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At least 505 records · Page 28Linked to original sources
PubMed2005

Triggered firing in pulmonary veins initiated by in vitro autonomic nerve stimulation.

BACKGROUND: Rapid firing within pulmonary vein sleeves frequently initiates atrial fibrillation. The role of the autonomic nervous system in facilitating spontaneous firing is unknown. OBJECTIVES: The purpose of this study was to determine if autonomic nerve stimulation within canine atrium and pulmonary vein sleeves initiates arrhythmia formation. METHODS: Extracellular bipolar and intracellular microelectrode recordings were obtained from isolated superfused canine pulmonary veins (N = 28) and right atrium (N = 5) during local autonomic nerve stimulation. RESULTS: Autonomic nerve stimulation decreased pulmonary vein sleeve action potential duration (APD90 = 160 +/- 17 to 92 +/- 24 ms; P < .01) and initiated rapid (782 +/- 158 bpm) firing from early afterdepolarizations in 22 of 28 pulmonary vein preparations. The initial spontaneous beat had a coupling interval of 97 +/- 26 ms. Failure to induce arrhythmia was associated with a failure to shorten APD90 (151 +/- 18 to 142 +/- 8 ms; P = .39). Muscarinic receptor blockade (atropine: 3.2 x 10(-8) M) prevented APD90 shortening in 8 of 8 preparations and suppressed firing in 6 of 8 preparations, whereas beta1-adrenergic receptor blockade (atenolol: 3.2 x 10(-8) M) suppressed firing in 8 of 8 preparations. Suppression of the Ca transient with ryanodine (10(-5) M) completely suppressed firing in 6 of 6 preparations. Inhibition of forward Na/Ca exchange by a transient increase in [Ca+2]o completely suppressed firing in 4 of 6 preparations. The same stimulus trains produce atropine-suppressed APD90 shortening in superfused right atrial free wall but fail to produce triggered arrhythmia. CONCLUSIONS: The data demonstrate triggered firing within canine pulmonary veins with combined parasympathetic and sympathetic nerve stimulation. Both an enhanced Ca transient and increased Na/Ca exchange may be required for arrhythmia formation.

Animals↗
PubMed2005

Evidence of self-sustained motoneuron firing in young and older adults.

Motoneurons demonstrate a type of self-sustained firing behavior that seems to be produced by a prolonged period of depolarization caused by intrinsic long-term changes in the motoneuron. Such self-sustained firing behavior has previously been reported in human motor units. The purpose of the present study was to investigate the occurrence of self-sustained firing behavior in older adults. Eight young (mean age 24 yrs) and eight older (mean age 73 yrs) individuals participated in the investigation. While subjects produced light dorsiflexion contractions, a brief vibration stimulus was applied to the tibialis anterior muscle. Motor unit recordings were also obtained from the tibialis anterior muscle. Self-sustained firing behavior was evidenced by the appearance of new motor unit recruitment following vibration, even as the motor units that fired before the vibratory stimulus maintained a steady firing rate. The proportion of motor units exhibiting self-sustained firing activity was similar in both young and older adults (approx. 23% of trials). We conclude that self-sustained firing behavior is a ubiquitous phenomenon that does not seem to be affected by the aging process.

Action Potentials↗
PubMed2004

Nitric oxide is involved in nicotine-induced burst firing of rat ventral tegmental area dopamine neurons.

In the present study, using single cell recordings in vivo and intracellular recordings in vitro from midbrain slices, the role of N-methyl-d-aspartate (NMDA) receptor signaling on firing activity in ventral tegmental area dopamine neurons elicited by nicotine was investigated in the rat. In accordance with previous studies, systemic nicotine (0.5 mg/kg s.c.) increased both firing rate and burst firing of dopamine neurons in vivo, and bath-applied nicotine (10 microM) increased firing rate in vitro. The competitive NMDA receptor antagonist CGP39551 (2.5 mg/kg i.p.) inhibited nicotine's effects on burst firing and also attenuated the nicotine-induced increase in firing rate. Moreover, although the nitric oxide (NO)-synthase inhibitor N-nitro-l-arginine-methyl-ester (l-NAME; 5.0 mg/kg i.p.) had no effect on cell firing by itself, it prevented the response to nicotine in vivo. In contrast, l-NAME (100 microM) did not influence nicotine's effect on dopamine cell firing in vitro, suggesting that the effect of l-NAME seen in vivo is dependent on presynaptic afferent input. The present study confirms previous results suggesting that the effect of systemically administered nicotine is in part presynaptic and mediated via NMDA receptors. The data also indicate that NO plays an important role in the previously demonstrated, indirect, glutamate-mediated excitation of these neurons by nicotine. By inference, our results provide additional support for the involvement of NO in nicotine dependence.

