Conditions Of Electrical Stimulation Research Articles

Modulation of cortical evoked potentials by stimulation of nucleus raphe magnus in rats.

1. In pentobarbital sodium-anesthetized rats, we evaluated changes in cortical evoked potentials (EPs) associated with electrical and chemical stimulation of nucleus raphe magnus (NRM). A condition-test (C-T) paradigm was used. Cortical EPs were produced by test stimuli delivered to a hindpaw or the thalamic ventral posterior lateral nucleus (VPL; electrical stimulation), or by photic stimulation of the eyes or electrical stimulation of contralateral homotopical cortex (transcallosal EPs). These test stimuli were then preceded by electrical or chemical conditioning stimulation (CS) delivered to NRM through a stereotaxically implanted electrode or injection cannula, respectively. Effects of CS on EPs produced by the test stimuli were characterized. 2. Electrical CS preceding a test stimulus delivered to the foot reduced the amplitude of EPs at thresholds as low as 10-25 microA. The magnitude of EP reduction was dependent on CS intensity, frequency, and the C-T interval. Optimal parameters were trains of 10 pulses (400 Hz) delivered at a C-T interval of 5-10 ms. Injection of glutamate and lidocaine into NRM demonstrated that these effects were due to activation of NRM neurons and not to current spread to medial lemniscus (ML). NRM CS also reduced cortical EPs produced by test stimulation in VPL but did not alter EPs from visual stimulation or from electrical stimulation of contralateral homotopical cortex. 3. These findings suggest that NRM CS attenuates EPs by inhibiting thalamic or thalamocortical afferent activity. Because NRM CS affected all components of the cortical EPs, the effect appears to involve alteration of general sensory activity and is not nociception specific.(ABSTRACT TRUNCATED AT 250 WORDS)

Periaqueductal gray matter and nucleus raphe magnus involvement in anterior pretectal nucleus-induced inhibition of jaw-opening reflex in rats

In previous studies we have shown that electrical stimulation of the cortex or anterior pretectal nucleus (APT) inhibits the jaw-opening reflex (JOR). In the present study we investigated whether these effects are mediated by a relay in the periaqueductal gray matter (PAG) or rostroventromedial medulla (RVM). Experiments were performed on chloralose-urethane anesthetized rats. The JOR which was elicited by electrical stimulation of the mandibular incisor tooth was monitored by recording the evoked digastric muscle activity. Conditioning stimulation (20 ms-train of 0.2 pulses at 400 Hz) was delivered to the facial area of the sensorimotor cortex, APT, PAG or nucleus raphe magnus (NRM) 50 ms prior to the test stimulus to the tooth that evoked the JOR. In addition, the effects of microinjections of glutamate into APT, PAG and NRM on the tooth-evoked JOR were also evaluated. The inhibition of the JOR by electrical and glutamate conditioning stimulation was found to be most potent for activation of the NRM and least potent for the APT. Local anesthetic (2% Iidocaine, 0.3–0.6 μl) block of the PAG could partially, significantly (P < 0.05) and reversibly reduce both the APT and cortical-induced depression of the JOR. Lidocaine block of the ventromedial pons reversible reduced the PAG, APT and cortical-induced inhibition of the JOR (P < 0.05). Lidocaine block of the lateral RVM had powerfully (P < 0.01) and reversibly reduced the PAG-induced inhibition, but had onaly a small effect (P < 0.05) on the APT-induced inhibition and no significant effect on the cortical-induced inhibition. Lidocaine block of NRM produced a small reversible reduction in the PAG- and APT-induced inhibition but had no significant effect on cortical-induced inhibition of the JOR. These findings suggest that the inhibitory effects of APT and cortical stimulation on the JOR are mediated in part by a relay in the PAG and that in addition the APT-induced inhibition may also be partly mediated by a relay in the RVM.

Hypothalamic influences on viscero‐somatic neurones in the lower thoracic spinal cord of the anaesthetized rat.

