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At least 109 records · Page 6Linked to original sources
PubMed1989

Differential effects of cholinergic drugs on discriminative cues and self-stimulation produced by electrical stimulation of the ventral tegmental area.

Cholinergic receptors have been shown to modulate a subset of discriminative cues produced by electrical stimulation of the ventral tegmental area (VTA) in rats. The present study identified the specific cholinergic receptor type modulating these electrical brain-stimulation (EBS) cues, and assessed whether these receptors also mediated the rewarding effects of VTA EBS. The EBS cues were enhanced by the acetylcholinesterase inhibitor physostigmine and the muscarinic receptor agonists pilocarpine and RS-86, whereas the nicotinic receptor agonist nicotine had no effect. The enhancing effects of pilocarpine or RS-86 were attenuated by the muscarinic antagonist scopolamine. The EBS cues were not affected when scopolamine was injected alone, although high doses disrupted discriminated responses. Intracranial self-stimulation (ICSS) rates were depressed by physostigmine and pilocarpine and increased by nicotine and scopolamine. These results indicated a facilitatory influence of muscarinic receptors on the EBS cues, and an inhibitory role in VTA ICSS. Nicotinic receptor activation did not affect the EBS cues, but facilitated ICSS. These differential effects of cholinergic receptor activation point to a dissociation of the specific EBS cues measured in this study from the rewarding effects of VTA stimulation.

Animals↗
PubMed1983

Effects of feedback stimulation training and cyclical electrical stimulation on knee extension in hemiparetic patients.

Positional feedback stimulation training and cyclical electrical stimulation were used in combination as a treatment for facilitating knee extension in hemiparetic patients. Forty adult hemiparetic patients who demonstrated minimal active control of their quadriceps femoris muscles were randomly assigned to control or study groups. The control patients received a program of physical therapy, and the study patients received the positional feedback stimulation training in addition to their therapy program. The stimulation training provided the patient with immediate auditory and visual feedback of his changing joint angle while he voluntarily extended his knee. When the patient reached a near maximal extension effort, electrical stimulation of the quadriceps femoris muscle was automatically triggered, completing the patient's available range of motion in extension. The stimulation training was supplemented with two hours of cyclical electrical stimulation daily. At the end of four weeks, analysis revealed a statistically significant increase in knee extension torque and active synergistic range of motion in the study group. No change was noted in their ability to extend their knees using isolated quadriceps femoris muscle control. This study suggests that positional feedback stimulation training is effective when used to augment a facilitation program for improving knee extension control in hemiparetic patients.

Adult↗
PubMed1985

Efflux of 3H-5-hydroxytryptamine from rat hypothalamic slices by continuous electrical stimulation: frequency-dependent responses to serotonergic antagonists and 5-hydroxytryptamine.

Rat hypothalamic slices were incubated with 3H-5-hydroxytryptamine and superfused in the presence of paroxetine to inhibit 5-hydroxytryptamine (5-HT) reuptake. The slices were continuously stimulated electrically with rectangular pulses at varying frequencies. Continuous stimulation for up to 42 min at 1 Hz or at 3 Hz evoked a steady efflux of tritium that slowly decayed with time. The efflux produced by continuous stimulation at 5 Hz declined more rapidly with time. Continuous stimulation at 1 Hz in the presence of increasing concentrations of unlabelled 5-HT produced a concentration-dependent decrease in tritium efflux. The presence of methiothepin (0.5 mumol/l), quipazine (10 mumol/l) and (-)- but not (+)-propranolol (1 mumol/l) attenuated this response to 5-HT. From these data, the apparent pA2 values were calculated and found to be in agreement with published values. Frequency-dependent responses were determined using a "cumulative stimulation" protocol whereby the slices were subjected to three consecutive 14 min periods of stimulation at increasing frequencies (1, 3 and then 5 Hz). Unlabelled 5-HT (1 mumol/l) inhibited electrically-evoked tritium efflux more at 1 than at 5 Hz. Methiothepin (0.5 mumol/l) and quipazine (10 mumol/l) enhanced the stimulated efflux in a manner inversely related to the frequency of stimulation. Neither (+)- nor (-)-propranolol enhanced stimulated tritium efflux at any of the three frequencies tested. It is concluded that continuous electrical stimulation of rat hypothalamic slices at a low frequency provides a rapid means of obtaining apparent affinities and intrinsic activities of drugs that modify the serotonergic autoreceptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMedDate not supplied

Structural alteration of hair cells in the contralateral ear resulting from extracochlear electrical stimulation.