2-Amino-5-phosphonovalerate↗
PubMed2005

Systematic variation in effects of serotonin and norepinephrine on repetitive firing properties of ventral horn neurons.

Spinal interneurons are essential integrators of descending and peripheral input that receive profuse monoaminergic influence from brainstem nuclei. In this study, the effects of the monoamines serotonin and norepinephrine on the intrinsic properties of ventral horn interneurons were investigated in a slice preparation of the lumbar cord of 7-19 day old rats. Three cell groups with distinct firing patterns in response to steps of injected current were observed and classified as repetitive-firing, initial-burst or single-spiking. Input conductance tended to be largest in single-spiking cells whereas repetitive-firing cells showed the greatest tendency for spontaneous firing and had the fastest rate of rise for the action potential. Rhythmic firing behaviors were defined by the frequency-current relation evoked by linearly increasing current ramps. The monoaminergic modulation of firing patterns and frequency-current relations was primarily studied in repetitive-firing cells. The frequency-current threshold current was decreased in cells with high pre-drug values and increased in cells with low pre-drug values. Therefore, monoamine administration decreased the input-output heterogeneity of the repetitive-firing cells by compressing the range of frequency-current threshold currents. This action of monoamines may have a key role in the suppression of sensory-evoked reflexes and the production of coordinated movement.

Animals↗
PubMed2006

SK Ca2+-activated K+ channel ligands alter the firing pattern of dopamine-containing neurons in vivo.

Apamin-sensitive, SK channels play an important role in generating the rhythmic firing patterns exhibited by midbrain dopamine neurons in vitro. However, their contribution to the firing properties of these cells in intact animals has yet to be determined. In the present series of experiments, extracellular single unit recording techniques were used to assess the central effects of prototypical SK channel ligands on the firing pattern of dopamine neurons in the substantia nigra of the chloral hydrate anesthetized rat. I.v. administration of the SK channel blocker apamin (0.4 mg/kg), increased bursting activity in approximately 50% of the dopamine neurons tested without altering average firing rate. The majority of these cells responded slowly to the effects of apamin, gradually transitioning from an irregular single spike to a phasic discharge composed of the same relative proportion of long (>or=three spike) and short (two spike) bursts as "natural" bursting activity recorded in drug naive animals. Local administration of apamin increased bursting activity in all cells tested. Systemic administration of the SK channel opener, 1-ethyl-2-benzimidazolinone (5-25 mg/kg) also had no effect on average firing rate but suppressed bursting activity and increased the precision of firing. The effects of 1-ethyl-2-benzimidazolinon on firing pattern were abolished when recording electrodes contained apamin (125 microM). These results suggest that SK channels actively contribute to the spontaneous firing patterns exhibited by dopamine neurons in vivo and provide additional support for the proposition that this channel could serve as a useful target for modifying their activity.

Action Potentials↗
PubMed2002

Repeated generalized audiogenic seizures induce plastic changes on acoustically evoked neuronal firing in the amygdala.

Repetition of audiogenic seizures (AGS) (AGS kindling) results in increases in the duration of convulsive behavior and the emergence of cortical epileptiform EEG activity. These changes involve expansion of the neuronal network subserving these seizures. The amygdala (AMG) is postulated to become involved in this expanded network, but the neurophysiological basis of this process is unknown. The present study examined changes in chronically-recorded extracellular neuronal firing patterns in the lateral nucleus of AMG (LAMG) induced by AGS kindling in behaving genetically epilepsy-prone rats (GEPR-9s). Before AGS kindling, onset-only (36.1%), onset-delayed (50%) and delayed-only (13.9%) patterns of response to acoustic stimuli were observed. Neuronal firing was greatly suppressed following systemically administered uncompetitive NMDA antagonist (ketamine, 30 mg/kg, i.p.) with complete recovery by 4 h. After AGS kindling, LAMG neurons displayed a significantly increased incidence of onset-only patterns (93.3%, at 0.5 Hz), and mean acoustic responsiveness was also significantly increased (516.2% of control). LAMG neurons fired tonically during tonic convulsions and exhibited burst firing during post-tonic clonus. Greater acoustically-induced synchronization of LAMG firing, as indicated by elevated responsiveness and increased concentration of firing near the stimulus onset, may be critical for mediating the behavioral and EEG changes induced by AGS kindling. LAMG neuronal firing increases induced by AGS kindling may initiate these pathophysiological alterations, in part, by enhanced glutamate receptor-mediated excitation. This possibility is supported by the previously observed ability of an NMDA antagonist to reverse AGS kindling when focally microinjected into AMG, and the blockade of LAMG firing by administration of an uncompetitive NMDA antagonist observed in the present study.

