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At least 343 records · Page 19Linked to original sources
PubMed1989

Giant fiber activation of flight muscles in Drosophila: asynchrony in latency of wing depressor fibers.

In Drosophila, brain stimulation of the giant fiber pathway brings about highly stereotyped electrical responses in target muscles involved in the escape response. Both the order of muscle response and the latency of that response are predictable in wild-type flies. The neuronal circuit to the targets is well defined and has been used in the analysis of a number of mutant phenotypes, including induced anomalies in temperature-sensitive (ts) mutations such as shibire (shi). It has been assumed that the stereotyped response includes simultaneous activation of all six fibers of the wing depressor muscle, DLM, resulting in equal latencies for all fibers. We report here a small, but distinct, inherent difference in latency between two sets of DLM fibers in a proportion of two wild-type strains as well as in a strain carrying the ts mutation shi. This difference may occur on one or both sides of an individual, is stable over time, and persists when the motor axon is stimulated peripherally. These results, due to the circuit leading to the target, suggest that the difference in latency arises peripherally. In flies reared at the shi permissive temperature (22 degrees C), the difference is more common in shi than in wild-type flies; however, in shi flies reared at 18 degrees C, the prevalence resembles that of wild-type flies. This indicates a subtle expression of the shi defect even at the presumed permissive temperature of 22 degrees C. The difference in latency is similar to that induced in shi flies whose development is affected by pupal heat pulse. Thus, correct interpretation of differences in latency, e.g., in shi/wild-type mosaic flies or in flies with mutations affecting the GF pathway, requires recognition of the inherent asynchrony that can occur between DLM fibers.

Animals↗
PubMed1998

Subcellular localization of dystrophin and vinculin in cardiac muscle fibers and fibers of the conduction system of the chicken ventricle.

The subcellular localization of dystrophin and vinculin was investigated in cardiac muscle fibers and fibers of the conduction system of the chicken ventricle by immunofluorescence confocal microscopy. In ventricular cardiac muscle fibers, strong staining with antibody against dystrophin appeared as regularly arranged transverse striations at the sarcolemmal surface, and faint but uniform staining was seen in narrow strips between these striations. In fibers of the ventricular conduction system, the sarcolemma was stained uniformly with this antibody, but strong staining was found as regular striations in many areas and as scattered patches in other areas of the sarcolemma. These intensely stained striations and scattered patches of dystrophin were colocalized with those of vinculin. Because dystrophin striations were located at the level of Z bands of the underlying myofibrils, they were regarded as the concentration of this protein at costameres together with vinculin. In fibers of the conduction system, myofibrils were close to the sarcolemma where dystrophin and vinculin assumed a striated pattern, at some distance from the cell membrane where these proteins exhibited a patchy distribution, and distant from the sarcolemma where dystrophin was uniformly distributed. These data suggest that the distribution patterns of dystrophin reflect the degree of association between the sarcolemma and underlying myofibrils.

Amino Acid Sequence↗
PubMed1988

Effect of acclimation temperature on the axon and fiber diameter spectra and thickness of myelin of fibers of the optic nerve of goldfish.

The optic nerves of common goldfish acclimated to 5 and 25 degrees C were fixed with glutaraldehyde in either phosphate buffer or PIPES with EGTA, post-fixed with osmium tetroxide, and examined by electron microscopy. The axon diameter spectra, from axons measured in electron micrographs and those measured on the electron microscope screen, differ noticeably with acclimation temperature. At the lower temperature, there is a definite shift toward the occurrence of larger fibers compared with the spectrum of the 25 degrees C fish. Although the number of fibers assessed is small compared with the total number in the goldfish nerve, these results confirm our previous study. These findings could be attributed to an increase in the number of new fibers during the acclimation to the higher temperature. We discuss this possibility and on the available evidence find it unlikely. Other changes in the axon and fiber are also seen with acclimation temperature. The axon to fiber diameter ratio, made directly from the electron micrographs, shows that axons from the nerves of the higher acclimation temperature fish possess consistently thicker myelin sheaths than are found for axons in nerves of the lower temperature fish. This finding is also in agreement with results obtained by us from measurements independent of each other.

Acclimatization↗
PubMed1988

Effects of psyllium fiber and short-chain organic acids derived from fiber breakdown on colonic epithelial cells from high-risk patients.

