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Biomedical subjects

D E Feldman

Publications and source records attributed to D E Feldman.

At least 19 recordsLinked to original sources
PubMed2007

Postnatal development of cannabinoid receptor type 1 expression in rodent somatosensory cortex.

Endocannabinoids are powerful modulators of synaptic transmission that act on presynaptic cannabinoid receptors. Cannabinoid receptor type 1 (CB1) is the dominant receptor in the CNS, and is present in many brain regions, including sensory cortex. To investigate the potential role of CB1 receptors in cortical development, we examined the developmental expression of CB1 in rodent primary somatosensory (barrel) cortex, using immunohistochemistry with a CB1-specific antibody. We found that before postnatal day (P) 6, CB1 receptor staining was present exclusively in the cortical white matter, and that CB1 staining appeared in the gray matter between P6 and P20 in a specific laminar pattern. CB1 staining was confined to axons, and was most prominent in cortical layers 2/3, 5a, and 6. CB1 null (-/-) mice showed altered anatomical barrel maps in layer 4, with enlarged inter-barrel septa, but normal barrel size. These results indicate that CB1 receptors are present in early postnatal development and influence development of sensory maps.

Age Factors↗
PubMed2006

Detecting non-Abelian statistics with an electronic Mach-Zehnder interferometer.

Fractionally charged quasiparticles in the quantum Hall state with a filling factor nu=5/2 are expected to obey non-Abelian statistics. We demonstrate that their statistics can be probed by transport measurements in an electronic Mach-Zehnder interferometer. The tunneling current through the interferometer exhibits a characteristic dependence on the magnetic flux and a nonanalytic dependence on the tunneling amplitudes which can be controlled by gate voltages.

Journal Article↗
PubMed2006

Conservative non-pharmacological treatment options are not frequently used in the management of hip osteoarthritis.

Osteoarthritis (OA) is the most frequent joint disorder in seniors. Systematic reviews suggest that conservative treatment is effective and preferred in mild-moderate cases. The objective of this study was to examine the proportion of patients receiving physiotherapy, exercise or walking aids, and to explore factors associated with their prescription. We conducted a retrospective survey of patients about to undergo total hip arthroplasty for hip osteoarthritis. Patients were asked about past prescriptions for cane use, physiotherapy and exercise. Of 161 patients (36.6% male, mean age 68.7+/-10.1 years), 76% were prescribed a cane (adherence=86.2%). The main reason for not using a cane was vanity. Of the 28.0% patients prescribed physiotherapy, 73.3% received exercises compared to only 2.6% of non-physiotherapy patients. Patients who were older or worked in manual labour were more likely to be prescribed a cane and less likely to be prescribed physiotherapy or exercises. Men were less likely than women to be prescribed all three, but only cane use was statistically significant across genders. In conclusion, physiotherapy and exercise are not commonly prescribed in patients with hip OA.

Aged↗
PubMed2005

Nonequilibrium quantum phase transition in itinerant electron systems.

We study the effect of the voltage bias on the ferromagnetic phase transition in a one-dimensional itinerant electron system. The applied voltage drives the system into a nonequilibrium steady state with a nonzero electric current. The bias changes the universality class of the second order ferromagnetic transition. While the equilibrium transition belongs to the universality class of the uniaxial ferroelectric, we find the mean-field behavior near the nonequilibrium critical point.

Journal Article↗
PubMed2005

Rectification in Luttinger liquids.

We investigate the rectification of an ac bias in Luttinger liquids in the presence of an asymmetric potential (the ratchet effect). We show that a strong repulsive electron interaction enhances the ratchet current in comparison with Fermi-liquid systems, and the dc I-V curve is strongly asymmetric in the low-voltage regime even for a weak asymmetric potential. At higher voltages the ratchet current exhibits an oscillatory voltage dependence.

Journal Article↗
PubMed2004

Liquid crystals in random porous media: disorder is stronger in low-density aerosils.

The nature of glass phases of liquid crystals in random porous media depends on the effective disorder strength. We study how the disorder strength depends on the density of the porous media and demonstrate that it can increase as the density decreases. We also show that the interaction of the liquid crystal with random porous media can destroy long-range order inside the pores.

Journal Article↗
PubMed2003

Electrical manipulation of nanomagnets.

We demonstrate that it is possible to manipulate the magnetic coupling between two nanomagnets by means of an ac electric field. In the scheme suggested, the magnetic coupling is mediated by a magnetic particle that is in contact with both nanomagnets via tunnel barriers. The time-dependent electric field is applied so that the height of first one barrier then the other is suppressed in an alternating fashion. We show that the result is a pumping of magnetization from one nanomagnet to the other through the mediating particle. The dynamics of the magnetization of the mediating particle allows the coupling to be switched between being ferromagnetic and being antiferromagnetic.

Journal Article↗
PubMed2002

Destruction of bulk ordering by surface randomness.

