Biomedical subjects

A Jayaraman

Publications and source records attributed to A Jayaraman.

At least 19 recordsLinked to original sources

PubMed2007

Resistance training and locomotor recovery after incomplete spinal cord injury: a case series.

STUDY DESIGN: Longitudinal intervention case series. OBJECTIVE: To determine if a 12-week resistance and plyometric training program results in improved muscle function and locomotor speed after incomplete spinal cord injury (SCI). SETTING: University research setting. METHODS: Three ambulatory individuals with chronic (18.7+/-2.2 months post injury) motor incomplete SCI completed 12 weeks of lower extremity resistance training combined with plyometric training (RPT). Muscle maximum cross-sectional area (max-CSA) of the knee extensor (KE) and plantar flexor (PF) muscle groups was determined using magnetic resonance imaging (MRI). In addition, peak isometric torque, time to peak torque (T (20-80)), torque developed within the initial 220 ms of contraction (torque(220)) and average rate of torque development (ARTD) were calculated as indices of muscle function. Maximal as well as self-selected gait speeds were determined pre- and post-RPT during which the spatio-temporal characteristics, kinematics and kinetics of gait were measured. RESULTS: RPT resulted in improved peak torque production in the KE (28.9+/-4.4%) and PF (35.0+/-9.1%) muscle groups, as well as a decrease in T(20-80), an increased torque(220) and an increase ARTD in both muscle groups. In addition, an increase in self-selected (pre-RPT=0.77 m/s; post-RPT=1.03 m/s) and maximum (pre-RPT=1.08 m/s; post-RPT=1.47 m/s) gait speed was realized. Increased gait speeds were accompanied by bilateral increases in propulsion and hip excursion as well as increased lower extremity joint powers. CONCLUSIONS: The combination of lower extremity RPT can attenuate existing neuromuscular impairments and improve gait speed in persons after incomplete SCI.

Adolescent↗

PubMed2006

Characterization of the domain chaos convection state by the largest Lyapunov exponent.

Using numerical integrations of the Boussinesq equations in rotating cylindrical domains with realistic boundary conditions, we have computed the value of the largest Lyapunov exponent lambda1 for a variety of aspect ratios and driving strengths. We study in particular the domain chaos state, which bifurcates supercritically from the conducting fluid state and involves extended propagating fronts as well as point defects. We compare our results with those from Egolf, [Nature 404, 733 (2000)], who suggested that the value of lambda1 for the spiral defect chaos state of a convecting fluid was determined primarily by bursts of instability arising from short-lived, spatially localized dislocation nucleation events. We also show that the quantity lambda1 is not intensive for aspect ratios Gamma over the range 20<Gamma<40 and that the scaling exponent of lambda1 near onset is consistent with the value predicted by the amplitude equation formalism.

Journal Article↗

PubMed2005

Lower extremity skeletal muscle function in persons with incomplete spinal cord injury.

STUDY DESIGN: A cross-sectional study design. OBJECTIVES: To characterize and specifically quantify impairments in muscle function after chronic incomplete spinal cord injury (SCI). SETTING: University of Florida, Gainesville, FL, USA. METHODS: Voluntary and electrically elicited contractile measurements were performed and voluntary activation deficits were quantitatively determined in the knee extensor and ankle plantar flexor muscle groups in 10 individuals with chronic incomplete SCI (C5-T8, ASIA C or D) and age-, gender-, height- and body weight matched healthy controls. RESULTS: Persons with incomplete-SCI were able to produce only 36 and 24% of the knee extensor torque and 38 and 26% of the plantar flexor torque generated by noninjured controls in the self-reported less-involved and more-involved limbs, respectively (P<0.05). In addition, both indices of explosive or instantaneous muscle strength, torque200 (absolute torque reached at 200 ms) and the average rate of torque development (ARTD) were dramatically reduced in the ankle plantar flexor and knee extensor muscle groups in persons with incomplete-SCI. However, the deficit in instantaneous muscle strength was most pronounced in the ankle plantar flexor muscles, with an 11.7-fold difference between the torque200 measured in the self-reported more involved limb and a 5-fold difference in the less-involved limb compared to control muscles. Voluntary activation deficits ranged between 42 and 66% in both muscle groups. Interestingly, electrically elicited contractile properties did not differ between the groups. CONCLUSION: The resultant impact of incomplete-SCI is that affected muscles not only become weak, but slow to develop voluntary torque. We speculate that the large deficit in torque200 and ARTD in the ankle plantar flexors muscles of persons with incomplete-SCI may limit locomotor function. The results presented in this study provide a quantitative and sensitive assessment of muscle function upon which future research examining rehabilitation programs aimed at restoring muscle function and promoting functional recovery after incomplete-SCI may be based.

