Single-fiber Technique Research Articles

Conductive Nanocomposite Aligned Fibers of PVA-AgNPs-PEDOT/PSS

Poly (vinyl alcohol)-silver nanoparticles (PVA:AgNPs), and poly (vinyl alcohol)-silver nanoparticles-poly (3, 4-ethylene dioxythiophene)/poly (styrene sulfonate) (PVA:AgNPs: PEDOT/ PSS) were generated as ultra-fine electrospun fibers using the aligned fiber mat and aligned single fiber techniques. SEM and TEM were used to confirm the morphology, diameter size, and fiber alignment of the ultra-fine fibers. A two-probe technique was utilized to assess the electrical conductivity of the ultrafine fibers. The highest conductivity of PVA:AgNPs, (10 %w/v:0.75 %w/v) with a fiber diameter of 0.152 μm, with voltage applied at 17.5 kV within a 20 min collection period in the electrospinning process, was 43.20 S/cm; whereas the highest conductivity of PVA:AgNPs: PEDOT/PSS, (10 %w/v:0.25 %w/v:0.084 %w/v), with a fiber diameter of 0.158 μm and voltage applied at 17.5 kV within a 45 min collection period in the electrospinning process, was 92.18 S/cm.

Increased adipogenic conversion of muscle satellite cells in obese Zucker rats

Visceral and intermuscular adipose tissue (IMAT) depots account for most obesity-related metabolic and cardiovascular complications. Muscle satellite cells (SCs) are mesenchymal stem cells giving rise to myotubes and also to adipocytes, suggesting their possible contribution to IMAT origin and expansion. We investigated the myogenic differentiation of SCs and the adipogenic potential of both preadipocytes and SCs from genetically obese Zucker rats (fa/fa), focusing on the role of Wnt signaling in these differentiation processes. SCs were isolated by single-fiber technique from flexor digitorum brevis muscle and preadipocytes were extracted from subcutaneous adipose tissue (AT). Morphological features and gene expression profile were evaluated during in vitro myogenesis and adipogenesis. Wingless-type MMTV integration site family member 10b (Wnt10b) expression was quantified by quantitative PCR in skeletal muscle and AT. We did not observe any difference in the proliferation rate and in the myogenic differentiation of SCs from obese and lean rats. However, a decreased insulin-induced glucose uptake was present in myotubes originating from fa/fa rats. Under adipogenic conditions, preadipocytes and SCs of obese animals displayed an enhanced adipogenesis. Wnt10b expression was reduced in obese rats in both muscle and AT. Our data suggest that the increase in different fat depots including IMAT and the reduced muscle insulin sensitivity, the major phenotypical alteration of obese Zucker rats, could be ascribed to an intrinsic defect, either genetically determined or acquired, still present in both muscle and fat precursors. The involvement of Wnt10b as a regulator of both adipogenesis and muscle-to-fat conversion is suggested.

Electrical resistivity of electroless nickel coated carbon fibers

Variation of electrical resistivity of electroless nickel-coated carbon fibers heat-treated at different temperatures was investigated. The electrical resistivity was measured using the single fiber technique. Measurement results showed that as the heat treatment temperature increased, the resistivity decreased to a temperature of approximately 300°C. A further increase of heat treatment temperature up to 450°C, however, resulted in an increase of resistivity. Structural study using X-ray diffraction indicated that a large proportion of Ni 3P is formed only above 300°C, which is responsible for the increase of resistivity. Also, the increase of resistivity was found to be more pronounced and occurs at lower temperatures for samples with higher phosphorous content.

