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At least 577 records · Page 32Linked to original sources
PubMed1998

Epidemiologic study of cats and dogs affected by the 1991 Oakland fire.

OBJECTIVE: To identify risk factors of pets affected by the 1991 Oakland, Calif fire for being lost, found, adopted, or reunited with owners. DESIGN: Retrospective cohort study. ANIMALS: 1,075 cats and 197 dogs affected by the fire and 221 cats and 128 dogs not affected by the fire. PROCEDURES: Records compiled from 1991 to 1995 by the Oakland Firestorm Pet Hotline were analyzed. RESULTS: Peak activity for the hotline was on days 3 and 4 after the fire, but decreased to a low, steady rate by day 21. Many pets were found that had been abandoned or were part of a large free-roaming population that existed at the time of the fire. Many were missing after the fire and presumed killed. The longer owners delayed looking for their pet, the lower the chance of being reunited. Pets wearing collars with the owners' names and addresses had a more than 10-fold chance of being reunited, compared with pets without collars. Increasing odds for adoption of lost pets was associated with their proximity to the fire. CLINICAL IMPLICATIONS: Hotlines set up after sudden impact disasters, such as the Oakland Firestorm Pet Hotline, will probably register primarily abandoned animals. Reunion of pets with their owners appears to be most likely for those that receive an overall better level of care than pets found at other times. Adoption of pets after this disaster was primarily by the person who found that animal and principally resulted when the pet was found close to the disaster area.

Animal Identification Systems↗
PubMed1998

Fire awareness in the office and laboratory.

Three elements are needed for a fire to start and flourish: heat, fuel, and oxygen. These elements form the three sides of the 'fire triangle', and the removal or isolation of any one will extinguish a fire. Such action forms the basis of fire fighting techniques currently in use by the fire authorities. Two sides of the fire triangle, fuel and oxygen, are always present in the workplace. This article looks at the common causes of fire in the workplace, and the precautions and control measures needed to prevent it.

Fires↗
PubMed2003

Sex differences in rabbit masseter motoneuron firing behavior.

To evaluate whether sex differences in the proportions of fibers of different phenotypes in the masseter muscle might be the result of differences in the behavior of their motoneurons, we studied the firing patterns of masseter motoneurons in adult male and female rabbits. Activity in individual motoneurons was determined from high spatial resolution EMG recordings made during cortically evoked rhythmic activation of the masticatory muscles. Although some motoneurons could be said to fire according to slow-tonic or fast-phasic patterns, most did not. In both sexes a substantial range of median firing rates and median firing durations was found. In adult males, masseter motoneurons fired more rapidly than those recorded from adult females. No significant sex differences in motoneuron firing duration were found. These results are consistent with the hypothesis that androgen-induced differences in rabbit masseter muscle fiber phenotype are a reflection of differences in motoneuron firing rate. Whether this effect of androgen is directly upon the motoneurons or is the result of a response of muscle fibers to androgen remains to be investigated.

Action Potentials↗
PubMed1986

[Quantity of weapon oils at the target as a function of shooting sequence and firing distance].

Five widely used gun oils were tested to see if they could be identified by gas chromatography. All oils in the test produced characteristic gas chromatograms and the test was highly sensitive in tracing the oils. Seven different weapons and various types of ammunition were used to perform firing tests involving an oil sold under the brand name of "Gun pro." The weapons were oiled and wiped dry and subsequently discharged at a cotton cloth target. Series of shots were fired from a maximal distance of 3 m, and the weapon was not cleaned between shots. Grease marks and powder-burn traces were extracted separately and the extracts, after adding an internal standard, were investigated by means of gas chromatography (gas chromatography unit by Perkin and Elmer). The largest quantities of oil were transmitted by indoor ammunition fired from a small-bore rifle. At a firing range of 20 cm, a decrease in the oil quantity could be observed up to the fourth discharge. When the firing range was varied there was a decrease in the oil quantity up to a distance of 80 cm. The first and the second discharge could be distinguished up to a firing range of 60 cm. With increasing force of the projectile and a decrease in the interior length of the gun barrel, the quantity of oil conveyed to the target also decreased. Additionally, the identifiability of the oil was investigated after firing at several layers of cloth and after storage of the samples (no losses occurred after a 1-month storage period).(ABSTRACT TRUNCATED AT 250 WORDS)

Firearms↗
PubMed1990

Development in the absence of spontaneous bioelectric activity results in increased stereotyped burst firing in cultures of dissociated cerebral cortex.