1. Single unit electrical activity has been recorded from thirty-four viscero-somatic neurones in the dorsal horn of the lower thoracic spinal cord (T9-T11) of chloralose-anaesthetized rats. All neurones were driven by natural and/or electrical stimulation within their somatic receptive fields and gave excitatory responses to electrical stimulation of the ipsilateral splanchnic nerve. Descending influences on these neurones were tested by electrical and chemical (microinjections of DL-homocysteic acid) stimulation of sites in the rostral hypothalamus. 2. The electrical activity of most viscero-somatic neurones (64%) was inhibited by electrical stimulation at sites throughout the anterior hypothalamus-preoptic region. In any one cell, responses to stimulation of visceral and somatic afferent fibres were inhibited to the same extent and any on-going activity was also depressed. Only one cell was driven by the conditioning stimulus and the electrical activity of the remaining cells (n = 7) was unaffected. 3. At certain hypothalamic sites the effects of electrical conditioning stimulation on the responses of viscero-somatic neurones were compared with those of local microinjection of DL-homocysteic acid. Electrical stimulation at all sites tested (n = 7) led to an inhibition of on-going and evoked neuronal activity. At two hypothalamic sites, both located in the ventral part of the preoptic area, microinjection of DL-homocysteic acid resulted in a complete abolition of the responses to the test stimuli and in a cessation of any on-going activity. Microinjection of DL-homocysteic acid at the remaining five sites had no detectable influences on dorsal horn activity. 4. The results of this study include the first description of input properties of viscero-somatic neurones in the lower thoracic spinal cord of the rat. In addition, these results demonstrate that transmission of visceral and somatic information through these neurones can be modulated by pathways that originate in the anterior hypothalamus-preoptic region of the ventromedial forebrain.

Augmentation of muscle nociceptive respiratory reflex facilitation by vagal afferents.

Vagal influence on the facilitation of phrenic neural activity during respiratory phase-locked, gastrocnemius muscle nerve nociceptive electrical stimulation was examined in anesthetized, glomectomized, paralyzed, and artificially ventilated cats. (1) In the vagi-intact state, respiratory reflex facilitation was characterized by a sharp rise in peak amplitude, maximum rate of rise or slope, and mean rate of rise of integrated phrenic nerve activity. This was greater during inspiratory phase-locked (T1-locked) muscle nerve electrical stimulation than during expiratory phase-locked (TE-locked) muscle nerve electrical stimulation. "Evoked post-inspiratory phrenic activity" during the early expiratory phase was also observed during TE-locked muscle nerve electrical stimulation. (2) Bilateral vagotomy significantly attenuated the respiratory facilitation during both T1- and TE-locked muscle nerve electrical stimulation. In particular, the "evoked post-inspiratory phrenic activity" during TE-locked muscle nerve electrical stimulation was also attenuated or almost completely abolished. (3) Conditioning electrical stimulation of the vagus nerve revealed facilitatory reflexes which co-exist with inspiratory inhibitory reflexes. (4) The "evoked post-inspiratory phrenic activity" during TE-locked muscle nerve electrical stimulation, which was attenuated or abolished after vagotomy, was restored after vagal T1-locked conditioning stimuli combined with TE-locked muscle nerve electrical stimulation. The results suggest that vagal facilitatory reflexes augment the respiratory reflex facilitation during muscle nociceptive stimulation.

Inhibition of monosynaptic reflexes in the human lower limb.

1. Presynaptic inhibition of muscle spindle Ia afferents by afferents from the same and other muscles has been studied in the human lower limb. The experiments have utilized conditioning of test monosynaptic reflexes by vibration of both the test and other muscles. 2. The pattern of inhibition invariably includes autogenetic actions. 3. There are powerful effects from flexor to extensor Ia afferents. Actions from flexor to flexor, and from extensor to extensor, are weaker. Actions from extensors to flexors are very weak. 4. The strength of presynaptic inhibition from one muscle type to another weakens as the muscles considered become more anatomically distant. 5. The inhibition studied both by vibration and by electrical conditioning stimulation of nerves becomes weaker during voluntary isometric contraction of the test muscle. It is strongest at rest and during antagonist contraction. 6. Evidence is provided suggesting that descending control is the primary cause of this modulation of inhibition during contraction. 7. Stimulation of afferents in cutaneous nerves reduces group I presynaptic inhibition of Ia afferents.

Comparison of Voluntary and Electrical Stimulation Contraction Torques

Informed male volunteers completed maximal isometric knee extension efforts under each of three contraction conditions: 1) voluntary, 2) electrical stimulation (ES) only, and 3) superimposed (ES superimposed onto voluntary). Ten subjects completed the three contraction conditions using each of the following current formats: 1) asymmetrical biphasic rectangular wave, 2) asymmetrical biphasic spike wave, and 3) symmetrical monophasic square wave. Under the voluntary and the superimposed contraction conditions no significant differences in mean torque were observed between the three current formats. However, under the ES contraction condition, the torque associated with the symmetrical monophasic square wave was significantly less than that associated with the other two current formats. As well, the torque associated with the asymmetrical biphasic spike wave was significantly less than that associated with the asymmetrical biphasic rectangular wave format. No significant difference was observed between the maximum voluntary contraction (MVC) and the superimposed contraction conditions for the groups receiving the asymmetrical biphasic spike and the symmetrical monophasic square wave current formats, or between all three contraction conditions for the group receiving the asymmetrical biphasic rectangular wave format. However, the ES condition was associated with significantly less torque than were the MVC and the superimposed conditions for the asymmetrical biphasic spike and the symmetrical monophasic square wave formats. In response to a posttest questionnaire, 18 of 30 subjects felt that the ES contraction produced greater torque than did MVC, and 26 subjects selected the superimposed condition as having produced greater torque than the ES condition. The different current formats, resulting in different levels of sensation and preception, and the different output capabilities of each electrical stimulator are considered to have been jointly responsible for the ES only torque discrepancies. It is suggested that ES does not recruit more motor units, resulting in a greater force of contraction, than are recruited under MVC.J Orthop Sports Phys Ther 1984;5(6):324-331.