Changes of trapezius muscle blood flow and electromyography in chronic neck pain due to trapezius myalgia

Chronic neck pain may increase the transmitter activity of neuropeptides in the upper cervical medulla causing impairment of the blood flow in the local muscle because of a lack of vasodilatatory substances excreted axonally. We have been using a new single-fibre technique for clinical determination of the microcirculation (LDF) in the trapezius muscles in relation to electromyography (EMG). This study pertains to the 76 patients (46 women and 30 men) who received a final diagnosis of chronic trapezius myalgia out of a total series of 300 cases with chronic neck pain which had been remitted to the National Insurance Administration Hospital in Tranås, Sweden, because their complaints interfered with their working ability. The purpose was to derive more objective medical information upon which to base rehabilitation. Sixty percent had continuous pain and 40% had pain after physical effort, or at work. Twenty healthy women volunteered to participate as a normal control group. The right and left trapezius muscles of all individuals were examined simultaneously with laser-Doppler flowmetry (LDF) and surface EMG during a fatiguing series of stepwise-increased contractions, each of 1 min duration with 1 min rest in between. The most painful side was compared with the opposite side in all patients and, in the female patients, also with the right shoulder of the healthy control women. The patients showed consistently low local blood flow in the painful side. The difference was statistically significant at low contraction intensities. Muscle tension was somewhat elevated, as evidenced by a slight increase of the rms-EMG that was statistically significant at high contraction intensities. The mean power frequency (MPF) of the EMG showed no change. The lowered local blood flow was not explained by a changed intramuscular pressure which is low in the trapezius during ordinary activities that do not normally impair the local blood flow (Larsson, S-E., Cai, H. and Öberg, P.Å., Microcirculation in the upper trapezius muscle during varying levels of static contraction, fatigue and recovery in healthy women. A study using percutaneus laser-Doppler flowmetry and surface electromyograpy, Eur. J. Appl. Physiol., 66 (1993) 483–488). We conclude that an impaired regulation of the microcirculation in the local muscle is of central importance in chronic trapezius myalgia, causing nociceptive pain which can be differentiated objectively from neuralgic neck-shoulder pain by the atraumatic technique described.

Differential Nerve Block

Clinically, differential block is manifested by the loss of small fiber mediated sensation (e.g., temperature) two or more dermatomes beyond the sensory limit for large fiber mediated sensations. These observations support the belief that sensitivity to local anesthetics is inversely proportional to axon diameter. This study reports the first measurements of differential sensitivity to lidocaine in individual myelinated and unmyelinated mammalian dorsal root axons. Lumbar dorsal roots and vagus nerves were isolated from anesthetized adult rats and maintained in vitro in a perfusion/recording chamber at 37 +/- 0.3 degrees C. Using single fiber techniques, evoked action potentials in individual myelinated and unmyelinated axons were digitized and recorded for subsequent analysis. Axons were exposed to lidocaine at 150, 260, or 520 microM. Sensitivity to local anesthetic was assessed by measuring the incidence of conduction block and the magnitude of conduction velocity slowing under steady-state conditions. Data were obtained from 77 dorsal root axons and 41 vagal axons. The estimated steady-state EC50 lidocaine concentration for myelinated dorsal root axons (232 microM) was comparable to that for unmyelinated axons (228 microM). Similarly, the incidence of conduction block was not significantly different among dorsal root axon groups. However, unmyelinated dorsal root axons were significantly less sensitive to the conduction velocity slowing effect of lidocaine than their myelinated counterparts (P < 0.01). The incidence of conduction block in short (mean length 13.5 mm) dorsal root axons was not significantly different from that in long (mean length 22.4 mm) axons. Compared with dorsal root axons, the estimated EC50s for vagal myelinated and unmyelinated axons (345 and 285 microM, respectively), while lower were not significantly different. However, the incidence of conduction block at 260 microM lidocaine was significantly lower (16.7% vs. 56.7%; P < 0.05) in vagal myelinated axons. Although no difference in sensitivity to the conduction blocking effects of lidocaine could be demonstrated among dorsal root axons, myelinated axons were more sensitive to the conduction velocity slowing effects of lidocaine. This differential effect cannot explain clinical observations of differential nerve block. Differential sensory block with lidocaine may depend on factors (e.g., physiologic function) related only indirectly to individual axon conduction velocity (diameter).

