Bullfrog Sciatic Nerve Research Articles

Fractal relaxation model with a nonlinear diffusion coefficient for fitting anomalous diffusion data in magnetic resonance imaging

In this paper a relaxation model of signal attenuation in diffusion-weighted magnetic resonance imaging (dMRI) with varying diffusion coefficient in terms of fractal derivative is proposed, in which the diffusion coefficient is a power law of the effective diffusion time. The relaxation model provides measures of diffusion constant, fractal dimension of diffusive trajectory of water molecule and the time power-law behavior of the diffusion coefficient. The proposed model was used to describe the magnetic resonance attenuation signal of the bullfrog sciatic nerve, and the corresponding spectral entropy was calculated to detect the environmental complexity in bullfrog sciatic nerve for water molecular diffusion. The results showed that the fractal derivative relaxation model (the VDC model) can accurately depict the diffusion pattern of water molecules in complex heterogeneous biological media at large b values. The VDC model provides an alternative theoretical reference for biological tissue detection based on time-dependent diffusion of water molecules.

Theoretical simulation of the selective stimulation of axons in different areas of a nerve bundle by multichannel near-infrared lasers.

Damaged nerve function can be repaired by applying external stimuli, and the selective stimulation of nerve fibers is the highest goal of nerve functional repair. This paper proposes a method of using multichannel near-infrared lasers to achieve the selective stimulation of axons in different areas in a mixed nerve bundle. An exposed bullfrog sciatic nerve was considered the object of study to realize the selective stimulation. A model was established by using COMSOL Multiphysics to simulate the temperature distribution of nerves under multichannel near-infrared laser stimulation. The results of this model showed that by changing the distance between the laser fiber and the nerve (d) or the power of the 4 lasers (P), the axons at different parts of the nerve bundle may be selectively stimulated. If only the axons located in the center are selected to be activated, it is necessary to set the d and P value in the four directions to the same value. If only axons on the nerve edge are selected for activation, we can reduce the d value of the nearest laser (or increase P) and increase the d value of lasers in other directions (or decrease P). If only axons in the shallow area below the surface between the two lasers are selected for activation, it is necessary to reduce the d value of the laser in two directions close there (or increase P) and increase the d value of the laser in the other two directions (or decrease P). If only the axons of the superficial region on the coordinate axis are activated, the d value of the laser in the farthest direction can be increased (or decrease P) and the d value of the other three lasers can be reduced (or increase P). Moreover, the results of animal experiments further verify the feasibility of our method to realize selective activation of the axons.

System Design and Experimental Research of Neural Signal Blocking based on Spike Trapping Principle.

Different neural signal blocking technologies provide potential therapy for various diseases caused by pathological or involuntary neural activities. In this paper, a novel neural signal blocking concept based on spike-trapping principle is introduced. The blocking system was designed and implemented. In the system, a compound action potential was induced by a proximal stimulus, and a blocking signal was generated after a neural signal was detected, which was applied to the distal end of the nerve to block the nerve conduction. The reliability of the system was verified on bullfrog sciatic nerve gastrocnemius muscle specimens. The optimal blocking signal parameters, the relationship between nerve diameter and blocking threshold voltage, and the nerve safety of blocking signals were explored. The experimental results show that the system is possible to block a pathological or involuntary neural signal automatically. The average voltage of block threshold and the minimum pulse width are -1.66 V and 120 ms, respectively. The blocking threshold decreases as the diameter of the nerve increases. The blocking signals at the threshold level are safe for the stimulated nerve.

Selective stimulation of bullfrog sciatic nerve by gold nanorod assisted combined electrical and near-infrared stimulation.

Selective stimulation of the nervous system is an important way to improve the therapeutic efficacy and minimize side effects. This paper introduces an improved method using combined electrical and near-infrared stimulation to realize selective excitation and inhibition of different sciatic nerve branches. Both the electrical stimulation and the near-infrared laser are added to the main trunk of the sciatic nerve, and gold nanorods are injected into the light irradiation point of the nerve to increase the absorption of light. Two cuff recording electrodes are added to the two sciatic nerve branches, respectively. The compound nerve action potential recorded by the cuff electrode is transmitted to the physiological signal instrument. In the experiment, selective activation and inhibition of the two nerve branches are achieved by adjusting the electrical stimulation parameters, the light stimulus parameters and the location of the light. These results demonstrate that combined electrical and near-infrared stimulation, which can effectively activate or suppress the different nerve fibers in the nerve fiber bundle, is suitable for selective regulation of peripheral nerve. Meanwhile, the photoelectric combined stimulation can reduce both the electrical energy and light energy needed for the stimulation, and reduce the electrical damage and light damage to the nerve.

