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At least 865 records · Page 48Linked to original sources
PubMed2006

Firing properties of anatomically identified neurons in the medial septum of anesthetized and unanesthetized restrained rats.

Cholinergic and GABAergic neurons in the medial septum-diagonal band of Broca (MS-DB) project to the hippocampus where they are involved in generating theta rhythmicity. So far, the functional properties of neurochemically identified MS-DB neurons are not fully characterized. In this study, MS-DB neurons recorded in urethane anesthetized rats and in unanesthetized restrained rats were labeled with neurobiotin and processed for immunohistochemistry against glutamic acid decarboxylase (GAD), parvalbumin (PV), and choline acetyltransferase (ChAT). The majority of the 90 labeled neurons (75.5%) were GAD+. Among them, 34.0% were also PV+, but none were ChAT+. Only 8.8% of the labeled neurons were found ChAT+. Remaining neurons (15.5%) were not identified. In anesthetized rats, all of the PV/GAD+ and 65% of GAD+ neurons exhibited burst-firing activity at the theta frequency. PV/GAD+ neurons displayed higher discharge rate and longer burst duration compared with GAD+ neurons. At variance, all of the ChAT+ neurons were slow-firing. Cluster-firing and tonic-firing were observed in GAD+ and unidentified neurons. In unanesthetized rats, during wakefulness or rapid eye movement sleep with hippocampal theta, the bursting neurons were PV/GAD+ or GAD+, whereas all of the ChAT+ neurons were slow-firing. Across the sleep-wake cycle, the GABAergic component of the septohippocampal pathway was always more active than the cholinergic one. The fact that cholinergic MS-DB neurons do not display theta-related bursting or tonic activity but have a very low firing rate questions how acetylcholine exerts its activating role in the septohippocampal system.

Anesthesia↗
PubMed1991

Sex differences in the basal firing rate and the responsiveness to opioid peptides of rat hippocampal neurons.

The basal firing rate and the responsiveness to dynorphin and leu-enkephalin of the neurons in the pyramidal cell layer of the hippocampus were studied in intact male, castrated male, castrated female, and castrated female rats injected s.c. with 20 micrograms estradiol benzoate (EB) for 3 days. Most of the neurons studied had low spontaneous firing rate (less than 5 Hz) and burst-like activity in all the groups. The basal firing rates in castrated males and females were not different from those in intact males and castrated females treated with EB, respectively. However, neurons in intact and castrated males had significantly higher firing rates than those in castrated females with and without EB treatment, respectively. When effective, both iontophoretically applied dynorphin and leu-enkephalin evoked predominantly excitatory responses. Either castration of males or EB treatment to castrated females did not affect the neuronal responsiveness to these peptides. On the other hand, the responsiveness of neurons to leu-enkephalin, but not to dynorphin, was significantly different between castrated male and female rats. These results suggest that sex steroids do not affect the basal firing rate as well as the responsiveness to opioid peptides of the pyramidal cells in the hippocampus in adult animals. However, sex differences in the basal firing rate and in the responsiveness to leu-enkephalin might account for the differences in hippocampal functions between male and female rats.

Action Potentials↗
PubMed1999

Firing shrinkage of porcelain-resin composites prepared by laser lithography.

Using porcelain and resin-mixed composites as experimental materials, cubic polymerized composites were prepared by the accumulation of thin slices cured by laser scanning. The composites were then fired, and bulk ceramic bodies were made. The optimal firing conditions of polymerized composites and firing shrinkage were investigated. The results showed that cubic ceramic bodies in a form homologous to that before firing could be reproduced. The volume shrinkage of fired ceramic bodies consisting of 1 g of ceramic powders and 0.3 g of epoxy resin was about 30% under all firing conditions, and there were no significant differences between specimens. It was suggested that with further research and development, three-dimensional forms for clinical use in dentistry could be manufactured by the proposed method.

Dental Porcelain↗
PubMed1999

Effects of fire on the demography of the endangered, geophytic herb Silene spaldingii (Caryophyllaceae).