The effect of a purified fiber, psyllium and the short-chain organic acids derived from fiber breakdown, were assayed on isolated colonic epithelial cells primary-cultured from patients at high-risk of colon cancer, due to adenoma growth or family history of colon cancer. Psyllium fiber provided colonocytes some protection from deoxycholic acid-induced lysis. Propionic acid, a product of fiber breakdown, was a potent colonocyte mitogen, suggesting that fiber could indirectly protect the colon by providing colonocyte nutrients.

Adult↗
PubMed1993

Are the fine-structural characteristics of mouse hippocampal mossy fiber synapses determined by the density of mossy fiber axons?

Heritable variation of mossy fiber synapses in hippocampal region CA3 was studied in the two inbred mouse strains C3H and CPB-K. Previous Timm studies had shown a larger mossy fiber projection in C3H mice. In contrast, synaptic boutons of CPB-K mice were larger in size and perimeter and were contacted by more dendritic spines than in C3H mice. These results point to an inverse relationship between the size of the mossy fiber projection and the number of spine synapses formed by an individual mossy fiber bouton. Thus, the fiber density of a projection may be crucial for the actual morphology of the synaptic contacts formed.

Animals↗
PubMed1993

The injury response of pulpal NPY-IR sympathetic fibers differs from that of sensory afferent fibers.

Light microscopic immunocytochemistry demonstrated that neuropeptide Y (NPY) containing sympathetic fibers in rat molars did not change morphology or staining characteristics after pulp exposure injury. This result, in combination with recent findings concerning NGF synthesis in injured pulp and NGF-receptor localization on pulpal sensory fibers, suggests that small diameter sensory fibers in pulp may be under NGF control, but NPY containing sympathetic efferent fibers are not. Thus, sympathetic fibers in tooth pulp have a different response to NGF compared to those in many other tissues.

Adrenergic Fibers↗
PubMed1994

Fibers immunoreactive for nerve growth factor receptor in adult rat cortex and hippocampus mimic the innervation pattern of AChE-positive fibers.

Numerous reports have indicated that nerve growth factor (NGF) exerts neurotrophic effects on the cholinergic neurons of the basal forebrain. Receptors for NGF (NGFR) have been demonstrated on cholinergic perikarya in the medial septum, diagonal band of Broca, and basal nucleus of Meynert. These neurons provide the major cholinergic innervation to the cerebral cortex and hippocampus, and previous studies have shown that their terminal plexuses also possess NGFR. However, these studies have shown only isolated examples of immunoreactive fibers. In the present paper we confirm and extend the observation of the presence of NGFR immunoreactivity in the hippocampus and cortex of adult rat by showing the entire plexus and demonstrating that the plexus is strikingly similar to the pattern of cholinergic innervation. Fibers stained for acetylcholinesterase (AChE) and NGFR immunoreactivity were found in all layers of the parietal cortex. Within the hippocampus, fibers were observed in all regions, but were most dense in the strata oriens, pyramidale, and radiatum of hippocampal subfields CA1 and CA3. Particularly intense staining was found throughout the dentate gyrus. Partial transections of the fimbria-fornix, which disrupt fibers projecting from the medial septum to the hippocampus, concomitantly abolish the innervation pattern of both NGFR and AChE. These results provide additional evidence that NGFR are associated with septohippocampal and basocortical cholinergic fibers.

Acetylcholinesterase↗
PubMed1999

Modulatory effect of imetit, a histamine H3 receptor agonist, on C-fibers, cholinergic fibers and mast cells in rabbit lungs in vitro.

The pharmacological mechanisms involved in the interactions between C-fibers, cholinergic fibers and mast cells were investigated in tracheally perfused rabbit lungs by measuring the simultaneous release of substance P and histamine in lung effluents. The amounts of substance P and histamine released in lung superfusates were measured by radioimmunoassay (RIA) after administration of capsaicin and carbachol. Capsaicin (10(-4) M) induced a simultaneous increase in substance P (273 +/- 56% of baseline) and histamine (460 +/- 138%) release. Similarly, carbachol (10(-4) M) caused an increase in the release of both substance P (367 +/- 111%) and histamine (1379 +/- 351%). The effect of capsaicin was prevented by pretreating the lungs with the tachykinin NK1 receptor antagonist SR 140333 (10(-7) M), and atropine (10(-6) M). SR 140333 prevented the carbachol-induced release of substance P but not of histamine. Exogenous substance P induced an increase in histamine release (136 +/- 7%) which was significantly greater in lungs perfused with the neutral endopeptidase inhibitor, thiorphan (10(-5) M) (272 +/- 35%). This effect was prevented by atropine (10(-6) M). Pretreatment of lungs with imetit (5 x 10(-8) M), a selective H3 receptor agonist, prevented the capsaicin-induced release of both mediators. Imetit also blocked the carbachol-induced release of substance P but not of histamine. Exogenous substance P-evoked histamine release was inhibited by imetit. Therefore, it can be concluded that substance P released through the action of capsaicin can activate cholinergic fibers, leading to cholinoceptor stimulation with subsequent activation of C-fibers and mast cells. While the presence of presynaptic H3 receptors modulating substance P-induced acetylcholine release was only surmised, the existence of modulating histamine H3 receptors on C-fibers was confirmed.

