the percentage of islet tissue and beta cells per pancreas, but the percentage of islet tissue expressed per unit body weight was similar in all four groups. These results show that in maternal protein deprivation, homeostatic mechanisms ensure a constant amount of pancreatic endocrine tissue per unit of body weight. However, there remain major structural changes in the size, shape, and composition of the islets. These results support the theory that early development profoundly affects the structure of the pancreas and may play a role in the later development of adult diseases, such as non-insulin-dependent diabetes mellitus.

Animal Nutritional Physiological Phenomena↗

PubMed1993

Structural changes in the middle ear tissues of the rat after fractionated irradiation.

Chronic suppurative otitis media often ensues in patients treated with irradiation against a head and neck tumor. In an experimental study, rats were exposed to irradiation to evaluate the sensitivity of the middle ear to an accumulated irradiation dose of 20-45 Gy. Observed otomicroscopically, all animals appeared to have normal tympanic membranes and no fluid developed in the middle ear space. Ten days after the irradiation, minor structural changes had occurred in the pars flaccida. The keratinizing epithelium had thickened and mitoses were seen histologically. The lamina propria was edematous and contained polymorphonuclear cells and macrophages. The middle ear mucosa from all other tissue sites appeared normal. Six months after irradiation only minor changes in the pars flaccida were evident: the lamina propria was thin and inelastic and macrophages were present in the stroma. It is inferred from this study that the middle ear of the rat is relatively resistant to irradiation.

Animals↗

PubMed2004

FTIR spectroscopy of the K photointermediate of Neurospora rhodopsin: structural changes of the retinal, protein, and water molecules after photoisomerization.

Neurospora rhodopsin (NR, also known as NOP-1) is the first rhodopsin of the haloarchaeal type found in eucaryotes. NR demonstrates a very high degree of conservation of the amino acids that constitute the proton-conducting pathway in bacteriorhodopsin (BR), a light-driven proton pump of archaea. Nevertheless, NR does not appear to pump protons, suggesting the absence of the reprotonation switch that is necessary for the active transport. The photocycle of NR is much slower than that of BR, similar to the case of pharaonis phoborhodopsin (ppR), an archaeal photosensory protein. The functional and photochemical differences between NR and BR should be explained in the structural context. In this paper, we studied the structural changes of NR following retinal photoisomerization by means of low-temperature Fourier transform infrared (FTIR) spectroscopy and compared the obtained spectra with those for BR. For the spectroscopic analysis, we established the light-adaptation procedure for NR reconstituted into 1,2-dimyristoyl-sn-glycero- 3-phosphocholine/1,2-dimyristoyl-sn-glycero-3-phosphate (DMPC/DMPA) liposomes, which takes approximately 2 orders of magnitudes longer than in BR. The structure of the retinal chromophore and the hydrogen-bonding strength of the Schiff base in NR are similar to those in BR. Unique spectral features are observed for the S-H stretching vibrations of cysteine and amide-I vibrations for NR before and after retinal isomerization. In NR, there are no spectral changes assignable to the amide bands of alpha helices. The most prominent difference between NR and BR was seen for the water O-D stretching vibrations (measured in D(2)O). Unlike for haloarchaeal rhodopsins such as BR and ppR, no O-D stretches of water under strong hydrogen-bonded conditions (<2400 cm(-1)) were observed in the NR(K) minus NR difference spectra. This suggests a unique hydrogen-bonded network of the Schiff base region, which may be responsible for the lack of the reprotonation switch in NR.

Amino Acid Sequence↗

PubMedDate not supplied

Persistent structural changes in the middle ear mucosa of the rat, after an experimentally induced episode of pneumococcal otitis media.

To examine the effect of a transient episode of purulent AOM on the middle ear mucosa, an animal model was used. Histological examination was performed after inoculation of pneumococci into the rat middle ear. At 4, 8 and 12 days, and at 2 months after the inoculation, rats were sacrificed on each occasion and samples taken from specific areas of the middle ear mucosa. Structural alterations were noted at all mucosal sites. The normally flat epithelium had become more cuboidal or cylindrical, and numerous ciliated cells occurred in areas originally devoid of these cells. Epithelial cells penetrated the subepithelium forming gland-like structures. In the early phase, day 4 and day 8, inflammatory cells invaded the subepithelial layer except in the tympanic membrane. At 2 months, with the tympanic membrane otimicroscopically and histologically normalized, the structural changes of the mucosa still persisted indicating that a transient episode of pneumococcal otitis media can cause persisting mucosal changes.

Acute Disease↗