Quantitative analysis of neuronal firing patterns was used to study the effects of chronic suppression of bioelectric activity (BEA) on functional development in primary cultures of fetal rat cerebral cortex. BEA was monitored with extracellular electrodes in active control cultures or, after return to control medium, in cultures chronically silenced with tetrodotoxin (TTX) at around 7, 14, 21 and 42 days in vitro. Spike trains of single neurons lasting up to 25 min duration were analyzed using a previously published set of computer programs. In control cultures, the main developmental trends seen in a previous study could be replicated. After development in the presence of TTX, activity levels were increased at all ages, and a high incidence was found of a single firing pattern characterized by stereotyped burst firing, while showing a low minute order variability in firing rate and low dependencies between successive intervals; conversely, the incidence of variable/non-burst firing was decreased relative to untreated cultures. The former firing pattern (i.e. non-variable bursting) could also be produced through acute addition of the GABA (A)-antagonist picrotoxin to control cultures, and resembled interictal burst firing observed in models of chronic epilepsy in vivo. These similarities suggest that chronic silencing of the cultures may have resulted in a functional disinhibition of the neuronal network; such disinhibition might be related to the increased cell death which we observed with chronic TTX-treatment in the same cultures.

Action Potentials↗
PubMed1984

Current-to-frequency transduction in CA1 hippocampal pyramidal cells: slow prepotentials dominate the primary range firing.

In order to study how hippocampal pyramidal cells transform a steady depolarization into discharges, CA1 pyramids (n = 32) were injected with 1.5 s long pulses of constant depolarizing current. The firing in response to weak currents was in most cells, characterized by low frequency (0.2-5 Hz), slowly increasing depolarizations preceding each action potential (slow prepotentials, SPPs), a long latency (0.2-5 s) to the initial spike and lack of adaptation. The SPPs, which lasted 30-2,000 ms, showed an increasing steepness with increasing current, and seemed to be a major regulating factor for the slow firing. In response to stronger currents the discharge had a high initial frequency (100-350 Hz), followed by adaptation to steady state firing (5-50 Hz). Thirty of 32 cells showed a dip in the frequency (n = 5), or a pause (n = 25) lasting 250-1,000 ms between the initial burst of firing and the steady state. The pause occurred only at intermediate current strengths. Additional spikes to the initial burst seemed to be recruited through the development of depolarizing waves. The initial slope of these waves resembled those of the SPPs. Similar waves occurred at the expected time of occasionally missing spikes during steady state firing. The variability (SD/mean) of the interspike intervals decreased with increasing frequency of firing. The frequency-current (f/I) relation for the steady state firing showed a simple linear or convex shape, and lacked a secondary range. In contrast, the f/I plots for the initial few interspike intervals had both primary, secondary and tertiary ranges, like motoneurones.

Action Potentials↗
PubMed1989

The role of calcium in the repetitive firing of neostriatal neurons.

