Hz Rms Research Articles

Multi-scale modelling of location- and frequency-dependent synaptic plasticity induced by transcranial magnetic stimulation in the dendrites of pyramidal neurons.

Repetitive transcranial magnetic stimulation (rTMS) induces long-term changes of synapses, but the mechanisms behind these modifications are not fully understood. Although there has been progress in the development of multi-scale modeling tools, no comprehensive module for simulating rTMS-induced synaptic plasticity in biophysically realistic neurons exists.. We developed a modelling framework that allows the replication and detailed prediction of long-term changes of excitatory synapses in neurons stimulated by rTMS. We implemented a voltage-dependent plasticity model that has been previously established for simulating frequency-, time-, and compartment-dependent spatio-temporal changes of excitatory synapses in neuronal dendrites. The plasticity model can be incorporated into biophysical neuronal models and coupled to electrical field simulations. We show that the plasticity modelling framework replicates long-term potentiation (LTP)-like plasticity in hippocampal CA1 pyramidal cells evoked by 10-Hz repetitive magnetic stimulation (rMS). This plasticity was strongly distance dependent and concentrated at the proximal synapses of the neuron. We predicted a decrease in the plasticity amplitude for 5 Hz and 1 Hz protocols with decreasing frequency. Finally, we successfully modelled plasticity in distal synapses upon local electrical theta-burst stimulation (TBS) and predicted proximal and distal plasticity for rMS TBS. Notably, the rMS TBS-evoked synaptic plasticity exhibited robust facilitation by dendritic spikes and low sensitivity to inhibitory suppression. The plasticity modelling framework enables precise simulations of LTP-like cellular effects with high spatio-temporal resolution, enhancing the efficiency of parameter screening and the development of plasticity-inducing rTMS protocols.

High-Frequency Repetitive Magnetic Stimulation Activates Bactericidal Activity of Macrophages via Modulation of p62/Keap1/Nrf2 and p38 MAPK Pathways.

The effects of repetitive magnetic stimulation (rMS) have predominantly been studied in excitable cells, with limited research in non-excitable cells. This study aimed to investigate the impact of rMS on macrophages, which are crucial cells in the innate immune defense. THP-1-derived macrophages subjected to a 5 min session of 10 Hz rMS exhibited increased Nrf2 activation and decreased Keap1 expression. We found that activation of the Nrf2 signaling pathway relied on rMS-induced phosphorylation of p62. Notably, rMS reduced the intracellular survival of Staphylococcus aureus in macrophages. Silencing Nrf2 using siRNA in THP-1-derived macrophages or utilizing Nrf2 knockout in alveolar macrophages abolished this effect. Additionally, rMS attenuated the expression of IL-1β and TNF-α inflammatory genes by S. aureus and inhibited p38 MAPK activation. These findings highlight the capacity of rMS to activate the non-canonical Nrf2 pathway, modulate macrophage function, and enhance the host's defense against bacterial infection.

Frequency-specific effects of repetitive magnetic stimulation on primary astrocyte cultures.

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive technique that uses magnetic pulses over the cranium to induce electrical currents in underlying cortical tissue. Although rTMS has shown clinical utility for a number of neurological conditions, we have only limited understanding of how rTMS influences cellular function and cell-cell interactions. In this study, we sought to investigate whether repeated magnetic stimulation (rMS) can influence astrocyte biology in vitro. We tested four different rMS frequencies and measured the calcium response in primary neonatal astrocyte cultures. We also tested the effect of rMS on astrocyte migration and proliferation in vitro. We tested 3 to 4 culture replicates and 17 to 34 cells for each rMS frequency (sham, 1 Hz, cTBS, 10 Hz and biomemetic high frequency stimulation - BHFS). Of all frequencies tested, 1 Hz stimulation resulted in a statistically significant rise in intracellular calcium in the cytoplasmic and nuclear compartments of the cultured astrocytes. This calcium rise did not affect migration or proliferation in the scratch assay, though astrocyte hypertrophy was reduced in response to 1 Hz rMS, 24 hours post scratch injury. Our results provide preliminary evidence that rMS can influence astrocyte physiology, indicating the potential for a novel mechanism by which rTMS can influence brain activity.