Chronic electrical stimulation of the auditory nerve in patients with profound sensori-neural deafness is becoming increasingly routine. Therefore, it is important to understand more about the long-term consequences of this procedure. Hitherto, structural studies in animals after electrocochlear stimulation have concentrated on the stimulated cochlea. Here we have examined the effects of unilateral extracochlear electrical stimulation on the spiral organ of both the ipsilateral and contralateral ears of the mature guinea pig, and have found alterations in the structure of the outer hair cells and their efferent nerve terminals in the contralateral as well as the ipsilateral cochlea. This is the first evidence for a structural influence of efferent activity on the cochlea. Although the importance of the efferent system, consisting of the crossed and uncrossed olivo-cochlear bundles, is well established in providing central control of the sensory pathways, its exact role in hearing is incompletely understood. However, it is known that the outer hair cells and their efferent innervation are important in their contribution to inner hair cell responses and in modulating the micromechanics of the whole cochlea. These efferent functions now appear to be related to an important part of cochlear morphology, and are also relevant to our understanding of cochlear neurobiology, normal development and the management of hearing disability in both adult and child.

Afferent Pathways↗
PubMed1991

Correlates of fatigue resistance in canine skeletal muscle stimulated electrically for up to one year.

In response to patterns of chronic electrical stimulation that increase its overall level of use, mammalian skeletal muscle becomes highly resistant to fatigue. The metabolic basis for this adaptation is well documented in the rabbit, but up to now it has not been possible to identify analogous changes in the dog. In this study, canine latissimus dorsi muscles were stimulated in situ for 2, 6 and 12 mo. Marked increases in fatigue resistance were consistently demonstrated. Citrate synthase and succinic dehydrogenase, conventionally used as markers of oxidative metabolism, did not increase in activity, but enzymes involved in major pathways supplying substrates to the tricarboxylic acid cycle increased up to threefold. Stimulation elevated the volume fraction of mitochondria 1.5-fold and that of lipid droplets 4.5-fold. After 6 mo of stimulation, mean fiber diameter had decreased by 30% and the area occupied by nonmuscle tissue had increased by 11%; these changes showed no further progression at 12 mo. Thus stimulated muscle becomes stably adapted to an increase in use, but the metabolic strategies for achieving increased fatigue resistance vary between species.

Adaptation, Physiological↗
PubMed1984

[Responses of enterometasympathetic neurons to transmural electric stimulation].

Transmural electrical stimulation evokes a multicomponent response in the enterometasympathetic ganglion, the response consisting of early low-amplitude APs and late single AP or bursts of APs. Some of the neurons developed a high-amplitude antidromic spike following the stimulation. Application of ganglio-blocking agent hexonium (10(-6) g/ml), solutions with high magnesium concentration (up to 10 mM) and high-frequency stimulation (30 Hz) led to disappearance of single APs but not the bursts of APs. This suggests that some components of the response are synaptically evoked in ortho- and antidromic stimulations. The remaining spikes reflect conduction of excitation along continuous nerve fibers. Transmural electrical stimulation leads to either increase or decrease in the spontaneous firing rate of neurons except the cells generating stable burst-like firing. Reasons and significance of these changes are discussed.

Animals↗
PubMed1994

Comparison of cervical magnetic stimulation and bilateral percutaneous electrical stimulation of the phrenic nerves in normal subjects.

