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PubMed2001

Enhanced visual spatial attention ipsilateral to rTMS-induced 'virtual lesions' of human parietal cortex.

The breakdown of attentional mechanisms after brain damage can have drastic behavioral consequences, as in patients suffering from spatial neglect. While much research has concentrated on impaired attention to targets contralateral to sites of brain damage, here we report the ipsilateral enhancement of visual attention after repetitive transcranial magnetic stimulation (rTMS) of parietal cortex at parameters known to reduce cortical excitability. Normal healthy subjects received rTMS (1 Hz, 10 mins) over right or left parietal cortex. Subsequently, detection of visual stimuli contralateral to the stimulated hemisphere was consistently impaired when stimuli were also present in the opposite hemifield, mirroring the extinction phenomenon commonly observed in neglect patients. Additionally, subjects' attention to ipsilateral targets improved significantly over normal levels. These results underline the potential of focal brain dysfunction to produce behavioral improvement and give experimental support to models of interhemispheric competition in the distributed brain network for spatial attention.

Adult↗
PubMed1979

A microprocessor controlled timing device for cardiac electrical stimulation.

A microcomputer controlled device for delivering precisely timed stimuli to cardiac chambers is described. Stimulation patterns are determined by software, rather than hardware design, resulting in enhanced flexibility. Additionally, by providing timing inputs to conventional laboratory stimulators, this instrument can convert these limited use devices into ones capable of generating complex cardiac stimulation patterns at moderate cost.

Cardiac Pacing, Artificial↗
PubMedDate not supplied

[Spectral correlation parameters of neocortical potentials in the rabbit undergoing paired isorhythmic stimulation].

At pairing of isorhythmic stimuli beyond the theta-rhythm frequency limits (3 and 8 Hz), in power spectra of EEGs of the sensorimotor and visual neocortical areas of rabbits, the frequencies are present both of the theta-range and of the stimulation frequency, in the background activity as well as during the stimulation. Both rhythms are in reciprocal relations. The frequency of the theta-rhythm approaches the frequency divisible by that of the stimulation. Under the action of the conditioned stimulus, crosscorrelation coefficients (CC) between the potentials of the areas under study decrease in most cases in comparison to their background values. Combination of the conditioned stimulus with the unconditioned one, leads approximately in equal number of cases to an increase or decrease of CC. After elimination of the stimuli, in most cases CC increases. CC of the background activity does not increase in the course of paired stimuli presentation though a conditioned response is being formed. At presence of stimuli frequency fluctuations simultaneously in the potentials of both areas, the rise of coherence function at this frequency does not occurs always. Thus, the above spectral-correlation parameters of rabbit's cortical potentials differ from those which arise at pairing of continuous nonrhythmic stimuli. This difference is probably due to different characteristics of the stimuli presented.

Animals↗
PubMed2000

The influence of mechanical, visual and contact chemical stimulation on the behavioural phase state of solitarious desert locusts (Schistocerca gregaria).

We investigated the influence of mechanical, visual and contact chemical stimulation on behavioural gregarization of fifth-instar solitarious nymphs of the desert locust. The stimuli were applied in two 2x2 factorial experimental designs, the first with contact chemical and mechanical stimuli, and the second with contact chemical and visual stimulation. Stimulus treatments were applied for a 4-5 h period, after which the behavioural phase state of individual locusts was measured using an assay based on multiple logistic regression analysis of behavioural variables. Mechanical stimulation was provided by showering test insects with millet seeds, thereby excluding the possibility of contact chemical self-stimulation by repeated contact with the same objects. Visual stimulation consisted of the sight of crowd-reared locusts, while contact chemical stimulation was a dichloromethane extract of cuticular hydrocarbons from gregarious nymphs applied to the perch of the test insect. Mechanical stimulation was powerfully gregarizing, whether alone or in combination with contact chemical stimuli. Application of cuticular extract to the perch had no measurable effect on behavioural phase state, either alone or when presented with mechanical or visual stimuli. Visual stimulation alone partly gregarized test locusts. These results appear to conflict with other reports of the gregarizing effect of cuticular hydrocarbons and possible reasons for this discrepancy are discussed.