Animals↗
PubMed1998

Patches of synchronized activity in the cerebellar cortex evoked by mossy-fiber stimulation: questioning the role of parallel fibers.

The discrepancy between the structural longitudinal organization of the parallel-fiber system in the cerebellar cortex and the functional mosaic-like organization of the cortex has provoked controversial theories about the flow of information in the cerebellum. We address this issue by characterizing the spatiotemporal organization of neuronal activity in the cerebellar cortex by using optical imaging of voltage-sensitive dyes in isolated guinea-pig cerebellum. Parallel-fiber stimulation evoked a narrow beam of activity, which propagated along the parallel fibers. Stimulation of the mossy fibers elicited a circular, nonpropagating patch of synchronized activity. These results strongly support the hypothesis that a beam of parallel fibers, activated by a focal group of granule cells, fails to activate the Purkinje cells along most of its length. It is thus the ascending axon of the granule cell, and not its parallel branches, that activates and defines the basic functional modules of the cerebellar cortex.

Animals↗
PubMed1983

Effects of dietary fiber on mucosal growth and cell proliferation in the small intestine of the rat: a comparison of oat bran, pectin, and guar with total fiber deprivation.

The effects of dietary fiber on small intestinal mucosal mass, morphology, and cytokinetics were studied by feeding three qualitatively different forms of fiber to 40 rats for 4 wk. A fiber-free diet was fed to the control group and a similar diet with either a 20% oat bran, 10% pectin, or 10% guar supplement to the other three groups. All groups of rats exhibited similar caloric intakes and weight gains. Only the guar diet produced a significant increase in mucosal mass, as demonstrated by 19.1% increase in mucosal weight (p less than 0.05), a 16.7% increase in RNA (p less than 0.05) and an increase in DNA from 38.3 +/- 1.8 (SEM) to 44.6 +/- 2.3 micrograms/cm intestine/100 g body weight (p less than 0.05) when compared to the controls. The pectin-diet produced a decrease in villus height from 102.1 +/- 2.4 to 94.3 +/- 2.4 cells but an increase in crypt column length from 25.3 +/- 0.6 to 27.4 +/- 0.4 cells when compared to the controls (p less than 0.05). The shift in labeling index distribution curves for pectin and guar to the right and for oat bran to the left indicated an increase and decrease respectively in labeling index. The higher rate of epithelial cell migration in the pectin- and guar-fed groups shortened their estimated villus cell transit times to 36.4 +/- 0.7 and 37.0 +/- 1.4 h, respectively, when compared with 42.6 +/- 1.2 h in the oat bran and 41.1 +/- 1.0 h in the control (p less than 0.05). These results show that the modulation of small intestinal mucosal structure and growth by dietary fiber appears to be mediated through alterations in cell proliferation and that these changes depend not only on the quantity but also the quality of the fiber present in the diet.

Animals↗
PubMed2001

Mitochondrial DNA deletion mutations colocalize with segmental electron transport system abnormalities, muscle fiber atrophy, fiber splitting, and oxidative damage in sarcopenia.