The Ca++ -dependence of the repetitive firing of neostriatal neurons was studied in an in vitro slice preparation of the rat neostriatum. Neuronal firing was evoked by injecting depolarizing currents of 100-200 ms duration. In normal conditions, the mode of firing was tonic and showed very little adaptation. The frequency-current relation was linear over a wide range of frequencies. The repetitive firing was first enhanced and later suppressed by Co++, Mn++ and Cd++. These effects on the repetitive firing by the Ca++ -channel blockers paralleled the suppression of the slow afterhyperpolarizing potential. The lowering (0.2 mM) of Ca++ had similar effects. In the presence of TEA (up to 10 mM), the cell fired both Na+ and Ca+ action potentials. The results suggest that, as in other CNS neurons of the vertebrate, in neostriatal neurons the slow afterhyperpolarizing potential (AHP) is due to a Ca++ -activated K+ -conductance, and that the AHP plays a crucial role in the repetitive firing of these neurons.

Action Potentials↗
PubMed1996

Activity of single motor units in attention-demanding tasks: firing pattern in the human trapezius muscle.

Activity of single motor units in relation to surface electromyography (EMG) was studied in 11 subjects in attention-demanding work tasks with minimal requirement of movement. In 53 verified firing periods, single motor units fired continuously from 30 s to 10 min (duration of the experiment work task) with a stable median firing rate in the range of 8-13 Hz. When the integrated surface EMG were stable, the motor units identified as a rule were continuously active with only small modulations of firing rate corresponding to low-amplitude fluctuations in surface EMG. Marked changes in the surface EMG, either sudden or gradual, were caused by recruitment or derecruitment of motor units, and not by modulations of the motor unit firing rate. Motor unit firing periods (duration 10 s-35 s) in low-level voluntary contractions (approximately 1%-5% EMGmax) performed by the same subjects showed median firing rates (7-12 Hz) similar to the observations in attention-related activation.

Action Potentials↗
PubMed1995

The potassium A-current, low firing rates and rebound excitation in Hodgkin-Huxley models.

It is widely believed, following the work of Connor and Stevens (1971, J. Physiol. Lond. 214, 31-53) that the ability to fire action potentials over a wide frequency range, especially down to very low rates, is due to the transient, potassium A-current (IA). Using a reduction of the classical Hodgkin-Huxley model, we study the effects of IA on steady firing rate, especially in the near-threshold regime for the onset of firing. A minimum firing rate of zero corresponds to a homoclinic bifurcation of periodic solutions at a critical level of stimulating current. It requires that the membrane's steady-state current-voltage relation be N-shaped rather than monotonic. For experimentally based generic IA parameters, the model does not fire at arbitrarily low rates, although it can for the more atypical IA parameters given by Connor and Stevens for the crab axon. When the IA inactivation rate is slow, we find that the transient potassium current can mediate more complex firing patterns, such as periodic bursting in some parameter regimes. The number of spikes per burst increases as gA decreases and as inactivation rate decreases. We also study how IA affects properties of transient voltage responses, such as threshold and firing latency for anodal break excitation. We provide mathematical explanations for several of these dynamic behaviors using bifurcation theory and averaging methods.

Action Potentials↗
PubMed1997

Suicidal behavior among Finnish fire setters.

Histories of serious suicide attempts and slashing were investigated among Finnish fire setters. Medical and criminal records of 304 fire setters were examined to compare those who had attempted suicide with those who had not, and those who had slashed themselves with those who had not using biological, diagnostic, and demographic variables. Major mood disorders, father's alcoholism, and suicidal motive of fire setting (self-immolation) were significantly associated with suicide attempts. Paternal violent alcoholism, father's criminality, and suicidal motive of fire setting were significantly associated with slashing. Among fire setters, non-lethal slashing is a predictor of serious suicidality. Associations between psychiatric diagnoses, family history, and suicidality among fire setters are similar to those reported for suicidal patients with mood and substance abuse diagnoses. Therefore, studying fire setters, who exhibit an extremely high incidence of suicidal behavior, is an effective way to elucidate psychobiology of suicidal behaviors.

Adolescent↗
PubMed2001

Modification of norepinephrine and serotonin, but not dopamine, neuron firing by sustained bupropion treatment.