Journal Article↗
PubMed1987

Staphylococcus aureus-stimulated human mononuclear leucocyte-conditioned medium augments the basal and stimuli-induced neutrophil respiratory burst and degranulation.

Culture medium conditioned by mononuclear leucocytes (MNL) stimulated by formalin-fixed heat-killed Staphylococcus aureus (sCM) modulated a number of neutrophil functions. The sCM inhibited the locomotion of human neutrophils in both the presence and absence of a chemotactic gradient generated with N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP). It also stimulated the oxygen-dependent respiratory burst as assessed by its ability to stimulate basal H2O2, superoxide and chemiluminescence production by neutrophils. Neutrophils treated with sCM also showed increased release of lysozyme but not beta-glucuronidase. In addition, the sCM-treated neutrophils showed a potentiated response to stimuli that bind surface receptors, i.e. FMLP and opsonized zymosan. The effects of sCM and either of the stimuli were synergistic. Examination of lysosomal enzyme release showed that sCM enhanced the release of lysozyme and beta-glucuronidase induced by either FMLP/cytochalasin B or zymosan. The response to phorbol myristate acetate (PMA), which bypasses the surface receptor, was also stimulated but compared poorly with the FMLP response. The sCM effects on the FMLP-induced chemiluminescence response occurred even when FMLP addition was delayed for 4 hr. Cells treated with sCM and washed retained the ability to show an enhanced FMLP response. The neutrophil-modulating activity was not produced by MNL cultured in the absence of bacteria.

Antigens, Bacterial↗
PubMed2006

Electro-olfactograms are present when odorous stimuli have not been perceived.

After chemical stimulation of the human olfactory epithelium it is possible to record a negative response (electro-olfactogram, EOG) which is interpreted as the summated generator potential of olfactory neurons. The aim of the present investigation was to test whether the EOG is present when olfactory stimuli have not been perceived. Stimulation was performed with vanillin and eugenol at supraliminal and subliminal levels. Twelve healthy volunteers participated in the experiments. Stimuli were applied at an interstimulus interval of approximately 60s. Although recordings were successful in 4 of the 12 subjects, for both stimulants EOG could be obtained even when the stimuli had not been perceived by the subjects. EOG recordings in response to supra- and subliminal stimuli exhibited no major differences, except for the onset of the EOG in response to subliminal eugenol-stimuli which were prolonged compared to supraliminal stimulation. All in all, the present data provide a physiological basis for the subliminal influence of odorous stimuli on human behavior.

Adult↗
PubMed1989

Acetyltransferase activity and production of platelet-activating factor by human neutrophils activated with various stimuli.

The acetyltransferase activity and biosynthesis of platelet-activating factor (PAF) were assessed in human neutrophils activated by 4 microM A23187, 20 ng/ml phorbol myristate acetate (PMA), and 10(-6) M n-formyl-methionyl-leucyl-phenylalanine (fMLP). All three agents elevated the acetyltransferase activity dose-dependently. There were no significant differences in the Km values for acetyl CoA between non-stimulated and stimulated cells. All three stimuli gave a similar Vmax value of acetyltransferase determined 10 min after stimulation, being more than twice as high as the control value. By contrast, the amount of PAF produced by the neutrophils differed with the stimuli, A23187 being by far the most potent. The time course of PAF synthesis, particularly when activated by PMA, did not parallel that of acetyltransferase activity; PMA-induced PAF production was negligible for the first 20 min and gradually increased to reach its plateau 60 min after stimulation, while enzyme activity was at its highest level 5 min after stimulation. These results suggest that the different stimuli activated the same acetyltransferase, and that there was an increase in the number of the enzyme molecules in the activated state. It is unlikely that a change in the biological activity of a preexisting enzyme without a change in the number of active enzyme molecules could be the cause. Certain factors other than acetyltransferase may also regulate the PAF biosynthesis induced by these stimuli.

Acetyltransferases↗
PubMed2006

Responses of Purkinje-cells of the cerebellar anterior vermis to stimulation of vestibular and somatosensory receptors.