The in vivo cellular impact of age-associated mitochondrial DNA mutations is unknown. We hypothesized that mitochondrial DNA deletion mutations contribute to the fiber atrophy and loss that cause sarcopenia, the age-related decline of muscle mass and function. We examined 82,713 rectus femoris muscle fibers from Fischer 344 x Brown Norway F1 hybrid rats of ages 5, 18, and 38 months through 1000 microns by serial cryosectioning and histochemical staining for cytochrome c oxidase and succinate dehydrogenase. Between 5 and 38 months of age, the rectus femoris muscle in the hybrid rat demonstrated a 33% decrease in mass concomitant with a 30% decrease in total fibers at the muscle mid-belly. We observed significant increases in the number of mitochondrial abnormalities with age from 289 +/- 8 ETS abnormal fibers in the entire 5-month-old rectus femoris to 1094 +/- 126 in the 38-month-old as calculated from the volume density of these abnormalities. Segmental mitochondrial abnormalities contained mitochondrial DNA deletion mutations as revealed by laser capture microdissection and whole mitochondrial genome amplification. Muscle fibers harboring mitochondrial deletions often displayed atrophy, splitting and increased steady-state levels of oxidative nucleic damage. These data suggest a causal role for age-associated mitochondrial DNA deletion mutations in sarcopenia.

Aging↗
PubMed1977

Degenerating nerve fiber products do not alter physiological properties of adjacent innervated skeletal muscle fibers.

Partial denervation of rat extensor digitorum longus and soleus muscles resulted in the appearance of denervated and innervated surface muscle fibers lying adjacent to one another. The denervated muscle fibers showed the typical signs of denervation while the innervated muscle fibers were similar to those of control muscles. We conclude that denervated fibers do not induce substantial physiological changes in adjacent innervated muscle fibers.

Action Potentials↗
PubMedDate not supplied

Dietary fiber and total enteral nutrition: fermentative assessment of five fiber supplements.

Total enteral nutrition (TEN) formulas supplemented with dietary fiber, typically soy polysaccharide, are in widespread clinical use. Five commercially available dietary fiber supplements obtained from fruits (apple, grapefruit, orange, prune, tomato) were examined for potential use in TEN formulas. In vitro fermentations of 0, 4, 8, 12, and 24 hours' duration with human fecal microbiota from three different donors were conducted to assess colonic fermentative effects. Short-chain fatty acid and hydrogen productions differed significantly with fiber source. The most rapid fermentation rate was with tomato followed by orange, grapefruit, apple, and finally prune fiber. Such differences in fermentability should be considered when fiber sources are selected to supplement TEN formulas.

Dietary Fiber↗
PubMed1997

Digestion and passage kinetics of forage fiber in dairy cows as affected by fiber-free concentrate in the diet.

Four ruminally and duodenally cannulated Holstein cows in early lactation were fed alfalfa [47% neutral detergent fiber (NDF)] or timothy silage (49% NDF) for ad libitum intake in a 4 x 4 Latin square experiment. Forages were supplemented with 8 or 12 kg/d of an essentially fiber-free concentrate to study digestion and passage kinetics of forage fiber in high producing dairy cows. Fractional digestion and passage rates of NDF in the rumen were derived from ruminal pool sizes. Alfalfa had a potentially digestible NDF fraction with a faster rate of digestion but a larger indigestible NDF fraction and, consequently, higher physical fill in the rumen than did timothy. However, dry matter intake did not differ between forages, primarily because of the higher fractional passage rates of alfalfa NDF. Although dry matter intake was 23.2 kg/d, fractional passage rates of forage NDF were generally lower than those usually assumed. Fractional rates of NDF digestion decreased equally for both forages as concentrate in the diet increased, but diets with alfalfa forage had the smallest quantitative reduction because of the markedly smaller ruminal pool size of potentially digestible NDF. The fractional passage rate of NDF decreased as concentrate in the diet increased for diets containing alfalfa but did not change for diets containing timothy. Consequently, as concentrate in the diet increased, digestibilities of NDF in the rumen and whole tract increased with alfalfa and decreased with timothy. Results suggest that fiber-free concentrate is useful when digestion and passage kinetics of specific forage fibers are being measured in high producing dairy cows.

Animal Feed↗
PubMed2001

Early onset of spontaneous activity in uninjured C-fiber nociceptors after injury to neighboring nerve fibers.

Ligation and transection of the L5 spinal nerve in the rat lead to behavioral signs of pain and hyperalgesia. Discharge of injured nociceptors has been presumed to play a role in generating the pain. However, A fibers, but not C fibers, in the injured L5 spinal nerve have been shown to develop spontaneous activity. Moreover, an L5 dorsal root rhizotomy does not reverse this pain behavior, suggesting that signals from other uninjured spinal nerves are involved. We asked if abnormal activity develops in an adjacent, uninjured root. Single nerve fiber recordings were made from the L4 spinal nerve after ligation and transection of the L5 spinal nerve. Within 1 d of the lesion, spontaneous activity developed in approximately half of the C fiber afferents. This spontaneous activity was at a low level (median rate, seven action potentials/5 min), originated distal to the dorsal root ganglion, and was present in nociceptive fibers with cutaneous receptive fields. The incidence and level of spontaneous activity were similar 1 week after injury. The early onset of spontaneous activity in uninjured nociceptive afferents could be the signal that produces the central sensitization responsible for the development of mechanical hyperalgesia. Because L4 afferents comingle with degenerating L5 axons in the peripheral nerve, we hypothesize that products associated with Wallerian degeneration lead to an alteration in the properties of the adjacent, uninjured afferents.