P292 10 Hz rTMS induces long-term depression of GABAergic neurotransmission

Question The cellular and molecular mechanisms of rTMS-induced neural plasticity remain not well understood. Recent experimental evidence obtained in mouse brain slice cultures disclosed that 10 Hz repetitive magnetic stimulation (rMS) induces long-term potentiation (LTP) of excitatory neurotransmission. These studies support the notion that rTMS acts through the induction of ‘LTP-like’ plasticity. Here, we tested whether rTMS increases cortical excitability by mediating long-term depression (LTD) of inhibitory neurotransmission. Methods Immunohistochemistry, fluorescence recovery after photobleaching, GABA-uncaging experiments and paired whole-cell patch clamp recordings were used in entorhino-hippocampal slice cultures to study the effects of 10 Hz rMS on structural and functional properties of inhibitory synapses of CA1 pyramidal neurons. Results We report that 10 Hz rMS reduces dendritic but not somatic GABAergic neurotransmission onto CA1 pyramidal neurons. These functional changes are accompanied by structural remodeling of inhibitory postsynapses and depend on the activation of voltage gated sodium channels, L-type voltage gated calcium channels, NMDA-receptors, and calcineurin protein phosphatases. Consistent with these findings, a reduction in gephyrin cluster sizes and numbers is detected in CA1 stratum radiatum 2 h after 10 Hz rTMS of anaesthetized mice. Conclusion rMS appears to be a potent tool to induce Ca 2+ -dependent structural and functional changes of both excitatory and inhibitory synapses. We propose that 10 Hz rTMS may shift excitation/inhibition-balance in neuronal networks by inducing LTP of excitatory and LTD of inhibitory neurotransmission. (Supported by DFG and Federal Ministry of Education and Research, Germany; GCBS-WP1.)

P300 Repetitive magnetic stimulation reverses the synaptic phenotype of cultured rat CA1 pyramidal neurons in a maternal immune activation model of schizophrenia

Question Gestational infection is a risk factor for psychiatric disorders. Accordingly, preclinical models of maternal immune activation (MIA) have been developed to study effects of gestational infection on neural and behavioral dysfunction in the offspring. Considering that early pre-symptomatic stages of schizophrenia may affect hippocampal circuits, we here established a hippocampal ‘organotypic in vitro MIA model’ based on the well-established polyinosinic-polycytidylic acid [Poly(I:C)] model of schizophrenia. We studied alterations in synaptic neurotransmission and tested whether repetitive magnetic stimulation (rMS) influences alterations in synaptic excitation/inhibition-balance in this model. Methods Entorhino-hippocampal slice cultures were prepared from litters of Poly(I:C) or vehicle-only injected pregnant dams. The effects of 10 Hz rMS on MIA associated alterations in synaptic properties were assessed in CA1 pyramidal neurons using whole-cell patch clamp recordings. Results Our experiments disclose an increase in inhibitory synaptic strength, while excitatory synapses on CA1 neurons are not changed in slice cultures prepared from Poly(I:C) offspring. This difference is also observed in cultures prepared from cross-fostered animals, thus confirming that gestational infection triggers the synaptic phenotype. Since our recent work has demonstrated that 10 Hz rMS can shift synaptic excitation/inhibition-balance toward excitation, we employed this rMS protocol to test whether we can influence the synaptic phenotype in the Poly(I:C) group. Indeed, 10 Hz rMS reversed the increased inhibitory synaptic strength without affecting excitatory synapses in MIA slice cultures. Conclusion These results suggest that rMS may exert positive effects under pathological conditions by restoring physiological synaptic excitation/inhibition-balance. We propose that ‘organotypic in vitro MIA models’ may serve as preclinical drug and intervention screening assays to evaluate and learn more about rTMS-based treatment strategies in psychiatric diseases associated with gestational infection. (Supported by Federal Ministry of Education and Research, Germany (BMBF, GCBS-WP1: 01EE1403B).).

Effect of magnetic stimulation in spinal cord on limb angiogenesis and implication: a pilot study.

