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Spike Activity (spike + activity)

Distribution by Scientific Domains

Medical Sciences	68%
Life Sciences	31%

Selected Abstracts

Effects of Potassium Concentration on Firing Patterns of Low-Calcium Epileptiform Activity in Anesthetized Rat Hippocampus: Inducing of Persistent Spike Activity

EPILEPSIA, Issue 4 2006
Zhouyan Feng
Summary:,Purpose: It has been shown that a low-calcium high-potassium solution can generate ictal-like epileptiform activity in vitro and in vivo. Moreover, during status epileptiform activity, the concentration of [K+]o increases, and the concentration of [Ca2+]o decreases in brain tissue. Therefore we tested the hypothesis that long-lasting persistent spike activity, similar to one of the patterns of status epilepticus, could be generated by a high-potassium, low-calcium solution in the hippocampus in vivo. Methods: Artificial cerebrospinal fluid was perfused over the surface of the exposed left dorsal hippocampus of anesthetized rats. A stimulating electrode and a recording probe were placed in the CA1 region. Results: By elevating K+ concentration from 6 to 12 mM in the perfusate solution, the typical firing pattern of low-calcium ictal bursts was transformed into persistent spike activity in the CA1 region with synaptic transmission being suppressed by calcium chelator EGTA. The activity was characterized by double spikes repeated at a frequency ,4 Hz that could last for >1 h. The analysis of multiple unit activity showed that both elevating [K+]o and lowering [Ca2+]o decreased the inhibition period after the response of paired-pulse stimulation, indicating a suppression of the after-hyperpolarization (AHP) activity. Conclusions: These results suggest that persistent status epilepticus,like spike activity can be induced by nonsynaptic mechanisms when synaptic transmission is blocked. The unique double-spike pattern of this activity is presumably caused by higher K+ concentration augmenting the frequency of typical low-calcium nonsynaptic burst activity. [source]

Search for cerebral G cluster neurons responding to taste stimulation with seaweed in Aplysia kurodai by the use of calcium imaging

DEVELOPMENTAL NEUROBIOLOGY, Issue 3 2003
Ryusuke Yoshida
Abstract The calcium imaging method can detect the spike activities of many neurons simultaneously. In the present experiments, this method was used to search for unique neurons contributing to feeding behavior in the cerebral ganglia of Aplysia kurodai. We mainly explored the neurons whose cell bodies were located in the G cluster and the neuropile region posterior to this cluster on the ventral surface of the cerebral ganglia. When the extract of the food seaweed Ulva was applied to the tentacle-lip region, many neurons stained with a calcium-sensitive dye, Calcium Green-1, showed changes in fluorescence. Some neurons showed rhythmic responses and others showed transient responses, suggesting that these neurons may be partly involved in the feeding circuits. We also identified three motor neurons among these neurons that showed rhythmic fluorescence responses to the taste stimulation. One of them was a motor neuron shortening the anterior tentacle (ATS), and the other two were motor neurons producing lip opening-like (LOG) and closing-like (LCG) movements, respectively. Application of the Ulva extract to the tentacle-lip region induced phase-locked rhythmic firing activity in these motor neurons, suggesting that these neurons may contribute to the rhythmic patterned movements of the anterior tentacles and lips during the ingestion of seaweed. © 2003 Wiley Periodicals, Inc. J Neurobiol 55: 299,314, 2003 [source]

Encoding of whisker input by cerebellar Purkinje cells

THE JOURNAL OF PHYSIOLOGY, Issue 19 2010
Laurens W. J. Bosman
The cerebellar cortex is crucial for sensorimotor integration. Sensorimotor inputs converge on cerebellar Purkinje cells via two afferent pathways: the climbing fibre pathway triggering complex spikes, and the mossy fibre,parallel fibre pathway, modulating the simple spike activities of Purkinje cells. We used, for the first time, the mouse whisker system as a model system to study the encoding of somatosensory input by Purkinje cells. We show that most Purkinje cells in ipsilateral crus 1 and crus 2 of awake mice respond to whisker stimulation with complex spike and/or simple spike responses. Single-whisker stimulation in anaesthetised mice revealed that the receptive fields of complex spike and simple spike responses were strikingly different. Complex spike responses, which proved to be sensitive to the amplitude, speed and direction of whisker movement, were evoked by only one or a few whiskers. Simple spike responses, which were not affected by the direction of movement, could be evoked by many individual whiskers. The receptive fields of Purkinje cells were largely intermingled, and we suggest that this facilitates the rapid integration of sensory inputs from different sources. Furthermore, we describe that individual Purkinje cells, at least under anaesthesia, may be bound in two functional ensembles based on the receptive fields and the synchrony of the complex spike and simple spike responses. The ,complex spike ensembles' were oriented in the sagittal plane, following the anatomical organization of the climbing fibres, while the ,simple spike ensembles' were oriented in the transversal plane, as are the beams of parallel fibres. [source]