Understanding the effects of disturbances such as fire on plant demography helps elucidate the mechanisms that cause changes in community composition. I studied the effects of spring and fall fires on Silene spaldingii, an endangered perennial herb of grasslands in northwest Montana. Individual S. spaldingii plants were mapped, and size and flowering were recorded for 1 yr prior and 5 yr subsequent to the burn treatments. Enhanced seedling recruitment (70-410%) and a 22% increase in population size were the principal effects of fire on S. spaldingii, and fall burn plots had lower recruitment than spring burn plots. These effects were apparent for 2-3 yr following the treatments. Fire had no detectable effect on the survival of adults or recruits of S. spaldingii. Silene spaldingii exhibits prolonged dormancy in which plants do not produce aboveground vegetation for one to several consecutive years. Results suggest that fire has a positive effect on the population dynamics of S. spaldingii by removing litter and creating safe sites for recruitment. Prescribed fire should be an important tool for managing populations of this rare plant.

Journal Article↗
PubMed2000

Membrane potential and firing rate in cat primary visual cortex.

We have investigated the relationship between membrane potential and firing rate in cat visual cortex and found that the spike threshold contributes substantially to the sharpness of orientation tuning. The half-width at half-height of the tuning of the spike responses was 23 +/- 8 degrees, compared with 38 +/- 15 degrees for the membrane potential responses. Direction selectivity was also greater in spike responses (direction index, 0.61 +/- 0.35) than in membrane potential responses (0.28 +/- 0.21). Threshold also increased the distinction between simple and complex cells, which is commonly based on the linearity of the spike responses to drifting sinusoidal gratings. In many simple cells, such stimuli evoked substantial elevations in the mean potential, which are nonlinear. Being subthreshold, these elevations would be hard to detect in the firing rate responses. Moreover, just as simple cells displayed various degrees of nonlinearity, complex cells displayed various degrees of linearity. We fitted the firing rates with a classic rectification model in which firing rate is zero at potentials below a threshold and grows linearly with the potential above threshold. When the model was applied to a low-pass-filtered version of the membrane potential (with spikes removed), the estimated values of threshold (-54.4 +/- 1.4 mV) and linear gain (7.2 +/- 0.6 spikes. sec(-1). mV(-1)) were similar across the population. The predicted firing rates matched the observed firing rates well and accounted for the sharpening of orientation tuning of the spike responses relative to that of the membrane potential. As it was for stimulus orientation, threshold was also independent of stimulus contrast. The rectification model accounted for the dependence of spike responses on contrast and, because of a stimulus-induced tonic hyperpolarization, for the response adaptation induced by prolonged stimulation. Because gain and threshold are unaffected by visual stimulation and by adaptation, we suggest that they are constant under all conditions.

Action Potentials↗
PubMed2000

Ionic currents and spontaneous firing in neurons isolated from the cerebellar nuclei.

Neurons of the cerebellar nuclei fire spontaneous action potentials both in vitro, with synaptic transmission blocked, and in vivo, in resting animals, despite ongoing inhibition from spontaneously active Purkinje neurons. We have studied the intrinsic currents of cerebellar nuclear neurons isolated from the mouse, with an interest in understanding how these currents generate spontaneous activity in the absence of synaptic input as well as how they allow firing to continue during basal levels of inhibition. Current-clamped isolated neurons fired regularly ( approximately 20 Hz), with shallow interspike hyperpolarizations (approximately -60 mV), much like neurons in more intact preparations. The spontaneous firing frequency lay in the middle of the dynamic range of the neurons and could be modulated up or down with small current injections. During step or action potential waveform voltage-clamp commands, the primary current active at interspike potentials was a tetrodotoxin-insensitive (TTX), cesium-insensitive, voltage-independent, cationic flux carried mainly by sodium ions. Although small, this cation current could depolarize neurons above threshold voltages. Voltage- and current-clamp recordings suggested a high level of inactivation of the TTX-sensitive transient sodium currents that supported action potentials. Blocking calcium currents terminated firing by preventing repolarization to normal interspike potentials, suggesting a significant role for K(Ca) currents. Potassium currents that flowed during action potential waveform voltage commands had high activation thresholds and were sensitive to 1 mm TEA. We propose that, after the decay of high-threshold potassium currents, the tonic cation current contributes strongly to the depolarization of neurons above threshold, thus maintaining the cycle of firing.

