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[Repeat evaluation of impulsiveness in a cohort of 155 patients with obsessive-compulsive disorder: 12 months prospective follow-up].

UNLABELLED: Relationships between OCD and impulsivity are currently under research. METHOD: In the phase 3 of the national study on OCD, 155 patients suffering from an OCD (DSM III-R criteria, score on NIMH-OC > or = 7) had entered a naturalistic follow-up of 12 months duration. Impulsivity was assessed by using the BDS (Behavioral Dyscontrol Scale, offautoquestionnaire of 24 items) at day 0, 6th and 12th months and a semi-structured interview for Obsessive-Compulsive Related Syndrome and Behaviors Spectrum, as defined by Hollander (DSM III-R criteria). RESULTS: Impulsivity was more intense in females (mean score on BDS 35.6 vs 31.9, p = 0.06), in patients with personal history of anxiety-depression (36.3 vs 32.3, p = 0.04) and suicidal behavior (38.3 vs 33.2, p = 0.06) and familial history of OCD (37.1 vs 33.0, p = 0.07). Moreover, syndromal typology of obsessions or compulsions did not seem to influence impulsivity. In contrast, presence of co-existing OC Related Syndrome was significantly linked to higher impulsivity score, especially with "Intermittent Explosive Syndrome" (mean score = 40.1 vs 30.8, p < 10(-4), "Compulsive Buying" (38.5 vs 32.4, p = 0.005), "Hypochondriasis" (36.7 vs 32.1, p = 0.02), "Dysmorphophobia" (37.1 vs 32.4, p = 0.02) and "Depersonnalization" (37.7 vs 32.9, p = 0.05). Paradoxically, impulsivity was augmented in patients with important to severe slowness syndrome (38.3 vs 31.8, p = 0.001). This mixed association between slowness and impulsivity can be an excellent testimony of "Dyscontrol" phenomenon. In 130 patients who had received an anti-obsessional pharmacologic treatment during 12 months follow-up, impulsivity score was gradually reduced from day 0 (mean score = 34.1) at M6 (24.8-22% reduction) and at M12 (20.1-36% reduction). After one year of follow-up, a decreased by > or = 50% of impulsivity score was observed in 42% of obsessional patients. Finally, the response rate of OCD to pharmacotherapy seemed to be modulated by the dimensions of impulsivity and slowness. In fact, the best results after 6 months of treatment were observed in the sub-groups presenting high level of "impulsivity" (62-66% were responders) versus 39% in the sub-group with important to severe slowness.

Adult↗

PubMed2005

The psychopharmacology of impulsive behaviour in rats VIII: effects of amphetamine, methylphenidate, and other drugs on responding maintained by a fixed consecutive number avoidance schedule.

RATIONALE: Impulsive behaviour is a component of psychiatric disorders such as bipolar disorder, attention deficit hyperactivity disorder (ADHD), or personality disorders. Most experimental studies on impulsive behaviour punish impulsive choices by loss or delay of reward. In the present study, impulsive behaviour was punished by an explicitly aversive stimulus, using a novel fixed consecutive number (FCN) schedule of electric shock avoidance. OBJECTIVES: This study was conducted to demonstrate stable performance using the FCN avoidance procedure, and examine the effects of drugs previously shown to affect impulsive behaviour using a conventional FCN schedule. METHODS: First, rats were trained in the appetitive FCN procedure. Pressing the right lever in an operant conditioning chamber after having pressed the left lever at least six times delivered a food pellet (FCN6). Responses on the right lever before completing this ratio resulted in a time out and restarted the ratio. The rats were then switched to FCN avoidance. Responses on the right lever made before completion of the ratio also resulted in food delivery, but were accompanied by an electric shock. RESULTS: Chlordiazepoxide (10.0 mg/kg), ethanol (1.0 g/kg), and haloperidol (0.1 mg/kg) increased impulsive behaviour by reducing the number of left lever responses made before the right lever was pressed. Imipramine (1.0-10.0 mg/kg) and desipramine (1.0-10.0 mg/kg) had no effect on impulsive choice. Amphetamine (0.4 and 0.8 mg/kg) and methylphenidate (6.0 mg/kg) significantly increased the mean chain length, and the proportion of very long chains, indicative of reduced impulsivity, although this did not improve efficiency. CONCLUSIONS: The increases in impulsivity produced by chlordiazepoxide, ethanol, and haloperidol were similar to those under appetitive FCN schedules. In contrast, amphetamine and methylphenidate, by reducing impulsivity in the FCN avoidance, induced effects opposite to those observed in an appetitive FCN procedure. These results suggest that the therapeutic actions of stimulants, to reduce impulsive behaviour in ADHD, may arise in part by increasing the control of behaviour by aversive stimuli.