Propagation of Action Potential Mediated by Microtubules May Involve in The Neural Quantum Mechanism

The traditional thoughts hold that action potential is a basis of neural information transmission. Previous studies have found that microtubules are structurally connected to some ion channels such as the subunits of sodium, potassium and calcium channels on axons, suggesting that microtubules may be related to the propagation of action potential. Moreover, recent studies have demonstrated that microtubule system network in the brain may be involved in the mechanism of photon quantum brain and the origin of consciousness. These studies indicate that the structural integrity of microtubules is closely related to the action potential. However, the detailed relationship between microtubules and action potential is not clear. Here, we found that the compound action potentials of bullfrog sciatic nerve were inhibited significantly by colchicine, a microtubule depolymerizer. The inhibitory effects presented time-dependent changes and even reached to a decrease of 57% after treatment for 480 min with 20 mM Colchicine. These results suggest that the propagation and transmission of action potentials are related to the stability of microtubule system and may involve in the neural quantum mechanism.

MRI-based assessment of function and dysfunction in myelinated axons

Repetitive electrical activity produces microstructural alteration in myelinated axons, which may afford the opportunity to noninvasively monitor function of myelinated fibers in peripheral nervous system (PNS)/CNS pathways. Microstructural changes were assessed via two different magnetic-resonance-based approaches: diffusion fMRI and dynamic T2 spectroscopy in the ex vivo perfused bullfrog sciatic nerves. Using this robust, classical model as a platform for testing, we demonstrate that noninvasive diffusion fMRI, based on standard diffusion tensor imaging (DTI), can clearly localize the sites of axonal conduction blockage as might be encountered in neurotrauma or other lesion types. It is also shown that the diffusion fMRI response is graded in proportion to the total number of electrical impulses carried through a given locus. Dynamic T2 spectroscopy of the perfused frog nerves point to an electrical-activity-induced redistribution of tissue water and myelin structural changes. Diffusion basis spectrum imaging (DBSI) reveals a reversible shift of tissue water into a restricted isotropic diffusion signal component. Submyelinic vacuoles are observed in electron-microscopy images of tissue fixed during electrical stimulation. A slowing of the compound action potential conduction velocity accompanies repetitive electrical activity. Correlations between electrophysiology and MRI parameters during and immediately after stimulation are presented. Potential mechanisms and interpretations of these results are discussed.

Gold nanorod-assisted near-infrared stimulation of bullfrog sciatic nerve.

Infrared neural stimulation (INS) is a new and developing approach for neural repair, with the advantages of being non-contact, spatially precise, and artifact-free. However, the disadvantage of infrared light is that it is difficult to stimulate deep tissue because of its weak penetrating power. Therefore, this paper introduces an improved method using near-infrared laser to stimulate bullfrog sciatic nerves because of its strong penetrating power. Meanwhile, gold nanorods (Au NRs) are injected into the nerve to increase the absorption of light. The mechanism is the instantaneous temperature rise caused by the absorption of infrared light by Au NRs. The compound muscle action potential (CMAP) associated with the irradiated sciatic nerve is recorded by a multi-channel physiological signal instrument. The peak to peak amplitude (Vpp) of CMAP for sciatic nerves injected with Au NRs increases significantly compared to the CMAP for control nerves without Au NRs. These results demonstrate INS by labeling nerves with nanoparticle exhibiting latent capacity to increase the efficiency, spatial resolution, and the neural responsivity, and especially, can increase the penetration depth and reduce the requisite radiant exposure level.

Self-Powered Nanocomposites under an External Rotating Magnetic Field for Noninvasive External Power Supply Electrical Stimulation.