Action Potentials↗
PubMed2002

Fires of endotracheal tubes of three different materials during carbon dioxide laser surgery.

The hazards of fire during CO2 laser surgery of the airway necessitate the use of special endotracheal tubes. We reviewed 227 cases receiving CO2 laser laryngeal surgery over the past 7 years, of whom 3 suffered the complications as a result of endotracheal fire. Tracheal tubes made of different materials were used among them, including silicone T-tube (Montgomery Safe-T-tube), jet ventilation tube and Xomed laser shield endotracheal tube. In addition, we tested in vitro the combustibility of endotracheal tubes of six different materials which included silicone T-tube, jet ventilation tube, Xomed laser shield endotracheal tube, stainless Laser-Flex tracheal tube, polyvinyl chloride (PVC) endotracheal tube and aluminum foil wrapped PVC endotracheal tube by exposing them to continuous operating CO2 laser in room air. The time to initiation of fire and burn through the lumen was 0.3 second for T-tube, 0.5 s for jet ventilation tube, 5 s for Xomed laser shield endotracheal tube, and 0.8 s for PVC endotracheal tube, respectively. The Laser-Flex tracheal tube (stainless) and aluminum foil wrapped PVC endotracheal tube did not catch fire after 30 s of CO2 laser irradiation. The silicone T-tube seemed to be the most dangerous. Jet ventilation tube and Xomed laser shield endotracheal tube have the risk of fire. Aluminum foil wrapped PVC endotracheal tube was reported to catch fire before. Therefore we are of the opinion that the stainless endotracheal tube is the safest tube during CO2 laser surgery.

Adult↗
PubMed2003

Persistent changes in spontaneous firing of Purkinje neurons triggered by the nitric oxide signaling cascade.

Many types of neurons fire spontaneously because of the activity of pacemaking ion channels. Although endogenous firing can serve as a persistent signal to downstream targets, little attention has been paid to factors that might modulate such intrinsic electrical activity. We tested for modulation of spontaneous firing of Purkinje neurons in cerebellar slices under conditions in which principal synaptic inputs were blocked. Loose-patch recordings from single neurons show that sustained (>40 min) increases in the spontaneous firing rate can be triggered by activation of the nitric oxide-cGMP signaling pathway. Inhibitors of soluble guanylate cyclase and protein kinase G block this modulation. Increases in firing rate are also observed after stimulation of parallel fibers but not in response to basket cell activity. These findings elucidate a novel role for the nitric oxide-cGMP signaling cascade in the brain. This mechanism could permit long-term adjustments in the baseline firing rate of endogenously active neurons in response to changes in afferent activity.

Action Potentials↗
PubMed1992

Comparison of effects of tetrahydropalmatine enantiomers on firing activity of dopamine neurons in substantia nigra pars compacta.

Extracellular single unit recording techniques were used to elucidate the effects of enantiomers of tetrahydropalmatine (THP) on the firing activity of dopamine (DA) neurons in substantia nigra pars compacta (SNC). (-)-THP rapidly reversed the apomorphine (Apo)-induced inhibition of the SNC DA cell firing activity (ED50 = 0.77, 0.52-1.14, mg.kg-1), while much larger doses of (+)-THP were required to reverse the Apo-induced inhibition (ED50 = 23, 15.2-34.7, mg.kg-1) and the maximal reversal caused by (+)-THP was 79 +/- 9% of the basal firing rate. In paralyzed rats, (-)-THP (0.5-16 mg.kg-1) significantly increased the spontaneous firing rate of SNC DA neurons dose-dependently, while (+)-THP did not until the dose reached 16 mg.kg-1. Pretreatment with (-)-THP 4 mg.kg-1 attenuated Apo-induced inhibition of SNC DA cell firing rate, while (+)-THP 32 mg.kg-1 revealed a similar potency to block the Apo-induced inhibition. In addition, (+)-THP did not potentiate the effect caused by d-amphetamine (Amp) as some behavioral experiments have shown, but large dose of (+)-THP (32 mg.kg-1) blocked the Amp-induced inhibition of SNC DA cell firing activity as (-)-THP (4 mg.kg-1) did. These results suggest that the interaction between D2 receptors and THP enantiomers has stereoselectivity and that (-)-THP is a D2 antagonist while (+)-THP seems to be not.

