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At least 1,423 records · Page 79Linked to original sources
PubMed1994

The influence of different electrode configurations on the inhibitory effect of subthreshold high-frequency stimuli.

Subthreshold stimuli trains may inhibit the response to a subsequent suprathreshold stimulus; the inhibitory effect decreases or even disappears when the subthreshold stimuli are delivered apart from the suprathreshold stimulus. The purpose of this study is to analyse, in atrial epicardium, the influence of different electrode configurations upon the inhibitory effect of subthreshold stimuli trains delivered at a short distance from the explored zone. In 18 anaesthetized dogs, the basal atrial effective refractory period was determined using an epicardial unipolar cathodal electrode. A second determination was performed when a subthreshold stimuli train (1 ms cathodal pulses, 800 Hz, and intensity 10% less than the diastolic threshold of the train) was delivered prior to the extrastimulus through: (a) 8 electrodes equidistant (4.5 mm) from the central test electrode (Group 1, n = 5); (b) a 1 mm wide ring electrode, 2.5 mm from the central test electrode (Group 2, n = 7); and (c) a 3.5 mm wide ring electrode, 2.5 mm from the central test electrode (Group 3, n = 6). A third determination was performed in all experiments delivering both the subthreshold stimuli train and the extrastimulus through the same central test electrode. Atrial effective refractory period did not vary significantly with respect to the basal values in Group 1 (141 +/- 22 vs 142 +/- 25 ms; ns) though it increased in Group 2 (168 +/- 27 vs 142 +/- 18 ms; P < 0.01) and in Group 3 (160 +/- 20 vs 133 +/- 25 ms; P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Effect of anodal high voltage pulsed current on edema formation in frog hind limbs.

We have recently demonstrated that some forms of cathodal high voltage pulsed current (HVPC) curb posttraumatic edema formation in frog hind limbs. The purpose of this study was to determine, by assessing the capacity of anodal HVPC to curb posttraumatic edema formation, whether polarity is an important variable. Fourteen anesthetized bullfrogs were placed on large dispersive electrodes lining body slings that maintained the frogs' limbs in a dependent position throughout data collection. The frogs' feet were traumatized by impact following initial measurement of limb volumes. At the commencement of each of four 30-minute treatments, hind limbs were immersed in separate beakers and briefly stimulated until motor threshold was determined. One limb, randomly selected, received anodal HVPC at 90% of motor threshold and 120 pulses per second; the other limb served as a control. Treatments were followed by 30-minute rests. Limb volumes were measured by water displacement immediately after trauma and following each treatment and rest period. Data were expressed as changes from pretrauma volumes in milliliters per kilogram of body weight. A repeated-measures analysis of variance was used to test for treatment effect. Despite an aggressive series of treatments, virtually symmetrical bilateral edema occurred; therefore, no treatment effect was evident. This result contrasts with treatment effects previously reported for cathodal HVPC.

Analysis of Variance↗
PubMed1992

Influence of high voltage pulsed current on edema formation following impact injury in rats.

High voltage pulsed current (HVPC) has been shown to be effective in curbing posttraumatic edema formation in frogs. The purpose of this study was to establish the utility of HVPC in controlling edema formation in a mammalian model. Both feet of 20 anesthetized rats were traumatized following initial determination of hind-limb volumes. Four 30-minute cathodal HVPC treatments at 120 pulses per second and 90% of visible motor threshold interspersed with 30-minute rest periods were applied to one randomly selected hind limb of each rat via the immersion technique. The other hind limb served as a control. Limb volumes were measured after each treatment and rest period. All data were expressed as changes from pretrauma limb volumes in milliliters per kilogram of body weight; these data were analyzed by repeated-measures analyses of variance and post hoc paired t tests. Volumes of untreated limbs were significantly greater than volumes of treated limbs after the second treatment. Evidence of significant treatment effects in frogs, and now rats, provides a compelling rationale for initiating trials of efficacy of cathodal HVPC in inhibiting acute edema formation in humans.

Animals↗
PubMed2004

BNCT microdosimetry at the tapiro reactor thermal column.