In decerebrate cats, sinusoidal rotation of the forepaw around the wrist modifies the activity of the ipsilateral forelimb extensor triceps brachii (TB) and leads to plastic changes of adaptive nature in the gain of vestibulospinal (VS) reflexes (VSRs). Both effects are depressed by functional inactivation of the cerebellar anterior vermis, which also decreases the gain of VSRs. In order to better understand the mechanisms of these phenomena, the simple spike activity of Purkinje (P-) cells was recorded from the vermal cortex of the cerebellar anterior lobe during individual and/or combined stimulation of somatosensory wrist, neck and vestibular receptors. About one third of the recorded units were affected by sinusoidal rotation of the ipsilateral forepaw around the wrist axis (0.16 Hz, +/-10 degrees ). Most of these neurons ( approximately 60%) increased their activity during ventral flexion of the wrist and decreased it during the oppositely directed movement, with an average phase lag of -141 degrees with respect to the position of maximal dorsiflexion. The remaining cells ( approximately 40%) were excited during dorsiflexion of the wrist, with an average phase lead of 59 degrees with respect to the extreme dorsal flexion. Both populations showed comparable response gains, with an average value of 0.42+/-0.52, S.D., imp/s/deg. About half of the recorded units were also tested during sinusoidal roll tilt of the animal around the longitudinal axis (0.16 Hz, +/-10 degrees ), leading to stimulation of labyrinthine receptors. When both stimuli were applied simultaneously, the responses to combined stimulation usually corresponded to the sum of individual responses. While the phase distribution of somatosensory responses was clearly bimodal, vestibular responses showed phase angle values uniformly scattered between +/-180 degrees and 0 degrees , so that, during combined stimulation, each neuron could be maximally activated by coupling the two stimuli with a particular phase relation. Finally, a proportion of the recorded neurons was also tested during sinusoidal rotation of the body around its longitudinal axis, with the head fixed in space, leading to stimulation of neck receptors. The proportion of neurons affected by individual stimulation of vestibular or neck receptors (81% and 72%, respectively) was larger than that of wrist-driven neurons. Convergence of signals from vestibular, somatosensory wrist and neck receptors was found in 18% of the neurons analyzed. In conclusion, the results of this study show that somatosensory signals from the forelimb: i) modulate the activity of a sizeable proportion of neurons located within the cerebellar anterior vermis and ii) interact widely with labyrinthine and neck signals at this level. Moreover, iii) this corticocerebellar region is largely dominated by vestibular and neck signals that may be utilized to build up a neuronal representation of the position of body in space. These findings suggest that: 1) the modulation of TB activity induced by rotation of the ipsilateral wrist may at least partially depend upon the simultaneous changes in P-cell activity and 2) the interaction of vestibular and somatosensory wrist signals at P-cell level may represent the substrate of the plastic changes that affect the VSR when animal tilt and wrist rotation are driven together. A preliminary report of these data has been presented [ Responses of cerebellar Purkinje cells to forepaw rotation in decerebrate cat. Pflügers Arch 440:R31].

Action Potentials↗
PubMed2004

Coordinate high-frequency pattern of stimulation and calcium levels control the induction of LTP in striatal cholinergic interneurons.

Current evidence appoints a central role to cholinergic interneurons in modulating striatal function. Recently, a long-term potentiation (LTP) of synaptic transmission has been reported to occur in these neurons. The relationship between the pattern of cortico/thalamostriatal fibers stimulation, the consequent changes in the intracellular calcium concentration ([Ca2+]i), and the induction of synaptic plasticity was investigated in striatal cholinergic interneurons from a rat corticostriatal slice preparation by means of combined electrophysiological intracellular recordings and microfluorometric techniques. Different protocols of stimulation were considered, varying both the frequency and the duration of the train of stimuli. High-frequency stimulation (HFS) (three trains at 100 Hz for 3 sec, 20-sec interval) induced a rise in [Ca2+]i, exceeding by fivefold the resting level, and caused a LTP of synaptic transmission. Tetanic stimulation delivered at lower frequencies (5-30 Hz) failed to induce long-term changes of synaptic efficacy. The observed elevation in [Ca2+]i during HFS was primarily mediated by L-type high-voltage activated (HVA)-Ca2+ channels, as it was fully prevented by nifedipine. Conversely, blockade of NMDA and AMPA glutamate receptor did not affect either LTP or the magnitude of the [Ca2+]i rise. Interestingly, the pharmacological analysis of the post-tetanic depolarizing postsynaptic potential (DPSP) revealed that LTP was attributable, to a large extent, to the potentiation of the GABA(A)-mediated component. In conclusion, the expression of LTP in striatal cholinergic interneurons is a selective response to a precise stimulation pattern of induction requiring a critical rise in [Ca2+]i.