Patterns of monosynaptic input to the giant interneurons 1?3 in the cereal system of the adult cockroach

1. The cerci of the cockroach Periplaneta americana bear filiform hair mechanoreceptors that are arranged in segmentally repeated rows and longitudinal columns. The monosynaptic connections between receptors of the same column or row and the 3 largest giant interneurons (GIs) were compared using the oil-gap single fibre technique. 2. For many columns, the synaptic efficacy of the afferents decreased gradually from the base to the tip of the cercus, but columns with an inverted gradient or without any gradient were also observed. On the ipsilateral side (relative to the GI axon), the inverted gradients were exclusively found for columns with short proximal hairs. For one column (d) and GI3, the ipsilateral and contralateral gradients were opposite. 3. Monosynaptic EPSPs evoked by stimulating different receptors of the same segment (segment 3) were of very different amplitudes, which partially account for the directional sensitivity of the GIs. Differences in the location, shape and size of the afferent terminals were not sufficient to explain these differences in connection strength. 4. No correlation was found between the size of the EPSPs produced by a sensory neuron and the length of its associated hair.

The effects of surface treatments of fibers on the interfacial properties in single-fiber composites

The interfacial properties between fibers and the matrix contribute to the overall properties in high performance composites. Plasma treatments (Ar, O2, CF4/O2, N2/H2) have been performed on carbon fibers to improve the fiber-matrix interaction. The treatment efficiency was checked by the single-fiber technique, while the surface chemistry and morphology were characterized by X-ray photoelectron spectroscopy (XPS), static secondary ion mass spectroscopy (SSIMS), and scanning electron microscopy (SEM). The O2- and N2/H2-plasma treatments proved most effective both for introducing oxygen-containing functionalities at the fiber surface and for improving the interfacial shear strength of carbon fiber/epoxy composites. A relationship between the oxygen concentration at the fiber surface and the interfacial shear strength is demonstrated.

Single-fiber laser Doppler flowmetry. A method for deep tissue perfusion measurements.

A laser Doppler flowmeter with one optical fibre guiding light to and from the tissue under study has been developed. The outer diameter of the probe equals the optical fibre diameter (0·5 mm). The small size makes it useful for studying the deep tissue perfusion in organs. Differential-channel operation was compared with the single-channel operation and the benefit of this technique was evaluated theoretically as well as in a fluid model resembling tissue perfusion. The signal-to-noise improvement ratio was calculated and found to be related to the number of coherence areas detected and to the broadband noise of the laser. In vivo experiments in the gastrocnemius muscle of the pig were performed to compare the results from the single-fibre technique with those of the electromagnetic flowmeter. Linear regression analysis of femoral blood flow data obtained with the electromagnetic flowmeter and local muscle blood flow measured with the single-fibre technique showed a correlation coefficient of 0·88 (n=36, p<0·001).

Analysis of postinspiratory activity of phrenic motoneurons with chemical and vagal reflexes.

We examined the effects of chemical and reflex drives on the postinspiratory inspiratory activity (PIIA) of phrenic motoneurons using a single-fiber technique. Action potentials from "single" fibers were recorded from the C5 phrenic root together with contralateral mass phrenic activity (also from C5) in anesthetized, paralyzed, and artificially ventilated cats with intact vagus and carotid sinus nerves. Nerve fibers were classified as "early" or "late" based on their onset of discharge in relation to mass phrenic activity during hyperoxic ventilation. Only the early fibers displayed PIIA but not the late fibers, even when their activity began earlier in inspiration with increased chemical drives. Isocapnic hypoxia increased, whereas hyperoxic hypercapnia shortened the duration of PIIA. Pulmonary stretch and "irritant" receptors inhibited PIIA. Hypercapnia and stimulation of peripheral chemoreceptors by lobeline excited both early and late units to the same extent, but hypoxic ventilation had a less marked excitatory effect on late fiber activity. Irritant receptor activation increased the activity of early more than late fibers. Hyperoxic hyperventilation eliminated late phrenic fiber activity, whereas early fibers became tonically active. Bilateral vagotomy abolished this sustained discharge in eight of nine early units, suggesting the importance of vagal afferents in producing tonic firing during hyperventilation. These results suggest that early and late phrenic fibers have different responses to chemical stimuli and to vagally mediated reflexes; late units do not discharge in postinspiratory period, whereas early fibers do; the PIIA is not affected in the same way by various chemical and vagal inputs; and early units that exhibit PIIA display tonic activity with hyperoxic hypocapnia.

