Quantal analysis of synaptic potentials in neurons of the central nervous system.
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Action Potentials↗
Biomedical subjects
S Redman
Publications and source records attributed to S Redman.
Comparison of a quantity-frequency method and a diary method of measuring alcohol consumption.
This study compared the results obtained with two measures of alcohol consumption, a quantity-frequency (QF) method and a retrospective diary method, using a worksite sample. In order to control for the possibility of order effects, a subsample was chosen for readministration of the alcohol measures, when the order of presentation of the two measures was reversed for half of the subsample. Varying the order of presentation of the alcohol consumption items did not significantly affect the results obtained, except for an interaction effect between drinking group and order of presentation. Although subjects reported greater alcohol use on the diary than on the QF method at lower levels of consumption, the findings were reversed for higher levels of consumption. The relationship between the two measures is linear, with slope less than 1. Overall, subjects reported statistically significantly more alcohol consumption on the diary (mean [+/- SD] = 18.3 +/- 19.1 drinks) than on the QF method (mean = 16.9 +/- 19.5 drinks). The diary measure identified 20.9% of drinkers reporting consumption of more than 28 drinks per week, compared with 17.8% for the QF. However, the diary measure identified only 10.6% of drinkers reporting more than 42 drinks per week, compared with 10.2% for the QF. Consequently, the usefulness of the diary in detecting heavy drinkers appears to decrease with increasing consumption. These findings suggest the need for careful selection of alcohol consumption measures for research purposes and the need for caution in comparing the results of studies using different measures of alcohol consumption.
Accidents, Occupational↗
Feasibility of sigmoidoscopic screening for colorectal cancer in the Hunter Region.
The success of a cancer detection programme depends on the co-operation of the target population. The aim of this study was to identify factors which might influence those at average and at higher risk of developing colorectal cancer to undergo a sigmoidoscopic screening test if offered. This was addressed by means of a household survey of individuals aged 40 years and over. Overall consent to undergo screening approximated 45%. There was a significant relationship between agreement to sigmoidoscopy and each of the following: age, marital status, educational level attained, and a previous episode of rectal bleeding. Individuals who had undergone sigmoidoscopy in the past were less willing to have the test performed again. Although individuals with a family history of bowel cancer in first-degree relatives perceived themselves as being more likely to develop colorectal cancer, this had no apparent impact on their willingness to have the test. The implications of these findings for community education programmes directed at colorectal cancer are discussed.
Adult↗
Filtering effects in reporting work injuries.
Research efforts in the field of occupational injuries have been hampered by difficulties in ascertaining true prevalence rates. Lack of accuracy in reporting and documentation of work injuries leads to loss of information and lack of comparability of work injury statistics. The paper explores some of the factors related to loss of information about work injuries and proposes a descriptive model of the information processing system. The Filter Model describes the way in which information about a given injury proceeds through a series of levels, from true prevalence of injuries in the workplace, to prevalence as indicated by national aggregate statistics. Between each level is a "filter" or barrier that is selectively permeable, ensuring that information about some, but not all, injuries will pass through to the next level. Consequently, the type of work injury data collected at each level will differ. The Filter Model can aid in choice of appropriate level of data for research purposes, and provides a framework for investigation into the nature and extent of filtering processes within work injury reporting systems.
Accidents, Occupational↗
Community views about the role of general practitioners in disease prevention.
The role of preventive medicine in reducing mortality and morbidity is now widely recognized. Although general practitioners appear to be in an excellent position to offer preventive care, there is evidence that they currently do not detect or intervene for common risk behaviours. One reason for this may be the general practitioner's perception that patients do not expect such preventive activities to be a part of the doctor's role. A postal survey of 309 people randomly selected from the community was undertaken to examine perceptions about the general practitioner's role in detection and intervention for smoking, alcohol abuse, emotional problems and hypertension. Responses to the survey from 264 usable questionnaires indicated that people in the community accepted the general practitioner's role in preventive care, with most respondents indicating that they would appreciate being asked about the risks examined, would like the offer of intervention and would try treatments in these areas offered by the doctor. Few respondents indicated that they would change doctors as a result of preventive activity.
Attitude to Health↗
Measuring quality of life in cancer patients.
The diagnosis and management of cancer can have a major impact on every aspect of a patient's quality of life. Despite its importance, quality of life is rarely a reported outcome in randomized clinical trials in cancer patients. Failure to collect quality-of-life information may reflect a lack of information among researchers and clinicians about the adequacy and relative merits of measures available for assessing quality of life. We reviewed the adequacy of the 17 existing scales for assessing quality of life in cancer patients against characteristics needed for an adequate measure. None of the existing measures met all of the criteria. Recommendations about the relative adequacy of existing scales were made.
Humans↗
The burden of illness that is imposed by drug abuse and the allocation of research monies in the field: three views.