Electrical stimulation in biology and gene expression has attracted considerable attention in recent years. However, it is inconvenient that the electric stimulation needs to be supplied an implanted power-transported wire connecting the external power supply. Here, we fabricated a self-powered composite nanofiber (CNF) and developed an electric generating system to realize electrical stimulation based on the electromagnetic induction effect under an external rotating magnetic field. The self-powered CNFs generating an electric signal consist of modified MWNTs (m-MWNTs) coated Fe3O4/PCL fibers. Moreover, the output current of the nanocomposites can be increased due to the presence of the magnetic nanoparticles during an external magnetic field is applied. In this paper, these CNFs were employed to replace a bullfrog's sciatic nerve and to realize the effective functional electrical stimulation. The cytotoxicity assays and animal tests of the nanocomposites were also used to evaluate the biocompatibility and tissue integration. These results demonstrated that this self-powered CNF not only plays a role as power source but also can act as an external power supply under an external rotating magnetic field for noninvasive the replacement of injured nerve.

Model study of combined electrical and near-infrared neural stimulation on the bullfrog sciatic nerve.

This paper implemented a model study of combined electrical and near-infrared (808nm) neural stimulation (NINS) on the bullfrog sciatic nerve. The model includes a COMSOL model to calculate the electric-field distribution of the surrounding area of the nerve, a Monte Carlo model to simulate light transport and absorption in the bullfrog sciatic nerve during NINS, and a NEURON model to simulate the neural electrophysiology changes under electrical stimulus and laser irradiation. The optical thermal effect is considered the main mechanism during NINS. Therefore, thermal change during laser irradiation was calculated by the Monte Carlo method, and the temperature distribution was then transferred to the NEURON model to stimulate the sciatic nerve. The effects on thermal response by adjusting the laser spot size, energy of the beam, and the absorption coefficient of the nerve are analyzed. The effect of the ambient temperature on the electrical stimulation or laser stimulation and the interaction between laser irradiation and electrical stimulation are also studied. The results indicate that the needed stimulus threshold for neural activation or inhibition is reduced by laser irradiation. Additionally, the needed laser energy for blocking the action potential is reduced by electrical stimulus. Both electrical and laser stimulation are affected by the ambient temperature. These results provide references for subsequent animal experiments and could be of great help to future basic and applied studies of infrared neural stimulation (INS).

SPR imaging combined with cyclic voltammetry for the detection of neural activity

Surface plasmon resonance (SPR) detects changes in refractive index at a metal-dielectric interface. In this study, SPR imaging (SPRi) combined with cyclic voltammetry (CV) was applied to detect neural activity in isolated bullfrog sciatic nerves. The neural activities induced by chemical and electrical stimulation led to an SPR response, and the activities were recorded in real time. The activities of different parts of the sciatic nerve were recorded and compared. The results demonstrated that SPR imaging combined with CV is a powerful tool for the investigation of neural activity.

Post stimulus effects of high frequency biphasic electrical current on a fibre's conductibility in isolated frog nerves

Objective. High frequency biphasic (HFB) electrical currents are widely used in nerve blocking studies. Their safety margins largely remain unknown and need to be investigated. Approach. This study, exploring the post stimulus effects of HFB electrical currents on a nerve's conductibility, was performed on bullfrog sciatic nerves. Both compound action potentials (CAPs) and differential CAPs (DCAPs, i.e. control CAPs subtracted by CAPs following HFB currents) were obtained, and N1 and N2 components, which were the first and second upward components of DCAPs, were used for analyses of the effects introduced by HFB electrical stimulation. Main results. First, HFB currents of 10 kHz at a completely blocking threshold were applied for 5 s. The maximum amplitudes and conducting velocities of the CAPs were significantly (P < 0.02) decreased within the observed period (60 s) following HFB currents. The DCAPs displayed clear N1 and N2 components, demonstrating respectively the losses of the fibres' normal conductibility and the appearances of new delayed conductions. Decreases of N1 amplitudes along time, regarded as the recovery of the nerve's conductibility, exhibited two distinct phases: a fast one lasting several seconds and a slow one lasting longer than 5 min. Further tests showed a linear relationship between the HFB stimulation durations and recovering periods of N1 amplitudes. Supra-threshold blocking did not cause higher N1 amplitudes. Significance. This study indicates that HFB electrical currents lead to long lasting post stimulus reduction of a nerve's conductibility, which might relate to potential nerve injuries. A possible mechanism, focusing on changes in intracellular and periaxonal ionic concentrations, was proposed to underlie the reduction of the nerve's conductibility and potential nerve injuries. Greater caution and stimulation protocols with greater safety margins should be explored when utilizing HFB electrical current to block nerve conductions.