Ionophoretic application of acetylcholine on to the dendrites of an identified giant interneurone (GI 1) in the cockroach Periplaneta americana

Acetylcholine was ionophoretically applied within the neuropile of the sixth abdominal ganglion of the cockroach Periplaneta americana and depolarizing responses were recorded from an identified giant interneurone (GI 1) using the oil-gap, single-fibre technique. Estimated peak concentrations in the range 1.0 × 10 −11M − 1.0 × 10 −8 M acetylcholine were present at the receptors, when this putative neurotransmitter was ionophoretically-applied, at threshold doses, to regions of the neuropile containing dendritic branches of GI 1. Using a stepping micro-drive unit for positioning the ionophoretic micropipette, it was shown that profiles of acetylcholine sensitivity correlated with the distribution of dendritic branches of GI 1 revealed by cobalt staining of the cell under test. It is concluded that acetylcholine receptors are widely distributed throughout the dendritic branches of GI 1 in the sixth abdominal ganglion. The results demonstrate the possibility of investigating the effects of locally-applied putative transmitter molecules and pharmacological agents on synaptic membranes of an identified neurone in the central nervous system of an insect.

Address of the president Sir Alan Hodgkin, O.M. at the Anniversary Meeting, 30 November 1973 (Thomas Young).

The Copley Medal is awarded to Professor A. F. Huxley, F. R. S. A. F. Huxley has made outstanding contributions to our knowledge of the nerve impulse and of the mechanism by which muscle fibres are caused to contract. Jointly with Hodgkin, he introduced the powerful method of intracellular recording from nerve cells and showed that during the propagation of an impulse the mem­brane potential reverses its sign, and does not simply fall towards zero as had been widely believed. This work - interrupted by the 1939-45 war, but later resumed - led to the proposal that the impulse arises from a transient influx of sodium ions through the axon membrane. The ‘ionic theory’ of nervous conduction was then established by a series of convincing experiments and calculations for which Huxley later shared the Nobel Prize. Huxley next turned his attention to the mechanism of muscular contraction. He equipped himself for this purpose by inventing a new type of interference microscope. In experiments on living isolated muscle fibres, Huxley showed that contraction is accompanied by a shortening of the isotropic band of each sarco­mere, while the remaining portion (the anisotropic band) retains approximately constant length. His findings complemented the important ultrastructural studies of H. E. Huxley and led them both to propose a ‘sliding filament’ mechanism as the basis of muscular motion. During further microscopic observations on the living muscle fibre, A. F. Huxley produced most striking evidence on the way in which an excitatory potential change of the surface membrane is communicated, through local tubular channels, to the interior of the fibre where it activates the contractile elements. In his most recent work, A. F. Huxley has continued to develop his single-fibre technique to resolve even finer details of the dynamic changes which occur during muscular activity. His work is characterized by a rare combination of profound theoretical insight, mathematical skill and superb technical mastery, all of which has enabled him to select problems of first-rate importance and to pursue them with outstanding success.

Address of the President Sir Alan Hodgkin, O. M. at the Anniversary Meeting, 30 November 1973