Acoustic Stimulation↗
PubMed1999

Synaptic excitability of the burst firing neurons in cat sensorimotor cortex in vitro.

We have recently reported that the burst firing neurons are found in layer III as well as in layer V of cat sensorimotor cortex in vitro. In the present study, we examined the synaptic excitability of layer III neurons by white matter stimulation and compared with their firing patterns against the current injections through the recording microelectrodes. The firing patterns of layer III neurons were classified into three main classes as in our previous study, i.e., (1) regular spiking (RS), i.e., the tonic firing that often exhibited spike-frequency adaptation, (2) burst-and-single spiking (BS), i.e., the initial bursting followed by tonic firing, (3) repetitive-bursting (RB), the burst firing that recurred at fast frequency. In RS cells, single action potential was superimposed on the largest EPSPs among all cell types analyzed. BS cells also fired single action potential and never exhibited burst firing synaptically. Only in a part of RB cells, synaptic bursting instead of single action potential was evoked on smaller EPSPs. IPSPs could be observed in about 60% of all the recorded RS and BS cells, however, they were observed in only 10% of the RB cells.

Animals↗
PubMed2001

Heterogeneity within geniohyoid motor unit subpopulations in firing patterns during breathing.

Respiratory motor units (MU) segregate into subpopulations, which differ in firing patterns during resting and stimulated breathing. For phrenic/diaphragm MUs, diversity also exists within subpopulations, and is greater for late than early-onset MUs. The present study characterized the extent of diversity within upper airway respiratory MU subpopulations by recording geniohyoid MUs in anesthetized cats. Inspiratory MUs (I-MU, n=21) had a wide range of firing durations (coefficient of variation (CV)=42%). In contrast, inspiratory-expiratory MUs (I/E-MU, n=19) had a narrow range of firing durations during inspiration (CV=13%), but a wide range of firing durations during expiration (CV=36%). Mean firing frequency had similar degrees of diversity among units for I-MU and I/E-MU (CV=31-40%). For I-MU firing duration correlated with mean firing frequency, whereas no such relationship was apparent for I/E-MU. Single-breath end-expiratory airway occlusion decreased heterogeneity in firing duration during inspiration and increased it during expiration, whereas end-inspiratory airway occlusion decreased heterogeneity during expiration. In conclusion, (a) there is considerable diversity within geniohyoid MU subpopulations receiving respiratory drive; (b) the degree of diversity within subpopulations differs for I-MU and I/E-MU; and (c) diversity within subpopulations in timing of activity is modulated by single-breath airway occlusion.

Airway Obstruction↗
PubMedDate not supplied

Near Poisson-type firing produced by concurrent excitation and inhibition.

The effect of inhibition on the firing variability is examined in this paper using the biologically-inspired temporal noisy-leaky integrator (TNLI) neuron model. The TNLI incorporates hyperpolarising inhibition with negative current pulses of controlled shapes and it also separates dendritic from somatic integration. The firing variability is observed by looking at the coefficient of variation (C(V)) (standard deviation/mean interspike interval) as a function of the mean interspike interval of firing (delta tM) and by comparing the results with the theoretical curve for random spike trains, as well as looking at the interspike interval (ISI) histogram distributions. The results show that with 80% inhibition, firing at high rates (up to 200 Hz) is nearly consistent with a Poisson-type variability, which complies with the analysis of cortical neuron firing recordings by Softky and Koch [1993, J. Neurosci. 13(1) 334-530]. We also demonstrate that the mechanism by which inhibition increases the C(V) values is by introducing more short intervals in the firing pattern as indicated by a small initial hump at the beginning of the ISI histogram distribution. The use of stochastic inputs and the separation of the dendritic and somatic integration which we model in TNLI, also affect the high firing, near Poisson-type (explained in the paper) variability produced. We have also found that partial dendritic reset increases slightly the firing variability especially at short ISIs.