Adult↗

PubMed2005

Computer simulation study of pattern transfer in AB diblock copolymer film adsorbed on a heterogeneous surface.

In this work we investigate how a pattern imposed in a copolymer film at a certain distance from the surface propagates through the film onto an adsorbing heterogeneous surface. We bias the copolymer film to adopt a specified target pattern and then use simulation to design a surface pattern that helps the adsorbed film to maintain that target pattern. We examine the effect of varying the copolymer chain length, the size of the target pattern, and the distance from the surface where the target pattern is applied, z', on the extent of pattern transfer. For each chain length, target pattern, and z' we compare the energy of the system when a pattern is applied in the bulk to the energy when no pattern is applied in order to understand why a certain pattern size is transferred to the surface with higher fidelity than the others. At constant chain length, pattern transfer is best when the pattern size brings the energy of the system close to the energy when no pattern is applied. At constant pattern size, pattern transfer is best in the systems with longer chains. This is because longer chains are more likely to adsorb as brushes and loops which then helps transfer the pattern through the adsorbed film down to the surface.

Adsorption↗

PubMed2005

Adsorption of comb copolymers on weakly attractive solid surfaces.

In this work continuum and lattice Monte Carlo simulation methods are used to study the adsorption of linear and comb polymers on flat surfaces. Selected polymer segments, located at the tips of the side chains in comb polymers or equally spaced along the linear polymers, are attracted to each other and to the surface via square-well potentials. The rest of the polymer segments are modeled as tangent hard spheres in the continuum model and as self-avoiding random walks in the lattice model. Results are presented in terms of segment-density profiles, distribution functions, and radii of gyration of the adsorbed polymers. At infinite dilution the presence of short side chains promotes the adsorption of polymers favoring both a decrease in the depletion-layer thickness and a spreading of the polymer molecule on the surface. The presence of long side chains favors the adsorption of polymers on the surface, but does not permit the spreading of the polymers. At finite concentration linear polymers and comb polymers with long side chains readily adsorb on the solid surface, while comb polymers with short side chains are unlikely to adsorb. The simple models of comb copolymers with short side chains used here show properties similar to those of associating polymers and of globular proteins in aqueous solutions, and can be used as a first approximation to investigate the mechanism of adsorption of proteins onto hydrophobic surfaces.

Journal Article↗

PubMed2004

Expression profiling analysis of the metabolic and inflammatory changes following burn injury in rats.

Burn injury initiates an inflammatory response as part of the healing process that is associated with extensive metabolic adjustments. While most studies have focused on understanding these changes from a biochemical perspective, not much work has been done to characterize these processes at the gene expression level. As a first step, we have comprehensively analyzed changes in gene expression in rat livers during the first 24 h after burn injury using Affymetrix GeneChips, which showed 339 genes to be differentially expressed at a statistical significance of P < 0.05 and changed at least twofold. Functional classification based on gene ontology terms indicated that two categories, metabolism (28%) and inflammation (14%), accounted for nearly 42%. Detailed analysis of the metabolism group of genes indicated that fatty acid (FA) and triglyceride (TG) biosynthesis in the liver were unchanged, whereas TG utilization, FA import, and beta-oxidation increased after burn injury. The increased FA pools after burn injury appear to serve as substrates for ATP production. Following burn injury, the cholesterol biosynthetic pathway was suppressed while cholesterol was increasingly imported and converted into bile acids. The inflammatory genes that were altered included several classic acute phase response markers, as well as genes involved in the complement, kinin, clotting, and fibrinolytic protein systems. These temporally coordinated changes in gene expression were also corroborated by biochemical measurements for FA, TG, cholesterol, and ATP. Together, these data indicate that FA are increasingly imported and oxidized in the liver to meet the enhanced energy demands arising from an inflammatory response during the first 24 h after burn injury.

Adenosine Triphosphate↗

PubMed2002

Pitting corrosion inhibition of aluminum 2024 by Bacillus biofilms secreting polyaspartate or gamma-polyglutamate.

Pitting corrosion of aluminum 2024 in Luria Bertani medium was reduced by the secretion of anionic peptides by engineered and natural Bacillus biofilms and was studied in continuous reactors using electrochemical impedance spectroscopy. Compared to sterile controls, pitting was reduced dramatically by the presence of the biofilms. The secretion of a 20 amino acid polyaspartate peptide by an engineered Bacillus subtilis WB600/pBE92-Asp biofilm slightly reduced the corrosion rate of the passive aluminum alloy at pH 6.5; however, the secretion of gamma-polyglutamate by a Bacillus licheniformis biofilm reduced the corrosion rate by 90% (compared to the B. subtilis WB600/pBE92 biofilm which did not secrete polyaspartate or gamma-polyglutamate). The corrosion potential ( E(corr)) of aluminum 2024 was increased by about 0.15-0.44 V due to the formation of B. subtilis and B. licheniformis biofilms as compared to sterile controls. The increase of E(corr) and the observed prevention of pitting indicate that the pitting potential ( E(pit)) had increased. This result and the further decrease of corrosion rates for the passive aluminum alloy suggest that the rate of the anodic metal dissolution reaction was reduced by an inhibitor produced by the biofilms. Purified gamma-polyglutamate also decreased the corrosion rates of aluminum 2024.