The lateral vestibular nucleus is a very important site for depressant actions of benzodiazepines on the crossed extensor reflex

We have reported that the crossed extensor reflex (CER) in Wistar male chloralose-anesthetized rats is very susceptible to the depressive action of benzodiazepine derivatives. The present study was designed to elucidate a possible site for this action in the central nervous system. Since the reflex contraction of the femoral quadriceps muscle elicited by an electrical stimulation of contralateral sciatic nerve was little influenced by diazepam (DZ) (0.05-2 mg/kg i.v.) in the chronic spinal rat, it is very probable that DZ may act first on supraspinal structures. DZ (2.5 μg) injected into the 4th ventricle produced much more potent and rapid inhibition of the CER than injection into the lateral ventricle. To find the most sensitive site involved in the area close to the 4th ventricle, microinjections of DZ in doses of 1 and 25 ng into the lateral vestibular nucleus (LVN) ipsilateral to the testing muscle produced a dose-dependent reflex depression which was clearly antagonized by Ro 15-1788, a benzodiazepine antagonist. Injections of 100 ng of DZ into other areas, i.e., the contralateral LVN, other subcerebellar nuclei, the red nucleus and the substantia nigra, produced no effects on the CER. Furthermore, electrolytic lesions of the ipsilateral LVN decreased the CER, while an electrical conditioning stimulation of the same nucleus increased it.

Peripheral afferent nerve impulses for conveying electroacupuncture effects on the jaw opening reflex evoked by tooth pulp stimulation in rat.

Effects of conditioning electrical stimulation of the nerves innervated around the meridian Ho-Ku point on the tooth-pulp evoked jaw opening reflex were investigated in Wistar albino rats. Changes of the threshold of the reflex were monitored before and after the conditioning stimulation. The increased changes of the threshold value gradually appeared and even after the cessation of the conditioning stimulation, its effect remained for several minutes. Of the three nerves in the brachial plexus (radial, median and ulnar), radial nerve was the most effective. The ipsilateral nerve stimulation was more effective on the threshold elevation of the reflex than the contralateral one. When the two nerves were stimulated simultaneously, the increase of the threshold value was sometimes observed as compared to the case of stimulating each nerve separately. However, in cases of the combination stimulation including radial nerve, the summation among the different impulses produced by the conditioning stimulation was scarcely observed; therefore, the effect was not reinforced.

The influence of naloxone on analgesia produced by peripheral conditioning stimulation

Conditioning electrical stimulation of peripheral nerves is presently routinely employed for alleviation of chronic pain in humans. Most commonly, high frequency stimulation of probably mainly coarse myelinated afferents from the skin is used as proposed in the gate theory of Melzack and Wall 25. However, only a limited number of patients benefit from such stimulation. To improve the results of such treatment we have developed a kind of acupuncture-like electrical stimulation where mixed nerves are stimulated with short trains of stimuli given at a slow repetition rate via surface electrodes to elicit muscle contractions. The compiled results of conditioning stimulation for analgesia were then markedly improved. To see whether the analgesia experienced by the chronic pain patients is mediated via links utilizing endorphins, the opiate antagonist naloxone was administered to these patients under double-blind conditions, saline being used as a placebo. We then found that 6 out of 10 patients receiving acupuncture-like stimulation but none out of 10 patients receiving high frequency stimulation of skin nerves, reported an inhibition of the stimulation-produced analgesia by naloxone. This indicates that the analgesia produced by acupuncture-like stimulation is mediated via mechanisms utilizing endorphins whereas the analgesia produced from high frequency stimulation of coarse cutaneous afferents is mediated via some other mechanism.

Regional properties of dorsal and ventral hippocampus in suppression of intralaminar thalamic unit responses.