A thermal column is available for dosimetric and radiobiological studies by the fast reactor TAPIRO, located at the ENEA research centre Casaccia. The TAPIRO neutron field has been studied (in the frame of LNL BNCT project) with a tissue-equivalent proportional counter, which has worked alternatively with an ordinary tissue-equivalent cathode and with a boron-enriched cathode. Measurements have been performed with polyethylene caps of different thickness. Both the absorbed dose and the microdosimetric-calculated biological effective dose show a maximum at approximately 0.5 mg cm(-2) of depth. The different dose components have been calculated and the results are discussed.

Body Burden↗
PubMed2001

External modulation of visual perception in humans.

Static and dynamic contrast sensitivities (sCS and dCS) were evaluated before, during, immediately after and 10 min after anodal and cathodal transcranial direct current stimulation (tDCS) applied to the occipital cortex of 15 healthy subjects. Using 4 c/d spatial and 4 Hz temporal frequencies significant sCS and dCS loss was found during and immediately after 7 min cathodal stimulation while anodal stimulation had no effect. Ten minutes after the end of the stimulation the sCS and dCS values had reached the baseline levels. Our results show that primary visual functions, such as contrast detection can be transiently altered by transcranial weak direct current stimulation, most probably modulating neural excitability, as has been shown in the motor cortex previously. The present study also support the view that this method using weak current can be a non-invasive promising tool to induce reversible focal changes in the nervous system.

Adult↗
PubMed2006

Contralateral and ipsilateral motor effects after transcranial direct current stimulation.

Transcranial direct current stimulation over the left motor area influenced both contralateral and ipsilateral finger sequence movements in seven healthy adults. Effects for the two hands were reversed: anodal stimulation improved right-hand performance significantly more than cathodal stimulation, whereas cathodal stimulation improved left-hand performance significantly more than anodal stimulation. The results show that stimulating a motor region directly, or indirectly by modulating activity in the homologous region on the opposite hemisphere, can affect motor skill acquisition, presumably by facilitating effective synaptic connectivity. This outcome provides evidence for the role of interhemispheric inhibition in corticomotor functioning, and also has implications for treatment methods aimed at facilitating motor recovery after stroke.

Electric Stimulation↗
PubMedDate not supplied

Newly developed drug delivery system in cancer chemotherapy using direct electric current.

To improve the antitumor effect of chemotherapy on a target organ, we experimentally investigated pharmacokinetic alteration of methotrexate (MTX) induced by an electric current in rats to ascertain whether the local concentration of MTX could be enhanced while reducing the concentration in blood. Six male Wistar rats had platinum electrodes introduced into both kidneys. Three rats were subjected to direct current (3.5 V, 50 microA) for 3 hours, while another three control rats received no current. While providing the current to the treated group, all of the rats were intravenously injected with MTX at a dose of 1 mg/kg. The MTX concentration in urine (excreted from each ureter) and serum was measured by fluorescence polarization immunoassay. Cumulative MTX renal excretion rate was significantly higher in the cathode than anode side in the treated group (p < 0.01). Serum MTX concentration at 0 to 5 min was significantly reduced in the treated group (p < 0.03). The first part of the area under the curve (i.e., alpha curve) was markedly increased in the treated group versus controls (p = 0.05). Electric therapy using a slight direct current could gather anionized MTX to the cathode, while reducing MTX concentration in the serum of experimental rats.

Animals↗
PubMed1991

Electric modification of kidney function. The excretion of radiographic contrast media and adriamycin.

The body consists of systems of conductive pathways for ionic flow of current induced by metabolic or injury potentials among tissues and cells. In vivo electrophoresis in biologically closed electric circuits (BCEC) are coupled to the mechanical transports of blood and lymph. Connections also exist with conductive media such as cerebrospinal fluid, bile, and urine. Artificial induction of current was applied over the kidneys in order to study modification of kidney function. It is thought that studies of this kind will increase our understanding of kidney function from a new angle of view and possibly add new therapeutic possibilities. In anesthetized pigs, one kidney was made anodic (electropositive) and the other cathodic (electronegative). Current was applied between electrodes in each ureter. Intravascularly injected, electronegatively charged aminotrizoate and ioxaglate were excreted mainly by the anodic kidney. Nonionic iohexol was urographically excreted by both kidneys. Excretion of electropositively charged Adriamycin by the cathodic kidney was identified macroscopically and by chemical analysis. Functional effects on the kidneys can be induced electrophoretically without causing injury.