Aluminum↗

PubMed2001

Rational selection and quantitative evaluation of antisense oligonucleotides.

Antisense oligonucleotides are an attractive therapeutic option to modulate specific gene expression. However, not all antisense oligonucleotides are effective in inhibiting gene expression, and currently very few methods exist for selecting the few effective ones from all candidate oligonucleotides. The lack of quantitative methods to rapidly assess the efficacy of antisense oligonucleotides also contributes to the difficulty of discovering potent and specific antisense oligonucleotides. We have previously reported the development of a prediction algorithm for identifying high affinity antisense oligonucleotides based on mRNA-oligonucleotide hybridization. In this study, we report the antisense activity of these rationally selected oligonucleotides against three model target mRNAs (human lactate dehydrogenase A and B and rat gp130) in cell culture. The effectiveness of oligonucleotides was evaluated by a kinetic PCR technique, which allows quantitative evaluation of mRNA levels and thus provides a measure of antisense-mediated decreases in target mRNA, as occurs through RNase H recruitment. Antisense oligonucleotides that were predicted to have high affinity for their target proved effective in almost all cases, including tests against three different targets in two cell types with phosphodiester and phosphorothioate oligonucleotide chemistries. This approach may aid the development of antisense oligonucleotides for a variety of applications.

Animals↗

PubMed2000

Dynamics of gene expression in rat hepatocytes under stress.

The response of cells to physical or biochemical stress involves concerted changes in the expression of a large number of genes encoding various functions. We have used a quantitative kinetic RT-PCR technique to follow the dynamics of changes in transcription factor and acute-phase mRNA levels in cultured rat hepatocytes subjected to either elevated temperature (40 degrees C) or exposure to the inflammatory cytokine interleukin-6. The profiles of transcription factor gene expression displayed rapid and coordinate regulation, attainment of new steady-states, transitions in some instances from up-regulation to down-regulation (or vice versa), and, for elevated temperature, multiple spikes of up-regulation. Transcripts of acute-phase genes generally displayed relatively small changes during the first few hours followed by more significant changes over the course of tens of hours (elevated temperature) to days (IL-6 exposure). These observations are all consistent with the notion of genetic reprogramming due to a network of interacting transcription factor proteins and transcripts. We utilized a simple transcription/translation model incorporating autoregulation to describe the dynamics of transcription factor gene expression. This model successfully described key features of the transcription factor dynamics, most notably the multiple spikes observed after exposure to elevated temperature. The dynamics of gene expression are rich in information that, with considerably more study, may eventually be exploited to provide insights into the interplay of genetic networks in regulating a variety of cellular responses.

Acute-Phase Reaction↗

PubMed1999

Inhibiting sulfate-reducing bacteria in biofilms on steel with antimicrobial peptides generated in situ.

In batch and continuous fermentations, the reduction in corrosion of SAE 1018 mild steel and 304 stainless steel caused by inhibition of the reference sulfate-reducing bacterium (SRB) Desulfovibrio vulgaris by a protective, antimicrobial-producing Bacillus brevis biofilm was investigated. The presence of D. vulgaris produced a thick black precipitate on mild steel and a higher corrosion rate in batch cultures than that seen in a mono-culture of non-antimicrobial-producing Pseudomonas fragi K upon the addition of SRB to the aerobic P. fragi K biofilm. In continuous reactors, the polarization resistance RP decreased for stainless stell and increased for mild steel upon the addition of SRB to a P. fragi K biofilm. Addition of either 200 micrograms/ml ampicillin, chloramphenicol, or ammonium molybdate to batch and continuous reactors after SRB had colonized the metal was ineffective in killing SRB, as inferred from the lack of change in both Rp and the impedance spectra. However, when ampicillin was added prior to SRB colonization, the growth of SRB was completely inhibited on stainless steel in continuous reactors. Prior addition of ampicillin was only able to delay the growth of SRB on mild steel in continuous reactors. External addition of the purified peptide antimicrobial agent gramicidin S prior to the addition of SRB also inhibited the growth of SRB on stainless steel in continuous reactors, and the SRB were also inhibited on stainless steel in both batch and continuous reactors by producing gramicidin S in situ in a protective biofilm when the gramicidin-S-overproducing strain Bacillus brevis 18 was used.

Anti-Bacterial Agents↗

PubMed1999

Axenic aerobic biofilms inhibit corrosion of copper and aluminum.