Effects of Potassium Concentration on Firing Patterns of Low-Calcium Epileptiform Activity in Anesthetized Rat Hippocampus: Inducing of Persistent Spike Activity

Neocortical Microenvironment in Patients with Intractable Epilepsy: Potassium and Chloride Concentrations

EPILEPSIA, Issue 2 2006
Ali Gorji
Summary:,Purpose: The regulation of extracellular ion concentrations plays an important role in neuronal function and epileptogenesis. Despite the many studies into the mechanisms of epileptogenesis in human experimental models, no data are available regarding the fluctuations of extracellular potassium ([K+]o) and chloride ([Cl,]o) concentrations, which could underlie seizure susceptibility in human chronically epileptic tissues in vivo. Methods: By using cerebral microdialysis during surgical resection of epileptic foci, the basic [K+]o and [Cl,]o as well as their changes after epicortical electric stimulation were studied in samples of dialysates obtained from 11 patients by ion-selective microelectrodes. Results: The mean basal values of [K+]o and [Cl,]o in all patients were 3.83 ± 0.08 mM and 122.9 ± 2.6 mM, respectively. However, significant differences were observed in the basal levels of both [K+]o and [Cl,]o between different patients. Statistically, no correlation was found between basal [K+]o or [Cl,]o and electrocorticogram (ECoG) spike activity, but in one patient, dramatically lowered baseline [Cl,]o was accompanied by enhanced ECoG spike activity. Application of epicortical electrical stimulation increased [K+]o but not [Cl,]o in all cases. According to the velocity as well as spatial distribution of [K+]o reduction to the prestimulation levels, three different types of responses were observed: slow decline, fast decline, and slow and fast declines at adjacent sites. Conclusions: These data may represent abnormalities in ion homeostasis of the epileptic brain. [source]

Intracellular Calcium Increase in Epileptiform Activity: Modulation by Levetiracetam and Lamotrigine

EPILEPSIA, Issue 7 2004
Antonio Pisani
Summary:,Purpose: Alterations in neuronal calcium (Ca2+) homeostasis are believed to play an essential role in the generation and propagation of epileptiform events. Levetiracetam (LEV) and lamotrigine (LTG), novel antiepileptic drugs (AEDs), were tested on epileptiform events and the corresponding elevations in intracellular Ca2+ concentration ([Ca2+]i) recorded from rat neocortical slices. Methods: Electrophysiological recordings were performed from single pyramidal neurons from a slice preparation. Spontaneous epileptiform events consisting of long-lasting, repetitive paroxysmal depolarization shifts (PDSs) and interictal spike activity were induced by reducing the magnesium concentration from the solution and by adding bicuculline and 4-aminopyridine. Simultaneously, microfluorimetric measurements of [Ca2+]i were performed. Optical imaging with Ca2+ indicators revealed a close correlation between Ca2+ transients and epileptiform events. Results: Both LEV and LTG were able to reduce both amplitude and duration of PDSs, as well as the concomitant elevation in [Ca2+]i, in a dose-dependent fashion. Whole-cell patch-clamp recordings from isolated neocortical neurons revealed that LEV significantly reduced N-, and partially P/Q-type high-voltage-activated (HVA) Ca2+ currents, whereas sodium currents were unaffected. Interestingly, the inhibitory effects of LEV were mimicked and occluded by LTG or by a combination of ,-conotoxin GVIA and ,-agatoxin IVA, selective blockers of N- and P/Q-type HVA channels, respectively, suggesting a common site of action for these AEDs. Conclusions: These results demonstrate that large, transient elevations in neuronal [Ca2+]i correlate to epileptiform discharges. The antagonistic effects of LEV and LTG on [Ca2+]i overload might represent the basis for their anticonvulsant efficacy and could preserve neuronal viability. [source]

Activity-dependent maturation of excitatory synaptic connections in solitary neuron cultures of mouse neocortex