Animals↗
PubMed2005

The cerebellum modulates rodent cortical motor output after repetitive somatosensory stimulation.

OBJECTIVE: To analyze the possible role of the cerebellum in the modulation of cortical motor output associated with repetitive electrical stimulation of the sciatic nerve in the rat. METHODS: A sustained somatosensory stimulation induces an increase in the intensity of the response of the rodent motor cortex. Wistar rats were anesthetized for surgical preparation using a continuous infusion of chloral hydrate. We analyzed the response evoked by electrical stimulation of the right motor cortex before (basal condition) and after peripheral electrical stimulation of the left sciatic nerve in rats with no cerebellar intervention (n = 6), and in control rats with Ringer's infusion via a microdialysis probe (n = 8) implanted in the left cerebellar nuclei. In addition, we investigated the effects of 1) the administration of ethanol (20 mmol/L) in the left cerebellar nuclei (n = 5); 2) the administration of tetrodotoxin (10 micromol/L), a sodium channel blocker, in the left cerebellar nuclei (n = 5); 3) electrical stimulation by deep cerebellar stimulation (frequency 100 Hz) on the left side (n = 5); or 4) electrical stimulation of the cerebellar nuclei on the right side (100 Hz; n = 6). For peripheral stimulation, all of the animals received 1 hour of electrical stimulation. Trains of stimulation consisted of five stimuli (duration of 1 stimulus, 1 ms) at a rate of 10 Hz. During stimulation of the motor cortex, peak-to-peak amplitudes in responses of the left calf muscle were analyzed. Motor threshold was defined as the lowest intensity eliciting at least 5 of 10 evoked responses with an amplitude greater than 20 muV. The intensity used was 130% of the motor threshold. RESULTS: In the basal condition (before repetitive stimulation), amplitudes of motor responses were similar in the six groups of rats (P = 0.40). In rats without cerebellar intervention, peripheral electrical stimulation was associated with an increase of motor response to 147.4 +/- 8.5% of baseline (P < 0.001). In rats with Ringer's infusion, the motor response increased to 141.6 +/- 7.9% of baseline (P < 0.001). The administration of ethanol in the cerebellum prevented the enhancement of the response ipsilaterally. The mean +/- standard deviation (SD) of motor responses was 105.7 +/- 6.2% of baseline measurements after stimulation of the sciatic nerve (P = 0.36). The same observation was made after the infusion of tetrodotoxin (mean +/- SD of motor responses: 107.1 +/- 7.4% after peripheral stimulation [P = 0.19] and after electrical stimulation of the cerebellum on the left side [mean +/- SD of motor responses, 104.3 +/- 8.5% after peripheral stimulation, P = 0.40]). However, electrical stimulation of cerebellar nuclei on the right side did not impair the modulation of cortical motor output by sciatic nerve stimulation (mean +/- SD of motor responses, 148.4 +/- 5.8% after peripheral stimulation, P < 0.001). CONCLUSION: Until now, the increase of motor output after peripheral nerve stimulation has been considered as a plasticity directly and solely dependent on cortical structures. We demonstrate that the cerebellum plays a key role in this form of neural plasticity.

Animals↗
PubMed1983

The utilization of transcutaneous electric nerve stimulation in postoperative ileus.

Pain stimuli with resulting sympathetic hyperactivity are responsible for the inhibition of intestinal motility. In this clinical study on 30 adult patients after laparotomy, the effect of intermittent transcutaneous stimulation with a diadynamic current on intestinal motility was determined. It was established that bowel sounds return soon after transcutaneous nerve stimulation, and more than 50% of the patients passed flatus within 24 hours after the commencement of stimulation.