Animals↗

PubMed1989

Hazard from weapons impulses: histological and electrophysiological evidence.

Current methods of rating the hazard of weapons impulses for the ear have recently been challenged by electrophysiological data from experiments with animal ears which indicate that the hazard from low-frequency impulses is much lower than the hazard from higher frequency impulses (Dancer et al., 1981; Price, 1986b). To supplement these data, histological data are reported here for 51 cats that were exposed on one occasion to either rifle or howitzer impulses at peak pressures from 145 to 155 dB or 153 to 166 dB, respectively. Histological procedures (scanning electron and light microscopy) were carried out over 2 months after the exposure and after electrophysiological measures had been made. For both types of impulse the losses tended to be in the middle of the cochlea in focused lesions, even though the spectral peaks of the acoustic stimuli had been at about 80 Hz (howitzer) and 1000 Hz (rifle). Outer hair cells were more susceptible than the inner hair cells and interindividual differences in effects were large. Furthermore, the two impulse sources were equally hazardous when the peak pressure of the rifle impulse was lower than the peak pressure of the howitzer impulse by about 9 dB. In terms of A-weighted energy, the exposures were equally hazardous when the rifle exposure contained about 35 times less energy than the howitzer exposure. The histological data are thus consistent with the electrophysiological data, which indicate that present standards for impulse noise exposure may overrate the hazard of low-frequency impulses relative to impulses in the midrange.

Animals↗

PubMed1999

Impulse encoding across the dendritic morphologies of retinal ganglion cells.

Nerve impulse entrainment and other excitation and passive phenomena are analyzed for a morphologically diverse and exhaustive data set (n = 57) of realistic (3-dimensional computer traced) soma-dendritic tree structures of ganglion cells in the tiger salamander (Ambystoma tigrinum) retina. The neurons, including axon and an anatomically specialized thin axonal segment that is observed in every ganglion cell, were supplied with five voltage- or ligand-gated ion channels (plus leakage), which were distributed in accordance with those found in a recent study that employed an equivalent dendritic cylinder. A wide variety of impulse-entrainment responses was observed, including regular low-frequency firing, impulse doublets, and more complex patterns involving impulse propagation failures (or aborted spikes) within the encoder region, all of which have been observed experimentally. The impulse-frequency response curves of the cells fell into three groups called FAST, MEDIUM, and SLOW in approximate proportion as seen experimentally. In addition to these, a new group was found among the traced cells that exhibited an impulse-frequency response twice that of the FAST category. The total amount of soma-dendritic surface area exhibited by a given cell is decisive in determining its electrophysiological classification. On the other hand, we found only a weak correlation between the electrophysiological group and the morphological classification of a given cell, which is based on the complexity of dendritic branching and the physical reach or "receptive field" area of the cell. Dendritic morphology determines discharge patterns to dendritic (synaptic) stimulation. Orthodromic impulses can be initiated on the axon hillock, the thin axonal segment, the soma, or even the proximal axon beyond the thin segment, depending on stimulus magnitude, soma-dendritic membrane area, channel distribution, and state within the repetitive impulse cycle. Although a sufficiently high dendritic Na-channel density can lead to dendritic impulse initiation, this does not occur with our "standard" channel densities and is not seen experimentally. Even so, impulses initiated elsewhere do invade all except very thin dendritic processes. Impulse-encoding irregularities increase when channel conductances are reduced in the encoder region, and the F/I properties of the cells are a strong function of the calcium- and Ca-activated K-channel densities. Use of equivalent dendritic cylinders requires more soma-dendritic surface area than real dendritic trees, and the source of the discrepancy is discussed.

Action Potentials↗

PubMed2005

Increased impulsivity associated with severity of suicide attempt history in patients with bipolar disorder.

