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Biomedical subjects

F Moss

Publications and source records attributed to F Moss.

At least 73 records · Page 4Linked to original sources
PubMed1994

Bistability and the dynamics of periodically forced sensory neurons.

Many neurons at the sensory periphery receive periodic input, and their activity exhibits entrainment to this input in the form of a preferred phase for firing. This article describes a modeling study of neurons which skip a random number of cycles of the stimulus between firings over a large range of input intensities. This behavior was investigated using analog and digital simulations of the motion of a particle in a double-well with noise and sinusoidal forcing. Well residence-time distributions were found to exhibit the main features of the interspike interval histograms (ISIH) measured on real sensory neurons. The conditions under which it is useful to view neurons as simple bistable systems subject to noise are examined by identifying the features of the data which are expected to arise for such systems. This approach is complementary to previous studies of such data based, e.g., on non-homogeneous point processes. Apart from looking at models which form the backbone of excitable models, our work allows us to speculate on the role that stochastic resonance, which can arise in this context, may play in the transmission of sensory information.

Acoustic Stimulation↗
PubMed1994

Periodic forcing of a K+ channel at various temperatures.

The random sequence of openings and closings of single ion channels and the channel conductances have been the object of intense study over the past two decades with a view toward illuminating the underlying kinetics of the channel protein molecules. Channels that are sensitive to voltage, such as many K(+)-selective channels, have been particularly useful, because the kinetic rates can be manipulated by changing the membrane voltage. Most such studies have been performed under stationary conditions and usually at a single temperature. Here we report the results of experiments with sinusoidal modulation of the membrane potential performed at several temperatures. Dwell time and cycle histograms, objects not normally associated with ion channel experiments, are herein reported. From the last, the transition probability densities for channel opening and closing events are obtained. A new and unusual phase anticipation is observed in the cycle histograms, and its temperature dependence is measured.

Animals↗
PubMed1993

Noise enhancement of information transfer in crayfish mechanoreceptors by stochastic resonance.

In linear information theory, electrical engineering and neurobiology, random noise has traditionally been viewed as a detriment to information transmission. Stochastic resonance (SR) is a nonlinear, statistical dynamics whereby information flow in a multi-state system is enhanced by the presence of optimized, random noise. A major consequence of SR for signal reception is that it makes possible substantial improvements in the detection of weak periodic signals. Although SR has recently been demonstrated in several artificial physical systems, it may also occur naturally, and an intriguing possibility is that biological systems have evolved the capability to exploit SR by optimizing endogenous sources of noise. Sensory systems are an obvious place to look for SR, as they excel at detecting weak signals in a noisy environment. Here we demonstrate SR using external noise applied to crayfish mechanoreceptor cells. Our results show that individual neurons can provide a physiological substrate for SR in sensory systems.

Action Potentials↗
PubMed1993

Pneumothorax in patients with AIDS.

Eighty-seven inpatients were treated for 93 episodes of Pneumocystis carinii at St Mary's Hospital between January 1989 and December 1990. During this period, 298 patients with the acquired immunodeficiency syndrome (AIDS) were treated at this hospital. Sixteen episodes of pneumothorax occurred and 12 of these, occurring in ten patients, were unrelated to procedure. In six of 12 (50%), the pneumothoraces occurred concurrently with Pneumocystis carinii pneumonia (PCP) and in ten (83%) cases there was a past history of PCP. Bilateral pneumothorax occurred in five cases (42%). In seven (58%) of the cases, patients had been using aerosolized pentamidine as prophylaxis for PCP. This retrospective study confirms the association of pneumothorax with current PCP and also shows an association with previous infection. The use of aerosolized pentamidine was not associated with pneumothorax development. It is important to suspect pneumothorax in a patient with PCP who deteriorates acutely. The high incidence of bilateral pneumothorax means that pleurodesis should be considered early.

AIDS-Related Opportunistic Infections↗
PubMed1992

Secondary care beyond Tomlinson: an opportunity to be seized or squandered?

The Tomlinson report's emphasis on primary care and its essentially quantitative analysis of hospital care in London leaves little space for a picture of how secondary care for Londoners should look. In this article Fiona Moss and Martin McNicol argue that most outpatient work does not need to be done in hospitals. With proper organisation and better premises a genuinely specialist consultative service can be provided in primary health care centres, with benefit to patients and communication between primary and secondary care doctors. Hospitals would then house those outpatient services that needed major investigative facilities and much reduced inpatient capacity. It may no longer be necessary for each acute unit to offer a full range of services. Such a pattern of secondary care will have implications for the organisation of accident and emergency services and for postgraduate training. Above all Moss and McNicol argue that Tomlinson's recommendations demand that general practitioners and specialists should re-examine the services hospitals provide and agree on the best settings for different sorts of health care and the most appropriate skills to provide it.

Communication↗
PubMed1992

The anxieties of new clinical students.

The specific anxieties of 74 medical students beginning their clinical training were assessed by means of a questionnaire at the start of the clinical introductory course at St Mary's Hospital Medical School, London. Situations differed in the amount of anxiety that they engendered, and students also differed in the number of situations that they found anxiety producing. Students particularly reported that interactions with senior staff on ward rounds were anxiety provoking. The same questionnaire was also distributed to 52 teaching hospital doctors who were asked to complete the questionnaire as they thought the students had done. Compared with students, the doctors considered more situations to be anxiety provoking, and they differed in their rank ordering of the situations. Doctors tended to overestimate anxiety concerning communication problems, and to underestimate anxiety concerning routine clinical tasks such as phlebotomy.

Anxiety↗
PubMed1991

Stochastic resonance in a single neuron model: theory and analog simulation.

Here, we consider a noisy, bistable, single neuron model in the presence of periodic external modulation. The modulation induces a correlated switching between states driven by the noise. The information flow through the system, from the modulation, or signal, to the output switching events, leads to a succession of strong peaks in the power spectrum. The signal-to-noise ratio (SNR) obtained from this power spectrum is a measure of the information content in the neuron response. With increasing noise intensity, the SNR passes through a maximum: an effect which has been called stochastic resonance, and which was first advanced as a possible explanation of the observed periodicity in the recurrences of the Earth's ice ages. We treat the problem within the framework of a recently developed approximate theory, valid in the limits of weak noise intensity, weak periodic forcing and low forcing frequency, for both additive and multiplicative noise. Moreover, we have constructed an analog simulator of the neuron which demonstrates the stochastic resonance effect, and with which we have measured the SNRs for comparison with the theoretical results. Our model should be of interest in situations where a single inherently noisy neuron is the receptor of a periodic signal, which is itself noisy, either from the network or from an external source.

Animals↗
PubMed1991

Differential expression of antigens by human small cell lung carcinoma in sections of tumour and in serous effusions.

Antigen expression by human small cell lung carcinoma cells in serous effusions was determined by staining smears of cells with a panel of four monoclonal antibodies including UJ13A (cluster 1 antigen) and CAM 5.2 (anti-cytokeratin) using an immunoalkaline phosphatase technique. This was quantified by counting the proportion of stained and unstained tumour cells and was compared with that of small cell lung carcinoma in sections of solid tumour. Differential expression of antigen expression was noted with significantly fewer small cell carcinoma cells in serous effusions staining with UJ13A or CAM 5.2. The reasons for this differential expression are unknown, but may reflect adaptation to a different environment or be a prerequisite for spread to serous space.

Antigens, Neoplasm↗