The views of politicians, experts in the field of drug abuse and randomly-selected members of the community were sought concerning the burden of illness that is imposed by the abuse of alcohol, tobacco, narcotic agents, prescribed drugs, cocaine, volatile substances, over-the-counter drugs and cannabis. Politicians and community members perceived illicit drugs to have the greatest associated burden. Experts ranked in descending order alcohol, tobacco, narcotic agents, prescribed drugs, cocaine, volatile substances, over-the-counter drugs and then cannabis to have the greatest burden of illness. Priorities that were perceived by each group for research funding corresponded with their judgements of the burden of illness. Experts' views on the burden of illness most closely matched the data that are available on drug-associated mortality. It is suggested that unless a close correspondence among the views of the three groups is present, conflict in regards to allocation of resources is likely.
Alcoholism↗
Assessing women's health needs.
It has been argued that women have specific health needs aside from those of the community as a whole. As a consequence, a move towards increased "earmarked" funding for women's health has occurred. However, some debate exists about the areas of women's health that are most in need of additional funding and about appropriate mechanisms to determine priority areas. The present study explored community perceptions of women's health needs. A sample of 157 women, who had been selected at random, were asked a series of questions about the health and social problems that are experienced by women. The questions assessed the self-reported prevalence of the problems and asked women to nominate those problems which were priorities for them personally, and for Australian women in general. The areas that were identified as priorities by this community survey were compared with those that were identified by means of other methods of needs analysis.
Adolescent↗
Rehabilitation programs for drink drivers: a critical appraisal.
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Accidents, Traffic↗
Agreement between two measures of alcohol consumption.
Responses on the Quantity-Frequency Questionnaire (QF) were compared with those on the self-report diary. The QF was administered to 778 general practice patients prior to their consultation and the same patients completed the diary at home within 24 hours. The diary overestimated the number of nondrinkers in the population relative to the QF and classified a higher proportion of patients as heavy drinkers. The QF failed to detect 78% of heavy drinkers identified by the diary. Significantly (p less than .001) more alcohol was reported to be consumed overall on the diary (mean, 10.51 drinks/week) than on the QF (mean, 6.87 drinks/week). The relationship between responses on the two measures was nonlinear. At low consumption levels patients indicated drinking twice as much on the diary as on the QF, but the magnitude of the reported consumption difference decreased with increasing consumption levels. The results are discussed in terms of their implications for self-report measures of alcohol consumption.
Adolescent↗
A filter and collection device for suction-assisted lipectomy.
The use of a stockinette as a collection and filtering device in suction-assisted lipectomy is described. Various sized stockinettes may be used depending on the volume of adipose tissue to be aspirated.
Equipment Design↗
Cardiovascular responses during cuff inflation in subjects who have been sensitised to the measurement of their blood pressure.
Changes in arterial pulse transit time, interbeat interval and the interval between the ECG signal and the arrival of the ensuing pulse at a peripheral site were recorded in response to the attachment and inflation of the cuff during blood pressure measurement. Two groups of subjects were used: a control group and a blood-pressure sensitised group. Blood-pressure sensitised individuals were defined as those who reported themselves to have been diagnosed as hypertensive by a physician, since it was hypothesised that learned or emotional responses to blood-pressure measurement would be greater in this group. No cardiovascular response to the blood-pressure measurement procedure was observed in the control group, but the blood-pressure sensitised group showed an increase in interbeat and a decrease in pulse transit time during cuff inflation. Decreases in pulse transit time are thought to reflect increases in diastolic blood pressure and arterial rigidity.
Blood Pressure↗
Theory and operation of a single microelectrode voltage clamp.
The theory of operation of a discontinuous single-electrode voltage clamp using an ideal microelectrode (infinite response speed) and fixed (current-passing) duty cycle has been previously described. In this paper, the theory is extended by considering a microelectrode which has a finite response speed, by allowing the duty cycle to be variable, and by considering the clamp noise. Formulate are derived for the relationships between the step response, the steady-state error, the steady-state ripple, and the stability, in terms of the cycling frequency, the duty cycle, the open loop gain, and the electrical resistance and capacitance of the microelectrode and the cell membrane. In addition, the amplification of the microelectrode noise by aliasing is analysed, the error due to incomplete decay of the microelectrode voltage is described, and the accuracy of averaging the peak current measurement is established. To achieve the fastest dynamic response and the smallest steady-state error, the cycling period should be made as small as possible, and the open-loop gain should be as large as possible, consistent with stability. Incomplete decay of the microelectrode voltage destabilizes the clamp, and can introduce a significant clamp error. The choice of duty cycle is a compromise between reducing the noise and the step response time while avoiding design problems in the current output circuit. The output noise is amplified by aliasing. It can be minimized for a given output filter cutoff frequency by keeping the cycling frequency as high as possible, and by the use of an anti-aliasing filter whose cutoff frequency must be set for each microelectrode.