Cervical magnetic stimulation is a new technique for stimulating the phrenic nerves, and may offer an alternative to percutaneous electrical stimulation for assessing diaphragmatic strength in normal subjects and patients in whom electrical stimulation is technically difficult or poorly tolerated. We compared cervical magnetic stimulation with conventional supramaximal bilateral percutaneous electrical stimulation in nine normal subjects. We measured oesophageal pressure (Poes), gastric pressure (Pgas) and transdiaphragmatic pressure (Pdi). The maximal relaxation rate (MRR) was also measured. The mean magnetic twitch Pdi was 36.5 cmH2O (range 27-48 cmH2O), significantly larger than electrical twitch Pdi, mean 29.7 cmH2O (range 22-40 cmH2O). The difference in twitch Pdi was explained entirely by twitch Poes, and it is possible that the magnetic technique stimulates some of the nerves to the upper chest wall muscles as well as the phrenic nerves. We compared bilateral, rectified, integrated, diaphragm surface electromyographic (EMG) responses in three subjects and found results within 10% in each subject, indicating similar diaphragmatic activation. The within occasion coefficient of variation, i.e. same subject/same session, was 6.7% both for magnetic and electrical twitch Pdi. The between occasion coefficient of variation, i.e. same subject/different days, was 6.6% for magnetic stimulation and 8.8% for electrical. There was no difference between relaxation rates measured with either technique. We conclude that magnetic stimulation is a reproducible and acceptable technique for stimulating the phrenic nerves, and that it provides a potentially useful alternative to conventional electrical stimulation as a nonvolitional test of diaphragm strength.

Action Potentials↗
PubMed2006

Eye position modulates the electromyographic responses of neck muscles to electrical stimulation of the superior colliculus in the alert cat.

Rapid gaze shifts are often accomplished with coordinated movements of the eyes and head, the relative amplitude of which depends on the starting position of the eyes. The size of gaze shifts is determined by the superior colliculus (SC) but additional processing in the lower brain stem is needed to determine the relative contributions of eye and head components. Models of eye-head coordination often assume that the strength of the command sent to the head controllers is modified by a signal indicative of the eye position. Evidence in favor of this hypothesis has been recently obtained in a study of phasic electromyographic (EMG) responses to stimulation of the SC in head-restrained monkeys (Corneil et al. in J Neurophysiol 88:2000-2018, 2002b). Bearing in mind that the patterns of eye-head coordination are not the same in all species and because the eye position sensitivity of phasic EMG responses has not been systematically investigated in cats, in the present study we used cats to address this issue. We stimulated electrically the intermediate and deep layers of the caudal SC in alert cats and recorded the EMG responses of neck muscles with horizontal and vertical pulling directions. Our data demonstrate that phasic, short latency EMG responses can be modulated by the eye position such that they increase as the eye occupies more and more eccentric positions in the pulling direction of the muscle tested. However, the influence of the eye position is rather modest, typically accounting for only 10-50% of the variance of EMG response amplitude. Responses evoked from several SC sites were not modulated by the eye position.

Action Potentials↗
PubMed1980

Effects of electrical stimulation on the enkephalins in guinea-pig small intestine.

When myenteric plexus-longitudinal muscle preparations of the guinea-pig small intestine are stimulated electrically in the presence of cycloheximide there is a decrease in the content of enkephalins which is taken to be due to their release. With supramaximal stimuli, the release per pulse is similar at 1 and 10 Hz but it is lower with submaximal than with maximal stimuli. Met-enkephalin is more readily released than Leu-enkephalin.

Animals↗
PubMed1986

Nerve mediated responses to drugs and electrical stimulation in aganglionic muscle segments in Hirschsprung's disease.