Animals↗
PubMed1988

Facilitated regeneration in the rat peripheral nervous system using applied electric fields.

The efficacy of applied electric fields in promoting regeneration of the transected and frozen rat sciatic nerve was studied. Three groups were studied at 6, 12, and 18 days post-lesion; nerves treated with 1.5 microA of direct current where the cathode was oriented distal to the lesion, nerves treated with the anode distal to the lesion, or no current delivered to the nerve. Regeneration in this severely damaged mammalian peripheral nerve model was quantitated by counting fluorescent antibody profiles to neurofilament protein distal to the lesion site. The results indicated that only cathodal current, applied distal to the lesion, significantly increased the rate of regeneration compared to controls. Such results help to elucidate mechanisms by which electric fields can facilitate regeneration in the mammalian nervous system.

Animals↗
PubMed1988

Therapeutic effects of silver nylon dressings with weak direct current on Pseudomonas aeruginosa-infected burn wounds.

The therapeutic and prophylactic effects of nylon dressings coated with metallic silver in a direct current circuit have been examined in a rat model of fatal burn wound sepsis. Male Sprague-Dawley rats weighing 325 +/- 25 grams with 20% full-thickness scald injuries were used. Therapeutic effects were examined at 4 or 24 hours after surface inoculation with a lethal dose of Pseudomonas aeruginosa (Strain 59-1244). When used as a surface anode with an implanted silver needle cathode, the silver nylon was therapeutic at currents between 0.4 and 40 microA when applied at either test time and continued for 5 days (p less than 0.001). When used as a cathode, silver nylon was not effective. Nylon cloth without a silver metal coating was not effective without applied current or when used as an anode. Silver nylon dressings placed at 4 hours after inoculation but without applied current showed significant effectiveness (p less than 0.01). This effect, however, was significantly less than that seen with silver nylon used as an anode (p less than 0.001). Barrier prophylactic effects were examined by placing silver nylon or uncoated nylon on burn wounds before inoculation with Pseudomonas aeruginosa. The uncoated nylon had no barrier effect. Silver nylon was found protective but applied current was not required for significant (p less than 0.001) barrier effect. These results indicate silver nylon dressings may be a valuable antimicrobial burn wound covering device.

Animals↗
PubMed1987

Mechanisms of nervous propagation along central motor pathways: noninvasive evaluation in healthy subjects and in patients with neurological disease.

Motor evoked potentials (MEPs) to scalp stimulation have been obtained in 45 control patients and in 70 patients with neurological diseases. Optimal responses were obtained through a pericranial cathode consisting of 6 to 12 regularly spaced, interconnected pericranial cathodal discs whose resistance was carefully balanced with that of a stimulating anodal disc placed on the appropriate scalp region. The foci of maximal response for proximal and distal upper limb muscles as well as for lower limb muscles were localized. The scalp to cervical cord central conduction time (CCT) along motor tracts governing the hand muscles was 5.21 +/- 0.42 ms. This index was highly correlated with the subject's height and stable in time when repeatedly tested. Collision between orthodromically and antidromically propagated motor impulses was obtained. Response facilitation was achieved by means of prestimulus voluntary contraction of the target muscle, continuous vibration of its tendon, or scalp stimulation with paired shocks. The presence of a premovement facilitation of MEPs was also demonstrated, as was the presumed presence of transcallosal facilitation. An efferent volley secondary to scalp stimulation was recorded from the nerve trunk. Abnormalities in MEP characteristics as well as in CCTs were found in patients with multiple sclerosis, amyotrophic lateral sclerosis, cord compression, and degenerative diseases of the central nervous system.

Adult↗
PubMed1988

Use of exogenous electric current in the treatment of delayed lesions in peripheral nerves.