Action Potentials↗
PubMed1991

Anesthetics and automaticity in latent pacemaker fibers: I. Effects of halothane, enflurane, and isoflurane on automaticity and recovery of automaticity from overdrive suppression in Purkinje fibers derived from canine hearts.

Knowledge of arrhythmic or antiarrhythmic actions of anesthetics on automaticity of latent pacemaker fibers has relevance to the intraoperative management of patients with bradyarrhythmia due to sinus node dysfunction or heart block. The authors determined the effects of halothane, enflurane, and isoflurane on automaticity and recovery of automaticity from overdrive suppression in canine Purkinje fibers derived from normal hearts. Purkinje fibers were superfused with a modified Krebs' solution (37 degrees C) containing epinephrine (2 or 15 microM) and equilibrated with a 97% O2-3% CO2 gas mixture (control). Transmembrane action potentials (AP) were recorded using standard microelectrode techniques. Purkinje fibers were then exposed to anesthetics at vaporizer settings of 0.75 or 1.5% (halothane), 1.75 or 3.5% (enflurane), and 1 or 2% (isoflurane), which were equivalent to measured superfusate concentrations of 0.22 or 0.47 mM (halothane), 0.44 or 0.94 mM (enflurane), and 0.28 or 0.53 mM (isoflurane). Compared to control, there was no significant effect of either concentration of the anesthetics on upstroke (phase 0) depolarization, AP amplitude or duration (50% repolarization), or maximum diastolic potential. All three anesthetics increased spontaneous rate. The increase in rate with all three anesthetics was due to enhanced diastolic depolarization (rate dV/dt, phase-4 depolarization). Recovery times from overdrive suppression were determined after 30 or 60 s of pacing at drive cycle lengths of 800, 500, and 400 ms and only at higher anesthetic concentrations. Recovery of automaticity was shortened by halothane only in slowly paced fibers exposed to the lower concentration of epinephrine. Under all other conditions recovery times were not affected by halothane.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed2000

Reactive extraction of penicillin G in hollow-fiber and hollow-fiber fabric modules.

Penicillin G (Pen G) can be rapidly extracted in hollow-fiber liquid-liquid contactors using N-lauryl-N-trialkylmethylamine (Amberlite LA-2) as the extractant. n-Butylacetate is much better than decanol as a diluent for such an extraction, although decanol can give a partition coefficient four times larger. The overall mass transfer coefficient found is a function of aqueous flow on the lumen side of the fiber, and is less dependent on shell-side flow. In backextraction, the overall mass transfer coefficient determined is only one tenth that of the forward extraction, primarily because the hydrophobic hollow fibers used have a high mass transfer resistance under these conditions. The mass transfer experiments show that hollow-fiber extraction of Pen G is competitive with centrifugal extraction. The prospects for extraction of other fermentation products with hollow fibers can be estimated based on the present study.

Amines↗
PubMed2000

Effect of Fiber-Polymer Interactions on Fracture Toughness Behavior of Carbon Fiber-Reinforced Epoxy Matrix Composites.

The effect of anodic oxidation on high-strength polyacrylonitrile-based carbon fibers has been studied in terms of fiber surface energetics and fracture toughness of the composites. According to contact angle measurements based on the wicking rate of a test liquid, anodic oxidation leads to an increase in surface free energy, mainly due to the increase of its specific (or polar) component. For the carbon-fiber-reinforced epoxy resin matrix system, a direct linear relationship is shown between the specific component and the critical stress intensity factor measured by the single edge notched beam fracture toughness test. From a surface-energetic point of view, the anodic treatment may be suitable for carbon fibers incorporated in a polar organic matrix, resulting in an increased specific component of the surface free energy. Good wetting plays an important role in improving the degree of adhesion at interfaces between fibers and matrices of the resulting composites. Copyright 2000 Academic Press.

Journal Article↗