ObjectiveTo investigate the effect of repetitive magnetic stimulation (rMS) of the spinal cord on limb angiogenesis in healthy rats and explore its implication for the treatment of lymphedema.MethodTwelve adult male Sprague-Dawley rats were divided into four groups as follows: sham rMS followed by tissue harvest 5 minutes later (group 1, n=2), 1 Hz rMS and tissue harvest 5 minutes later (group 2, n=3), 20 Hz rMS and tissue harvest 5 minutes later (group 3, n=3), 20 Hz rMS and tissue harvest 30 minutes later (group 4, n=4). Animals were treated with 20-minute rMS with 120% of the motor threshold on their left side of upper lumbar spinal cord. Expression of angiogenic factors, that is, Akt, phospho-Akt (pAkt), endothelial nitric oxide synthase (eNOS), phospho-eNOS (p-eNOS) were measured by western blot. Bilateral hindlimb muscles (quadriceps and gastrocnemius) were harvested.ResultsExpression of Akt in left quadriceps increased in group 4 compared with group 2 and 3 (3.4 and 5.3-fold each, p=0.026). Expression of eNOS in left plus right quadriceps markedly increased in group 3 and 4 compared with group 1 and 2 (p=0.007). Expressions of eNOS, Akt and p-eNOS, pAkt in gastrocnemius were not comparable between four groups (p>0.05).ConclusionRepetitive magnetic stimulation of the spinal cord may exert an angiogenic effect closely linked to lymphangiogenesis. It has clinical implication for the possible therapy of lymphedema caused by breast, cervical or endometrial cancer operation. Future studies with the specific lymphatic endothelial cell markers are required to confirm the effect of rMS on lymphangiogenesis.

Abstract A47: Possible effect of repetitive magnetic stimulation of the spinal cord on the limb angiogenesis in healthy rats and its clinical implication for the treatment of lymphedema

Abstract Objective: To investigate the effect of repetitive magnetic stimulation of the spinal cord on limb angiogenesis in healthy rats and explore its implication for the treatment of lymphedema. Methods: Twelve adult male Sprague-Dawley rats were divided into four groups as follows: sham repetitive magnetic stimulation (rMS) followed by tissue harvest 5 minutes later (group 1, n=2), 1 Hz rMS and tissue harvest 5 minutes later (group 2, n=3), 20Hz rMS and tissue harvest 5 minutes later (group 3, n=3), 20Hz rMS and tissue harvest 30 minutes later (group 4, n=4). Animals were treated with 20-minute rMS with 120% of the motor threshold on their left side of upper lumbar spinal cord. Expression of angiogenic factors, that is, Akt, phospho-Akt, endothelial nitric oxide synthase (eNOS), phospho-eNOS were measured by Western blot. Bilateral hindlimb muscles (quadriceps and gastrocnemius) were harvested. Results: Expression of eNOS in quadriceps muscle was markedly increased in group 3 and 4 (6.4 and 7.7-fold each compared with group 1, p=0.04). Also, expression of eNOS in gastrocnemius muscle was increased in group 2 and 3 than in group 1 (p=0.02). Expression of Akt in gastrocnemius muscle tends to increase in rMS- treated groups than in sham rMS group (p>0.05). Expression of phospho-Akt and phospho-eNOS were not comparable between four groups (p>0.05). Conclusion: Repetitive magnetic stimulation of the spinal cord may exert an angiogenic effect closely linked to lymphangiogenesis. It has clinical implication for the possible therapy of lymphedema caused by breast, cervical or endometrial cancer operation. Future studies with the specific lymphatic endothelial cell markers are required to confirm the effect of repetitive magnetic stimulation on lymphangiogenesis. Citation Information: Clin Cancer Res 2010;16(14 Suppl):A47.

Low-noise electrometer and its low-noise cryogenic probe with completely guarded sample chamber

We describe a low-noise cryogenic probing system capable of measuring currents at the femtoAmpere (fA) level with integration time ⩽1 s and current noise spectra at the 1 fA/√Hz level with the sample cooled to cryogenic temperatures. The system consists of a low-noise electrometer and a low-noise cryogenic probe with completely guarded sample chamber. The low-noise electrometer has amplification of 0.1 V/1 pA with f3 dB=70 Hz, 1.1 V/pA with f3 dB=20 Hz, and/or 10.1 V/pA with f3 dB=1.4 Hz, and input current noise power density of 0.4 fA/√Hz rms and input voltage noise power density of ≈0.3 μV/√Hz rms at 1 Hz frequency. With the cryogenic probe, the entire measurement system has input current noise of 0.8 fA/√Hz rms at 1 Hz. The completely guarded sample chamber reduces parasitic conductance to <10−16 S and parasitic capacitance to ⩽15 fF between pairs of pins for current–voltage measurements. With this instrumentation, we are able to characterize the current and current noise of quantum well infrared photodetectors for sensitive zero-background applications.