Adult↗
PubMed1973

Neuromuscular transmission in a mammalian preparation in the absence of blocking drugs and the effect of D-tubocurarine.

1. Neuromuscular transmission in the presence and absence of D-tubocurarine was examined in cut muscle preparations of the rat diaphragm using intracellular recording techniques. The method of localizing the end-plates is described and evidence is presented indicating that end-plate potential (e.p.p.) recordings were made close to the end-plate region and that reliable estimates of the quantum content of e.p.p.s could be made.2. During repetitive nerve stimulation at rates between 2 and 10 Hz, e.p.p. amplitudes declined in response to the first 6-8 stimuli to reach a plateau level which was maintained for 1500 stimuli. At higher rates of stimulation some 500-700 stimuli were needed before a plateau level of amplitude was reached. It was demonstrated that these amplitude changes reflected similar changes in the quantal release of ACh.3. Tubocurarine in a concentration of 4 x 10(-8) g/ml. had no effect on quantal release but did reduce quantal size. In the presence of tubocurarine, 8 x 10(-8) g/ml., small reductions in the quantum content of the first e.p.p. in response to a train of stimuli and the maintained quantal release were observed. In the presence of tubocurarine 4 x 10(-7) g/ml., the quantum content of the first e.p.p. and the maintained release were further reduced, to the level previously described for curarized preparations. At this concentration a significant effect of tubocurarine upon the presynaptic measurements could be detected (t test). Studies on single junctions revealed that the post- and presynaptic effects of tubocurarine developed with different time courses.4. Neuromuscular preparations in vivo have been reported to be much more resistant to maintatined stimulation than curarized neuromuscular preparations in vitro. It is suggested that this disparity is explained by the presynaptic action of tubocurarine.5. From the quantal release rates of the present investigation and reports of ACh release/stimulus/end-plate in previous investigations it can be calculated that a quantum of ACh contains between 12,000 and 21,000 molecules.

Acetylcholine↗
PubMed1992

Changes in the distributed temporal response properties of SI cortical neurons reflect improvements in performance on a temporally based tactile discrimination task.

1. Temporal response characteristics of neurons were sampled in fine spatial grain throughout the hand representations in cortical areas 3a and 3b in adult owl monkeys. These monkeys had been trained to detect small differences in tactile stimulus frequencies in the range of 20-30 Hz. Stimuli were presented to an invariant, restricted spot on a single digit. 2. The absolute numbers of cortical locations and the cortical area over which neurons showed entrained frequency-following responses to behaviorally important stimuli were significantly greater when stimulation was applied to the trained skin, as compared with stimulation on an adjacent control digit, or at corresponding skin sites in passively stimulated control animals. 3. Representational maps defined with sinusoidal stimuli were not identical to maps defined with just-visible tapping stimuli. Receptive-field/frequency-following response site mismatches were recorded in every trained monkey. Mismatches were less frequently recorded in the representations of control skin surfaces. 4. At cortical locations with entrained responses, neither the absolute firing rates of neurons nor the degree of the entrainment of the response were correlated with behavioral discrimination performance. 5. All area 3b cortical locations with entrained responses evoked by stimulation at trained or untrained skin sites were combined to create population peristimulus time and cycle histograms. In all cases, stimulation of the trained skin resulted in 1) larger-amplitude responses, 2) peak responses earlier in the stimulus cycle, and 3) temporally sharper responses, than did stimulation applied to control skin sites. 6. The sharpening of the response of cortical area 3b neurons relative to the period of the stimulus could be accounted for by a large subpopulation of neurons that had highly coherent responses. 7. Analysis of cycle histograms for area 3b neuron responses revealed that the decreased variance in the representation of each stimulus cycle could account for behaviorally measured frequency discrimination performance. A strong correlation between these temporal response distributions and the discriminative performances for stimuli applied at all studied skin surfaces was even stronger (r = 0.98) if only the rising phases of cycle histogram were considered in the analysis. 8. The responses of neurons in area 3a could not account for measured differences in frequency discrimination performance. 9. These representational changes did not occur in monkeys that were stimulated on the same schedule but were performing an auditory discrimination task during skin stimulation. 10. It is concluded that by behaviorally training adult owl monkeys to discriminate the temporal features of a tactile stimulus, distributed spatial and temporal response properties of cortical neurons are altered.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1977

The intensity-dependent changes of the visual evoked responses in man to patterned and blank stimulation.