We demonstrate that the arbitrarily weak quenched disorder on the surface of a system of continuous symmetry destroys long-range order in the bulk, and, instead, quasi-long-range order emerges. Correlation functions are calculated exactly for the two- and three-dimensional XY models with surface randomness via the functional renormalization group. Even at strong quenched disorder the three-dimensional XY model possesses topological order. We also determine roughness of a domain wall in the presence of surface disorder.

Journal Article↗
PubMed2002

Critical exponents of the random-field O(N) model.

The critical behavior of the random-field Ising model has long been a puzzle. Different methods predict that its critical exponents in D dimensions are the same as in the pure (D-2)-dimensional ferromagnet with the same number of the magnetization components contrary to the experiments and simulations. We calculate the exponents of the random-field O(N) model with the (4+epsilon)-expansion and obtain values different from the exponents of the pure ferromagnet in 2+epsilon dimensions. An infinite set of relevant operators missed in previous studies leads to a breakdown of the (6-epsilon)-expansion.

Journal Article↗
PubMed2001

Changing trends in mortality and admissions to hospital for elderly patients with congestive heart failure in Montreal.

BACKGROUND: Congestive heart failure (CHF) is a common disease requiring admission to hospital among elderly people and is associated with a high mortality rate. The objective of this study was to examine trends in CHF mortality and admissions to hospital in Montreal between 1990 and 1997 for individuals aged 65 years or more. METHODS: We obtained information about deaths from the Quebec Death Certificate Registry database and information about admissions to hospital from the Quebec Med-Echo database. Patients with a primary diagnosis that was classified as ICD-9 code 428 were considered cases of CHF. RESULTS: Although age-adjusted rates of mortality from CHF did not change significantly between 1990 and 1997, the annual rate of admission to hospital for CHF increased from 92 per 10,000 population in 1990/91 to 124 per 10,000 population in 1997/98 (p < 0.01). Deaths due to CHF, expressed as a proportion of all cardiovascular deaths, increased among women from 5.6% in 1990 to 6.2% in 1997 (p = 0.01). The rate of readmission for all causes following a first admission for CHF during that year rose over the study period from 16.6% to 22.0% within one month (p < 0.001) and from 46.7% to 49.4% within 6 months (p = 0.03). Conversely, mean annual length of stay per admission decreased from 16.4 days in 1990/91 to 12.2 days in 1997/98. INTERPRETATION: The increase in rates of admission to hospital for CHF and the stable rates of CHF mortality suggest that the management of CHF and its antecedents has improved in recent years.

Aged↗
PubMed2001

A new critical period for sensory map plasticity.

The development of neural circuits is influenced by sensory experience during restricted critical periods early in life. A novel critical period is demonstrated for plasticity of the whisker map in layer 2/3 of rat primary somatosensory cortex. Sensory experience during this period guides initial formation of whisker receptive fields.

Animals↗
PubMed2001

Risk factors for the development of low back pain in adolescence.

A previous history and earlier onset of low back pain are associated with chronic low back pain in adults, implying that prevention in adolescence may have a positive impact in adulthood. The study objectives were to determine the incidence of low back pain in a cohort of adolescents and to ascertain risk factors. A cohort of 502 high school students in Montreal, Canada, was evaluated during 1995-1996 at three separate times, 6 months apart. The outcome was low back pain occurrence at a frequency of at least once a week in the previous 6 months. Of the 377 adolescents who did not complain of low back pain at the initial evaluation, 65 developed low back pain over the year (cumulative incidence, 17 percent). Risk factors associated with development of low back pain were high growth (odds ratio = 3.09; 95 percent confidence interval (CI): 1.53, 6.01), smoking (odds ratio = 2.20; 95% CI: 1.38, 3.50), tight quadriceps femoris (odds ratio = 1.02; 95% CI: 1.00, 1.05), tight hamstrings (odds ratio = 1.04; 95% CI: 1.01, 1.06), and working during the school year (odds ratio = 1.33; 95% CI: 1.03, 1.71). Modifying such risk factors as smoking and poor leg flexibility may potentially serve to prevent the development of low back pain in adolescents.

Adolescent↗
PubMed2001

'Inverse' melting of a vortex lattice.

Inverse melting is the process in which a crystal reversibly transforms into a liquid or amorphous phase when its temperature is decreased. Such a process is considered to be very rare, and the search for it is often hampered by the formation of non-equilibrium states or intermediate phases. Here we report the discovery of first-order inverse melting of the lattice formed by magnetic flux lines in a high-temperature superconductor. At low temperatures, disorder in the material pins the vortices, preventing the observation of their equilibrium properties and therefore the determination of whether a phase transition occurs. But by using a technique to 'dither' the vortices, we were able to equilibrate the lattice, which enabled us to obtain direct thermodynamic evidence of inverse melting of the ordered lattice into a disordered vortex phase as the temperature is decreased. The ordered lattice has larger entropy than the low-temperature disordered phase. The mechanism of the first-order phase transition changes gradually from thermally induced melting at high temperatures to a disorder-induced transition at low temperatures.