RATIONALE: Bupropion is widely used in the treatment of depression and as an anti-craving medication for the cessation of tobacco smoking. Because it is a very weak inhibitor of norepinephrine (NE) and dopamine (DA) reuptake, its mechanisms of action remain to be elucidated. METHODS: Bupropion was administered subcutaneously via osmotic minipumps over 2 days to determine its effects on the spontaneous firing activity of NE, serotonin (5-HT), and DA neurons in the brain of anaesthetised male Sprague-Dawley rats. This treatment was used in order to obtain levels of the parent compound and its putatively active metabolites that would more adequately reflect the clinical condition than utilizing acute injections. RESULTS: When given by minipump for 2 days, bupropion produced a dose-dependent attenuation of the mean spontaneous firing NE neurons (7.5 mg/kg per day: 15%; 15 mg/kg per day: 61%; 30 mg/kg per day: 80%) which was reversed by the alpha 2-adrenoceptor antagonist idazoxan. At the highest regimen, the mean firing rate of 5-HT neurons was 100% higher than in control rats, but unaffected in NE-lesioned rats. In contrast, DA neurons in the ventral tegmental area displayed a normal firing rate during the latter bupropion treatment. CONCLUSIONS: Sustained bupropion administration decreased the firing rate of NE neurons due to an increased activation of their inhibitory somatodendritic alpha 2-adrenoceptors. This effect of the bupropion treatment would be attributable mainly to an enhancement of NE release and not to reuptake inhibition. This contention is based essentially on the observation that NE reuptake blockers leave unaltered the firing rate of 5-HT neurons, whereas bupropion enhanced it via a NE-dependent mechanism. The present study did not put into evidence any DA activity of bupropion at the level of the cell body of mesolimbic/cortical DA neurons at a regimen exerting profound alterations of the firing activity of NE and 5-HT neurons.

Action Potentials↗
PubMed1998

Potassium currents modulation of calcium spike firing in dendrites of cerebellar Purkinje cells.

The pattern of sustained Ca2+ spike firing was investigated, using macropatch clamp and intracellular recordings, in guinea pig cerebellar Purkinje cells. Under our standard experimental conditions (30 degrees C, 5 mM [K+]o, 2 mM [Ca2+]o, 1 microM tetrodotoxin), each firing period started with uniform firing and gradually turned into a doublet pattern with a large spike afterhyperpolarization (AHP) between the doublets. Macropatch clamp recordings from localized dendritic regions revealed that each doublet is composed of two similar inward current deflections. This result indicated, for both peaks, an active process in the recording site and contradicted the possibility that they reflect firing in two completely separated dendritic regions. When [K+]o was increased the transition to a doublet pattern occurred earlier and the doublets became more pronounced. A similar but more prominent effect occurred following application of 1-10 microM 4-aminopyridine, which also reduced the threshold, increased the spike amplitude, and shortened the initial delay of evoked Ca2+ spike firing. In contrast, membrane depolarization, increased [Ca2+]o, and application of quinidine (but not apamine) markedly suppressed the generation of doublet pattern. During uniform initial firing, a short hyperpolarizing pulse that mimicked a large AHP induced a subsequent doublet. A short depolarizing pulse following a single spike induced an artificial doublet followed by a large AHP. These results indicate that the pattern of Ca2+ spike firing in the dendrites of Purkinje cells is dynamically modulated by a highly aminopyridine-sensitive K+ current, and probably also by a Ca2+-activated potassium current.

4-Aminopyridine↗
PubMed1975

Hypothalamic supraoptic neurones: rates and patterns of action potential firing during water deprivation in the unanaesthetized monkey.