The activity of isolated muscle strips from normal and aganglionic human large bowel was studied in vitro. The intrinsic nerves were stimulated electrically and by nicotinic agonists. The ganglionic preparations displayed a strong inhibitory response due to the release of both norepinephrine and a noncholinergic, nonadrenergic inhibitory neurotransmitter. In the aganglionic strips (obtained from patients with Hirschsprung's disease), nerve activation tended to evoke contraction, apparently due to enhancement in the release of acetylcholine. At the same time, the release of norepinephrine appeared to be less than normal. A particularly interesting finding in the aganglionic muscle strips was the presence of a substantial inhibitory response due to the release of a noncholinergic, nonadrenergic substance. These results provide further evidence for the importance of the innervation of the aganglionic segment in Hirschsprung's disease.

Child↗
PubMed1983

Responses to electrical stimulation of denervated human muscle fibres recorded with single fibre EMG.

Denervated muscle fibres were stimulated electrically with needle electrodes introduced close to a recording single fibre electrode. The denervated muscle fibre could be driven with rates up to 100 Hz. The jitter was large at threshold but low at suprathreshold stimulus strength. There was evidence of discrete low threshold sites along the denervated muscle fibre, seen as stepwise latency change on smoothly changing stimulus strength, hepatic activation from other fibres and also as extra-discharges originating from such sites.

Action Potentials↗
PubMed1989

Release of gamma-[3H]aminobutyric acid (GABA) from electrically stimulated rat cortical slices and its modulation by GABAB autoreceptors.

Slices of rat temporo-parietal cortex were prelabeled with gamma-[3H]aminobutyric acid ([3H]GABA), in the presence of the glial GABA uptake inhibitor beta-alanine. The slices were then superfused with a medium containing the GABA transaminase inhibitor aminooxyacetic acid and stimulated electrically (5 min, 2 msec, 36 mA at 5 or 10 Hz), in the presence of the neuronal GABA reuptake inhibitor SK&F 89976A [N-(4,4-diphenyl-3-butenyl)-nipecotic acid] and of beta-alanine. Representative experiments showed that the tritium released could be accounted for almost entirely by authentic [3H]GABA. The electrically evoked overflow of [3H]GABA was tetrodotoxin sensitive and largely calcium-dependent. Exogenous GABA, added to the superfusion medium at 3 to 30 microM, reduced in a concentration-dependent manner the electrically evoked (5 Hz) release of [3H]GABA. The GABAB receptor agonist (-)-baclofen, but not the GABAA receptor agonist muscimol, mimicked GABA and produced a concentration-inhibition curve almost superimposable to that of the natural transmitter. The effects of GABA and of (-)-baclofen were much more pronounced at 5 than at 10 Hz. The GABA-induced inhibition of [3H]GABA release was sensitive to the novel GABAB receptor antagonist beta-(p-chlorophenyl)-3-amino propyl phosphonic acid which, by itself, increased the [3H]GABA overflow. The inhibitory effect of GABA was not counteracted by the GABAA receptor antagonists bicuculline or SR 95531 [2-(3'-carbethoxy-2'-propenyl)-3-amino-6-paramethoxy-phenyl-pyr idazinium bromide]. The results are compatible with the presence in the rat cerebral cortex of autoreceptors mediating inhibition of GABA release and belonging to the GABAB type. These autoreceptors may be activated tonically under physiological conditions.

Animals↗
PubMed2001

Facilitation of motor evoked potentials in the anterior tibial muscle by repetitive subthreshold electrical stimulation.

Subthreshold electrical stimulation with an intensity less than the threshold for evoking M-waves is applied repetitively to the common peroneal nerve via surface electrodes. The stimulation intensity is varied by adjusting the pulse width from 0 to 240 micros, while the pulse interval (40 ms) and current amplitude are kept constant. Single magnetic stimuli are applied to the motor cortex using a circular coil. Motor evoked potentials are recorded from the anterior tibial muscle in six normal subjects for various subthreshold stimulation intensities. Signal processing (filtering in the time and frequency domains) removes the artifact caused by the subthreshold electrical stimulation from the motor evoked potential. Statistically significant motor evoked potential facilitation (p < 0.05) is observed for pulse widths ranging from 72 to 240 micros in all the tested subjects. A pulse width corresponding to 90% of the electrical threshold facilitated the motor evoked potential in five of the six subjects.