BACKGROUND: Impulsivity is a prominent and measurable characteristic of bipolar disorder that can contribute to risk for suicidal behavior. The purpose of this study was to investigate the relationship between impulsivity and severity of past suicidal behavior, a potential predictor of eventual suicide, in patients with bipolar disorder. METHOD: In bipolar disorder subjects with either a definite history of attempted suicide or no such history, impulsivity was assessed with both a questionnaire (Barratt Impulsiveness Scale) and behavioral laboratory performance measures (immediate memory/delayed memory tasks). Diagnosis was determined with the Structured Clinical Interview for DSM-IV. Interviews of patients and review of records were used to determine the number of past suicide attempts and the medical severity of the most severe attempt. RESULTS: Subjects with a history of suicide attempts had more impulsive errors on the immediate memory task and had shorter response latencies, especially for impulsive responses. Impulsivity was highest in subjects with the most medically severe suicide attempts. Effects were not accounted for by presence of depression or mania at the time of testing. Barratt Impulsiveness Scale scores were numerically, but not significantly, higher in subjects with suicide attempts. A history of alcohol abuse was associated with greater probability of a suicide attempt. Multivariate analysis showed that ethanol abuse history and clinical state at the time of testing did not have a significant effect after impulsivity was taken into account. DISCUSSION: These results suggest that a history of severe suicidal behavior in patients with bipolar disorder is associated with impulsivity, manifested as a tendency toward rapid, unplanned responses.

Adult↗

PubMed1999

Impulsivity: a discussion of clinical and experimental findings.

Impulsivity can often be an important clinical problem in psychiatry and neurology. In psychiatry, the manifestation of impulsive behaviour in syndromes such as personality disorders, attention deficit hyperactivity disorder and in substance abuse may be different, and this has led to conflicting definitions. There has also been a tendency to concentrate on the nature of the behavioural manifestation (problems with the law, aggression, drug use, behavioural problems in school) rather than shared psychological processes, and to ignore the fact that impulsivity can also have positive aspects. In a normal population, the personality trait of impulsivity has been analysed using personality inventory questionnaires. Analysis of these data lead to the suggestion that impulsivity as commonly defined and understood may be made up of several independent factors, which may have separate biological bases. These self-rating questionnaires have been complemented by objective tests that are now often computerized, and which have been used in man (e.g. with criminal offenders, children, or patients who have undergone brain surgery). Some of these tests, such as the differential reinforcement of low rates procedure or the delay of reinforcement procedure, have also been used to study impulsivity in animals. Analysis of the behavioural principles of these tests suggests that they too may reflect different aspects of impulsivity. Many different biological systems have been proposed to contribute to the neurobiological basis of impulsivity. The serotonergic neurotransmitter system has recently received the most attention, with evidence of its involvement coming from animal studies as well as from studies in psychiatric patients. The frontal lobes have been proposed to play an important role in regulating impulsivity, although it unclear how specific this is. None of this biological knowledge has yet led to reliable pharmacotherapy for excessive impulsivity and, as yet, there is little understanding of the mechanisms by which those drugs, which have been found empirically to have some efficacy (e.g. the psychomotor stimulants in attention deficit hyperactivity disorder), exert their therapeutic effect. By bringing together knowledge from different areas of research it is hoped that a cross fertilization will be achieved, which will lead to a sharpening of concepts, an improvement in methodology and the stimulation of biological studies.

Adult↗

PubMed2006

Impulsivity predicts treatment outcome in obese children.

Treatment for obesity is still running short, particularly on the long term. However, some people do take advantage of treatments and are able to retain their weight loss. What makes the difference between those who can keep their weight loss and those who cannot? One possible predictor of relapse in obesity treatment is impulsivity. Overall, obese people are found to be more impulsive than lean people, especially obese binge eaters. Intuitively, it would make sense that the most impulsive people are less able to keep control over eating behaviour. Therefore, impulsivity could serve as an obstacle for treatment. In the present study impulsivity was measured with a behavioural task (the stop signal task) in 26 obese children. Overweight of the children was measured before and after treatment and at 6 and 12 months follow ups. The results show that impulsivity was related to overweight at all moments: The most impulsive children were the most overweight ones; even after 12 months. Moreover, impulsivity predicted therapy success: the most impulsive children lost less weight. Impulsivity appears to contribute to the difference between succeeding or failing in attempts to lose weight.

Child↗

PubMed2006

Characterization of impulsivity in suicide completers: clinical, behavioral and psychosocial dimensions.