Extracellularly recorded action potentials were obtained from hypothalamic supraoptic neurones in unanaesthetized rhesus monkeys. Rates and patterns of firing were studied during an initial control period, during 5 successive days of water deprivation and during 4 further days when drinking water was again available. During water deprivation, plasma osmolarity increased progressively from about 300 mOsmoles/kg to about 340 mOsmoles/kg; control values were again reached after 3 days of rehydration. Systematic changes in action potential firing accompanied the changes in plasma osmolarity. Under control conditions, the majority of cells fire slowly and irregularly (type i), whilst a few cells exhibited phases of alternating activity and silence (type p). As dehydration progresses, the frequency of neuronal firing increase and the pattern of firing changes. By the third day the majority of cells are type p with few type i cells being found. By the fourth day, the population consists of type p cells with some others showing a high continuous rate of firing (type c). By the fifth day, these two cell types are found in approximately equal proportions. Rehydration of the animal reverses the situation. We propose that type i cells contribute little, if at all, to hormone secretion, while type p and type c cells would be in a more actively secreting state. According to this view, the three firing patterns would represent different activity states of the same functional population stimulated by the unspecific stimulus of water deprivation rather than functionally different neurones. However, the use of stimuli which selectively release either oxytocin or vasopressin may be needed to answer this problem.

Action Potentials↗
PubMed1978

Comparison of firing patterns in oxytocin- and vasopressin-releasing neurones during progressive dehydration.

The electrical activity of neurosecretory cells in the supraoptic nucleus of the urethane-anaesthetized lactating rat was examined after periods of water deprivation ranging from 0-24 h. Supraoptic units were identified by antidromic activation following stimulation of the neurohypophysis, and classified as oxytocin or vasopressin cells according to their response during reflex milk ejection. In 65 vasopressin cells, dehydration increased the mean firing rate from 2.1 spikes/sec at 0 h to 6.8 spikes/sec at 24 h and caused a change from a slow irregular to a phasic firing pattern. Thus, after 6 h or more of dehydration, 84-100% of the vasopressin cells fired phasically, compared to 12% under normal conditions. In phasic vasopressin cells , the intraburst firing rates were closely related to the stages of dehydration, rising from a mean of 6.3 spikes/sec at 6 h to 12.0 spikes/sec at 24 h. However, no systematic relationship was observed between the stages of dehydration and the mean burst or silence durations. In 77 identified oxytocin units, dehydration increased the firing rate from 0.9 spikes/sec to 2.8 spikes/sec after 24 h, but only 3 (4%) of the cells showed phasic firing. Instead, the oxytocin units changed from a slow irregular to a fast continuous discharge. In conclusion, both vasopressin and oxytocin neurones are activated during chronic dehydration, but there is a marked difference in the pattern of their response. The phasic firing of the vasopressin cells may be important in increasing the occurrence of short interspike intervals and thus facilitating hormone release.

Action Potentials↗
PubMed1981

Self-inhibition alters firing patterns of neurons in Aplysia buccal ganglia.

The functional consequences of cholinergic self-inhibitory synaptic potentials (SISPs) upon firing patterns were examined in pairs of electrotonically coupled neurons of Aplysia buccal ganglia. In each neuron, the size of the peak SISP current decrements exponentially with increased number of previous conditioning action potentials (APs). To determine the effect of SISPs on the firing patterns of each cell, AP trains elicited by constant-current steps with the SISP intact were compared to those with the SISP blocked by curare. The SISP prolonged initial interspike intervals, providing an early supplement to accommodation, and produced a 75% increase in the sensitivity of firing frequency vs injected current plots for the first ISI. Firing rates were more regular in the presence of the SISP. However, the efficacy of the SISP, like the size of the underlying current, decrements with repetition. SISP effects were also studied in electrotonically coupled pairs of self-inhibitory neurons. Although the SISP altered the shape of the hyperpolarizing component of coupling potentials, DC coupling between the neurons was unaffected. Firing synchrony in coupled pairs stimulated with long DC pulses was assessed with cross-correlation histograms. In 60 mM Ca2+, the SISP sharpens the central peak of synchrony and deepens the flanking troughs, increasing the probability of synchronous firing within +/- 4 msec by 76%. The major determinants of synchrony were found to be common input, SISP-dependent regularity of firing, and the depolarizing phase of the coupling potential, rather than the SISP-enhanced hyperpolarizing phase.