Alkaloids↗
PubMed2004

Biphasic firing response of nucleus accumbens neurons elicited by THPB-18 and its correlation with DA receptor subtypes.

AIM: To investigate the possibility whether THPB-18 (l-12-shloroscoulerine) possesses the D1 agonist-D2 antagonist action on meso-accumbens-mPFC DA system. METHODS: Single unit spontaneous firing activity was recorded in the nucleus accumbens (NAc) neurons of naive and unilateral-6-hydroxydopamine (6-OHDA)-lesioned Sprague-Dawley rats. The effects of drugs applied intravenously or iontophoretically were determined by the change of firing rates. RESULTS: Under normal conditions, the systemic administration of THPB-18 produced a decrease-increase biphasic firing pattern in the NAc neurons during cumulative doses. High dose of THPB-18 was capable of reversing the inhibition induced by both D2 agonist LY171555 and D1/D2 agonist APO on NAc firing activity. Spiperone pretreatment could not block the high dose of THPB-18-induced firing rate increase, which was reversed by the D1 selective antagonist SCH23390. The tested NAc neurons were effectively inhibited by iontophoretically applied THPB-18 in 90 % of 6-OHDA-lesioned rats, while THPB-18 caused variable effects on the firing of NAc neurons in the neurons of unlesioned rats. The inhibitory effect of THPB-18 was blocked by iontophoretic application of SCH23390, but not D2 antagonist spiperone. CONCLUSION: Similar to L-stepholidine, THPB-18 also possesses the D1 agonistic-D2 antagonistic dual action on the VTA-NAc DA system.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1990

Firing properties of hippocampal neurons in a visually symmetrical environment: contributions of multiple sensory cues and mnemonic processes.

The location-specific firing of hippocampal place cells can easily be brought under the control of experimenter-defined cues. Nevertheless, there is evidence that these firing fields are not determined just by immediate sensory input, but also by earlier states of the nervous system (O'Keefe and Speakman, 1987). Here, we report further on the roles of multiple visual cues and mnemonic processes in determining the firing of place cells. Rats were trained to chase food pellets in a cylinder with homogeneous gray walls and 1 white cue card. After a cell's field was recorded in this "standard" condition, probe sessions were conducted in which a second card was placed 180 degrees away from the first. This configuration created a diametrically symmetrical environment in which pairs of locations 180 degrees apart were identical with respect to views of the wall and cards. If place cells are strongly controlled by these immediately available views, firing in the 2-card configuration should be diametrically symmetrical. Alternatively, because the rat moves freely in the cylinder, information is available that pairs of visually identical places are not truly the same. If some mnemonic process stores and updates information about the rat's paths during the session, it is possible that the firing pattern will be different in 2 such places, especially because the original training was conducted in the 1-card, asymmetrical environment. Thirteen of 18 cells had a single, asymmetric firing pattern after the second card was introduced; the field was the same size and shape as in the 1-card configuration and in the same spatial relation to 1 of the 2 cards. The field position during 2-card sessions could be rotated 180 degrees by starting the rat by one card or the other. In further probe sessions in which the cue cards, entry location, and background cues were, in various combinations, rotated in relation to each other, these cells always showed a single field, similar in size and shape to that in the standard, and in the same relationship as in the standard to as many cues as possible. The remaining 5 cells showed complex changes over repeated 2-card sessions, and 3 of these showed paired fields, 180 degrees apart for at least some of the sessions. In one case, the second field disappeared with repeated exposures to 2 cards; in another, the second field persisted when only 1 card was used. We conclude that place cells are influenced both by the immediate sensory configuration and by internal neural states related to earlier experience in the environment.