BACKGROUND: Impulsivity is a personality trait thought to be linked to suicide. Yet, not all suicides are highly impulsive. We aimed to better understand clinical, behavioral and psychosocial correlates of the association between suicide and impulsive behavior. METHODS: One hundred sixty four suicide cases with impulsivity scores based on the Barratt Impulsivity Scale (BIS) were investigated. To examine the most extreme phenotypes, one hundred suicide cases, representing subjects with BIS scores above the 70th percentile and below the 30th percentile, were compared on clinical, behavioral and psychosocial suicide risk factors assessed by way of structured psychological autopsy methods with best informants. RESULTS: The impulsive suicide cases were significantly younger, exhibited higher measures of aggressive behavior, and were more likely to have a cluster B diagnosis as well as lifetime and 6-month prevalence of alcohol and drug abuse/dependence. They also differed significantly from their non-impulsive counterparts on all subscales of the TCI except for Harm Avoidance and Reward Dependence. Impulsive suicide completers were more likely to have had a history of childhood abuse and to have experienced a triggering life event up to a week preceding their death. A multivariate analysis indicated that 6-month prevalence of substance abuse/dependence and high aggressive behavior remained significant even after controlling for other significant variables. LIMITATIONS: This study was carried out using proxy-based interviews. CONCLUSIONS: Most of the known clinical and behavioral risk factors commonly associated with suicide are particularly valid for impulsive suicide completers. Further, triggering and adverse life events seem to play a role primarily in impulsive suicide.

Adult↗

PubMed2005

Self-reported psychotic symptoms predict impulsivity among African-American patients in an urban non-psychiatric medical setting.

A variety of epidemiological studies have documented self-reported psychotic symptoms among individuals in the general population. Research has not been conducted on the associations between self-reported psychotic symptoms and enduring personality characteristics, such as impulsivity, among participants in non-psychiatric settings. We hypothesized that impulsivity scores, as measured by the Barratt Impulsiveness Scale (BIS-11), would be predicted partly by the presence of one or more of a variety of positive psychotic experiences, determined by the revised Symptom Checklist-90. The sample consisted of 100 African-American men and women seeking care in medical clinics in an urban public sector hospital. The sample was divided into those participants endorsing one or more of six psychotic symptoms and those not reporting psychotic symptoms. Multiple linear regression models examined predictors of impulsivity (as measured by the BIS-11 total score and the two derived subscales), including the effect of self-reported positive psychotic symptoms. The presence of psychotic symptoms was predictive of the total impulsivity score and the ideo-motor impulsivity subscale score, even after adjustment for the effects of other correlates of impulsivity, including gender, homelessness, history of conviction for a misdemeanor or felony, and history of past treatment or hospitalization for psychiatric or substance abuse problems. The findings suggest that there is an important link between the presence of self-reported psychotic symptoms and impulsivity, especially ideo-motor impulsivity, in a general sample of low-income African-American men and women seeking ambulatory medical care. Further research on self-reported psychotic symptoms in non-psychiatric populations is needed, as well as research on the personality correlates of such symptoms, including impulsivity.

Adolescent↗

PubMed2002

Increased impulsivity in cocaine dependent subjects independent of antisocial personality disorder and aggression.

Several previous studies show a relationship between impulsivity and substance abuse; however, it is unclear whether the increased impulsivity seen in substance dependent groups is specifically related to substance abuse, or if it is due to concomitant antisocial personality disorder (ASPD) or aggression. The issue of whether impulsivity is specifically related to substance abuse is important since it has a bearing on risk factors for development of substance abuse. To determine whether cocaine dependent subjects show increased impulsivity independent of ASPD, the Barratt impulsiveness scale (BIS-11), a delayed reward laboratory measure of impulsivity, and the life history of aggression scale were administered to 49 cocaine dependent subjects and 25 controls. Results showed that cocaine dependent subjects with ASPD were more impulsive and aggressive than controls, but cocaine dependent subjects without ASPD were also more impulsive compared to controls. Controlling for aggression history, cocaine dependent subjects without ASPD continued to have elevated impulsivity as measured by the BIS-11, but not the delayed reward task. This study supports the hypothesis that the increased impulsivity as measured by the BIS-11 in cocaine dependent individuals is not exclusively due to concomitant increases in aggression or ASPD.

Adult↗

PubMed1998

Impulsivity, personality disorders and pathological gambling severity.