AbstractIn chloralose‐anesthetized. Flaxedil‐paralyzed cats, the suppression of extralemniscal thalamic units by the dorsal and ventral hippocampus was investigated. Unitary responses to test somatic stimuli, recorded in centrolateral and neighboring thalamic nuclei, were interacted with conditioning electrical stimulation in different regions around the hippocampal arch, including the parahippocampal gyrus (entorhinal and retrosplenial areas).Stimulation of dorsal (DHC) and ventral (VHC) hippocampus suppressed roughly equal proportions of responses. However, within each of DHC and VHC, effectiveness depended on the region stimulated. In DHC, Fields CA1 and CA3, subiculum (SUB), and retrosplenial area, but not field CA4 with dentate gyrus (FD), while stimulation of CA1 or subiculum was almost ineffective at currents below 1.0 mA. In VHC the regions were ranked for effectiveness as follows: entorhinal cortex = CA3 &gt; FD &gt;SUB &gt;CAI.No topographic relationship was found between hippocampal region and thalamic loci for unit suppression. Lemniscal‐type unit responses in ventrobasal thalamus were unaffected by stimulation of the hippocampus or parahippocampal gyrus.Interruption of the fornix‐fimbria system prevented suppression elicited from CA1 of DHC or from CA3 of VHC, but not from FD of VHC. It had no effect on suppression elicited from retrosplenial or entorhinal cortex.Hippocampal regional variation of effectiveness in suppressing extralemniscal pathways may contribute to the differential behavioral involvements reported for different hippocampal structures.

Increase of pain threshold as a function of conditionsing electrical stimulation. An experimental study with application to electro-acupuncture for pain suppression.

Previous studies have shown that 2 Hz electrical conditioning stimulation of hands and cheeks increased the tooth pain threshold. In the present study the relation between strength of conditioning stimulation and amplitude of pain threshold increase is elucidated. Intense conditioning stimulation, giving subjective beating sensations and extensive muscles twitches, is required to obtain a substantial pain threshold increase. The results are discussed in relation to intensities used in electro-acupuncture and to interindividual variation of the effect. It is suggested that pain relief is obtained due to an inhibitory feed-back mechanism activated, not via low threshold afferents but via high threshold afferents.

On Acupuncture Analgeisa and the Mechanism of Pain

The effect on the experimental tooth pain threshold of conditioning electrical stimulation via needles or surface electrodes applied to the hands and cheeks was studied in 34 dental students. Conditioning stimulation with 2/sec. gave a slowly increasing pain threshold followed by a slow return to the control level in the post-conditioning period. In each individual the amplitude of the threshold increase was reproduceable. It was concluded that these effects are not due to motivational but to more basic neurophysiological mechanisms. The pain threshold was increased mainly by segmental conditioning stimulation; segmentally unrelated stimulation gave usually only small effects. Conditioning stimulation with 100/sec. produced only a strict segmental short-lasting effect. Effects with characteristics of both 2/sec. and 100/sec. were obtained by conditioning at 10/sec. It is suggested that the transmission of impulses from the pain afferents to ascending pathways is controlled at the segmental level by (a) presynaptic inhibition within the group of afferents giving rise to the flexion reflex of which the pain afferents are assumed to be a part; (b) postsynaptic inhibition between alternate pathway excited by flexion reflex afferents; and (c) descending control from supraspinal systems which may utilize similar segmental mechanisms as the primary afferents.

大脳辺縁系の光誘発電位に対する=干渉の特異性

Photic evoked potentials recorded in the visual cortex and lateral geniculate body to the conditioning electrical stimulation of the limbic system were investigated in 58 rabbits.The conditioning electrical stimulation of the septum, hippocampus and latera l geniculate body with a train of high frequency (100Hz) inhibited cortical photic evoked potentials, whereas that with a train of low frequency (3-5Hz) facilitated them. Cortical photic evoked potentials following the conditioning electrical stimulation of the amygdala with a train of low frequency had tendency to be facilitated. However, the conditioning stimulation with a train of high frequency arbitrarily inhibited and/or facilitated cortical photic evoked potentials.Relationships between the anatom ical designation of the septum and the interactions to the photic evoked potential were analyzed. The conditioning electrical stimulation of medial and lateral nuclei of the septum with a train of high and low frequencies produced attenuation and potentiation of cortical photic potentials respectively, whereas the conditioning stimulation of dorsal nucleus on the septum facilitated cortical evoked potentials irrespective to a train of high and low frequencies.The photic evoked potentials in the la teral geniculate body following the conditioning electrical stimulation of the septum, amygdala and hippocampus had no tendency to be attenuated and/or facilitated irrespective to a train of high and low frequencies.Lesions in the peni- and para-ventricular areas of the hypothalamu s, nucl, reuniens and mammillary body abolished these responses suggesting that these areas are the pathway mediating the projections of the rhinencephalon to the visual cortex via the mesencephalic reticular formation.