Action Potentials↗
PubMed1987

[Correlation of the discharge frequency of a firing motor neuron and the efficiency of an excitatory volley of Ia-afferents in man].

Single motor unit potentials of the flexor carpi ulnaris muscle were recorded during voluntary contraction and H-reflex was evoked. The afferent volley effectiveness was estimated by the firing index of a motoneuron. The background firing rate of motor units ranged from 3.3 to 16.0 imp/s. Afferent volley effectiveness depended on the background firing rate of fast muscle units under study like slow soleus muscle units investigated earlier. The effectiveness of afferent volley decreased with the motor units firing rate growth. At all range of firing rate the efficiency of afferent volley was higher for motor units of fast muscle as compared to slow muscle. It is suggested that the motoneuron excitability changes within the interspike interval underlay the relationship between the motoneuron firing rate and effectiveness of the excitatory afferent volley.

Efficiency↗
PubMed1996

Phasic firing of single neurons in the rat nucleus accumbens correlated with the timing of intravenous cocaine self-administration.

To examine potential neural mechanisms involved in cocaine self-administration, the activity of single neurons in the nucleus accumbens of rats was recorded during intravenous cocaine self-administration. Lever pressing was reinforced according to a fixed-ratio 1 schedule. On a time base comparable to the interinfusion interval, half the neurons exhibited phasic firing patterns time locked to the cocaine reinforced level press. For almost all neurons, this pattern consisted of a change in firing rate postpress, typically a decrease, followed by a reversal of that change. The postpress change was closely related to the lever press. Typically, it began within the first 0.2 min postpress and culminated within the first 1.0 min postpress. For a small portion of responsive neurons, the reversal of the postpress change was punctate and occurred within 1-3 min of either the last lever press or the next lever press so that firing was stable during much of the interinfusion interval. For the majority of neurons, the reversal was progressive; it began within 2 min after the previous level press, and it was not complete until the last 0.1-2.0 min before the next lever press. The duration of this progressive reversal, but not of the postpress change, was positively correlated with the interinfusion interval. Thus, in addition to exhibiting changes in firing related to the occurrence of self-infusion, the majority of neurons also exhibited progressive changes in firing related to the spacing of infusions. In a structure that has been shown to be necessary for cocaine self-administration, such a firing pattern is a likely neurophysiological component of the mechanism that transduces declining drug levels into increased drug-related appetitive behavior. It is, thus, a neural mechanism that may contribute to compulsive drug-maintained drug taking.

Animals↗
PubMed1983

[Fire fighting with nitrogen in the German coal mining industry].

Fire-fighting methods using inert gases have been known for decades. In December 1974, for the first time in the German coalmining industry, liquid nitrogen was gasified at the surface and fed to a mine fire underground. This developed into a standard fire-fighting procedure in mines and has been used in numerous cases. The great advantage of this method for the mine rescue operations is the elimination of explosion hazards and the possibility to create better working conditions. The example of a large scale fire in 1982 illustrates how fire zones can be stopped and reopened in immediate succession, if some requirements are fulfilled. The neutralization method sets new technical and safety tasks for the mine rescue services. Instruction on working in a low oxygen environment now represents a particularly important part of their training.

Coal Mining↗
PubMed1996

Congenital anomalies among the offspring of fire fighters.