Investigation of the Mechanism of Polar Excitations on Frog Sciatic Nerve by Optical Stimulation

We observed nerve excitations on bullfrog sciatic nerves by an optical stimulation using a Holmium YAG (Ho:YAG) laser with the laser power over 2.0 [W]. The laser power was higher the amplitude of the action potential was bigger. However, when the laser power over 10.0 [W], the laser gave damage to the sciatic nerve and the action potential decreased. Not only the action potential was evoked by the high temperature but also the sciatic nerve was damaged by an overlarge temperature. These results show the possibility that the single wavelength laser can use to position estimation of epileptogenic focus and irreversible blocking of propagation of epilepsy seizure.

ウシガエルの坐骨神経を用いたパルス磁気刺激の局在性の検討

ウシガエルの坐骨神経を用いたパルス磁気刺激の局在性の検討

Effect of 1.5 T steady magnetic field on neuroconduction of a bullfrog sciatic nerve in a partially active state within several hours after extraction

The bullfrog sciatic nerve within six hours after extraction was determined from the change with time in the action potential and the impedance to be a partially active nerve. Steady magnetic fields have been determined to be ineffective in the neuroconduction in the fresh nerve just after extraction. Although ion motions involved in the neuroconduction in the partially active nerve are not normal, it was confirmed that a 1.5 T steady magnetic field is ineffective in the neuroconduction in the partially active nerve. The obtained results suggest that the neuroconduction in damaged nerves is not affected by the 1.5 T steady magnetic field used in MRI.

Differential contribution of Na +-K + pump and K + conductance to the post-tetanic hyperpolarization of the subtypes of tetrodotoxin-resistant C-fibers in the isolated bullfrog sciatic nerve

The post-tetanic hyperpolarizations (PTHPs) of the fast and slow tetrodotoxin-resistant (TTX-R) C-fibers were recorded from isolated bullfrog sciatic nerves using a modified vaseline gap method. Under control solutions, the monophasic fast and slow TTX-R C-fibers compound action potentials (C-CAPs) increased in amplitude up to 133.9±17.9% (mean±SD; n=9) and 167.0±41.5% ( n=7), respectively, shortly after tetanic stimulation. The recovery time constants of the fast and slow ones were 66.5 and 101.2 s, respectively. Significant differences between the rates of amplitude augmentation of the fast and slow TTX-R C-CAPs were found for the most pairs of measured points ( P<0.05 or P<0.01). After application of ouabain solutions, the augmentation of the fast TTX-R C-CAP was inhibited to an insignificant level, while that of the slow TTX-R C-CAP remained significant with the recovery time constant being 90.9 s. After additional application of TEA, the post-tetanic augmentation of the slow TTX-R C-CAP was blocked. These results suggest that Na +-K + pump contributes to the PTHPs of the fast and slow TTX-R C-fibers and that K + conductance contributes only to the PTHP of the slow TTX-R C-fibers, indicating differential modulation of the firing rate of each TTX-R C-fibers group.

Evidence for the involvement of Na +-K + pump and K + conductance in the post-tetanic hyperpolarization of the tetrodotoxin-resistant C-fibers in the isolated bullfrog sciatic nerve

The post-tetanic hyperpolarizations (PTHPs) were recorded from the isolated bullfrog sciatic nerves using a modified vaseline gap method. Repetitive stimulation of tetrodotoxin-resistant (TTX-R) C-fibers produced frequency- and activity-dependent PTHPs. The ouabain solutions (0.1 mM), the solutions (0.1 mM ouabain+2 mM tetraethylammonium (TEA)) and 5 mM TEA solutions reduced the PTHP amplitude to 56.2±10.7% (mean±SD, n=9), to 37.0±12.3% ( n=8), to 76.0±10.9% ( n=5) of the control value, respectively. Each pair of the three solutions revealed a significant difference in their effects on the PTHP ( P<0.01). Furthermore, the Li–Ringer solutions and the solutions (Li–Ringer+2 mM TEA) reduced the PTHP amplitude as well, thus resembling ouabain effects. These results strongly suggest that the repetitive stimulation of TTX-R C-fibers activates the membrane Na +-K + pump resulting in a major part of the PTHP and induces TEA-sensitive K + conductance composing a minor part of the PTHP, which might modulate repetitive firing of TTX-R C-fibers.