Journal Article↗
PubMed2001

Adaptive axonal remodeling in the midbrain auditory space map.

The auditory space map in the external nucleus of the inferior colliculus (ICX) of barn owls is highly plastic, especially during early life. When juvenile owls are reared with prismatic spectacles (prisms) that displace the visual field laterally, the auditory spatial tuning of neurons in the ICX adjusts adaptively to match the visual displacement. In the present study, we show that this functional plasticity is accompanied by axonal remodeling. The ICX receives auditory input from the central nucleus of the inferior colliculus (ICC) via topographic axonal projections. We used the anterograde tracer biocytin to study experience-dependent changes in the spatial pattern of axons projecting from the ICC to the ICX. The projection fields in normal adults were sparser and more restricted than those in normal juveniles. The projection fields in prism-reared adults were denser and broader than those in normal adults and contained substantially more bouton-laden axons that were appropriately positioned in the ICX to convey adaptive auditory spatial information. Quantitative comparison of results from juvenile and prism-reared owls indicated that prism experience led to topographically appropriate axonal sprouting and synaptogenesis. We conclude that this elaboration of axons represents the formation of an adaptive neuronal circuit. The density of axons and boutons in the normal projection zone was preserved in prism-reared owls. The coexistence of two different circuits encoding alternative maps of space may underlie the ability of prism-reared owls to readapt to normal conditions as adults.

Acoustic Stimulation↗
PubMed2000

Timing-based LTP and LTD at vertical inputs to layer II/III pyramidal cells in rat barrel cortex.

Experience-dependent plasticity in somatosensory (S1) and visual (V1) cortex involves rapid depression of responses to a deprived sensory input (a closed eye or a trimmed whisker). Such depression occurs first in layer II/III and may reflect plasticity at vertical inputs from layer IV to layer II/III pyramids. Here, I describe a timing-based, associative form of long-term potentiation and depression (LTP/LTD) at this synapse in S1. LTP occurred when excitatory postsynaptic potentials (EPSPs) led single postsynaptic action potentials (APs) within a narrow temporal window, and LTD occurred when APs led EPSPs within a significantly broader window. This long LTD window is unusual among timing-based learning rules and causes EPSPs that are uncorrelated with postsynaptic APs to become depressed. This behavior suggests a simple model for depression of deprived sensory responses in S1 and V1.

2-Amino-5-phosphonovalerate↗
PubMed2000

Protein folding in vivo: the importance of molecular chaperones.

The contribution of the two major cytosolic chaperone systems, Hsp70 and the cylindrical chaperonins, to cellular protein folding has been clarified by a number of recent papers. These studies found that, in vivo, a significant fraction of newly synthesized polypeptides transit through these chaperone systems in both prokaryotic and eukaryotic cells. The identification and characterization of the cellular substrates of chaperones will be instrumental in understanding how proteins fold in vivo.

Animals↗
PubMed2000

[Pulsed dye laser vs EKL-Compact lithotriptor in the treatment of distal ureteral lithiasis].

OBJECTIVES: Our results in the treatment of distal ureteral calculus with pulsed dye lasertripsy (Pulsolith) and the EKL-Compact (Olympus) electrokinetic lithotriptor are analyzed. METHODS: The time interval compared was 12 months for both cases; lasertripsy was utilized in 57 and electrokinetic energy in 61 cases. All patients underwent IVP or radiological and/or US evaluation of the urinary tree to determine the size and location of the calculus, and a complete routine presurgical assessment. Epidural anesthesia was administered in all patients, as well as prophylactic antibiotics. The approach and endoscopic technique using the 7.9-9.8 FR ureteroscopes (Olympus), stone removal with long forceps and ureteral dilatation with the Uromat hydraulic pump are described. All but 9 patients had a 5 FR catheter indwelling for 24 hours to avoid the postureteroscopy colic pain caused by perilithiasic ureteral edema. RESULTS: Our success rate was 93% for both modalities of stone fragmentation. Fragmentation with ultrasound was required in 4 cases of failed lasertripsy and 3 cases of failed lithotripsy with electrokinetic energy. There were 7 cases with mucosal laceration from ureteroscope insertion and punctate mechanical perforation of the ureteral mucosa produced by the laser fiber. There were no complications with the use of EKL-C except for small areas of petechiae. CONCLUSION: Analysis of our results for both treatment modalities, as well as their advantages and disadvantages, showed stone fragmentation with the EKL-C to be the treatment of choice. We have utilized this system in our unit since December 1994 because of its efficacy. Furthermore, it is easy to use, to transport inside and outside the hospital, easy to assemble and low-cost.

Adult↗