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2005
Naoki Takada
Abstract Activity plays important roles in the formation and maturation of synaptic connections. We examined these roles using solitary neocortical excitatory neurons, receiving only self-generated synaptic inputs, cultured in a microisland with and without spontaneous spike activity. The amplitude of excitatory postsynaptic currents (EPSCs), evoked by applying brief depolarizing voltage pulses to the cell soma, continued to increase from 7 to 14 days in culture. Short-term depression of EPSCs in response to paired-pulse or 10-train-pulse stimulation decreased with time in culture. These developmental changes were prevented when neurons were cultured in a solution containing tetrodotoxin (TTX). The number of functional synapses estimated by recycled synaptic vesicles with FM4-64 was significantly smaller in TTX-treated than control neurons. However, the miniature EPSC amplitude remained unchanged during development, irrespective of activity. Transmitter release probability, assessed by use-dependent blockade of N -methyl- d -aspartate receptor-mediated EPSCs with MK-801, was higher in TTX-treated than control neurons. Therefore, the activity-dependent increase in EPSC amplitude was mainly ascribed to the increase in synapse number, while activity-dependent alleviation of short-term depression was mostly ascribed to the decrease in release probability. The effect of activity blockade on short-term depression, but not EPSC amplitude, was reversed after 4 days of TTX removal, indicating that synapse number and release probability are controlled by activity in very different ways. These results demonstrate that activity regulates the conversion of immature synapses transmitting low-frequency input signals preferentially to mature synapses transmitting both low- and high-frequency signals effectively, which may be necessary for information processing in mature cortex. [source]

The isochronic band hypothesis and climbing fibre regulation of motricity: an experimental study

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2001
Masaji Fukuda
Abstract The dynamic organization of the olivocerebellar afferent input to Purkinje cells was examined in rat cerebellar cortex. The distribution of synchronous Purkinje cell complex spike activity was characterized, bilaterally, utilizing multiple electrode recordings in crus IIa folium under ketamine anaesthesia. The results confirmed the existence of rostrocaudal complex spike isochronicity bands with a mediolateral width of 500 µm. For a given band, no finer spatial submicrostructures could be discerned at a first-order approximation (two-dimensional projection). Closer analysis determined that isochronicity between bands is not continuous in space but demonstrates discrete discontinuities at the mediolateral boundaries. Principal component multivariate analysis revealed that the first principal component of the spatio-temporal variance is synchronicity along the rostrocaudal band with a decreased level of coupling in the mediolateral direction at the band boundary. Furthermore, this discrete banding isochronicity is organized by the distribution of feedback inhibition from the cerebellar nuclei on to the inferior olive nucleus. The usual multiple band structure can be dynamically altered to a single wide-band dynamic architecture, or to other patterns of activity, as may be required by movement coordination. [source]

Bilaterally synchronous complex spike Purkinje cell activity in the mammalian cerebellum

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 2 2001
Tomoya Yamamoto
Abstract Complex spike activity was simultaneously recorded from 96 Purkinje cells in the rat cerebellar cortex. Rostrocaudal complex spike synchronicity bands were studied in crus I, IIa and IIb and in vermal lobule 6c. Detailed analysis in crus IIa revealed that complex spike activity was staggered sequentially with a 20,50 cm/sec ,propagation velocity' in the mediolateral direction, and that such activity was bilaterally synchronous. The ,propagation' of complex spike activity was symmetrical between right and left crus IIa. Temporally, the neurons that aligned in the rostrocaudal direction typically generated complex spikes close to simultaneously. The correlation of complex spike firing was high between crus IIa and crus IIb, moderate between crus IIa and vermis 6c, and relatively low between Purkinje cells in crus I and crus IIa. These results indicate that, whilst discrete boarders exist between different isochronicity bands, these bands do communicate with each other in the mediolateral direction via slow ,propagation waves' that loosely bind their activity. The results indicate that the olivocerebellar system is organized, bilaterally, to take advantage of the timing signals generated at the inferior olive nucleus. [source]

Direct Inhibitory Effect of Glucocorticoids on Corticotrophin-Releasing Hormone Gene Expression in Neurones of the Paraventricular Nucleus in Rat Hypothalamic Organotypic Cultures

JOURNAL OF NEUROENDOCRINOLOGY, Issue 9 2008
B. Bali
Corticotrophin-releasing hormone (CRH) in the parvocellular neurosecretory neurones of hypothalamic paraventricular nucleus governs neuroendocrine stress cascade and is the major target of the negative feedback effect of corticosteroids. To assess whether glucocorticoids exert their inhibitory effect on CRH expression directly on parvocellular neurones or indirectly through a complex neuronal circuit, we examined the effect of corticosterone (CORT) and dexamethasone (DEX) on CRH mRNA levels in slice explant cultures of the rat hypothalamus. Organotypic slice cultures were prepared from 6 days old rat pups and maintained in vitro for 14 days. CRH mRNA expression was measured by in situ hybridisation histochemistry. Under basal conditions, CRH mRNA expressing cells were exclusively revealed in the paraventricular region along the third ventricle. Inhibition of action potential spike activity by tetrodotoxin (TTX, 1 ,m) reduced CRH mRNA signal in the organotypic cultures. CORT (500 nm) or DEX (50 nm) treatment for 24 h significantly inhibited CRH expression in the parvocellular neurones and this effect of corticosteroids was not affected following blockade of voltage dependent sodium channels by TTX. Forskolin-stimulated CRH mRNA levels in the paraventricular nucleus were also inhibited by CORT or DEX in the presence and in the absence of TTX. These studies identify paraventricular CRH neurones as direct target of corticosteroid feedback. Type II corticosteroid receptor agonists act directly on paraventricular neurones to inhibit basal and forskolin-induced CRH mRNA expression in explant cultures of the rat hypothalamus. [source]