Animals↗
PubMed1985

Effects of clonidine on neuronal firing evoked by a noxious stimulus.

When norepinephrine was applied microiontophoretically to certain neurons in the pontine reticular formation of rats, it produced an increase in neuronal firing like that produced by noxious stimulation. Previous studies have shown that both noxious stimulus- and norepinephrine-evoked increases in neuronal firing are mediated by alpha-adrenoceptors. These neurons were unresponsive to non-noxious stimuli, suggesting that they might play a role in nociception. Microiontophoretic or systemic administration of the selective alpha 2-adrenoceptor agonist clonidine significantly attenuated noxious stimulus-evoked firing, but had little effect on firing evoked by norepinephrine. This effect of clonidine could be prevented by the alpha 2-adrenoceptor antagonists piperoxan and yohimbine. These antagonists, when given alone, increased noxious stimulus-evoked firing, but had no effect on firing evoked by norepinephrine. In contrast, the selective alpha 1-adrenoceptor antagonist ARC-239 (2-(2,4-(o-methoxyphenyl)-piperazin-1-yl)ethyl-4,4-dimethyl-1,3-(2 H,4) isoquinolindione dihydrochloride) attenuated both noxious stimulus- and norepinephrine-evoked firing. These data are consistent with the hypothesis that presynaptic alpha 2-adrenoceptors modulate the release of norepinephrine. Furthermore, these data suggest that the pontine reticular formation is one site at which clonidine could act to produce analgesia.

Animals↗
PubMed1991

Instability of motor unit firing rates during prolonged isometric contractions in human masseter.

The firing patterns of up to 4 concurrently active masseter motor units were studied with intramuscular electrodes during a continuous isometric contraction of 15 min duration, in which the subject maintained the mean firing rate of one selected unit at 10 Hz. With this paradigm the net excitation (i.e. mean firing rate) of one unit in the muscle was controlled. This served as the reference for the functional state of other active units during the prolonged contraction. With the mean firing rate of one unit in the muscle fixed, 58% of other active units showed a slow, statistically-significant change in mean firing rate over the 15 min. The initial firing rate of the units did not influence the change in rate. The original firing rate hierarchy, which in short-term contractions reflects the recruitment order, was altered during the prolonged contraction. The explanation for these differential changes in motoneuron net excitation is not clear; they could be intrinsic to the motoneurons or perhaps mediated by reflex pathways. The selective facilitation or suppression of some motor units with continuous activation means that the original size-structured combination of motor units can be modified during a prolonged contraction.

Adolescent↗
PubMed1992

Subthalamic nucleus cell firing in the 6-OHDA-treated rat: basal activity and response to haloperidol.

Single unit recordings from neurons of the subthalamic nucleus were made in control and 6-hydroxydopamine (6-OHDA)-treated rats anesthetized with chloral hydrate. Subthalamic nucleus cells in this preparation exhibited a wide range of firing rates and three different firing patterns. These patterns were defined as 'burst', 'normal', and 'mixed' based on comparisons of their interspike interval histograms. Four to 6 weeks after 6-OHDA treatment there was no change in the basal firing rates of subthalamic nucleus cells, but there was a significant shift in firing pattern, with a smaller proportion of cells exhibiting the 'normal' firing pattern. The response of subthalamic nucleus neurons to acute administration of haloperidol was also altered in 6-OHDA-treated rats tested 4-6 weeks post-lesion, with a significantly greater proportion of cells responding to doses of haloperidol as low as 0.2 mg/kg (i.v.) with increases in firing rate of 20% or more. These results suggest that the subthalamic nucleus is probably not involved in the increases in basal levels of dopamine cell activity observed previously in the 6-OHDA-treated rat, but may play a role in the acute induction of depolarization block of dopamine cell firing in response to haloperidol administration in this model.

Action Potentials↗