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At least 109 records · Page 6Linked to original sources
PubMed2002

Firing patterns of inferior colliculus neurons-histology and mechanism to change firing patterns in rat brain slices.

An in vitro slice preparation was used for intracellular recording from rat central nucleus of inferior colliculus neurons (CNIC). Stable intracellular recordings were made on 184 neurons, 27 of which were successfully stained with iontophoresed biocytin. Twenty one of those were classified as flat (F), four as less flat (LF) and the remaining two neurons as unclassified neurons. Recording in response to depolarizing current steps revealed five firing patterns: onset, adapting (regularly and irregularly), regular and bursting. The onset neurons showed non-linear current-voltage (I-V) relationship, whereas the rest had linear current-voltage relationship. Preconditioning hyperpolarizations changed the response pattern of CNIC neurons. It is concluded that there is no anatomy and physiology correlation and the levels of membrane potential may be important in the production of some firing patterns.

Action Potentials↗
PubMed1999

Fire-diffuse-fire model of dynamics of intracellular calcium waves.

When Ca2+ is released from internal stores in living cells, the resulting wave of increased concentration can travel without deformation (continuous propagation) or with burst-like behavior (saltatory propagation). We analyze the "fire-diffuse-fire" model in order to illuminate the differences between these two modes of propagation. We show that the Ca2+ release wave in immature Xenopus oocytes and cardiac myocytes is saltatory, whereas the fertilization wave in the mature oocyte is continuous.

Animals↗
PubMed2003

Sparks and waves in a stochastic fire-diffuse-fire model of Ca2+ release.

Calcium ions are an important second messenger in living cells. Indeed, calcium signals in the form of waves have been the subject of much recent experimental interest. It is now well established that these waves are composed of elementary stochastic release events (calcium puffs or sparks) from spatially localized calcium stores. Here we develop a computationally inexpensive model of calcium release, based upon a stochastic generalization of the fire-diffuse-fire threshold model. Our model retains the discrete nature of calcium stores, but also incorporates a notion of release probability via the introduction of threshold noise. Numerical simulations of the model illustrate that stochastic calcium release leads to the spontaneous production of calcium sparks that may merge to form saltatory waves. In the parameter regime where deterministic waves exist, it is possible to identify a critical level of noise, defining a nonequilibrium phase transition between propagating and abortive structures. A statistical analysis shows that this transition is the same as for models in the directed percolation universality class. Moreover, in the regime where no initial structure can survive deterministically, threshold noise is shown to generate a form of array enhanced coherence resonance, whereby all calcium stores release periodically and simultaneously.

Biophysical Phenomena↗
PubMed2004

Directed percolation in a two-dimensional stochastic fire-diffuse-fire model.

We establish, from extensive numerical experiments, that the two dimensional stochastic fire-diffuse-fire model belongs to the directed percolation universality class. This model is an idealized model of intracellular calcium release that retains both the discrete nature of calcium stores and the stochastic nature of release. It is formed from an array of noisy threshold elements that are coupled only by a diffusing signal. The model supports spontaneous release events that can merge to form spreading circular and spiral waves of activity. The critical level of noise required for the system to exhibit a nonequilibrium phase transition between propagating and nonpropagating waves is obtained by an examination of the local slope delta (t) of the survival probability Pi(t) proportional exp [-delta(t)] for a wave to propagate for a time t .

Action Potentials↗
PubMed1990

[Reactions at the nonprecious metal-ceramic interface during porcelain firing. (3) A commercial alloy forming much Cr oxide during firing].

To examine the interface reaction between porcelain and a commercial Ni-Cr dental alloy (containing higher Cr and Mo) during porcelain firing, electron probe microanalyzer (EPMA) and X-ray diffraction have been used to characterize the interface which has emerged by means of selective dissolution of the alloy caused by a bromine-methanol solution. Much Cr oxide was formed at the early stage of firing, and remained in the reaction layer even if the holding time at 960 degrees C was up to 8 minutes. As a result, many Cr atoms diffused into the porcelain layer, most of which was found to form oxides through X-ray diffraction. Moreover, the porcelain layer nearest to the oxide layer was deduced to be modified seriously.

Chromium↗
PubMed1987

Fire prevention in the United States. Are the home fires still burning?

Injury and death from burns have reached epidemic levels in the United States during the past quarter-century. Yet preventive action on both local and national administrative levels has been dismally inadequate and underfunded. Identifying and recognizing both the etiologies of burn injuries and the statistical magnitude of the problem will, it is hoped, stimulate dedication of more resources and personnel to reducing the hazards of fire and the resulting loss of life, productivity, and property in the next two decades. Public education and national awareness are first steps to creation of a consumer and popular demand worthy of national action.

Adolescent↗
PubMed1997

Fighting fire with fire.

Post-traumatic stress disorder (PTSD) is a relatively recent diagnostic category, but it has long been recognised that trauma can produce persistent psychological sequelae. Paul Wheble describes how he successfully used cognitive behavioural therapy to help Alec, a fire-fighter, come to terms with an horrific accident 16 years previously.

Fires↗
PubMed1978

Hippocampal place units in the freely moving rat: why they fire where they fire.