The visual evoked responses (VERs) to blank and checkerboard-patterned stimuli of 6 degrees angular subtense were recorded referentially (OZ--A2) in 10 dark-adapted subjects using a range of 5.27 log units of intensity (maximum luminance = 6420 cd/m2). The mean peak latencies of the prominent positive-negative deflection of the VERs to the blank stimuli exhibit an exponential shortening with the rise of log stimulation intensity. The peak latencies of the positive-negative deflection of the VERs to the checkerboard-pattern stimulation at low and moderate intensities are by about 50 ms shorter, with the latency of the negative peak of the response to the patterned stimulation corresponding to the positive peak latency of the response to the blank stimuli. Accordingly, the VERs to both types of stimulation are of opposite polarity. With a further increase of the stimulation intensity, the latency of the negative peak of the VER to patterned stimulation gradually lengthens due to the glaring effects of the patterned stimuli. Therefore, at high stimulation intensities the VERs to both types of stimuli are of the same polarity. The mean peak-to-peak amplitudes of the VERs to both types of stimulation differ significantly at high-intensity end of the photostimulation range only, the amplitude of the VER to the patterned stimulation being higher.

Adult↗
PubMed1978

On the stimulation of rat thymocyte 3-O-methyl-glucose transport by mitogenic stimuli.

Pretreatment of rat thymus lymphocytes with N-ethyl-maleimide prevents the stimulation of 3-O-methyl-glucose transport by concanavalin A or ionophore A23187 but does not affect the ability of concanavalin A to induce a rapid increase in cellular Ca2+take. N-ethyl-maleikide added after concanavalin A amplifies rather than prevents the subsequent stimulation of 3-O-methyl-glucose transport. Incubation of thymocytes with concanavalin A produces a decrease of 43% in the apparent Ki for phloretin, a competitive inhibitor of 3-O-methyl-glucose transport, without affecting the apparent Km for the substrate. Similarly, very low concentrations of cytochalasin B inhibit concanavalin A-stimulated glucose transport preferentially, without markedly affecting the unstimulated transport rates. The similarity between concanavalin A-stimulated 3-O-methyl-glucose transport in thymocytes and insulin-stimulated glucose transport in adipose tissue, with particular emphasis on the effects of the modifying agents described in this paper, is discussed.

Animals↗
PubMed1995

Effect of hemisphere-selective repetitive magnetic brain stimulation on middle cerebral artery blood flow velocity.

The changes of cerebral hemodynamics following repetitive hemisphere-selective magnetic stimulation over the motor cortex were investigated in 8 healthy volunteers. Bilateral simultaneous monitoring of middle cerebral artery blood flow velocity was done using transcranial Doppler ultrasonography during magnetic stimulation with single, double and triple stimuli with interstimulus intervals of 100 msec. Magnetic cortex stimulation was followed by a significant increase of ipsilateral flow velocity ranging from 5.3% +/- 2.7% for single stimuli up to 8.5% +/- 4.1% for triple stimuli and by a smaller increase of contralateral flow velocity. The ipsilateral increases are comparable to those measured previously during voluntary finger movements and indicate a physiological cortex stimulation. In parallel, the average sum of the baseline to peak hand motor response amplitudes increased from 1.5 +/- 0.7 mV (single stimuli) to 4.5 +/- 3.2 mV (triple stimuli). The increase of flow velocity in the non-stimulated hemisphere occurred during the absence of motor responses and might reflect a transcallosal activation of inhibitory neuronal structures. The occurrence of maximum velocity responses within 2-3 heartbeats following the first cortex stimulus points to a fast adjustment of cerebral perfusion in response to transcranial brain stimulation. No significant change of flow velocity was observed following motor responses evoked by unilateral magnetic stimulation of the brachial plexus or following acoustic artifacts of the coil discharge.

Adult↗