AIMS: The present study seeks to replicate and expand findings from earlier studies that pathological gamblers manifest elevated traits of impulsivity. Secondly, the study aims to elucidate the relationship between impulsivity, indices reflecting severity of pathological gambling and other measures of psychopathology and personality dysfunction. DESIGN: Case series. PARTICIPANTS: Eighty-two consecutive gamblers, seeking treatment for problem gambling. SETTING: Impulse Disorders Research Unit, School of Psychiatry, University of New South Wales, Australia. MEASUREMENTS: Semi-structured interview designed to obtain demographic information and gambling history, the South Oaks gambling Screen, the Eysenck Impulsivity Scale, the Personality Disorder Questionnaire-Revised, the Beck Depression Inventory and the Beck Anxiety Inventory. FINDINGS: Results show elevated traits of impulsivity among clinic samples of pathological gamblers compared to normative data and show that impulsivity is related to the severity of gambling behaviour as measured by the South Oaks Gambling Questionnaire. A principal component analysis of the Eysenck Impulsivity Scale and the personality Disorder Questionnaire-Revised, demonstrated that the concept of the "antisocial-impulivist" identified to Blaszczynski, Steel & McConaghy (1997) is not only characterized by impulsivity and antisocial personality disorder but also by high loadings from other cluster B and cluster C personality disorders. CONCLUSION. This research supports the role of the construct of impulsivity in mediating the severity of gambling behaviour and associated behavioural and psychological disturbance among pathological gamblers presenting for treatment. Impulsivity is best understood as part of a general personality disorder structure characterized primarily by DSM-III-R Axis II cluster B and some cluster C personality disorder.

Adult↗

PubMed1995

The significance of aggression and impulsivity for self-mutilative behavior.

Self-mutilative behavior (SMB) is presented as a specific form of inwardly directed aggressiveness which is thought to be associated with problems of impulse control. Conceptual problems concerning impulsivity and impulsive aggression are discussed. Among different forms of dyscontrolled behavior, SMB is of special heuristic interest because of distinction can be made between patients committing impulsive and those committing premeditated self-harming actions. Psychometric and biological measures of impulsivity and aggressiveness were assessed in self-mutilators in comparison to depressives and normal probands. Self-mutilators were differentiated into two subgroups, those with an impulsive (ISMB) and those with a premeditated (PSMB) form of SMB, and depressives were also differentiated into two subgroups, those with a history of suicide attempts and those without. Only patients with ISMB (and depressives with a history of suicide attempts) showed an enduring tendency towards dyscontrolled patterns of behavior and cognition; therefore, SMB cannot be generally regarded as an indicator of high impulsivity or an impulse control disorder. Measures of impulsivity and aggressiveness did not behave analogically to each other and aggressive or autoaggressive modes of behavior should not be generally used as an index of impulsivity. A reduction of serotonergic activity, proved by a blunted prolactin response to D-fenfluramine, was found in all patient-groups in comparison to normal probands. Prolactin response after D-fenfluramine challenge turned out to be most blunted among self-mutilators with ISMB and among depressives with a history of suicide attempts.

Adult↗

PubMed2000

Serotonin, impulsivity, and alcohol use disorders in the older adolescent: a psychobiological study.

BACKGROUND: Alcohol use disorders (AUDs) among adolescents are associated with a high prevalence of conduct disorder (CD), much as type II alcoholism in adults is associated with impulsive-aggressive behavior and antisocial personality traits. Adults with impulsive personality disorders and AUD demonstrate diminished central serotonergic responsiveness to serotonergic agonists. Dysregulation of central serotonergic function may contribute to a vulnerability to impulsive-aggressive behavior, CD, and AUD. We studied older adolescents, both male and female, to examine the relationships between sex, dispositional impulsivity, aggressivity, CD, and responsiveness to serotonergic challenge with d,l fenfluramine (FEN) early in the development of AUD. METHODS: Thirty-six adolescents between the ages of 16 and 21 years were assessed for DSM-IV AUD and other Axis I disorders by using the Psychoactive Substance Use Disorders section of the Structured Clinical Interview for DSM III-R, the Schedule for Affective Disorders and Schizophrenia for School-Age Children-Present and Lifetime Version, and CD interviews. Impulsivity and aggressivity were assessed by the Barratt Impulsiveness Scale, Lifetime History of Aggression, Buss-Durkee Hostility Inventory, Eysenck Impulsiveness Questionnaire, Youth Self Report, and Multidimensional Personality Questionnaires. FEN was administered as 0.8 mg/kg to a maximum of 60 mg, and blood was sampled at fixed intervals for prolactin, cortisol, fenfluramine, and norfenfluramine levels. RESULTS: Eighteen adolescents (12 male, 6 female) with AUD scored significantly higher on all measures of impulsivity and aggressivity compared with 18 healthy controls (12 male, 6 female). There were no significant differences between groups in peak prolactin or cortisol responses (minus baseline), or area-under-the-curve determinations (AUC); however, 9 subjects with AUD and comorbid CD had significantly elevated cortisol AUC levels compared with subjects with AUD and no CD or with normal controls. In the total sample, cortisol AUC was associated positively with measures of aggression. CONCLUSIONS: Adolescents with early-onset AUD are characterized by impulsivity and aggressivity compared with healthy peers but do not demonstrate the diminished prolactin or cortisol responses to FEN characteristic of adult alcoholics with impulsive-aggression.

