			Home About us Contact

Extracellular Electrodes (extracellular + electrode)

Distribution by Scientific Domains

Medical Sciences	75%

Selected Abstracts

Effect of Interictal Spikes on Single-Cell Firing Patterns in the Hippocampus

EPILEPSIA, Issue 4 2007
Jun-Li Zhou
Summary:,Purpose: The interictal EEG spike(s) is the hallmark of the epileptic EEG. While focal interictal spike (IS) have been associated with transitory cognitive impairment, with the type of deficit dependent on where in the cortex the IS arises, the mechanism by which IS result in transitory dysfunction is not known. The purpose of this study was to determine the effect of IS on single-cell firing patterns in freely moving rats with a prior history of seizures. Methods: We studied IS in two seizure models; pilocarpine-induced status epilepticus and recurrent flurothyl models. The effect of spontaneous hippocampal spikes on action potentials (APs) of CA1 cells in rats walking in a familiar environment was investigated using 32 extracellular electrodes. We also compared the effect of spikes on two types of hippcampal cells; place cells that discharge rapidly only when the rat's head is in a specific part of the environment, the so-called firing field, and interneurons, which are a main source of inhibition in the hippocampus. Results: IS were associated with a decreased likelihood of AP compared with IS-free portions of the record. Compared to pre-IS baseline, IS were followed by significant decreases in CA1 APs for periods up to 2 s following the IS in both models. When occurring in flurries, IS were associated with a pronounced decrease in APs. The response to IS was cell-dependent; IS resulted in decreases in AP firing after the IS in interneurons but not place cells. Conclusions: This study demonstrates that IS have substantial effects on cellular firing in the hippocampus and that these effects last far longer than the spike and slow wave. Furthermore, the effect of IS on cellular firing was cell specific, affecting interneurons more than place cells. These findings suggest that IS may contribute to seizure-induced cognitive impairment by altering AP firing in a cell-specific manner. [source]

Cooling Abolishes Neuronal Network Synchronization in Rat Hippocampal Slices

EPILEPSIA, Issue 6 2002
Sam P. Javedan
Summary: ,Purpose: We sought to determine whether cooling brain tissue from 34 to 21°C could abolish tetany-induced neuronal network synchronization (gamma oscillations) without blocking normal synaptic transmission. Methods: Intracellular and extracellular electrodes recorded activity in transverse hippocampal slices (450,500 ,m) from Sprague,Dawley male rats, maintained in an air,fluid interface chamber. Gamma oscillations were evoked by afferent stimulation at 100 Hz for 200 ms. Baseline temperature in the recording chamber was 34°C, reduced to 21°C within 20 min. Results: Suprathreshold tetanic stimuli evoked membrane potential oscillations in the 40-Hz frequency range (n = 21). Gamma oscillations induced by tetanic stimulation were blocked by bicuculline, a ,-aminobutyric acid (GABA)A -receptor antagonist. Cooling from 34 to 21°C reversibly abolished gamma oscillations in all slices tested. Short, low-frequency discharges persisted after cooling in six of 14 slices. Single-pulse,evoked potentials, however, were preserved after cooling in all cases. Latency between stimulus and onset of gamma oscillation was increased with cooling. Frequency of oscillation was correlated with chamber cooling temperature (r = 0.77). Tetanic stimulation at high intensity elicited not only gamma oscillation, but also epileptiform bursts. Cooling dramatically attenuated gamma oscillation and abolished epileptiform bursts in a reversible manner. Conclusions: Tetany-induced neuronal network synchronization by GABAA -sensitive gamma oscillations is abolished reversibly by cooling to temperatures that do not block excitatory synaptic transmission. Cooling also suppresses transition from gamma oscillation to ictal bursting at higher stimulus intensities. These findings suggest that cooling may disrupt network synchrony necessary for epileptiform activity. [source]

Role of GABAA inhibition in modulation of pyramidal tract neuron activity during postural corrections

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2007
Zinaida A. Tamarova
Abstract In a previous study we demonstrated that the activity of pyramidal tract neurons (PTNs) of the motor cortex is modulated in relation to postural corrections evoked by periodical tilts of the animal. The modulation included an increase in activity in one phase of the tilt cycle and a decrease in the other phase. It is known that the motor cortex contains a large population of inhibitory GABAergic neurons. How do these neurons participate in periodic modulation of PTNs? The goal of this study was to investigate the role of GABAA inhibitory neurons of the motor cortex in the modulation of postural-related PTN activity. Using extracellular electrodes with attached micropipettes, we recorded the activity of PTNs in cats maintaining balance on a tilting platform both before and after iontophoretic application of the GABAA receptor antagonists gabazine or bicuculline. The tilt-related activity of 93% of PTNs was affected by GABAA receptor antagonists. In 88% of cells, peak activity increased by 75 ± 50% (mean ± SD). In contrast, the trough activity changed by a much smaller value and almost as many neurons showed a decrease as showed an increase. In 73% of the neurons, the phase position of the peak activity did not change or changed by no more than 0.1 of a cycle. We conclude that the GABAergic system of the motor cortex reduces the posture-related responses of PTNs but has little role in determining their response timing. [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]