A commonly observed clinical problem following nerve injury is the incomplete recovery of function associated with the formation of a neuroma in continuity. In the present study, exogenous direct electric current was tested for its ability to promote growth of axons through a neuroma-like lesion. Neuroma-like structures were created by crushing rat sciatic nerves at two sites 4 mm apart and applying phenol to the intermediate region. A bulbous axonally impenetrable structure is formed 3 weeks later. At that time, silicone cuffs were sewn onto the nerve proximal to the phenol application site and 7 mm distally. In experimental groups, cuffs were attached to wires leading to a subcutaneously implanted Traxon power source, the distal cuff being cathodal. In control groups, cuffs were not electrically connected. In electrically active groups, substantial numbers of myelinated axons were seen distal to the cathode 3 weeks after implantation. Four times fewer fibers were observed in control groups. Footprint patterns from electrically active animals revealed a significant improvement over control neuroma preparations, as quantitated using the Sciatic Functional Index.

Animals↗
PubMed1987

Development of porcine pancreatic hydrolases and their isoenzymes from the fetal period to adulthood.

The appearance and activity of various porcine pancreatic hydrolases were studied during fetal and postnatal development. Quantitatively, the enzyme activities in activated pancreas homogenates were low but increased during the second half of the fetal period, using the substrates Bz-Arg-pNA for measuring anodal and cathodal trypsin, Suc-Phe-pNA (chymotrypsin A and C, and elastase II) and Suc-(Ala)3-pNA (elastase I and protease E). Postnatally, after an initial decrease during the first week, the enzyme activities increased markedly, especially from 10-14 weeks to 6 months. The individual hydrolases were identified after electrophoretic separation in agarose gel and staining with various substrates either directly in the gel or after transfer to nitrocellulose membranes (enzymoblotting). During the fetal period, chymotrypsin A and B, elastase II, carboxypeptidase A, and amylase appeared at approximately 65 days and anodal trypsin, at approximately 76 days. After birth, new proteinases appeared after the first week including chymotrypsin C, cathodal trypsin, and protease E, whereas elastase I was found from 5 weeks after birth. Concomitantly, unidentified "fetal proteinase(s)" with caseinolytic, Ac-Phe-beta NE and CBZ-Ala-beta NE activities began to diminish and disappeared 10-14 weeks after birth. This study showed a marked increase in the overall pancreatic enzyme activities, as well as an age-dependent expression of the variety of pancreatic hydrolases during porcine ontogeny.

Aging↗
PubMedDate not supplied

Characterization of hemoglobin Hotel Dieu in a Puerto Rican adolescent.

PURPOSE: Hemoglobin Hotel Dieu (HbHD) is a high-oxygen affinity variant of HbA never before reported in a Hispanic patient. This Hb variant was first reported in 1981 by Blouquit et al. in a white person with erythrocytosis with a substitution in the beta 99 aspartic acid residue by glycine. METHODS: A 13-year-old Puerto Rican boy had pain in his chest, headaches, easy fatigability, and high Hb (as high as 19.1 g/dl). Protein analysis was performed by cellulose acetate, citrate agar, and isoelectric focusing electrophoresis and high-pressure liquid chromatography (HPLC), polymerase chain reaction (PCR) amplification, and DNA sequencing of the second exon of the beta gene in samples obtained from the mother, father, and the patient, and DNA fingerprinting to determine paternity. RESULTS: The variant found in the patient migrated on cellulose acetate electrophoresis to a cathodic position relative to HbF, and a band cathodal to HbA and close to HbF on isoelectric focusing electrophoresis. The patient showed an abnormal well-resolved peak on HPLC with a retention time slightly shorter than that for HbS. DNA analysis by direct sequencing of the PCR product demonstrated heterozygosity for codon 99 (GAT-->GGT) in the patient but not in either parent. DNA fingerprinting by multiplex PCR amplification of three simple tandem repeat loci showed that the patient shared alleles in all three loci with both parents, ruling out nonpaternity. CONCLUSIONS: The protein and DNA analysis indicate that the erythrocytosis is caused by the presence of HbHD in this Hispanic adolescent.

Adolescent↗
PubMed2004

Oscillatory brain activity and transcranial direct current stimulation in humans.