Neurons↗
PubMed1997

Management of imported fire ant allergy: results of a survey.

BACKGROUND: Fire ant allergy is a significant health problem in the southern United States. Management of fire ant allergy is less clearly defined than management of allergy to the winged Hymenoptera. OBJECTIVE: To determine how fire ant allergy is managed by practicing allergists. METHODS: A survey form was developed and distributed to American College of Allergy, Asthma & Immunology members practicing in fire ant endemic states. Completed forms were returned to the American College of Allergy, Asthma & Immunology central office and forwarded to the authors for analysis. RESULTS: Three hundred twenty-nine of 879 (37.4%) surveys were returned; 81% of respondents have evaluated patients with imported fire ant allergy. Immunotherapy is used by 96.7% of respondents to treat fire ant allergy. A wide range of maintenance dosages are prescribed. Skin testing is the most common diagnostic method. Systemic reactions to stings while on maintenance immunotherapy were reported by 19%. Allergists utilize different criteria in consideration for stopping immunotherapy; 19% continue it indefinitely. CONCLUSIONS: There are many areas of general uniformity and other areas of divergence in how allergists manage imported fire ant allergy. These findings suggest continued need for further investigation regarding the efficacy, dosage, and duration of immunotherapy, as well as further elucidation of the natural history of fire ant allergy.

Ant Venoms↗
PubMed2000

The variability of basal action potential firing is positively correlated with bursting in hypothalamic oxytocin neurones.

Magnocellular oxytocin neurones are proposed as a suitable system for studying the mechanisms involved in the regulation of neuronal bursting activity. They display high frequency (50 sp./s) bursts of spikes (approximately every 300 s), in response to specific stimuli, which are superimposed on a variable level of basal activity and are tightly co-ordinated as a result of network interactions. The relationship between the strength of the bursting activity (as quantified by burst amplitude and interburst interval) and the characteristics of the interburst basal activity were assessed. During control conditions, mean basal activity and variability of firing increased just before bursts. During experimental conditions leading to burst facilitation, burst amplitude increased and interburst interval decreased while a sustained increase in mean firing rate occurred. Variability of firing (measured by both the standard deviation of firing rate, and the index of dispersion which corrected this standard deviation for differences in mean firing rate), increased demonstrating an increase in spike clustering greater than expected as a result of increased basal activity. When bursting was restrained (i.e. interburst interval increased), mean basal activity increased substantially, but index of dispersion decreased. A narrowing of the interspike interval distribution occurred, indicating increased regularity of firing. The aspect of basal activity most strongly correlated with bursting was variability of firing rate. The strongest correlate of burst amplitude was the standard deviation of mean firing rate, whereas the strongest and most consistent correlate of interburst interval was the index of dispersion. In conclusion, bursting behaviour is most strongly related to the irregularity rather than the level of basal activity.

Action Potentials↗
PubMed1984

Imported fire ant allergy. Perspectives on diagnosis and treatment.

As the imported fire ant relentlessly expands its territory, more and more people are at risk of the insects' discomforting and sometimes dangerous stings. Thus, all primary care physicians in fire ant-infested areas should be familiar with diagnosis and treatment of fire ant stings and of allergic reactions to the stings. Fire ant venom is unique when compared with other Hymenoptera venoms, as it consists mainly of nonallergenic alkaloids that are of small molecular weight with only a small percentage of allergenic proteins. Fire ant wholebody extract, unlike other Hymenoptera wholebody extracts, retains its allergenic activity and is an adequate material for use in diagnostic testing and immunotherapy. Diagnosis of fire ant allergy can be readily made by the radioallergosorbent test (RAST) or by skin testing using fire ant wholebody extract. Immunotherapy with fire ant whole-body extract in allergic individuals can prevent serious recurrent systemic reactions.

Animals↗
PubMedDate not supplied

Characteristics of fire station walk-in patients.