Place units in the dorsal hippocampus of the freely-moving rat signal the animal's position in an environment (place field). In the present experiments, thirty four place units were recorded in two different environments: one, a small platform where the rat had received neither training nor reward; the other, an elevated T-maze inside a set of black curtains where the rat had been trained on a place discrimination. The places within the curtained enclosure were specified by four cues (a light, a card, a fan, and a buzzer) in addition to the food. Other cues were eliminated by rotating the maze and the four controlled cues relative to the external world from trial-to-trial. Some units had place fields in both environments while others only had a place field in one. No relationship could be seen between the place fields of units with fields in both environments. All twelve units tested extensively in the controlled enclosure had place fields related to the controlled cues. Probe experiments in which only some of the controlled cues were available showed that some of these units were being excited by one or two cues while others were influenced in a more complex way. The fields of these latter units were maintained by any two of the 4 cues and were due to inhibitory influences which suppressed the unit firing over the rest of the maze.

Acoustic Stimulation↗
PubMed1989

Survey of whole body-extract immunotherapy for imported fire ant- and other hymenoptera-sting allergy. Report of the Fire Ant Subcommittee of the American Academy of Allergy and Immunology.

A survey of 5300 allergists was conducted to determine the number and geographic distribution of patients receiving immunotherapy for imported fire ant (IFA) allergy in the United States and Canada. Responses were received from 1293 physicians who reported a total of 2573 patients being treated in 28 states. Most patients were from the southeast, but some patients were reported to be receiving IFA immunotherapy in areas outside the boundaries of known IFA infestation. Although IFA is a widespread health hazard in the southeast, it appears to exert an uneven impact on allergy practice in this region. Of the 1293 physicians responding to the survey, 117 (9%) reported the use of whole body extract (WBE) in the treatment of 1746 patients with winged Hymenoptera-sting allergy. Continued use of WBE immunotherapy was reported by physicians from all regions of the United States and from Canada. The largest numbers of patients receiving winged WBE immunotherapy were reported from Texas (641), Pennsylvania (246), Florida (129), and Canada (127). The results of this survey suggest a need for continuing medical education regarding (1) the magnitude of the health hazard posed by the IFA and (2) the efficacy of venom versus WBE in the treatment of winged Hymenoptera-sting allergy.

Animals↗
PubMed1999

Sodium dynamics underlying burst firing and putative mechanisms for the regulation of the firing pattern in midbrain dopamine neurons: a computational approach.

A physiologically based multicompartmental computational model of a midbrain dopamine (DA) neuron, calibrated using data from the literature, was developed and used to test the hypothesis that sodium dynamics drive the generation of a slow oscillation postulated to underlie NMDA-evoked bursting activity in a slice preparation. The full compartmental model was reduced to three compartments and ultimately to two variables, while retaining the biophysical interpretation of all parameters. A phase-plane analysis then suggested two mechanisms for the regulation of the firing pattern: (1) bursting activity is favored by manipulations that enhance the region of negative slope in the whole-cell IV curve and inhibited by those manipulations, such as increasing linear currents, that tend to dampen this region and (2) assuming a region of negative slope is present in the IV curve, the bias of the system can be altered, either enabling or disabling bursting. The model provides a coherent framework for interpreting the effects of glutamate, aspartate, NMDA, and GABA agonists and antagonists under current-clamp conditions, as well as the effects of NMDA and barium under voltage-clamp conditions.

Calibration↗
PubMed1980

Glucose suppresses basal firing and haloperidol-induced increases in the firing rate of central dopaminergic neurons.

In the rat, doses of glucose sufficient to raise glucose concentrations in the blood to levels equivalent to those produced by a meal or stress suppress the firing of dopamine-containing neurons located within the substantia nigra. Glucose also prevents or reverses the increase in discharge rates of dopaminergic cells normally elicited by the antipsychotic agent haloperidol.

Action Potentials↗
PubMed2003

An information theoretic approach to the contributions of the firing rates and the correlations between the firing of neurons.

To analyze the extent to which populations of neurons encode information in the numbers of spikes each neuron emits or in the relative time of firing of the different neurons that might reflect synchronization, we developed and analyzed the performance of an information theoretic approach. The formula quantifies the corrections to the instantaneous information rate that result from correlations in spike emission between pairs of neurons. We showed how these cross-cell terms can be separated from the correlations that occur between the spikes emitted by each neuron, the auto-cell terms in the information rate expansion. We also described a method to test whether the estimate of the amount of information contributed by stimulus-dependent synchronization is significant. With simulated data, we show that the approach can separate information arising from the number of spikes emitted by each neuron from the redundancy that can arise if neurons have common inputs and from the synergy that can arise if cells have stimulus-dependent synchronization. The usefulness of the approach is also demonstrated by showing how it helps to interpret the encoding shown by neurons in the primate inferior temporal visual cortex. When applied to a sample dataset of simultaneously recorded inferior temporal cortex neurons, the algorithm showed that most of the information is available in the number of spikes emitted by each cell; that there is typically just a small degree (approximately 12%) of redundancy between simultaneously recorded inferior temporal cortex (IT) neurons; and that there is very little gain of information that arises from stimulus-dependent synchronization effects in these neurons.

Algorithms↗
PubMed1999

Fast global oscillations in networks of integrate-and-fire neurons with low firing rates.

We study analytically the dynamics of a network of sparsely connected inhibitory integrate-and-fire neurons in a regime where individual neurons emit spikes irregularly and at a low rate. In the limit when the number of neurons --> infinity, the network exhibits a sharp transition between a stationary and an oscillatory global activity regime where neurons are weakly synchronized. The activity becomes oscillatory when the inhibitory feedback is strong enough. The period of the global oscillation is found to be mainly controlled by synaptic times but depends also on the characteristics of the external input. In large but finite networks, the analysis shows that global oscillations of finite coherence time generically exist both above and below the critical inhibition threshold. Their characteristics are determined as functions of systems parameters in these two different regions. The results are found to be in good agreement with numerical simulations.

Algorithms↗