Adult↗
PubMed2002

Modelling the response of scalp sensory receptors to transcranial electrical stimulation.

Transcranial electrical stimulation of the brain causes considerable discomfort to the patient. The purpose of the study was to find out whether this could be affected by the choice of stimulation parameters. A spherical volume conductor model of the head and active compartmental models of a pyramidal motor nerve and scalp nociceptor were used in combination to simulate the scalp nociception to transcranial electrical stimulation. Scalp nociceptors were excited at distances of several centimetres from the electrodes. The size of the excited scalp area correlated with the length of the stimulation pulse. The area was 12.3, 20.4 and 26.0 cm2, for a 10 micros, 100 micros and 1 ms constant current pulse, respectively. With a 100 micros constant current pulse, the threshold for motor excitation was 205mA and, for nociception, it was 51 mA. There was no significant difference between constant current and capacitor discharge pulses or between electrodes of different sizes. The results imply that the use of very short stimulation pulses can reduce the pain. If a topical anaesthesia is used to reduce the pain, it has to be applied on a large area around the electrodes.

Computer Simulation↗
PubMed1991

Axotomy-induced changes in rabbit hindlimb nerves and the effects of chronic electrical stimulation.

Chronic electrical stimulation and extracellular recording combined with morphological examination of nerves in this study provided a detailed description of the time course and extent of fiber atrophy when the trophic influence of the target was removed by ligation of axotomized nerves and neural activity was replaced by chronic stimulation. The major findings are that decline in amplitude of compound action potentials (CAPs) and fiber diameters is rapid after axotomy and is not reversed or prevented by chronic electrical stimulation, as would be predicted if neural activity played an essential role in maintaining normal fiber caliber. Chronic stimulation had a small short-term sparing effect in the first month after axotomy but was counterproductive over long periods. Comparison of the time course of the decline in CAP amplitude and reduction of fiber diameters with described alterations in mRNA expression of neurofilament protein indicates that the early atrophy is too rapid to be accounted for by reduced synthesis and transport of neurofilaments. It is more likely to result from modification of axonal proteins after axotomy. Replacement of neural activity with stimulation may reduce the initial atrophy but, over longer periods, exacerbates the atrophy, possibly by affecting the synthesis and transport of cytoskeletal proteins. These studies show that the trophic control of nerve fiber size is mediated primarily by functional contacts with peripheral targets and that neural activity plays a relatively small role. Without functional contacts, nerve fibers decline in diameter to stable but lower values. The atrophy was exacerbated by imposing neural activity on the relatively quiescent axotomized neurons.

Action Potentials↗
PubMed2005

Clinical application of acceleration sensor to detect the swing phase of stroke gait in functional electrical stimulation.

Functional electrical stimulation (FES) can improve the gait of stroke patients by stimulating the peroneal nerve in the swing phase of the affected leg, causing dorsiflexion of the foot that allows the toes to clear the ground. A sensor can trigger the electrical stimulation automatically during the stroke gait. We previously used a heel sensor system, which detects the contact pressure of the heel, in FES to correct foot drop gait. However, the heel sensor has disadvantages in cosmetics and durability. Therefore, we have replaced the heel sensor with an acceleration sensor that can detect the swing phase based on the acceleration speed of the affected leg, using a machine learning technique (Neural Network). We have used a signal for heel contact in a gait using the heel sensor before training with the Neural Network. The accuracy of the Neural Network detector was compared with a swing phase detector based on the heel sensor. The Neural Network detector was able to detect similarly the swing phase in the heel sensor. The largest difference in timing of the swing phase was less than 60 milliseconds in normal subjects and 80 milliseconds in stroke patients. We were able to correct foot drop gait using FES with an acceleration sensor and Neural Network detector. The present results indicate that an acceleration sensor positioned on the thigh, which is cosmetically preferable to systems in which the sensor is farther from the entry point of the electrodes, is useful for correction of stroke gait using FES.

Adult↗