A case-control study has been conducted to determine the association between employment as a fire fighter and congenital heart defects among the offspring. Cases were fathers of all children born between 1979 and 1986 in Ontario, Canada, who were diagnosed with a cardiac congenital anomaly during the first year of life (n = 9340). Matched controls (n = 9340), defined as fathers whose child did not have a congenital anomaly, were randomly selected from the Ontario birth certificate file. In order to identify those fathers who had been employed as a fire fighter, the cases and controls were linked to a cohort of Metropolitan Toronto fire fighters. Eleven cases and nine controls worked as fire fighters, giving an odds ratio of 1.22 (95 percent confidence interval 0.46-3.33). This study had sufficient power to detect the level of risk reported in one previous study; however, these results do not support a hypothesis of elevated risk of cardiac congenital anomalies among the offspring of fire fighters.

Adult↗
PubMed2002

Occupational burns from oxygen resuscitator fires: the hazard of aluminum regulators.

BACKGROUND: There have been over 30 incidents of oxygen resuscitator fires over the last 6 years, causing severe burns to a number of fire fighters, emergency medical service personnel, health care workers, and patients. The National Institute for Occupational Safety and Health (NIOSH) was requested to investigate three such incidents. METHODS: NIOSH conducted site investigations of the incidents, and the requesters also sent the involved oxygen resuscitators to a forensic engineering company for a causal analysis. RESULTS: The investigated fires were associated with aluminum regulators, all from one manufacturer, on compressed pure oxygen cylinders. The investigations indicated that the cause of the fires was an initial small ignition in the high-pressure area of the aluminum regulator, which then consumed itself in a massive burnout. CONCLUSIONS: Aluminum regulators used with high-pressure oxygen systems are subject to rare, but potentially catastrophic combustion in normal use. Replacement of such regulators with those made of more fire-resistant materials or designs, as well as education and improved safety practices are needed to reduce this hazard.

Accidents, Occupational↗
PubMedDate not supplied

Predictors of weight increases over 7 years in fire fighters and paramedics.

BACKGROUND: Excess body weight among adults is associated with increased risk of disease. Therefore, we sought predictors of weight gain that might be used to prevent increases in weight. METHODS: Participants were 438 male fire service personnel, 20-58 years of age, who filled out a questionnaire in 1984 and were weighed in 1984 and 1991. RESULTS: Sixty-five percent gained > or = 5 lb, 42.1% gained > or = 10 lb, and 26.1% gained > or = 15 lb. Unmarried fire fighters gained 11.7 lb; those married or living as married gained 7.0 lb (P < 0.001). Black non-Hispanics increased by 15.7 lb, white Hispanics by 8.9 lb, and white non-hispanics by 6.7 lb (P < 0.001). New ex-smokers gained 13.0 lb; all other fire fighters gained 7.7 lb (P < 0.004). Fire fighters who reported eating "faster" at the station than elsewhere gained 9.9 lb compared with 6.8 lb for all others (P < 0.006). Those worried over financial security gained 11.2 lb versus nonworriers who gained 7.4 lb (P < 0.005). CONCLUSION: Prevention programs will reach fire fighters likely to gain the most weight if aimed at those who are unmarried, younger, black, recent ex-smokers, fast eaters, and experiencing certain stressful life events.

Adult↗
PubMed1985

Accidental fire deaths. The 5-year Metropolitan Dade Country experience from 1979 until 1983.

Accidental fire deaths that occurred in Metropolitan Dade County, encompassing Miami, Fla., USA, during the years from 1979 until 1983 were studied. A total of 108 cases were collected, representing 6.1% of the nontraffic-related accidents during this 5-year period, and analyzed as to the age, race, sex, cause of death of the victim along with the blood alcohol content at autopsy, toxicologic analysis, location of the fire, and how the fire started. Essentially, the victims ages cluster in the 0-5 years and does 70 years, although other age groups are evenly distributed. A white male population predominates. The cause of death is listed as either smoke inhalation or thermal injury. Most toxicologic analyses were not performed due to the high rate of fire rescue intervention and at least emergency room hospitalization prior to death. Carboxyhemoglobin levels, when analyzed, ranged from less than 20% to over 80%. In a smaller group of cases, cyanide was analyzed for and was found negative (or none detected) in the majority of the cases. More fires occurred in residences and started due to cigarette smoking or electric malfunction.

Adolescent↗