Adolescent↗

PubMed2005

The active head-impulse test in unilateral peripheral vestibulopathy.

BACKGROUND: The head-impulse test, which is sensitive and specific for detecting severe unilateral peripheral vestibulopathy, is an accepted part of the neurological examination, especially in patients with vertigo and balance disorders. OBJECTIVE: To discover if the head-impulse test is just as useful diagnostically when patients are asked to rotate their own heads, the active head-impulse test, rather than when the clinician does so as in the standard passive head-impulse test. METHODS: Clinical observation of compensatory saccades and search coil measurement of compensatory eye rotations, during active and passive horizontal head-impulses in 6 patients with total unilateral vestibular deafferentation. RESULTS: Clinical observation showed the expected compensatory saccades with rotations toward the side with the lesion with passive head-impulses but not with active head-impulses. Search coil recordings revealed 2 reasons for this. With active head-impulses not only was vestibulo-ocular reflex gain higher, but compensatory saccade latency was shorter resulting in an occult saccade that occurred during, rather than after, head rotation. CONCLUSIONS: Passive head-impulses are necessary to detect a severe unilateral peripheral vestibulopathy; active head-impulses will produce a false-negative result.

Adult↗

PubMed1982

A model for impulse frequency modulation used in neural encoding.

The impulse rate at the output of a neural encoder can be interpreted as the sum of the mean impulse rate plus a noise component. From literature models are known which describe the transient phenomena of the encoder as far as the mean impulse rate is concerned. In this paper in addition the noise phenomenon is treated by a model which is in agreement with results derived from measurements. This model consists of two parts, a multiplicative and an additive estimator. The first one is similar to the automatic gain control system known from literature. This system estimates the amplification of the impulse rate due to the step input of the neural encoder. Multiplying the impulse rate with the inverse of this factor inhibits the change of the impulse rate. The second estimator calculates the step size of the impulse rate which is subtracted from the output of the encoder. Again the change of the impulse rate is inhibited. The comparison of the impulse rates simulated by the model and given by published measurements shows a good agreement for the properties of the mean impulse rate and the variance of the imposed noise.

Animals↗

PubMed1987

Latency of gustatory neural impulses initiated in frog tongue.

Latencies of gustatory neural impulses evoked by stimulation of the bullfrog tongue with the 4 basic taste substances (NaCl, acetic acid, quinine-HCl(Q-HCl), sucrose), CaCl2 and water were studied by recording antidromic impulses conducted to the fungiform papillae. Mean latencies of the impulses ranged from 58 to 107 ms when very strong stimuli, such as 2 M NaCl, 0.1 M acetic acid, 0.1 M Q-HCl, 2 M sucrose and 1 M CaCl2, were applied. Mean latency in response to water was 2.41 s. The time required for arrival of an applied taste stimulus on the taste receptor membrane was a mean of 20.1 ms. The time required for antidromic conduction from the impulse initiation site to the recording site was a mean of 2.4 ms. Electrical stimulation of the fungiform papilla with a strong intensity produced the impulse with a long and fluctuating latency. The mean minimum latency of the fluctuating impulse, from which the conduction time was subtracted, was 5.3 ms. Mechanical destruction of the taste disk situated at the top of the fungiform papilla resulted in a disappearance of the fluctuating impulse, suggesting that this was initiated synaptically via a depolarization of taste cells by electrical current. The minimum 5.3-ms latency was likely to be the time required from the onset of taste cell depolarization to the initiation of an impulse at the first node of Ranvier of myelinated gustatory fiber. These results indicate that the latencies of 58-107 ms by strong taste stimulation were composed of the 30- to 79-ms latency of taste cell receptor potential and the remaining 28 ms latency, which was the sum of the time of stimulant diffusion, the time from taste cell depolarization to the first impulse and the time of impulse conduction.