Passive, light intensity-independent interferometricmethod for fibre Bragggrating interrogation

The authors describe a passive technique for sensing the strain-induced wavelength shift of a fibre Bragg grating (FBG) using a Mach-Zehnder interferometer that utilises a 3/spl times/3 coupler. Laboratory data show that a resolution of /spl sim/10 n/spl epsiv///spl radic/(Hz) RMS is achievable with inherent insensitivity to source intensity variations.

Novel nulling/balancing technique for fiber optic magnetic gradiometer

A technique for balancing a fiber-optic magnetic gradiometer configured as a Mach-Zehnder interferometer is presented. The method uses different dither frequencies for nulling the DC field experienced by each transducer and a third frequency common to both transducers for detecting the gradient. The method overcomes the hysteresis when each transducer is separately nulled, and the balance is performable in real time. Noise spectra are shown in the near DC and a gradient sensitivity of 0.14 gamma /ft- square root Hz RMS at 0.22 Hz is demonstrated. This is believed to be the most sensitive direct measurement of a magnetic field gradient by a fiber-optic sensor that has been reported. >

Precision optical-frequency-difference measurements.

We demonstrate a new form of interferometry which is independent of Maxwell's equations and measures optical frequency differences rather than wavelength ratios. Stable laser and electro-optic FM sideband techniques make a direct measurement of the mode spacing of a high finesse cavity with subhertz precision (0.4 Hz rms) over a 50-THz region. Experiments indicate errors below ${10}^{\mathrm{\ensuremath{-}}10}$ over a 50-THz bandwidth and that improvements of several orders of magnitude are possible. New variables for interferometry simplify the use of multilayer dielectric mirrors and are directly measurable in situ. .AE

A fast-response field tracking proton magnetometer for field programming and plotting

A commercially available Robinson NMR oscillator has been adapted to provide a high-speed field tracking proton magnetometer covering the range 2.4-4.7 kG. Particular features of the instrument are an inherent search characteristic with search rates as high as 350 G s-1, and a 2 ms response time to field changes using 217 Hz field modulation of only 1.8 G peak to peak. Extremely high locking accuracy is achieved with the oscillator frequency deviation less than 1.3 Hz RMS in a constant field. This performance is made possible by using a new type of detector which measures each resonance position independently, and which is inherently free of zero drifts and systematic offsets. The instrument is designed as a sampled-data system, and it can achieve the forward transfer function G(z)=1/(z-1) giving complete error correction in one half cycle of the modulation. Measured and theoretical responses to a step function of magnetic field are compared. A frequency to voltage converter is incorporated which enables high-resolution ESR spectra to be plotted as a function of field. The instrument also serves as a very flexible field programmer and has proved valuable in locking the magnetic field to the address ramp of a signal accumulation over long periods.

The Measurement of Oscillator Noise at Microwave Frequencies

Improved measurement methods are presented for measuring both AM noise and FM noise from microwave oscillators, The Schottky barrier diode detector is used to measure AM noise 170 dB below the carrier in a 1 Hz bandwidth. A new discriminator is presented that has a measurement threshold below 0.001 Hz rms in a 1 Hz bandwidth. The use of a storage oscilloscope and wave analyzer to study noise modulation is discussed. The new discriminator and storage oscilloscope can be used for short-term stability measurements for intervals up to 100 seconds.

A Microwave System for Measurements of AM and FM Noise Spectra

This paper describes a noise measuring system with a high degree of flexibility in regard to video frequency coverage as well as radio frequency coverage. Noise systems for S, X, and Ku-bands were constructed to obtain high sensitivity at spectral frequencies from several Hz to 30 MHz off the carrier. The measured limiting sensitivities of the X-band set over the video range 20 Hz to 325 kHz with an input power of 10 mW are --145 dB for AM noise and 0.02 Hz rms for FM noise in a 100-Hz measuring bandwidth.