The Copley Medal is awarded to Professor A. F. Huxley, F. R. S. A. F. Huxley has made outstanding contributions to our knowledge of the nerve impulse and of the mechanism by which muscle fibres are caused to contract. Jointly with Hodgkin, he introduced the powerful method of intracellular recording from nerve cells and showed that during the propagation of an impulse the membrane potential reverses its sign, and does not simply fall towards zero as had been widely believed. This work – interrupted by the 1939–45 war, but later resumed – led to the proposal that the impulse arises from a transient influx of sodium ions through the axon membrane. The ‘ionic theory’ of nervous conduction was then established by a series of convincing experiments and calculations for which Huxley later shared the Nobel Prize. Huxley next turned his attention to the mechanism of muscular contraction. He equipped himself for this purpose by inventing a new type of interference microscope. In experiments on living isolated muscle fibres, Huxley showed that contraction is accompanied by a shortening of the isotropic band of each sarcomere, while the remaining portion (the anisotropic band) retains approximately constant length. His findings complemented the important ultrastructural studies of H. E. Huxley and led them both to propose a ‘sliding filament’ mechanism as the basis of muscular motion. During further microscopic observations on the living muscle fibre, A. F. Huxley produced most striking evidence on the way in which an excitatory potential change of the surface membrane is communicated, through local tubular channels, to the interior of the fibre where it activates the contractile elements. In his most recent work, A. F. Huxley has continued to develop his single-fibre technique to resolve even finer details of the dynamic changes which occur during muscular activity. His work is characterized by a rare combination of profound theoretical insight, mathematical skill and superb technical mastery, all of which has enabled him to select problems of first-rate importance and to pursue them with outstanding success.

Mode of action of diethyl ether in blocking neuromuscular transmission.

The action of diethyl ether has been studied on frog sciatic nerve-sartorius muscle preparations in vitro using modern single fiber techniques. At a concentration of ether which blocks the indirect twitch, the muscle fibers can be stimulated directly. They have normal resting potentials and the action potentials elicited show only minor changes in form. The neuromuscular block produced by ether is not effectively antagonized by edrophonium or succinylcholine. Ether causes reduction in the amplitude, and prolongation of the time course, of both the end-plate potential, and the miniature end-plate potential. Ether diminishes the sensitivity of the muscle postjunctional membrane to quaternary ammonium compounds such as carbamylcholine. The mechanism of the neuromuscular blocking action of ether differs from that of d-tubocurarine. It is suggested that ether causes changes in the behavior of the permeability controlling mechanisms which are engaged subsequent to receptor site activation.

The taste response of the isolated barbel of the catfish

1. 1. The taste responses from the isolated barbel of the catfish, Parasilurus asotus Linné, were studied electrophysiologically, using single fiber techniques and the electronic summator. 2. 2. The majority of single fibers in the barbels responded to hydrochloric acid and salt, but not to sucrose and quinine. The pattern of relative effectiveness of these substances differed from fiber to fiber and no classification of fiber types was clear. 3. 3. The pattern of effectiveness of monovalent salts, NH 4Cl, NaCl and LiCl, also varied from fiber to fiber. 4. 4. Potassium chloride and calcium chloride of 0·25-1·0 M caused irreversible change in the taste responses. Urethane and cocaine also abolished the taste response.

Microwave Dielectric Measurements on Single Fibers

Microwave techniques which have proved successful at frequencies of 3,000 and 9,300 Mc for the determination of the complex dielectric constant of fiber bundles have been extended to include a frequency of 26,000 Mc, where for the first time measure ments on a single wool fiber have proved to be feasible. Such measurements make it possible to compare directly the results of electrical and mechanical measurements on the same single fiber. In addition, the single-fiber technique has provided a con venient, rapid, and nondestructive method for the determination of the average mass of adjacent 1-cm sections of the fiber along its length. Variations as large as two-fold in mass per unit length are sometimes encountered within a single wool fiber. The occurrence of these variations and their effect upon mechanical measurements are discussed.

Action currents in single afferent nerve fibres elicited by stimulation of the skin of the toad and the cat.

conclusions. With this technique it is easy to record sensory discharges in single nerve fibres which develop overwhelmingly large action potentials or in fibres with especially low threshold for sensory stimuli. It is, however, extremely difficult to explore the behaviour of nerve endings which on stimulation give rise to a limited number of small action potentials, because the discharges in these fibres may be completely masked by those in other predominant fibres. This and other defects of the technique can undoubtedly be circumvented by using a single isolated fibre of the desired size for the experiments. Since 1942 one of. us (LT.), in collaboration with several co-workers who changed from time to time, has devoted much effort to exploring the physiological properties of various sensory nerve endings with the single fibre technique. By means of the experimental set-up we are using now, it is possible to observe afferent impulses in a single nerve fibre, either myelinated