OBJECTIVE: To characterize the use of fire stations for walk-in health care and compare utilization patterns of fire stations in lower-income areas with those in higher-income areas. METHODS: The study was a retrospective review of emergency medical services (EMS) medical forms of patients who presented directly to a fire station for medical care during a 12-month period. RESULTS: During the study period, there were a total of 56,600 EMS calls by the studied fire department, with 155 visits by persons presenting to 19 fire stations in the 12 zip code areas. Of these, 131 were eligible for inclusion in our study. Of the 131 visits, 76 of 131 (58%) occurred in zip codes where more than 20% of residents lived below poverty level. Patients presenting to the fire station for medical care were disproportionately male, 84 of 131 (64%), aged 31-50 years, 61 of 131 (47%). Leading chief complaints were abrasion/laceration/hematoma, 20 of 131 (15%), shortness of breath, 18 of 131 (14%), loss of consciousness/syncope/dizziness/weakness, 17 of 131 (13%), musculoskeletal pain, 17 of 131 (13%), and chest pain, 14 of 131 (11%). Suicide, assault, alcohol, or substance intoxication (SAAD) was associated with 47 of 131 (36%) visits. Following evaluation at the fire station, 97 of 131 (82%) were transported by EMS; few patients were transported by private vehicle (n = 11) or did not need transport (n = 12). CONCLUSIONS: In the authors' EMS system, the use of fire stations for walk-in health occurs disproportionately in areas of poverty. SAAD features are present in more than one third of the visits.

Adolescent↗
PubMed1962

Interpretation of the repetitive firing of nerve cells.

Eccentric cells of Limulus respond with repetitive firing to sustained depolarizing currents. Following stimulation with a step of current, latency is shorter than first interval and later intervals increase progressively. A shock of intensity twice threshold can evoke firing 25 msec. after an impulse. But in the same cell, a current step twice rheobase evokes a second impulse more than 50 msec. after the first, and current intensity must be raised to over five times rheobase to obtain a first interval of about 25 msec. Repetitive firing was evoked by means of trains of shocks. With stimuli of moderate intensity, firing was evoked by only some of the shocks and intervals between successive impulses increased with time. This is ascribed to accumulation of refractoriness with successive impulses. Higher frequencies of firing are obtained with shocks of intensity n x threshold than with constant currents of intensity n x rheobase. It is concluded that prolonged currents depress the processes leading to excitation and that (in the cells studied) repetitive firing is controlled both by the after-effects of firing (refractoriness) and by the depressant effects of sustained stimuli (accommodation). Development of subthreshold "graded activity" is an important process leading to excitation of eccentric cells, but is not the principal factor determining frequency of firing in response to constant currents.

Animals↗
PubMed1999

Firing properties of single vasoconstrictor neurones in human subjects with high levels of muscle sympathetic activity.

1. Single-unit recordings were made from 19 postganglionic muscle vasoconstrictor axons via tungsten microelectrodes in the peroneal nerve in seven healthy subjects with many multi-unit sympathetic discharges at rest ('high group', 75 +/- 5 multi-unit bursts per 100 heart beats, mean +/- s.e.m.). The results were compared with previous data from 14 units in subjects with 21 +/- 2 multi-unit bursts per 100 heart beats ('low group'). 2. In the 'high group' the units fired spontaneously in 35 +/- 4 % of all cardiac intervals. One unit only ever fired once per cardiac interval, 14 units (74 %) generated maximally two to three spikes, and four units (21 %) up to four to five spikes. Of those cardiac intervals in which a unit fired, a single spike occurred in 78 %, two spikes in 18 %, three spikes in 4 % and four spikes in less than 1 % of cardiac intervals. Measured as the inverse of all interspike intervals, the mean rate was 0.33 +/- 0.04 Hz and the mean intraburst frequency 22.2 +/- 1.6 Hz. Most results were similar to those in the 'low group', but in the 'low group' heart rate was higher (64.5 vs. 50.4 beats min-1) and mean firing frequency was higher (0.49 +/- 0.06 Hz). 3. During increases of multi-unit burst activity evoked by sustained inspiratory-capacity apnoea the firing probability of nine units in the 'high group' increased from 33 +/- 6 to 56 +/- 3 % of the cardiac intervals. Simultaneously, the incidence of single spikes decreased and the incidence of multiple spikes per cardiac interval increased, resulting in an increase of mean firing frequency from 0. 23 +/- 0.04 Hz at rest to 1.04 +/- 0.14 Hz during the apnoea. 4. We conclude that single muscle vasoconstrictor neurones usually fire only a solitary spike during sympathetic bursts both in subjects with a high and in subjects with a low number of bursts at rest. Presumably, differences in the numbers of bursts are due mainly to differences in firing probability and recruitment of sympathetic fibres. During acute increases of multi-unit activity, both increases in discharge frequency and recruitment of additional neurones contribute to the increased intensity of an individual sympathetic burst.