Tetrodotoxin-induced conduction blockade is prolonged by hyaluronic acid with and without bupivacaine

ACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 1 2004
M. F. Stevens
Background:, In isolated nerves, tetrodotoxin (TTX) blocks nerve conduction longer than bupivacaine. In vivo, however, both substances block nerve conduction to an equal duration, presumably because the hydrophilic TTX binds only weakly to the perineural tissue. High molecular weight hyaluronic acid (HA) prolongs the action of local anaesthetics several-fold. We tested whether admixture of HA enhances the binding of TTX to the perineural tissue and thus induces an ultralong conduction block after a single application. Methods:, In 12 anaesthetized rabbits, the minimal blocking concentrations of TTX, TTX and HA (TTX/HA) and bupivacaine with HA (bupivacaine/HA) were determined by blocking the natural spike activity of the aortic nerve. In 18 other animals, equipotent concentrations of either TTX, TTX/HA or TTX/bupivacaine/HA were applied topically to the aortic nerve. After disappearance of the spike activity, the wound was closed to simulate the clinical situation of a single shot nerve block. The time until recovery of spike activity was determined. The nerves were examined for signs of neurotoxicity 24 h after the application of the drugs. Data are presented as means ± SD and compared by ANOVA and Student's t -test for unpaired data. Results:, The conduction block by TTX/bupivacaine/HA (10.1 ± 1.9 h) or TTX/HA (9.3 ± 1.0 h) was significantly longer than that of plain TTX (7.9 ± 1.0 h). Neurotoxicity was not observed. Conclusions:, Both HA and HA/bupivacaine prolong the TTX-induced conduction blockade of the aortic nerve of rabbits in vivo. No signs of neurotoxicity were observed. [source]

Spatial determination of successive spikes in the isolated cat duodenum

NEUROGASTROENTEROLOGY & MOTILITY, Issue 6 2004
W. J. E. P. Lammers
Abstract, In seven isolated segments of the feline duodenum, the timings of all spikes and the locations of all spike patches that occurred after 12,16 successive slow waves were analysed. Simultaneous recordings were performed during 1-min periods using 240 extracellular electrodes (24 × 10 array; interelectrode distance 2 mm) positioned onto the serosal surface. In all seven preparations, spikes always occurred during the first half of the slow wave cycle. From preparation to preparation, and within 1-min periods in each preparation, there was limited variation in the spike,spike intervals, in the times between the spikes and the preceding slow wave and in the number of spikes at each electrode site. In contrast, the number of electrode sites that recorded spikes and the number of spike patches both showed great variability between preparations and sometimes within a single preparation. In addition, the location of spikes and spike patches was not random but was significantly concentrated in certain areas, often located along the anti-mesenteric border, while other sites showed little or no spike activity. In conclusion, spikes and spike patches tend to occur significantly in some areas and not in others. This spatial heterogeneity will play a role in intestinal motility. [source]

Hyperventilation-stage electroencephalography in lateral temporal lobe epilepsy

ACTA NEUROPSYCHIATRICA, Issue 1 2007
Shuichiro Asano
Background:, To observe spike activity in electroencephalograms (EEGs), patients with symptomatic partial epilepsy are rarely monitored during the hyperventilation stages. Case:, A 38-year-old woman suffered from a ruptured arteriovenous malformation in the left temporal lobe. One and a half years later, the patient experienced her first generalized convulsion. EEG showed small spikes in the posterior of the left temporal lobe, which was observed during the hyperventilation and posthyperventilation stages. Because the location of the spikes correlated with the site of the lesion as observed from radiographic findings, she was diagnosed with lateral temporal lobe epilepsy. Drug treatment resulted in no further convulsive episodes and the patient has since returned to work. Conclusion:, EEG recordings during hyperventilation should be regarded as an effective technique in analyzing epilepsy because of its ease and cost-effectiveness compared with other methods such as single-photon emission computed tomography. [source]