Animals↗
Psychological stress and arterial pulse transit time.
Progress in isolating the psychological factors contributing to the development of arterial hypertension has been retarded by the absence of suitable, non-invasive and continuous measures of significant aspects of cardiovascular activity. Pulse transit time may help to resolve this problem since it reflects changes in arterial elasticity and diastolic blood pressure. A method of recording pulse transit time is described. Significant decreases in pulse transit time were observed in response to a cold pressor test, a video game, a reaction-time task and problem solving, regardless of site of measurement or method of pulse transduction.
Adolescent↗
A shielded microelectrode suitable for single-electrode voltage clamping of neurones in the CNS.
The fabrication of a shielded microelectrode is described which has a time constant of about 3 microseconds, regardless of its depth in neural tissue. The shield is insulated from surrounding tissue with an insulation resistance which exceeds 1000 M omega, and the insulation will withstand +/- 15 V. Because of its narrow profile, the electrode is suitable for in vivo intracellular recordings from motoneurones and other large neurones of the CNS. The small time constant and the high breakdown resistance of the electrode make it suitable for use with single-electrode voltage clamp circuitry to voltage clamp motoneurone somata using switching rates in excess of 30 kHz.
Animals↗
The time course of synaptic potentials evoked in cat spinal motoneurones at identified group Ia synapses.
Excitatory post-synaptic potentials (e.p.s.p.s) were evoked in motoneurones by impulses in single group Ia axons. After recording the e.p.s.p., the motoneurone and the group Ia axon were injected with horseradish peroxidase. The morphological details of the connexion formed by each group Ia axon with a motoneurone were subsequently reconstructed. Four Ia axon-motoneurone pairs were obtained. The electrotonic distance from the soma to each synaptic bouton in the connexion was calculated. The electrotonic lengths of those dendrites on which synaptic connexions were found were also calculated. The shape indices of each recorded e.p.s.p. and the standard cable model of the motoneurone were used to calculate the electrotonic distance from the soma to the point on the equivalent dendritic cable at which the e.p.s.p. originated. This distance was compared with the distance obtained from the reconstruction of the synaptic connexion at which the e.p.s.p. was generated. For two of the four connexions, the locations calculated by both methods agreed to within 0.1 lambda. Similar agreement could only be obtained for the other two connexions if synaptic transmission did not occur at some of the boutons in the termination. Evidence that some boutons were not involved in transmission is presented in the following paper (Redman & Walmsley, 1983).
Animals↗
Amplitude fluctuations in synaptic potentials evoked in cat spinal motoneurones at identified group Ia synapses.
Excitatory post-synaptic potentials (e.p.s.p.s) were evoked in spinal motoneurones (of anaesthetized cats) by impulses in single group Ia axons. The morphological details of the Ia axon-motoneurone connexion involved in generating each e.p.s.p. were subsequently reconstructed, as described by Redman & Walmsley (1983). The fluctuation pattern of the peak amplitude of each e.p.s.p. was determined using a deconvolution method, taking into account the recording noise. Four e.p.s.p.s were analysed. One did not fluctuate in amplitude; the others fluctuated between discrete amplitudes which were separated by quantal increments. The number of increments which must be added to produce the largest peak amplitude of each e.p.s.p. was always less than, or equal to, the number of synaptic boutons in the connexion at which the e.p.s.p. was generated. The results are consistent with the hypothesis that transmission occurs in an all-or-none manner at each synaptic bouton. Different boutons in the termination of a Ia axon with a motoneurone have different probabilities of releasing transmitter, and this probability is sometimes zero at low stimulation rates. The results support the idea that the discrete amplitudes of an evoked e.p.s.p. result from intermittent transmission, in an all-or-none manner, at some or all of the boutons in the termination.
Animals↗
The recovery of a random variable from a noisy record with application to the study of fluctuations in synaptic potentials.
Analysis of fluctuations in the amplitude of evoked synaptic potentials can be severely handicapped by the presence of spontaneous synaptic potentials and recording noise. A numerical procedure has been described whereby it is possible to remove some of the masking effects of this noise from the underlying distribution of the fluctuating synaptic potentials. it is not necessary to make an initial assumption about the type of distribution which will best describe the fluctuations. To use this technique, it is necessary to measure the histograms which approximate the probability densities of both the noise, and the noisy evoked potential. It is also necessary to assume that the statistical mechanisms generating the noise are independent of those mechanisms which cause the fluctuation in synaptic transmission, and that the noise and the evoked potentials add linearly. The statistical reliability of the technique depends upon the amount of noise present, and the sample size. Problems of resolution which arise from finite sampling and high noise levels are discussed.
Afferent Pathways↗