Adult↗
PubMed1994

Defluoridation of drinking water with pottery: effect of firing temperature.

Excessive fluoride (F) in drinking water should be removed, but simple, inexpensive methods of fluoride removal are not readily available. This study examines the F(-)-binding capacity of clay and clayware, especially the effect of the firing temperature on the F(-)-binding process. A series of pots were made from ordinary potter's clay and fired at 500-1000 degrees C. Likewise, small clay bricks were fired and then crushed and sieved. NaF solutions containing 10 mg/l F- (10 ppm F-) were prepared. Suitable aliquots of the solutions were poured into clay pots or exposed to powdered clayware. Samples were taken at storage periods of 30 min to 20 days and analyzed for F- by ion-selective electrodes. The rate and capacity of F(-)-binding in the clayware varied with the firing temperature. Clay fired at approximately 600 degrees C was most effective. Temperatures over 700 degrees C caused a decline in F(-)-binding, and pottery fired at 900 degrees C and above seemed unable to remove F- from water. Pots fired at 500 degrees C or less cracked in water. The findings indicate that clayware, fired at an optimal temperature, may be of practical value for partial defluoridation of drinking water.

Aluminum Silicates↗
PubMed2004

Comparison of the firing patterns of human postganglionic sympathetic neurones and spinal alpha motoneurones during brief bursts.

Focal recordings from individual postganglionic sympathetic neurones in awake human subjects have revealed common firing properties. One of the most striking features is that they tend to fire only once per sympathetic burst. Why this should be so is not known, but we propose that the short duration of the burst may limit the number of times a sympathetic neurone can fire. Indeed, while the normal variation in cardiac interval and burst duration is too narrow to reveal a correlation between burst duration and the number of spikes generated, we know that spike generation is doubled when burst duration is doubled following ectopic heart beats. To test the hypothesis that the burst duration constrains the firing of individual sympathetic neurones to one per burst, we used the human skeletomotor system as a model for the sympathetic nervous system, which allowed us to vary burst duration and amplitude experimentally. Intramuscular recordings were made from 27 single motor units (alpha motoneurones) in the tibialis anterior or soleus muscles of seven subjects; multiunit EMG activity was recorded via surface electrodes and blood pressure was recorded continuously. Subjects were instructed to generate EMG bursts of varying amplitude in the intervals between heart beats. By constraining the firing of alpha motoneurones to brief ( approximately 400 ms) bursts we could emulate real sympathetic bursts. Individual motoneurones generated 0-7 spikes during the emulated sympathetic bursts, with firing patterns similar to those exhibited by real sympathetic neurones. Eleven motor units showed significant positive linear correlations between the number of spikes they generated within a burst and its amplitude, whereas for 17 motor units there were significant positive correlations between the number of spikes and burst duration. This indicates that burst duration is a major determinant of the number of times an alpha motoneurone will fire during a brief burst, and we suggest that the same principle may explain the firing pattern typical of human sympathetic neurones.

Action Potentials↗
PubMed1966

Synaptic stimulation superimposed on motoneurones firing in the 'secondary range' to injected current.

1. This paper extends the work on the ;primary range' of firing (Granit, Kernell & Lamarre, 1966), in lumbar motoneurones to the ;secondary range'. By definition the latter begins when, with stronger currents, the linear curve relating firing rate to injected current in the primary range undergoes a fairly sudden increase of slope.2. It was shown that motoneurones firing at the higher frequencies of the secondary range were partially inactivated. Yet such firing rates were within the physiological range.3. Algebraical summation of firing rates, when present in the secondary range, implied at the same time that the synaptic amount added was diminished by comparison with what it had been within the primary range.4. Superimposed synaptic excitatory stimuli did not (as in the ;primary range') regularly add their effect algebraically on to the rate of firing achieved by injected currents alone. More commonly the synaptic effect of the constant input underwent a progressive increase throughout the secondary range.5. Superimposed inhibitory stimuli regularly reduced the slope constant as determined by trans-membrane current alone and, by counter-acting inactivation, made the motoneurone approach the mode of firing characteristic of the ;primary range'.6. The latter finding emphasizes the significance of analysing firing motoneurones with the aid of ;slope constants' and provides inhibition with a new role in the integrative behaviour of motoneurones, as considered in the Discussion.

Animals↗