Tetrodotoxin-resistant Na + spikes of C fibers have at least two subtypes in the isolated bullfrog sciatic nerve

The C fiber compound action potentials (C-CAPs) were studied for their properties with the vaseline gap method from the isolated bullfrog sciatic nerve. Two components (the fast and the slow C-CAPs) were found to be Na + dependent and tetrodotoxin-resistant. The conduction velocities of the fast and the slow C-CAPs were 0.61±0.06 m/s ( n=13) and 0.42±0.05 m/s ( n=8), respectively; their time constants were 11.4±1.7 ms and 16.3±1.7 ms, respectively, with both parameters being significantly different at P<0.01. The slow C-CAP had about 1.3 times higher threshold than that of the fast C-CAP, with a significant difference ( P<0.01). They showed differential sensitivity to lidocaine and Cd 2+. Capsaicin reduced the amplitudes of both fast and slow C-CAPs, but not abolished. These findings indicate that C fibers have at least two subtypes with different properties.

C fiber generates a slow Na + spike in the frog sciatic nerve

The present study was carried out to examine the properties of A and C fibers in the bullfrog sciatic nerves by applying several agents through perfusing solutions between stimulating and recording electrodes. The compound action potentials (CAPs) of A β and A δ fibers were tetrodotoxin (TTX)-sensitive and were abolished in Na +-free solution. However, C fiber CAP was TTX-insensitive although CAP disappeared in Na +-free solution. Moreover, C fiber CAP was not blocked by Ca 2+ channel blockers and its chronaxy (2 ms) and conduction velocity (0.70 m/s) indicate that the time constant of C fiber CAP is relatively large (2.88 ms). These suggest that a slow Na + channel, which is TTX-resistant, contributes to C fiber action potentials.

Does nerve impulse activity modulate fast axonal transport?

The possibility that the amount of newly synthesized material made available for fast axonal transport is regulated by nerve impulse activity was examined in an in vitro preparation of bullfrog dorsal root ganglia (DRG) and sciatic nerve. Under conditions that precluded effects of impulse activity on either uptake or incorporation of precursor, patterned stimulation of the sciatic nerve (1 out of every 2 s) produced a frequency- and time-dependent decrease in the amount of radiolabeled protein accumulating at a nerve ligature. The response to patterned stimulation was significantly greater than that to continuous stimulation when the same number of stimuli were delivered. In unligated nerve preparations, patterned stimulation decreased the amplitude of the transport profile with no concomitant change in the wave front distance. Nerve stimulation produced no observable ultrastructural alterations within neuronal cell bodies of the DRG. We propose that the physiological significance of these results is not that nerve impulse activity decreases fast axonal transport, but that the amount of transport increases during periods of electrical quiescence. According to this hypothesis, activity-dependent macromolecules of the axolemma and nerve terminals are replenished during periods when the neuron is firing less frequently. These findings are discussed in light of reports that chronic in vivo stimulation increases the amount of fast-transported, radiolabeled protein (Chan et al., 1989) and that TTX-blockade of neuronal activity has no effect on protein transport (Edwards and Grafstein, 1984; Riccio and Matthews, 1985).

Heat production associated with a propagated impulse in bullfrog myelinated nerve fibers.

By using heat-sensors constructed with thin film of polyvinylidene fluoride, it was found possible to detect the heat generated by myelinated fibers in the bullfrog sciatic nerve in association with a propagated impulse. The quantity of heat generated (about 0.4 microcal/g at 4.5 degrees C) is roughly two orders of magnitude smaller than that observed in nerves containing only non-myelinated nerve fibers. The smallness of the heat observed is attributed to the localization of the heat sources at the nodes of Ranvier. The major portion of the heat generated is re-absorbed by the nerve.