The aim of this study was to induce changes of the oscillatory activity in the visual cortex of healthy human subjects by modulation of neuronal excitability using weak transcranial direct current stimulation (tDCS). tDCS is a non-invasive stimulation method which induces prolonged, polarity-dependent increases or reductions in cortical excitability. An increase in high frequency oscillatory activity in the beta and gamma frequency ranges is closely related in time to the N70 peak of the primary visual evoked potential (VEP), which is an early sensory component of visual activation. Therefore this potential can be used to observe tDCS-induced changes related to oscillatory activity. VEPs were recorded using sinusoidal luminance gratings in an on/off mode before, immediately after and 10, 20, 30 min after the end of 10 min anodal or cathodal stimulation. Cathodal stimulation significantly decreased while anodal stimulation slightly increased the normalized beta and gamma frequency powers. We have shown here that tDCS transiently and reversibly changed the organized cortical activity elicited by visual stimulation. Since gamma activity is also related to a higher level of information processing, tDCS might be a suitable method to affect higher order cognitive processes.

Adult↗
PubMed2005

Transcranial direct current stimulation of the unaffected hemisphere in stroke patients.

Recovery of function after a stroke is determined by a balance of activity in the neural network involving both the affected and the unaffected brain hemispheres. Increased activity in the affected hemisphere can promote recovery, while excessive activity in the unaffected hemisphere may represent a maladaptive strategy. We therefore investigated whether reduction of the excitability in the unaffected hemisphere by cathodal transcranial direct current stimulation could result in motor performance improvement in stroke patients. We compared these results with excitability-enhancing anodal transcranial direct current stimulation of the affected hemisphere and sham transcranial direct current stimulation. Both cathodal stimulation of the unaffected hemisphere and anodal stimulation of the affected hemisphere (but not sham transcranial direct current stimulation) improved motor performance significantly. These results suggest that the appropriate modulation of bihemispheric brain structures can promote motor function recovery.

Aged↗
PubMed2006

Testing for causality with transcranial direct current stimulation: pitch memory and the left supramarginal gyrus.

Neuroimaging studies have implicated the left supramarginal gyrus in short-term auditory memory processing, including memory for pitch. The present study investigated the causal role of the left supramarginal gyrus in short-term pitch memory by comparing the effects of cathodal transcranial direct current stimulation when applied over the left or right supramarginal gyrus with sham transcranial direct current stimulation. Only cathodal transcranial direct current stimulation over the left supramarginal gyrus had a detrimental effect on short-term pitch-memory performance in 11 adult participants. These results provide support for the important role of the left supramarginal gyrus in short-term memory for pitch information, and they further demonstrate the potential of transcranial direct current stimulation to modulate the functional contribution of a brain area to a particular cognitive process.

Analysis of Variance↗
PubMed1990

Influence of applied electrical fields on yeast and hyphal growth of Candida albicans.

Yeast cells of Candida albicans which had been attached to polylysine-coated microscope slides were induced to form buds or germ tubes in the presence of external electrical fields. The sites of budding and germ tube formation and the growth of germ tubes and hyphal branches were polarized preferentially towards the cathode. Buds were not converted to pseudohyphae or germ tubes by the field and the field had no effect on the positioning of nuclei or septa in the yeast cell or germ tube. Buds were less polarized than germ tubes at any given applied voltage. The polarization of buds reached a peak at an electrical field of 12 mV per cell. Polarization of germ tubes was biphasic, increasing rapidly with increasing field strengths up to 5 mV per cell, and then more slowly in stronger fields. An electrical field was only required for a fraction of the time taken for germ tubes to start to form, so cells retained a memory of experiencing an electrical field which influenced the selection of sites of evagination. Increasing the electrical field delayed the time of germ tube evagination and inhibited the rate of germ tube extension. Unlike previous findings with other filamentous fungi, germ tubes grew unidirectionally towards the cathode for extended periods and did not deviate to a perpendicular orientation. This result suggests that the septal pore of the filamentous form may have high electrical resistance and would act as an effective barrier to solute transport between intercalary compartments.

Candida albicans↗