Animals↗

PubMed1992

Impulse conduction in sympathetic nerve terminals in the guinea-pig vas deferens and the role of the pelvic ganglia.

Focal extracellular recording techniques were used to study nerve impulse propagation and the intermittent transmitter release mechanism in sympathetic nerve terminals of the guinea-pig vas deferens in vitro. In particular, the nature of impulse propagation in postganglionic nerve fibres was characterized following pre- or postganglionic stimulation. Conventional intracellular recording techniques were also used to study directly ganglionic transmission in cell bodies in the anterior pelvic ganglia. When brief electrical stimuli were applied to the hypogastric nerve trunk close to the prostatic end of the vas deferens, the nerve terminal impulses recorded extracellularly could be evoked either directly by stimulation of the parent axon (i.e. postganglionically) or indirectly by stimulation of the preganglionic nerve fibre. In 364 separate recordings, nerve terminal impulse conduction failure was not observed during trains of stimuli at 1 Hz. However, apparent "intermittent conduction" of nerve impulses was noted on 16 occasions. In these fibres, the degree of intermittent conduction decreased as the frequency of stimulation was increased. Conduction in these intermittent fibres was reversibly interrupted by removing calcium from the Krebs' solution or by the addition of the ganglion blocker, hexamethonium (30-100 microM). Thus, the cause of intermittent conduction is failure of the transmission of excitation in the sympathetic ganglia. Impulses evoked by postganglionic stimulation never failed to propagate into the nerve terminals, and changes in the shape or amplitude of the nerve terminal impulse during trains of stimuli were not detected. One effect of stimulation was a frequency-dependent increase in the latency of the nerve terminal impulse which developed during the train of stimuli. Thus, intermittence of transmitter release from individual varicosities cannot be attributed to failure of impulse propagation in sympathetic nerve terminals. Transmission in the anterior pelvic ganglia was investigated directly by making intracellular recordings from cell bodies whose terminals projected to the vas deferens. Many cell bodies received a strong synaptic input which generated an action potential in the postganglionic cell body on a one-to-one basis. However, in some cell bodies there was a low safety factor for the generation of the action potential by the excitatory postsynaptic potential. The safety factor for generating an action potential in the postganglionic cell body was raised by increasing the frequency of stimulation. These findings suggest that peripheral ganglia are not simple one-to-one relay stations, but may well play an important role in controlling the patterns of nerve impulse traffic in postganglionic sympathetic neurons.

Animals↗

PubMed2003

Effects of heating and cooling on nerve terminal impulses recorded from cold-sensitive receptors in the guinea-pig cornea.

An in vitro preparation of the guinea-pig cornea was used to study the effects of changing temperature on nerve terminal impulses recorded extracellularly from cold-sensitive receptors. At a stable holding temperature (31-32.5 degrees C), cold receptors had an ongoing periodic discharge of nerve terminal impulses. This activity decreased or ceased with heating and increased with cooling. Reducing the rate of temperature change reduced the respective effects of heating and cooling on nerve terminal impulse frequency. In addition to changes in the frequency of activity, nerve terminal impulse shape also changed with heating and cooling. At the same ambient temperature, nerve terminal impulses were larger in amplitude and faster in time course during heating than those recorded during cooling. The magnitude of these effects of heating and cooling on nerve terminal impulse shape was reduced if the rate of temperature change was slowed. At 29, 31.5, and 35 degrees C, a train of 50 electrical stimuli delivered to the ciliary nerves at 10-40 Hz produced a progressive increase in the amplitude of successive nerve terminal impulses evoked during the train. Therefore, it is unlikely that the reduction in nerve terminal impulse amplitude observed during cooling is due to the activity-dependent changes in the nerve terminal produced by the concomitant increase in impulse frequency. Instead, the differences in nerve terminal impulse shape observed at the same ambient temperature during heating and cooling may reflect changes in the membrane potential of the nerve terminal associated with thermal transduction.

Action Potentials↗