The corrosion behavior of unalloyed copper and aluminum alloy 2024 in modified Baar's medium has been studied with continuous reactors using electrochemical impedance spectroscopy. An axenic aerobic biofilm of either Pseudomonas fragi K or Bacillus brevis 18 was able to lessen corrosion as evidenced by a consistent 20-fold increase in the low-frequency impedance value of copper as well as by a consistent four- to seven-fold increase in the polarization resistance of aluminum 2024 after six days exposure compared to sterile controls. This is the first report of axenic aerobic biofilms inhibiting generalized corrosion of copper and aluminum. Addition of the representative sulfate-reducing bacterium (SRB) Desulfovibrio vulgaris (to simulate consortia corrosion behavior) to either the P. fragi K or B. brevis 18 protective biofilm on copper increased the corrosion to that of the sterile control unless antibiotic (ampicillin) was added to inhibit the growth of SRB in the biofilm.

Aluminum↗

PubMed1998

Characterization of axenic Pseudomonas fragi and Escherichia coli biofilms that inhibit corrosion of SAE 1018 steel.

Corrosion inhibition of SAE 1018 steel by Pseudomonas fragi and Escherichia coli biofilms has been evaluated using batch cultures in rich medium (LB) and seawater-mimicking medium (VNSS) at 23 degrees C and 30 degrees C with or without daily medium replenishment. Biofilm components have been stained simultaneously for polysaccharide (calcofluor) and live and dead cells (Live/Dead Baclit viability kit) and visualized using confocal scanning laser microscopy (CSLM). Image analysis was used to quantify the relative proportions of live cells, dead cells, polysaccharide and void space in the biofilm. This staining technique and examination of the architecture of biofilms responsible for inhibiting metal corrosion revealed that both Ps. fragi and E. coli produce polysaccharide only in the seawater medium; in rich medium, the biofilm consisted mainly of a layer of sessile cells near the biofilm-metal interface and sparse thick clumps of cells at the biofilm-liquid interface. Biofilms of both strains had a higher proportion of live cells in the rich medium than in the seawater-mimicking medium at the higher temperature, and more live cells were present at the higher temperature for LB medium. The corrosion inhibition observed (2.3-6.9-fold in 8 d) was not significantly affected by medium type or replenishment. Increase in the cellular content of the biofilms, as a result of increasing temperature, led to a reduction in corrosion.

Biofilms↗

PubMed1997

Axenic aerobic biofilms inhibit corrosion of SAE 1018 steel through oxygen depletion.

Corrosion inhibition of SAE 1018 steel by pure-culture biofilms of Pseudomonas fragi and Escherichia coli DH5 alpha has been evaluated in complex Luria-Bertani medium, seawater-mimicking medium, and modified Baar's medium at 30 degrees C. In batch cultures, both bacteria inhibited corrosion three to six fold compared to sterile controls, and the corrosion was comparable to that observed in anaerobic sterile media. To corroborate this result, a continuous reactor and electrochemical impedance spectroscopy were used to show that both P. fragi K and E. coli DH5 alpha decreased the corrosion rate by 4- to 40-fold as compared to sterile controls; this matched the decrease in corrosion found with sterile medium in the absence of oxygen and with E. coli DH5 alpha grown anaerobically. In addition, the requirement for live respiring cells was demonstrated by the increase in the corrosion rate that was observed upon killing the P. fragi K biofilm in continuous cultures, and it was shown that fermentation products do not cause an increase in corrosion. Hence, pure-culture biofilms inhibit corrosion of SAE 1018 steel by depleting oxygen at the metal surface.

Aerobiosis↗

PubMed1997

Importance of biofilm formation for corrosion inhibition of SAE 1018 steel by axenic aerobic biofilms.

To investigate if corrosion inhibition by aerobic biofilms is a general phenomenon, carbon steel (SAE 1018) coupons were exposed to a complex liquid medium (Luria-Bertani) and seawater-mimicking medium (VNSS) containing fifteen different pure-culture bacterial suspensions representing seven genera. Compared to sterile controls, the mass loss in the presence of these bacteria (which are capable of developing a biofilm to various degrees) decreased by 2- to 15-fold. The extent of corrosion inhibition in LB medium depended on the nature of the biofilm: an increased proportion of live cells, observed with confocal scanning laser microscopy (CSLM) and image analysis, decreased corrosion. Corrosion inhibition in LB medium was greatest with Pseudomonas putida (good biofilm formation), while metal coupons exposed to Streptomyces lividans in LB medium (poor biofilm formation) corroded in a manner similar to the sterile controls. Pseudomonas mendocina KR1 reduced corrosion the most in VNSS. It appears that only a small layer of active, respiring cells is required to inhibit corrosion, and the corrosion inhibition observed is due to the attached biofilm.

Biofilms↗

PubMed1996